WorldWideScience

Sample records for plant creep failure

  1. Residual stress measurements with barkhausen noise in power plant creep failure analysis

    Energy Technology Data Exchange (ETDEWEB)

    Karvonen, I. [CoMoTest Oy, Maentsaelae (Finland)] Suominen, L. [Stresstech Oy, Jyvaeskylae (Finland)

    1997-12-31

    Continuously developing power and process industry needs predictive maintenance inspection methods in order to prevent failures with correctly timed and properly specified measures. Materials` monitoring has traditionally been non-destructive inspection to detect growing cracks or other deficiencies. Recently, after the development of portable stress measurement systems, some advances has been reached. Based on stress anomalies due to creep, fatigue or corrosion, new applications have been found in the use of Barkhausen noise inspection. When the Barkhausen noise findings have been simultaneously confirmed with other stress measuring methods, a wider acceptance of the application of the method can be proposed. (orig.) 7 refs.

  2. Creep-Fatigue Failure Diagnosis

    Directory of Open Access Journals (Sweden)

    Stuart Holdsworth

    2015-11-01

    Full Text Available Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis.

  3. Multiaxial Creep-Fatigue and Creep-Ratcheting Failures of Grade 91 and Haynes 230 Alloys Toward Addressing Design Issues of Gen IV Nuclear Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, Tasnim [North Carolina State Univ., Raleigh, NC (United States); Lissenden, Cliff [Penn State Univ., University Park, PA (United States); Carroll, Laura [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-04-01

    The proposed research will develop systematic sets of uniaxial and multiaxial experimental data at a very high temperature (850-950°C) for Alloy 617. The loading histories to be prescribed in the experiments will induce creep-fatigue and creep-ratcheting failure mechanisms. These experimental responses will be scrutinized in order to quantify the influences of temperature and creep on fatigue and ratcheting failures. A unified constitutive model (UCM) will be developed and validated against these experimental responses. The improved UCM will be incorporated into the widely used finite element commercial software packages ANSYS. The modified ANSYS will be validated so that it can be used for evaluating the very high temperature ASME-NH design-by-analysis methodology for Alloy 617 and thereby addressing the ASME-NH design code issues.

  4. Failure of bacterial streamers in creeping flows

    Science.gov (United States)

    Biswas, Ishita; Ghosh, Ranajay; Sadrzadeh, Mohtada; Kumar, Aloke

    2016-11-01

    In the recent years, the dynamical response of filamentous bacterial aggregates called bacterial streamer in creeping flows has attracted attention. We report the observation of 'necking-type' instability leading to failure in bacterial (Pseudomonas fluorescens) streamers formed in creeping flows. Quantification of the failure process was made possible through the use of 200 nm red fluorescent polystyrene tracer particles embedded in the bacterial extracellular polymeric substances (EPS). The nonlinear failure behavior shows distinct phases of deformation with mutually different characteristic times, which end with a distinct localized failure of the streamer. We also develop a simplified analytical model to describe the experimental observations of the failure phenomena. The theoretical power law relationship between critical stretch ratio and the fluid velocity scale matches closely experimental observations.

  5. Creep failure of a spray drier

    CSIR Research Space (South Africa)

    Carter, P

    1998-06-01

    Full Text Available , and creep. The calculations pointed to creep, and no positive metallurgic or physical evidence was discovered to support any of the hypotheses. However, the compression stresses implied that creep deformation could have occurred without inducing discernible...

  6. Brittle Creep Failure, Critical Behavior, and Time-to-Failure Prediction of Concrete under Uniaxial Compression

    Directory of Open Access Journals (Sweden)

    Yingchong Wang

    2015-01-01

    Full Text Available Understanding the time-dependent brittle deformation behavior of concrete as a main building material is fundamental for the lifetime prediction and engineering design. Herein, we present the experimental measures of brittle creep failure, critical behavior, and the dependence of time-to-failure, on the secondary creep rate of concrete under sustained uniaxial compression. A complete evolution process of creep failure is achieved. Three typical creep stages are observed, including the primary (decelerating, secondary (steady state creep regime, and tertiary creep (accelerating creep stages. The time-to-failure shows sample-specificity although all samples exhibit a similar creep process. All specimens exhibit a critical power-law behavior with an exponent of −0.51 ± 0.06, approximately equal to the theoretical value of −1/2. All samples have a long-term secondary stage characterized by a constant strain rate that dominates the lifetime of a sample. The average creep rate expressed by the total creep strain over the lifetime (tf-t0 for each specimen shows a power-law dependence on the secondary creep rate with an exponent of −1. This could provide a clue to the prediction of the time-to-failure of concrete, based on the monitoring of the creep behavior at the steady stage.

  7. Unexpected damage and/or failures caused by creep below the limit temperature for creep design; Ovaentade krypskador och/eller haverier orsakade av krypmekanismer under graenstemperaturen

    Energy Technology Data Exchange (ETDEWEB)

    Storesund, Jan; Eklund, Anders; Taflin, Anders; Thunvik, Thomas

    2006-07-15

    Recently, several cases of cracking caused by creep have occurred in components operating at temperatures below the specified limit temperature for creep. Components operating below this limit temperature have not been designed with due regard to creep cracking and have accordingly not been subjected to inspection for creep damage. This work has surveyed the extent of these cases of creep damage by reviewing earlier failures and performed metallographic studies of damaged components and made parametric calculations of creep crack growth below the limit temperature. The following critical parameters have been determined for power plants: Creep damage below the transition temperature does not usually occur until operating times above 200.000 hours. Time to rupture differs from ordinary creep crack growth because these cracks have substantially longer incubation time of 20-30 years, with relative low creep deformation, and after that a rapid creep crack growth with only some few years to the creep rupture. Operation at 470-480 deg C, i.e. up to some 10 deg C below the transition temperature for a material like EN 13CrMo4-5, can be expected to result in severe creep damages comparable with ordinary creep failures at stressed locations. Operation at a temperature of 450-460 deg C can give rise to creep damage, however, this damage shows a more sparse occurrence. Creep damaged welds occurring below the limit temperature show cracks at the melting junction of the weld bead in opposite to ordinary creep damages. System stresses can also cause a more rapid crack growth. An international survey also shows that the variation of creep strength values between individual steel batches are just as wide as for ordinary creep. Based on this work, the following complementary recommendations can be issued: Elastic stress analysis (based on expansion calculations) can also be recommended for the identification of areas with intensified stresses. One should also perform a complete

  8. Long-term creep-rupture failure envelope of epoxy

    Science.gov (United States)

    Melo, José Daniel D.; de Medeiros, Antonio M.

    2014-02-01

    An accelerated testing methodology based on the time-temperature superposition principle has been proposed in the literature for the long-term creep strength of polymer matrices and polymer composites. Also, it has been suggested that a standard master curve may be a feasible assumption to describe the creep behavior in both tension and compression modes. In the present research, strength master curves for an aerospace epoxy (8552) were generated for tension and compression, by shifting strength data measured at various temperatures. The shift function is obtained from superposition of creep-compliance curves obtained at different temperatures. A standard master curve was presented to describe the creep-rupture of the polymer under tension and compression. Moreover, long-term creep-rupture failure envelopes of the polymer were presented based on a two-part failure criterion for homogeneous and isotropic materials. Ultimately, the approach presented allows the prediction of creep-rupture failure envelopes for a time-dependent material based on tensile strengths measured at various temperatures, considering that the ratio between tensile and compressive strengths is known.

  9. Some new pre-warning criteria for creep slope failure

    Institute of Scientific and Technical Information of China (English)

    HACK; Robert

    2011-01-01

    The forecasting of the failure time of a slope remains a worldwide problem because of many different possibilities of geological conditions in combination with many varying external factors such as climate and vegetation,and not well-defined or unknown time effects in deformation and failure models.The aim of this paper is to suggest a new method to carry out the phase division and to explore tangential angular features of the displacement-time curve of creep slopes as well as the acceleration characteristics in the process of slope deformation and the pre-warning criteria for critical failure.An imminent failure is pro-ceeded with usually three basic deformation phases,namely primary creep("decelerated") ,secondary creep("steadystate") and tertiary creep("accelerated") .Mostly,only during the accelerated phase the imminence of a possible slope failure is rec-ognized.The analysis of displacement data from a series of landslides allowed to recognize different evolutionary patterns of displacement.A quantitative approach was proposed to describe the tangential angle of the displacement-time curve and a new criterion based on the angle was put forward to divide the accelerated phase into three sub-phases:initial acceleration,medium acceleration,and the critical failure.A pre-warning criterion for critical failure is also proposed consequently. Changes of acceleration showed completely different characteristics from those of cumulative displacement and displacement in the process of slope deformation.The values of acceleration usually oscillate around 0 prior to the critical failure phase,whereas the acceleration increases abruptly when the deformation moves into the critical failure phase.This allows,therefore,for a method to forecast the time of the failure.So it is possible to define different alert acceleration threshold values to be used for emergency management.

  10. Micromechanics of intergranular creep failure under cyclic loading

    DEFF Research Database (Denmark)

    van der Giessen, Erik; Tvergaard, Viggo

    1996-01-01

    This paper is concerned with a micromechanical investigation of intergranular creep failure caused by grain boundary cavitation under strain-controlled cyclic loading conditions. Numerical unit cell analyses are carried out for a planar polycrystal model in which the grain material and the grain...... boundaries are modelled individually. The model incorporates power-law creep of the grains, viscous grain boundary sliding between grains as well as the nucleation and growth of grain boundary cavities until they coalesce and form microcracks. Study of a limiting case with a facet-size microcrack reveals...... a relatively simple phenomenology under either balanced loading, slow-fast loading or balanced loading with a hold period at constant tensile stress. Next, a (non-dimensionalized) parametric study is carried out which focusses on the effect of the diffusive cavity growth rate relative to the overall creep rate...

  11. Creep test observation of viscoelastic failure of edible fats

    Energy Technology Data Exchange (ETDEWEB)

    Vithanage, C R; Grimson, M J; Wills, P R [Department of Physics, University of Auckland, Private Bag 92019 (New Zealand); Smith, B G, E-mail: cvit002@aucklanduni.ac.nz [Food Science Programmes, Department of Chemistry, University of Auckland, Private Bag 92019 (New Zealand)

    2011-03-01

    A rheological creep test was used to investigate the viscoelastic failure of five edible fats. Butter, spreadable blend and spread were selected as edible fats because they belong to three different groups according to the Codex Alimentarius. Creep curves were analysed according to the Burger model. Results were fitted to a Weibull distribution representing the strain-dependent lifetime of putative fibres in the material. The Weibull shape and scale (lifetime) parameters were estimated for each substance. A comparison of the rheometric measurements of edible fats demonstrated a clear difference between the three different groups. Taken together the results indicate that butter has a lower threshold for mechanical failure than spreadable blend and spread. The observed behaviour of edible fats can be interpreted using a model in which there are two types of bonds between fat crystals; primary bonds that are strong and break irreversibly, and secondary bonds, which are weaker but break and reform reversibly.

  12. Study of creep cavity growth for power plant lifetime assessment

    Energy Technology Data Exchange (ETDEWEB)

    Wu Rui; Sandstroem, Rolf

    2001-01-01

    This report aims to the sub project lifetime assessment by creep (livslaengdspredikteringar vid kryp), which is involved in the project package strength in high temperature power plant, KME 708. The physical creep damage includes mainly cavities and their development. Wu and Sandstroem have observed that cavity size increases linearly with increasing creep strain in a 12%Cr steel. Sandstroem has showed that, based on the relations between the nucleation and growth of creep cavities with creep strain, the physical creep damage can be modelled as a function of creep strain. In the present paper the growth of creep cavity radius R in relation to time t and strain {epsilon} in low alloy and 12%Cr steels as well as a Type 347 steel has been studied. The results exhibit that the power law cavity radius with creep time (R-t) and with creep strain (R-{epsilon}) relations are found for these materials at various testing conditions. The power law R-t and R-{epsilon} relations are in most cases dependent and independent on testing conditions, respectively. The empirical power law R-{epsilon} relations give a description of cavity evolution, which can be used for lifetime assessment. Experimental data have also been compared to the estimations by the classical models for cavity growth, including the power law growth due to Hancock, the diffusion growth due to Speight and Harris, the constrained diffusion growths due to Dyson and due to Rice and the enhanced diffusion growth due to Beere. It appears that the constraint diffusion growth models give a reasonable estimation of R-{epsilon} relation in many cases. The diffusion growth model is only applicable for limited cases where the power over t in R-t relation takes about 1/3. The power law and the enhanced diffusion models are found in most cases to overestimate the cavity growth.

  13. Evaluation of creep damage in power plant applications

    Energy Technology Data Exchange (ETDEWEB)

    Auerkari, P.; Salonen, J. [VTT Manufacturing Technology, Espoo (Finland)] McNiven, U. [IVO Generation Services Ltd., Naantali (Finland)] Roennberg, J. [Imatran Voima Oy, Vantaa (Finland)] Borggreen, K. [FORCE Institute, Broendby (Germany)

    1997-12-31

    Metallographic inspection of creep cavitation damage provides routine support for maintenance scheduling of high temperature components in power plants. The available European inspection experience has been reviewed, particularly considering the performance of thick-section steam systems outside the boiler. Applications are highlighted with examples from plant. (orig.) 8 refs.

  14. Finite Element Creep-Fatigue Analysis of a Welded Furnace Roll for Identifying Failure Root Cause

    Science.gov (United States)

    Yang, Y. P.; Mohr, W. C.

    2015-11-01

    Creep-fatigue induced failures are often observed in engineering components operating under high temperature and cyclic loading. Understanding the creep-fatigue damage process and identifying failure root cause are very important for preventing such failures and improving the lifetime of engineering components. Finite element analyses including a heat transfer analysis and a creep-fatigue analysis were conducted to model the cyclic thermal and mechanical process of a furnace roll in a continuous hot-dip coating line. Typically, the roll has a short life, heat transfer analysis was conducted to predict the temperature history of the roll by modeling heat convection from hot air inside the furnace. The creep-fatigue analysis was performed by inputting the predicted temperature history and applying mechanical loads. The analysis results showed that the failure was resulted from a creep-fatigue mechanism rather than a creep mechanism. The difference of material properties between the filler metal and the base metal is the root cause for the roll failure, which induces higher creep strain and stress in the interface between the weld and the HAZ.

  15. New martensitic steels for fossil power plant: Creep resistance

    Science.gov (United States)

    Kaybyshev, R. O.; Skorobogatykh, V. N.; Shchenkova, I. A.

    2010-02-01

    In this paper, we consider the origin of high-temperature strength of heat-resistant steels belonging to martensitic class developed on the basis of the Fe—9%Cr alloy for the boiler pipes and steam pipelines of power plants at steam temperatures of up to 620°C and pressures to 300 atm. In addition, we give a brief information on the physical processes that determine the creep strength and consider the alloying philosophy of traditional heat-resistant steels. The effect of the chemical and phase composition of heat-resistant steels and their structure on creep strength is analyzed in detail. It is shown that the combination of the solid-solution alloying by elements such as W and Mo, as well as the introduction of carbides of the MX type into the matrix with the formation of a dislocation structure of tempered martensite, ensures a significant increase in creep resistance. The steels of the martensitic class withstand creep until an extensive polygonization starts in the dislocation structure of the tempered martensite(“troostomartensite”), which is suppressed by V(C,N) and Nb(C,N) dispersoids. Correspondingly, the service life of these steels is determined by the time during which the dispersed nanocarbonitrides withstand coalescence, while tungsten and molybdenum remain in the solid solution. The precipitation of the Laves phases Fe2(W,Mo) and the coalescence of carbides lead to the development of migration of low-angle boundaries, and the steel loses its ability to resist creep.

  16. Modelling the impact of creep on the probability of failure of a solid oxidefuel cell stack

    DEFF Research Database (Denmark)

    Greco, Fabio; Frandsen, Henrik Lund; Nakajo, Arata

    2014-01-01

    In solid oxide fuel cell (SOFC) technology a major challenge lies in balancing thermal stresses from an inevitable thermal field. The cells are known to creep, changing over time the stress field. The main objective of this study was to assess the influence of creep on the failure probability...... of an SOFC stack. A finite element analysis on a single repeating unit of the stack was performed, in which the influence of the mechanical interactions,the temperature-dependent mechanical properties and creep of the SOFC materials are considered. Moreover, stresses from the thermo-mechanical simulation...... of sintering of the cells have been obtained and were implemented into the model of the single repeating unit. The significance of the relaxation of the stresses by creep in the cell components and its influence on the probability of cell survival was investigated. Finally, the influence of cell size...

  17. Some numerical approaches of creep, thermal shock, damage and delayed failure of ceramics and refractories

    Indian Academy of Sciences (India)

    Michel Boussuge

    2001-04-01

    Numerical simulation is now very often used to predict the behaviour of components in service conditions. This paper is interested in specific approaches concerning ceramic materials and refractories. Creep can be satisfactorily described by a kinematic hardening, and exhibits different creep rates in tension and compression. Concerning the thermal shock of materials, the numerical approach depends whether or not the material is able to develop a sprayed out damage, leading to micro- or macro-cracking. Finally, delayed failure at high temperature can be considered as a consequence of creep, but the random aspect of failure seriously complicates the numerical models. The lack of experimental data presently limits the calibration and the validation of the numerical models.

  18. Delaunay-Network Modelling of Creep Failure in Regular Polycrystalline Aggregates by Grain Boundary Cavitation

    NARCIS (Netherlands)

    Burg, M.W.D. van der; Giessen, E. van der

    1994-01-01

    In polycrystalline materials at elevated temperatures subjected to stationary loading, creep fracture occurs as a result of failure mechanisms on the size scale of grains, namely the nucleation and diffusive growth of cavities until coalescence leads to microcracks. In this paper, a polycrystalline

  19. Estimating the creep strain to failure of PP at different load levels based on short term tests and Weibull characterization

    Directory of Open Access Journals (Sweden)

    L. M. Vas

    2012-12-01

    Full Text Available The short and long term creep behavior is one of the most important properties of polymers used for engineering applications. In order to study this kind of behavior of PP tensile and short term creep measurements were performed and analyzed using long term creep behavior estimating method based on short term tensile and creep tests performed at room temperature, viscoelastic behavior, and variable transformations. Applying Weibull distribution based approximations for the measured curves predictions for the creep strain to failure depending on the creep load were determined and the parameters were found by fitting the measurements. The upper, mean, and lower estimations as well as the confidence interval for the means give a possibility for designers' calculations at arbitrary creep load levels.

  20. Post-test creep analysis of piping failure tests in wind project

    Energy Technology Data Exchange (ETDEWEB)

    Chino, E.; Maruyama, Y.; Yuchi, Y.; Shibazaki, H.; Nakamura, H.; Hidaka, A.; Kudo, T.; Hashimoto, K. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Maeda, A. [Applied and Scientific Systems Department, MRI Systems Inc., Tokyo (Japan)

    2000-11-01

    Thermal and structural responses of the reactor coolant piping under elevated temperature and pressure conditions are being investigated in piping failure tests in WIND (Wide Range Piping Integrity Demonstration) project at JAERI (Japan Atomic Energy Research Institute). The elasto-plastic creep analysis was performed with ABAQUS code for the test using a nuclear grade type 316 stainless steel pipe, which had an outer diameter of 114.3 mm and a wall thickness of 13.5 mm. The major material properties at elevated temperature needed for the analysis were measured for specimen sectioned from the test pipe. Based on the measured creep data, a creep constitutive equation including the tertiary stage was developed and incorporated into ABAQUS code. We compared the results of the three-dimensional analysis with those of two-dimensional analysis and the piping failure test. The comparison showed that the piping failure timing and deformation of pipe obtained from the three dimensional analysis underestimated the test results, and that temperature history at the elevated temperature should be adequately considered. (author)

  1. Investigation of Macroscopic Brittle Creep Failure Caused by Microcrack Growth Under Step Loading and Unloading in Rocks

    Science.gov (United States)

    Li, Xiaozhao; Shao, Zhushan

    2016-07-01

    The growth of subcritical cracks plays an important role in the creep of brittle rock. The stress path has a great influence on creep properties. A micromechanics-based model is presented to study the effect of the stress path on creep properties. The microcrack model of Ashby and Sammis, Charles' Law, and a new micro-macro relation are employed in our model. This new micro-macro relation is proposed by using the correlation between the micromechanical and macroscopic definition of damage. A stress path function is also introduced by the relationship between stress and time. Theoretical expressions of the stress-strain relationship and creep behavior are derived. The effects of confining pressure on the stress-strain relationship are studied. Crack initiation stress and peak stress are achieved under different confining pressures. The applied constant stress that could cause creep behavior is predicted. Creep properties are studied under the step loading of axial stress or the unloading of confining pressure. Rationality of the micromechanics-based model is verified by the experimental results of Jinping marble. Furthermore, the effects of model parameters and the unloading rate of confining pressure on creep behavior are analyzed. The coupling effect of step axial stress and confining pressure on creep failure is also discussed. The results provide implications on the deformation behavior and time-delayed rockburst mechanism caused by microcrack growth on surrounding rocks during deep underground excavations.

  2. Investigation of Rock Failure Pattern in Creep by Digital Speckle Correlation Method

    Directory of Open Access Journals (Sweden)

    Yunliang Tan

    2013-01-01

    Full Text Available In order to study the mechanical characteristics from creep deformation to failure of rock, the tests of uniaxial compression and pushing steel-plate anchored in rock were performed, by using RLJW-2000 servo test synchronizing with Digital Speckle Correlation Method (DSCM. The investigations showed that for a uniaxial compressive specimen, when load arrived at 0.5σc, displacement clusters orderly formed, which was ahead of the macrocreep strain occurring in a slight jump mode when load arrived at 0.7σc. When the load level arrived at 0.8σc, displacement clusters gathered to be a narrow band. After that, the specimen abruptly fractured in a shear mode. In the creep pushing steel-plate test, when pushing force arrived at 25 kN, crack began to occur, the horizontal displacement field as well as shear strain field concentrated continuously along the interface between steel-plate and rock, and a new narrow concentrating band gathered in the upper layer. When pushing force arrived at 27.5 kN, another new narrow shear deformation band formed in the lower layer. Then, the steel-plate was pushed out quickly accompanying strong creep deformation.

  3. Nonlinear deformation and localized failure of bacterial streamers in creeping flows

    Science.gov (United States)

    Biswas, Ishita; Ghosh, Ranajay; Sadrzadeh, Mohtada; Kumar, Aloke

    2016-08-01

    We investigate the failure of bacterial floc mediated streamers in a microfluidic device in a creeping flow regime using both experimental observations and analytical modeling. The quantification of streamer deformation and failure behavior is possible due to the use of 200 nm fluorescent polystyrene beads which firmly embed in the extracellular polymeric substance (EPS) and act as tracers. The streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer far from the walls. We investigate this deformation and failure behavior for two separate bacterial strains and develop a simplified but nonlinear analytical model describing the experimentally observed instability phenomena assuming a necking route to instability. Our model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibiting excellent qualitative and quantitative agreeing with the experimental rupture behavior.

  4. Analytical study on creep behavior of a tube of coolant piping system in nuclear power plant. Contract research

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Noriyuki [Kyushu Univ., Fukuoka (Japan); Hagihara, Seiya [Saga Univ., Saga (Japan); Chino, Eiichi; Maeda, Akio [MRI Systems Inc., Tokyo (Japan); Maruyama, Yu; Hashimoto, Kazuichiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2001-10-01

    During severe accident of a light water reactor (LWR), reactor coolant piping would be damaged when the piping is subjected to high internal pressure and very high temperature due to heat transfer from high-temperature gas and decay heat from wall-deposited fission product (FP), both from degraded core. In such a case, high-temperature fast creep deformation could be the main cause for the pipe failure. For the evaluation of piping integrity during severe accidents, a method to predict such high-temperature fast creep deformation should be developed, using a creep constitutive equation considering tertiary creep behavior which has not been considered well in the pipe failure analyses. In this study, a creep constitutive equation was developed first based on the Kachanov-Ravotnov isotropic damage rule that considers the tertiary creep behavior. JAERI creep tensile test data for both nuclear-grade cold-drawn SUS316N and hot-extruded SUS316 materials were used to determine coefficients of the developed constitutive equation. Using the developed constitutive equation, finite element analyses were performed for local creep deformation of coolant piping under two temperature conditions: uniform temperature and temperature gradient. The analytical results indicated the damage variable being integrated following the evolution of creep damage can indicate pipe wall internal damage condition quantitatively. The damage variable was confirmed further to be able to reproduce the observation in JAERI piping failure tests, that is, pipe failure from the wall outside. (author)

  5. A Universal Reduced Rupture Creep Approach for Prediction of Long Term Failure Behavior of Aged Glass Polymers from the Short Term Test of Rupture Creep Compliance by the Unified Master Curved Extrapolation

    Institute of Scientific and Technical Information of China (English)

    Guang-jun Song; Da-ming Wu; Wei-yue Song; Ming-shi Song; Gui-xian Hu

    2012-01-01

    The prediction of long term failure behaviors and lifetime of aged glass polymers from the short term tests of reduced rupture creep compliance (or strain) is one of difficult problems in polymer science and engineering.A new "universal reduced rupture creep approach" with exact theoretical analysis and computations is proposed in this work.Failure by creep for polymeric material is an important problem to be addressed in the engineering.A universal equation on reduced extensional failure creep compliance for PMMA has been derived.It is successful in relating the reduced extensional failure creep compliance with aging time,temperature,levels of stress,the average growth dimensional number and the parameter in K-W-W function.Based on the universal equation,a method for the prediction of failure behavior,failure strain criterion,failure time of PMMA has been developed which is named as a universal "reduced rupture creep approach".The results show that the predicted failure strain and failure time of PMMA at different aging times for different levels of stress are all in agreement with those obtained directly from experiments,and the proposed method is reliable and practical.The dependences of reduced extensional failure creep compliance on the conditions of aging time,failure creep stress,the structure of fluidized-domain constituent chains are discussed.The shifting factor,exponent for time-stress superposition at different levels of stress and the shifting factor,exponent for time-time aging superposition at different aging time are theoretically defined respectively.

  6. Long-term Creep Life Prediction and Its Reliability on HAZ Failure Data of Grade 91 Steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Jang, Jin Sung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jae Young [Pukyong National University, Busan (Korea, Republic of)

    2015-10-15

    Long-term creep life prediction on Grade 91 HAZ failure data was performed by LM parameter, and its reliability was successfully demonstrated using SCRI model based on Z-parameter. To improve the creep life prediction at the low stress range of high temperature range, the master curve with a 'sinh' function was newly proposed. By Monte-Carlo simulation, reliability assessment was made using the chosen service temperature and stress conditions. carbide/nitride forming elements such as V and Nb along with controlled addition of N in the plain 9Cr. 1Mo steel, offers a good combination of high creep strength and ductility over prolonged exposures at elevated temperatures. The choice of Gr. 91 steel for sodium-cooled fast reactor (SFR) applications is guided by its low thermal expansion coefficient and high resistance to stress corrosion cracking in water-steam systems compared to austenitic stainless steels.

  7. Modeling Creep-Fatigue-Environment Interactions in Steam Turbine Rotor Materials for Advanced Ultra-supercritical Coal Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Chen [General Electric Global Research, Niskayuna, NY (United States)

    2014-04-01

    The goal of this project is to model creep-fatigue-environment interactions in steam turbine rotor materials for advanced ultra-supercritical (A-USC) coal power Alloy 282 plants, to develop and demonstrate computational algorithms for alloy property predictions, and to determine and model key mechanisms that contribute to the damages caused by creep-fatigue-environment interactions.

  8. Small punch creep test: A promising methodology for high temperature plant components life evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Tettamanti, S. [CISE SpA, Milan (Italy); Crudeli, R. [ENEL SpA, Milan (Italy)

    1998-12-31

    CISE and ENEL are involved for years in a miniaturization creep methodology project to obtain similar non-destructive test with the same standard creep test reliability. The goal can be reached with `Small punch creep test` that collect all the requested characteristics; quasi nondestructive disk specimens extracted both on external or internal side of components, than accurately machined and tested on little and cheap apparatus. CISE has developed complete creep small punch procedure that involved peculiar test facility and correlation`s law comparable with the more diffused isostress methodology for residual life evaluation on ex-serviced high temperature plant components. The aim of this work is to obtain a simple and immediately applicable relationship useful for plant maintenance managing. More added work is need to validate the Small Punch methodology and for relationship calibration on most diffusion high temperature structural materials. First obtained results on a comparative work on ASTM A355 P12 ex-serviced pipe material are presented joint with a description of the Small Punch apparatus realized in CISE. (orig.) 6 refs.

  9. Predicting the creep life and failure mode of low-alloy steel weldments

    Energy Technology Data Exchange (ETDEWEB)

    Brear, J.M.; Middleton, C.J.; Aplin, P.F. [ERA Technology Ltd., Leatherhead (United Kingdom)

    1998-12-31

    This presentation reviews and consolidates experience gained through a number of research projects and practical plant assessments in predicting both the life and the likely failure mode and location in low alloy steel weldments. The approach adopted begins with the recognition that the relative strength difference between the microstructural regions is a key factor controlling both life and failure location. Practical methods based on hardness measurement and adaptable to differing weld geometries are presented and evidence for correlations between hardness ratio, damage accumulation and strain development is discussed. Predictor diagrams relating weld life and failure location to the service conditions and the hardness of the individual microstructural constituents are suggested and comments are given on the implications for identifying the circumstances in which Type IV cracking is to be expected. (orig.) 6 refs.

  10. Creep and creep-fatigue behavior of high chromium steel weldment

    Institute of Scientific and Technical Information of China (English)

    Yukio TAKAHASHI; Masaaki TABUCHI

    2011-01-01

    Manuscript received I December 2010; in revised form 9 March 2011Strength of welded joints of high chromium steels is one of the important concerns for fabricators and operators of ultra supercritical thermal power plants. A number of creep as well as creep-fatigue tests with tensile hold have been carried out on the welded joints of two types of high chromium steels widely used in Japan, I.e. Grade 91 and 122 steels. It was found that failure occurred in fine grain heat-affected zone in all the creep-fatigue tests, even at a relatively low temperature and fairly short time where failure occurred in plain base metal region in simple creep testing. Four procedures were used to predict failure lives and their results were compared with the test results. A newly proposed energy-based approach gave the best estimation of failure life, without respect of the material and temperature.

  11. A Creep Damage Model for High-Temperature Deformation and Failure of 9Cr-1Mo Steel Weldments

    Directory of Open Access Journals (Sweden)

    Mehdi Basirat

    2015-08-01

    Full Text Available A dislocation-based creep model combined with a continuum damage formulation was developed and implemented in the finite element method to simulate high temperature deformation behavior in modified 9Cr-1Mo steel welds. The evolution of dislocation structures was considered as the main driving mechanism for creep. The effect of void growth, precipitate coarsening, and solid solution depletion were considered to be the operating damage processes. A semi-implicit numerical integration scheme was developed and implemented in the commercial finite element code ABAQUS-Standard as a user material subroutine. Furthermore, several creep tests of modified 9Cr-1Mo steel welded specimens were conducted at temperatures between 550–700 °C and stresses between 80–200 MPa. The accuracy of the model was verified by comparing the finite element results with experiments. The comparison between the experimental and computational results showed excellent agreement. The model can be used to simulate and predict the creep-damage behavior of Cr-Mo steel components used as structural applications in power plants.

  12. Review of creep resistant alloys for power plant applications

    Directory of Open Access Journals (Sweden)

    A. Nagode

    2011-01-01

    Full Text Available A paper describes the most popular alloys for power plant application as well as the most promising alloys for future application in that technology. The components in power plants operate in severe conditions (high temperatures and pressures and they are expected reliable service for 30 years and more. The correct choice of the material is, thus, of a very importance. The paper describes the development as well as advantages and disadvantages of convenient ferritic/martensitic steels, ferritic/bainitic steels, austenitic stainless steels and the new alloys for the application at temperatures of 650°C and more.

  13. Experimental and analytical study of creep cracks damage in high temperature sodium plant branch connections

    Energy Technology Data Exchange (ETDEWEB)

    Corsi, F.; Fabi, A.; Di Giamberardino, P.; Botti, G.; Pasquale, G.; Dapor, V.

    1989-05-01

    A brief description of the operating conditions of the ESPRESSO sodium plant is given. The structural integrity problems of some ''T'' branch connections in the sodium plant are then presented. During a thermal cycling test a hydraulic packing loss is pointed out by a small amount of sodium leakage. Radiographic examinations revealed both a crack in the entire thickness and second partial crack in another branch connection. A series of technological tests was executed in which the presence of the cracks clearly indicated creep damage. To clarify the structural reliability of the most critical components a theoretical analysis of creep damage for the two branch connections was performed in detail. For this aim both elastic and inelastic analyses were carried out, with the general purpose CASTEM system developed at CEA Saclay, to determine the stress fields of the two components. The study tried to take into account the effects of the residual welding stresses in the creep regime. The main conclusions concerning the applications of the different existing rules are presented and compared. (orig./HP).

  14. Recent advances in creep-resistant steels for power plant applications

    Indian Academy of Sciences (India)

    P J Ennis; A Czyrska-Filemonowicz

    2003-06-01

    The higher steam temperatures and pressures required to achieve increase in thermal efficiency of fossil fuel-fired power-generation plants necessitate the use of steels with improved creep rupture strength. The 9% chromium steels developed during the last three decades are of great interest in such applications. In this report, the development of steels P91, P92 and E911 is described. It is shown that the martensitic transformation in these three steels produces high dislocation density that confers significant transient hardening. However, the dislocation density decreases during exposure at service temperatures due to recovery effects and for long-term creep strength the sub-grain structure produced under different conditions is most important. The changes in the microstructure mean that great care is needed in the extrapolation of experimental data to obtain design values. Only data from tests with rupture times above 3,000 h provide reasonable extrapolated values. It is further shown that for the 9% chromium steels, oxidation resistance in steam is not sufficiently high for their use as thin-walled components at temperatures of 600°C and above. The potential for the development of steels of higher chromium contents (above 11%) to give an improvement in steam oxidation resistance whilst maintaining creep resistance to the 9% chromium steels is discussed.

  15. On the microstructural basis of creep strength and creep-fatigue interaction in 9-12 % Cr steels for application in power plants

    Energy Technology Data Exchange (ETDEWEB)

    Chilukuru, H.

    2007-03-06

    As part of the efforts of preserving the environment it is necessary to reduce of the CO2 emissions from power plants. This can be done by increasing the plant efficiency. Research groups around the world are engaged in developing new steels capable of sustaining higher stresses and temperatures envisaged for high-efficiency power plants. Research carried out in Europe is organized within the COST Programme (Co-Operation in Science and Technology) aiming at replacing the conventional steels of type X20CrMoV121 by the new class of 9-12% Cr-steels with modified composition. The resistance of materials against deformation at elevated temperatures depends on their microstructure. Frequently in 9-12% Cr-steels improved short-term creep properties do not persist in the long-term service [1, 2, 3, 4, 5, 6]. This is related with insufficient microstructural stability. Hardening contributions in 9-12% Cr-steels come from solute atoms of the ferritic matrix, from dislocations, and from precipitates of foreign phases within the matrix. The term ''carbide stabilized substructure hardening'' of 9-12% Cr steels [7, 8] indicates that the hardening contributions are interdependent. The dislocations are the carriers of plastic deformation. They interact with each other, with solute atoms and with precipitates. The dislocation-dislocation interaction leads to formation of planar dislocation networks constituting low-angle boundaries. They form a subgrain structure within the grains. At present, a full and detailed understanding of the effects exerted by the different components of microstructure on creep strength is still lacking. The present work makes a contribution to the efforts of understanding the microstructural basis of creep strength and of creep-fatigue interaction by transmission electron microscopic structure investigations coupled with creep tests. Investigations by transmission electron microscopy (TEM) were carried out with regard to hardening by

  16. Environmental effect of S02-bearing atmosphere on the creep fatigue failure of aluminide-coated MM-002 nickel-base superalloy at 870°C

    CSIR Research Space (South Africa)

    Aghion, E

    1995-04-15

    Full Text Available High-temperature low-cycle fatigue (HTLCF) failure mechanisms of aluminide-coated MAR-M002 nickel-base superalloy in air, argon and Ar+5% SO2 atmospheres were investigated at 870°C. The loading conditions were constant and consisted of creep tension...

  17. Simulated acid rain alters litter decomposition and enhances the allelopathic potential of the invasive plant Wedelia trilobata (Creeping Daisy)

    Science.gov (United States)

    Invasive species and acid rain cause global environmental problems. Limited information exists, however, concerning the effects of acid rain on the invasiveness of these plants. For example, creeping daisy, an invasive exotic allelopathic weed, has caused great damage in southern China where acid ra...

  18. Guideline for inspection of plant concerning creep below the limit temperature; Stoed vid besiktning av anlaeggningar avseende krypning under graenstemperaturen

    Energy Technology Data Exchange (ETDEWEB)

    Storesund, Jan; Bjurstroem, Henrik; Weilin Zang; Andersson-Frejd, Ulf

    2007-12-15

    In an earlier report from Vaermeforsk, Inspecta and AaF mapped the extent of the problem of creep damage in several components of steam systems in power plants, which systems operate at temperatures below the lower limit for creep. Recommendations were issued regarding inspection of components where creep damage may occur. The authorities have issued a new regulation, AFS 2005:3 regarding inspection of pressure vessels, extending the requirement for inspection against creep fracture down to 350 deg C. This extensive inspection and testing is though considered as costly by the plants. A simplified inspection routine has been requested so that status regarding creep in exposed components may be determined at a more reasonable cost. In the present follow-up project, the goal was to provide a more comprehensive basis for the recommendations on methods for identifying exposed components. This has included: Collecting information from the replica tests that have been carried out during 2006 and 2007 as a complement to the documentation in the earlier project; Verifying the usability of analyses of elastic stresses; Additional simulations with FEM with the purpose of identifying critical geometries of components and positions. Information has been gathered from 11 replica inspections during the last two years. Creep damage has been observed in every case. In two of them, micro and macro cracks were observed. Eight of the remaining nine had significant occurrences of creep cavities. Damage has occurred also below 450 deg C, which was hitherto unknown. Excessive temperatures may have occurred in one of the two cases; defects and high system stresses are the probable causes of the other case. Positions where the most severe creep damage was observed were not the same as those with the highest stresses in the elastic stresses analysis. Therefore, components which are prone to damage according to experience, e.g. T-joints, should also be tested, even if the utilisation is

  19. Creep behavior of microbiotic crust

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The creep behavior of microbiotic crust at room temperature was revealed by the creep bending tests of cantilever beam under constant-load conditions.The variation in the deflection with time can be depicted well by a standard creep curve.Creep rupture is a fundamental failure mechanism of microbiotic crust due to creep.A simple theory was then applied to describe this new me-chanical behavior.The existence of creep phenomenon brings into question the validity of widely used methods for measuring the strength of microbiotic crust.

  20. The Next Generation Nuclear Plant Graphite Creep Experiment Irradiation in the Advanced Test Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Blaine Grover

    2010-10-01

    The United States Department of Energy’s Next Generation Nuclear Plant (NGNP) Program will be irradiating six gas reactor graphite creep experiments in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The ATR has a long history of irradiation testing in support of reactor development and the INL has been designated as the United States Department of Energy’s lead laboratory for nuclear energy development. The ATR is one of the world’s premiere test reactors for performing long term, high flux, and/or large volume irradiation test programs. These graphite irradiations are being accomplished to support development of the next generation reactors in the United States. The graphite experiments will be irradiated over the next six to eight years to support development of a graphite irradiation performance data base on the new nuclear grade graphites now available for use in high temperature gas reactors. The goals of the irradiation experiments are to obtain irradiation performance data, including irradiation creep, at different temperatures and loading conditions to support design of the Next Generation Nuclear Plant (NGNP) Very High Temperature Gas Reactor, as well as other future gas reactors. The experiments will each consist of a single capsule that will contain six stacks of graphite specimens, with half of the graphite specimens in each stack under a compressive load, while the other half of the specimens will not be subjected to a compressive load during irradiation. The six stacks will have differing compressive loads applied to the top half of each pair of specimen stacks, while a seventh stack will not have a compressive load. The specimens will be irradiated in an inert sweep gas atmosphere with on-line temperature and compressive load monitoring and control. There will also be the capability of sampling the sweep gas effluent to determine if any oxidation or off-gassing of the specimens occurs during initial start-up of

  1. Experimental study of a macrocrack propagation in a concrete specimen subjected to creep loading

    Directory of Open Access Journals (Sweden)

    Martin E.

    2013-07-01

    Full Text Available Structures managers need a better prediction of the delayed failure of concrete structures, especially for very important structures like nuclear power plant encasement. Sustained loadings at high level (above 75% of loading capacity of the structure, can lead to structure failure after some time. In this study, a series of 4-point bending tests were performed in order to characterize the creep behaviour of pre-cracked beams under high load level. The specimens were made of normal strength concrete. A power law relationship is observed between the secondary deflection creep rate and the failure time. It is also shown that when crack propagation occurs during the creep loading, the creep deflection rate increases with the creep loading level and with the crack propagation rate.

  2. Compaction creep of sands due to time-dependent grain failure : Effects of chemical environment, applied stress, and grain size

    NARCIS (Netherlands)

    Brzesowsky, R. H.; Hangx, S. J. T.; Brantut, N.; Spiers, C. J.

    2014-01-01

    Time-dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production-induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical

  3. A Critical Analysis of the Conventionally Employed Creep Lifing Methods

    Directory of Open Access Journals (Sweden)

    Zakaria Abdallah

    2014-04-01

    Full Text Available The deformation of structural alloys presents problems for power plants and aerospace applications due to the demand for elevated temperatures for higher efficiencies and reductions in greenhouse gas emissions. The materials used in such applications experience harsh environments which may lead to deformation and failure of critical components. To avoid such catastrophic failures and also increase efficiency, future designs must utilise novel/improved alloy systems with enhanced temperature capability. In recognising this issue, a detailed understanding of creep is essential for the success of these designs by ensuring components do not experience excessive deformation which may ultimately lead to failure. To achieve this, a variety of parametric methods have been developed to quantify creep and creep fracture in high temperature applications. This study reviews a number of well-known traditionally employed creep lifing methods with some more recent approaches also included. The first section of this paper focuses on predicting the long-term creep rupture properties which is an area of interest for the power generation sector. The second section looks at pre-defined strains and the re-production of full creep curves based on available data which is pertinent to the aerospace industry where components are replaced before failure.

  4. Long-term creep strength degradation in T122/P122 steels for USC power plants

    Energy Technology Data Exchange (ETDEWEB)

    Igarashi, M.; Yoshizawa, M. [Corporate Research and Development Laboratories, Hyogo (Japan); Iseda, A. [Tubular Products Technology Department, Tokyo (Japan); Matsuo, H.; Kan, T. [Quality Control and Technical Service Department, Hyogo (Japan)

    2006-07-01

    Creep rupture and deformation behavior of KA-SUS410J3 type steels (equivalent to ASME P122/T122) with different Cr content and the resultant matrix phases such as {alpha}' (martensite) and {alpha}'+ {delta} (martensite and deltaferrite) has been studied using creep testing and a detailed TEM observation. New allowable tensile stress values of the steels with two different Cr content levels set using the region splitting method in Japan are tabulated. Long-term creep rupture strength, in particular, of the {alpha}'+ {delta} dual phase steel is found to be lower than that expected from the short-term creep testing. Fine grain microstructure is found to enhance the creep deformation at lower stress region and decrease in fine MX and unequal distribution of MX in the ferrite matrix are to be the major causes of the strength degradation in the {alpha}'+ {delta} dual phase steel with the higher Cr content. It is concluded that the heterogeneous creep deformation is much more pronounced at lower stress level in the dual phase steel, which is due to inhomogeneous microstructure consisting of {alpha}'+{delta} phase matrix and the relevant heterogeneous distribution of fine precipitates such as MX and M{sub 23}C{sub 6} in the {delta} ferrite matrix and near the interface between the soft {delta} ferrite and the hard martensite ({alpha}') phases. Homogeneous microstructure is a key for achieving the long-term creep strength in the advanced ferritic steels at elevated temperatures over 600 C. KA-SUS410J2TB steel (designated as HCM12) is found to exhibit a similar creep strength degradation, which is mainly due to a similar microstructure of KA-SUS410J3 type steel with the higher Cr content. (orig.)

  5. Long-term creep deformation characteristics of advanced ferritic steels for USC power plants

    Energy Technology Data Exchange (ETDEWEB)

    Yoshizawa, M. [Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, Amagasaki, Hyogo, 660-0891 (Japan); Igarashi, M. [Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, Amagasaki, Hyogo, 660-0891 (Japan)

    2007-01-15

    Creep rupture and deformation behavior of T122-type steels with different matrix phases such as {alpha}' (martensite) and {alpha}{sup '}+{delta} (martensite and delta-ferrite) at different stress levels has been studied using creep testing and a detailed FE-STEM microscopy. Long-term creep rupture strength of the dual phase steel is found to be lower than that expected from the short-term creep testing. Fine grain microstructure enhances the creep deformation of the dual phase steel at lower stress region, but is not the major factor on the degradation. Decrease in fine MX and unequal distribution of MX in the ferrite matrix are found to be the major causes of the strength degradation in the dual phase steel with the higher Cr content. It is thus concluded that the heterogeneous creep deformation is much more pronounced at lower stress level in the dual phase steel, which is due to inhomogeneous microstructure consisting of {alpha}{sup '}+{delta} phase matrix and the relevant heterogeneous distribution of fine precipitates such as MX and M{sub 23}C{sub 6} in the {delta}-ferrite matrix and near the interface between {delta}/{gamma}.

  6. Long-term creep deformation characteristics of advanced ferritic steels for USC power plants

    Energy Technology Data Exchange (ETDEWEB)

    M. Yoshizawa; M. Igarashi [Sumitomo Metal Industries, Ltd., Hyogo (Japan). Corporate Research and Development Laboratories

    2007-01-15

    Creep rupture and deformation behavior of T122-type steels with different matrix phases such as {alpha}{prime} (martensite) and {alpha}{prime}+{delta} (martensite and delta-ferrite) at different stress levels has been studied using creep testing and a detailed FE-STEM microscopy. Long-term creep rupture strength of the dual phase steel is found to be lower than that expected from the short-term creep testing. Fine grain microstructure enhances the creep deformation of the dual phase steel at lower stress region, but is not the major factor on the degradation. Decrease in fine MX and unequal distribution of MX in the ferrite matrix are found to be the major causes of the strength degradation in the dual phase steel with the higher Cr content. It is thus concluded that the heterogeneous creep deformation is much more pronounced at lower stress level in the dual phase steel, which is due to inhomogeneous microstructure consisting of {alpha}{prime}+{delta} phase matrix and the relevant heterogeneous distribution of fine precipitates such as MX and M{sub 23}C{sub 6} in the {delta}ferrite matrix and near the interface between {delta}/{gamma}.

  7. Physical Metallurgy of Modern Creep-Resistant Steel for Steam Power Plants: Microstructure and Phase Transformations

    Directory of Open Access Journals (Sweden)

    V. C. Igwemezie

    2016-01-01

    Full Text Available The fact that the microstructure of steel depends on its composition and the heat treatment given to it has been heavily exploited in the design of steel for power plant applications. To obtain a steel that can function at the higher temperature where power plants operate without failure for extended life, heat treatment is needed to produce fine and highly stable dispersion of carbides, nitrides, and intermetallic compounds in the microstructure of the material. A significant contribution also comes from solid solution strengthening by substitutional solutes. We review here various types of phases, microstructures, functions, and interacting effects of the various alloying elements in the design of steel for modern power plant application.

  8. Deterministic Multiaxial Creep and Creep Rupture Enhancements for CARES/Creep Integrated Design Code

    Science.gov (United States)

    Jadaan, Osama M.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep rupture criterion. However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of sum, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of Ns methodology and the

  9. Tensile Creep and Fatigue of Sylramic-iBN Melt-Infiltrated SiC Matrix Composites: Retained Properties, Damage Development, and Failure Mechanisms

    Science.gov (United States)

    Morscher, Greg; Gowayed, yasser; Miller, Robert; Ojard, Greg; Ahmad, Jalees; Santhosh, Unni; John, Reji

    2008-01-01

    An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of ceramic matrix composites (CMC) envisioned for use in gas turbine engine applications are essential for component design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxidation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204 C for the SiC/SiC CMC system consisting of Sylramic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated (MI) SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room temperature to determine the residual properties. The retained properties of most of the composites subjected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the as-produced elastic modulus. It was observed that during creep, residual stresses in the composite are altered to some extent which results in an increased compressive stress in the matrix upon cooling and a subsequent increased stress required to form matrix cracks. Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature retained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution of stress-dependent matrix cracking at 1204 C was similar to the as-produced composites at room temperature; however, matrix crack growth occurred over time and typically did not appear to propagate through thickness except at final failure crack. Failure of the composites was due to either oxidation-induced unbridged crack growth, which dominated the higher stress regime (> 179 MPa) or controlled by degradation of the fibers, probably caused by

  10. Failure investigation of a secondary super heater tube in a 140 MW thermal power plant

    Directory of Open Access Journals (Sweden)

    Atanu Saha

    2017-04-01

    Full Text Available This article describes the findings of a detailed investigation into the failure of a secondary super heater tube in a 140 MW thermal power plant. Preliminary macroscopic examinations along with visual examination, dimensional measurement and chemical analysis were carried out to deduce the probable cause of failure. In addition optical microscopy was a necessary supplement to understand the cause of failure. It was concluded that the tube had failed due to severe creep damage caused by high metal temperature during service. The probable causes of high metal temperature may be in sufficient flow of steam due to partial blockage, presence of thick oxide scale on ID surface, high flue gas temperature etc. rupture.

  11. Creep modelling of particle strengthened steels

    OpenAIRE

    Magnusson, Hans

    2010-01-01

    Materials used in thermal power plants have to resist creep deformation for time periods up to 30 years. Material evaluation is typically based on creep testing with a maximum duration of a few years. This information is used as input when empirically deriving models for creep. These kinds of models are of limited use when considering service conditions or compositions different from those in the experiments. In order to provide a more general model for creep, the mechanisms that give creep s...

  12. Investigation of valve failure problems in LWR power plants

    Energy Technology Data Exchange (ETDEWEB)

    None

    1980-04-01

    An analysis of component failures from information in the computerized Nuclear Safety Information Center (NSIC) data bank shows that for both PWR and BWR plants the component category most responsible for approximately 19.3% of light water reactor (LWR) power plant shutdowns. This investigation by Burns and Roe, Inc. shows that the greatest cause of shutdowns in LWRs due to valve failures is leakage from valve stem packing. Both BWR plants and PWR plants have stem leakage problems (BWRs, 21% and PWRs, 34%).

  13. Study on creep-fatigue damage evaluation for advanced 9%-12% chromium steels under stress controlled cycling

    Institute of Scientific and Technical Information of China (English)

    Peng ZHAO; Fuzhen XUAN

    2011-01-01

    Creep-fatigue interaction is one of the main damage mechanisms in high temperature plants and their components. Assessment of creep-fatigue properties is of practical importance for design and operation of high temperature components. However, the standard evaluation techniques, i.e. time fraction rule and ductility exhaustion one have limitations in accounting for the effects of control mode on the cyclic deformations. It was found that conventional linear cumulative damage rule failed in accurately evaluating the creep-fatigue life under stress controlled condition. The calculated creep damages by time fraction rule were excessively high, which led to overly conservative prediction of failure lives. In the present study, it was suggested that such over estimation of creep damage was mainly caused by anelastic strain upon stress loading. For precise assessment under conditions of stress control, a modified creep damage model accounting for the effect of anelastic creep was proposed. The assessments of creep fatigue data under stress controlled condition were performed with the new approach developed in this paper for a rotor material and a boiler material used in ultra supercritical power plants. It was shown that a more moderate amount of creep damage was obtained by the new model, which gave better predictions of failure life.

  14. Cast Steels for Creep-resistant Parts Used in Heat Treatment Plants

    Directory of Open Access Journals (Sweden)

    A. Drotlew

    2012-12-01

    Full Text Available Creep-resistant parts of heat treatment furnaces are in most cases made from high-alloyed chromium-nickel and nickel-chromium ironalloys, both cast and wrought. This paper presents the types of casting alloys used for this particular purpose, since the majority of furnace components are made by the casting process. Standards were cited which give symbols of alloy grades used in technical specifications by the domestic industry. It has been indicated that castings made currently are based on a wider spectrum of the creep-resistant alloy grades than the number of alloys covered by the standards. Alloy grades recommended by the technical literature for individual parts of the furnace equipment were given. The recommendations reflect both the type of the technological process used and the technical tasks performed by individual parts of the furnace equipment. Comments were also made on the role of individual alloying elements in shaping the performance properties of castings.

  15. Cast Steels for Creep-Resistant Parts Used in Heat Treatment Plants

    Directory of Open Access Journals (Sweden)

    Drotlew A.

    2012-12-01

    Full Text Available Creep-resistant parts of heat treatment furnaces are in most cases made from high-alloyed chromium-nickel and nickel-chromium iron alloys, both cast and wrought. This paper presents the types of casting alloys used for this particular purpose, since the majority of furnace components are made by the casting process. Standards were cited which give symbols of alloy grades used in technical specifications by the domestic industry. It has been indicated that castings made currently are based on a wider spectrum of the creep-resistant alloy grades than the number of alloys covered by the standards. Alloy grades recommended by the technical literature for individual parts of the furnace equipment were given. The recommendations reflect both the type of the technological process used and the technical tasks performed by individual parts of the furnace equipment. Comments were also made on the role of individual alloying elements in shaping the performance properties of castings.

  16. Creep/Stress Rupture Behavior and Failure Mechanisms of Full CVI and Full PIP SiC/SiC Composites at Elevated Temperatures in Air

    Science.gov (United States)

    Bhatt, R. T.; Kiser, J. D.

    2017-01-01

    SiC/SiC composites fabricated by melt infiltration are being considered as potential candidate materials for next generation turbine components. However these materials are limited to 2400 F application because of the presence of residual silicon in the SiC matrix. Currently there is an increasing interest in developing and using silicon free SiC/SiC composites for structural aerospace applications above 2400 F. Full PIP or full CVI or CVI + PIP hybrid SiC/SiC composites can be fabricated without excess silicon, but the upper temperature stress capabilities of these materials are not fully known. In this study, the on-axis creep and rupture properties of the state-of-the-art full CVI and full PIP SiC/SiC composites with Sylramic-iBN fibers were measured at temperatures to 2700 F in air and their failure modes examined. In this presentation creep rupture properties, failure mechanisms and upper temperature capabilities of these two systems will be discussed and compared with the literature data.

  17. Deformation and crack growth response under cyclic creep conditions

    Energy Technology Data Exchange (ETDEWEB)

    Brust, F.W. Jr. [Battelle Memorial Institute, Columbus, OH (United States)

    1995-12-31

    To increase energy efficiency, new plants must operate at higher and higher temperatures. Moreover, power generation equipment continues to age and is being used far beyond its intended original design life. Some recent failures which unfortunately occurred with serious consequences have clearly illustrated that current methods for insuring safety and reliability of high temperature equipment is inadequate. Because of these concerns, an understanding of the high-temperature crack growth process is very important and has led to the following studies of the high temperature failure process. This effort summarizes the results of some recent studies which investigate the phenomenon of high temperature creep fatigue crack growth. Experimental results which detail the process of creep fatigue, analytical studies which investigate why current methods are ineffective, and finally, a new approach which is based on the T{sup *}-integral and its ability to characterize the creep-fatigue crack growth process are discussed. The potential validity of this new predictive methodology is illustrated.

  18. Development of creep damage assessment system for aged thermal power plant

    Energy Technology Data Exchange (ETDEWEB)

    Nonaka, Isamu [IshikawaJima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Umaki, Hideo [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Nishida, Hidetalca [The Chugoku Electric Power Co., Inc., Hiroshima (Japan); Yamaguchi, Hiroshi [The Chugoku Electric Power Co., Inc., Hiroshima (Japan)

    1998-12-31

    IHI has developed the Creep Damage Assessment System to identify voids by processing an image observed by a small laser microscope with an advanced image processing technique jointly with Chugoku Electric Power Co., Inc. The result can be obtained immediately on the spot. Application tests of the system at the Unit No.3 boiler of the Kudamatsu Power Station showed good operability, adaptability to the environment, and accuracy. The new system can easily indicate damage conditions in parts during the periodical inspection, allowing rapid maintenance. Time reduction required for assessment and increased reliability of equipment can be also achieved. (orig.)

  19. Effect of creep stress on the microstructure of 9-12% Cr steel for rotor materials.

    Science.gov (United States)

    Dong, Jiling; He, Yinsheng; Kim, Minsoo; Shin, Keesam

    2013-08-01

    High-chromium heat-resistant steel has been widely used as the key material to improve the condition of steam pressure and temperature in the modern high-efficiency power plants. Despite the use of the steel above 550°C for several decades, its major failure is owing to the creep fracture. In this study, the effect of creep stress on the microstructure in 9-12% Cr steel has been investigated microscopically, and it is clarified that the creep stress enhances precipitation of Laves phase and influences the lath width and dislocation density in lath interior.

  20. Characterisation of the micro- and nanoscale structure of new creep-resistant steels for use in advanced USC steam power plants

    Energy Technology Data Exchange (ETDEWEB)

    Zielinska-Lipiec, A.; Czyrska-Filemonowicz, A. [AGH University of Science & Technology, Krakow (Poland)

    2007-05-15

    The microstructure in the as received condition and after long-term creep exposure (up to about 57000 h at 600 and 650{sup o}C of the martensitic 9-12% chromium steels (P92, P91, E911, CB6) developed for advanced ultra supercritical coal-fired power plants has been investigated. Using analytical TEM statistical quantitative analyses were undertaken to determine the micro- and nanoscale structure parameters (dislocation density within the subgrains, the width of the martensite laths/subgrains and the particles parameters). Results of the TEM analyses reveal significant influence of a microstructure after initial heat treatment on the creep strength.

  1. Creep damage and expected creep life for welded 9-11% Cr steels

    Energy Technology Data Exchange (ETDEWEB)

    Auerkari, P. [VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 (Finland)]. E-mail: Pertti.Auerkari@vtt.fi; Holmstroem, S. [VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 (Finland); Veivo, J. [VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 (Finland); Salonen, J. [VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 (Finland)

    2007-01-15

    The damage mechanisms affecting engineering steels at high-temperatures include creep cavitation and cracking that can form the path for final failure in susceptible locations such as welds. The evolution of observed damage is widely used in condition monitoring, timing of inspections and support of life management. However, the damage evolution is material dependent, and requires confirmation from inspection data. For most low-alloy steels, compilations of inspection data have been applied to establish guidelines for this purpose. Useful experience of the in-service damage is less easily available from newer steels, and infrequently reported from e.g. the 9-11% chromium (Cr) steels that are used in hot steam lines of power plants. However, even then the expected damage evolution can be characterised by using high tensile multi-axiality for damage acceleration. This approach is also useful for ductile steels with relatively slow development of creep cavitation in conventional creep testing. The inspection experience shows very modest creep cavitation in the conventional 11% Cr steel X20CrMoV11-1 even after long-term service. This is of particular interest also because early creep failures have been reported from steam systems made of P91 (X10CrMoVNb9-1). The differences between these steels appear to be largely related to the extent precipitation hardening is utilized in providing creep strength. With more efficient precipitation hardening, P91 and other new high chromium steels are more susceptible than X20 to deviations in e.g. heat treatments.

  2. Research on the creep damage and interfacial failure of dissimilar metal welded joint between 10Cr9Mo1VNbN and 12Cr1MoV steel

    Institute of Scientific and Technical Information of China (English)

    张建强; 赵海燕; 吴甦; 鹿安理; 王煜; 章应霖

    2004-01-01

    The mechanical properties, creep damage, creep rupture strength and features of interfacial failures of welded joints between martensite (SA213T91) and pearlite steel (12Cr1MoV) have been investigated by means of argon tungsten pulsed arc welding, high temperature accelerated simulation, creep rupture, mechanical property tests and scanning electronic microscope (SEM). The research results indicate that the mechanical properties of overmatched and medium matched joint deteriorate obviously, and they are susceptible to creep damage and failure after accelerated simulation operation 500h, in the condition of preheat 250℃, and post welding heat treatment 750℃×1h. However, the mechanical properties of undermatched joint are the best, the interfacial failure tendency of undermatched welded joint is less than those of medium and overmatched welded joint. Therefore, it is reasonable that low alloy material TR31 is used as the filler metal of weld between SA213T91and 12Cr1MoV steel.

  3. Creep-Fatigue Damage Investigation and Modeling of Alloy 617 at High Temperatures

    Science.gov (United States)

    Tahir, Fraaz

    The Very High Temperature Reactor (VHTR) is one of six conceptual designs proposed for Generation IV nuclear reactors. Alloy 617, a solid solution strengthened Ni-base superalloy, is currently the primary candidate material for the tubing of the Intermediate Heat Exchanger (IHX) in the VHTR design. Steady-state operation of the nuclear power plant at elevated temperatures leads to creep deformation, whereas loading transients including startup and shutdown generate fatigue. A detailed understanding of the creep-fatigue interaction in Alloy 617 is necessary before it can be considered as a material for nuclear construction in ASME Boiler and Pressure Vessel Code. Current design codes for components undergoing creep-fatigue interaction at elevated temperatures require creep-fatigue testing data covering the entire range from fatigue-dominant to creep-dominant loading. Classical strain-controlled tests, which produce stress relaxation during the hold period, show a saturation in cycle life with increasing hold periods due to the rapid stress-relaxation of Alloy 617 at high temperatures. Therefore, applying longer hold time in these tests cannot generate creep-dominated failure. In this study, uniaxial isothermal creep-fatigue tests with non-traditional loading waveforms were designed and performed at 850 and 950°C, with an objective of generating test data in the creep-dominant regime. The new loading waveforms are hybrid strain-controlled and force-controlled testing which avoid stress relaxation during the creep hold. The experimental data showed varying proportions of creep and fatigue damage, and provided evidence for the inadequacy of the widely-used time fraction rule for estimating creep damage under creep-fatigue conditions. Micro-scale damage features in failed test specimens, such as fatigue cracks and creep voids, were quantified using a Scanning Electron Microscope (SEM) to find a correlation between creep and fatigue damage. Quantitative statistical

  4. Deterministic and Probabilistic Creep and Creep Rupture Enhancement to CARES/Creep: Multiaxial Creep Life Prediction of Ceramic Structures Using Continuum Damage Mechanics and the Finite Element Method

    Science.gov (United States)

    Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and

  5. Seismic Creep

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden erupture associated with an earthquake. It is a usually slow deformation...

  6. Creeping eruption

    Science.gov (United States)

    ... are infected. Symptoms Symptoms of creeping eruption include: Blisters Itching , may be more severe at night Raised, ... enter the body through bare feet, so wearing shoes in areas where hookworm infestations are known to ...

  7. TOPICAL REVIEW: Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

    National Research Council Canada - National Science Library

    Fujio Abe

    2008-01-01

    .... Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine dispersion...

  8. Constitutive Expression of Rice MicroRNA528 Alters Plant Development and Enhances Tolerance to Salinity Stress and Nitrogen Starvation in Creeping Bentgrass.

    Science.gov (United States)

    Yuan, Shuangrong; Li, Zhigang; Li, Dayong; Yuan, Ning; Hu, Qian; Luo, Hong

    2015-09-01

    MicroRNA528 (miR528) is a conserved monocot-specific small RNA that has the potential of mediating multiple stress responses. So far, however, experimental functional studies of miR528 are lacking. Here, we report that overexpression of a rice (Oryza sativa) miR528 (Osa-miR528) in transgenic creeping bentgrass (Agrostis stolonifera) alters plant development and improves plant salt stress and nitrogen (N) deficiency tolerance. Morphologically, miR528-overexpressing transgenic plants display shortened internodes, increased tiller number, and upright growth. Improved salt stress resistance is associated with increased water retention, cell membrane integrity, chlorophyll content, capacity for maintaining potassium homeostasis, CATALASE activity, and reduced ASCORBIC ACID OXIDASE (AAO) activity; while enhanced tolerance to N deficiency is associated with increased biomass, total N accumulation and chlorophyll synthesis, nitrite reductase activity, and reduced AAO activity. In addition, AsAAO and COPPER ION BINDING PROTEIN1 are identified as two putative targets of miR528 in creeping bentgrass. Both of them respond to salinity and N starvation and are significantly down-regulated in miR528-overexpressing transgenics. Our data establish a key role that miR528 plays in modulating plant growth and development and in the plant response to salinity and N deficiency and indicate the potential of manipulating miR528 in improving plant abiotic stress resistance.

  9. Penstock failure detection system at the "Valsan" hydro power plant

    Science.gov (United States)

    Georgescu, A. M.; Coşoiu, C. I.; Alboiu, N.; Hlevca, D.; Tataroiu, R.; Popescu, O.

    2012-11-01

    "Valsan" is a small Hydro Power Plant, 5 MW, situated at about 160 km north of Bucharest, Romania, on the small "Valsan" river in a remote mountainous area. It is equipped with a single Francis turbine. The penstock is located in the access shaft of the HPP. "Hidroelectrica", the Romanian company that operates the HPP, was trying to implement a remote penstock failure detection system. Starting from a classic hydraulic problem, the authors of the paper derived a method for failure detection and localization on the pipe. The method assumes the existence of 2 flow meters and 2 pressure transducers at the inlet and outlet of the pressurized pipe. Calculations have to be based on experimental values measured in a permanent regime for different values of the flow rate. The method was at first tested on a pipe, in the Hydraulic Laboratory of the Technical University of Civil Engineering Bucharest. Pipe failure was modelled by opening of a valve on a tee branch of the analyzed pipe. Experimental results were found to be in good agreement with theoretical ones. The penstock of the "Valsan" HPP, was modelled in EPANET, in order to: i) test the method at a larger scale; ii) get the right flow and pressure transducers that are needed to implement it. At the request of "Hidroelectrica" a routine that computes the efficiency of the turbine was added to the monitoring software. After the system was implemented, another series of measurements were performed at the site in order to validate it. Failure was modelled by opening an existing valve on a branch of the penstock. Detection of the failure was correct and almost instantaneous, while failure location was accurate within 5% of the total penstock length.

  10. Leningrad nuclear power plant pressure tube failure investigations

    Energy Technology Data Exchange (ETDEWEB)

    Bruchertseifer, H.; Bart, G.; Restani, R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Aden, V.G.; Abramov, V.Y.; Kalachikov, V.E.; Kozlov, A.V. [Research and Development Inst. of Power Engineering (RDIPE), Moscow and Sverdlovsk (Russian Federation); Subbotin, A.V.; Smirnov, E.A. [Moscow Engineering Physics Inst., Moscow (Russian Federation)

    1996-09-01

    During March 1992 a fuel pressure tube of a reactor channel of the Leningrad Nuclear Power Plant underwent a temperature excursion after a coolant flow blockage and was destroyed. In the following, within the Swiss Eastern European aid program a collaboration was set up for a project between the Moscow Research and Development Institute of Power Engineering, the designer of the RBMK-reactors, and the Paul Scherrer Institute. An intensive failure analysis program was started, based on modern equipment available at PSI for analysis of highly radioactive material and on the experience of both institutes in investing failures of reactor structure materials, with the goal of establishing the accident temperature evolution in time. This report presents the results of studies undertaken in order to determine the parameters which govern the events during the accident obtained from an analysis of the tube failure material together with evaluations of the apparent phase and structure changes. Our analysis of experimental data for oxygen distribution and the diffusion coefficient calculations showed that the temperatures exceeded 1300{sup o}C, which is much higher than results from previous studies performed in standard failure post-irradiation examination. The results obtained are important in that they have allowed to revise the previous assessments of the initial thermal conditions of the accident progression. In particular, they already served as a basis for determining the efficiency of the RBMK safety improvement measures carried out in response to the accident. (author) 8 figs., 5 refs.

  11. Deformation and failure behaviour of pipe bends subject to internal pressure and constant additional moment in the creep range; Verformungs- und Versagensverhalten von Rohrbogen unter Innendruck und konstantem Zusatzmoment im Kriechbereich

    Energy Technology Data Exchange (ETDEWEB)

    Kussmaul, K. [Staatliche Materialpruefungsanstalt (MPA), Univ. Stuttgart (Germany); Maile, K. [Staatliche Materialpruefungsanstalt (MPA), Univ. Stuttgart (Germany); Purper, H. [Staatliche Materialpruefungsanstalt (MPA), Univ. Stuttgart (Germany)

    1996-08-01

    A series of failures on pipe bends, which occurred in the creep range, necessitated the carrying out of the research project `Internal pressure tests on pipe bends of heat-resistant steels with additionally applied bending moments at temperatures within the creep range` for the formulation of principles and regulations for qualifying design and expert assessment of creep-stressed pipe bends. The incidence of failure on pipe bends can be described on the basis of the results obtained (assessment of cause of damage, characterization of time-dependent stress condition); therefore a catastrophic failure can be excluded by monitoring of pipe bends. Proposals for revising the existing regulation (TRD 301) are focussed on avoiding this kind of damage. (orig.) [Deutsch] Eine Reihe von Schaeden an Rohrbogen, die im Zeitstandbereich beansprucht waren, erforderten die Durchfuehrung des Forschungsvorhabens `Innendruckversuche an Rohrbogen aus warmfesten Staehlen mit zusaetzlich aufgebrachten Biegemonmenten bei Temperaturen im Kriechbereich` zur Schaffung von Grundlagen und Regeln fuer eine qualifizierte Auslegung und Begutachtung kriechbeanspruchter Rohrbogen. Auf der Grundlage der erzielten Ergebnisse (Bewertung des Schaedigungsablaufes, Charakterisierung des zeitabhaengigen Beanspruchungszustandes) ist der Versagensablauf an Rohrbogen beschreibbar; es kann daher in der Ueberwachung von Rohrbogen ein katastrophales Versagen ausgeschlossen werden. Vorschlaege zur Modifizierung des bestehenden Regelwerkes (TRD 301) konzentrieren sich darauf, derartige Schaeden zu vermeiden. (orig.)

  12. On the microstructural basis of creep strength and creep-fatigue interaction in 9-12% Cr steels for application in power plants

    OpenAIRE

    Chilukuru, Hemambar

    2007-01-01

    As part of the efforts of preserving the environment it is necessary to reduce of the CO2 emissions from power plants. This can be done by increasing the plant efficiency. Research groups around the world are engaged in developing new steels capable of sustaining higher stresses and temperatures envisaged for high-efficiency power plants. Research carried out in Europe is organized within the COST Programme (Co-Operation in Science and Technology) aiming at replacing the conventional steels o...

  13. TOPICAL REVIEW: Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

    Directory of Open Access Journals (Sweden)

    Fujio Abe

    2008-01-01

    Full Text Available It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of creep strength and for improving long-term creep strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher creep strength at 650 °C than existing high-strength steels used for thick section boiler components.

  14. Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants.

    Science.gov (United States)

    Abe, Fujio

    2008-01-01

    It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of creep strength and for improving long-term creep strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher creep strength at 650 °C than existing high-strength steels used for thick section boiler components.

  15. Micromechanical studies of cyclic creep fracture under stress controlled loading

    DEFF Research Database (Denmark)

    van der Giessen, Erik; Tvergaard, Viggo

    1996-01-01

    This paper deals with a study of intergranular failure by creep cavitation under stress-controlled cyclic loading conditions. Loading is assumed to be slow enough that diffusion and creep mechanisms (including grain boundary sliding) dominate, leading to intergranular creep fracture. This study i...

  16. Micromechanical studies of cyclic creep fracture under stress- controlled loading

    NARCIS (Netherlands)

    Giessen, E. van der; Tvergaard, V.

    1996-01-01

    This paper deals with a study of intergranular failure by creep cavitation under stress-controlled cyclic loading conditions. Loading is assumed to be slow enough that diffusion and creep mechanisms (including grain boundary sliding) dominate, leading to intergranular creep fracture. This study is

  17. Design of the Next Generation Nuclear Plant Graphite Creep Experiments for Irradiation in the Advanced Test Reactor

    Energy Technology Data Exchange (ETDEWEB)

    S. Blaine Grover

    2009-05-01

    The United States Department of Energy’s Next Generation Nuclear Plant (NGNP) Program will be irradiating six gas reactor graphite creep experiments in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The ATR has a long history of irradiation testing in support of reactor development and the INL has been designated as the new United States Department of Energy’s lead laboratory for nuclear energy development. The ATR is one of the world’s premiere test reactors for performing long term, high flux, and/or large volume irradiation test programs. These graphite irradiations are being accomplished to support development of the next generation reactors in the United States. The graphite experiments will be irradiated over the next six to eight years to support development of a graphite irradiation performance data base on the new nuclear grade graphites now available for use in high temperature gas reactors. The goals of the irradiation experiments are to obtain irradiation performance data at different temperatures and loading conditions to support design of the Next Generation Nuclear Plant Very High Temperature Gas Reactor, as well as other future gas reactors. The experiments will each consist of a single capsule that will contain seven separate stacks of graphite specimens. Six of the specimen stacks will have half of their graphite specimens under a compressive load, while the other half of the specimens will not be subjected to a compressive load during irradiation. The six stacks will be organized into pairs with a different compressive load being applied to the top half of each pair of specimen stacks. The seventh stack will not have a compressive load on the graphite specimens during irradiation. The specimens will be irradiated in an inert sweep gas atmosphere with on-line temperature and compressive load monitoring and control. There will also be the capability of sampling the sweep gas effluent to determine if any

  18. Creep rupture behavior of unidirectional advanced composites

    Science.gov (United States)

    Yeow, Y. T.

    1980-01-01

    A 'material modeling' methodology for predicting the creep rupture behavior of unidirectional advanced composites is proposed. In this approach the parameters (obtained from short-term tests) required to make the predictions are the three principal creep compliance master curves and their corresponding quasi-static strengths tested at room temperature (22 C). Using these parameters in conjunction with a failure criterion, creep rupture envelopes can be generated for any combination of in-plane loading conditions and ambient temperature. The analysis was validated experimentally for one composite system, the T300/934 graphite-epoxy system. This was done by performing short-term creep tests (to generate the principal creep compliance master curves with the time-temperature superposition principle) and relatively long-term creep rupture tensile tests of off-axis specimens at 180 C. Good to reasonable agreement between experimental and analytical results is observed.

  19. The effect of environment on the creep deformation of ultra-high purity nickel-chromium-iron alloys at 360 degrees Celcius

    Science.gov (United States)

    Paraventi, Denise Jean

    2000-10-01

    Steam generators in pressurized water nuclear power plants have experienced significant problems with intergranular stress corrosion cracking (IGSCC) on the inner diameter of steam generator tubing for over 25 years. In the course of research to understand IGSCC, it has been shown that creep deformation may play a significant role in the cracking of commercial Alloy 600 (Ni-16Cr-9Fe-0.03C). The primary water environment can cause decreases in creep resistance (i.e., faster creep rates, shorter time to failure, and higher creep strains). During corrosion under the conditions of interest, both hydrogen reduction and metal dissolution occur. One or both may contribute to the enhancement of creep. The purpose of this work was to isolate the mechanism by which the water environment causes the creep deformation to increase. Activation area and activation enthalpy for glide were measured in argon and primary water on high purity Ni-16Cr-9Fe alloys. The results indicated that the activation area was reduced by primary water, consistent with a hydrogen enhanced plasticity mechanism for enhanced creep. The stress dependence of creep was also examined in argon and primary water. The results indicated that the internal stress of the alloy is reduced by the primary water environment. Lower internal stress is consistent with both a hydrogen model as well as a vacancy-aided climb model for enhanced creep. To isolate the effect of hydrogen on the creep of the alloy, experiments were conducted in a dissociated hydrogen environment. The results indicated that hydrogen would only increase the steady state creep rate if present before loading of the samples. However, if the sample was already in steady state creep and hydrogen introduced, a transient in the creep strain was observed. The creep rate returned to the original steady state rate in a short time. The results indicate that while hydrogen does affect the steady state creep to an extent, hydrogen cannot completely account for

  20. Numerical Simulation on Interfacial Creep Failure of Dissimilar Metal Welded Joint between HR3C and T91 Heat-Resistant Steel

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jianqiang; TANG Yi; ZHANG Guodong; ZHAO Xuan; GUO Jialin; LUO Chuanhong

    2016-01-01

    The maximum principal stress, von Mises equivalent stress, equivalent creep strain, stress triaxiality in dissimilar metal welded joints between austenitic (HR3C) and martensitic heat-resistant steel (T91) are simulated by FEM at 873 K and under inner pressure of 42.26 MPa. The results show that the maximum principal stress and von Mises equivalent stress are quite high in the vicinity of weld/T91 interface, creep cavities are easy to form and expand in the weld/T91 interface. There are two peaks of equivalent creep strains in welded joint, and the maximum equivalent creep strain is in the place 27-32 mm away from the weld/T91 interface, and there exists creep constrain region in the vicinity of weld/T91 interface. The high stress triaxiality peak is located exactly at the weld/T91 interface. Accordingly, the weld/T91 interface is the weakest site of welded joint. Therefore, using stress triaxiality to describe creep cavity nucleation and expansion and crack development is reasonable for the dissimilar metal welded joint between austenitic and martensitic steel.

  1. Creep Behavior and Microstructure Evolution of P92 Steel During Creep Test at 873 K

    Science.gov (United States)

    Zhang, Zuogui; Shi, Kexian; Wang, Yanfeng; Lin, Fusheng

    In this paper, the creep behavior of P92 steel has been analyzed by creep strain and creep rate variations after the creep tests were stopped at the steady-state creep stage. The microstructure evolution of the P92 steel at the steady-state stage during creep test at 873 K under different load stresses of 125-160 MPa were studied by using a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM). The grain boundary characteristics in the P92 steels during creep test were investigated by an electron backscattered diffraction (EBSD) technique. Experimental results showed that with increasing load stresses from 125 MPa to 160 MPa, creep rates of the P92 steels increased in Norton's power law relation and creep times to the steady-state creep stage decreased. With decreasing load stresses and increasing creep times, martensite lath microstructure occurred recovery and the dislocation densities in ferritic matrix decreased. M23C6 particles located in prior austenite grain, sub-grain and lath boundaries showed slight coarsening. Some Laves phase particles precipitated in the grain boundaries for the P92 specimens after creep test under a load stress of 125 MPa. Comparing to as-tempered P92 steel, the volume fractions of LAGBs are lower and the volume fraction of HAGBs are higher with decreasing load stresses and increasing creep times. It is considered that understanding on creep behavior and microstructual evolution of the P92 steels during creep test will effectively support life design and assessment of the high temperature metal parts in fossil-fired power plant.

  2. Influence of creep and cyclic oxidation in thermal barrier coatings

    Energy Technology Data Exchange (ETDEWEB)

    Seiler, Philipp; Baeker, Martin; Roesler, Joachim [Technische Univ. Braunschweig (Germany). Inst. fuer Werkstoffe

    2012-01-15

    The lifetime of thermal barrier coating systems is limited by cracks close to the interfaces, causing delamination. To study the failure mechanisms, a simplified model system is analysed which consists of a bond-coat bulk material, a thermally grown oxide, and an yttria-stabilised zirconia topcoat. The stresses in the model system are calculated using a finite element model which covers the simulation of full thermal cycles, creep in all layers, and the anisotropic oxidation during dwelling. Creep in the oxide and the thermal barrier coating is varied with the use of different creep parameter sets. The influence of creep in the bondcoat is analysed by using two different bond-coat materials: fast creeping Fecralloy and slow creeping oxide dispersion strengthened MA956. It is shown that creep in the bondcoat influences the lifetime of the coatings. Furthermore, a fast creeping thermally grown oxide benefits the lifetime of the coating system. (orig.)

  3. Design of heat treatments for 9-12%Cr steels to optimise creep resistance for power plant applications

    Energy Technology Data Exchange (ETDEWEB)

    Morris, P.F.; Sachadel, U.A.; Clarke, P.D. [Tata Steel Europe, Rotherham (United Kingdom). Swinden Technology Centre; CRD and T, IJmuiden (Netherlands)

    2010-07-01

    Optimisation of the creep rupture properties of Steel 92 (9%Cr, 0.5%Mo, 2%W) by modification of heat treatment and C:N ratio has been studied. It was shown that a higher austenization temperature and double tempering at lower temperature can significantly extend creep life of the standard composition. The increase in austenization temperature from 1060 C and double tempering at 660 C/3h instead of single tempering at 780 C/2h resulted in the increase of stress rupture life from 1,734 to 6,179h at 650 C/110MPa. Even greater improvement in creep life was achieved by the combination of the modified heat treatment and decreased C:N ratio. In this case the creep life was extended to 10,255 h at 650 C/110MPa. A further increase in austenitization temperature to 1200 C for the decreased C:N ratio variant extended the rupture life to 17,118h. Initial results indicate that this modified heat treatment schedule does not result in notch brittle behaviour and most of the improvement in creep strength remains after a simulated post weld heat treatment at 740 C. The stress rupture programme is continuing and at 600 C test durations are approaching 60,000h. To explain the effect on rupture life thermodynamic calculations, microscopic investigations and a literature study were performed. Electron metallography investigations revealed that the lower tempering temperature resulted in a finer distribution of nano-size particles. Calculations show that increasing the austenitization temperature gave more dissolved B, N, C, Nb and V. The lower C:N ratio resulted in a higher atomic fraction of N in nano-size particles on subsequent tempering. Dissolved B should stabilize M{sub 23}M{sub 6} and dissolved N, C, Nv, and V should allow precipitation of a higher volume fraction of nano-size carbo-nitrides during tempering. Literature data suggest that lower tempering temperatures could also change their type from MX to M{sub 2}X. (orig.)

  4. Probabilistic damage estimation in piping components against thermal creep and fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Appalanaidu, Y., E-mail: appusir@gmail.com; Gupta, Sayan, E-mail: gupta.sayan@gmail.com

    2014-07-01

    Highlights: • Modeling temperature fluctuations of fluid temperature as a random process. • Fitting a random process model from measurement data. • Estimating random thermal creep damage using Monte Carlo simulations. • Analytical expressions for estimating rain-flow cycle random fatigue damage. • Use engineering models for fatigue–creep interactions to estimate failure probability. - Abstract: This study focusses on probabilistic damage estimation of piping components that carry high temperature fluids in nuclear power plants, when the fluid temperature has random temporal fluctuations. The damaging mechanisms considered are thermal creep and fatigue induced by the thermal stresses. First, a stochastic model for the random temporal fluctuations in the temperature of the fluid is fitted from measured data. The thermal multiaxial stresses generated due to the loadings are non-Gaussian random processes in time. Consequently, the creep and the fatigue damage induced in the structure are also random processes and at any specified time instant, the residual life can be quantified in a probabilistic sense. Monte Carlo simulations are carried out to investigate the random creep damage growth while an analytical approach is used to obtain estimates of the expected fatigue damage. Questions related to the accuracy of the estimates with random process models vis-a-vis random variable models for the temperature fluctuations are examined. Finally, estimates of the failure probability are obtained by considering some models available in the literature for the creep–fatigue interaction effects.

  5. Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

    OpenAIRE

    Abe, Fujio

    2008-01-01

    It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine ...

  6. TOPICAL REVIEW: Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

    OpenAIRE

    Fujio Abe

    2008-01-01

    It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine ...

  7. TOPICAL REVIEW: Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

    OpenAIRE

    Fujio Abe

    2008-01-01

    It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine ...

  8. Characterisation of creep cavitation damage in a stainless steel pressure vessel using small angle neutron scattering

    CERN Document Server

    Bouchard, P J; Treimer, W

    2002-01-01

    Grain-boundary cavitation is the dominant failure mode associated with initiation of reheat cracking, which has been widely observed in austenitic stainless steel pressure vessels operating at temperatures within the creep range (>450 C). Small angle neutron scattering (SANS) experiments at the LLB PAXE instrument (Saclay) and the V12 double-crystal diffractometer of the HMI-BENSC facility (Berlin) are used to characterise cavitation damage (in the size range R=10-2000 nm) in a variety of creep specimens extracted from ex-service plant. Factors that affect the evolution of cavities and the cavity-size distribution are discussed. The results demonstrate that SANS techniques have the potential to quantify the development of creep damage in type-316H stainless steel, and thereby link microstructural damage with ductility-exhaustion models of reheat cracking. (orig.)

  9. The Impact of Weld Metal Creep Strength on the Overall Creep Strength of 9% Cr Steel Weldments

    OpenAIRE

    Mayr, Peter; Mitsche, Stefan; Cerjak, Horst; Allen, Samuel Miller

    2010-01-01

    In this work, three joints of a X11CrMoWVNb9-1-1 (P911) pipe were welded with three filler metals by conventional arc welding. The filler metals varied in creep strength level, so that one overmatched, one undermatched, and one matched the creep strength of the P911 grade pipe base material. The long-term objective of this work was to study the influence of weld metal creep strength on the overall creep behavior of the welded joints and their failure mechanism. Uniaxial creep tests at 600°C a...

  10. Vegetative tillering in creeping bentgrass

    NARCIS (Netherlands)

    Cattani, D.J.

    2000-01-01

    Growth and development of creeping bentgrass ( Agrostis stolonifera L.) under non-competitive and competitive conditions were studied.Growth chamber experiments under non-competitive conditions with high and low tiller producing bentgrass populations produced plants with differing tiller appearance

  11. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    Energy Technology Data Exchange (ETDEWEB)

    Lissenden, Cliff [Pennsylvania State Univ., State College, PA (United States); Hassan, Tasnin [North Carolina State Univ., Raleigh, NC (United States); Rangari, Vijaya [Tuskegee Univ., Tuskegee, AL (United States)

    2014-10-30

    The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched

  12. The creep experiment and theoretical model analysis of gascontaining coal

    Institute of Scientific and Technical Information of China (English)

    YIN Guang-zhi; ZHANG Dong-ming; WANG Wei-zhong

    2007-01-01

    A creep experiment of preformed molding coal under different confining pressures were carried out using self-developed 3-triaxial creep loading device for gas-containing coal, which loaded by Shimadzu AGI-250 kN electrical servo-controlled stiffness testing machine. Based on the experimental results, the variation trend of axial deformation under different stress states was studied, and creep failure characteristics of gascontaining coal under different confining pressures were analyzed. The experimental results were identified with seven-component nonlinear viscoelasto-plastic creep model (Hohai model), and the creep material parameters were obtained. The experimental result complies well with the theoretical value of this model. It indicates that creep constitutive relation of gas-containing coal can be expressed by nonlinear viscoelasto-plastic creep model correctly.

  13. Renal failure caused by chemicals, foods, plants, animal venoms, and misuse of drugs. An overview.

    Science.gov (United States)

    Abuelo, J G

    1990-03-01

    Nephrotoxicity caused by contrast media and drugs is a frequent cause of renal failure in medical practice. However, there are only sporadic cases of renal failure caused by chemicals, foods, plants, animal venoms, and misused or illegal drugs, and standard medical textbooks are limited in the coverage given to the subject. This review provides a referenced compilation of these lesser-known nephrotoxins and gives an overview of renal failure caused by substances other than properly used medications.

  14. FDD-1 System On-line Monitoring Fuel Rod Failure of Nuclear Power Plant

    Institute of Scientific and Technical Information of China (English)

    CHENPeng; ZHANGYing-chao; JISong-tao; GAOYong-guang; YINZhen-guo; HANChuan-bin

    2003-01-01

    The FDD-1 system developed by CIAE for on-line monitoring fuel rod failure of nuclear power plant consists of γ-ray detector, γ-ray spectrum analyzer, computer, and an analysis code for evaluating the status of fuel rod failure. It would be determined that the fuel rod failure occurs when a large amount of γ activity increases in the primary system measured by γ-ray detector near the CVCS.

  15. Degradation and failure of bolting in nuclear power plants: Volume 2: Final report

    Energy Technology Data Exchange (ETDEWEB)

    Nickell, R.E.

    1988-04-01

    A four-year program to resolve the generic safety issue of bolting degradation and failure in nuclear power plants has developed guidelines for material selection, bolting preload control, and plant operation, as well as a realistic method for evaluating the structural integrity of bolted joints. These measures can help improve plant availability while reducing radiation exposure and costs of maintenance and inspection. This report provides the technical basis for resolution of the generic issue of bolting degradation and failure in nuclear power plants.

  16. ANALYSIS METHODS ON STABILITY OF TALL AND BEDDIIG CREEP SLOPE

    Institute of Scientific and Technical Information of China (English)

    RUIYongqin; JIANGZhiming; LIUJinghui

    1995-01-01

    Based on the model of slope engineering geology,the creep and its failure mechanism of tall and bedding slope are deeply analyzed in this paper .The creep laws of weak intercalations are also discussed.The analysis om the stability of creep slope and the age forecasting of sliding slope have been conducted through mumerical simulations using Finite Element Method (FEM)and Dintimct Element Method(DEM).

  17. Creep in structures

    Energy Technology Data Exchange (ETDEWEB)

    Zyczkowski, M. (Krakow Univ. of Technology (Poland). Inst. of Mechanics and Machine Design) (ed.)

    1991-01-01

    This volume contains 81 papers divided into three almost equal parts: Constitutive equations, combined loadings; damage, creep crack growth, creep rupture; structures, analytical and numerical methods, optimal design. (orig.).

  18. Simultaneous consolidation and creep

    DEFF Research Database (Denmark)

    Krogsbøll, Anette

    1997-01-01

    Materials that exhibit creep under constant effective stress typically also show rate dependent behavior. The creep deformations and the rate sensitive behavior is very important when engineering and geological problems with large time scales are considered. When stress induced compaction...

  19. Modelling of creep damage development in ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)

    1998-12-31

    The physical creep damage, which is observed in fossil-fired power plants, is mainly due to the formation of cavities and their interaction. It has previously been demonstrated that both the nucleation and growth of creep cavities can be described by power functions in strain for low alloy and 12 % CrMoV creep resistant steels. It possible to show that the physical creep damage is proportional to the product of the number of cavities and their area. Hence, the physical creep damage can also be expressed in terms of the creep strain. In the presentation this physical creep damage is connected to the empirical creep damage classes (1-5). A creep strain-time function, which is known to be applicable to low alloy and 12 % CrMoV creep resistant steels, is used to describe tertiary creep. With this creep strain - time model the residual lifetime can be predicted from the observed damage. For a given damage class the remaining life is directly proportional to the service time. An expression for the time to the next inspection is proposed. This expression is a function of fraction of the total allowed damage, which is consumed till the next inspection. (orig.) 10 refs.

  20. Creep Damage Analysis of a Lattice Truss Panel Structure

    Science.gov (United States)

    Jiang, Wenchun; Li, Shaohua; Luo, Yun; Xu, Shugen

    2017-01-01

    The creep failure for a lattice truss sandwich panel structure has been predicted by finite element method (FEM). The creep damage is calculated by three kinds of stresses: as-brazed residual stress, operating thermal stress and mechanical load. The creep damage at tensile and compressive loads have been calculated and compared. The creep rate calculated by FEM, Gibson-Ashby and Hodge-Dunand models have been compared. The results show that the creep failure is located at the fillet at both tensile and creep loads. The damage rate at the fillet at tensile load is 50 times as much as that at compressive load. The lattice truss panel structure has a better creep resistance to compressive load than tensile load, because the creep and stress triaxiality at the fillet has been decreased at compressive load. The maximum creep strain at the fillet and the equivalent creep strain of the panel structure increase with the increase of applied load. Compared with Gibson-Ashby model and Hodge-Dunand models, the modified Gibson-Ashby model has a good prediction result compared with FEM. However, a more accurate model considering the size effect of the structure still needs to be developed.

  1. Brittle and compaction creep in porous sandstone

    Science.gov (United States)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate

  2. Simultaneous consolidation and creep

    DEFF Research Database (Denmark)

    Krogsbøll, Anette

    1997-01-01

    Materials that exhibit creep under constant effective stress typically also show rate dependent behavior. The creep deformations and the rate sensitive behavior is very important when engineering and geological problems with large time scales are considered. When stress induced compaction...... (consolidation) is retarded by slow drainage of excess pore pressure it is expected that consolidation and creep occur simultaneously. A constitutive model adressing the problems of rate sensitive behavior and simultaneous consolidation and creep is presented....

  3. Low temperature creep plasticity

    Directory of Open Access Journals (Sweden)

    Michael E. Kassner

    2014-07-01

    Full Text Available The creep behavior of crystalline materials at low temperatures (T < 0.3Tm is discussed. In particular, the phenomenological relationships that describe primary creep are reviewed and analyzed. A discussion of the activation energy for creep at T < 0.3Tm is discussed in terms of the context of higher temperature activation energy. The basic mechanism(s of low temperature creep plasticity are discussed, as well.

  4. Expression of a novel antimicrobial peptide Penaeidin4-1 in creeping bentgrass (Agrostis stolonifera L. enhances plant fungal disease resistance.

    Directory of Open Access Journals (Sweden)

    Man Zhou

    Full Text Available BACKGROUND: Turfgrass species are agriculturally and economically important perennial crops. Turfgrass species are highly susceptible to a wide range of fungal pathogens. Dollar spot and brown patch, two important diseases caused by fungal pathogens Sclerotinia homoecarpa and Rhizoctonia solani, respectively, are among the most severe turfgrass diseases. Currently, turf fungal disease control mainly relies on fungicide treatments, which raises many concerns for human health and the environment. Antimicrobial peptides found in various organisms play an important role in innate immune response. METHODOLOGY/PRINCIPAL FINDINGS: The antimicrobial peptide - Penaeidin4-1 (Pen4-1 from the shrimp, Litopenaeus setiferus has been reported to possess in vitro antifungal and antibacterial activities against various economically important fungal and bacterial pathogens. In this study, we have studied the feasibility of using this novel peptide for engineering enhanced disease resistance into creeping bentgrass plants (Agrostis stolonifera L., cv. Penn A-4. Two DNA constructs were prepared containing either the coding sequence of a single peptide, Pen4-1 or the DNA sequence coding for the transit signal peptide of the secreted tobacco AP24 protein translationally fused to the Pen4-1 coding sequence. A maize ubiquitin promoter was used in both constructs to drive gene expression. Transgenic turfgrass plants containing different DNA constructs were generated by Agrobacterium-mediated transformation and analyzed for transgene insertion and expression. In replicated in vitro and in vivo experiments under controlled environments, transgenic plants exhibited significantly enhanced resistance to dollar spot and brown patch, the two major fungal diseases in turfgrass. The targeting of Pen4-1 to endoplasmic reticulum by the transit peptide of AP24 protein did not significantly impact disease resistance in transgenic plants. CONCLUSION/SIGNIFICANCE: Our results

  5. Failure of steam line causes determined by NDT testing in power and heating plants

    Directory of Open Access Journals (Sweden)

    Srdjan Bulatovic

    2013-10-01

    Full Text Available This paper examines leakage and damages of steam and provides an overview of NDT testing in order to determine the cause of steam lines failure in power plants and heating plants. This approach may be applied to similar structures and its application in preventive maintenance would help extend the life of steam pipes.

  6. Creep in ceramics

    CERN Document Server

    Pelleg, Joshua

    2017-01-01

    This textbook is one of its kind, since there are no other books on Creep in Ceramics. The book consist of two parts: A and B. In part A general knowledge of creep in ceramics is considered, while part B specifies creep in technologically important ceramics. Part B covers creep in oxide ceramics, carnides and nitrides. While covering all relevant information regarding raw materials and characterization of creep in ceramics, the book also summarizes most recent innovations and developments in this field as a result of extensive literature search.

  7. Effect of precipitates on long-term creep deformation properties of P92 and P122 type advanced ferritic steels for USC power plants

    Energy Technology Data Exchange (ETDEWEB)

    Yoshizawa, M., E-mail: yoshizaw-mtr@sumitomometals.co.jp [Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, Amagasaki, Hyogo 660-0891 (Japan); Igarashi, M.; Moriguchi, K. [Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, Amagasaki, Hyogo 660-0891 (Japan); Iseda, A. [Tubular Products Technology Department, Sumitomo Metal Industries, Ltd., 1-8-11 Harumi, Chuo-ku, Tokyo 104-6111 (Japan); Armaki, Hassan Ghassemi; Maruyama, K. [Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aobayama, Sendai 980-8579 (Japan)

    2009-06-15

    Long-term creep rupture strengths and the microstructural stability of ASME P92 and P122 pipes have been studied using creep testing at the temperatures from 550 to 700 deg. C and detailed scanning transmission electron microscopy. Creep rupture strength of P92 is found to be more stable than that of P122 at temperatures over 600 deg. C, which is mainly due to the difference in their Cr content. P122 type model steel with reduced Cr content, 9%Cr, has been prepared to explore the effect of Cr on the stability of MX and formation of Z-phase during creep deformation. MX in 9%Cr steel is found to be stable even after prolonged exposure at 650 deg. C, while Cr and Fe concentration to MX without marked coarsening has been observed in 10.5%Cr steel after aging for 10,000 h at 650 deg. C. This seems to lead to the transition of MX carbonitride into the Z-phase after aging for 23,000 h, which requires ordering in a M{sub 2}N lattice to achieve a tetragonal Z-phase to be stable. Creep deformation behavior in the transient creep region of the steels is almost same up to about 7000 h, while in the acceleration creep region the creep rate of 10.5%Cr steel becomes much faster than that of 9%Cr steel, resulting in shorter rupture life. It is obvious that the creep rupture strength degradation starts prior to the formation of Z-phase in 10.5%Cr steel. It is thus concluded that Z-phase is not a necessary factor for degradation of creep rupture strength but the instability of the fine precipitates such as Cr{sub 2}(C, N) caused by the compositions change like Cr supply to MX carbonitride is more essential.

  8. Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Przystupa, Marek A.

    2007-12-13

    Harper-Dorn (H-D) creep is observed in metals and geological materials exposed to very low stresses at temperatures close to the melting point. It is one of several types of creep processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring creep and Coble creep being two other important processes. H-D creep can be somewhat insidious because the creep rates are much larger than those expected for Nabarro-Herring or Coble creep. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earth’s mantle all involve very low stresses, an understanding of the factors controlling H-D creep is critical in preventing failures associated with those higher-than-expected creep rates. The purpose of this investigation was to obtain missing microstructural information on the evolution of the dislocation structures during static annealing of materials with fcc, bcc and hcp structure and use obtained results to test predictive capabilities of the dislocation network theory of H-D creep. In our view the evolutionary processes during static annealing and during Harper-Dorn creep are intimately related. The materials used in this study were fcc aluminum, hcp zinc and bcc tin. All characterizations of dislocation structures, densities and dislocation link length distributions were carried out using the etch pit method. To obtain quantitative information on the evolution of the dislocation networks during annealing the pure fcc aluminum samples were pre-deformed by creep at 913 and 620 K and then annealed. The higher deformation temperature was selected to generate starting dislocation networks similar to those forming during Harper-Dorn creep and the lower, to obtain higher dislocation densities suitable for reliable estimates of the parameters of the network growth law. The measured experimental link length distribution were, after scaling, (1) the same for all annealing

  9. Creep and creep rupture of fiber reinforced polymers: Long term variability

    Science.gov (United States)

    Jensen, Eric M.

    Fiber reinforced polymers continue to be used in ever increasing quantities for large weight critical structures which are designed to be in service for decades. Catastrophic failure of these structures can have dire consequences. Therefore, long term creep and creep rupture predictions are of critical importance. To this end, a multiscale creep rupture model based on the kinetic concept of strength is developed to predict failure. A linkage between damage evolution and the apparent modulus degradation is proposed, which allows for the prediction of creep strain. This combined creep strain and creep rupture model is implemented in a progressive failure user subroutine for finite element software. Model calibration experiments were conducted on Panex 35/M9.7 material system. Combining structural quantification, full field strain measurements and finite element simulations, mechanisms behind material variability and scatter have been identified and modeled resulting in improved life predictions. The material data collected and a video of the two-dimensional strain evolution during a transverse load and unload test have been provided as supplemental materials.

  10. Performance Based Failure Criteria of the Base Isolation System for Nuclear Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jung Han; Kim, Min Kyu; Choi, In Kil [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2013-10-15

    The realistic approach to evaluate the failure state of the base isolation system is necessary. From this point of view, several concerns are reviewed and discussed in this study. This is the preliminary study for the performance based risk assessment of a base isolated nuclear power plant. The items to evaluate the capacity and response of an individual base isolator and a base isolation system were briefly outlined. However, the methodology to evaluate the realistic fragility of a base isolation system still needs to be specified. For the quantification of the seismic risk for a nuclear power plant structure, the failure probabilities of the structural component for the various seismic intensity levels need to be calculated. The failure probability is evaluated as the probability when the seismic response of a structure exceeds the failure criteria. Accordingly, the failure mode of the structural system caused by an earthquake vibration should be defined first. The type of a base isolator appropriate for a nuclear power plant structure is regarded as an elastometric rubber bearing with a lead core. The failure limit of the lead-rubber bearing (LRB) is not easy to be predicted because of its high nonlinearity and a complex loading condition by an earthquake excitation. Furthermore, the failure mode of the LRB system installed below the nuclear island cannot be simply determined because the basemat can be sufficiently supported if the number of damaged isolator is not much.

  11. Advances in the assessment of creep data

    Energy Technology Data Exchange (ETDEWEB)

    Holdsworth, S.R.

    2010-07-01

    Many of the classical models representing the creep and rupture behaviour of metals were developed prior to and during the 1950s and 1960s, and their subsequent exploitation, in particular for the assessment of large creep property datasets, was initially limited by the capability of the analytical tools available at the time. The formation of ECCC (the European Creep Collaborative Committee) in 1991, with a main objective of providing reliable peer reviewed long-time creep property values for European Design and Product Standards, led to the development of rigorous assessment procedures such as PD6605 and DESA incorporating post assessment tests to verify: physical realism, effectiveness of model-fit within the range of the source experimental data, and extrapolation credibility. The first ECCC assessment recommendations published in 1996 undoubtedly provided a catalyst for others to exploit the availability of low cost, powerful desktop computers to develop rigorous methodologies for the physically realistic analysis of uniaxial and multi-axial data for the reliable and accurate characterisation of creep strain, and rupture strength and ductility properties. More recent improvements in data assessment methodologies have been driven by the need to effectively model the creep deformation and rupture characteristics of the complex new generation alloys and fabrications being designed to cater for the continually evolving requirements of modern advanced power plant. These advances in the assessment of creep data are reviewed. (orig.)

  12. Creep Damage Characteristics of Soft Rock under Disturbance Loads

    Institute of Scientific and Technical Information of China (English)

    Fu Zhiliang; Guo Hua; Gao Yanfa

    2008-01-01

    This article focuses on the process of rock creep damage and micro-damage evolution properties of gray green mudstone under impacting disturbance load conditions for the first time using the real time computerized tomography (CT) testing technique. The results indicate that axial load comes into limit strength neighborhood, rock micro-crack links into larger crack, creep rate increases in a short time, larger plastic deformation happens; this is called disturbance accelerating creep stage. When rock is within limit strength neighborhood, there occurs creep micro-damage under smaller disturbance load. When disturbance load is larger, rock directly enters into disturbance accelerating creep stage, failure occurs instantaneously. On the basis of experimental research, the CT scanning method was used to describe the creep micro-damage of soft rock, also helpful in the prediction of roadways' service life and evaluation of geotechnicai engineering stability.

  13. The role of creep in high temperature low cycle fatigue.

    Science.gov (United States)

    Manson, S. S.; Halford, G. R.; Spera, D. A.

    1971-01-01

    The significance of the role that creep can play in governing high-temperature, low-cycle fatigue resistance is investigated by conducting strain cycling tests on two high-temperature stainless steel alloys and making concurrent measurements of stress, temperature, and strain at various frequencies. The results are then analyzed in terms of damage imposed by creep and fatigue components. It is shown that creep can play an important and sometimes dominant role in low cycle fatigue at high temperatures. The results of the study include the findings that: (1) the simple life-fraction theory described is adequate for calculating creep damage when the cyclic creep rupture curve is used as a basis for analysis; (2) a method of universal slopes originally developed for room temperature use is sufficiently accurate at high temperature to be used to calculate pure fatigue damage; and (3) a linear creep-fatigue damage rule can explain the transitions observed from one failure mode to another.

  14. Creep Effects in Pultruded FRP Beams

    Science.gov (United States)

    Boscato, G.; Casalegno, C.; Russo, S.

    2016-03-01

    The paper presents results of two creep tests on pultruded open-section GFRP beams aimed to evaluate the long-term deformations, the residual deflection after unloading, and the influence of creep strains on the flexuraltorsional buckling phenomenon. Two beams were subjected to a constant load for about one year. Then one of the beams was unloaded to evaluate its residual deflection. For the other beam, the load was increased up to failure, and the residual buckling strength was compared with that of a similar beam tested up to failure. The parameters of the Findley power law are evaluated, and the experimental results are compared with those of numerical analyses and with available formulations for prediction of the time-dependent properties of composite beams. Results of the investigation testify, in particular, to a noninsignificant time-dependent increment in deflections of the beams and to a significant reduction in their buckling strength due to creep deformations.

  15. Study of creep cavitation in a stainless steel weldment

    OpenAIRE

    Jazaeri, H.; Bouchard, P. J.; Hutchings, M; Lindner, P.

    2012-01-01

    A study of creep cavities near reheat cracking in AISI Type 316H austenitic stainless steel headers, removed from long-time high temperature operation in nuclear power plants, is reported. It is shown how application of scanning electron microscopy (SEM), cryogenic fractography and small angle neutron scattering (SANS) can be applied, in a complementary way, to observe and quantify creep cavitation damage. Creep cavities in the vicinity of the crack are found to be mainly surrounding inter-gr...

  16. Creep and creep damage in copper under uniaxial/multiaxial loading

    Energy Technology Data Exchange (ETDEWEB)

    Auerkari, Pertti; Holmstroem, Stefan; Salonen, Jorma [VTT Industrial Systems, Espoo (Finland)

    2003-08-01

    Multiaxial tensile loading is known to enhance accumulation of creep cavitation and cracking damage in polycrystalline metals under given equivalent loading stress and temperature. To study whether this could potentially lead to significant creep damage under long-term repository conditions, multiaxial creep testing and damage evaluation has been initiated. Multiaxial creep testing of OFP copper has been performed using sharp notches in compact tension (CT) specimens. The loading conditions (reference stress and temperature) have been selected to produce an estimated time to either failure or at least to measurable creep damage within the maximum intended testing time or about 5000 hours. For appropriate material and finite element (FE) modelling to set correct loading in multiaxial testing and to obtain a reasonable stress state conversion, parallel uniaxial creep testing has also been performed on the same material. In addition, to support the uniaxial testing and materials modelling, an overall creep rupture life assessment was performed for OFP copper, based on ECCC guidelines and PD6605 including uniaxial creep testing data from the literature. To observe potential creep damage, the multiaxial tests have been also interrupted for metallography about every 2000 h of testing, and inspected by scanning electron microscopy (SEM) for indications of damage. For comparison, metallographic inspection including transmission electron microscopy (TEM) was performed for the same material in as-new state. The initial as-new state as well as later tested states of the material appear to involve grain boundary phases, which are sometimes apparent in SEM but can also require TEM to be resolved. Until now, the multiaxial creep test at lowest reference stress (46 MPa/150 deg C) has been interrupted at 3000, 5000 and 7000 h of testing for inspection in SEM. In these inspections, only occasional scattered evidence of some possible cavitation damage has been found so far. On the

  17. CREEP AND CREEP-FATIGUE OF ALLOY 617 WELDMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Jill; Carroll, Laura; Wright, Richard

    2014-08-01

    The Very High Temperature Reactor (VHTR) Intermediate Heat Exchanger (IHX) may be joined to piping or other components by welding. Creep-fatigue deformation is expected to be a predominant failure mechanism of the IHX1 and thus weldments used in its fabrication will experience varying cyclic stresses interrupted by periods of elevated temperature deformation. These periods of elevated temperature deformation are greatly influenced by a materials’ creep behavior. The nickel-base solid solution strengthened alloy, Alloy 617, is the primary material candidate for a VHTR-type IHX, and it is expected that Alloy 617 filler metal will be used for welds. Alloy 617 is not yet been integrated into Section III of the Boiler and Pressure Vessel Code, however, nuclear component design with Alloy 617 requires ASME (American Society of Mechanical Engineers) Code qualification. The Code will dictate design for welded construction through significant performance reductions. Despite the similar compositions of the weldment and base material, significantly different microstructures and mechanical properties are inevitable. Experience of nickel alloy welds in structural applications suggests that most high temperature failures occur at the weldments or in the heat-affected zone. Reliably guarding against this type of failure is particularly challenging at high temperatures due to the variations in the inelastic response of the constituent parts of the weldment (i.e., weld metal, heat-affected zone, and base metal) [ref]. This work focuses on the creep-fatigue behavior of nickel-based weldments, a need noted during the development of the draft Alloy 617 ASME Code Case. An understanding of Alloy 617 weldments when subjected to this important deformation mode will enable determination of the appropriate design parameters associated with their use. Specifically, the three main areas emphasized are the performance reduction due to a weld discontinuity in terms of the reduced number of

  18. Failure of Titanium Condenser Tubes after 24 Years Power Plant Service

    DEFF Research Database (Denmark)

    Montgomery, Melanie; Enemark, Allan; Hangaard, Anders

    2014-01-01

    a plant trip. In addition, small amounts of titanium hydride were revealed to be present in the tubes within the tubesheet indicating that the carbon steel tubesheet was corroding due to ingress of salt water. Although this was not the reason for the failure, it indicated the need for repair of the epoxy......The titanium condenser has been in operation for 24 years at Amager unit 3 power plant. In February 2012, the plant was contaminated by seawater due to a failed condenser tube and some tubes were plugged. A month later, the plant tripped again. Small leaks were found again and finally approx. 200...

  19. Cumulative creep fatigue damage in 316 stainless steel

    Science.gov (United States)

    Mcgaw, Michael A.

    1989-01-01

    The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

  20. Correlation of Creep Behavior of Domal Salts

    Energy Technology Data Exchange (ETDEWEB)

    Munson, D.E.

    1999-02-16

    The experimentally determined creep responses of a number of domal salts have been reported in, the literature. Some of these creep results were obtained using standard (conventional) creep tests. However, more typically, the creep data have come from multistage creep tests, where the number of specimens available for testing was small. An incremental test uses abrupt changes in stress and temperature to produce several time increments (stages) of different creep conditions. Clearly, the ability to analyze these limited data and to correlate them with each other could be of considerable potential value in establishing the mechanical characteristics of salt domes, both generally and specifically. In any analysis, it is necessary to have a framework of rules to provide consistency. The basis for the framework is the Multimechanism-Deformation (M-D) constitutive model. This model utilizes considerable general knowledge of material creep deformation to supplement specific knowledge of the material response of salt. Because the creep of salt is controlled by just a few micromechanical mechanisms, regardless of the origin of the salt, certain of the material parameters are values that can be considered universal to salt. Actual data analysis utilizes the methodology developed for the Waste Isolation Pilot Plant (WIPP) program, and the response of a bedded pure WIPP salt as the baseline for comparison of the domal salts. Creep data from Weeks Island, Bryan Mound, West Hackberry, Bayou Choctaw, and Big Hill salt domes, which are all sites of Strategic Petroleum Reserve (SPR) storage caverns, were analyzed, as were data from the Avery Island, Moss Bluff, and Jennings salt domes. The analysis permits the parameter value sets for the domal salts to be determined in terms of the M-D model with various degrees of completeness. In turn this permits detailed numerical calculations simulating cavern response. Where the set is incomplete because of the sparse database, reasonable

  1. Tube failures due to cooling process problem and foreign materials in power plants

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, J. [Kapar Energy Ventures Sdn Bhd, Jalan Tok Muda, Kapar 42200 (Malaysia); Purbolaksono, J., E-mail: judha@uniten.edu.m [Department of Mechanical Engineering, Universiti Tenaga Nasional, Km 7 Jalan Kajang-Puchong, Kajang 43009, Selangor (Malaysia); Beng, L.C. [Kapar Energy Ventures Sdn Bhd, Jalan Tok Muda, Kapar 42200 (Malaysia)

    2010-07-15

    Cooling process which uses water for heat transfer is an essential factor in coal-fired and nuclear plants. Loss of cooling upset can force the plants to shut down. In particular, this paper reports visual inspections and metallurgical examinations on the failed SA210-A1 right-hand side (RHS) water wall tube of a coal-fired plant. The water wall tube showed the abnormal outer surface colour and has failed with wide-open ductile rupture and thin edges indicating typical signs of short-term overheating. Metallurgical examinations confirmed the failed tube experiencing higher temperature operation. Water flow starvation due to restriction inside the upstream tube is identified as the main root cause of failure. The findings are important to take failure mitigation actions in the future operation. Discussion on the typical problems related to the cooling process in nuclear power plants is also presented.

  2. Creep strength and ductility of 9 to 12% chromium steels

    DEFF Research Database (Denmark)

    Hald, John

    2004-01-01

    Steels", which covers creep data development and analysis for parent materials and welds of all ferritic creep resistant steels ranging from low alloy steels up to 12%Cr steels. The opinions stated in the paper represent the views of the author rather than the whole ECCC WG3A group.......The present paper focuses in on long-term creep properties of parent material of the new 9-12%Cr creep resistant steels, P91, E911 and P92 developed for use in advanced ultrasupercritical power plants. These steels have been at the center of activities in the ECCC Working Group 3A (WG3A) "Ferritic...

  3. Creep strength and ductility of 9 to 12% chromium steels

    DEFF Research Database (Denmark)

    Hald, John

    2004-01-01

    The present paper focuses in on long-term creep properties of parent material of the new 9-12%Cr creep resistant steels, P91, E911 and P92 developed for use in advanced ultrasupercritical power plants. These steels have been at the center of activities in the ECCC Working Group 3A (WG3A) "Ferritic...... Steels", which covers creep data development and analysis for parent materials and welds of all ferritic creep resistant steels ranging from low alloy steels up to 12%Cr steels. The opinions stated in the paper represent the views of the author rather than the whole ECCC WG3A group....

  4. Nondestructive evaluation of creep-fatigue damage: an interim report. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Nickell, R.E.

    1977-02-01

    In view of the uncertainties involved in designing against creep-fatigue failure and the consequences of such failures in Class 1 nuclear components that operate at elevated temperature, the possibility of intermittent or even continuous non-destructive examination of these components has been considered. In this interim report some preliminary results on magnetic force and ultrasonic evaluation of creep-fatigue damage in an LMFBR steam generator material are presented. These results indicate that the non-destructive evaluation of pure creep damage will be extremely difficult. A set of biaxial creep-fatigue tests that are designed to discriminate between various failure theories is also described.

  5. Impact of mechanical- and maintenance-induced failures of main reactor coolant pump seals on plant safety

    Energy Technology Data Exchange (ETDEWEB)

    Azarm, M A; Boccio, J L; Mitra, S

    1985-12-01

    This document presents an investigation of the safety impact resulting from mechanical- and maintenance-induced reactor coolant pump (RCP) seal failures in nuclear power plants. A data survey of the pump seal failures for existing nuclear power plants in the US from several available sources was performed. The annual frequency of pump seal failures in a nuclear power plant was estimated based on the concept of hazard rate and dependency evaluation. The conditional probability of various sizes of leak rates given seal failures was then evaluated. The safety impact of RCP seal failures, in terms of contribution to plant core-melt frequency, was also evaluated for three nuclear power plants. For leak rates below the normal makeup capacity and the impact of plant safety were discussed qualitatively, whereas for leak rates beyond the normal make up capacity, formal PRA methodologies were applied. 22 refs., 17 figs., 19 tabs.

  6. Analysis of Emergency Diesel Generators Failure Incidents in Nuclear Power Plants

    Science.gov (United States)

    Hunt, Ronderio LaDavis

    In early years of operation, emergency diesel generators have had a minimal rate of demand failures. Emergency diesel generators are designed to operate as a backup when the main source of electricity has been disrupted. As of late, EDGs (emergency diesel generators) have been failing at NPPs (nuclear power plants) around the United States causing either station blackouts or loss of onsite and offsite power. These failures occurred from a specific type called demand failures. This thesis evaluated the current problem that raised concern in the nuclear industry which was averaging 1 EDG demand failure/year in 1997 to having an excessive event of 4 EDG demand failure year which occurred in 2011. To determine the next occurrence of the extreme event and possible cause to an event of such happening, two analyses were conducted, the statistical and root cause analysis. Considering the statistical analysis in which an extreme event probability approach was applied to determine the next occurrence year of an excessive event as well as, the probability of that excessive event occurring. Using the root cause analysis in which the potential causes of the excessive event occurred by evaluating, the EDG manufacturers, aging, policy changes/ maintenance practices and failure components. The root cause analysis investigated the correlation between demand failure data and historical data. Final results from the statistical analysis showed expectations of an excessive event occurring in a fixed range of probability and a wider range of probability from the extreme event probability approach. The root-cause analysis of the demand failure data followed historical statistics for the EDG manufacturer, aging and policy changes/ maintenance practices but, indicated a possible cause regarding the excessive event with the failure components. Conclusions showed the next excessive demand failure year, prediction of the probability and the next occurrence year of such failures, with an

  7. Development of simplified evaluation method for creep-fatigue crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Miura, Naoki [Central Research Institute of Electric Power Industry, 2-11-1 Iwado-Kita, Komae-shi, Tokyo 201-8511 (Japan)], E-mail: miura@criepi.denken.or.jp; Takahashi, Yukio [Central Research Institute of Electric Power Industry, 2-11-1 Iwado-Kita, Komae-shi, Tokyo 201-8511 (Japan); Nakayama, Yasunari; Fujishita, Kenichi; Shimakawa, Takashi [Kawasaki Plant Systems Ltd., 2-11-1 Minami-Suna, Koto-ku, Tokyo 136-8588 (Japan)

    2008-02-15

    In the design assessment of fast reactor plant components, prevention of crack initiation from defect-free structures is a main concern. However, existence of initial defects such as weld defects cannot be entirely excluded and this potential cracks are to be evaluated to determine if initiated cracks do not lead to component failure instantly. Therefore, evaluation of structural integrity in the presence of crack-like defects is also important to complement the formal design assessment. The authors have been developing a guideline for assessing long-term structural integrity of fast reactor components using detailed inelastic analysis and nonlinear fracture mechanics. This guideline consists of two parts, evaluation of defect-free structures and flaw evaluation. In the latter, creep-fatigue is considered to be one of the most essential driving force for crack propagation at high operating temperature exceeding 500 deg. C. The uses of J-integral-type parameters (fatigue J-integral range and creep J-integral) are recommended to describe creep-fatigue crack propagation behavior in the guideline. This paper gives an outline of the simplified evaluation method for creep-fatigue crack propagation.

  8. (Irradiation creep of graphite)

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, C.R.

    1990-12-21

    The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

  9. Digital control systems in nuclear power plants: Failure information, modeling concepts, and applications

    Energy Technology Data Exchange (ETDEWEB)

    Galyean, W.J.

    1993-06-23

    This report briefly describes some current applications of advanced computerized digital display and control systems at US commercial nuclear power plants and presents the results of a literature search that was made to gather information on the reliability of these systems. Both hardware and software reliability were addressed in this review. Only limited failure rate information was found, with the chemical process industry being the primary source of information on hardware failure rates and expert opinion the primary source for software failure rates. Safety-grade digital control systems are typically installed on a functional like-for-like basis, replacing older analog systems without substantially changing interactions with other plant systems. Future work includes performing a limited probabilistic risk assessment of a representative DCS to assess its risk significance.

  10. Digital control systems in nuclear power plants: Failure information, modeling concepts, and applications. Revision 1

    Energy Technology Data Exchange (ETDEWEB)

    Galyean, W.J.

    1993-06-23

    This report briefly describes some current applications of advanced computerized digital display and control systems at US commercial nuclear power plants and presents the results of a literature search that was made to gather information on the reliability of these systems. Both hardware and software reliability were addressed in this review. Only limited failure rate information was found, with the chemical process industry being the primary source of information on hardware failure rates and expert opinion the primary source for software failure rates. Safety-grade digital control systems are typically installed on a functional like-for-like basis, replacing older analog systems without substantially changing interactions with other plant systems. Future work includes performing a limited probabilistic risk assessment of a representative DCS to assess its risk significance.

  11. Creep properties and simulation of weld repaired low alloy heat resistant CrMo and Mo steels at 540 deg C. Sub project 1 - Ex-serviced parent metal and virgin weld metals

    Energy Technology Data Exchange (ETDEWEB)

    Rui Wu; Storesund, Jan; Borggreen, Kjeld; Weilin Zang

    2006-10-15

    Many existing power generating and process plants, where low alloy heat resistant CrMo(V) steels are extensively used for critical components, have exceeded their design lifetime of usually 100,000 hours. Assessment of residual lifetime and extension of economic life by weld repair have become increasingly important and attractive. This project aims at i) performing weld repair and determining the degree of mismatching, ii) evaluating the creep properties of weld repairs, iii) analysing creep behaviour of weld repair and providing necessary data for further reliable simulations of weld repair creep behaviour in long term service, and iv), simulating and assessing lifetime and creep damage evolution of weld repair. Weld repair using 10 CrMo 9 10, 13 CrMo 4 4 and 15 Mo 3 consumables has been carried out in a service-exposed 10 CrMo 9 10 pipe. Creep specimens have been extracted from the service-exposed 10 CrMo 9 10 parent metal (PM), from the virgin 10 CrMo 9 10 weld metal (WM), from the virgin 13 CrMo 4 4 WM as well as from the virgin 15 Mo 3 WM. Iso-thermal uniaxial creep tests have been performed at 540 deg C in air. Pre- and post-metallography are carried out on the selected samples. FEM simulations using obtained creep data are executed. Pre-test metallography shows normal and acceptable weld repairs at given welding conditions. Creep tests demonstrate that the virgin 10 CrMo 9 10, 13 CrMo 4 4 and 15 Mo 3 WMs have apparently longer creep lifetime than the service-exposed CrMo 9 10 PM at higher stresses than 110 MPa. Among the weld metals, the longest creep lifetime is found in 10 CrMo 9 10. Higher creep strength and lower creep strain rate in the weld metals indicate an overmatch weld. At 95 MPa, however, lifetime of 13 CrMo 4 4 WM is surprisingly short (factors which may shorten lifetime are discussed and one more test will start to verify creep strength at low stress) and tests are still running for other two weld metals. More results regarding low stress

  12. Experimental Investigation on Creep Deformation Behavior of Medium-strength Marble Rock

    Directory of Open Access Journals (Sweden)

    Li Yong

    2014-01-01

    Full Text Available The creep deformation behavior of rocks has significant effect on the stability of underground structures. This study presents the short-term and creep deformation behavior of medium-strength marble rock using a conventional uniaxial compression testing machine and a servo-controlled rheology testing machine. The uniaxial compressive strength is obtained by the uniaxial compression testing machine. During the creep behavior test, two types of rock specimens (dry and water-saturated are specified to be used to perform the uniaxial creep tests. Two rheological failure modes and the relationship curves between axial/circumferential strain and stress levels of marble specimens are also obtained from the creep test results. Eventually, the creep deformation behaviors are compared with those of typical soft rocks. These creep curves combined with a given creep constitutive model would provide accurate parameters for long-term stability analyses of actual projects.

  13. Life Assessment for Cr-Mo Steel Dissimilar Joints by Various Filler Metals Using Accelerated Creep Testing

    Science.gov (United States)

    Petchsang, S.; Phung-on, I.; Poopat, B.

    2016-12-01

    Accelerated creep rupture tests were performed on T22/T91 dissimilar metal joints to determine the fracture location and rupture time of different weldments. Four configurations of deposited filler metal were tested using gas tungsten arc welding to estimate the service life for Cr-Mo steel dissimilar joints at elevated temperatures in power plants. Results indicated that failure in all configurations occurred in the tempered original microstructure and tempered austenite transformation products (martensite or bainite structure) as type IV cracking at the intercritical area of the heat-affected zone (ICHAZ) for both T22 and T91 sides rather than as a consequence of the different filler metals. Creep damage occurred with the formation of precipitations and microvoids. The correlation between applied stress and the Larson-Miller parameter (PLM) was determined to predict the service life of each material configuration. Calculated time-to-failure based on the PLM and test results for both temperature and applied stress parameters gave a reasonable fit. The dissimilar joints exhibited lower creep rupture compared to the base material indicating creep degradation of the weldment.

  14. Experimental Research on Creep Characteristics of Nansha Soft Soil

    Directory of Open Access Journals (Sweden)

    Qingzi Luo

    2014-01-01

    Full Text Available A series of tests were performed to investigate the creep characteristics of soil in interactive marine and terrestrial deposit of Pearl River Delta. The secondary consolidation test results show that the influence of consolidation pressure on coefficient of secondary consolidation is conditional, which is decided by the consolidation state. The ratio of coefficient of secondary consolidation and coefficient of compressibility Ca/Cc is almost a constant, and the value is 0.03. In the shear-box test, the direct sheer creep failure of soil is mainly controlled by shear stress rather than the accumulation of shear strain. The triaxial creep features are closely associated with the drainage conditions, and consolidation can weaken the effect of creep. When the soft soil has triaxial creep damage, the strain rate will increase sharply.

  15. Creep damage development in welded X20 and P91

    Energy Technology Data Exchange (ETDEWEB)

    Brett, Steve; Holmstrom, Stefan; Hald, John; Borg, Ulrik; Aakjaer Jensen, Soeren; Vulpen, Rijk Van; Degnan, Craig; Vinter Dahl, Kristian; Vilhelmsen, Tommy

    2011-03-15

    The Martensitic steel X20CrMoV121 (hereinafter called X20) and the modified 9Cr1Mo steel (hereinafter called P91) have been used for a number of years in high temperature applications since they posses superior creep strength compared to low alloyed steels. Due to the simple fact that very few failures were observed, almost no knowledge as to the evolution of creep damage in welds were available despite long operation times exceeding well over 100.000 hours. It has been suggested that X20 will develop creep damage in a different manner compared to low alloyed steel, i.e damage initiation should be slow followed by accelerated growth. The research work presented in this report included systematic investigations of the first components of X20, which has developed creep during long-term operation. All of the investigated components showed creep damage evolution similar to low alloy steels

  16. Long-term compressive creep deformation and damage in acrylic bone cements.

    Science.gov (United States)

    Chwirut, D J

    1984-01-01

    Compressive creep tests were performed on five commercially available acrylic bone cements under conditions simulating in vivo usage. Measured creep strains are quite large, generally exceeding elastic strains. Large variations in creep response were noted among the various cements, with a carbon-reinforced cement by far the most resistant to creep. The empirical model epsilon = a exp(b sigma)tn was found to predict creep strains within about 10% of the measured values. Microscopic examination of some specimens after testing revealed significant cracking, resulting from long-term loading, that could be a contributing cause of time-dependent failure.

  17. Creep in amorphous metals

    Directory of Open Access Journals (Sweden)

    Michael E. Kassner

    2015-01-01

    Full Text Available This paper reviews the work on creep behavior of amorphous metals. There have been, over the past several years, a few reviews of the mechanical behavior of amorphous metals. Of these, the review of the creep properties of amorphous metals by Schuh et al. though oldest of the three, is particularly noteworthy and the reader is referred to this article published in 2007. The current review of creep of amorphous metals particularly focuses on those works since that review and places the work prior to 2007 in a different context where new developments warrant.

  18. Radionuclide Release after End Fitting Failure Accident in CANDU-6 Plant

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Hoon; Kim, Yun Ho; Lee, Kwang Ho [Korea Electric Power Corporation Research Institute, Daejeon (Korea, Republic of)

    2010-10-15

    The total amount of mass and energy discharged into containment building from primary heat transport system in the event of end fitting failure accident in CANDU-6 plant is similar to that of small loss of coolant accident. But the ejection of fuel bundles into fuelling machine room is unique phenomenon and causes radio nuclides release from the physically broken fuel rod to outside containment building. The only objective of containment behavior analysis for end fitting failure event is to assess the amount of radio nuclides release to the ambient atmosphere. Radionuclide release rates in case of end fitting failure with all safety system available, that is containment building is intact, as well as with containment system impairment are analyzed with GOTHIC and SMART code

  19. A Study on Estimating the Next Failure Time of Compressor Equipment in an Offshore Plant

    Directory of Open Access Journals (Sweden)

    SangJe Cho

    2016-01-01

    Full Text Available The offshore plant equipment usually has a long life cycle. During its O&M (Operation and Maintenance phase, since the accidental occurrence of offshore plant equipment causes catastrophic damage, it is necessary to make more efforts for managing critical offshore equipment. Nowadays, due to the emerging ICTs (Information Communication Technologies, it is possible to send health monitoring information to administrator of an offshore plant, which leads to much concern on CBM (Condition-Based Maintenance. This study introduces three approaches for predicting the next failure time of offshore plant equipment (gas compressor with case studies, which are based on finite state continuous time Markov model, linear regression method, and their hybrid model.

  20. DETERMINATION OF CREEP PARAMETERS FROM INDENTATION CREEP EXPERIMENTS

    Institute of Scientific and Technical Information of China (English)

    岳珠峰; 万建松; 吕震宙

    2003-01-01

    The possibilities of determining creep parameters for a simple Norton law material are explored from indentation creep testing. Using creep finite element analysis the creep indentation test technique is analyzed in terms of indentation rates at constant loads. Emphasis is placed on the relationships between the steady creep behavior of indentation systems and the creep property of the indented materials. The role of indenter geometry, size effects and macroscopic constraints is explicitly considered on indentation creep experiments. The influence of macroscopic constraints from the material systems becomes important when the size of the indenter is of the same order of magnitude as the size of the testing material. Two methods have been presented to assess the creep property of the indented material from the indentation experimental results on the single-phase-material and two-phase-material systems. The results contribute to a better mechanical understanding and extending the application of indentation creep testing.

  1. Accelerated Creep Testing of High Strength Aramid Webbing

    Science.gov (United States)

    Jones, Thomas C.; Doggett, William R.; Stnfield, Clarence E.; Valverde, Omar

    2012-01-01

    A series of preliminary accelerated creep tests were performed on four variants of 12K and 24K lbf rated Vectran webbing to help develop an accelerated creep test methodology and analysis capability for high strength aramid webbings. The variants included pristine, aged, folded and stitched samples. This class of webbings is used in the restraint layer of habitable, inflatable space structures, for which the lifetime properties are currently not well characterized. The Stepped Isothermal Method was used to accelerate the creep life of the webbings and a novel stereo photogrammetry system was used to measure the full-field strains. A custom MATLAB code is described, and used to reduce the strain data to produce master creep curves for the test samples. Initial results show good correlation between replicates; however, it is clear that a larger number of samples are needed to build confidence in the consistency of the results. It is noted that local fiber breaks affect the creep response in a similar manner to increasing the load, thus raising the creep rate and reducing the time to creep failure. The stitched webbings produced the highest variance between replicates, due to the combination of higher local stresses and thread-on-fiber damage. Large variability in the strength of the webbings is also shown to have an impact on the range of predicted creep life.

  2. Biaxial Creep Specimen Fabrication

    Energy Technology Data Exchange (ETDEWEB)

    JL Bump; RF Luther

    2006-02-09

    This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

  3. Irradiation Creep in Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

  4. Steam explosions-induced containment failure studies for Swiss nuclear power plants

    Energy Technology Data Exchange (ETDEWEB)

    Zuchuat, O.; Schmocker, U. [Swiss Federal Nuclear Safety Inspectorate, Villigen (Switzerland); Esmaili, H.; Khatib-Rahbar, M.

    1998-01-01

    The assessment of the consequences of both in-vessel and ex-vessel energetic fuel-coolant interaction for Beznau (a Westinghouse pressurized water reactor with a large, dry containment), Goesgen (a Siemens/KWU pressurized water reactor with a large, dry containment) and Leibstadt (a General Electric boiling water reactor-6 with a free standing steel, MARK-III containment) nuclear power plants is presented in this paper. The Conditional Containment Failure Probability of the steel containment of these Swiss nuclear power plants is determined based on different probabilistic approaches. (author)

  5. Creep Resistant Zinc Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Frank E. Goodwin

    2002-12-31

    This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.

  6. Creep Resistant Zinc Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Frank E. Goodwin

    2002-12-31

    This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.

  7. Creep of Uncoated and Cu-Cr Coated NARloy-Z

    Science.gov (United States)

    Walter, R. J.; Chiang, K. T.

    1998-01-01

    Stress rupture creep tests were performed on uncoated and Cu-30vol%Cr coated NARloy-Z copper alloy specimens exposed to air at 482 C to 704 C. The results showed that creep failure in air of unprotected NARloy-Z was precipitated by brittle intergranular surface cracking produced by strain assisted grain boundary oxidation (SAGBO) which in turn caused early onset of tertiary creep. For the protected specimens, the Cu-Cr coating remained adherent throughout the tests and was effective in slowing down the rate of oxygen absorption, particularly at the higher temperatures, by formation of a continuous chromium oxide scale. As the result of reducing oxygen ingress, the coating prevented SAGBO initiated early creep failure, extended creep deformation and increased the creep rupture life of NARloy-Z over the entire 482 C to 704 C test temperature range.

  8. Probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP)

    Energy Technology Data Exchange (ETDEWEB)

    Greenfield, M.A. [Univ. of California, Los Angeles, CA (United States); Sargent, T.J. [Univ. of Chicago, IL (United States)]|[Stanford Univ., CA (United States). Hoover Institution

    1998-01-01

    In its most recent report on the annual probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP), the annual failure rate is calculated to be 1.3E({minus}7)(1/yr), rounded off from 1.32E({minus}7). A calculation by the Environmental Evaluation Group (EEG) produces a result that is about 4% higher, namely 1.37E({minus}7)(1/yr). The difference is due to a minor error in the US Department of Energy (DOE) calculations in the Westinghouse 1996 report. WIPP`s hoist safety relies on a braking system consisting of a number of components including two crucial valves. The failure rate of the system needs to be recalculated periodically to accommodate new information on component failure, changes in maintenance and inspection schedules, occasional incidents such as a hoist traveling out-of-control, either up or down, and changes in the design of the brake system. This report examines DOE`s last two reports on the redesigned waste hoist system. In its calculations, the DOE has accepted one EEG recommendation and is using more current information about the component failures rates, the Nonelectronic Parts Reliability Data (NPRD). However, the DOE calculations fail to include the data uncertainties which are described in detail in the NPRD reports. The US Nuclear Regulatory Commission recommended that a system evaluation include mean estimates of component failure rates and take into account the potential uncertainties that exist so that an estimate can be made on the confidence level to be ascribed to the quantitative results. EEG has made this suggestion previously and the DOE has indicated why it does not accept the NRC recommendation. Hence, this EEG report illustrates the importance of including data uncertainty using a simple statistical example.

  9. Corium Configuration and Penetration Tube Failure for Fukushima Daiichi Nuclear Power Plant

    Energy Technology Data Exchange (ETDEWEB)

    An, Sang Mo; Lee, Jae Bong; Kim, Hwan Yeol; Song, Jin Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    For the LWRs (light water reactors), the penetration tubes at the reactor vessel lower head are regarded as the most vulnerable structures along with a global vessel failure during a severe accident because they can be seriously damaged by a corium melt or debris relocated into the lower plenum of the vessel. The research on the penetration tube failure is of higher importance in the BWRs, as it could lead to melt discharge into the containment and subsequent release of radioactive materials to the environment due to the containment failure. There are more than one hundred of penetration tubes in the Fukushima Daiichi NPPs (nuclear power plants), such as ICM-GTs (in-core monitoring guide tubes), CRGTs (control rod guide tubes) and drain tubes. The ICM-GTs include SRMs (source range monitors), IRMs (intermediate range monitors), LPRMs (local power range monitors) and TIPs (traversing in-core probes), which are much thinner than other tubes. The experimental researches to investigate the corium configuration and the penetration tube failure for the Fukushima Daiichi NPPs were introduced and some meaningful results were summarized. It was shown that the corium ingot was separated into two layers, of which the upper layer was metal-rich while the lower one was oxide-rich. It seemed that B{sub 4}C would contribute to reducing the density of the metallic melt. The two-layered configuration will provide useful information to understand the core melt progression and post-recovery actions for the Fukushima Daiichi NPPs. In addition, we performed a large scale penetration tube failure experiment for the SRM/IRM guide tube, and showed high possibilities of large amount of corium discharge out of the reactor vessel lower head, which followed by the tube melting in a very short time. We are planning to perform the penetration tube failure experiments for another dry tube of ICM-GT (LPRM guide tube), and later for the wet tube (CRGT)

  10. Creep of fibrous composite materials

    DEFF Research Database (Denmark)

    Lilholt, Hans

    1985-01-01

    Models are presented for the creep behaviour of fibrous composite materials with aligned fibres. The models comprise both cases where the fibres remain rigid in a creeping matrix and cases where the fibres are creeping in a creeping matrix. The treatment allows for several contributions to the cr......Models are presented for the creep behaviour of fibrous composite materials with aligned fibres. The models comprise both cases where the fibres remain rigid in a creeping matrix and cases where the fibres are creeping in a creeping matrix. The treatment allows for several contributions...... such as Ni + W-fibres, high temperature materials such as Ni + Ni3Al + Cr3C2-fibres, and medium temperature materials such as Al + SiC-fibres. For the first two systems reasonable consistency is found for the models and the experiments, while for the third system too many unquantified parameters exist...

  11. Development of Web-Based Common Cause Failure (CCF) Database Module for Nuclear Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun-Gyo; Hwang, Seok-Won; Shin, Tae-young [Korea Hydro and Nuclear Power Co. Ltd., Daejeon (Korea, Republic of)

    2015-05-15

    Probabilistic safety assessment (PSA) has been used to identify risk vulnerabilities and derive the safety improvement measures from construction to operation stages of nuclear power plants. In addition, risk insights from PSA can be applied to improve the designs and operation requirements of plants. However, reliability analysis methods for quantitative PSA evaluation have essentially inherent uncertainties, and it may create a distorted risk profiles because of the differences among the PSA models, plant designs, and operation status. Therefore, it is important to ensure the quality of the PSA model so that analysts identify design vulnerabilities and utilize risk information. Especially, the common cause failure (CCF) has been pointed out as one of major issues to be able to cause the uncertainty related to the PSA analysis methods and data because CCF has a large influence on the PSA results. Organization for economic cooperation and development /nuclear energy agent (OECD/NEA) has implemented an international common cause failure data exchange (ICDE) project for the CCF quality assurance through the development of the detailed analysis methodologies and data sharing. However, Korea Hydro and Nuclear Power company (KHNP) does not have the basis for the data gathering and analysis for CCF analyses. In case of methodology, the Alpha Factor parameter estimation, which can analyze uncertainties and estimate an interface factor (Impact Vector) with an ease, is ready to be applied rather than the Multi Greek Letter (MGL) method. This article summarizes the development of the plant-specific CCF database (DB) module considering the raw data collection and the analysis procedure based on the CCF parameter calculation method of ICDE. Although the portion affected by CCF in the PSA model is quite a large, the development efforts of the tools to collect and analyze data were insufficient. Currently, KHNP intends to improve PSA quality and ensure CCF data reliability by

  12. A Research Status on High-Temperature Creep of Alloy 617 for Use in VHTR System

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo-Gon; Park, Jae-Young; Kim, Eung-Seon; Kim, Yong-Wan; Kim, Min-Hwan [KAERI, Daejeon (Korea, Republic of); Kim, Seon-Jin [Pukyong National Univ., Busan (Korea, Republic of)

    2016-05-15

    In this study, a research status on creep works of Alloy 617 conducting at KAERI was introduced and summarized. Various experimental creep data and creep constants obtained in the air/helium environments and base/weld metals were presented and discussed using various creep equations and parameters. The draft Code Case is a modification from ASME Section III Subsection NH that was put forth by a special task force of the ASME subgroup that deals with elevated temperature design. The primary intended application of the draft Code Case is a VHTR. Presently, various creep data for Alloy 617 are being accumulated through Generation-IV forum (GIF) Material Handbook Database of a next-generation nuclear plant research and development. As per this, a new Alloy 617 Code Case is planned to be approved by 2017. However, to do so, various creep data and creep constants in air/helium environments, and base/weld metals etc. should be obtained to help draft the new Code Case, and creep behavior should be investigated through systematic analysis of a wide range of creep temperature and stress conditions. Using various creep equations and parameters, the creep constants were determined for design use of Alloy 617. The stress of the He environment was more reduced than that of the air one. As the stress increases, the creep rate of WM was significantly lower than that of BM. The reason for this was that the rupture elongation of WM was largely reduced compared with that of BM.

  13. Influence of Grain Boundary Character on Creep Void Formation in Alloy 617

    Science.gov (United States)

    Lillo, Thomas; Cole, James; Frary, Megan; Schlegel, Scott

    2009-12-01

    Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP), which will operate at temperatures exceeding 760 °C and a helium pressure of approximately 7 MPa. Observations of the crept microstructure using optical microscopy indicate creep stress does not significantly influence the creep void fraction at a given creep strain over the relatively narrow set of creep conditions studied. Void formation was found to occur only after significant creep in the tertiary regime (>5 pct total creep strain) had occurred. Also, orientation imaging microscopy (OIM) was used to characterize the grain boundaries in the vicinity of creep voids that develop during high-temperature creep tests (900 °C to 1000 °C at creep stresses ranging from 20 to 40 MPa) terminated at creep strains ranging from 5 to 40 pct. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular, or 45 deg to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids, while coincident site lattice (CSL)-related grain boundaries did not appear to be consistently associated with void development. Similar results were found in oxygen-free, high-conductivity (OFHC) copper, severely deformed using equal channel angular extrusion, and creep tested at 450 °C and 14 MPa.

  14. Analysis of Multistage and Other Creep Data for Domal Salts

    Energy Technology Data Exchange (ETDEWEB)

    Munson, D.E.

    1998-10-01

    There have existed for some time relatively sparse creep databases for a number of domal salts. Although all of these data were analyzed at the time they were reported, to date there has not been a comprehensive, overall evaluation within the same analysis framework. Such an evaluation may prove of value. The analysis methodology is based on the Multimechanism Deformation (M-D) description of salt creep and the corresponding model parameters determined from conventional creep tests. The constitutive model of creep wss formulated through application of principles involved in micromechanical modeling. It was possible, at minimum, to obtain the steady state parameters of the creep model from the data on the domal salts. When this was done, the creep of the domal salts, as compared to the well-defined Waste Isolation Pilot Plant (WIPP) bedded clean salt, was either essentially identical to, or significantly harder (more creep resistant) than WIPP salt. Interestingly, the domal salts form two distinct groups, either sofl or hard, where the difference is roughly a factor often in creep rate between the twcl groups. As might be expected, this classification corresponds quite well to the differences in magnitude of effective creep volume losses of the Strategic Petroleum Reserve (SPR) caverns as determined by the CAVEMAN cavern pressure history analysis, depending upon the specific dome or region within the dome. Creep response shoulcl also correlate to interior cavern conditions that produce salt falls. WMle, in general, the caverns in hard sah have a noticeably greater propensity for salt falls, a smaller number of similar events are exhibited even in the caverns in soft salt.

  15. Development of a constitutive model for the plastic deformation and creep of copper and its use in the estimate of the creep life of the copper canister

    Energy Technology Data Exchange (ETDEWEB)

    Pettersson, Kjell [Matsafe AB, Stockholm (Sweden)

    2006-12-15

    A previously developed model for the plastic deformation and creep of copper (included as an Appendix to the present report) has been used as the basis for a discussion on the possibility of brittle creep fracture of the copper canister during long term storage of nuclear waste. Reported creep tests on oxygen free (OF) copper have demonstrated that copper can have an extremely low creep ductility. However with the addition of about 50 ppm phosphorus to the copper it appears as if the creep brittleness problem is avoided and that type of copper (OFP) has consequently been chosen as the canister material. It is shown in the report that the experiments performed on OFP copper does not exclude the possibility of creep brittleness of OFP copper in the very long term. The plasticity and creep model has been used to estimate creep life under conditions of intergranular creep cracking according to a model formulated by Cocks and Ashby. The estimated life times widely exceed the design life of the canister. However the observations of creep brittleness in OF copper indicate that the Cocks-Ashby model probably does not apply to the OF copper. Thus additional calculations have been done with the plasticity and creep model in order to estimate stress as a function of time for the probably most severe loading case of the canister with regard to creep failure, an earth quake shear. Despite the fact that the stress in the canister will remain at the 100 MPa level for thousands of years after an earth quake the low temperature, about 50 deg C or less, will make the solid state diffusion process assumed to control the brittle cracking process, too slow to lead to any significant brittle creep cracking in the canister.

  16. Creep of timber joints

    NARCIS (Netherlands)

    Van de Kuilen, J.W.G.

    2008-01-01

    A creep analysis has been performed on nailed, toothed-plates and split-ring joints in a varying uncontrolled climate. The load levels varied between 30% and 50% of the average ultimate short term strength of these joints, tested in accordance with ISO 6891. The climate in which the tests were

  17. Creep Feeding Beef Calves

    OpenAIRE

    2005-01-01

    Creep feeding is the managerial practice of supplying supplemental feed (usually concentrates) to the nursing calf. Milk from a lactating beef cow furnishes only about 50 percent of the nutrients that a 3-4 month-old calf needs for maximum growth.

  18. Creep fatigue damage under multiaxial conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lobitz, D.W.; Nickell, R.E.

    1977-01-01

    When structural components are subjected to severe cyclic loading conditions with intermittent periods of sustained loading at elevated temperature, the designer must guard against a failure mode caused by the interaction of time-dependent and time-independent deformation. This phenomena is referred to as creep-fatigue interaction. The most elementary form of interaction theory (called linear damage summation) is now embodied in the ASME Boiler and Pressure Vessel Code. In recent years, a competitor for the linear damage summation theory has emerged, called strainrange partitioning. This procedure is based upon the visualization of the cyclic strain in a uniaxial creep-fatigue test as a hysteresis loop, with the inelastic strains in the loop counter-balanced in one of two ways. The two theories are compared and contrasted in terms of ease of use, possible inconsistencies, and component life prediction. Future work to further test the damage theories is recommended. (TFD)

  19. Creep behaviour and creep mechanisms of normal and healing ligaments

    Science.gov (United States)

    Thornton, Gail Marilyn

    Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep

  20. The Sensitivity Analysis of Axial Pressure Tube Creep Profile for Dryout Power in PHWR

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Euiseung; Kim, Youngae [KHNP CRI, Daejeon (Korea, Republic of)

    2016-10-15

    The Stern Laboratory performed the CHF tests with only one axial pressure tube creep profile per 3.3%, 5.1% peak crept channel and made CHF correlation including creep factor from the CHF test results. Wolsong nuclear power plants also have utilized the same CHF correlation derived by CNL. Pressure tube diameter creep rate is function of fast neutron, coolant temperature, and coolant pressure in a channel. It means that various axial pressure tube creep profiles exist in PHWR due to the history of operating conditions. Usually, CHF correlation is used during ROP(Regional Overpower Protection) Trip Setpoint Analysis or Safety Analysis in PHWR. The sensitivity analysis for CHF effects using various creep profiles is needed. This paper summarizes the comparison results of dryout power between CHF test creep profile and estimated creep profiles of Wolsong units. The effect of axial pressure tube creep profile for dryout power in fuel channel is evaluated by using Stern Lab. CHF test creep profile and 380 channel creep profiles of Wolsong. The dryout powers at 3.3% and 5.1% test conditions are slightly smaller when using 380 Wolsong channels creep profiles. These also show that the simulated dryout powers maintain consistency regardless of flow conditions.

  1. Evaluation of microstructure and creep damage in high-Cr ferritic steel welds

    Institute of Scientific and Technical Information of China (English)

    Masaaki TABUCHI; Hiromichi HONGO

    2011-01-01

    11Cr-0.4Mo-2W-CuVNb steel (ASME Gr.122) is used for boiler components in ultrasupercritical (USC) thermal power plants. The creep strength of high-Cr steel welds decreases due to the formation of Type Ⅳ creep damage in the heat-affected zone (HAZ) during long-term use at high temperatures. In the present study, the processes and mechanisms of Type Ⅳ creep damage were elucidated by investigating the long-term creep strength, microstructure and damage behavior of Gr.122 steel welds.Creep tests using thick welded joints were interrupted at several time steps, and the initiation, evolution and distribution of creep damage were measured. It was found that the formation and growth of creep damage was suppressed during the steadystate stage; creep voids formed at 0.5 of life, and coalesced to form a crack after 0.9of life. Type Ⅳ creep damage was mostly observed in the area about 30% below the surface of the plate. Differences in creep damage behavior between Gr.122 and Gr.91 steel welds were examined. Experimental creep damage distribution was compared with computed versions using the finite element method and damage mechanics.

  2. Recent Methodologies for Creep Deformation Analysis and Its Life Prediction

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo-Gon; Park, Jae-Young; Iung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-10-15

    To design the high-temperature creeping materials, various creep data are needed for codification, as follows: i) stress vs. creep rupture time for base metals and weldments (average and minimum), ii) stress vs. time to 1% total strain (average), iii) stress vs. time to onset of tertiary creep (minimum), and iv) constitutive eqns. for conducting time- and temperature- dependent stress-strain (average), and v) isochronous stress-strain curves (average). Also, elevated temperature components such as those used in modern power generation plant are designed using allowable stress under creep conditions. The allowable stress is usually estimated on the basis of up to 10{sup 5} h creep rupture strength at the operating temperature. The master curve of the “sinh” function was found to have a wider acceptance with good flexibility in the low stress ranges beyond the experimental data. The proposed multi-C method in the LM parameter revealed better life prediction than a single-C method. These improved methodologies can be utilized to accurately predict the long-term creep life or strength of Gen-IV nuclear materials which are designed for life span of 60 years.

  3. Experimental study and modelling of high temperature creep flow and damage behaviour of 9Cr1Mo-NbV steel weldments; Etude experimentale et modelisation, du comportement, de l'endommagement et de la rupture en fluage a haute temperature de joint soudes en acier 9Cr1Mo-NbV

    Energy Technology Data Exchange (ETDEWEB)

    Gaffard, V

    2004-12-15

    Chromium martensitic stainless steels are under development since the 70's with the prospect of using them as structural components in thermal and nuclear power plants. The modified 9Cr1Mo-NbV steel is already used, especially in England and Japan, as a material for structural components in thermal power plants where welding is a commonly used joining technique. New generations of chromium martensitic stainless steels with improved mechanical properties for high pressure and temperature use are currently under development. However, observations of several in-service premature failures of welded components in 9Cr1Mo-NbV steel, outline a strong need for understanding the high temperature creep flow and damage behaviour of 9Cr1Mo-NbV steels and weldments. The present study aimed at experimentally determining and then modelling the high temperature creep flow and damage behaviour of both 9Cr1Mo-NbV steels and weldments (typically in the temperature range from 450 C to 650 C). The base metal was first studied as the reference material. It was especially evidenced that tempered chromium martensitic steels exhibit a change in both creep flow and damage behaviour for long term creep exposure. As a consequence, the classically performed extrapolation of 1,000 hours creep data to 100,000 hours creep lifetime predictions might be very hazardous. Based on experimental observations, a new model, integrating and coupling multiple creep flow and damage mechanisms, was developed in the framework of the mechanics of porous media. It was then successfully used to represent creep flow and damage behaviour of the base metal from high to low stress levels even for complex multiaxial loading conditions. Although the high temperature creep properties of the base metal are quite good, the occurrence of premature failure in weldments in high temperature creep conditions largely focused the attention of the scientific community. The lower creep strength of the weld component was also

  4. Creep-fatigue modelling in structural steels using empirical and constitutive creep methods implemented in a strip-yield model

    Science.gov (United States)

    Andrews, Benjamin J.

    The phenomena of creep and fatigue have each been thoroughly studied. More recently, attempts have been made to predict the damage evolution in engineering materials due to combined creep and fatigue loading, but these formulations have been strictly empirical and have not been used successfully outside of a narrow set of conditions. This work proposes a new creep-fatigue crack growth model based on constitutive creep equations (adjusted to experimental data) and Paris law fatigue crack growth. Predictions from this model are compared to experimental data in two steels: modified 9Cr-1Mo steel and AISI 316L stainless steel. Modified 9Cr-1Mo steel is a high-strength steel used in the construction of pressure vessels and piping for nuclear and conventional power plants, especially for high temperature applications. Creep-fatigue and pure creep experimental data from the literature are compared to model predictions, and they show good agreement. Material constants for the constitutive creep model are obtained for AISI 316L stainless steel, an alloy steel widely used for temperature and corrosion resistance for such components as exhaust manifolds, furnace parts, heat exchangers and jet engine parts. Model predictions are compared to pure creep experimental data, with satisfactory results. Assumptions and constraints inherent in the implementation of the present model are examined. They include: spatial discretization, similitude, plane stress constraint and linear elasticity. It is shown that the implementation of the present model had a non-trivial impact on the model solutions in 316L stainless steel, especially the spatial discretization. Based on these studies, the following conclusions are drawn: 1. The constitutive creep model consistently performs better than the Nikbin, Smith and Webster (NSW) model for predicting creep and creep-fatigue crack extension. 2. Given a database of uniaxial creep test data, a constitutive material model such as the one developed for

  5. Reassembling Surveillance Creep

    DEFF Research Database (Denmark)

    Bøge, Ask Risom; Lauritsen, Peter

    2017-01-01

    We live in societies in which surveillance technologies are constantly introduced, are transformed, and spread to new practices for new purposes. How and why does this happen? In other words, why does surveillance “creep”? This question has received little attention either in theoretical...... development or in empirical analyses. Accordingly, this article contributes to this special issue on the usefulness of Actor-Network Theory (ANT) by suggesting that ANT can advance our understanding of ‘surveillance creep’. Based on ANT’s model of translation and a historical study of the Danish DNA database......, we argue that surveillance creep involves reassembling the relations in surveillance networks between heterogeneous actors such as the watchers, the watched, laws, and technologies. Second, surveillance creeps only when these heterogeneous actors are adequately interested and aligned. However...

  6. Quantitative analysis of microstructure deformation in creep fenomena of ferritic SA-213 T22 and austenitic SA-213 TP304H material

    Science.gov (United States)

    Mulyana, Cukup; Taufik, Ahmad; Gunawan, Agus Yodi; Siregar, Rustam Efendi

    2013-09-01

    The failure of critical component of fossil fired power plant that operated in creep range (high stress, high temperature and in the long term) depends on its microstructure characteristics. Ferritic low carbon steel (2.25Cr-1Mo) and Austenitic stainless alloy (18Cr-8Ni) are used as a boiler tube in the secondary superheater outlet header to deliver steam before entering the turbin. The tube failure is occurred in a form of rupture, resulting trip that disrupts the continuity of the electrical generation. The research in quantification of the microstructure deformation has been done in predicting the remaining life of the tube through interrupted accelerated creep test. For Austenitic Stainless Alloy (18Cr-8Ni), creep test was done in 550°C with the stress 424.5 MPa and for Ferritic Low Carbon Steel (2.25Cr-1Mo) in 570°C with the stress 189 MPa. The interrupted accelerated creep test was done by stopping the observation in condition 60%, 70%, 80% and 90% of remaining life, the creep test fracture was done before. Then the micro hardness test, photo micro, SEM and EDS were obtained from those samples. Refer to ASTM E122, microstructure parameters were calculated. The results indicated that there are a consistency of decreasing their grain diameters, increasing their grain size numbers, micro hardness, and the length of crack or void number per unit area with the decreasing of remaining life. While morphology of grain (stated in parameter α=LV/LH) relatively constant for austenitic. However, for ferritic the change of morphology revealed significantly. Fracture mode propagation of ferritic material is growth with voids transgranular and intergranular crack, and for austenitic material the fracture growth with intergranular creep fracture void and wedge crack. In this research, it was proposed a formulation of mathematical model for creep behavior corresponding their curve fitting resulted for the primary, secondary and tertiary in accelerated creep test. In

  7. Degradation and failure of bolting in nuclear power plants: Volume 1

    Energy Technology Data Exchange (ETDEWEB)

    Nickell, R.E.

    1988-04-01

    These two volumes provide the documentation for industry resolution of the US Nuclear Regulatory Commission (NRC) generic issue B-29, Degradation and Failure of Bolting in Nuclear Power Plants. The issue was identified as a consequence of concerns about the structural integrity of component supports circa 1980. When bolting integrity became a separate issue in 1982, the utility industry responded by forming a Task Group on Bolting under the aegis of the Atomic Industrial Forum (AIF) and the Materials Properties Council (MPC). The AIF/MPC Task Group on Bolting formulated a comprehensive nineteen-task action plan aimed at resolution of the issue, with implementation of the plan, the responsibility of EPRI and the affected Owner's Groups. EPRI organized a matrix-managed Generic Bolted Joint Integrity Program to carry out the research, with the results reported herein.

  8. Jojoba could stop the desert creep

    Energy Technology Data Exchange (ETDEWEB)

    1982-03-25

    The Sahara desert is estimated to be expanding at a rate of 5km a year. The Sudanese government is experimenting with jojoba in six different regions as the bush has the potential to stop this ''desert creep''. The plant, a native to Mexico, is long known for its resistance to drought and for the versatile liquid wax that can be extracted from its seeds. It is estimated that one hectare of mature plants could produce 3000 kg of oil, currently selling at $50 per litre, and so earn valuable foreign currency.

  9. Experimental investigation of creep behavior of clastic rock in Xiangjiaba Hydropower Project

    Directory of Open Access Journals (Sweden)

    Yu ZHANG

    2015-01-01

    Full Text Available There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock, triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other hand, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.

  10. Circular Functions Based Comprehensive Analysis of Plastic Creep Deformations in the Fiber Reinforced Composites

    Science.gov (United States)

    Monfared, Vahid

    2016-06-01

    Analytically based model is presented for behavioral analysis of the plastic deformations in the reinforced materials using the circular (trigonometric) functions. The analytical method is proposed to predict creep behavior of the fibrous composites based on basic and constitutive equations under a tensile axial stress. New insight of the work is to predict some important behaviors of the creeping matrix. In the present model, the prediction of the behaviors is simpler than the available methods. Principal creep strain rate behaviors are very noteworthy for designing the fibrous composites in the creeping composites. Analysis of the mentioned parameter behavior in the reinforced materials is necessary to analyze failure, fracture, and fatigue studies in the creep of the short fiber composites. Shuttles, spaceships, turbine blades and discs, and nozzle guide vanes are commonly subjected to the creep effects. Also, predicting the creep behavior is significant to design the optoelectronic and photonic advanced composites with optical fibers. As a result, the uniform behavior with constant gradient is seen in the principal creep strain rate behavior, and also creep rupture may happen at the fiber end. Finally, good agreements are found through comparing the obtained analytical and FEM results.

  11. Circular Functions Based Comprehensive Analysis of Plastic Creep Deformations in the Fiber Reinforced Composites

    Science.gov (United States)

    Monfared, Vahid

    2016-12-01

    Analytically based model is presented for behavioral analysis of the plastic deformations in the reinforced materials using the circular (trigonometric) functions. The analytical method is proposed to predict creep behavior of the fibrous composites based on basic and constitutive equations under a tensile axial stress. New insight of the work is to predict some important behaviors of the creeping matrix. In the present model, the prediction of the behaviors is simpler than the available methods. Principal creep strain rate behaviors are very noteworthy for designing the fibrous composites in the creeping composites. Analysis of the mentioned parameter behavior in the reinforced materials is necessary to analyze failure, fracture, and fatigue studies in the creep of the short fiber composites. Shuttles, spaceships, turbine blades and discs, and nozzle guide vanes are commonly subjected to the creep effects. Also, predicting the creep behavior is significant to design the optoelectronic and photonic advanced composites with optical fibers. As a result, the uniform behavior with constant gradient is seen in the principal creep strain rate behavior, and also creep rupture may happen at the fiber end. Finally, good agreements are found through comparing the obtained analytical and FEM results.

  12. Steady-State Creep of Rock Salt: Improved Approaches for Lab Determination and Modelling

    Science.gov (United States)

    Günther, R.-M.; Salzer, K.; Popp, T.; Lüdeling, C.

    2015-11-01

    Actual problems in geotechnical design, e.g., of underground openings for radioactive waste repositories or high-pressure gas storages, require sophisticated constitutive models and consistent parameters for rock salt that facilitate reliable prognosis of stress-dependent deformation and associated damage. Predictions have to comprise the active mining phase with open excavations as well as the long-term development of the backfilled mine or repository. While convergence-induced damage occurs mostly in the vicinity of openings, the long-term behaviour of the backfilled system is dominated by the damage-free steady-state creep. However, because in experiments the time necessary to reach truly stationary creep rates can range from few days to years, depending mainly on temperature and stress, an innovative but simple creep testing approach is suggested to obtain more reliable results: A series of multi-step tests with loading and unloading cycles allows a more reliable estimate of stationary creep rate in a reasonable time. For modelling, we use the advanced strain-hardening approach of Günther-Salzer, which comprehensively describes all relevant deformation properties of rock salt such as creep and damage-induced rock failure within the scope of an unified creep ansatz. The capability of the combination of improved creep testing procedures and accompanied modelling is demonstrated by recalculating multi-step creep tests at different loading and temperature conditions. Thus reliable extrapolations relevant to in-situ creep rates (10^{-9} to 10^{-13} s^{-1}) become possible.

  13. Creep buckling analysis of shells

    Energy Technology Data Exchange (ETDEWEB)

    Stone, C.M.; Nickell, R.E.

    1977-01-01

    The current study was conducted in an effort to determine the degree of conservatism or lack of conservatism in current ASME design rules concerning time-dependent (creep) buckling. In the course of this investigation, certain observations were made concerning the numerical solution of creep buckling problems. It was demonstrated that a nonlinear finite element code could be used to solve the time-dependent buckling problem. A direct method of solution was presented which proved to be computationally efficient and provided answers which agreed very well with available analytical solutions. It was observed that the calculated buckling times could vary widely for small errors in computed displacements. The presence of high creep strain rates contributed to the prediction of early buckling times when calculated during the primary creep stage. The predicted time estimates were found to increase with time until the secondary stage was reached and the estimates approached the critical times predicted without primary creep. It can be concluded, therefore, that for most nuclear piping components, whose primary creep stage is small compared to the secondary stage, the effect of primary creep is negligible and can be omitted from the calculations. In an evaluation of the past and current ASME design rules for time-dependent, load controlled buckling, it was concluded that current use of design load safety factors is not equivalent to a safety factor of ten on service life for low creep exponents.

  14. Preconsolidation Pressure and Creep Settlements

    DEFF Research Database (Denmark)

    Thorsen, Grete

    1995-01-01

    of oedometer tests with undisturbed samples have been analysed by means of different methods to determine the pre-consolidation pressure. An attempt is made to estimate the creep rates on the basis of AMS 14C-datings of the sediments and a model for creep determination proposed by Moust Jacobsen....

  15. Above- and Belowground Trophic Interactions on Creeping Thistle (Cirsium arvense) in High- and Low-Diversity Plant Communities: Potential for Biotic Resistance?

    NARCIS (Netherlands)

    Bezemer, T.M.; Graça, O.; Rousseau, P.; Putten, van der W.H.

    2004-01-01

    The capacity of local communities to control introduced plants is called biotic resistance. Biotic resistance has been almost exclusively tested for plant competition and above-ground herbivores and pathogens, while neglecting root herbivores and soil pathogens. Here, we present biotic resistance by

  16. Above- and Belowground Trophic Interactions on Creeping Thistle (Cirsium arvense) in High- and Low-Diversity Plant Communities: Potential for Biotic Resistance?

    NARCIS (Netherlands)

    Bezemer, T.M.; Graça, O.; Rousseau, P.; Van der Putten, W.H.

    2004-01-01

    The capacity of local communities to control introduced plants is called biotic resistance. Biotic resistance has been almost exclusively tested for plant competition and aboveground herbivores and pathogens, while neglecting root herbivores and soil pathogens. Here, we present biotic resistance by

  17. Above- and Belowground Trophic Interactions on Creeping Thistle (Cirsium arvense) in High- and Low-Diversity Plant Communities: Potential for Biotic Resistance?

    NARCIS (Netherlands)

    Bezemer, T.M.; Graça, O.; Rousseau, P.; Van der Putten, W.H.

    2004-01-01

    The capacity of local communities to control introduced plants is called biotic resistance. Biotic resistance has been almost exclusively tested for plant competition and aboveground herbivores and pathogens, while neglecting root herbivores and soil pathogens. Here, we present biotic resistance by

  18. Above- and Belowground Trophic Interactions on Creeping Thistle (Cirsium arvense) in High- and Low-Diversity Plant Communities: Potential for Biotic Resistance?

    NARCIS (Netherlands)

    Bezemer, T.M.; Graça, O.; Rousseau, P.; Putten, van der W.H.

    2004-01-01

    The capacity of local communities to control introduced plants is called biotic resistance. Biotic resistance has been almost exclusively tested for plant competition and above-ground herbivores and pathogens, while neglecting root herbivores and soil pathogens. Here, we present biotic resistance by

  19. Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Przystupa, Marek A.

    2007-12-13

    Harper-Dorn (H-D) creep is observed in metals and geological materials exposed to very low stresses at temperatures close to the melting point. It is one of several types of creep processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring creep and Coble creep being two other important processes. H-D creep can be somewhat insidious because the creep rates are much larger than those expected for Nabarro-Herring or Coble creep. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earth’s mantle all involve very low stresses, an understanding of the factors controlling H-D creep is critical in preventing failures associated with those higher-than-expected creep rates. The purpose of this investigation was to obtain missing microstructural information on the evolution of the dislocation structures during static annealing of materials with fcc, bcc and hcp structure and use obtained results to test predictive capabilities of the dislocation network theory of H-D creep. In our view the evolutionary processes during static annealing and during Harper-Dorn creep are intimately related. The materials used in this study were fcc aluminum, hcp zinc and bcc tin. All characterizations of dislocation structures, densities and dislocation link length distributions were carried out using the etch pit method. To obtain quantitative information on the evolution of the dislocation networks during annealing the pure fcc aluminum samples were pre-deformed by creep at 913 and 620 K and then annealed. The higher deformation temperature was selected to generate starting dislocation networks similar to those forming during Harper-Dorn creep and the lower, to obtain higher dislocation densities suitable for reliable estimates of the parameters of the network growth law. The measured experimental link length distribution were, after scaling, (1) the same for all annealing

  20. Rationalization of Creep Data of Creep-Resistant Steels on the Basis of the New Power Law Creep Equation

    Science.gov (United States)

    Wang, Q.; Yang, M.; Song, X. L.; Jia, J.; Xiang, Z. D.

    2016-07-01

    The conventional power law creep equation (Norton equation) relating the minimum creep rate to creep stress and temperature cannot be used to predict the long-term creep strengths of creep-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of creep determined on the basis of this equation depend on creep temperature and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law creep equation can be resolved if the new power law equation is used to rationalize the creep data. The new power law creep equation takes a form similar to the conventional power law creep equation but has a radically different capability not only in rationalizing creep data but also in predicting the long-term creep strengths from short-term test data. These capabilities of the new power law creep equation are demonstrated using the tensile strength and creep test data measured for both pipe and tube grades of the creep-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).

  1. Evaluation of creep-fatigue crack growth for large-scale FBR reactor vessel and NDE assessment

    Energy Technology Data Exchange (ETDEWEB)

    Joo, Young Sang; Kim, Jong Bum; Kim, Seok Hun; Yoo, Bong

    2001-03-01

    Creep fatigue crack growth contributes to the failure of FRB reactor vessels in high temperature condition. In the design stage of reactor vessel, crack growth evaluation is very important to ensure the structural safety and setup the in-service inspection strategy. In this study, creep-fatigue crack growth evaluation has been performed for the semi-elliptical surface cracks subjected to thermal loading. The thermal stress analysis of a large-scale FBR reactor vessel has been carried out for the load conditions. The distributions of axial, radial, hoop, and Von Mises stresses were obtained for the loading conditions. At the maximum point of the axial and hoop stress, the longitudinal and circumferential surface cracks (i.e. PTS crack, NDE short crack and shallow long crack) were postulated. Using the maximum and minimum values of stresses, the creep-fatigue crack growth of the proposed cracks was simulated. The crack growth rate of circumferential cracks becomes greater than that of longitudinal cracks. The total crack growth of the largest PTS crack is very small after 427 cycles. The structural integrity of a large-scale reactor can be maintained for the plant life. The crack depth growth of the shallow long crack is faster than that of the NDE short crack. In the ISI of the large-scale FBR reactor vessel, the ultrasonic inspection is beneficial to detect the shallow circumferential cracks.

  2. Creep Burst Testing of a Woven Inflatable Module

    Science.gov (United States)

    Selig, Molly M.; Valle, Gerard D.; James, George H.; Oliveras, Ovidio M.; Jones, Thomas C.; Doggett, William R.

    2015-01-01

    A woven Vectran inflatable module 88 inches in diameter and 10 feet long was tested at the NASA Johnson Space Center until failure from creep. The module was pressurized pneumatically to an internal pressure of 145 psig, and was held at pressure until burst. The external environment remained at standard atmospheric temperature and pressure. The module burst occurred after 49 minutes at the target pressure. The test article pressure and temperature were monitored, and video footage of the burst was captured at 60 FPS. Photogrammetry was used to obtain strain measurements of some of the webbing. Accelerometers on the test article measured the dynamic response. This paper discusses the test article, test setup, predictions, observations, photogrammetry technique and strain results, structural dynamics methods and quick-look results, and a comparison of the module level creep behavior to the strap level creep behavior.

  3. Standard test method for creep-fatigue testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2009-01-01

    1.1 This test method covers the determination of mechanical properties pertaining to creep-fatigue deformation or crack formation in nominally homogeneous materials, or both by the use of test specimens subjected to uniaxial forces under isothermal conditions. It concerns fatigue testing at strain rates or with cycles involving sufficiently long hold times to be responsible for the cyclic deformation response and cycles to crack formation to be affected by creep (and oxidation). It is intended as a test method for fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. The cyclic conditions responsible for creep-fatigue deformation and cracking vary with material and with temperature for a given material. 1.2 The use of this test method is limited to specimens and does not cover testing of full-scale components, structures, or consumer products. 1.3 This test method is primarily ...

  4. Machinery failure analysis and troubleshooting practical machinery management for process plants

    CERN Document Server

    Bloch, Heinz P

    2012-01-01

    Solve the machinery failure problems costing you time and money with this classic, comprehensive guide to analysis and troubleshooting  Provides detailed, complete and accurate information on anticipating risk of component failure and avoiding equipment downtime Includes numerous photographs of failed parts to ensure you are familiar with the visual evidence you need to recognize Covers proven approaches to failure definition and offers failure identification and analysis methods that can be applied to virtually all problem situations Demonstr

  5. Review of Physical Metallurgy of Creep Steel for the Design of Modern Steam Power Plants – Fundamental Theories and Parametric Models

    Directory of Open Access Journals (Sweden)

    V. C. Igwemezie

    2015-12-01

    Full Text Available The need for electricity supply has increased tremendously in recent time thereby necessitating an improvement in the efficiency of steam power plant. A greater efficiency leads to a saving in fuel for a given electricity output with a consequential reduction in the rate at which damage is done to the earth’s environment. This paper looks at the physical metallurgy theories and parametric models that have been the bases in the design of steel for power plant applications.

  6. Negative creep in nickel base superalloys

    DEFF Research Database (Denmark)

    Dahl, Kristian Vinter; Hald, John

    2004-01-01

    Negative creep describes the time dependent contraction of a material as opposed to the elongation seen for a material experiencing normal creep behavior. Negative creep occurs because of solid state transformations that results in lattice contractions. For most applications negative creep will h...

  7. Standard test method for creep-fatigue crack growth testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneous materials by use of pre-cracked compact type, C(T), test specimens subjected to uniaxial cyclic forces. It concerns fatigue cycling with sufficiently long loading/unloading rates or hold-times, or both, to cause creep deformation at the crack tip and the creep deformation be responsible for enhanced crack growth per loading cycle. It is intended as a guide for creep-fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. Therefore, this method requires testing of at least two specimens that yield overlapping crack growth rate data. The cyclic conditions responsible for creep-fatigue deformation and enhanced crack growth vary with material and with temperature for a given material. The effects of environment such as time-dependent oxidation in enhancing the crack growth ra...

  8. EVALUATION OF THE TIME DEPENDENT FAILURE ASSESSMENT CURVES FOR 10CrMo910 AND 316 SS AT 550℃

    Institute of Scientific and Technical Information of China (English)

    F.Z.Xuan; S.D.Tu; Z.D.Wang; C.W.Ma

    2004-01-01

    10CrMo910 and 316 stainless steel are widely adopted in high temperature structures of power generations, chemical processing plants and petroleum refineries. In this work, a total of 10000 hour tensile creep test on 16 specimens of such two materials was conducted at 550℃. On the basis of the experimental results, the isochronous stress-strain curves and time-dependent failure assessment curves of the two materials were given. Finally, the formulae of time dependent failure assessment curve for 10CrMo910 and 316 stainless steel corresponding to long-term creep cases, which could be utilized in the high temperature defects assessment, were established. The procedure for defining the time-dependent failure assessment curves was also presented.

  9. Regulatory analysis for the resolution of Generic Safety Issue 29: Bolting degradation or failure in nuclear power plants

    Energy Technology Data Exchange (ETDEWEB)

    Chang, T.Y.

    1991-09-01

    Generic Safety Issue (GSI)-29 deals with staff concerns about public risk due to degradation or failure of safety-related bolting in nuclear power plants. The issue was initiated in November 1982. Value-impact studies of a mandatory program on safety-related bolting for operating plants were inconclusive: therefore, additional regulatory requirements for operating plants could not be justified in accordance with provisions of 10 CFR 50.109. In addition, based on operating experience with bolting in both nuclear and conventional power plants, the actions already taken through bulletins, generic letters, and information notices, and the industry-proposed actions, the staff concluded that a sufficient technical basis exists for the resolution of GSI-29. The staff further concluded that leakage of bolted pressure joints is possible but catastrophic failure of a reactor coolant pressure boundary joint that will lead to significant accident sequences is highly unlikely. For future plants, it was concluded that a new Standard Review Plant section should be developed to codify existing bolting requirements and industry-developed initiatives. 9 refs., 1 tab.

  10. Survey of creep damage in a T-joint from a retired steam pipe system; Kartlaeggning av krypskador i ett T-stycke fraan ett utrangerat aangnaet

    Energy Technology Data Exchange (ETDEWEB)

    Storesund, Jan

    2009-06-15

    Unexpected failures and cracking have recently occurred in steam piping by creep although the service temperatures have been significantly below the limit temperature for creep rupture. Characterisation of such damage, mapping of the presence in Swedish plants and better knowledge of the presumptions for the phenomenon have been received in previous Vaermeforsk projects. A steam pipe system that never had been inspected or tested with respect to creep was replica tested at a number of test positions. The steam data was 450 deg C and 65 bars and the age was 35 years of almost continuous operation. Extensive creep damage was found in one T-joint. This component was the object of interest in the present project. Metallographic investigations were carried out by cutting the T-joint into sections for through thickness examinations of possible creep damage as well as characterisation of the microstructure. Ten sections were selected at different positions of four welds that the T-joint covered. In addition to the characterisation by means of creep damage and possible microstructure degradation or other anomalies the purpose of the investigation was to find out if the replica testing was a conservative method or not. Other expectations on the project were to gain additional knowledge of the creep phenomena's below the limit temperature and a verification of the computation models for crack propagation that were used in the previous Vaermeforsk projects in the area. Nine chemical analyses were performed on all different parent and weld metals of the T-joints. Most analyses resulted in a composition close to the nominal one, that is 13CrMo4-4 steel, the most frequently used heat resistant steel in steam piping for steam temperatures around the limit temperature in Sweden. The parent metal in which the creep cracks were found, however, had a composition that corresponds to 0,5Cr0,6Mo0,3V steel, a low alloy steel that is liable to cracking. Furthermore the branch part of

  11. Creep in electronic ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.

    2000-04-27

    High-temperature creep measurements combined with microstructural investigations can be used to elucidate deformation mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.

  12. Creep strength and microstructural evolution of 9-12% Cr heat resistant steels during creep exposure at 600 C and 650 C

    Energy Technology Data Exchange (ETDEWEB)

    Mendez Martin, Francisca [Graz Univ. of Technology (Austria). Inst. for Materials Science and Welding; Panait, Clara Gabriela [MINES ParisTech, UMR CNRS, Evry (France). Centre des Materiaux; V et M France CEV, Aulnoye-Aymeries (France); Bendick, Walter [Salzgitter Mannesmann Forschung GmbH (SZMF), Duisburg (DE)] (and others)

    2010-07-01

    9-12% Cr heat resistant steels are used for applications at high temperatures and pressures in steam power plants. 12% Cr steels show higher creep strength and higher corrosion resistance compared to 9% Cr steels for short term creep exposure. However, the higher creep strength of 12 %Cr steels drops increasingly after 10,000-20,000 h of creep. This is probably due to a microstructural instability such as the precipitation of new phases (e.g. Laves phases and Z-phases), the growth of the precipitates and the recovery of the matrix. 9% Cr and 12% Cr tempered martensitic steels that have been creep tested for times up to 50,000 h at 600 C and 650 C were investigated using Transmission Electron Microscopy (TEM) on extractive replicas and thin foils together with Backscatter Scanning Electron Microscopy (BSE-SEM) to better understand the different creep behaviour of the two different steels. A significant precipitation of Laves phase and low amounts of Z-phase was observed in the 9% Cr steels after long-term creep exposure. The size distribution of Laves phases was measured by image analysis of SEM-BSE images. In the 12% Cr steel two new phases were identified, Laves phase and Z-phase after almost 30,000 h of creep test. The quantification of the different precipitated phases was studied. (orig.)

  13. Study of Inverse Creep In Textile Yarns

    Directory of Open Access Journals (Sweden)

    P.G. Patil

    2009-12-01

    Full Text Available Creep has been known and studied for textilematerials for decades. In comparison, a newlyobserved phenomenon of inverse creep seems not tohave received much attention. A new instrument hasbeen fabricated to measure creep and inverse creep intextile materials particularly yarns. Creep and Inversecreep measurements of nylon multifilament yarn,polyester multifilament yarn, cotton and wool yarn atdifferent levels of stress have been studied using thenew instrument and results are reported in the presentpaper.

  14. Service life prediction. Development of models for predicting the service life of power plant components subject to thermomechanical creep fatigue; Lebensdauervorhersage. Entwicklung von Modellen zur Lebensdauervorhersage von Kraftwerksbauteilen unter thermisch-mechanischer Kriechermuedungsbeanspruchung. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Cui, L.; Scholz, A. [Technische Univ. Darmstadt (Germany). Institut fuer Werkstoffkunde; Hartrott, P. von; Schlesinger, M. [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

    2009-07-01

    Extensive use is made of massive components of heat resistant and highly heat resistant materials in installations of the power and heating industry. These components are exposed to varying thermomechanical stress as a result of ramping-up and down processes. In this research project two computer-assisted methods of predicting service life until crack initiation were extended to include cases of thermomechanical multi-axis stress conducive to creep fatigue and of superposition of high-cycle stress on power plant components. Investigations were limited to rotor steel of type X12CrMoWVNbN10-1-1. Complex thermomechanical multi-axis experiments were performed on round, notched and cruciform test specimens of close-to-life dimensions in order to demonstrate by experiment the validity of these models. The results of these calculations showed an acceptable degree of agreement between experiment and simulation for both models. Calculations on earlier TMF experiments performed at IfW on hollow specimens of 1%CrMoNiV showed good predictability for both the SARA and the ThoMat programme. Calculations on experiments performed at MPA Stuttgart on model bodies consisting of the same 1%CrMoNiV showed a predictability of acceptable variability considering the complexity of the stresses involved. A further outcome of this project is that the use of SARA appears universally suitable for the construction of new plants and in the service area, while the use of ThoMat appears suited for detail optimisation in the development process.

  15. Mechanics of Failure Mechanisms in Structures

    CERN Document Server

    Carlson, R L; Craig, J I

    2012-01-01

    This book focuses on the mechanisms and underlying mechanics of failure in various classes of materials such as metallic, ceramic, polymeric, composite and bio-material.  Topics include tensile and compressive fracture, crack initiation and growth, fatigue and creep rupture in metallic materials, matrix cracking and delamination and environmental degradation in polymeric composites, failure of bio-materials such as prosthetic heart valves and prosthetic hip joints, failure of ceramics and ceramic matrix composites, failure of metallic matrix composites, static and dynamic buckling failure, dynamic excitations and creep buckling failure in structural systems. Chapters are devoted to failure mechanisms that are characteristic of each of the materials.  The work also provides the basic elements of fracture mechanics and studies in detail several niche topics such as the effects of toughness gradients, variable amplitude loading effects in fatigue, small fatigue cracks, and creep induced brittleness. Furthe...

  16. Plasticity and creep of metals

    CERN Document Server

    Rusinko, Andrew

    2011-01-01

    Here is a systematic presentation of the postulates, theorems and principles of mathematical theories of plasticity and creep in metals, and their applications. Special attention is paid to analysis of the advantages and shortcomings of the classical theories.

  17. null Seismic Creep, null Images

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Seismic creep is the constant or periodic movement on a fault as contrasted with the sudden rupture associated with an earthquake. It is a usually slow deformation...

  18. Research on the closure and creep mechanism of circular tunnels

    Institute of Scientific and Technical Information of China (English)

    LI Lian-chong; TANG Chun-an; MA Tian-hui; ZHAO Xing-dong

    2008-01-01

    A numerical code called Rock Failure Process Analysis (RFPA2D) was employed to investigate the closure, damage and failure behavior of the horizontal tunnels. In his code the time-dependent deformation was described in terms of evolution of mesoscopic structure, leading to progressive degradation of elastic modulus and failure strength of material. In terms of material degradation, a series of numerical simulations were performed to study the convergence and subsequent failure in circular tunnels. The numerical esults provide a complete illumination for the closure, damage and failure behavior with different loading conditions. It is shown that the depth and the ratio of far field stresses play an important role in the creep behavior of tunnels. Creep failure is expected to occur in the direction of the smallest far field stress component, which means that rheological failure of tunnels is influenced not only by the rock characteristic around the tunnels but also by the orientation and distribution of far field stress on a global scale.

  19. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    Science.gov (United States)

    Song, Gian; Sun, Zhiqian; Li, Lin; Xu, Xiandong; Rawlings, Michael; Liebscher, Christian H.; Clausen, Bjørn; Poplawsky, Jonathan; Leonard, Donovan N.; Huang, Shenyan; Teng, Zhenke; Liu, Chain T.; Asta, Mark D.; Gao, Yanfei; Dunand, David C.; Ghosh, Gautam; Chen, Mingwei; Fine, Morris E.; Liaw, Peter K.

    2015-01-01

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures. PMID:26548303

  20. Contemporary overview of soil creep phenomenon

    Directory of Open Access Journals (Sweden)

    Kaczmarek Łukasz

    2017-06-01

    Full Text Available Soil creep deformation refers to phenomena which take place in many areas and research in this field of science is rich and constantly developing. The article presents an analysis of the literature on soil creep phenomena. In light of the complexity of the issues involved and the wide variety of perspectives taken, this attempt at systematization seeks to provide a reliable review of current theories and practical approaches concerning creep deformation. The paper deals with subjects such as definition of creep, creep genesis, basic description of soil creep dynamics deformation, estimation of creep capabilities, various fields of creep occurrence, and an introduction to creep modeling. Furthermore, based on this analysis, a new direction for research is proposed.

  1. Significance of primary irradiation creep in graphite

    Energy Technology Data Exchange (ETDEWEB)

    Erasmus, Christiaan, E-mail: christiaan.erasmus@gmail.com [Pebble Bed Modular Reactor (Proprietary) Limited, PO Box 9396, Centurion 0046 (South Africa); Kok, Schalk [Advanced Mathematical Modelling, CSIR Modelling and Digital Science, Pretoria 0001 (South Africa); Hindley, Michael P. [Pebble Bed Modular Reactor (Proprietary) Limited, PO Box 9396, Centurion 0046 (South Africa)

    2013-05-15

    Traditionally primary irradiation creep is introduced into graphite analysis by applying the appropriate amount of creep strain to the model at the initial time-step. This is valid for graphite components that are subjected to high fast neutron flux fields and constant stress fields, but it does not allow for the effect of movement of stress locations around a graphite component during life, nor does it allow primary creep to be applied rate-dependently to graphite components subject to lower fast neutron flux. This paper shows that a differential form of primary irradiation creep in graphite combined with the secondary creep formulation proposed by Kennedy et al. performs well when predicting creep behaviour in experimental samples. The significance of primary irradiation creep in particular in regions with lower flux is investigated. It is shown that in low flux regions with a realistic operating lifetime primary irradiation creep is significant and is larger than secondary irradiation creep.

  2. Contemporary overview of soil creep phenomenon

    Science.gov (United States)

    Kaczmarek, Łukasz; Dobak, Paweł

    2017-06-01

    Soil creep deformation refers to phenomena which take place in many areas and research in this field of science is rich and constantly developing. The article presents an analysis of the literature on soil creep phenomena. In light of the complexity of the issues involved and the wide variety of perspectives taken, this attempt at systematization seeks to provide a reliable review of current theories and practical approaches concerning creep deformation. The paper deals with subjects such as definition of creep, creep genesis, basic description of soil creep dynamics deformation, estimation of creep capabilities, various fields of creep occurrence, and an introduction to creep modeling. Furthermore, based on this analysis, a new direction for research is proposed.

  3. Investigation of the effect of aggregates' morphology on concrete creep properties by numerical simulations

    Energy Technology Data Exchange (ETDEWEB)

    Lavergne, F. [Université Paris-Est, Laboratoire Navier (ENPC, IFSTTAR, CNRS), 77455 Marne-la-Vallée Cedex (France); Sab, K., E-mail: karam.sab@enpc.fr [Université Paris-Est, Laboratoire Navier (ENPC, IFSTTAR, CNRS), 77455 Marne-la-Vallée Cedex (France); Sanahuja, J. [Département Mécanique des Matériaux et des Composants, EDF R& D, Site des Renardières, Avenue des Renardières, 77818 Moret-Sur-Loing Cedex (France); Bornert, M. [Université Paris-Est, Laboratoire Navier (ENPC, IFSTTAR, CNRS), 77455 Marne-la-Vallée Cedex (France); Toulemonde, C. [Département Mécanique des Matériaux et des Composants, EDF R& D, Site des Renardières, Avenue des Renardières, 77818 Moret-Sur-Loing Cedex (France)

    2015-05-15

    Prestress losses due to creep of concrete is a matter of interest for long-term operations of nuclear power plants containment buildings. Experimental studies by Granger (1995) have shown that concretes with similar formulations have different creep behaviors. The aim of this paper is to numerically investigate the effect of size distribution and shape of elastic inclusions on the long-term creep of concrete. Several microstructures with prescribed size distribution and spherical or polyhedral shape of inclusions are generated. By using the 3D numerical homogenization procedure for viscoelastic microstructures proposed by Šmilauer and Bažant (2010), it is shown that the size distribution and shape of inclusions have no measurable influence on the overall creep behavior. Moreover, a mean-field estimate provides close predictions. An Interfacial Transition Zone was introduced according to the model of Nadeau (2003). It is shown that this feature of concrete's microstructure can explain differences between creep behaviors.

  4. Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.

    Science.gov (United States)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2014-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry

  5. Assessment of long-term creep strength of grade 91 steel

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Kazuhiro; Sawada, Kota; Kushima, Hideaki [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan)

    2010-07-01

    In 2004 and 2005 long-term creep rupture strength of ASME Grade 91 type steels of plate, pipe, forging and tube materials was evaluated in Japan by means of region splitting analysis method in consideration of 50% of 0.2% offset yield stress. According to the evaluated 100,000h creep rupture strength of 94MPa for plate, pipe and forging steels and 92MPa for tube steel at 600 C, allowable tensile stress of the steels regulated in the Interpretation for the Technical Standard for Thermal Power Plant was slightly reduced. New creep rupture data of the steels obtained in the long-term indicate further reduction of long-term creep rupture strength. Not only creep rupture strength, but also creep deformation property of the ASME Grade 91 steel was investigated and need of reevaluation of long-term creep strength of Grade 91 steel was indicated. A refinement of region splitting analysis method for creep rupture like prediction was discussed. (orig.)

  6. Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds

    Energy Technology Data Exchange (ETDEWEB)

    Dr. F. W. Brust; Dr. G. M. Wilkowski; Dr. P. Krishnaswamy; Mr. Keith Wichman

    2010-01-27

    methods often need to be addressed as plants age. Shutdown inspection intervals can only be designed using creep and creep-fatigue crack growth techniques. (5) The use of crack growth procedures can aid in examining the seriousness of creep damage in structural components. How cracks grow can be used to assess margins on components and lead to further safe operation. After examining the pros and cons of all these methods, the R5 code was chosen as the most up-to-date and validated high temperature creep and creep fatigue code currently used in the world at present. R5 is considered the leader because the code: (1) has well established and validated rules, (2) has a team of experts continually improving and updating it, (3) has software that can be used by designers, (4) extensive validation in many parts with available data from BE resources as well as input from Imperial college's database, and (5) was specifically developed for use in nuclear plants. R5 was specifically developed for use in gas cooled nuclear reactors which operate in the UK and much of the experience is based on materials and temperatures which are experienced in these reactors. If the next generation advanced reactors to be built in the US used these same materials within the same temperature ranges as these reactors, then R5 may be appropriate for consideration of direct implementation within ASME code NH or Section XI. However, until more verification and validation of these creep/fatigue crack growth rules for the specific materials and temperatures to be used in the GEN IV reactors is complete, ASME should consider delaying this implementation. With this in mind, it is this authors opinion that R5 methods are the best available for code use today. The focus of this work was to examine the literature for creep and creep-fatigue crack growth procedures that are well established in codes in other countries and choose a procedure to consider implementation into ASME NH. It is very important to

  7. Large earthquakes and creeping faults

    Science.gov (United States)

    Harris, Ruth A.

    2017-01-01

    Faults are ubiquitous throughout the Earth's crust. The majority are silent for decades to centuries, until they suddenly rupture and produce earthquakes. With a focus on shallow continental active-tectonic regions, this paper reviews a subset of faults that have a different behavior. These unusual faults slowly creep for long periods of time and produce many small earthquakes. The presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail, but there is also the question of how creeping faults contribute to seismic hazard. It appears that well-recorded creeping fault earthquakes of up to magnitude 6.6 that have occurred in shallow continental regions produce similar fault-surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude. The behavior of much larger earthquakes on shallow creeping continental faults is less well known, because there is a dearth of comprehensive observations. Computational simulations provide an opportunity to fill the gaps in our understanding, particularly of the dynamic processes that occur during large earthquake rupture and arrest.

  8. Creep Behaviour of Modified Mar-247 Superalloy

    Directory of Open Access Journals (Sweden)

    Cieśla M.

    2016-06-01

    Full Text Available The paper presents the results of analysis of creep behaviour in short term creep tests of cast MAR-247 nickel-based superalloy samples made using various modification techniques and heat treatment. The accelerated creep tests were performed under temperature of 982 °C and the axial stresses of σ = 150 MPa (variant I and 200 MPa (variant II. The creep behaviour was analysed based on: creep durability (creep rupture life, steady-state creep rate and morphological parameters of macro- and microstructure. It was observed that the grain size determines the creep durability in case of test conditions used in variant I, durability of coarse-grained samples was significantly higher.

  9. PROBABILITY OF FAILURE OF THE TRUDOCK CRANE SYSTEM AT THE WASTE ISOLATION PILOT PLANT (WIPP)

    Energy Technology Data Exchange (ETDEWEB)

    Greenfield, M.A.; Sargent, T.J.

    2000-05-01

    This probabilistic analysis of WIPP TRUDOCK crane failure is based on two sources of failure data. The source for operator errors is the report by Swain and Guttman, NUREG/CR-1278-F, August 1983. The source for crane cable hook breaks was initially made by WIPP/WID-96- 2196, Rev. O by using relatively old (1970s) U.S. Navy data (NUREG-0612). However, a helpful analysis by R.K. Deremer of PLG guided the authors to values that were more realistic and more conservative, with the recommendation that the crane cable/hook failure rate should be 2.5 x 10-6 per demand. This value was adopted and used. Based on these choices a mean failure rate of 9.70 x 10-3(1/yr) was calculated. However, a mean rate by itself does not reveal the level of confidence to be associated with this number. Guidance to making confidence calculations came from the report by Swain and Guttman, who stated that failure data could be described by lognormal distributions. This is in agreement with the widely use d reports (by DOE and others) NPRD-95 and NPRD-91, on failure data. The calculations of confidence levels showed that the mean failure rate of 9.70x 10-3(1/yr) corresponded to a percentile value of approximately 71; i.e. there is a 71% likelihood that the failure rate is less than 9.70x 10-3(1/yr). One also calculated that there is a 95% likelihood that the failure rate is less than 29.6x 10-3(1/yr). Or, as stated previously, there is a 71% likelihood that not more than one dropped load will occur in 103 years. Also, there is a 95% likelihood that not more than one dropped load will occur in approximately 34 years. It is the responsibility of DOE to select the confidence level at which it desires to operate.

  10. Development status und future possibilities for martensitic creep resistant steels

    Energy Technology Data Exchange (ETDEWEB)

    Hald, J. [Technical Univ. Denmark, Lyngby (Denmark). Dept. of Mechanical Engineering

    2010-07-01

    In the last four decades new stronger modified 9%Cr martensitic creep resistant steels have been introduced in power plants, which has enabled increases in maximum achievable steam conditions from the previous 250 bar and 540-560 C up to the values of 300 bar and 600-620 C currently being introduced all over the world. In order to further increase the steam parameters of steel based power plants up to a target value of 650 C/325 bar it is necessary to double the creep strength of the martensitic steels. At the same time the resistance against steam oxidation must be improved by an increase of the chromium content in the steels from 9% to 12%. However, so far all attempts to make stronger 12%Cr steels have led to breakdowns in long-term creep strength. Significant progress has been achieved in the understanding of microstructure stability of the martensitic 9-12%Cr steels: Observed microstructure instabilities in 11-12%Cr steels are explained by Z-phase precipitation, which dissolves fine MN nitrides. Improved understanding of effects of B and N on long-term creep properties has formed the basis of a series of new stronger 9%Cr test alloys with improved creep strength. In parallel 9%Cr test steels with low C content show very promising behavior in long-term tests. However, the 9%Cr steels must be surface coated to protect against steam oxidation at high temperature applications above 620%C. A possibility to use fine Z-phases for strengthening of the martensitic steels has been identified, and this opens a new pathway for development of stable strong 12%Cr steels. There are still good prospects for the realization of a 325 bar / 650 C steam power plant all based on steel. (orig.)

  11. Computer Simulation of the Indentation Creep Tests on Particle-Reinforced Composites

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A systematical simulation has been carried out on the indentation creep test on particle-reinforced composites. The deformation, failure mechanisms and life are analyzed by three reasonable models. The following five factors have been considered simultaneously: creep property of the particle, creep property of the matrix, the shape of the particle,the volume fraction of the particle and the size (relative size to the particle) of the indentation indenter. For all the cases, the power law respecting to the applied stress can be used to model the steady indentation creep depth rate of the indenter, and the detail expressions have been presented. The computer simulation precision is analyzed by the two-phase model and the three-phase model. Two places of the stress concentration are found in the composites.One is ahead of the indentation indenter, where the high stress state is deduced by the edge of the indenter and will decrease rapidly near to a steady value with the creep time. The other one is at the interface, where the high stress state is deduced by the misfit of material properties between the particles and matrix. It has been found that the creep dissipation energy density other than a stress parameter can be used to be the criterion to model the debonding of the interfaces. With the criterion of the critical creep dissipation energy density, a power law to the applied stress with negative exponent can be used to model the failure life deduced by the debonding of interfaces. The influences of the shape of the particles and the matching of creep properties of particle and matrix can be discussed for the failure. With a crack model, the further growth of interface crack is analyzed, and some important experimental phenomena can be predicted. The failure mechanism which the particle will be punched into matrix has been also discussed. The critical diflerences between the creep properties of the particles and matrix have been calculated,after a parameter has

  12. Brittle Creep of Tournemire Shale: Orientation, Temperature and Pressure Dependences

    Science.gov (United States)

    Geng, Zhi; Bonnelye, Audrey; Dick, Pierre; David, Christian; Chen, Mian; Schubnel, Alexandre

    2017-04-01

    Time and temperature dependent rock deformation has both scientific and socio-economic implications for natural hazards, the oil and gas industry and nuclear waste disposal. During the past decades, most studies on brittle creep have focused on igneous rocks and porous sedimentary rocks. To our knowledge, only few studies have been carried out on the brittle creep behavior of shale. Here, we conducted a series of creep experiments on shale specimens coming from the French Institute for Nuclear Safety (IRSN) underground research laboratory located in Tournemire, France. Conventional tri-axial experiments were carried under two different temperatures (26˚ C, 75˚ C) and confining pressures (10 MPa, 80 MPa), for three orientations (σ1 along, perpendicular and 45˚ to bedding). Following the methodology developed by Heap et al. [2008], differential stress was first increased to ˜ 60% of the short term peak strength (10-7/s, Bonnelye et al. 2016), and then in steps of 5 to 10 MPa every 24 hours until brittle failure was achieved. In these long-term experiments (approximately 10 days), stress and strains were recorded continuously, while ultrasonic acoustic velocities were recorded every 1˜15 minutes, enabling us to monitor the evolution of elastic wave speed anisotropy. Temporal evolution of anisotropy was illustrated by inverting acoustic velocities to Thomsen parameters. Finally, samples were investigated post-mortem using scanning electron microscopy. Our results seem to contradict our traditional understanding of loading rate dependent brittle failure. Indeed, the brittle creep failure stress of our Tournemire shale samples was systematically observed ˜50% higher than its short-term peak strength, with larger final axial strain accumulated. At higher temperatures, the creep failure strength of our samples was slightly reduced and deformation was characterized with faster 'steady-state' creep axial strain rates at each steps, and larger final axial strain

  13. Creep behaviour at high temperatures of fine SiC and alumina based fibres

    Energy Technology Data Exchange (ETDEWEB)

    Berger, M.H.; Bunsell, A.R. (Ecole Nationale Superieure des Mines, 91 - Evry (France). Centre des Materiaux)

    1999-01-01

    The creep behaviours of fine ceramic fibres based on silicon carbide and alpha-alumina have been compared. Fibres based on alpha-alumina and composed of isotropic faceted submicronic grains show superplastic behaviour from 1300 C. A mullite/alpha-alumina fibre with curved and elongated grains exhibits lower creep rates but large grains which grow on the surface of the fibre from 1200 C considerably reduce the time to failure in creep. The microstructures and creep strengths of SiC based fibres are strongly dependent on the oxygen content and carbon to silicon ratio. An oxygen content of 5 wt% induces an intergranular oxygen rich phase to be formed which facilitates creep. The creep strength of a fibre containing 0.5 wt% of oxygen can be improved by a heat treatment which increases the crystallinity of the fibre. The structure of a stoichiometric SiC fibre is shown to be composed of larger and faceted grains, to have a higher elastic modulus and an improved resistance to creep. However SiC based fibre are limited in air at high temperatures by the oxidation of the surface. (orig.) 13 refs.

  14. Steam oxidation scale growth and thermal insulation effect on creep life of creep strength enhanced ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Masuyama, Fujimitsu; Tokunaga, Tatsuya [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; Takao, Mikito [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; JFE Steel Corporation (Japan); Arakawa, Katsutoshi [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; Kobe Steel Ltd. (Japan)

    2010-07-01

    Creep strength enhanced ferritic steels, such as T91 and T23 are extensively used worldwide for superheater and reheater tubes, not only in advanced power plants but also in plants with conventional steam conditions. However when these steel tubes are used at higher metal temperature, steam oxidation problems are recently experienced resulting in turbine side erosion, and overheating of tubes leading to creep rupture due to scale blockage in tube bends or scale insulation effect due to thick scale, and separation and exfoliation of the scale. In the present study, steam oxidation growth tests of T91, T92, T23 and T22 were conducted to develop steam oxidation growth rate and scale behavior. Then using the steam oxidation growth data measured the metal temperature changes with scale growth were calculated considering the insulation effect of steam oxidation scale. Consequently the creep lives affected by steam oxidation scale growth were predicted as a function of time and temperature increase for creep strength enhanced ferritic steels. (orig.)

  15. Damage mechanics - failure modes

    Energy Technology Data Exchange (ETDEWEB)

    Krajcinovic, D.; Vujosevic, M. [Arizona State Univ., Tempe, AZ (United States)

    1996-12-31

    The present study summarizes the results of the DOE sponsored research program focused on the brittle failure of solids with disordered microstructure. The failure is related to the stochastic processes on the microstructural scale; namely, the nucleation and growth of microcracks. The intrinsic failure modes, such as the percolation, localization and creep rupture, are studied by emphasizing the effect of the micro-structural disorder. A rich spectrum of physical phenomena and new concepts that emerges from this research demonstrates the reasons behind the limitations of traditional, deterministic, and local continuum models.

  16. Thermal Creep Force: Analysis And Application

    Science.gov (United States)

    2016-06-01

    Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis and Dissertation Collection 2016-06 Thermal creep force: analysis and...CALIFORNIA DISSERTATION Approved for public release; distribution is unlimited THERMAL CREEP FORCE: ANALYSIS AND APPLICATION by David...blank) 2. REPORT DATE June 2016 3. REPORT TYPE AND DATES COVERED Doctoral Dissertation 4. TITLE AND SUBTITLE THERMAL CREEP FORCE: ANALYSIS

  17. Ultrasonic evaluation of creep damage of Cr-Mo-V steel by acoustic microscopy

    Institute of Scientific and Technical Information of China (English)

    WEI Tingcun

    2004-01-01

    The evaluation of creep damages of Cr-Mo-V steel used in the gas turbine of power plant has been carried out using the line-focus-beam (LFB) acoustic microscopy. The velocity of leaky surface acoustic wave (LSAW) propagated near the specimen surface was used for the quantitative evaluations, which was measured by LFB acoustic microscopy using the v(z) curve analysis method. It has been shown that with the increase of creep damage fraction of metal material the LSAW velocity decreases obviously, which suggests the possibility of nondestructive and quantitative evaluations of creep damages in metal materials by acoustic microscopy.

  18. Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds

    Energy Technology Data Exchange (ETDEWEB)

    Dr. F. W. Brust; Dr. G. M. Wilkowski; Dr. P. Krishnaswamy; Mr. Keith Wichman

    2010-01-27

    methods often need to be addressed as plants age. Shutdown inspection intervals can only be designed using creep and creep-fatigue crack growth techniques. (5) The use of crack growth procedures can aid in examining the seriousness of creep damage in structural components. How cracks grow can be used to assess margins on components and lead to further safe operation. After examining the pros and cons of all these methods, the R5 code was chosen as the most up-to-date and validated high temperature creep and creep fatigue code currently used in the world at present. R5 is considered the leader because the code: (1) has well established and validated rules, (2) has a team of experts continually improving and updating it, (3) has software that can be used by designers, (4) extensive validation in many parts with available data from BE resources as well as input from Imperial college's database, and (5) was specifically developed for use in nuclear plants. R5 was specifically developed for use in gas cooled nuclear reactors which operate in the UK and much of the experience is based on materials and temperatures which are experienced in these reactors. If the next generation advanced reactors to be built in the US used these same materials within the same temperature ranges as these reactors, then R5 may be appropriate for consideration of direct implementation within ASME code NH or Section XI. However, until more verification and validation of these creep/fatigue crack growth rules for the specific materials and temperatures to be used in the GEN IV reactors is complete, ASME should consider delaying this implementation. With this in mind, it is this authors opinion that R5 methods are the best available for code use today. The focus of this work was to examine the literature for creep and creep-fatigue crack growth procedures that are well established in codes in other countries and choose a procedure to consider implementation into ASME NH. It is very important to

  19. Creep behavior of hand-mixed Simplex P bone cement under cyclic tensile loading.

    Science.gov (United States)

    Verdonschot, N; Huiskes, R

    1994-01-01

    Acrylic cement, used for the fixation of total hip replacements and other orthopedic implants, is a subject of renewed scientific interest as a result of recent hypotheses about dynamic, long-term mechanical failure mechanisms suspected to play a role in prosthetic loosening. Little is known, however, about the long-term mechanical behavior of cement. In this study, the dynamic creep deformation of hand mixed acrylic cement was examined in laboratory tests. Strain patterns found represented the familiar creep process consisting of a primary, a secondary, and a tertiary creep phase. Specimens dynamically loaded with a maximum stress of 3 MPa from 0 were subject to creep of about 50% of the elastic strain after 250 000 loading cycles. A linear relationship between the logarithmic values of the creep-strain and the number of loading cycles was found. Specimens exposed to higher loads showed significantly higher creep-strains. No relationship could be established between the strain levels and the porosity of the specimens. Specimens dynamically loaded with a maximal stress of 7 or 11 MPa from 0 failed during the tests. The number of loading cycles to failure was similar to fatigue strength data reported in earlier literature.

  20. Creep and Creep-Fatigue of Alloy 617 Weldments

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Jill K. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, Laura J. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Wright, Richard N. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2014-08-01

    Alloy 617 is the primary candidate material for the heat exchanger of a very high temperature gas cooled reactor intended to operate up to 950°C. While this alloy is currently qualified in the ASME Boiler and Pressure Vessel Code for non-nuclear construction, it is not currently allowed for use in nuclear designs. A draft Code Case to qualify Alloy 617 for nuclear pressure boundary applications was submitted in 1992, but was withdrawn prior to approval. Prior to withdrawal of the draft, comments were received indicating that there was insufficient knowledge of the creep and creep-fatigue behavior of Alloy 617 welds. In this report the results of recent experiments and analysis of the creep-rupture behavior of Alloy 617 welds prepared using the gas tungsten arc process with Alloy 617 filler wire. Low cycle fatigue and creep-fatigue properties of weldments are also discussed. The experiments cover a range of temperatures from 750 to 1000°C to support development of a new Code Case to qualify the material for elevated temperature nuclear design. Properties of the welded material are compared to results of extensive characterization of solution annealed plate base metal.

  1. Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures

    Science.gov (United States)

    Sabour, Mohammad Hossein

    Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of

  2. Failure mode analysis for lime/limestone FGD systems. Volume 3. Plant profiles. Part 2

    Energy Technology Data Exchange (ETDEWEB)

    Kenney, S.M.; Rosenberg, H.S.; Nilsson, L.I.O.; Oxley, J.H.

    1984-08-01

    Plant profiles are given for the following plants: Tombigbee 2, 3; Apache 2, 3; Cholla 1, 2; Four Corners 1, 2, 3; Laramie River 1; Green 1, 2; Duck Creek 1; Craig 1, 2; Conesville 5, 6; Coal Creek 1, 2; Elrama 1, 2, 3, 4; and Phillips 1, 2, 3, 4, 5, 6. (DLC)

  3. A review of creep analysis and design under multi-axial stress states

    Energy Technology Data Exchange (ETDEWEB)

    Yao, H.-T. [School of Mechanical and Power Engineering, East China University of Science and Technology, 130, Meilong Street, PO Box 402, Shanghai 200237 (China); Xuan Fuzhen [School of Mechanical and Power Engineering, East China University of Science and Technology, 130, Meilong Street, PO Box 402, Shanghai 200237 (China)], E-mail: fzxuan@ecust.edu.cn; Wang Zhengdong; Tu Shantung [School of Mechanical and Power Engineering, East China University of Science and Technology, 130, Meilong Street, PO Box 402, Shanghai 200237 (China)

    2007-10-15

    The existence of multi-axial states of stress cannot be avoided in elevated temperature components. It is essential to understand the associated failure mechanisms and to predict the lifetime in practice. Although metal creep has been studied for about 100 years, many problems are still unsolved, in particular for those involving multi-axial stresses. In this work, a state-of-the-art review of creep analysis and engineering design is carried out, with particular emphasis on the effect of multi-axial stresses. The existing theories and creep design approaches are grouped into three categories, i.e., the classical plastic theory (CPT) based approach, the cavity growth mechanism (CGM) based approach and the continuum damage mechanics (CDM) based approach. Following above arrangements, the constitutive equations and design criteria are addressed. In the end, challenges on the precise description of the multi-axial creep behavior and then improving the strength criteria in engineering design are presented.

  4. Creep Resistance of VM12 Steel

    Directory of Open Access Journals (Sweden)

    Zieliński A.

    2016-09-01

    Full Text Available This article presents selected material characteristics of VM12 steel used for elements of boilers with super- and ultra-critical steam parameters. In particular, abridged and long-term creep tests with and without elongation measurement during testing and investigations of microstructural changes due to long-term impact of temperature and stress were carried out. The practical aspect of the use of creep test results in forecasting the durability of materials operating under creep conditions was presented. The characteristics of steels with regard to creep tests developed in this paper are used in assessment of changes in functional properties of the material of elements operating under creep conditions.

  5. Creep rupture of fiber bundles

    DEFF Research Database (Denmark)

    Linga, G.; Ballone, P.; Hansen, Alex

    2015-01-01

    The creep deformation and eventual breaking of polymeric samples under a constant tensile load F is investigated by molecular dynamics based on a particle representation of the fiber bundle model. The results of the virtual testing of fibrous samples consisting of 40000 particles arranged on Nc=4...

  6. Vegetative tillering in creeping bentgrass

    NARCIS (Netherlands)

    Cattani, D.J.

    2000-01-01

    Growth and development of creeping bentgrass ( Agrostis stolonifera L.) under non-competitive and competitive conditions were studied.

    Growth chamber experiments under non-competitive conditions with high and low tiller producing bentgrass populations

  7. Creep at very low rates

    CSIR Research Space (South Africa)

    Nabarro, FRN

    2002-02-01

    Full Text Available The creep rate in a land-based power station must be less than 10(-11) s(-1). At these low rates of deformation the transport of matter occurs by the migration of vacancies rather than by the glide of dislocations. A quantitative understanding...

  8. Failure Analysis of PRDS Pipe in a Thermal Power Plant Boiler

    Science.gov (United States)

    Ghosh, Debashis; Ray, Subrata; Mandal, Jiten; Mandal, Nilrudra; Shukla, Awdhesh Kumar

    2016-06-01

    The pressure reducer desuperheater (PRDS) pipeline is used for reducing the pressure and desuperheating of the steam in different auxiliary pipeline. When the PRDS pipeline is failed, the reliability of the boiler is affected. This paper investigates the probable cause/causes of failure of the PRDS tapping line. In that context, visual inspection, outside diameter and wall thickness measurement, chemical analysis, metallographic examination and hardness measurement are conducted as part of the investigative studies. Apart from these tests, mechanical testing and fractographic analysis are also conducted as supplements. Finally, it has been concluded that the PRDS pipeline has mainly failed due to graphitization due to prolonged exposure of the pipe at higher temperature. The improper material used is mainly responsible for premature failure of the pipe.

  9. Impression creep technique-An overview

    Energy Technology Data Exchange (ETDEWEB)

    Sastry, D.H. [Department of Metallurgy, Indian Institute of Science, Bangalore (India)]. E-mail: dhsastry@hotmail.com

    2005-11-15

    Impression creep technique is a modified indentation creep test wherein the conical or ball indenter is replaced by a cylindrical, flat bottomed punch. The usefulness of this technique, pioneered by Prof. Li, is illustrated by application to a variety of problems in this laboratory. High temperature creep behavior of a number of metals and alloys, particularly estimation of the thermal activation parameters aiding the identification of the rate controlling mechanisms of creep, has been investigated. The technique has also been exploited to assess the 'single crystal' creep behavior vis a vis that of a polycrystalline sample. Utilizing the impression creep test, the creep behavior of individual zones in steel weldments has been examined. The simplicity and the utility of the impression creep test have been further demonstrated by its application to the study of superplastic behavior in alloys. This paper presents a cross section of the results obtained in the above investigations. It is concluded that the impression creep test technique is capable of yielding much of the information that can be obtained from tensile creep testing. Furthermore, it can provide data which are either impossible or extremely difficult to obtain with conventional creep testing.

  10. A less expensive solution for thrust-bearing failures at the Sao Simao hydroelectric power plant - Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Porto, Licinio Cesar [Sinergia Engenheiros Consultores Ltda., Belo Horizonte, MG (Brazil)]. E-mail: licinio@sinergia.eng.br; Machado, Luiz; Koury, Ricardo Nicolau Nassar; Porto, Matheus Pereira; Coelho, Fernanda Gomes [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica]. E-mails: luizm@demec.ufmg.br; koury@ufmg.br; matheusporto@oi.com.br; fernanda@sinergia.eng.br

    2008-07-01

    After twenty years without any apparent problems on their combined guides and thrust bearings operations, the six 280 MW hydrogenerators of the Sao Simao Hydroelectric Power Plant of Brazil were failing. Sao Simao is the largest Power Plant of Companhia Energetica de Minas Gerais (CEMIG), one of the major Brazilian electric utility company, with a total installed potential higher than 5,400 MW. The source of the failure was the melting of the thrust pad Babbit lining. The machines began showing performance failures, leading to a sudden interruption in their operations. This caused considerable losses with high direct and indirect costs. The solution proposed by the bearing manufacturer was an improvement to the bearing design and the installation of new water-oil heat exchangers. The direct cost of their solution was estimated at US$ 2,000,000.00 (two million dollars). In a search for a less expensive alternative, CEMIG commenced a parallel study that was to focus on the heat exchangers. A calculation model was used to consider not only the thermal features of the oil circulation system but also the suitability of its pumps and piping system. This model predicted that an increase in the surface of the heat exchange area could solve the problem. A spare heat exchanger was then installed in one machine already possessing two heat exchangers. The rated output test results fulfilled preliminary predictions, eliminating the risk of additional Babbit lining failures. As a consequence of CEMIG's successful modeling test implementation, heat exchangers were added to the remaining machines. This alternative solution had a total direct cost of US$ 600,000.00 (six hundred thousand dollars) with an indirect cost much less than the alternative presented by the manufacturer for its short cessation period. This paper discusses in detail all this study stages. (author)

  11. A BRIEF REVIEW OF MODELS REPRESENTING CREEP OF ALLOY 617

    Energy Technology Data Exchange (ETDEWEB)

    Swindeman, Robert W [ORNL; Swindeman, Michael [University of Dayton Research Institute; Ren, Weiju [ORNL

    2005-01-01

    Alloy 617 is being considered for the construction of components to operate in the Next Generation Nuclear Plant (NGNP). Service temperatures will range from 650 to 1000 C. To meet the needs of the conceptual designers of this plant, a materials handbook is being developed that will provide information on alloy 617, as well as other materials of interest. The database for alloy 617 to be incorporated into the handbook was produced in the 1970s and 1980s, while creep and damage models were developed from the database for use in the design of high-temperature gas-cooled reactors. In the work reported here, the US database and creep models are briefly reviewed. The work reported represents progress toward a useful model of the behavior of this material in the temperature range of 650 to 1000 C.

  12. Creep in Topopah Spring Member welded tuff. Yucca Mountain Site Characterization Project

    Energy Technology Data Exchange (ETDEWEB)

    Martin, R.J. III; Boyd, P.J.; Noel, J.S. [New England Research, Inc., White River Junction, VT (United States); Price, R.H. [Sandia National Labs., Albuquerque, NM (United States)

    1995-06-01

    A laboratory investigation has been carried out to determine the effects of elevated temperature and stress on the creep deformation of welded tuffs recovered from Busted Butte in the vicinity of Yucca Mountain, Nevada. Water saturated specimens of tuff from thermal/mechanical unit TSw2 were tested in creep at a confining pressure of 5.0 MPa, a pore pressure of 4.5 MPa, and temperatures of 25 and 250 C. At each stress level the load was held constant for a minimum of 2.5 {times} 10{sup 5} seconds and for as long as 1.8 {times} 10{sup 6} seconds. One specimen was tested at a single stress of 80 MPa and a temperature of 250 C. The sample failed after a short time. Subsequent experiments were initiated with an initial differential stress of 50 or 60 MPa; the stress was then increased in 10 MPa increments until failure. The data showed that creep deformation occurred in the form of time-dependent axial and radial strains, particularly beyond 90% of the unconfined, quasi-static fracture strength. There was little dilatancy associated with the deformation of the welded tuff at stresses below 90% of the fracture strength. Insufficient data have been collected in this preliminary study to determine the relationship between temperature, stress, creep deformation to failure, and total failure time at a fixed creep stress.

  13. Modification of creep and low cycle fatigue behaviour induced by welding

    Directory of Open Access Journals (Sweden)

    A. Carofalo

    2014-10-01

    Full Text Available In this work, the mechanical properties of Waspaloy superalloy have been evaluated in case of welded repaired material and compared to base material. Test program considered flat specimens on base and TIG welded material subjected to static, low-cycle fatigue and creep test at different temperatures. Results of uniaxial tensile tests showed that the presence of welded material in the gage length specimen does not have a relevant influence on yield strength and UTS. However, elongation at failure of TIG material was reduced with respect to the base material. Moreover, low-cycle fatigue properties have been determined carrying out tests at different temperature (room temperature RT and 538°C in both base and TIG welded material. Welded material showed an increase of the data scatter and lower fatigue strength, which was anyway not excessive in comparison with base material. During test, all the hysteresis cycles were recorded in order to evaluate the trend of elastic modulus and hysteresis area against the number of cycles. A clear correlation between hysteresis and fatigue life was found. Finally, creep test carried out on a limited number of specimens allowed establishing some changes about the creep rate and time to failure of base and welded material. TIG welded specimen showed a lower time to reach a fixed strain or failure when a low stress level is applied. In all cases, creep behaviour of welded material is characterized by the absence of the tertiary creep.

  14. Matrix cracking and creep behavior of monolithic zircon and zircon silicon carbide fiber composites

    Science.gov (United States)

    Anandakumar, Umashankar

    In this study, the first matrix cracking behavior and creep behavior of zircon matrix silicon carbide fiber composites were studied, together with the fracture and creep behavior of the monolithic zircon. These behaviors are of engineering and scientific importance, and the study was aimed at understanding the deformation mechanisms at elevated temperatures. The first matrix cracking behavior of zircon matrix uniaxially reinforced with silicon carbide fiber (SCS-6) composites and failure behavior of monolithic zircon were studied as a function of temperature (25°C, 500°C, and 1200°C) and crack length in three point bending mode. A modified vicker's indentation technique was used to vary the initial crack length in monolithic and composite samples. The interfacial shear strength was measured at these temperatures from matrix crack saturation spacing. The composites exhibited steady state and non steady state behaviors at the three different temperatures as predicted by theoretical models, while the failure stress of zircon decreased with increasing stress. The intrinsic properties of the composites were used to numerically determine the results predicted by three different matrix cracking models based on a fracture mechanics approach. The analysis showed that the model based on crack bridging analysis was valid at 25°C and 500°C, while a model based on statistical fiber failure was valid at 1200°C. Microstructural studies showed that fiber failure in the crack wake occurred at or below the matrix cracking stress at 1200°C, and no fiber failure occurred at the other two temperatures, which validated the results predicted by the theoretical models. Also, it was shown that the interfacial shear stress corresponding to debonding determined the matrix cracking stress, and not the frictional shear stress. This study showed for the first time, the steady state and non-steady state matrix cracking behavior at elevated temperatures, the difference in behavior between

  15. Effects of plastic pre-straining level on the creep deformation, crack initiation and growth behaviour of 316H stainless steel

    OpenAIRE

    Mehmanparast, Ali; Davies, C M; Dean, David W.; Nikbin, Kamran

    2016-01-01

    The effects of the material pre-straining level, in the form of plastic pre-compression at room temperature, on the tensile, creep deformation, creep crack initiation and growth behaviour of 316H stainless steel have been examined at 550 °C. Experiments have been performed on the 4%, 8% and 12% pre-compressed specimens and the results are compared with existing data on the pre-compressed material to investigate the change in mechanical response, creep failure, creep crack initiation and growt...

  16. Creep-fatigue interactions in an austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Majumdar, S; Maiya, P S

    1978-01-01

    A phenomenological model of the interaction between creep and fatigue in Type 304 stainless steel at elevated temperatures is presented. The model is based on a crack-growth equation and an equation governing cavity growth, expressed in terms of current plastic strain and plastic strain rate. Failure is assumed to occur when a proposed interaction equation is satisfied. Various parameters of the equations can be obtained by correlation with continuously cycling fatigue and monotonic creep-rupture test data, without the use of any hold-time fatigue tests. Effects of various wave shapes such as tensile, compressive, and symmetrical hold on the low-cycle fatigue life can be computed by integrating the damage-rate equations along the appropriate loading path. Microstructural evidence in support of the proposed model is also discussed.

  17. A code for simulation of human failure events in nuclear power plants: SIMPROC

    Energy Technology Data Exchange (ETDEWEB)

    Gil, Jesus, E-mail: jesus.gil@indizen.co [Indizen Technologies S.L., Pablo Iglesias 2-3 oB-2, 28003 Madrid (Spain); Fernandez, Ivan, E-mail: ivan.fernandez@indizen.co [Indizen Technologies S.L., Pablo Iglesias 2-3 oB-2, 28003 Madrid (Spain); Murcia, Santiago, E-mail: santiago.murcia@indizen.co [Indizen Technologies S.L., Pablo Iglesias 2-3 oB-2, 28003 Madrid (Spain); Gomez, Javier, E-mail: javier.mundina@indizen.co [Indizen Technologies S.L., Pablo Iglesias 2-3 oB-2, 28003 Madrid (Spain); Marrao, Hugo, E-mail: hmarrao@indizen.co [Indizen Technologies S.L., Pablo Iglesias 2-3 oB-2, 28003 Madrid (Spain); Queral, Cesar, E-mail: cesar.queral@upm.e [ETSI Minas - Universidad Politecnica de Madrid, Alenza 4, 28003 Madrid (Spain); Exposito, Antonio, E-mail: antonio.exposito@upm.e [ETSI Minas - Universidad Politecnica de Madrid, Alenza 4, 28003 Madrid (Spain); Rodriguez, Gabriel, E-mail: gabriel.rodriguez.martin@upm.e [ETSI Minas - Universidad Politecnica de Madrid, Alenza 4, 28003 Madrid (Spain); Ibanez, Luisa, E-mail: luisa.ibanez@upm.e [ETSI Minas - Universidad Politecnica de Madrid, Alenza 4, 28003 Madrid (Spain); Hortal, Javier, E-mail: fjhr@csn.e [Consejo de Seguridad Nuclear, Justo Dorado 11, 28040 Madrid (Spain); Izquierdo, Jose M., E-mail: jmir@csn.e [Consejo de Seguridad Nuclear, Justo Dorado 11, 28040 Madrid (Spain); Sanchez, Miguel, E-mail: msp@csn.e [Consejo de Seguridad Nuclear, Justo Dorado 11, 28040 Madrid (Spain); Melendez, Enrique, E-mail: ema@csn.e [Consejo de Seguridad Nuclear, Justo Dorado 11, 28040 Madrid (Spain)

    2011-04-15

    Over the past years, many Nuclear Power Plant organizations have performed Probabilistic Safety Assessments to identify and understand key plant vulnerabilities. As part of enhancing the PSA quality, the Human Reliability Analysis is essential to make a realistic evaluation of safety and about the potential facility's weaknesses. Moreover, it has to be noted that HRA continues to be a large source of uncertainty in the PSAs. Within their current joint collaborative activities, Indizen, Universidad Politecnica de Madrid and Consejo de Seguridad Nuclear have developed the so-called SIMulator of PROCedures (SIMPROC), a tool aiming at simulate events related with human actions and able to interact with a plant simulation model. The tool helps the analyst to quantify the importance of human actions in the final plant state. Among others, the main goal of SIMPROC is to check the Emergency Operating Procedures being used by operating crew in order to lead the plant to a safe shutdown plant state. Currently SIMPROC is coupled with the SCAIS software package, but the tool is flexible enough to be linked to other plant simulation codes. SIMPROC-SCAIS applications are shown in the present article to illustrate the tool performance. The applications were developed in the framework of the Nuclear Energy Agency project on Safety Margin Assessment and Applications (SM2A). First an introductory example was performed to obtain the damage domain boundary of a selected sequence from a SBLOCA. Secondly, the damage domain area of a selected sequence from a loss of Component Cooling Water with a subsequent seal LOCA was calculated. SIMPROC simulates the corresponding human actions in both cases. The results achieved shown how the system can be adapted to a wide range of purposes such as Dynamic Event Tree delineation, Emergency Operating Procedures and damage domain search.

  18. A review of poisonous plants that cause reproductive failure and malformations in the ruminants of Brazil.

    Science.gov (United States)

    Riet-Correa, Franklin; Medeiros, Rosane M T; Schild, Ana Lucia

    2012-04-01

    The objective of this review is to provide a report on toxic plants causing reproductive problems in ruminants in Brazil. Aspidosperma pyrifolium causes abortion or stillbirth in goats, as well as most likely in sheep and cattle, in the semiarid regions of Northeastern Brazil. Intoxications by Ateleia glazioveana, Tetrapterys acutifolia and T. multiglandulosa result in abortion and neonatal mortality in cattle and sheep, and the same signs have been experimentally observed in goats. These three plants can also cause cardiac fibrosis and a nervous disease with spongiosis of the central nervous system. Other plants known to cause abortion include Enterolobium contortisiliquum, E. gummiferum, Stryphnodendron coriaceum, S. obovatum and S. fissuratum. These plants can also cause digestive signs and photosensitization. Abortions have been reported in animals intoxicated by nitrates and nitrites as well. Infertility, abortions and the birth of weak offspring have been reported in animals intoxicated by plants containing swainsonine, including Ipomoea spp., Turbina cordata and Sida carpinifolia. Trifolium subterraneum causes estrogenism in cattle. Mimosa tenuiflora and, most likely, M. ophthalmocentra cause malformations and embryonic mortality in goats, sheep and cattle in the semiarid regions of Northeastern Brazil. Copyright © 2011 John Wiley & Sons, Ltd.

  19. Time-dependent Creep Crack Growth Behavior of Alloy 617 at 800 .deg. C

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woogon; Kim, Minhwan; Kim, Yongwan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jaeyoung; Ekaputra, I. M. W. [Pukyong National Univ., Busan (Korea, Republic of)

    2014-05-15

    The VHTR components are designed to be used for a 60 year lifetime at a high temperature, the creep crack growth (CCG) behavior as well as creep behavior is very important for the design application due to creep damage during the long service life at elevated temperatures. Alloy 617 is a major candidate material for the IHX component. The design of the component, which will operate well into the creep range, will require a good understanding of creep crack growth deformation. Efforts are now being undertaken in the Generation IV program to provide data needed for the design and licensing of the nuclear plants, and with this goal in mind, to meet the needs of the conceptual designers of the VHTR system, 'Gen-IV Materials Handbook DB' is being established through an international collaboration program of several GIF (Gen-IV Forum) countries. CCG experimental data should be prepared to 'the Gen-IV Materials Handbook DB' website, because the CCG data for Alloy 617 are not available in the ASME design code. In this paper, experimental creep crack growth data were obtained through a series of CCG tests performed under different applied loads at 800 .deg. C. The CCG behavior was characterized in terms of the C{sup *} fracture mechanics parameter, and the CCGR equation for Alloy 617 was presented. Experimental CCG data of Alloy 617 were obtained from a series of creep crack growth tests under different applied loads at 800 .deg. C.

  20. Creep and fracture of a model yoghurt

    Science.gov (United States)

    Manneville, Sebastien; Leocmach, Mathieu; Perge, Christophe; Divoux, Thibaut

    2014-11-01

    Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the failure scenario of a model yoghurt, namely a casein gel, is reminiscent of brittle solids: after a primary creep regime characterized by a macroscopically homogeneous deformation and a power-law behavior which exponent is fully accounted for by linear viscoelasticity, fractures nucleate and grow logarithmically perpendicularly to shear, up to the sudden rupture of the gel. A single equation accounting for those two successive processes nicely captures the full rheological response. The failure time follows a decreasing power-law with the applied shear stress, similar to the Basquin law of fatigue for solids. These results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers and exemplify protein gels as model, brittle-like soft solids. Work funded by the European Research Council under Grant Agreement No. 258803.

  1. Agrobacterium-mediated transformation of creeping bentgrass using GFP as a reporter gene.

    Science.gov (United States)

    Yu, T T; Skinner, D Z; Liang, G H; Trick, H N; Huang, B; Muthukrishnan, S

    2000-01-01

    Creeping bentgrass (Agrostis palustris Huds.) is a cool season grass widely used on putting greens in golf courses. Transformation of creeping bentgrass has been conducted using microprojectile bombardment and protoplast electroporation. The objective of our study is to develop an alternative and more efficient approach in transforming the grass using Agrobacterium (strain EHA 101). This technique was effective in transforming 40-day old calli derived from mature seeds cultured on MS medium supplemented with 2,4-D, kinetin, and sucrose. Dozens of transgenic plants have been produced from two independent transformed calli. Presence of functional green fluorescence protein (GFP) was detected in leaves, stems, and roots of transgenic seedlings. Four putative transgenic plants and two control plants were randomly chosen and analyzed by Southern blot analysis. Bands corresponding to the GFP gene were clearly shown in transgenic plants. These results indicated that Agrobacterium transformation can successfully be applied to creeping bentgrass.

  2. Early Detection of Plant Equipment Failures: A Case Study in Just-in-Time Maintenance

    Energy Technology Data Exchange (ETDEWEB)

    Parlos, Alexander G.; Kim, Kyusung; Bharadwaj, Raj M.

    2001-06-17

    The development and testing of a model-based fault detection system for electric motors is briefly presented. The fault detection system was developed using only motor nameplate information. The fault detection results presented utilize only motor voltage and current sensor information, minimizing the need for expensive or intrusive sensors. Dynamic recurrent neural networks are used to predict the input-output response of a three-phase induction motor while using an estimate of the motor speed signal. Multiresolution (or wavelet) signal-processing techniques are used in combination with more traditional methods to estimate fault features for use in winding insulation and motor mechanical and electromechanical failure detection.

  3. Decentralized Adaptive Control of Systems with Uncertain Interconnections, Plant-Model Mismatch and Actuator Failures

    Science.gov (United States)

    Patre, Parag; Joshi, Suresh M.

    2011-01-01

    Decentralized adaptive control is considered for systems consisting of multiple interconnected subsystems. It is assumed that each subsystem s parameters are uncertain and the interconnection parameters are not known. In addition, mismatch can exist between each subsystem and its reference model. A strictly decentralized adaptive control scheme is developed, wherein each subsystem has access only to its own state but has the knowledge of all reference model states. The mismatch is estimated online for each subsystem and the mismatch estimates are used to adaptively modify the corresponding reference models. The adaptive control scheme is extended to the case with actuator failures in addition to mismatch.

  4. Creep crack growth in a reactor pressure vessel steel at 360 deg C

    Energy Technology Data Exchange (ETDEWEB)

    Rui Wu; Seitisleam, F.; Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)

    1998-12-31

    Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.

  5. Creep Behavior in Interlaminar Shear of a SiC/SiC Ceramic Composite with a Self-healing Matrix

    Science.gov (United States)

    Ruggles-Wrenn, M. B.; Pope, M. T.

    2014-02-01

    Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1,200 °C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbide overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16-22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Larger creep strains were accumulated in steam. However, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.

  6. Response of Triaxial State of Stress to Creep Rupture Life and Ductility of 316 LN Austenitic Stainless Steel

    Science.gov (United States)

    Goyal, Sunil; Laha, K.; Bhaduri, A. K.

    2016-12-01

    In the present investigation, the effect of triaxial state of stress on creep rupture life and ductility of 316 LN stainless steel has been assessed. The creep tests were carried out on both smooth and notched specimens of the steel at 873 K in the stress range of 270-340 MPa. The notched specimens had root radius ranging from 0.83 mm to 5 mm. The detailed finite element analysis has been carried out to assess the triaxial state of stress across the notch incorporating Norton's law as creep deformation governing mechanism. The creep rupture life of the steel increased in presence of triaxial stresses and extent of which was more at lower net applied stresses and higher triaxiality (sharper notch). The reduction in effective stress in presence of notch resulted in higher creep rupture life of the steel under triaxial stresses. The fracture surfaces revealed mixed mode failure consisting of dimple ductile and intergranular creep cavitation for all testing conditions, however, extent of cavitation was higher for relatively higher triaxialities and lower net applied stresses. The creep ductility of the steel was found to decrease drastically under triaxial state of stress. The triaxial rupture life and creep ductility of the steel have been assessed based on different models on incorporating different components of stresses at the skeletal point.

  7. Response of Triaxial State of Stress to Creep Rupture Life and Ductility of 316 LN Austenitic Stainless Steel

    Science.gov (United States)

    Goyal, Sunil; Laha, K.; Bhaduri, A. K.

    2017-02-01

    In the present investigation, the effect of triaxial state of stress on creep rupture life and ductility of 316 LN stainless steel has been assessed. The creep tests were carried out on both smooth and notched specimens of the steel at 873 K in the stress range of 270-340 MPa. The notched specimens had root radius ranging from 0.83 mm to 5 mm. The detailed finite element analysis has been carried out to assess the triaxial state of stress across the notch incorporating Norton's law as creep deformation governing mechanism. The creep rupture life of the steel increased in presence of triaxial stresses and extent of which was more at lower net applied stresses and higher triaxiality (sharper notch). The reduction in effective stress in presence of notch resulted in higher creep rupture life of the steel under triaxial stresses. The fracture surfaces revealed mixed mode failure consisting of dimple ductile and intergranular creep cavitation for all testing conditions, however, extent of cavitation was higher for relatively higher triaxialities and lower net applied stresses. The creep ductility of the steel was found to decrease drastically under triaxial state of stress. The triaxial rupture life and creep ductility of the steel have been assessed based on different models on incorporating different components of stresses at the skeletal point.

  8. Microstructure and creep behavior of magnesium-aluminum alloys containing alkaline and rare earth additions

    Science.gov (United States)

    Saddock, Nicholas David

    additional bulk strain accumulated, strain localized along grain boundaries between grains with significantly different Schmid factors. At these locations cavities and cracks formed that led to the eventual creep failure. Grain size influenced the plastic strain distribution during creep.

  9. Creep properties of phosphorus alloyed oxygen free copper under multiaxial stress state

    Energy Technology Data Exchange (ETDEWEB)

    Rui Wu; Sandstroem, Rolf; Seitisleam, Facredin

    2009-10-15

    Phosphorus alloyed oxygen free copper (Cu-OFP) canisters are planned to be used for spent nuclear fuel in Sweden. The copper canisters will be subjected to creep under multiaxial stress states in the repository. Creep tests have therefore been carried out at 75 deg C using double notch specimens with notch acuities of 0.5, 2, 5, and 18.8, respectively. The creep lifetime for notched specimens is considerably longer than that for the smooth one at a given net section stress, indicating that the investigated Cu-OFP is notch insensitive (notch strengthening). The notch strengthening factor in time is, for instance, greater than 70 at 180 MPa for the bluntest notch (notch acuity = 0.5). The creep lifetime is notch acuity dependent. The sharper the notch, the longer the creep lifetime is. The creep deformation is to a significant extent concentrated to the region around the notches. Different deformation on the two notches is observed. Both axial and radial strains on the failed notch are several times larger than those on the unbroken one. Linear relation between the axial and the radial strains on the notches is found. Transgranular failure is predominant, independent of stress, rupture time, and notch acuity. Adjacent to fracture, elongated grains along the stress direction, separate pores and cavities are often visible. On the unbroken notch, fewer separate cavities and cracks are only seen intergranularly for the sharper notches (notch acuity > 2). To interpret the tests for the notched creep specimens, finite element computations have been performed. A fundamental model for primary and secondary creep without fitting parameters has been used as constitutive equation. The FEM-modelling could represent the creep strain versus time curves for the notched specimens in a satisfactory way. In these curves the strain on loading is included. From the FEM-computations a stationary creep stress could be assessed, which is close to the reference stress. For a given

  10. Construction of in-situ creep strain test facility for the SFR fuel cladding

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sang Gyu; Heo, Hyeong Min; Kim, Jun Hwan; Kim, Sung Ho [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    In this study, in-situ laser inspection creep test machine was developed for the measuring the creep strain of SFR fuel cladding materials. Ferritic-martensitic steels are being considered as an attractive candidate material for a fuel cladding of a SFR due to their low expansion coefficients, high thermal conductivities and excellent irradiation resistances to a void swelling. HT9 steel (12CrMoVW) is initially developed as a material for power plants in Europe in the 1960. This steel has experienced to expose up to 200dpa in FFTE and EBR-II. Ferritic-Martensitic steel's maximum creep strength in existence is 180Mpa for 106 hour 600 .deg., but HT9 steel is 60Mpa. Because SFR is difficult to secure in developing and applying materials, HT9 steel has accumulated validated data and is suitable for SFR component. And also, because of its superior dimensional stability against fast neutron irradiation, Ferritic-martensitic steel of 9Cr and 12Cr steels, such as HT9 and FC92(12Cr-2W) are preferable to utilize in the fuel cladding of an SFR in KAERI. The pressurized thermal creep test of HT9 and FC92 claddings are being conducted in KAERI, but the change of creep strain in cladding is not easy to measure during the creep test due to its pressurized and closed conditions. In this paper, in-situ laser inspection pressurized creep test machine developed for SFR fuel cladding specimens is described. Moreover, the creep strain rate of HT9 at 650 .deg. C was examined from the in-situ laser inspection pressurized creep test machine.

  11. Creep of Structural Nuclear Composites

    Energy Technology Data Exchange (ETDEWEB)

    Will Windes; R.W. Lloyd

    2005-09-01

    A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600º C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.

  12. High-pressure creep tests

    Science.gov (United States)

    Bhattacharyya, S.; Lamoureux, J.; Hales, C.

    1986-01-01

    The automotive Stirling engine, presently being developed by the U.S. Department of Energy and NASA, uses high-pressure hydrogen as a working fluid; its long-term effects on the properties of alloys are relatively unknown. Hence, creep-rupture testing of wrought and cast high-temperature alloys in high-pressure hydrogen is an essential part of the research supporting the development of the Stirling cycle engine. Attention is given to the design, development, and operation of a 20 MPa hydrogen high-temperature multispecimen creep-rupture possessing high sensitivity. This pressure vessel allows for the simultaneous yet independent testing of six specimens. The results from one alloy, XF-818, are presented to illustrate how reported results are derived from the raw test data.

  13. Creep Damage Evaluation in High-Pressure Rotor Based on Hardness Measurement

    Science.gov (United States)

    Cardoso, B. R.; Matt, C. F. T.; Furtado, H. C.; de Almeida, L. H.

    2015-07-01

    A creep life consumption study was conducted in a high-pressure turbine rotor belonging to a 363 MW thermal power plant. The component is manufactured with 30CrMoV412 steel, which is a typical 1CrMoV forged rotor steel, having operated for 112,000 h, under a pressure of 17.6 MPa and temperature of 520 °C. The main objective of this paper is to evaluate the applicability of hardness tests as a tool for structural integrity analysis in the field. Two methods for estimating creep remaining life based on hardness measurements were used. Furthermore, metallographic replicas made during unit shutdown were observed by scanning electron microscopy, in order to detect creep voids and also to corroborate the results for accumulated creep damage obtained based on hardness measurements.

  14. Safety assessment for electricity generation failure accident of gas cooled nuclear power plant using system dynamics (SD) method

    Energy Technology Data Exchange (ETDEWEB)

    Woo, Tae Ho [Seoul National Univ. (Korea, Republic of). Dept. of Nuclear Engineering

    2013-04-15

    The power production failure happens in the loss of coolant of the nuclear power plants (NPPs). The air ingress is a serious accident in gas cooled NPPs. The quantification of the study performed by the system dynamics (SD) method which is processed by the feedback algorithms. The Vensim software package is used for the simulation, which is performed by the Monte-Carlo method. Two kinds of considerations as the economic and safety properties are important in NPPs. The result shows the stability of the operation when the power can be decided. The maximum value of risk is the 11.77 in 43rd and the minimum value is 0.0 in several years. So, the success of the circulation of coolant is simulated by the dynamical values. (orig.)

  15. The independence of irradiation creep in austenitic alloys of displacement rate and helium to dpa ratio

    Energy Technology Data Exchange (ETDEWEB)

    Garner, F.A.; Toloczko, M.B. [Pacific Northwest National Lab., Richland, WA (United States); Grossbeck, M.L. [Oak Ridge National Lab., TN (United States)

    1997-04-01

    The majority of high fluence data on the void swelling and irradiation creep of austenitic steels were generated at relatively high displacement rates and relatively low helium/dpa levels that are not characteristic of the conditions anticipated in ITER and other anticipated fusion environments. After reanalyzing the available data, this paper shows that irradiation creep is not directly sensitive to either the helium/dpa ratio or the displacement rate, other than through their possible influence on void swelling, since one component of the irradiation creep rate varies with no correlation to the instantaneous swelling rate. Until recently, however, the non-swelling-related creep component was also thought to exhibit its own strong dependence on displacement rate, increasing at lower fluxes. This perception originally arose from the work of Lewthwaite and Mosedale at temperatures in the 270-350{degrees}C range. More recently this perception was thought to extend to higher irradiation temperatures. It now appears, however, that this interpretation is incorrect, and in fact the steady-state value of the non-swelling component of irradiation creep is actually insensitive to displacement rate. The perceived flux dependence appears to arise from a failure to properly interpret the impact of the transient regime of irradiation creep.

  16. Cumulative creep-fatigue damage evolution in an austenitic stainless steel

    Science.gov (United States)

    Mcgaw, Michael A.

    1992-01-01

    A model of cumulative creep-fatigue damage has been developed which is based on the use of damage curve equations to describe the evolution of creep-fatigue damage for four basic creep-fatigue cycle types. These cycle types correspond to the four fundamental cycles of the Strain Range Partitioning Life Prediction approach of Manson, Halford, and Hirschberg. A concept referred to as Damage Coupling is introduced to analytically account for the differences in the nature of the damage introduced by each cycle type. For application of this model, the cumulative creep-fatigue damage behavior of type 316 stainless steel at 816 C has been experimentally established for the two-level loading cases involving fatigue and creep-fatigue, in various permutations. The tests were conducted such that the lower life (high strain) cycling was applied first, for a controlled number of cycles, and the higher life (lower strain) cycling was conducted at the second level, to failure. The proposed model correlated the majority of the observed cumulative creep-fatigue data.

  17. Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure.

    Science.gov (United States)

    Zhang, Yu; Chen, Zhimin; An, Wei; Xiao, Shumin; Yuan, Hongying; Zhang, Dongqing; Yang, Min

    2015-04-01

    Membrane bioreactors (MBR) are highly efficient at intercepting particles and microbes and have become an important technology for wastewater reclamation. However, many pathogens can accumulate in activated sludge due to the long residence time usually adopted in MBR, and thus may pose health risks when membrane integrity problems occur. This study presents data from a survey on the occurrence of water-borne Giardia pathogens in reclaimed water from a full-scale wastewater treatment plant with MBR experiencing membrane integrity failure, and assessed the associated risk for green space irrigation. Due to membrane integrity failure, the MBR effluent turbidity varied between 0.23 and 1.90 NTU over a period of eight months. Though this turbidity level still met reclaimed water quality standards (≤5 NTU), Giardia were detected at concentrations of 0.3 to 95 cysts/10 L, with a close correlation between effluent turbidity and Giardia concentration. All β-giardin gene sequences of Giardia in the WWTP influents were genotyped as Assemblages A and B, both of which are known to infect humans. An exponential dose-response model was applied to assess the risk of infection by Giardia. The risk in the MBR effluent with chlorination was 9.83×10(-3), higher than the acceptable annual risk of 1.0×10(-4). This study suggested that membrane integrity is very important for keeping a low pathogen level, and multiple barriers are needed to ensure the biological safety of MBR effluent.

  18. Creep Strength of Discontinuous Fibre Composites

    DEFF Research Database (Denmark)

    Pedersen, Ole Bøcker

    1974-01-01

    relation between stress and strain rate. Expressions for the interface stress, the creep velocity profile adjacent to the fibres and the creep strength of the composite are derived. Previous results for the creep strength, sc = aVfs0 ( \\frac[( Î )\\dot] [( Î )\\dot] 0 )1/nr1 + 1/n c=Vf001n1+1n in which[( Î...... )\\dot] is the composite creep rate,V f is the fibre volume fraction,sgr 0,epsi 0 andn are the constants in the matrix creep law. The creep strength coefficient agr is found to be very weakly dependent onV f and practically independent ofn whenn is greater than about 6....

  19. Flexural creep behaviour of jute polypropylene composites

    Science.gov (United States)

    Chandekar, Harichandra; Chaudhari, Vikas

    2016-09-01

    Present study is about the flexural creep behaviour of jute fabric reinforced polypropylene (Jute-PP) composites. The PP sheet and alkali treated jute fabric is stacked alternately and hot pressed in compression molding machine to get Jute-PP composite laminate. The flexural creep study is carried out on dynamic mechanical analyzer. The creep behaviour of the composite is modeled using four-parameter Burgers model. Short-term accelerated creep testing is conducted which is later used to predict long term creep behaviour. The feasibility of the construction of a master curve using the time-temperature superposition (TTS) principle to predict long term creep behavior of unreinforced PP and Jute-PP composite is investigated.

  20. Creep of parylene-C film

    KAUST Repository

    Lin, Jeffrey Chun-Hui

    2011-06-01

    The glass transition temperature of as-deposited parylene-C is first measured to be 50°C with a ramping-temperature-dependent modulus experiment. The creep behavior of parylene-C film in the primary and secondary creep region is then investigated below and above this glass transition temperature using a dynamic mechanical analysis (DMA) machine Q800 from TA instruments at 8 different temperatures: 10, 25, 40, 60, 80, 100, 120 and 150°C. The Burger\\'s model, which is the combined Maxwell model and Kelvin-Voigt model, fits well with our primary and secondary creep data. Accordingly, the results show that there\\'s little or no creep below the glass transition temperature. Above the glass transition temperature, the primary creep and creep rate increases with the temperature, with a retardation time constant around 6 minutes. © 2011 IEEE.

  1. Room temperature creep in metals and alloys

    Energy Technology Data Exchange (ETDEWEB)

    Deibler, Lisa Anne [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Materials Characterization and Performance

    2014-09-01

    Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 Tm for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

  2. Creep and stick-slip in subglacial granular beds forced by ocean tides

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Beem, Lucas H.

    rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in driving stresses or pore-water pressure, caused by ocean tides, give rise to strain-rate dependent creeping motion at stress levels below the point of failure, while disruption...

  3. Creep and stick-slip in subglacial granular beds forced by variations in water pressure

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Beem, Lucas H.

    of grain and fluid dynamics to show that rapid rearrangements of load-bearing force chains within the granular sediments drive mechanical transitions between stability and failure. Cyclic variations in driving stresses or pore-water pressure give rise to strain-rate dependent creeping motion at stress...

  4. Creep Rupture Life Prediction Based on Analysis of Large Creep Deformation

    OpenAIRE

    YE Wenming; HU Xuteng; Ma, Xiaojian; SONG Yingdong

    2016-01-01

    A creep rupture life prediction method for high temperature component was proposed. The method was based on a true stress-strain elastoplastic creep constitutive model and the large deformation finite element analysis method. This method firstly used the high-temperature tensile stress-strain curve expressed by true stress and strain and the creep curve to build materials' elastoplastic and creep constitutive model respectively, then used the large deformation finite element method to calcula...

  5. A Creep Model for High Density Snow

    Science.gov (United States)

    2017-04-01

    Director of ERDC-CRREL was Dr. Lance Hansen, and the Director was Dr. Robert E. Davis. COL Bryan S. Green was Commander of ERDC, and Dr. David W...Station, Green - land, and that will be founded on a compacted snow surface. The defor- mation of snow under a constant load (creep deformation, or...developed in this study are enough similar to the generalized creep model used in the ABAQUS finite element software that the ABAQUS creep model was used

  6. Analogy betwen dislocation creep and relativistic cosmology

    OpenAIRE

    J.A. Montemayor-Aldrete; J.D. Muñoz-Andrade; Mendoza-Allende, A.; Montemayor-Varela, A.

    2005-01-01

    A formal, physical analogy between plastic deformation, mainly dislocation creep, and Relativistic Cosmology is presented. The physical analogy between eight expressions for dislocation creep and Relativistic Cosmology have been obtained. By comparing the mathematical expressions and by using a physical analysis, two new equations have been obtained for dislocation creep. Also, four new expressions have been obtained for Relativistic Cosmology. From these four new equations, one may determine...

  7. Engineering tools for robust creep modelling

    OpenAIRE

    Holmström, Stefan

    2010-01-01

    High temperature creep is often dealt with simplified models to assess and predict the future behavior of materials and components. Also, for most applications the creep properties of interest require costly long-term testing that limits the available data to support design and life assessment. Such test data sets are even smaller for welded joints that are often the weakest links of structures. It is of considerable interest to be able to reliably predict and extrapolate long term creep beha...

  8. Creep Resistance of VM12 Steel

    OpenAIRE

    Zieliński A.; Golański G.; Dobrzański J.; Sroka M.

    2016-01-01

    This article presents selected material characteristics of VM12 steel used for elements of boilers with super- and ultra-critical steam parameters. In particular, abridged and long-term creep tests with and without elongation measurement during testing and investigations of microstructural changes due to long-term impact of temperature and stress were carried out. The practical aspect of the use of creep test results in forecasting the durability of materials operating under creep conditions ...

  9. Optimization of High Temperature Hoop Creep Response in ODS-Fe3Al Tubes

    Energy Technology Data Exchange (ETDEWEB)

    Kad, B.K.; Heatherington, J.H.; McKamey, C.; Wright, I.; Sikka, V.; Judkins, R.

    2003-04-22

    Oxide dispersion strengthened (ODS) Fe3Al alloys are currently being developed for heat-exchanger tubes for eventual use at operating temperatures of up to 1100 C in the power generation industry. The development challenges include (a) efforts to produce thin walled ODS-Fe3Al tubes, employing powder extrusion methodologies, with (b) adequate increased strength for service at operating temperatures to (c) mitigate creep failures by enhancing the as-processed grain size. A detailed and comprehensive research and development methodology is prescribed to produce ODS-Fe3Al thin walled tubes. Current single step extrusion consolidation methodologies typically yield 8ft. lengths of 1-3/8 inch diameter, 1/8 inch wall thickness ODS-Fe3Al tubes. The process parameters for such consolidation methodologies have been prescribed and evaluated as being routinely reproducible. Recrystallization treatments at 1200 C produce elongated grains (with their long axis parallel to the extrusion axis), typically 200-2000 {micro}m in diameter, and several millimeters long. The dispersion distribution is unaltered on a micro scale by recrystallization, but the high aspect ratio grain shape typically obtained limits grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloys requires an understanding and manipulating the factors that control grain alignment and recrystallization behavior. Current efforts are focused on examining the processing dependent longitudinal vs. transverse creep anisotropy, and exploring post-extrusion methods to improve hoop creep response in ODS-Fe3Al alloy tubes. In this report we examine the mechanisms of hoop creep failure and describe our efforts to improve creep performance via variations in thermal-mechanical treatments.

  10. Progress Report on Long Hold Time Creep Fatigue of Alloy 617 at 850°C

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, Laura Jill [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-10-01

    Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep-fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutes at the 1.0% strain range. The creep-fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep-fatigue data are calculated for the creep-fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.

  11. Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

    Science.gov (United States)

    Wen, Xingshuo

    The Very High Temperature Reactor (VHTR) is one of the leading concepts of the Generation IV nuclear reactor development, which is the core component of Next Generation Nuclear Plant (NGNP). The major challenge in the research and development of NGNP is the performance and reliability of structure materials at high temperature. Alloy 617, with an exceptional combination of high temperature strength and oxidation resistance, has been selected as a primary candidate material for structural use, particularly in Intermediate Heat Exchanger (IHX) which has an outlet temperature in the range of 850 to 950°C and an inner pressure from 5 to 20MPa. In order to qualify the material to be used at the operation condition for a designed service life of 60 years, a comprehensive scientific understanding of creep behavior at high temperature and low stress regime is necessary. In addition, the creep mechanism and the impact factors such as precipitates, grain size, and grain boundary characters need to be evaluated for the purpose of alloy design and development. In this study, thermomechanically processed specimens of alloy 617 with different grain sizes were fabricated, and creep tests with a systematic test matrix covering the temperatures of 850 to 1050°C and stress levels from 5 to 100MPa were conducted. Creep data was analyzed, and the creep curves were found to be unconventional without a well-defined steady-state creep. Very good linear relationships were determined for minimum creep rate versus stress levels with the stress exponents determined around 3-5 depending on the grain size and test condition. Activation energies were also calculated for different stress levels, and the values are close to 400kJ/mol, which is higher than that for self-diffusion in nickel. Power law dislocation climb-glide mechanism was proposed as the dominant creep mechanism in the test condition regime. Dynamic recrystallization happening at high strain range enhanced dislocation climb and

  12. Creep Behavior of Passive Bovine Extraocular Muscle

    OpenAIRE

    Lawrence Yoo; Hansang Kim; Andrew Shin; Vijay Gupta; Demer, Joseph L.

    2011-01-01

    This paper characterized bovine extraocular muscles (EOMs) using creep, which represents long-term stretching induced by a constant force. After preliminary optimization of testing conditions, 20 fresh EOM samples were subjected to four different loading rates of 1.67, 3.33, 8.33, and 16.67%/s, after which creep was observed for 1,500 s. A published quasilinear viscoelastic (QLV) relaxation function was transformed to a creep function that was compared with data. Repeatable creep was observed...

  13. Creep characterization of solder bumps using nanoindentation

    Science.gov (United States)

    Du, Yingjie; Liu, Xiao Hu; Fu, Boshen; Shaw, Thomas M.; Lu, Minhua; Wassick, Thomas A.; Bonilla, Griselda; Lu, Hongbing

    2017-08-01

    Current nanoindentation techniques for the measurement of creep properties are applicable to viscoplastic materials with negligible elastic deformations. A new technique for characterization of creep behavior is needed for situations where the elastic deformation plays a significant role. In this paper, the effect of elastic deformation on the determination of creep parameters using nanoindentation with a self-similar nanoindenter tip is evaluated using finite element analysis (FEA). It is found that the creep exponent measured from nanoindentation without taking into account of the contribution of elastic deformation tends to be higher than the actual value. An effective correction method is developed to consider the elastic deformation in the calculation of creep parameters. FEA shows that this method provides accurate creep exponent. The creep parameters, namely the creep exponent and activation energy, were measured for three types of reflowed solder bumps using the nanoindentation method. The measured parameters were verified using FEA. The results show that the new correction approach allows extraction of creep parameters with precision from nanoindentation data.

  14. Prediction and Monitoring Systems of Creep-Fracture Behavior of 9Cr-1Mo Steels for Teactor Pressure Vessels

    Energy Technology Data Exchange (ETDEWEB)

    Potirniche, Gabriel [Univ. of Idaho, Moscow, ID (United States); Barlow, Fred D. [Univ. of Idaho, Moscow, ID (United States); Charit, Indrajit [Univ. of Idaho, Moscow, ID (United States); Rink, Karl [Univ. of Idaho, Moscow, ID (United States)

    2013-11-26

    A recent workshop on next-generation nuclear plant (NGNP) topics underscored the need for research studies on the creep fracture behavior of two materials under consideration for reactor pressure vessel (RPV) applications: 9Cr-1Mo and SA-5XX steels. This research project will provide a fundamental understanding of creep fracture behavior of modified 9Cr-1Mo steel welds for through modeling and experimentation and will recommend a design for an RPV structural health monitoring system. Following are the specific objectives of this research project: Characterize metallurgical degradation in welded modified 9Cr-1Mo steel resulting from aging processes and creep service conditions; Perform creep tests and characterize the mechanisms of creep fracture process; Quantify how the microstructure degradation controls the creep strength of welded steel specimens; Perform finite element (FE) simulations using polycrystal plasticity to understand how grain texture affects the creep fracture properties of welds; Develop a microstructure-based creep fracture model to estimate RPVs service life; Manufacture small, prototypic, cylindrical pressure vessels, subject them to degradation by aging, and measure their leak rates; Simulate damage evolution in creep specimens by FE analyses; Develop a model that correlates gas leak rates from welded pressure vessels with the amount of microstructural damage; Perform large-scale FE simulations with a realistic microstructure to evaluate RPV performance at elevated temperatures and creep strength; Develop a fracture model for the structural integrity of RPVs subjected to creep loads; and Develop a plan for a non-destructive structural health monitoring technique and damage detection device for RPVs.

  15. The influence of the crust layer on RPV structural failure under severe accident condition

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Jianfeng, E-mail: jianfeng-mao@163.com [Institute of Process Equipment and Control Engineering, Zhejiang University of Technology Hangzhou, Zhejiang 310032 (China); Engineering Research Center of Process Equipment and Re-manufacturing, Ministry of Education (China); Li, Xiangqing [Institute of Process Equipment and Control Engineering, Zhejiang University of Technology Hangzhou, Zhejiang 310032 (China); Bao, Shiyi [Institute of Process Equipment and Control Engineering, Zhejiang University of Technology Hangzhou, Zhejiang 310032 (China); Engineering Research Center of Process Equipment and Re-manufacturing, Ministry of Education (China); Luo, Lijia [Institute of Process Equipment and Control Engineering, Zhejiang University of Technology Hangzhou, Zhejiang 310032 (China); Gao, Zengliang [Institute of Process Equipment and Control Engineering, Zhejiang University of Technology Hangzhou, Zhejiang 310032 (China); Engineering Research Center of Process Equipment and Re-manufacturing, Ministry of Education (China)

    2017-05-15

    Highlights: • The crust layer greatly affects the RPV structural behavior. • The RPV failure is investigated in depth under severe accident. • The creep and plastic damage mainly contribute to RPV failure. • An elastic core in RPV wall is essential for ensuring RPV integrity. • The multiaxial state of stress accelerates the total damage evolution. - Abstract: The so called ‘in-vessel retention (IVR)’ is regarded as a severe accident (SA) mitigation strategy, which is widely used in most of advanced nuclear power plants. The effectiveness of IVR strategy is to employ the external water flooding to cool the reactor pressure vessel (RPV). The RPV integrity has to be maintained within a required period during the IVR period. The degraded melting core is assumed to be arrested in the lower head (LH) to form the melting pool that is bounded by upper, side and lower crusts. Consequently, the existence of the crust layer greatly affects the RPV structural behavior as well as failure process. In order to disclose this influence caused by the crust layer, a detailed investigation is conducted by using numerical simulation on the two RPVs with and without crust layer respectively. Taking the RPV without crust layer as a basis for the comparison, the present study assesses the likelihood and potential failure location, time and mode of the LH under the loadings of the critical heat flux (CHF) and slight internal pressure. Due to the high temperature melt on the inside and nucleate boiling on the outside, the RPV integrity is found to be compromised by melt-through, creep, elasticity, plasticity as well as thermal expansion. Through in-depth investigation, it is found that the creep and plasticity are of vital importance to the final structural failure, and the introduction of crust layer results in a significant change on field parameters in terms of temperature, deformation, stress(strain), triaxiality factor and total damage.

  16. Analysis of Creep Rupture Data of Alloy 617 for VHTR Application

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Kim, Min Whan; Kim, Yong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jae Young; Ekaputr, I. M. W. [Pukyong National Univ., Busan (Korea, Republic of)

    2013-10-15

    A new Alloy 617 Code Case is planned to be approved by 2015. In this study, the creep rupture data of Alloy 617, which were produced through a series of creep tests at 850-950 .deg. C at the Korea Atomic Energy Research Institute (KAERI), were analyzed using various creep laws, and the material constants were obtained and discussed.A very high temperature reactor (VHTR) is one of the most promising Gen-IV reactors for the economic production of electricity and hydrogen. Its major components are the reactor internals, reactor pressure vessel (RPV), hot gas ducts (HGD), and intermediate heat exchangers (IHX). Since the VHTR components are designed to be used for a 60 year lifetime at a high temperature, the creep behavior is very important for the design application due to creep damage during the long service life at elevated temperatures. Alloy 617 is a candidate IHX structural material because of its high temperature creep properties. However, the ASME design code for Alloy 617 was not developed for design use. Therefore, material works to complete the ASME Alloy 617 code case development are ongoing according to a next-generation nuclear plant (NGNP) research and development plan. Through this plan, a new Alloy 617 Code Case is planned to be approved by 2015. In this study, the creep rupture data of Alloy 617, which were produced through a series of creep tests at 850-950 .deg. C at the Korea Atomic Energy Research Institute (KAERI), were analyzed using various creep laws, and the material constants were obtained and discussed. Creep rupture data of Alloy 617 tested at 850-950 .deg. C were analyzed using various creep laws, and material constants were obtained. The MMGR reduced the data scattering, and was well fitted for straight line of m ≅ 1.0 as m=0.97. The MMGR showed a better plot than the MGR. In the plot of ZHP and stress, a straight line was for n'=5.87 regardless of the three different temperatures. Thus, it can be inferred that the same creep

  17. Shaking table tests on failure characteristics of base isolation system for a DFBR plant

    Energy Technology Data Exchange (ETDEWEB)

    Sato, N. E-mail: shuoh@psa.kajima.co.jp; Kato, A.; Fukushima, Y.; Iizuka, M

    2002-03-01

    The building of a demonstration fast breeder reactor (DFBR) plant in Japan is planed to be base isolated in the horizontal direction. To verify the seismic safety of the isolation system, a series of shaking table tests was conducted using a reduced scale model with three types of base isolation system, natural rubber bearing with steel damper (NRB+SD), lead rubber bearing (LRB), and high damping rubber bearing (HRB). The results of these tests showed NRB+SD, LRB and HRB were within the stable domain (not hardening) at 1xS2 (maximum acceleration 3.80 m s{sup -2}) input, and were nearly hardening at 2xS2 input. None of the rubber bearings broke at 3xS2 input, which was the design limit. All these bearings broke at over 4xS2 input.

  18. DETERMINATION OF CREEP PROPERTIES OF THERMAL BARRIER COATING(TBC) SYSTEMS FROM THE INDENTATION CREEP TESTING WITH ROUND FLAT INDENTERS

    Institute of Scientific and Technical Information of China (English)

    B. Zhao; B.X. Xu; J. Liu; Z.F. Yue

    2004-01-01

    Indentation creep behavior with cylindrical flat indenters on the thermal barrier coating (TBC) was studied by finite element method (FEM). On the constant applied indentation creep stress, there is a steady creep rate for each case studied for different creep properties of the TBC system. The steady creep depth rate depends on the applied indentation creep stress and size of the indenters as well as the creep properties of the bond coat of the TBC and the substrate. The possibilities to determine the creep properties of a thermal barrier system from indention creep testing were discussed. As an example, with two different size indenters, the creep properties of bond coat of the TBC system can be derived by an inverse FEM method. This study not only provides a numerical method to obtain the creep properties of the TBC system, but also extends the application of indentation creep method with cylindrical flat indenters.

  19. Design of a Programmable System for Failure Modes and Effect Analysis of Steam-Power Plant Based on the Fault Tree Analysis

    Directory of Open Access Journals (Sweden)

    Dr. Zuhair I. Ahmad Al- Dauod

    2005-01-01

    Full Text Available In this paper, the system of the power plant has been investigated as a special type of industrial systems, which has a significant role in improving societies since the electrical energy has entered all kinds of industries, and it is considered as the artery of modern life. The aim of this research is to construct a programming system, which could be used to identify the most important failure modes that are occur in a steam type of power plants. Also the effects and reasons of each failure mode could be analyzed through the usage of this programming system reaching to the basic events (main reasons that causing each failure mode. The construction of this system for FMEA is depending on the logical relationships of the fault tree analysis for the systems that contained in the power station. The designing of such system could be used as an assistance tool for the specialist user (the power engineer in identifying of all reasons and effects for any type of failures. So this is help to fastening the repairing operation of the identified failure mode to improve the efficiency of operating system as represented by the maintainability, which is a function of system reliability. The selection of the steam type of power generation systems for the application of this study, because this type is the most common type of Iraqi power plants. While such the designed system could be programmed to be use in another types of industrial systems.

  20. Light water reactor lower head failure analysis

    Energy Technology Data Exchange (ETDEWEB)

    Rempe, J.L.; Chavez, S.A.; Thinnes, G.L. [EG and G Idaho, Inc., Idaho Falls, ID (United States)] [and others

    1993-10-01

    This document presents the results from a US Nuclear Regulatory Commission-sponsored research program to investigate the mode and timing of vessel lower head failure. Major objectives of the analysis were to identify plausible failure mechanisms and to develop a method for determining which failure mode would occur first in different light water reactor designs and accident conditions. Failure mechanisms, such as tube ejection, tube rupture, global vessel failure, and localized vessel creep rupture, were studied. Newly developed models and existing models were applied to predict which failure mechanism would occur first in various severe accident scenarios. So that a broader range of conditions could be considered simultaneously, calculations relied heavily on models with closed-form or simplified numerical solution techniques. Finite element techniques-were employed for analytical model verification and examining more detailed phenomena. High-temperature creep and tensile data were obtained for predicting vessel and penetration structural response.

  1. Experimental Study on Creep Characterization and Lifetime Estimation of RPV Material at 723-1023 K

    Science.gov (United States)

    Xie, Lin-Jun; Ning, Dong; Yang, Yi-zhong

    2017-02-01

    During the plant operation, nuclear reactor pressure vessel (RPV) is the most critical pressure boundary component for integrity and safety in a light-water reactor. In this paper, the creep behavior and properties for RPV metallic material are studied by conducting constant-temperature and constant-load creep tests at 723, 823, 923 and 1023 K. The θ projection constitutive model was established based on a creep method to describe the high-temperature creep behavior of RPV material. The material parameter θ would be obtained based on experimental data by depending on numerical optimization techniques. The relationship between and among θ, T and σ was evaluated, and the coefficients a i , b i , c i and d i were obtained. Based on the short-term tests at a high temperature, the values for long-term creep data could be predicted in accordance with parameter θ. Moreover, rupture life, the minimum creep rate and the time reaching to an arbitrary strain can be calculated and may be used to evaluate the damage behavior and properties, so as to be used as a reference for design and safety assessment.

  2. Creep-Fatigue Relationsihps in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

    Science.gov (United States)

    Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac

    2009-01-01

    The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

  3. Damage Susceptibility of Grain Boundaries in HT9 Steel Subjected to High-Temperature Creep

    Science.gov (United States)

    Leng, Zhe; Field, David P.

    2012-10-01

    HT9 steel is an attractive ferritic/martensitic steel that is used in components of nuclear and fossil power plants because of its high strength and good swelling resistance. Specific phenomena (such as segregation, voiding, cracking, etc.) are prevalent along grain boundaries since these interfaces act as efficient sources for vacancies. The accumulation of vacancies in grain boundaries may result in intergranular fracture. In this study, HT9 steel was subjected to creep tests at elevated temperature (about 0.5 T m) and two different creep conditions (where creep lifetimes were about 100 and about 1000 hours, respectively). The grain boundaries in HT9 steel after creep tests were studied by the use of scanning electron microscopy in order to establish the relationship between the grain boundary structure and creep damage. Images and data obtained using electron backscatter diffraction reveal a high susceptibility of high-angle boundaries to creep cavitation, as expected. In addition, the Σ3 boundaries are also susceptible to damage under these conditions at a similar or even higher rate as compared with random high-angle boundaries.

  4. Making Ice Creep in the Classroom

    Science.gov (United States)

    Prior, David; Vaughan, Matthew; Banjan, Mathilde; Hamish Bowman, M.; Craw, Lisa; Tooley, Lauren; Wongpan, Pat

    2017-04-01

    Understanding the creep of ice has direct application to the role of ice sheet flow in sea level and climate change and to modelling of icy planets and satellites of the outer solar system. Additionally ice creep can be used as an analogue for the high temperature creep of rocks, most particularly quartzites. We adapted technologies developed for ice creep experiments in the research lab, to build some inexpensive ( EU200) rigs to conduct ice creep experiments in an undergraduate (200 and 300 level) class in rock deformation. The objective was to give the students an experience of laboratory rock deformation experiments so that they would understand better what controls the creep rate of ice and rocks. Students worked in eight groups of 5/6 students. Each group had one deformation rig and temperature control system. Each group conducted two experiments over a 2 week period. The results of all 16 experiments were then shared so that all students could analyse the mechanical data and generate a "flow law" for ice. Additionally thin sections were made of each deformed sample so that some microstructural analysis could be incorporated in the data analysis. Students were able to derive a flow law that showed the relationship of creep rate to both stress and temperature. The flow law matches with those from published research. The class did provide a realistic introduction to laboratory rock deformation experiments and helped students' understanding of what controls the creep of rocks.

  5. Significance of primary irradiation creep in graphite

    CSIR Research Space (South Africa)

    Erasmus, C

    2013-05-01

    Full Text Available Traditionally primary irradiation creep is introduced into graphite analysis by applying the appropriate amount of creep strain to the model at the initial time-step. This is valid for graphite components that are subjected to high fast neutron flux...

  6. Creep behavior of passive bovine extraocular muscle.

    Science.gov (United States)

    Yoo, Lawrence; Kim, Hansang; Shin, Andrew; Gupta, Vijay; Demer, Joseph L

    2011-01-01

    This paper characterized bovine extraocular muscles (EOMs) using creep, which represents long-term stretching induced by a constant force. After preliminary optimization of testing conditions, 20 fresh EOM samples were subjected to four different loading rates of 1.67, 3.33, 8.33, and 16.67%/s, after which creep was observed for 1,500 s. A published quasilinear viscoelastic (QLV) relaxation function was transformed to a creep function that was compared with data. Repeatable creep was observed for each loading rate and was similar among all six anatomical EOMs. The mean creep coefficient after 1,500 seconds for a wide range of initial loading rates was at 1.37 ± 0.03 (standard deviation, SD). The creep function derived from the relaxation-based QLV model agreed with observed creep to within 2.7% following 16.67%/s ramp loading. Measured creep agrees closely with a derived QLV model of EOM relaxation, validating a previous QLV model for characterization of EOM biomechanics.

  7. Creep Behavior of Passive Bovine Extraocular Muscle

    Directory of Open Access Journals (Sweden)

    Lawrence Yoo

    2011-01-01

    Full Text Available This paper characterized bovine extraocular muscles (EOMs using creep, which represents long-term stretching induced by a constant force. After preliminary optimization of testing conditions, 20 fresh EOM samples were subjected to four different loading rates of 1.67, 3.33, 8.33, and 16.67%/s, after which creep was observed for 1,500 s. A published quasilinear viscoelastic (QLV relaxation function was transformed to a creep function that was compared with data. Repeatable creep was observed for each loading rate and was similar among all six anatomical EOMs. The mean creep coefficient after 1,500 seconds for a wide range of initial loading rates was at 1.37±0.03 (standard deviation, SD. The creep function derived from the relaxation-based QLV model agreed with observed creep to within 2.7% following 16.67%/s ramp loading. Measured creep agrees closely with a derived QLV model of EOM relaxation, validating a previous QLV model for characterization of EOM biomechanics.

  8. Premature failure of dissimilar metal weld joint at intermediate temperature superheater tube

    Directory of Open Access Journals (Sweden)

    Mohammed Al Hajri

    2015-04-01

    Full Text Available Dissimilar metal weld (DMW joint between alloyed steel (AS and stainless steel (SS failed at one of intermediate temperature superheater (ITSH tube in steam/power generation plant boiler. The premature failure was detected after a relatively short time of operation (8 years where the crack propagated circumferentially from AS side through the ITSH tube. Apart from physical examination, microstructural studies based on optical microscopy, SEM and EDX analysis were performed. The results of the investigation point out the limitation of Carbides precipitation at the alloyed steel/welding interface. This is synonym of creep stage I involvement in the failure of ITSH. Improper post-welding operation and bending moment are considered as root causes of the premature failure.

  9. A microstructural study of creep and thermal fatigue deformation in 60Sn-40Pb solder joints

    Energy Technology Data Exchange (ETDEWEB)

    Tribula, D.

    1990-06-02

    Thermal fatigue failures of solder joints in electronic devices often arise from cyclic shear strains imposed by the mismatched thermal expansion coefficients of the materials that bind the joint as temperature changes are encountered. Increased solder joint reliability demands a fundamental understanding of the metallurigical mechanisms that control the fatigue to design accurate accelerated probative tests and new, more fatigue resistant solder alloys. The high temperatures and slow strain rates that pertain to thermal fatigue imply that creep is an important deformation mode in the thermal fatigue cycle. In this work, the creep behaviour of a solder joint is studied to determine the solder's microstructural response to this type of deformation and to relate this to the more complex problem of thermal fatigue. It is shown that creep failures arise from the inherent inhomogeneity and instability of the solder microstructure and suggest that small compositional changes of the binary near-eutectic Pn-Sn alloy may defeat the observed failure mechanisms. This work presents creep and thermal fatigue data for several near-eutectic Pb-Sn solder compositions and concludes that a 58Sn-40Pb-2In and a 58Sn-40Pb-2Cd alloy show significantly enhanced fatigue resistance over that of the simple binary material. 80 refs., 33 figs., 1 tab.

  10. Irradiation creep of vanadium-base alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, H.; Billone, M.C.; Strain, R.V.; Smith, D.L. [Argonne National Lab., IL (United States); Matsui, H. [Tohoku Univ. (Japan)

    1998-03-01

    A study of irradiation creep in vanadium-base alloys is underway with experiments in the Advanced Test Reactor (ATR) and the High Flux Isotope Reactor (HFIR) in the United States. Test specimens are thin-wall sealed tubes with internal pressure loading. The results from the initial ATR irradiation at low temperature (200--300 C) to a neutron damage level of 4.7 dpa show creep rates ranging from {approx}0 to 1.2 {times} 10{sup {minus}5}/dpa/MPa for a 500-kg heat of V-4Cr-4Ti alloy. These rates were generally lower than reported from a previous experiment in BR-10. Because both the attained neutron damage levels and the creep strains were low in the present study, however, these creep rates should be regarded as only preliminary. Substantially more testing is required before a data base on irradiation creep of vanadium alloys can be developed and used with confidence.

  11. Creep resistant high temperature martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2017-01-31

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, copper, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  12. Creep resistant high temperature martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2015-11-13

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6 carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  13. Creep behavior of Zr-Nb alloys

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Yong Chan; Kim, Young Suk; Cheong, Yong Mu; Kwon, Sang Chul; Kim, Sung Soo; Choo, Ki Nam [Korea Atomic Energy Research Institute, Taejeon (Korea)

    2000-01-01

    The creep characteristics of Zirconium alloy is affected by several parameters. Out-reactor creep increases both with an increasing amount of Nb, Sn and S contained in alpha-Zr and decreases with the increasing volume of alpha-Zr. Especially, the creep of Zr-2.5Nb alloy depends on the solubility of Nb in alpha-Zr, which is associated with the decomposition of beta-Zr. Since Zr of the hcp structure is strongly anisotropic, it shows the characteristics of texture and results in the anisotropy of creep. Due to the circumferential texture of Zr-2.5%Nb alloy (CANDU Pressure tube), the longitudinal slip is easier than the circumferential one, resulting in the high creep rate. The irradiation creep also increases with increasing neutron fluence. The neutron irradiation increases the strength of the zirconium alloys but decreases their creep strength. In contrast to the out-reactor creep, the irradiation creep is little sensitive to temperature, resulting in the lower activation energy. The most important factor to affect the in-reactor and out-reactor creep of niobium containing alloys seems to be the solution hardening by Nb or Sn which is soluble in alpha-zirconium and the texture as well. Irradiation growth is the mechanism which is caused only by the irradiation. It becomes saturated at lower fluence than the critical fluence but beyond it, shows the break-away growth. The onset of accelerated irradiation growth corresponds with the c-dislocation loop formation, though its mechanism needs better understanding. Generally, the irradiation growth of Zr-Nb alloys increases with an increase in fluence, cold working, dislocation, density and temperature, and with a decrease in the grain size. 141 refs., 59 figs., 10 tabs. (Author)

  14. Creep-rupture reliability analysis

    Science.gov (United States)

    Peralta-Duran, A.; Wirsching, P. H.

    1985-01-01

    A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep.

  15. Prediction of Prestressing Losses by Concrete Creep and Shrinkage

    Energy Technology Data Exchange (ETDEWEB)

    Woo, S.K. [Korea Electric Power Research Institute, Taejon (Korea)

    1999-07-01

    In this study, the personal-computer program was developed to predict prestressing losses of containment structures induced by concrete creep and shrinkage in nuclear power plants. Thie program is composed of three major parts in which are the pre-processor, calculation module and post-processor. Input data for this program are: material properties of concrete, rebar, liner and duct, test results of concrete creep and shrinkage, relative humidity, dimension of containment structures, and the number of prestressing tendon related in containment structures. To obtain better results, this program was designed to reflect the prestressing losses due to influence that occurred after prestressing of each tendon, thus it can predict prestressing losses and allowable prestressing forces of each tendon. As a case study, this program was applied to containment structures of Youngkwang 3 and 4 NPP's and analytical results were compared with test results in Inservice Inspection of containment structures. From this comparison, it was proved that this program could well predict prestressing losses by concrete creep and shrinkage. (author). 4 refs., 1 fig., 3 tabs.

  16. Studies on Creep Deformation and Rupture Behavior of 316LN SS Multi-Pass Weld Joints Fabricated with Two Different Electrode Sizes

    Science.gov (United States)

    Vijayanand, V. D.; Kumar, J. Ganesh; Parida, P. K.; Ganesan, V.; Laha, K.

    2017-02-01

    Effect of electrode size on creep deformation and rupture behavior has been assessed by carrying out creep tests at 923 K (650 °C) over the stress range 140 to 225 MPa on 316LN stainless steel weld joints fabricated employing 2.5 and 4 mm diameter electrodes. The multi-pass welding technique not only changes the morphology of delta ferrite from vermicular to globular in the previous weld bead region near to the weld bead interface, but also subjects the region to thermo-mechanical heat treatment to generate appreciable strength gradient. Electron backscatter diffraction analysis revealed significant localized strain gradients in regions adjoining the weld pass interface for the joint fabricated with large electrode size. Larger electrode diameter joint exhibited higher creep rupture strength than the smaller diameter electrode joint. However, both the joints had lower creep rupture strength than the base metal. Failure in the joints was associated with microstructural instability in the fusion zone, and the vermicular delta ferrite zone was more prone to creep cavitation. Larger electrode diameter joint was found to be more resistant to failure caused by creep cavitation than the smaller diameter electrode joint. This has been attributed to the larger strength gradient between the beads and significant separation between the cavity prone vermicular delta ferrite zones which hindered the cavity growth. Close proximity of cavitated zones in smaller electrode joint facilitated their faster coalescence leading to more reduction in creep rupture strength. Failure location in the joints was found to depend on the electrode size and applied stress. The change in failure location has been assessed on performing finite element analysis of stress distribution across the joint on incorporating tensile and creep strengths of different constituents of joints, estimated by ball indentation and impression creep testing techniques.

  17. Microstructure and properties degradation of P/T 91, 92 steels weldments in creep conditions

    Directory of Open Access Journals (Sweden)

    Falat L.

    2012-01-01

    Full Text Available The studies were performed on dissimilar ferritic/austenitic weldments between 9Cr tempered martensitic steels of the grades either P/T 91 or 92 and unstabilised AISI316H austenitic steel. The welded joints were fabricated using the fusion welding by tungsten inert gas (TIG method with Ni-based filler metal. Microstructural analyses were performed using light and electron microscopy. Microstructural gradient in heat-affected zone (HAZ of 9Cr steels remained preserved during creep exposure. All weldments fractured by the type IV failure within their intercritical HAZ (ICHAZ regions. The most remarkable microstructural change during creep was the precipitation of intermetallic Laves phase. Experimentally determined phases of the samples after creep exposure are in good agreement with equilibrium thermodynamic calculations.

  18. Computational Design of Creep-Resistant Alloys and Experimental Validation in Ferritic Superalloys

    Energy Technology Data Exchange (ETDEWEB)

    Liaw, Peter

    2014-12-31

    A new class of ferritic superalloys containing B2-type zones inside parent L21-type precipitates in a disordered solid-solution matrix, also known as a hierarchical-precipitate strengthened ferritic alloy (HPSFA), has been developed for high-temperature structural applications in fossil-energy power plants. These alloys were designed by the addition of the Ti element into a previously-studied NiAl-strengthened ferritic alloy (denoted as FBB8 in this study). In the present research, systematic investigations, including advanced experimental techniques, first-principles calculations, and numerical simulations, have been integrated and conducted to characterize the complex microstructures and excellent creep resistance of HPSFAs. The experimental techniques include transmission-electron microscopy, scanningtransmission- electron microscopy, neutron diffraction, and atom-probe tomography, which provide detailed microstructural information of HPSFAs. Systematic tension/compression creep tests revealed that HPSFAs exhibit the superior creep resistance, compared with the FBB8 and conventional ferritic steels (i.e., the creep rates of HPSFAs are about 4 orders of magnitude slower than the FBB8 and conventional ferritic steels.) First-principles calculations include interfacial free energies, anti-phase boundary (APB) free energies, elastic constants, and impurity diffusivities in Fe. Combined with kinetic Monte- Carlo simulations of interdiffusion coefficients, and the integration of computational thermodynamics and kinetics, these calculations provide great understanding of thermodynamic and mechanical properties of HPSFAs. In addition to the systematic experimental approach and first-principles calculations, a series of numerical tools and algorithms, which assist in the optimization of creep properties of ferritic superalloys, are utilized and developed. These numerical simulation results are compared with the available experimental data and previous first

  19. RNA-Seq analysis of the Sclerotinia homoeocarpa--creeping bentgrass pathosystem.

    Directory of Open Access Journals (Sweden)

    Angela M Orshinsky

    Full Text Available Sclerotinia homoeocarpa causes dollar spot disease, the predominate disease on highly-maintained turfgrass. Currently, there are major gaps in our understanding of the molecular interactions between S. homoeocarpa and creeping bentgrass. In this study, 454 sequencing technology was used in the de novo assembly of S. homoeocarpa and creeping bentgrass transcriptomes. Transcript sequence data obtained using Illumina's first generation sequencing-by-synthesis (SBS were mapped to the transcriptome assemblies to estimate transcript representation in different SBS libraries. SBS libraries included a S. homoeocarpa culture control, a creeping bentgrass uninoculated control, and a library for creeping bentgrass inoculated with S. homoeocarpa and incubated for 96 h. A Fisher's exact test was performed to determine transcripts that were significantly different during creeping bentgrass infection with S. homoeocarpa. Fungal transcripts of interest included glycosyl hydrolases, proteases, and ABC transporters. Of particular interest were the large number of glycosyl hydrolase transcripts that target a wide range of plant cell wall compounds, corroborating the suggested wide host range and saprophytic abilities of S. homoeocarpa. Several of the multidrug resistance ABC transporters may be important for resistance to both fungicides and plant defense compounds. Creeping bentgrass transcripts of interest included germins, ubiquitin transcripts involved in proteasome degradation, and cinnamoyl reductase, which is involved in lignin production. This analysis provides an extensive overview of the S. homoeocarpa-turfgrass pathosystem and provides a starting point for the characterization of potential virulence factors and host defense responses. In particular, determination of important host defense responses may assist in the development of highly resistant creeping bentgrass varieties.

  20. Minimization of the energy loss of nuclear power plants in case of partial in-core monitoring system failure

    Science.gov (United States)

    Zagrebaev, A. M.; Ramazanov, R. N.; Lunegova, E. A.

    2017-01-01

    In this paper we consider the optimization problem minimize of the energy loss of nuclear power plants in case of partial in-core monitoring system failure. It is possible to continuation of reactor operation at reduced power or total replacement of the channel neutron measurements, requiring shutdown of the reactor and the stock of detectors. This article examines the reconstruction of the energy release in the core of a nuclear reactor on the basis of the indications of height sensors. The missing measurement information can be reconstructed by mathematical methods, and replacement of the failed sensors can be avoided. It is suggested that a set of ‘natural’ functions determined by means of statistical estimates obtained from archival data be constructed. The procedure proposed makes it possible to reconstruct the field even with a significant loss of measurement information. Improving the accuracy of the restoration of the neutron flux density in partial loss of measurement information to minimize the stock of necessary components and the associated losses.

  1. Critical review of creep FRAPCON-3 model under dry storage conditions

    Energy Technology Data Exchange (ETDEWEB)

    Feria, F.; Herranz, L.E. [Unit of Nuclear Safety Research, CIEMAT, Avda. Complutense 22, Madrid, Madrid 28040 (Spain)

    2009-06-15

    There is a general agreement that cladding creep rupture is the most likely and limiting failure mechanism of spent fuel in dry storage compared to other potential mechanisms, like stress corrosion cracking and/or delayed hydride cracking. Nevertheless, occurrence of creep rupture is very improbable since both decay heat and hoop stress tend to decrease throughout dry storage. In spite of this, the current trend to higher burn up levels needs further attention that ensures safe storage of spent fuel irradiated over 45 GWd/MTU. An extensive work has been carried out during the last four decades in the area of in-reactor creep modelling. Unfortunately, the in-reactor conditions are so different from those prevailing under dry storage, that all the experience gained cannot be extrapolated in a straightforward manner. On the other side, as creep tests simulating conditions throughout a 20-40 year dry storage are impractical, post-irradiation cladding creep behaviour has been modelled by means of time-temperature dependent laws developed on the basis of currently available zirconium alloys data. Additionally, some tests have been exploring the effect of irradiation, hydrogen distribution and material composition on the materials creep behaviour. Adaptation of fuel performance codes initially developed for normal and off-normal reactor operation is not an easy task either. Creep modelling is usually dependent of host codes because a good part of its validation and update has been carried out in an integral way, and as a consequence its independent performance assessment is not an easy task. This work examines the current capability of FRAPCON-3 to model creep behaviour under dry storage conditions. To do so, a review of its major fundamentals has been done and its range of applicability discussed. Once its main approximations and drawbacks have been identified, an attempt to overcome some of them has been intended by implementing an alternative expression for creep under

  2. ESTIMATION MODEL OF RESIDUAL LIFE-TIME OF LOCOMOTIVE FRAME BOGIE WITH ALLOWANCE FOR CREEP

    Directory of Open Access Journals (Sweden)

    V. R. Skalskyi

    2014-12-01

    Full Text Available Purpose. The problem of determining the residual life of frame bogie elements of locomotives is a great importance for predicting their work safely and avoidance potential failures on the track. This especially concern cases when such elements have creep-fatigue cracks which grow under action of cyclic loading with excerpts T1 in the cycle and reach their critical size. Here the question of the propagation of such defects (cracks arises, their kinetics and about the period of subcritical cracks growth. The aim is to develop a calculation model for determination the period of subcritical creep-fatigue cracks growth in the bogies frames of electric locomotive. The model takes into account the basic parameters of load, geometry of the construction element and cracks. Methodology. The calculation model for determination the period of subcritical creep-fatigue cracks growth in structural elements of frame under conditions of variable load time has been formulated. It is based on the first law of thermodynamics concerning to mechanics of solids slow fracture at low temperature creep and variable loadings. It is assumed that the period of unsteady creep dominates here (the first section of the creep curve. Low-temperature creep is creep of materials at temperatures T0 < 0,5Tmp, where Tmp − the melting point of the material. Findings. The analytical formula for the determination of the stress intensity factor of truck bolster with technological hole has been obtained. It is shown that by experimentally established constants of the material using the proposed analytical relations can easily determine residual resource of the bogie frame elements. Originality. The new mathematical model for describing the kinetics of creep-fatigue cracks growth in the frames bogies of electric locomotive under variable in time loadings with various time excerpts and on this base the period determination of subcritical crack growth has been proposed. Practical value

  3. Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

    Energy Technology Data Exchange (ETDEWEB)

    Templeton, D C; Nadeau, R; Burgmann, R

    2007-07-09

    Repeating earthquakes (REs) are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. We investigate the occurrence of these REs along faults in central California to determine which faults exhibit creep and the spatio-temporal distribution of this creep. At the juncture of the San Andreas and southern Calaveras-Paicines faults, both faults as well as a smaller secondary fault, the Quien Sabe fault, are observed to produce REs over the observation period of March 1984-May 2005. REs in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time. Cumulative slip over the observation period at individual sequence locations is determined to range from 5.5-58.2 cm on the San Andreas fault, 4.8-14.1 cm on the southern Calaveras-Paicines fault, and 4.9-24.8 cm on the Quien Sabe fault. Creep at depth appears to mimic the behaviors seen of creep on the surface in that evidence of steady slip, triggered slip, and episodic slip phenomena are also observed in the RE sequences. For comparison, we investigate the occurrence of REs west of the San Andreas fault within the southern Coast Range. Events within these RE sequences only occurred minutes to weeks apart from each other and then did not repeat again over the observation period, suggesting that REs in this area are not produced by steady aseismic creep of the surrounding fault surface.

  4. Deformation by grain boundary sliding and slip creep versus diffusional creep

    Energy Technology Data Exchange (ETDEWEB)

    Ruano, O A; Sherby, O D; Wadsworth, J

    1998-11-04

    A review is presented of the debates between the present authors and other investigators regarding the possible role of diffusional creep in the plastic flow of polycrystalline metals at low stresses. These debates are recorded in eleven papers over the past seventeen years. ln these papers it has been shown that the creep rates of materials in the so-called "diffusional creep region" are almost always higher than those predicted by the diffusional creep theory. Additionally, the predictions of grain size effects and stress exponents from diffusional creep theory are often not found in the experimental data. Finally, denuded zones have been universally considered to be direct evidence for diffusional creep; but, those reported in the literature are shown to be found only under conditions where a high stress exponent is observed. Also, the locations of the denuded zones do not match those predicted. Alternative mechanisms are described in which diffusion-controlled dislocation creep and/or grain boundary sliding are the dominant deformation processes in low-stress creep. It is proposed that denuded zones are formed by stress-directed grain boundary migration with the precipitates dissolving in the moving grain boundaries. The above observations have led us to the conclusion that grain boundary sliding and slip creep are in fact the principal mechanisms for observations of plastic flow in the so-called "diffusional creep regions".

  5. On the prediction of long term creep strength of creep resistant steels

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Mi; Wang, Qiao; Song, Xin-Li; Jia, Juan; Xiang, Zhi-Dong [Wuhan University of Science and Technology (China). The State Key Laboratory of Refractories and Metallurgy

    2016-02-15

    When the conventional power law creep equation is applied to rationalise the creep data of creep resistant steels, its parameters depend strongly on stress and temperature and hence cannot be used to predict long term creep properties. Here, it is shown that this problem can be resolved if it is modified to satisfy two boundary conditions, i.e. when σ (stress) = 0, ε{sub min} (minimum creep rate) = 0, and when σ = σ{sub TS} (tensile stress at creep temperature T), ε{sub min} = ∞. This can be achieved by substituting the reference stress σ{sub 0} in the conventional equation by the term (σ{sub TS} - σ). The new power law creep equation describing the stress and temperature dependence of minimum creep rate can then be applied to predict long term creep strength from data of short term measurements. This is demonstrated using the creep and tensile strength data measured for 11Cr-2W-0.4Mo-1Cu-Nb-V steel (tube).

  6. Creep and Fracture of a Protein Gel under Stress

    Science.gov (United States)

    Leocmach, Mathieu; Perge, Christophe; Divoux, Thibaut; Manneville, Sébastien

    2014-07-01

    Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the failure scenario of a protein gel is reminiscent of brittle solids: after a primary creep regime characterized by a power-law behavior whose exponent is fully accounted for by linear viscoelasticity, fractures nucleate and grow logarithmically perpendicularly to shear, up to the sudden rupture of the gel. A single equation accounting for those two successive processes nicely captures the full rheological response. The failure time follows a decreasing power law with the applied shear stress, similar to the Basquin law of fatigue for solids. These results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers and exemplify protein gels as model, brittlelike soft solids.

  7. Coarsening behaviour of M23C6 carbides in creep-resistant steel exposed to high temperatures

    OpenAIRE

    M. Godec; Skobir Balantič, D. A.

    2016-01-01

    High operating temperatures can have very deleterious effects on the long-term performance of high-Cr, creep-resistant steels used, for example, in the structural components of power plants. For the popular creep-resistant steel X20CrMoV12.1 we analysed the processes of carbide growth using a variety of analytical techniques: transmission electron microscopy (TEM) and diffraction (TED), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The evolution of the micro...

  8. The influence of grain boundary structure on diffusional creep

    DEFF Research Database (Denmark)

    Thorsen, Peter Anker; Bilde-Sørensen, Jørgen

    1999-01-01

    A Cu-2wt%Ni-alloy was deformed in tension in the diffusional creep regime (Nabarro-Herring creep). A periodic grid consisting of alumina was deposited on the surface of the creep specimen prior to creep. This makes it possible to separate the deformation caused by grain boundary sliding from...

  9. Creep Behavior of High-Strength Concrete Subjected to Elevated Temperatures

    Directory of Open Access Journals (Sweden)

    Minho Yoon

    2017-07-01

    Full Text Available Strain is generated in concrete subjected to elevated temperatures owing to the influence of factors such as thermal expansion and design load. Such strains resulting from elevated temperatures and load can significantly influence the stability of a structure during and after a fire. In addition, the lower the water-to-binder (W–B ratio and the smaller the quantity of aggregates in high-strength concrete, the more likely it is for unstable strain to occur. Hence, in this study, the compressive strength, elastic modulus, and creep behavior were evaluated at target temperatures of 100, 200, 300, 500, and 800 °C for high-strength concretes with W–B ratios of 30%, 26%, and 23%. The loading conditions were set as non-loading and 0.33fcu. It was found that as the compressive strength of the concrete increased, the mechanical characteristics deteriorated and transient creep increased. Furthermore, when the point at which creep strain occurred at elevated temperatures after the occurrence of transient creep was considered, greater shrinkage strain occurred as the compressive strength of the concrete increased. At a heating temperature of 800 °C, the 80 and 100 MPa test specimens showed creep failure within a shrinkage strain range similar to the strain at the maximum load.

  10. Creep Behavior of High-Strength Concrete Subjected to Elevated Temperatures.

    Science.gov (United States)

    Yoon, Minho; Kim, Gyuyong; Kim, Youngsun; Lee, Taegyu; Choe, Gyeongcheol; Hwang, Euichul; Nam, Jeongsoo

    2017-07-11

    Strain is generated in concrete subjected to elevated temperatures owing to the influence of factors such as thermal expansion and design load. Such strains resulting from elevated temperatures and load can significantly influence the stability of a structure during and after a fire. In addition, the lower the water-to-binder (W-B) ratio and the smaller the quantity of aggregates in high-strength concrete, the more likely it is for unstable strain to occur. Hence, in this study, the compressive strength, elastic modulus, and creep behavior were evaluated at target temperatures of 100, 200, 300, 500, and 800 °C for high-strength concretes with W-B ratios of 30%, 26%, and 23%. The loading conditions were set as non-loading and 0.33fcu. It was found that as the compressive strength of the concrete increased, the mechanical characteristics deteriorated and transient creep increased. Furthermore, when the point at which creep strain occurred at elevated temperatures after the occurrence of transient creep was considered, greater shrinkage strain occurred as the compressive strength of the concrete increased. At a heating temperature of 800 °C, the 80 and 100 MPa test specimens showed creep failure within a shrinkage strain range similar to the strain at the maximum load.

  11. Enhancement in creep resistance of Ti–6Al–4V alloy due to boron addition

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Gaurav [Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India); Satyanarayana, D.V.V. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Pederson, Robert [Research and Technology Centre, GKN Aerospace Engine Systems, S-46181 Trollhättan (Sweden); Division of Materials Science, Luleä University of Technology, S-97187 Luleä (Sweden); Datta, Ranjan [International Centre for Materials Science, JNCASR, Jakkur PO, Bangalore 560064 (India); Ramamurty, Upadrasta, E-mail: ramu@materials.iisc.ernet.in [Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India); Centre of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)

    2014-03-01

    The addition of B, up to about 0.1 wt%, to Ti–6Al–4V (Ti64) reduces its as-cast grain and colony sizes by an order of magnitude. In this paper, the creep resistance of this alloy modified with 0.06 and 0.11 wt% B additions was investigated in the temperature range of 475–550 °C and compared with that of the base alloy. Conventional dead-weight creep tests as well as stress relaxation tests were employed for this purpose. Experimental results show that the B addition enhances both elevated temperature strength and creep properties of Ti64, especially at the lower end of the temperatures investigated. The steady state creep rate in the alloy with 0.11 wt% B was found to be an order of magnitude lower than that in the base alloy, and both the strain at failure as well as the time for rupture increases with the B content. These marked improvements in the creep resistance due to B addition to Ti64 were attributed primarily to the increased number of inter-phase interfaces – a direct consequence of the microstructural refinement that occurs with the B addition – that provide resistance to dislocation motion.

  12. Effect of cyclic loading on the creep performance of silicon nitride

    Energy Technology Data Exchange (ETDEWEB)

    Wereszczak, A.A.; Ferber, M.K.; Kirkland, T.P. [Oak Ridge National Lab., TN (United States). High Temperature Materials Lab.; Lin, C.K.J. [National Central Univ., Chung-Li (Taiwan, Province of China). Dept. of Mechanical Engineering

    1995-04-01

    Tension-tension cyclic fatigue tests (triangular waveform, {sigma}{sub max} = 100 MPa, R = 0.1) were conducted on hot isostatically pressed (HIPed) silicon nitride at frequencies spanning several orders of magnitude (5.6 {times} 10{sup {minus}6} to 0.1 Hz or 10{sup {minus}3} MPa/s to 18 MPa/s) at 1,370 C in air. The amount of cyclic creep strain was found to be a function of the frequency or stressing rate with greater strains to failure observed as the frequency or stressing rate decreased. The total strain was viewed as the sum of elastic, anelastic (or transient recoverable), and plastic (viscous or non-recoverable) strain contributions, after the empirical Pao and Marin model. The plastic strain was found to be the dominant component of the total creep and was unsatisfactorily represented by the Pao and Marin model. To circumvent this, a time exponent was introduced in the plastic strain term in the Pao and Marin model. This modification resulted in good correlation between model and experiment at the slower frequencies examined but over-predicted the cyclic creep strain at the faster frequencies. The utility of using the modified Pao and Marin model to predict cyclic creep response from static creep and strain relaxation tests is described.

  13. Creep Properties of the As-Cast Al-A319 Alloy: T4 and T7 Heat Treatment Effects

    Science.gov (United States)

    Erfanian-Naziftoosi, Hamid R.; Rincón, Ernesto J.; López, Hugo F.

    2016-08-01

    In this work, the creep behavior of a commercial Al-A319 alloy was investigated in the temperature range of 413 K to 533 K (140 °C to 260 °C). Tensile creep specimens in the as-cast condition and after heat treating by solid solution (T4) and by aging (T7) were tested in a stress range varying from 60 to 170 MPa. It was found that steady-state creep strain rate was significantly low in the T7 condition when compared with either the T4 or as-cast alloy conditions. As a result, the time to failure behavior considerably increased. The experimentally determined creep exponents measured from the stress-strain curves were 4 for the as-cast alloy, 7.5 in the solid solution, and 9.5 after aging. In particular, after solid solution a grain substructure was found to develop which indicated that creep in a constant subgrain structure was active, thus accounting for the n exponent of 7.5. In the aged condition, a stress threshold is considered to account for the power law creep exponent n of 9.5. Moreover, It was found that the creep activation energy values were rather similar for the alloys in the as-cast (134 kJ/mol) and T4 (146 kJ/mol) conditions. These values are close to the one corresponding to pure Al self-diffusion (143 kJ/mol). In the aged alloy, the apparent creep activation energy (202 kJ/mol) exceeded that corresponding to Al self-diffusion. This deviation in activation energy is attributed to the effect of temperature on the alloy elastic modulus. Microstructural observations using transmission electron microscopy provided further support for the various dislocation-microstructure interactions exhibited by the alloy under the investigated creep conditions and implemented heat treatments.

  14. ANALYSIS ON PSEUDO-STEADY INDENTATION CREEP

    Institute of Scientific and Technical Information of China (English)

    Hidenari Takagi; Ming Dao; Masami Fujiwara

    2008-01-01

    Theoretical analysis and finite element (FE) simulation have been carried out for a constant specific load rate (CSLR) indentation creep test.Analytical results indicate that both the representative stress and the indentation strain rate become constant after a transient period. Moreover,the FE simulation reveals that both the contours of equivalent stress and equivalent plastic strain rate underneath the indenter evolve with geometrical self-similarity.This suggests that pseudo-steady indentation creep occurs in the region beneath the indenter.The representative points in the region are defined as the ones with the equivalent stress equal to the representative stress.In addition,it is revealed that the proportionality between indentation strain rate and equivalent plastic strain rate holds at the representative points during the pseudo-steady inden tation creep of a power law material.A control volume (CV) beneath the indenter,which governs the indenter velocity,is identified.The size of the CV at the indented surface is approximately 2.5 times the size of the impression.The stress exponent for creep can be obtained from the pseudo steady indentation creep data.These results demonstrate that the CSLR testing technique can be used to evaluate creep parameters with the same accuracy as conventional uniaxial creep tests.

  15. Superheater failures in ultra supercritical boilers - cases from Fynsvaerket, Vestkraft, and Skaerbaekvaerket power plants; Ueberhitzerschaeden in Kesseln mit fortschrittlichen Dampfparametern - Fallbeispiele aus den Kraftwerken Fynsvaerket, Vestkraft und Skaerbaekvaerket

    Energy Technology Data Exchange (ETDEWEB)

    Blum, R.; Larsen, O.H.; Henriksen, N.

    1999-12-01

    Superheater and reheater failures are well known problems in existing power boilers and a potential problem of great importance in new ultra supercritical (USC) plants. Unexpected shut downs caused by leaking superheater and reheater tubes affect the availability of the plant and thereby the overall plant economics. Overheating due to an incorrect balance of the actual temperature level, heat flux and cooling causes most of the superheater and reheater failures. Elsam has been dealing with these problems for many years, and based on experience gained from in service plants and from different in-plant test facilities a powerful simulation calculation programme has been set up. Using this programme it has been possible to explain the failures, assess the remaining lifetime of superheater or reheater sections and make correct simulations and assessments of superheater and reheater design in new boilers with advanced steam parameters. A detailed description of this calculation programme has been given in former papers. In this paper, examples of such evaluations will be given describing three cases where severe superheater failures were experienced in supercritical once through boilers. (orig.) [German] Ueberhitzer- und Zwischenueberhitzerschaeden sind in bestehenden Kraftwerkskesseln bekannt und stellen ein potentielles Problem groesster Wichtigkeit in neuen Anlagen mit fortgeschrittenen Dampfparametern dar. Unerwartete Betriebsunterbrechungen durch Leckagen von Ueberhitzer- und Zwischenueberhitzerrohren beeintraechtigen die Kraftwerksverfuegbarkeit und dadurch die Wirtschaftlichkeit. Ueberhitzung als Folge von Temperaturschieflagen, von inkorrekten Waermestromdichten und Kuehlung verursacht die meisten Ueberhitzer- und Zwischenueberhitzerschaeden. ELSAM befasst sich seit vielen Jahren mit diesem Problem. Anhand der Erfahrungen aus den Anlagen in Betrieb und Ergebnissen von verschiedenen Teststaenden in Kraftwerken wurde ein leistungsfaehiges Computerprogramm

  16. Irradiation creep of dispersion strengthened copper alloy

    Energy Technology Data Exchange (ETDEWEB)

    Pokrovsky, A.S.; Barabash, V.R.; Fabritsiev, S.A. [and others

    1997-04-01

    Dispersion strengthened copper alloys are under consideration as reference materials for the ITER plasma facing components. Irradiation creep is one of the parameters which must be assessed because of its importance for the lifetime prediction of these components. In this study the irradiation creep of a dispersion strengthened copper (DS) alloy has been investigated. The alloy selected for evaluation, MAGT-0.2, which contains 0.2 wt.% Al{sub 2}O{sub 3}, is very similar to the GlidCop{trademark} alloy referred to as Al20. Irradiation creep was investigated using HE pressurized tubes. The tubes were machined from rod stock, then stainless steel caps were brazed onto the end of each tube. The creep specimens were pressurized by use of ultra-pure He and the stainless steel caps subsequently sealed by laser welding. These specimens were irradiated in reactor water in the core position of the SM-2 reactors to a fluence level of 4.5-7.1 x 10{sup 21} n/cm{sup 2} (E>0.1 MeV), which corresponds to {approx}3-5 dpa. The irradiation temperature ranged from 60-90{degrees}C, which yielded calculated hoop stresses from 39-117 MPa. A mechanical micrometer system was used to measure the outer diameter of the specimens before and after irradiation, with an accuracy of {+-}0.001 mm. The irradiation creep was calculated based on the change in the diameter. Comparison of pre- and post-irradiation diameter measurements indicates that irradiation induced creep is indeed observed in this alloy at low temperatures, with a creep rate as high as {approx}2 x 10{sup {minus}9}s{sup {minus}1}. These results are compared with available data for irradiation creep for stainless steels, pure copper, and for thermal creep of copper alloys.

  17. PERFORMANCE IMPROVEMENT OF CREEP-RESISTANT FERRITIC STEEL WELDMENTS THROUGH THERMO-MECHANICAL TREATMENT AND ALLOY DESIGN

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, Yukinori [ORNL; Babu, Prof. Sudarsanam Suresh [University of Tennessee, Knoxville (UTK); Shassere, Benjamin [ORNL; Yu, Xinghua [ORNL

    2016-01-01

    Two different approaches have been proposed for improvement of cross-weld creep properties of the high temperature ferrous structural materials for fossil-fired energy applications. The traditional creep strength-enhanced ferritic (CSEF) steel weldments suffer from Type IV failures which occur at the fine-grained heat affected zone (FGHAZ). In order to minimize the premature failure at FGHAZ in the existing CSEF steels, such as modified 9Cr-1Mo ferritic-martensitic steels (Grade 91), a thermo-mechanical treatment consisting of aus-forging/rolling and subsequent aus-aging is proposed which promotes the formation of stable MX carbonitrides prior to martensitic transformation. Such MX remains undissolved during welding process, even in FGHAZ, which successfully improves the cross-weld creep properties. Another approach is to develop a new fully ferrtic, creep-resistant FeCrAl alloy which is essentially free from Type IV failure issues. Fe-30Cr-3Al base alloys with minor alloying additions were developed which achieved a combination of good oxidation/corrosion resistance and improved tensile and creep performance comparable or superior to Grade 92 steel.

  18. Small punch creep test in a 316 austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Saucedo-Munoz, M. L.; Komazaki, S. I.; Hashida, T.; Lopez-Hirata, V. M.

    2015-03-30

    The small punch creep test was applied to evaluate the creep behavior of a 316 type austenitic stainless steel at temperatures of 650, 675 and 700 degree centigrade. The small punch test was carried out using a creep tester with a specimen size of 10x10x0.3 mm at 650, 675 and 700 degree centigrade using loads from 199 to 512 N. The small punch creep curves show the three stages found in the creep curves of the conventional uniaxial test. The conventional creep relationships which involve parameters such as creep rate, stress, time to rupture and temperature were followed with the corresponding parameters of small punch creep test and they permitted to explain the creep behavior in this steel. The mechanism and activation energy of the deformation process were the grain boundary sliding and diffusion, respectively, during creep which caused the intergranular fracture in the tested specimens. (Author)

  19. Low-temperature creep of austenitic stainless steels

    Science.gov (United States)

    Reed, R. P.; Walsh, R. P.

    2017-09-01

    Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

  20. Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior

    Science.gov (United States)

    Tewari, S.N.

    1995-01-01

    Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.

  1. Negative creep during compressive creep of as-cast ZA27 alloy

    Institute of Scientific and Technical Information of China (English)

    魏晓伟; 沈保罗; 易勇

    2003-01-01

    The negative creep during compressive creep deformation of as-cast ZA27 alloy was investigated at the temperature range of 20-160℃ and at compressive stress levels from 50-137.5MPa with special apparatus. Results show that the negative creep in the alloy occurred respectively at 20℃ (50MPa, 87.5MPa and 100MPa), 60℃(50MPa and 87.5MPa) and 100℃(50MPa). According to the phase transformation and theoretical analysis, the negative creep resulted from volume expansion caused by four-phase transformation α+ε→T′+η in the alloy. The theoretical analysis is consistent with the experiment results. And the values of negative creep depended on the difference between the compressive creep deformation and the volume expansion.

  2. Simple Creep Test For Ceramic Fibers

    Science.gov (United States)

    Dicarlo, James A.; Morscher, Gregory N.

    1994-01-01

    Simple bend-stress-relaxation test yields information on creep-related properties of polycrystalline ceramic fibers. Determination of these properties important part of efforts to develop ceramic composite materials that retain mechanical strength and resistance to creep at high temperatures. Present test measures effects of time, temperature, and applied strain on creep-related relaxation of bend stress in ceramic fiber of almost any diameter in almost any environment, without need for contact sensors. Degree of relaxation of bend stress determined from radii of curvature.

  3. Modeling creep behavior of fiber composites

    Science.gov (United States)

    Chen, J. L.; Sun, C. T.

    1988-01-01

    A micromechanical model for the creep behavior of fiber composites is developed based on a typical cell consisting of a fiber and the surrounding matrix. The fiber is assumed to be linearly elastic and the matrix nonlinearly viscous. The creep strain rate in the matrix is assumed to be a function of stress. The nominal stress-strain relations are derived in the form of differential equations which are solved numerically for off-axis specimens under uniaxial loading. A potential function and the associated effective stress and effective creep strain rates are introduced to simplify the orthotropic relations.

  4. Creep of plain weave polymer matrix composites

    Science.gov (United States)

    Gupta, Abhishek

    Polymer matrix composites are increasingly used in various industrial sectors to reduce structural weight and improve performance. Woven (also known as textile) composites are one class of polymer matrix composites with increasing market share mostly due to their lightweight, their flexibility to form into desired shape, their mechanical properties and toughness. Due to the viscoelasticity of the polymer matrix, time-dependent degradation in modulus (creep) and strength (creep rupture) are two of the major mechanical properties required by engineers to design a structure reliably when using these materials. Unfortunately, creep and creep rupture of woven composites have received little attention by the research community and thus, there is a dire need to generate additional knowledge and prediction models, given the increasing market share of woven composites in load bearing structural applications. Currently, available creep models are limited in scope and have not been validated for any loading orientation and time period beyond the experimental time window. In this thesis, an analytical creep model, namely the Modified Equivalent Laminate Model (MELM), was developed to predict tensile creep of plain weave composites for any orientation of the load with respect to the orientation of the fill and warp fibers, using creep of unidirectional composites. The ability of the model to predict creep for any orientation of the load is a "first" in this area. The model was validated using an extensive experimental involving the tensile creep of plain weave composites under varying loading orientation and service conditions. Plain weave epoxy (F263)/ carbon fiber (T300) composite, currently used in aerospace applications, was procured as fabrics from Hexcel Corporation. Creep tests were conducted under two loading conditions: on-axis loading (0°) and off-axis loading (45°). Constant load creep, in the temperature range of 80-240°C and stress range of 1-70% UTS of the

  5. Linear logarithmic model for concrete creep:II. Prediction formulas for description of creep behaviour

    OpenAIRE

    Larson, Mårten; Jonasson, Jan-Erik

    2003-01-01

    A reliable modelling of the young concrete creep behaviour is of great importance for consistent thermal crack risk estimations that shall contribute to assure a desired service lifetime and function of a structure. All-embracing creep tests aimed for thermal stress analyses are often very time consuming and thereby also costly to perform. Therefore thermal stress calculations in everyday engineering practice are often performed with standard sets of creep data involving no or very limited la...

  6. TRACKING GENE FLOW FROM A GENETICALLY MODIFIED CREEPING BENTGRASS -- METHODS, MEASURES AND LESSONS LEARNED

    Science.gov (United States)

    Creeping bentgrass (CBG) expressing an engineered gene for resistance to glyphosate herbicide is one of the first genetically modified (GM) perennial crops to undergo regulatory review for commercial release by the US Department of Agriculture Animal Plant Health and Inspection S...

  7. Creep strength and rupture ductility of creep strength enhanced ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Kushima, Hideaki; Sawada, Kota; Kimura, Kazuhiro [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan)

    2010-07-01

    Creep strength and rupture ductility of Creep Strength Enhanced Ferritic (CSEF) steels were investigated from a viewpoint of stress dependence in comparison with conventional low alloy ferritic creep resistant steels. Inflection of stress vs. time to rupture curve was observed at 50% of 0.2% offset yield stress for both CSEF and conventional ferritic steels. Creep rupture ductility tends to decrease with increase in creep exposure time, however, those of conventional low alloy steels indicate increase in the long-term. Creep rupture ductility of the ASME Grades 92 and 122 steels indicates drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of the ASME Grades 92 and 122 steels is well described by stress ratio to 0.2% offset yield stress, regardless of temperature. Drop of creep rupture ductility is caused by inhomogeneous recovery at the vicinity of prior austenite grain boundary, and remarkable drop of creep rupture ductility of CSEF steels should be derived from those stabilized microstructure. (orig.)

  8. Failure data specialization in quantitative risk assessments of process plants; Especializacao de dados de falha em analise quantitativa de riscos de plantas de processo

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, Antonio C.O. [Bayer S.A., Sao Paulo, SP (Brazil); Melo, P.F. Frutuoso e [Universidade Federal, Rio de Janeiro, RJ (Brazil). Coordenacao dos Programas de Pos-graduacao de Engenharia

    2005-07-01

    The aim of this paper is to show the Bayesian inference in reliability studies, which are used to failures rates updating in safety analyses. It is developed the impact of its using in quantitative risks assessments for industrial process plants. With this approach we find a structured and auditable way of showing the difference between an industrial installation with a good project and maintenance structure from another one that shows a low level of quality in these areas. In general the evidence from failures rates and as follow the frequency of occurrence from scenarios, which the risks taken in account in ERA, are taken from generics data banks, instead of, the installation in analysis. When using the plant data we need special effort to develop a data bank, that is, a maintenance managing system, which allows the data insertion as for example the SAP{sup R} and its PM module. (author)

  9. Creep Aging Behavior Characterization of 2219 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Lingfeng Liu

    2016-06-01

    Full Text Available In order to characterize the creep behaviors of 2219 aluminum alloy at different temperatures and stress levels, a RWS-50 Electronic Creep Testing Machine (Zhuhai SUST Electrical Equipment Company, Zhuhai, China was used for creep experiment at temperatures of 353~458 k and experimental stresses of 130~170 MPa. It was discovered that this alloy displayed classical creep curve characteristics in its creep behaviors within the experimental parameters, and its creep value increased with temperature and stress. Based on the creep equation of hyperbolic sine function, regression analysis was conducted of experimental data to calculate stress exponent, creep activation energy, and other related variables, and a 2219 aluminum alloy creep constitutive equation was established. Results of further analysis of the creep mechanism of the alloy at different temperatures indicated that the creep mechanism of 2219 aluminum alloy differed at different temperatures; and creek characteristics were presented in three stages at different temperatures, i.e., the grain boundary sliding creep mechanism at a low temperature stage (T < 373 K, the dislocation glide creep mechanism at a medium temperature stage (373 K ≤ T < 418 K, and the dislocation climb creep mechanism at a high temperature stage (T ≥ 418 K. By comparative analysis of the fitting results and experiment data, they were found to be in agreement with the experimental data, revealing that the established creep constitutive equation is suitable for different temperatures and stresses.

  10. Two-parameter Failure Model Improves Time-independent and Time-dependent Failure Predictions

    Energy Technology Data Exchange (ETDEWEB)

    Huddleston, R L

    2004-01-27

    A new analytical model for predicting failure under a generalized, triaxial stress state was developed by the author and initially reported in 1984. The model was validated for predicting failure under elevated-temperature creep-rupture conditions. Biaxial data for three alloy steels, Types 304 and 316 stainless steels and Inconel 600, demonstrated two to three orders of magnitude reduction in the scatter of predicted versus observed creep-rupture times as compared to the classical failure models of Mises, Tresca, and Rankine. In 1990, the new model was incorporated into American Society of Mechanical Engineers (ASME) Code Case N47-29 for design of components operating under creep-rupture conditions. The current report provides additional validation of the model for predicting failure under time-independent conditions and also outlines a methodology for predicting failure under cyclic, time-dependent, creep-fatigue conditions. The later extension of the methodology may have the potential to improve failure predictions there as well. These results are relevant to most design applications, but they have special relevance to high-performance design applications such as components for high-pressure equipment, nuclear reactors, and jet engines.

  11. Two-parameter Failure Model Improves Time-independent and Time-dependent Failure Predictions

    Energy Technology Data Exchange (ETDEWEB)

    Huddleston, R L

    2004-01-27

    A new analytical model for predicting failure under a generalized, triaxial stress state was developed by the author and initially reported in 1984. The model was validated for predicting failure under elevated-temperature creep-rupture conditions. Biaxial data for three alloy steels, Types 304 and 316 stainless steels and Inconel 600, demonstrated two to three orders of magnitude reduction in the scatter of predicted versus observed creep-rupture times as compared to the classical failure models of Mises, Tresca, and Rankine. In 1990, the new model was incorporated into American Society of Mechanical Engineers (ASME) Code Case N47-29 for design of components operating under creep-rupture conditions. The current report provides additional validation of the model for predicting failure under time-independent conditions and also outlines a methodology for predicting failure under cyclic, time-dependent, creep-fatigue conditions. The later extension of the methodology may have the potential to improve failure predictions there as well. These results are relevant to most design applications, but they have special relevance to high-performance design applications such as components for high-pressure equipment, nuclear reactors, and jet engines.

  12. Creep behavior in interlaminar shear of a Hi-Nicalon™/SiC–B{sub 4}C composite at 1200 °C in air and in steam

    Energy Technology Data Exchange (ETDEWEB)

    Ruggles-Wrenn, M.B., E-mail: marina.ruggles-wrenn@afit.edu; Pope, M.T.; Zens, T.W.

    2014-07-29

    Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200 °C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Similar creep strains were accumulated in air and in steam. Furthermore, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. The tested specimens were also examined using electron probe microanalysis (EPMA) with wavelength dispersive spectroscopy (WDS). Analysis of the fracture surfaces revealed significant surface oxidation, but only trace amounts of boron and carbon. Cross sectional analysis showed increasing boron concentration in the specimen interior.

  13. Creep behavior in interlaminar shear of a Hi-NicalonTM/ SiC-B4C composite at 1200∘C in air and in steam

    Directory of Open Access Journals (Sweden)

    Ruggles-Wrenn Marina

    2015-01-01

    Full Text Available Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1200∘C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI. The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-NicalonTM fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16–22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Similar creep strains were accumulated in air and in steam. Furthermore, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. The tested specimens were also examined using electron probe microanalysis (EPMA with wavelength dispersive spectroscopy (WDS. Analysis of the fracture surfaces revealed significant surface oxidation, but only trace amounts of boron and carbon. Cross sectional analysis showed increasing boron concentration in the specimen interior.

  14. Documentation for the viscoplastic and creep program

    DEFF Research Database (Denmark)

    Bellini, Anna

    2004-01-01

    of this workpackage is to simulate creep behavior of aluminum cast samples subjected to high temperature. In this document a two-state variables unified model is applied in order to simulate creep behavior and time-dependent metallurgical changes. The fundamental assumption of the unified theory is that creep...... and viscoplasticity, which are both irreversible strains developed because of dislocations motion in the material structure, can be modelled through the implementation of a similar plastic strain velocity law, generally called flow rule. The document shows how to obtain the material data needed for the simulation...... is run using the material data obtained through the mentioned experimental study. The results obtained for the simulation of tensile tests and of creep tests are compared with experimental curves, showing a good agreement. Moreover, the document describes the results obtained during the first...

  15. Implications of Jeffreys-Lomnitz Transient Creep

    Science.gov (United States)

    Strick, Ellis

    1984-01-01

    In 1958 Jeffreys proposed a power law generalization of the logarithmic transient creep earlier attributed to Lomnitz. Although Jeffreys' power law form was admittedly defective in that it became unbounded at infinite time, he did apply it to the viscoelastic behavior of the earth-moon system. Since then it has been successfully applied by many investigators to mantle rehology and Chandler wobble. Experimental seismic studies indicate that most rock types exhibit the almost constant Q behavior which Lomnitz showed to be associated with his logarithmic creep. In this paper, we study not only the Q behavior related to Jeffreys' power law creep but also other mechanical properties such as a precise spring-dashpot ladder network realization are developed. In addition, a very simple physically realizable modification of this ladder network leads to a boundedness at long times of Jeffreys' creep in a manner which does not affect his successful application at finite times.

  16. Rock bending creep and disturbance effects

    Institute of Scientific and Technical Information of China (English)

    付志亮; 郑颖人; 刘元雪

    2008-01-01

    The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting the self-developed gravitation level style rock creep test machine and bending creep test system,and the constitutive equations were established.It is found that fracture morphology of rock beams under no disturbance load is regular,cracking position of fractures is on part of loading concentration,the crack starts from a neutral plane.However,fracture morphology of rock beams under disturbance load is irregular,cracking position of fractures deviates from a neutral plane.Delayed instability of rock beam occurs for some time under constant disturbance load.When disturbance load is beyond a certain range,suddenly instability of occurs rock beam in a certain time.The results show that there is a guiding significance for creep stability in the geotechnical engineering fields.

  17. Analytic Creep Durability of Rotating Uniform Disks

    Directory of Open Access Journals (Sweden)

    Yuriy Nyashin

    1998-01-01

    Full Text Available Turbine disks of aircraft engines in operation are subjected to alternating thermocyclic deformation under high temperatures. Operation gives rise to sufficiently high stresses and subsequent creep damaging effects.

  18. Inversion of hysteresis and creep operators

    Science.gov (United States)

    Krejčí, Pavel; Al Janaideh, Mohammad; Deasy, Fergal

    2012-05-01

    The explicit inversion formula for rate dependent Prandtl-Ishlinskii operators is extended to cases without the threshold dilation condition. This solves a problem in hysteresis and creep modeling of magnetostrictive behavior.

  19. Creep of frozen soil by damage mechanics

    Institute of Scientific and Technical Information of China (English)

    苗天德; 魏雪霞; 张长庆

    1995-01-01

    A microstructure damage theory for creep of frozen soil under the frame of damage mechan-ics is presented.Based on the test study and microscope observation,several internal variables are chosen tocharacterize the microstructure changes and the evolution equations of these internal variables are developed.The theory can describe both the "hardening" and "softening" behavior in the creep process.A detailed analysis hasbeen made for the uniaxial compressure and compared with the test data.

  20. Hydrogen diffusion and effect on degradation in welded microstructures of creep-resistant low-alloyed steels

    Energy Technology Data Exchange (ETDEWEB)

    Rhode, Michael

    2016-04-04

    The main challenge for the future is to further increase the power plant thermal efficiency independent of the type of power plant concept, i.e. fossil-fired or nuclear power plant, where the material selection can directly affect reduction of CO{sub 2} emissions. In power plant design, welding is the most applied manufacturing technique in component construction. The necessary weld heat input causes metallurgical changes and phase transitions in the heat affected zone (HAZ) of the base materials and in the deposited weld metal. The weld joint can absorb hydrogen during welding or in later service - This absorption can cause degradation of mechanical properties of the materials, and in certain loading conditions, hydrogen-assisted cold cracks can occur. This cracking phenomenon can appear time delayed due to the temperature dependency of the hydrogen diffusion and the presence of a ''critical'' hydrogen concentration. Additionally, each specific weld microstructure shows a certain hydrogen diffusion and solubility that contribute to susceptibility of the cracking phenomenon. Therefore hydrogen cannot be neglected as possible failure effect, which was identified recently in the case of T24 creep-resistant tube-to-tube weld joints. It is necessary to identify and assess the hydrogen effect in weld joints of low-alloyed steel grades for to improve further early detection of possible failures. For each specific weld joint microstructure, it is necessary to separate the interdependencies between mechanical load and the hydrogen concentration. The diffusivity and solubility must be considered to identify hydrogen quantities in the material at any given time. In this case, the effects of mechanical loading were dealt with independently. For the characterization of the mechanical properties, hydrogen charged tensile specimens were investigated for the base materials and thermally simulated HAZ microstructures. The hydrogen diffusion was characterized

  1. An analysis of the annual probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP)

    Energy Technology Data Exchange (ETDEWEB)

    Greenfield, M.A. [Univ. of California, Los Angeles, CA (United States); Sargent, T.J.

    1995-11-01

    The Environmental Evaluation Group (EEG) previously analyzed the probability of a catastrophic accident in the waste hoist of the Waste Isolation Pilot Plant (WIPP) and published the results in Greenfield (1990; EEG-44) and Greenfield and Sargent (1993; EEG-53). The most significant safety element in the waste hoist is the hydraulic brake system, whose possible failure was identified in these studies as the most important contributor in accident scenarios. Westinghouse Electric Corporation, Waste Isolation Division has calculated the probability of an accident involving the brake system based on studies utilizing extensive fault tree analyses. This analysis conducted for the U.S. Department of Energy (DOE) used point estimates to describe the probability of failure and includes failure rates for the various components comprising the brake system. An additional controlling factor in the DOE calculations is the mode of operation of the brake system. This factor enters for the following reason. The basic failure rate per annum of any individual element is called the Event Probability (EP), and is expressed as the probability of failure per annum. The EP in turn is the product of two factors. One is the {open_quotes}reported{close_quotes} failure rate, usually expressed as the probability of failure per hour and the other is the expected number of hours that the element is in use, called the {open_quotes}mission time{close_quotes}. In many instances the {open_quotes}mission time{close_quotes} will be the number of operating hours of the brake system per annum. However since the operation of the waste hoist system includes regular {open_quotes}reoperational check{close_quotes} tests, the {open_quotes}mission time{close_quotes} for standby components is reduced in accordance with the specifics of the operational time table.

  2. Creep behaviour of a polymer-based underground support liner

    Science.gov (United States)

    Guner, Dogukan; Ozturk, Hasan

    2017-09-01

    All underground excavations (tunnels, mines, caverns, etc.) need a form of support to ensure that excavations remain safe and stable for the designed service lifetime. In the last decade, a new support material, thin spray-on liner (TSL) has started to take place of traditional underground surface supports of bolts and shotcrete. TSLs are generally cement, latex, polymer-based and also reactive or non-reactive, multi-component materials applied to the rock surface with a layer of few millimeter thickness. They have the advantages of low volume, logistics, rapid application and low operating cost. The majority of current TSLs are two-part products that are mixed on site before spraying onto excavation rock surfaces. Contrary to the traditional brittle supports, the high plastic behaviour of TSLs make them to distribute the loads on larger lining area. In literature, there is a very limited information exist on the creep behavior of TSLs. In this study, the creep behavior of a polymer-based TSL was investigated. For this purpose, 7-day cured dogbone TSL specimens were tested under room temperature and humidity conditions according to ASTM-D2990 creep testing standard. A range of dead weights (80, 60, 40, and 20 % of the tensile strength) were applied up to 1500 hours. As a result of this study, the time-dependent strain behavior of a TSL was presented for different constant load conditions. Moreover, a new equation was derived to estimate tensile failure time of the TSL for a given loading condition. If the tensile stress acting on the TSL is known, the effective permanent support time of the TSL can be estimated by the proposed relationship.

  3. Creep fatigue assessment for EUROFER components

    Energy Technology Data Exchange (ETDEWEB)

    Özkan, Furkan, E-mail: oezkan.furkan@partner.kit.edu; Aktaa, Jarir

    2015-11-15

    Highlights: • Design rules for creep fatigue assessment are developed to EUROFER components. • Creep fatigue assessment tool is developed in FORTRAN code with coupling MAPDL. • Durability of the HCPB-TBM design is discussed under typical fusion reactor loads. - Abstract: Creep-fatigue of test blanket module (TBM) components built from EUROFER is evaluated based on the elastic analysis approach in ASME Boiler Pressure Vessel Code (BPVC). The required allowable number of cycles design fatigue curve and stress-to-rupture curve to estimate the creep-fatigue damage are used from the literature. Local stress, strain and temperature inputs for the analysis of creep-fatigue damage are delivered by the finite element code ANSYS utilizing the Mechanical ANSYS Parametric Design Language (MAPDL). A developed external FORTRAN code used as a post processor is coupled with MAPDL. Influences of different pulse durations (hold-times) and irradiation on creep-fatigue damage for the preliminary design of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) are discussed for the First Wall component of the TBM box.

  4. Examination of observed and predicted measures of creep cavitation damage accumulation

    Energy Technology Data Exchange (ETDEWEB)

    Brear, J.M.; Church, J.M. [ERA Technology Ltd., Leatherhead (United Kingdom); Eggeler, G. [University of Bochum-Ruhr (Germany)

    1998-12-31

    Brittle intergranular cavitation represents a primary degradation mechanism for high temperature plant operating within the creep range. Fundamental to formulating estimates of remanent life, or consumed life fraction for such components are: the observation and quantification of the level of actual creep cavitation, typically using an A-parameter type approach, and the correlation of observed creep damage accumulation with some phenomenological model which characterizes the rate of damage evolution and, thereby, rupture lifetime. The work described here treats inhomogeneous damage accumulation - in otherwise uniform material and loading situations. Extensions to the A-parameter are considered as a practical measure of damage localization and an extension of the Kachanov-Rabotnov continuum damage mechanics model is proposed to allow theoretical treatment. (orig.) 4 refs.

  5. Cr concentration dependence of overestimation of long term creep life in strength enhanced high Cr ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Maruyama, K., E-mail: maruyama@material.tohoku.ac.j [Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aobayama, Sendai 980-8579 (Japan); Ghassemi Armaki, H.; Chen, R.P.; Yoshimi, K. [Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aobayama, Sendai 980-8579 (Japan); Yoshizawa, M.; Igarashi, M. [Corporate Research and Development Laboratories, Sumitomo Metal Industry, Ltd., 1-8 Fuso-Cho, Amagasaki 660-0891 (Japan)

    2010-06-15

    Creep rupture data and microstructural degradation during aging of high Cr ferritic boiler steels with enhanced creep strength have been studied with special attention to prediction of long term creep rupture life. Tempered lath martensite structure in the high Cr ferritic steels remains unchanged during short term aging, whereas static recovery of the lath martensite structure proceeds when diffusion distance during aging becomes sufficiently long as is the case in long term creep. The static recovery brings about premature failure in long term creep and decreases in apparent activation energy for creep life. The decrease in activation energy is responsible for overestimation of rupture life reported in strength enhanced high Cr ferritic steels. The boundary from a short term region with high activation energy Q{sub H} to a long term region with low activation energy Q{sub L} moves towards longer time with decreasing Cr concentration. The difference in activation energy (Q{sub H} - Q{sub L}) primarily determines the extent of overestimation of rupture life predicted from short term data. In general, the extent of overestimation is less serious at 9%Cr as compared to 12%Cr.

  6. Damage prediction of HP40Nb steel with coupled creep and carburization based on the continuum damage mechanics

    Institute of Scientific and Technical Information of China (English)

    Limin SHEN; Jianming GONG; Yong JIANG; Luyang GENG

    2012-01-01

    HP40Nb steel,used as a candidate material for ethylene cracking furnace tube,suffers creep and carburization damage from the complex environment of high temperature,high carbon potential and low oxygen partial pressure,and they lead to failure of the furnace tubes ahead of designed life.In order to investigate damage evolution under the complex condition,coupled creep damage and carburization damage constitutive equations were developed according to continuum damage mechanics theory.Based on the finite element ABAQUS code,user subroutines were developed for analyzing damage evolution of ethylene furnace tube under the action of coupled creepcarburization.The results show that carburization accelerates the damage process dramatically,damage value reaches the critical value along the inner surface after serving for 75,000 h under the action of creep-carburization,meanwhile the damage value is only 0.53 along the outer surface after operating the same time under the action of creep alone,which means that microcracks are generated along the inner surface under the action of coupled creep-carburization,fracture begins along the outer surface of tube under the action of creep alone.

  7. Creep behaviour and microstructural evolution in P23/P91 dissimilar welds

    Energy Technology Data Exchange (ETDEWEB)

    Vodarek, V. [Technical Univ. of Ostrava (Czech Republic); Kubon, Z.; Strilkova, L. [MATERIALS AND METALLURGICAL RESEARCH Ltd., Ostrava (Czech Republic); Hainsworth, S.V. [Leicester Univ. (United Kingdom). Dept. of Engineering

    2010-07-01

    The structural integrity of welded components operated at elevated temperatures is of key importance in power plant applications. Long-term creep exposure of dissimilar welds is accompanied by redistribution of interstitial elements which strongly affects microstructural evolution in the vicinity of the fusion zone between low and high alloy materials. This paper summarises results of studies on creep rupture properties and minor phase evolution in the P23/P71 heterogeneous welds duing creep exposure at 500, 550 and 600 C for durations exceeding 60 000 hours. The composition of filler material in Weld A corresponded to that of P91 steel, whilst for Weld B the low alloy filler material of P23 type composition was used. Results of creep rupture tests on the cross weld specimens are close to, or slightly below, the lower limit of the {+-}20% scatter band around the standardized curve for creep strength of the P23 steel. Experimental data on microstructural evolution have been compared with results of thermodynamic and kinetic simulations. The predicted minor phase evolution close to the P23/P91 interface was confirmed by microstructural investigations. Some differences between calculations and experimental studies were found for the P23 steel. It was demonstrated that undissolved fine MX particles in the partly decarburized zone of the P23 (WM23) steel significantly delayed recrystallization of the bainitic matrix. (orig.)

  8. Detection of generator bearing inner race creep by means of vibration and temperature analysis

    DEFF Research Database (Denmark)

    Skrimpas, Georgios Alexandros; Dragiev, Ivaylo G.; Hilmisson, Reynir

    2015-01-01

    damages and development. Detection of bearing creep can be achieved reliably based on continuous trending of the amplitude of vibration running speed harmonic and temperature absolute values. In order to decrease the number of condition indicators which need to be assessed, it is proposed to exploit......Vibration and temperature analysis are the two dominating condition monitoring techniques applied to fault detection of bearing failures in wind turbine generators. Relative movement between the bearing inner ring and generator axle is one of the most severe failure modes in terms of secondary...... a weighted average descriptor calculated based on the 3rd up to 6th harmonic orders. Two cases of different bearing creep severity are presented, showing the consistency of the combined vibration and temperature data utilization. In general, vibration monitoring reveals early signs of abnormality several...

  9. Growth and physiological responses of creeping bentgrass (Agrostis stolonifera) to elevated carbon dioxide concentrations

    OpenAIRE

    Patrick Burgess; Bingru Huang

    2014-01-01

    The atmospheric carbon dioxide level has increased and is predicted to continue increasing, which may affect various aspects of plant growth. The objective of this study was to investigate the effects of doubling the carbon dioxide level on the growth and physiological activities of a widely utilized cool-season turfgrass species, creeping bentgrass (Agrostis stolonifera L. ‘Penncross’). ‘Penncross’ plants were established in fritted clay medium and maintained under well-irrigated and well-fe...

  10. Failure Criteria for Reinforced Materials

    DEFF Research Database (Denmark)

    Rathkjen, Arne

    Failure of materials is often characterized as ductile yielding, brittle fracture, creep rupture, etc., and different criteria given in terms of different parameters have been used to describe different types of failure. Only criteria expressing failure in terms of stress are considered in what...... place until the matrix, the continuous component of the composite, fails. When an isotropic matrix is reinforced as described above, the result is an anisotropic composite material. Even if the material is anisotropic, it usually exhibits a rather high degree of symmetry and such symmetries place...... certain restrictions on the form of the failure criteria for anisotropic materials. In section 2, some failure criteria for homogenous materials are reviewed. Both isotropic and anisotropic materials are described, and in particular the constraints imposed on the criteria from the symmetries orthotropy...

  11. Preliminary Investigations of Creep Strain of Neogene Clay from Warsaw in Drained Triaxial Tests Assisted by Computed Microtomography

    Science.gov (United States)

    Kaczmarek, Łukasz Dominik; Dobak, Paweł Józef; Kiełbasiński, Kamil

    2017-06-01

    The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly "brittle" character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.

  12. Demonstration of creep during filtration

    DEFF Research Database (Denmark)

    Christensen, Morten Lykkegaard; Bugge, Thomas Vistisen; Kirchheiner, Anders Løvenbalk

    The classical filtration theory assumes a unique relationship between the local filter cake porosity and the local effective pressure. For a number of compressible materials, it has however been observed that during the consolidation stage this may not be the case. It has been found that the prod......The classical filtration theory assumes a unique relationship between the local filter cake porosity and the local effective pressure. For a number of compressible materials, it has however been observed that during the consolidation stage this may not be the case. It has been found...... that the production of filtrate also depends on the characteristic time for the filter cake solids to deform. This is formulated in the Terzaghi-Voigt model in which a secondary consolidation is introduced. The secondary consolidation may be visualized by plots of the relative cake deformation (U) v.s. the square...... magnitude as the primary consolidation (defined by the hydraulic retardation), the creep phenomenon may occur during filtration. This will lead to Ruth's plots characterized by a concave with two (more or less) distinct slopes. The slopes are defined by the relationship between the porosity...

  13. The investigation of expanded polystyrene creep behaviour

    Directory of Open Access Journals (Sweden)

    Zhukov Aleksey

    2017-01-01

    Full Text Available The results obtained in long-term testing under constant compressive stress of the cut from the Slabs EPS 50/100 and EPS 150 with the density ranging from 15 to 24 kg/m3, which were manufactured by the same manufacturer by foaming EPS solid granules (beads in closed volume. The creep strain of the above described specimens was used as a criterion for estimating the deformability of the EPS slabs under long-term compressive stress. It was measured using special stands EN 1606, maintaining constant stress during the fixed time interval tn=122 days. Creep strains were determined by the methods described in EN 1606 for constant stress σc=0.35σ10% (compressive stress σ10% was determined in accordance with EN 826:2013. The long-term compressive stress measurement error did not exceed 1 %, while the creep strain measurement error was not larger than 0,005 mm. The tests were conducted at the ambient temperature of (23±2°С and relative humidity of (50±5 %.The long-term constant compressive load σc=0.35σ10%. The method of mathematical and statistical experimental design optimization models taking into account the thickness of specimens is proposed to determine the creep compliance Ic (tn the creep strain εc (tn and predictive point estimate of creep strain εc (T. Graphical interpretation of the abstained models is also presented. It should be noted that the abstained equations may be used in practice for estimating the creep strains at time tn=122 days and predictive estimates of εc (T for the load time of 10 years.

  14. PENGARUH RANGKAK CREEP PADA BANGUNAN TINGGI

    Directory of Open Access Journals (Sweden)

    David Budiono

    2003-01-01

    Full Text Available Inelastic deformation due to creep can cause dramatic change of end moment of beams. In this study the influence of creep to end moments is compared with the ones calculated using direct and sequential load methods. An approximate method using Equivalent Modulus of Elasticity is proposed. Four shear wall frame buildings, 10, 20, 30, and 40 stories with 30 cm shear wall are subjected to 5, 10, 15, and 20 years creep. It is shown that the difference between the 5, 10, 15, and 20 years creep are not significant. Compared to the sequential method, the direct method gives a better result to the creep. It is also shown that except for the 10 story building, the end moments caused by the development of creep deformation can cause cracks, thus the ability of the beams to redistribute the end moment must be assured. Abstract in Bahasa Indonesia : Perubahan bentuk inelastis yang disebabkan oleh rangkak (creep dapat menyebabkan perubahan momen pada tumpuan balok. Penelitian ini mempelajari pengaruh rangkak dan membandingkan hasil perhitungan yang diperoleh terhadap metode pembebanan langsung dan pembebanan sequential. Untuk memperhitungkan pengaruh rangkak, diusulkan suatu metode penyederhanaan di mana digunakan konsep Modulus Elastisitas Ekivalen. Dalam penelitian ini ditinjau 4 buah bangunan, yaitu bangunan 10, 20, 30 dan 40 lantai dengan dinding geser tebal 30 cm., pengaruh rangkak diperhatikan pada saat bangunan berumur 5, 10, 15, dan 20 tahun. Hasil penelitian menunjukkan bahwa tidak ada perbedaan yang berarti antara rangkak 5, 10, 15, dan 20 tahun. Dibandingkan dengan metode sequential, metode pembebanan langsung lebih mendekati hasil yang diberikan perhitungan dengan memasukkan pengaruh rangkak. Juga ditunjukkan bahwa selain pada bangunan 10 lantai, akibat rangkak akan terjadi retak pada beberapa tumpuan, sehingga dalam perencanaan harus dimungkinkan terjadinya redistribusi momen dari tumpuan ke lapangan.

  15. Ground failure in direct current systems of the Itaipu Hydroelectric Power Plant, Parana, Brazil. Impact in the operation; Falla a tierra en sistemas de corriente continua en la Central Hidroelectrica Itaipu, PR, Brasil. Impacto en la operacion

    Energy Technology Data Exchange (ETDEWEB)

    Soto Santacruz, Heriberto [Itaipu Binacional, Foz do Iguacu, PR (Brazil)]. E-mail: soto@itaipu.gov.py

    1998-07-01

    The objective of this work is to share with other companies the operation experience obtained by researching the direct current systems ground failure, in the Itaipu Hydroelectric Power Plant. During the research process electrical and/or electronic components can be damaged, and also human failures can occurred during the circuit connection and disconnection manoeuvres, necessary for the identification of the components causing the failures.

  16. The material concept in German light water reactors. Contribution to plant safety economic efficiency and failure provision; Das Werkstoffkonzept in deutschen Leichtwasserreaktoren. Beitrag zur Anlagensicherheit, Wirtschaftlichkeit und Schadensvorsorge

    Energy Technology Data Exchange (ETDEWEB)

    Ilg, Ulf [EnBW Kernkraft GmbH (Germany). Kernkraftwerk Philippsburg; Koenig, Guenter [EnBW Kernkraft GmbH (Germany). Kernkraftwerk Neckarwestheim; Erve, Manfred [AREVA NP GmbH, Erlangen (Germany)

    2008-07-01

    In the design and construction stage of nuclear power plants relevant decisions may affect the service life of a component, and thus influence safety and availability of the plant. The German ''basic safety concept'' has an important effect on the quality of the BOL (begin of life) status. Materials selection and qualification are of significant importance for the component lifetime and the profitability of the plant. Examples for the implementation of this concept are demonstrated for the steam generator tubing material Incoloy 800, the inside-plated ferritic compound tubes as control rod drive mechanism nozzle through the RPV head of BWR plants that are not susceptible for corrosion enhanced cracking that was observed for Inconel 600 tubing. A fundamental failure analysis of crack formation in Ti stabilized austenitic pipes of BWR plants found since 1993 were definitely identified as intergranular stress corrosion caused by a local sensitization of the welding process induced overheated structured in the heat affected zone. This allowed target-oriented mitigation measures. The safety culture implemented in German nuclear plants in connection with the break preclusion or integrity concept, respectively, including a continuous actualization with respect to the state-of-the art are the technical prerequisites for damage precaution and possible life time extension.

  17. Statistical analysis of the nuclear power plant equipment failure data in non-homogeneous flow of events

    Directory of Open Access Journals (Sweden)

    A.V. Antonov

    2016-12-01

    Full Text Available Operation of technical equipment involves three consecutive stages, each of which is characterized by a particular trend in the behavior of the failure flow parameter (FFP. The FFP value is approximately constant during normal operation. In this case, the equipment operation process is assumed to be temporally homogeneous and the reliability indicators are calculated by conventional methods. At the burn-in stage, the FFP decreases with time while increasing at the aging stage. Therefore, the operating times between two successive failures at the burn-in and aging stages are not similarly distributed random values and the flow of events cannot be assumed to be recurrent. It shall be taken into account in the reliability performance calculation that the flow of failures is temporally inhomogeneous. The paper describes a method to estimate the NPP equipment reliability indicators allowing the potential inhomogeneity of the failure flow to be taken into account. The specific nature of incoming statistical data on failures is shown. The application of the normalizing flow function model for the calculation of required reliability indicators is described. A practical example of an analysis of data on the Bilibino NPP CPS KNK-56 component failures is presented.

  18. 核电厂可修设备失效数据的处理方法%Failure Data Process Considering Trend of Failure Rate for Repairable Equipments in Nuclear Power Plants

    Institute of Scientific and Technical Information of China (English)

    王大林; 刘井泉; 黄祥瑞

    2011-01-01

    To solve the problem of failure data processing for reliability assessment for repairable facilities in nuclear power plants,a improved approach based on the renewal theory,trend testing and Weibull process(a kind of NHP)is proposed. After analyzing the error risk of traditional life data processing methods,an actual example is calculated based on the failure data of water-cooling pumps in generator stator at some nuclear power stations to compare the two processing methods. The result proves that Weibull process fitting reflects the failure characteristics of repairable equipments failures with less complicate calculation process.%针对核电厂设备可靠性评估对失效数据处理的需求,基于统计的经典寿命数据处理方法分析了核电厂可修设备失效数据处理中的缺点,提出应用基于威布尔( Weibull)过程的数据处理方法处理可修设备现场数据,并以某核电厂定子冷却水用泵失效数据为例进行了实例计算,对两种方法处理结果进行了比较分析.计算证明,引入威布尔过程拟合数据处理方法可更好地符合可修设备失效特点,且计算过程不复杂.

  19. Uniaxial and Multiaxial Creep Testing of Copper

    Energy Technology Data Exchange (ETDEWEB)

    Auerkari, Pertti; Holmstroem, Stefan; Veivo, Juha; Salonen, Jorma; Nenonen, Pertti; Laukkanen, Anssi [VTT Industrial Systems, Helsinki (Finland)

    2003-12-01

    Multiaxial (compact tension, CT) creep testing has been performed for copper with 79 ppm phosphorus and 60 ppm oxygen. The test load levels were selected according to results from preceding uniaxial creep testing and FE analysis of the CT specimens. Interrupted testing was used for metallographic inspection of the specimens for creep damage. After 7,900 h and 10,300 h of testing at 150 deg C and 46 MPa (reference stress), inspected CT specimens showed cavity indications with a low maximum density (<100/mm{sup 2}) and a typical maximum dimension of less than about 1 {mu}m near the notch tip. From previous experience on creep cavitation damage, the expected minimum life to crack initiation at the notch tip would be at least 40,000 hours, but could be considerably longer because the cavity indications are suspected to originate at least partly from precipitates in specimen preparation. The interrupted testing of CT specimens also showed a 'segregation zone' along some grain boundaries, mainly near the notch tip. This zone appears to contain more P and O than the surrounding matrix, but less than the narrow grain boundary films that are already present in the as-new material. The zone is readily etched and shows a relatively sharp edge towards the matrix without an obvious phase boundary. Using converted multiaxial (CT) testing results, the predicted isothermal uniaxial creep life at 150 deg C/46 MPa is about 1,900 years. The corresponding creep life directly predicted from uniaxial data is 3,100 years, when estimated from a parametric best fit expression according to PD6605. Although the two results are satisfactorily within a factor of two in time, the uncertainties in the extended extrapolations remain large. Further testing is recommended, with at least two creep enhancing factors present. Such testing could include notched creep testing at 120-180 deg C in a corrosive environment, and notched model vessel creep testing at elevated pressure. It is also

  20. Analysis of Superheater Work Under Creep Conditions

    Directory of Open Access Journals (Sweden)

    Piotr Duda

    2015-03-01

    Full Text Available The aim of this article is work modelling of superheater SH3. It is made of the austenitic stainless steel Super 304H. Its design temperature T is 604 C, and the design pressure P acting on the inner surface of the pipes is 284 bar. The high temperature is the reason of the superheater work under creep conditions. In this article calculations of the optimally mounted coil superheater SH3 are presented. The calculations are carried out first on the basis of the applicable European standards and with the help of the Auto Pipe program. Then, calculations are performed using the ANSYS program based on conducted creep tests and proposed creep equation. The coefficients in creep equation are determined based on the research conducted at the Instytut Metalurgii Żelaza in Gliwice. The model approximates the creep strain as the function of time and stress and this function is presented in the form of a three-dimensional surface . The results of calculations by both methods will be compared and conclusions will be presented. The performed analyzes can estimate the superheater coil remnant life and the usage after the selected time of its operation.

  1. Application of Failure Mode and Effect Analysis (FMEA), cause and effect analysis, and Pareto diagram in conjunction with HACCP to a corn curl manufacturing plant.

    Science.gov (United States)

    Varzakas, Theodoros H; Arvanitoyannis, Ioannis S

    2007-01-01

    The Failure Mode and Effect Analysis (FMEA) model has been applied for the risk assessment of corn curl manufacturing. A tentative approach of FMEA application to the snacks industry was attempted in an effort to exclude the presence of GMOs in the final product. This is of crucial importance both from the ethics and the legislation (Regulations EC 1829/2003; EC 1830/2003; Directive EC 18/2001) point of view. The Preliminary Hazard Analysis and the Fault Tree Analysis were used to analyze and predict the occurring failure modes in a food chain system (corn curls processing plant), based on the functions, characteristics, and/or interactions of the ingredients or the processes, upon which the system depends. Critical Control points have been identified and implemented in the cause and effect diagram (also known as Ishikawa, tree diagram, and the fishbone diagram). Finally, Pareto diagrams were employed towards the optimization of GMOs detection potential of FMEA.

  2. Corrosion Failure Analysis of Heat Exchangers in Nuclear Power Plant%核电站换热器腐蚀失效原因分析

    Institute of Scientific and Technical Information of China (English)

    姜媛媛; 刘飞华; 白荣国; 费克勋; 崔智勇; 孙永亮

    2012-01-01

      By researching corrosion failure cases of heat exchangers in nuclear power plant, the corrosion failure of heat exchangers were analyzed. The corrosion causes and mechanisms of the heat exchangers were analyzed. It also provided some suggestions on anti-corrosion and maintenance management.%  通过对大亚湾、岭澳核电站换热器失效案例进行调研,分析了引起核电站换热器腐蚀失效的原因,并进行机理分析,最后对核电站换热器的防腐蚀管理及维修策略管理提出建议。

  3. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    Energy Technology Data Exchange (ETDEWEB)

    Bimal K. Kad

    2005-02-28

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  4. Multi-scale investigation of tensile creep of ultra-high performance concrete for bridge applications

    Science.gov (United States)

    Garas Yanni, Victor Youssef

    achieving satisfactory microstructural refinement at the same temperature input despite the maximum temperature applied. For the first time, the presence of a 10 microm (394 micro inch) wide porous fiber-cementitious matrix interface was demonstrated by nanoindentation and SEM for non-thermally treated UHPC only. Tensile creep at 90 days increased by 64% and 46% upon eliminating fibers for thermally and non-thermally treated UHPC, respectively. Increases in creep upon reducing the fiber content suggested that fibers carry part of the sustained load and thus reduce creep. Tensile creep strain was proportional to the stress applied up to 60% of the ultimate strength. No tensile creep failure occurred for a period of 1 year for pre-cracked UHPC under stress level of 40%. Also, no tensile creep failure occurred for a period of 90 days under stress level of 60%. Tensile creep failure occurred at stress levels of 70% and 80%. This study showed that fibers cannot be accounted for as shear reinforcement in lieu of stirrups unless micro-defect-free fiber-matrix interface is achieved.

  5. Application range affected by software failures in safety relevant instrumentation and control systems of nuclear power plants; Auswirkungsbereiche von Softwarefehlern in sicherheitstechnisch wichtigen Einrichtungen von Kernkraftwerken

    Energy Technology Data Exchange (ETDEWEB)

    Jopen, Manuela; Mbonjo, Herve; Sommer, Dagmar; Ulrich, Birte

    2017-03-15

    This report presents results that have been developed within a BMUB-funded research project (Promotion Code 3614R01304). The overall objective of this project was to broaden the knowledge base of GRS regarding software failures and their impact in software-based instrumentation and control (I and C) systems. To this end, relevant definitions and terms in standards and publications (DIN, IEEE standards, IAEA standards, NUREG publications) as well as in the German safety requirements for nuclear power plants were analyzed first. In particular, it was found that the term ''software fault'' is defined differently and partly contradictory in the considered literature sources. For this reason, a definition of software fault was developed on the basis of the software life cycle of software-based I and C systems within the framework of this project, which takes into account the various aspects relevant to software faults and their related effects. It turns out that software failures result from latent faults in a software-based control system, which can lead to a non-compliant behavior of a software-based I and C system. Hereby a distinction should be made between programming faults and specification faults. In a further step, operational experience with software failures in software-based I and C systems in nuclear facilities and in nonnuclear sector was investigated. The identified events were analyzed with regard to their cause and impacts and the analysis results were summarized. Based on the developed definition of software failure and on the COMPSIS-classification scheme for events related to software based I and C systems, the COCS-classification scheme was developed to classify events from operating experience with software failures, in which the events are classified according to the criteria ''cause'', ''affected system'', ''impact'' and ''CCF potential''. This

  6. Creep behavior and in-depth microstructural characterization of dissimilar joints

    Directory of Open Access Journals (Sweden)

    F Kauffmann, T Klein, A Klenk and K Maile

    2013-01-01

    Full Text Available The 700 °C power plants currently under development will utilize Ni-base alloys such as alloy 617 for components to be operated at temperatures >650 °C. Due to economic reasons for components or parts of components which are subjected to temperatures <650 °C, 2% Cr or 9–12% Cr steels is used, depending on the required mechanical properties. This makes the dissimilar joining of Ni-base alloys and Cr steels a necessity in these plants. Experimental investigations show that these joints have to be identified as weak points with regard to damage development under creep and creep-fatigue loading. The present investigation focuses on welds between the alloy 617 and 2% Cr steel. Under creep load the fracture occurs near the fusion line between the 2% Cr steel base metal and alloy 617 weld metal. To explain the reasons for this fracture location, the microstructure of this fusion line was investigated using TEM and FIB techniques after welding and after creep loading. The TEM investigations have shown a small zone in the weld metal near the fusion line exhibiting chromium depletion and clearly reduced amounts of chromium carbides, leading to a weakening of this zone.

  7. Creep behavior and in-depth microstructural characterization of dissimilar joints

    Science.gov (United States)

    Kauffmann, F.; Klein, T.; Klenk, A.; Maile, K.

    2013-02-01

    The 700 °C power plants currently under development will utilize Ni-base alloys such as alloy 617 for components to be operated at temperatures >650 °C. Due to economic reasons for components or parts of components which are subjected to temperatures steels is used, depending on the required mechanical properties. This makes the dissimilar joining of Ni-base alloys and Cr steels a necessity in these plants. Experimental investigations show that these joints have to be identified as weak points with regard to damage development under creep and creep-fatigue loading. The present investigation focuses on welds between the alloy 617 and 2% Cr steel. Under creep load the fracture occurs near the fusion line between the 2% Cr steel base metal and alloy 617 weld metal. To explain the reasons for this fracture location, the microstructure of this fusion line was investigated using TEM and FIB techniques after welding and after creep loading. The TEM investigations have shown a small zone in the weld metal near the fusion line exhibiting chromium depletion and clearly reduced amounts of chromium carbides, leading to a weakening of this zone.

  8. Creep curve modelling of a conventionally cast nickel base superalloy

    Energy Technology Data Exchange (ETDEWEB)

    Lupinc, V.; Maldini, M. [CNR - IENI, Milan (Italy); Poggio, E.; Vacchieri, E. [Ansaldo Energia S.p.A., Genoa (Italy)

    2010-07-01

    Constant load creep tests on Rene 80, a nickel base superalloy for gas turbine blade application, were run in the temperature interval 800-950 C with applied stresses producing rupture times up to 1000 h. Creep curves are generally dominated by a long accelerating/tertiary creep that follows a relatively small decelerating/primary creep. No steady state stage has been observed. Analysis of the creep curves has shown that a single damage parameter can describe the long accelerating/tertiary state in the explored temperature range. The damage appears to be dependent on the accumulated creep strain and, as a first approximation, independent on the applied stress and temperature. The whole creep curve, primary and tertiary stages, has been modelled by a simple set of coupled differential equations obtained using the formalism of the Continuum Damage Mechanics. The proposed set of equations has an analytical solution, strain vs. time, for creep curves at constant temperature and stress. (orig.)

  9. Effect of loading rate on creep of phosphorous doped copper

    Energy Technology Data Exchange (ETDEWEB)

    Andersson-Oestling, Henrik C.M.; Sandstroem, Rolf (Swerea KIMAB (Sweden))

    2011-12-15

    Creep testing of copper intended for nuclear waste disposal has been performed on continuous creep tests machines at a temperature of 75 deg C. The loading time has been varied from 1 hour to 6 months. The rupture strain including both loading and creep strains does not differ from traditional dead weight lever creep test rigs. The loading strain increases with increasing loading time, at the expense of the creep strain. The time dependence of the creep strain has been modelled taking athermal plastic deformation and creep into account. During loading the contribution to the strain from the athermal plastic deformation dominates until the stress is close to the constant load level. When the constant load has been reached there is no more athermal strain and all of the strain comes from creep

  10. Creep Properties of Walikukun (Schouthenia ovata Timber Beams

    Directory of Open Access Journals (Sweden)

    Ali Awaludin

    2016-09-01

    Full Text Available This study presents an evaluation of creep constants of Walikukun (Schoutheniaovata timber beams when rheological model of four solid elements, which is obtained byassembling Kelvin and Maxwell bodies in parallel configuration, was adopted. Creep behaviorobtained by this method was further discussed and compared with creep behavior developedusing phenomenological model of the previous study. Creep data of previous study was deformationmeasurement of Walikukun beams having cross-section of 15 mm by 20 mm with a clearspan of 550 mm loaded for three weeks period under two different room conditions: with andwithout Air Conditioner. Creep behavior given by both four solid elements model and phenomenological(in this case are power functions had good agreement during the period of creepmeasurement, but they give different prediction of creep factor beyond this period. The powerfunction of phenomenological model could give a reasonable creep prediction, while for the foursolid elements model a necessary modification is required to adjust its long-term creep behavior.

  11. Homogenized Creep Behavior of CFRP Laminates at High Temperature

    Science.gov (United States)

    Fukuta, Y.; Matsuda, T.; Kawai, M.

    In this study, creep behavior of a CFRP laminate subjected to a constant stress is analyzed based on the time-dependent homogenization theory developed by the present authors. The laminate is a unidirectional carbon fiber/epoxy laminate T800H/#3631 manufactured by Toray Industries, Inc. Two kinds of creep analyses are performed. First, 45° off-axis creep deformation of the laminate at high temperature (100°C) is analyzed with three kinds of creep stress levels, respectively. It is shown that the present theory accurately predicts macroscopic creep behavior of the unidirectional CFRP laminate observed in experiments. Then, high temperature creep deformations at a constant creep stress are simulated with seven kinds of off-axis angles, i.e., θ = 0°, 10°, 30°, 45°, 60°, 75°, 90°. It is shown that the laminate has marked in-plane anisotropy with respect to the creep behavior.

  12. Creep Strength of Dissimilar Welded Joints Using High B-9Cr Steel for Advanced USC Boiler

    Science.gov (United States)

    Tabuchi, Masaaki; Hongo, Hiromichi; Abe, Fujio

    2014-10-01

    The commercialization of a 973 K (700 °C) class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project initiated in Japan in 2008. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 923 K to 973 K (650 °C to 700 °C), and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 923 K (650 °C). In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type IV failure in the heat-affected zone (HAZ) is a concern. Thus, the high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in weldments, is a candidate material for the Japanese A-USC boiler. In the present study, creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. In the HAZ of the high B-9Cr steels, fine-grained microstructures were not formed and the grain size of the base metal was retained. Consequently, the creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5 to 10 times longer than that of the conventional 9Cr steel welded joints at 923 K (650 °C).

  13. Creep Rupture Life Prediction Based on Analysis of Large Creep Deformation

    Directory of Open Access Journals (Sweden)

    YE Wenming

    2016-08-01

    Full Text Available A creep rupture life prediction method for high temperature component was proposed. The method was based on a true stress-strain elastoplastic creep constitutive model and the large deformation finite element analysis method. This method firstly used the high-temperature tensile stress-strain curve expressed by true stress and strain and the creep curve to build materials' elastoplastic and creep constitutive model respectively, then used the large deformation finite element method to calculate the deformation response of high temperature component under a given load curve, finally the creep rupture life was determined according to the change trend of the responsive curve.The method was verified by durable test of TC11 titanium alloy notched specimens under 500 ℃, and was compared with the three creep rupture life prediction methods based on the small deformation analysis. Results show that the proposed method can accurately predict the high temperature creep response and long-term life of TC11 notched specimens, and the accuracy is better than that of the methods based on the average effective stress of notch ligament, the bone point stress and the fracture strain of the key point, which are all based on small deformation finite element analysis.

  14. Creep motion of a model frictional system

    CERN Document Server

    Blanc, Baptiste; Géminard, Jean-Christophe

    2011-01-01

    We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the springs we observe a reptation of the chain. We account for the average reptation velocity theoretically. The velocity of small systems exhibits a series of plateaus as a function of the incline angle. Due to elastic e ects, there exists a critical amplitude below which the reptation is expected to cease. However, rather than a full stop of the creep, we observe in numerical simulations a transition between a continuous-creep and an irregular-creep regime when the critical amplitude is approached. The latter transition is reminiscent of the transition between the continuous and the irregular compaction of granular matter submitted to periodic temperature changes.

  15. Transitional Thermal Creep of Early Age Concrete

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Anders Boe; Damkilde, Lars; Freiesleben Hansen, Per

    1999-01-01

    Couplings between creep of hardened concrete and temperature/water effects are well-known. Both the level and the gradients in time of temperature or water content influence the creep properties. In early age concrete the internal drying and the heat development due to hydration increase the effect...... of these couplings. The purpose of this work is to set up a mathematical model for creep of concrete which includes the transitional thermal effect. The model govern both early age concrete and hardened concrete. The development of the material properties in the model are assumed to depend on the hydration process...... and the thermal activation of the water in the microstructure. The thermal activation is assumed to be governed by the Arrhenius principle and the activation energy of the viscosity of water is found applicable in the analysis of experimental data. Changes in temperature create an imbalance in the microstructure...

  16. Transitional Thermal Creep of Early Age Concrete

    DEFF Research Database (Denmark)

    Hauggaard, A. B.; Damkilde, L.; Hansen, Per Freiesleben

    1999-01-01

    Couplings between creep of hardened concrete and temperature/water effects are well-known. Both the level and the gradients in time of temperature or water content influence the creep properties. In early age concrete the internal drying and the heat development due to hydration increase the effect...... of these couplings. The purpose of this work is to set up a mathematical model for creep of concrete that includes the transitional thermal effect. The model governs both early age concrete and hardened concrete. The development of the material properties in the model is assumed to depend on the hydration process...... and the thermal activation of water in the microstructure. The thermal activation is assumed to be governed by the Arrhenius principle, and the activation energy of the viscosity of water is found applicable in the analysis of the experimental data. Changes in temperature create an imbalance in the microstructure...

  17. Measurement of local creep properties in stainless steel welds

    OpenAIRE

    Sakanashi, Y.; Gungor, S; Bouchard, J.

    2012-01-01

    A high temperature measurement system for creep deformation based on the digital image correlation (DIC) technique is described. The new system is applied to study the behaviour of a multi-pass welded joint in a high temperature tensile test and a load controlled creep test at 545°C. Spatially resolved tensile properties and time dependent creep deformation properties across a thick section type 316 stainless steel multi-pass welded joint are presented and discussed. Significantly lower creep...

  18. Nanoindentation investigation of creep properties of calcium silicate hydrates

    OpenAIRE

    Vandamme, Matthieu; ULM, Franz Josef

    2013-01-01

    The creep properties of calcium silicate hydrates (C-S-H) are assessed by means of nanoindentation creep experiments on a wide range of substoichiometric cement pastes. We observe that, after a few seconds, the measured creep compliance of C-S-H is very well captured by a logarithmic time function. The rate of the logarithmic creep is found to scale in a unique manner with indentation modulus, indentation hardness, and packing density, independent of processing, mix proportions, indenter geom...

  19. Electric failure on the reactor n.3 of the nuclear power plant of Dampierre; Defaillance electrique sur le reacteur n. 3 de la centrale nucleaire de Dampierre

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2007-05-15

    This note of information resumes the progress of the electric failure on the reactor n.3 of the nuclear power plant of Dampierre, the organization during the incident, it establishes then a comparison with the incident arisen to Forsmark in 2006 and reminds that it lead in an inspection on behalf of the Asn which noticed that all the procedures had been respected by the operators and did not noticed any abnormality in the maintenance. This event was classified at the level 1 of the international nuclear event scale (INES). (N.C.)

  20. Recommendation for Creep and Creep-fatigue assessment for P91 Components

    OpenAIRE

    Pohja, Rami; HOLMSTROM BJORN; LEE Hyeong-Yeon

    2015-01-01

    This report is based on the results and experience gained in assessing both public domain and MATTER data, some previously reported in the MATTER deliverable D4.5: “Creep-fatigue interaction rules for P91” and some assessed here. A number of methods, including interaction diagram based methods and simplified methods, have been compared for predicting the creep-fatigue life of P91 steel. The effect of cyclic softening on creep properties have been considered in the evaluations presented in thi...

  1. The Creep Properties of Fine Sandstone under Uniaxial Tensile Stress

    Directory of Open Access Journals (Sweden)

    Jiang Haifei

    2015-09-01

    Full Text Available A graduated uniaxial direct tensile creep test for fine sandstone is conducted by adopting a custom-designed direct tensile test device for rock. The experiment shows that the tensile creep of fine sandstone has similar creep curve patterns to those of compression creep, while the ratios of the creep strain to the total strain obtained in the tensile tests are substantially higher than those obtained for similar compression tests, which indicates that the creep ability of rock in the tensile process is higher than that in the uniaxial compression process. Based on the elastic modulus in the approximately linear portion of the obtained isochronous stress-strain curves of the tensile creep, the time dependence of the elasticity modulus for the Kelvin model is evaluated, and a revised generalized Kelvin model is obtained by substitution into the generalized Kelvin model. A new viscousplastic model is proposed to describe the accelerated creep properties, and this model is combined in series with the revised generalized Kelvin model to form a new nonlinear viscoelastic-plastic creep model that can describe the properties of attenuation creep, steady creep, and accelerated creep. Comparison of the test and theoretical curves demonstrates that they are nearly identical, which verifies the performance of the model.

  2. New constitutive model for the study of creeping solids

    Institute of Scientific and Technical Information of China (English)

    王世文; 杨兆建; 冯建玲

    2002-01-01

    In this paper, a incremental form of constitutive laws for creeping studies are proposed. The equations are based on the concept of creep hardening surface. Damage effects were introduced to the new constitutive relations to study solids creeping effects with pre-existing damages. The present formula is easy to be adopted into other numerical procedures such as finite element methods.

  3. Nanoindentation creep versus bulk compressive creep of dental resin-composites.

    Science.gov (United States)

    El-Safty, S; Silikas, N; Akhtar, R; Watts, D C

    2012-11-01

    To evaluate nanoindentation as an experimental tool for characterizing the viscoelastic time-dependent creep of resin-composites and to compare the resulting parameters with those obtained by bulk compressive creep. Ten dental resin-composites: five conventional, three bulk-fill and two flowable were investigated using both nanoindentation creep and bulk compressive creep methods. For nano creep, disc specimens (15mm×2mm) were prepared from each material by first injecting the resin-composite paste into metallic molds. Specimens were irradiated from top and bottom surfaces in multiple overlapping points to ensure optimal polymerization using a visible light curing unit with output irradiance of 650mW/cm(2). Specimens then were mounted in 3cm diameter phenolic ring forms and embedded in a self-curing polystyrene resin. Following grinding and polishing, specimens were stored in distilled water at 37°C for 24h. Using an Agilent Technologies XP nanoindenter equipped with a Berkovich diamond tip (100nm radius), the nano creep was measured at a maximum load of 10mN and the creep recovery was determined when each specimen was unloaded to 1mN. For bulk compressive creep, stainless steel split molds (4mm×6mm) were used to prepare cylindrical specimens which were thoroughly irradiated at 650mW/cm(2) from multiple directions and stored in distilled water at 37°C for 24h. Specimens were loaded (20MPa) for 2h and unloaded for 2h. One-way ANOVA, Levene's test for homogeneity of variance and the Bonferroni post hoc test (all at p≤0.05), plus regression plots, were used for statistical analysis. Dependent on the type of resin-composite material and the loading/unloading parameters, nanoindentation creep ranged from 29.58nm to 90.99nm and permanent set ranged from 8.96nm to 30.65nm. Bulk compressive creep ranged from 0.47% to 1.24% and permanent set ranged from 0.09% to 0.38%. There was a significant (p=0.001) strong positive non-linear correlation (r(2)=0.97) between bulk

  4. Failure Analysis towards Reliable Performance of Aero-Engines

    Directory of Open Access Journals (Sweden)

    T. Jayakumar

    1999-10-01

    Full Text Available Aero-engines are critical components whose reliable performance decides the primary safety of anaircrafthelicopter. This is met by rigorous maintenance schedule with periodic inspection/nondestructive testingof various engine components. In spite of these measures, failure of areo-engines do occur rather frequentlyin comparison to failure of other components. Systematic failure analysis helps one to identify root causeof the failure, thus enabling remedial measures to prevent recurrence of such failures. Turbine blades madeof nickel or cobalt-based alloys are used in aero-engines. These blades are subjected to complex loadingconditions at elevated temperatures. The main causes of failure of blades are attributed to creep, thermalfatigue and hot corrosion. Premature failure of blades in the combustion zone was reported in one of theaero-engines. The engine had both the compressor and the free-turbine in a common shaft. Detailedfailure analysis revealed the presence of creep voids in the blades that failed. Failure of turbine bladeswas also detected in another aero-engine operating in a coastal environment. In this failure, the protectivecoating on the blades was cracked at many locations. Grain boundary spikes were observed on these locations.The primary cause of this failure was the hot corrosion followed by creep damage

  5. FAILURES AND THE LIFE OF FURNACE TUBES

    Institute of Scientific and Technical Information of China (English)

    F.Z.Shen; Y.Ding; D.M.Hou; Z.P.Ning; Y.Lü; T.B.Dong; A.R.Tuohuti

    2004-01-01

    It is showed after the furnace tubes serviced for 8-10 years that the density of damage in the HAZ (heat affected zone) of the weld has higher than in parent metals, though the depth of damage is not equal to. By the test of creep crack growth, it is also acquired that under same mechanic parameter C* (t), the rate of creep crack growth in the HAZ is more than twice as fast as in parent metals. Two mechanisms (overheating and thermal shock) of failure occurred in an accident are presented. The stress of thermal shock is analyzed, in which the change of the elasticity modulus with the radius ET = f(r) is considered. Based on it, the safety region of the thermal shock is obtained. Finally, two sets of curves for the safe life are suggested which can facilitate to estimate the remaining life of HK-40 or HP-Nb tubes by their creep rupture data.

  6. The use of indentor testing in determining the creep properties locally - a review; Nyttjande av indentorteknik foer bestaemning av krypegenskaper lokalt - litteraturstudie

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Peder [Det Norske Veritas AB, Stockholm (Sweden)

    2000-07-01

    A review has been performed with the purpose of examining what has been published regarding the creep indentation technique. In the reference list a selected choice of published papers is presented. Furthermore, the use of the technique is explained, a presentation is made of the parameters that are possible to determine and, finally, the limitations of the technique are discussed. In the investigated publications, the theoretical aspects of the indentation technique are discussed, as well as the possibilities of applying the technique in practice. From the published material, it is obvious that creep indentation testing is a technique suitable when the creep deformation properties of a material are to be determined. It seems though, that the technique so far mostly has been used in academically designed experiments and not in a larger industrial scale. The creep indentation testing technique seems to be a good complement to conventional uniaxial creep testing in determining the creep deformation properties of a material. Especially in testing of the creep deformation properties of weldments and parts of weldments, such as HAZ, the indentation testing technique can prove to be advantageous, as only a small amount of material is needed. In the line of business of plants operating in the high temperature range, where materials experience creep, there should be an interest in seeing a development of a testing standard for the creep indentation technique. This could be performed by doing a more comprehensive analysis of a selected choice of published papers, putting together their differences and similarities after which verifying experiments are pursued. In the end, it should be possible to come up with a draft standard for creep indentation testing.

  7. The use of indentor testing in determining the creep properties locally - a review; Nyttjande av indentorteknik foer bestaemning av krypegenskaper lokalt - litteraturstudie

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Peder [Det Norske Veritas AB, Stockholm (Sweden)

    2000-07-01

    A review has been performed with the purpose of examining what has been published regarding the creep indentation technique. In the reference list a selected choice of published papers is presented. Furthermore, the use of the technique is explained, a presentation is made of the parameters that are possible to determine and, finally, the limitations of the technique are discussed. In the investigated publications, the theoretical aspects of the indentation technique are discussed, as well as the possibilities of applying the technique in practice. From the published material, it is obvious that creep indentation testing is a technique suitable when the creep deformation properties of a material are to be determined. It seems though, that the technique so far mostly has been used in academically designed experiments and not in a larger industrial scale. The creep indentation testing technique seems to be a good complement to conventional uniaxial creep testing in determining the creep deformation properties of a material. Especially in testing of the creep deformation properties of weldments and parts of weldments, such as HAZ, the indentation testing technique can prove to be advantageous, as only a small amount of material is needed. In the line of business of plants operating in the high temperature range, where materials experience creep, there should be an interest in seeing a development of a testing standard for the creep indentation technique. This could be performed by doing a more comprehensive analysis of a selected choice of published papers, putting together their differences and similarities after which verifying experiments are pursued. In the end, it should be possible to come up with a draft standard for creep indentation testing.

  8. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

    Science.gov (United States)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

  9. Multi Resolution In-Situ Testing and Multiscale Simulation for Creep Fatigue Damage Analysis of Alloy 617

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yongming [Arizona State Univ., Tempe, AZ (United States). School for Engineering of Matter, Transport and Energy; Oskay, Caglar [Vanderbilt Univ., Nashville, TN (United States). Dept. of Civil and Environmental Engineering

    2017-04-30

    This report outlines the research activities that were carried out for the integrated experimental and simulation investigation of creep-fatigue damage mechanism and life prediction of Nickel-based alloy, Inconel 617 at high temperatures (950° and 850°). First, a novel experimental design using a hybrid control technique is proposed. The newly developed experimental technique can generate different combinations of creep and fatigue damage by changing the experimental design parameters. Next, detailed imaging analysis and statistical data analysis are performed to quantify the failure mechanisms of the creep fatigue of alloy 617 at high temperatures. It is observed that the creep damage is directly associated with the internal voids at the grain boundaries and the fatigue damage is directly related to the surface cracking. It is also observed that the classical time fraction approach does not has a good correlation with the experimental observed damage features. An effective time fraction parameter is seen to have an excellent correlation with the material microstructural damage. Thus, a new empirical damage interaction diagram is proposed based on the experimental observations. Following this, a macro level viscoplastic model coupled with damage is developed to simulate the stress/strain response under creep fatigue loadings. A damage rate function based on the hysteresis energy and creep energy is proposed to capture the softening behavior of the material and a good correlation with life prediction and material hysteresis behavior is observed. The simulation work is extended to include the microstructural heterogeneity. A crystal plasticity finite element model considering isothermal and large deformation conditions at the microstructural scale has been developed for fatigue, creep-fatigue as well as creep deformation and rupture at high temperature. The model considers collective dislocation glide and climb of the grains and progressive damage accumulation of

  10. Renewal theory applied to creep and inelastic behavior of copper

    Energy Technology Data Exchange (ETDEWEB)

    Gibbons, K.A.; Cook, D.E. [Wright-Patterson Air Force Base, Dayton, OH (United States); Bearden, K.L. [Air Force Academy, Colorado Springs, CO (United States)

    1995-12-31

    A series of constant load creep tests on C11000 copper are described. The copper microstructure was closely controlled through appropriate heat treatment. Renewal theory was applied to interpret creep test data while developing the parameters of a general inelasticity model suitable for prediction. Creep experiments were predicted using renewal theory. Time varying load and load control stress-strain experiments were also predicted using renewal inelasticity theory. Results show that renewal theory is an efficient and effective approach to modeling creep of copper, needing a limited number of parameters. The simplicity of applying this theory to creep, variable load conditions, and a stress-strain experiment predictions for copper has been demonstrated.

  11. Creep rupture behavior of welded Grade 91 steel

    Energy Technology Data Exchange (ETDEWEB)

    Shrestha, Triratna [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Basirat, Mehdi [Department of Mechanical Engineering, University of Idaho, Moscow, ID 83844 (United States); Alsagabi, Sultan; Sittiho, Anumat [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Charit, Indrajit, E-mail: icharit@uidaho.edu [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Potirniche, Gabriel P. [Department of Mechanical Engineering, University of Idaho, Moscow, ID 83844 (United States)

    2016-07-04

    Creep rupture behavior of fusion welded Grade 91 steel was studied in the temperature range of 600 – 700 °C and at stresses of 50–200 MPa. The creep data were analyzed in terms of the Monkman-Grant relation and Larson-Miller parameter. The creep damage tolerance factor was used to identify the origin of creep damage. The creep damage was identified as the void growth in combination with microstructural degradation. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy and deformed microstructure examined by transmission electron microscopy, to further elucidate the rupture mechanisms.

  12. Creep properties and microstructure of the new wrought austenitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Vlasak, T.; Hakl, J.; Novak, P. [SVUM a.s., Prague (Czech Republic); Vyrostkova, A. [Slovak Academy of Sciences, Kosice (Slovakia). Inst. of Materials Research

    2010-07-01

    The contribution is oriented on the new wrought austenitic steel BGA4 (Cr23Ni15Mn6Cu3W1.5NbVMo) developed by the British Corus Company. Our main aim is to present creep properties studied in SVUM a.s. Prague during COST 536 programme. The dependencies of the creep strength, strength for specific creep strain and minimum creep strain rate were evaluated on the basis of long term creep tests carried out at temperature interval (625; 725) C. Important part of a paper is metallographic analysis. (orig.)

  13. Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J; Huang, M; Niu, X; soboyejo, W

    2006-10-09

    In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).

  14. Prognostic Significance of Creeping Proteinuria in the First Year After Transplantation.

    Science.gov (United States)

    Calabuig, Asunción Sancho; Martínez, Eva Gavela; Berga, Julia Kanter; Catalán, Sandra Beltrán; Bernabeu, Ana Isabel Avila; Mateu, Luis Manuel Pallardó

    2015-12-01

    Proteinuria changes have a prognostic significance in proteinuric nephropathies. Proteinuria has been related to kidney transplant outcomes, but there are no information about the impact of increasing proteinuria during the first year on long-term graft and patient survival. Retrospective cohort study of 591 kidney transplants to analyze the effect on long-term prognosis of: proteinuria at 3 (n = 591) and 12 (n = 583) months (no proteinuria: 150-299 mg/24 hours, 300-999 mg/24 hours, and ≥1 g/24 hours), and changes in proteinuria during the first year in such patients with proteinuria at 3 months (reduction ≥50% of proteinuria from 3 to 12 months, variation proteinuria") (n = 283). Higher levels of proteinuria, at both 3 and 12 months, were progressively related to lower graft survival (P Proteinuria at 12 months was related to mortality (P = 0.026). Creeping proteinuria, which was present in 35 patients (12.4%), was related to graft failure (P proteinuria at 3 months. De novo HLA antibody development was the only factor related to creeping proteinuria (hazard ratio, 2.946; 95% confidence interval, 1.158-7.491; P = 0.023). Creeping proteinuria during the first year was associated with long-term graft failure and mortality and could be considered as a surrogate of kidney disease progression in the renal transplant population, as it is in proteinuric nephropathies. It could also be viewed as an expression of immunological damage.

  15. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Bimal Kad

    2007-09-30

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program were to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined was iterative and intended to systematically (i) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, to be (ii) evaluated at 'in-service' loads at service temperatures and environments. Our report outlines the significant hoop creep enhancements possible via secondary cross-rolling and/or flow-forming operations. Each

  16. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Bimal K. Kad

    2006-09-30

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (a) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (b) evaluated at ''in-service'' loads at service temperatures and environments. In this 12th quarter of performance, program activities are concluded for Task 2 and continuing

  17. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes for Hoop Creep Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Bimal K. Kad

    2006-04-10

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (2) evaluated at ''in-service'' loads at service temperatures and environments. This research program is being conducted in collaboration with the DOE's Oak Ridge National

  18. Steady-state creep in the mantle

    Directory of Open Access Journals (Sweden)

    G. RANALLI

    1977-06-01

    Full Text Available SUMMARY - The creep equations for steady-state flow of olivine at high
    pressure and temperature are compared in an attempt to elucidate the rheological
    behaviour of the mantle. Results are presented in terms of applied deformation
    maps and curves of effective viscosity v depth.
    In the upper mantle, the transition stress between dislocation and diffusion
    creep is between 10 to 102 bar (as orders of magnitude for grain sizes from
    0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
    viscosity, than under oceans. Predominance of one creep mechanism above the
    others depends on grain size, strain rate, and volume fraction of melt; the
    rheological response can be different for different geodynamic processes.
    In the lower mantle, on the other hand, dislocation creep is predominant
    at all realistic grain sizes and strain rates. If the effective viscosity has to be only
    slightly higher than in the upper mantle, as some interpretations of glacioisostatic
    rebound suggest, then the activation volume cannot be larger than
    11 cm3 mole^1.

  19. Creep measurements on curing epoxy systems

    DEFF Research Database (Denmark)

    Kammer, Charlotte; Szabo, Peter

    1998-01-01

    The chemical curing of a stoichiometric mixture of the diglycidyl ether of bisphenol A and a 1,3-bis-(aminomethyl)-cyclohexane is studied.Creep experiments are combined with measurements in a Differential Scanning Calorimeter (DSC) to determine the change in bulk viscosity due to network formation....

  20. First principles model of carbonate compaction creep

    Science.gov (United States)

    Keszthelyi, Daniel; Dysthe, Dag Kristian; Jamtveit, Bjørn

    2016-05-01

    Rocks under compressional stress conditions are subject to long-term creep deformation. From first principles we develop a simple micromechanical model of creep in rocks under compressional stress that combines microscopic fracturing and pressure solution. This model was then upscaled by a statistical mechanical approach to predict strain rate at core and reservoir scale. The model uses no fitting parameter and has few input parameters: effective stress, temperature, water saturation porosity, and material parameters. Material parameters are porosity, pore size distribution, Young's modulus, interfacial energy of wet calcite, the dissolution, and precipitation rates of calcite, and the diffusion rate of calcium carbonate, all of which are independently measurable without performing any type of deformation or creep test. Existing long-term creep experiments were used to test the model which successfully predicts the magnitude of the resulting strain rate under very different effective stress, temperature, and water saturation conditions. The model was used to predict the observed compaction of a producing chalk reservoir.

  1. Irreversible thermodynamics of creep in crystalline solids

    Science.gov (United States)

    Mishin, Y.; Warren, J. A.; Sekerka, R. F.; Boettinger, W. J.

    2013-11-01

    We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a nonhydrostatically stressed multicomponent solid medium with nonconserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution, which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general expression for the entropy production rate and use it to identify of the relevant fluxes and driving forces and to formulate phenomenological relations among them taking into account symmetry properties of the material. As a simple application, we analyze a one-dimensional model of a bicrystal in which the grain boundary acts as a sink and source of vacancies. The kinetic equations of the model describe a creep deformation process accompanied by grain boundary migration and relative rigid translations of the grains. They also demonstrate the effect of grain boundary migration induced by a vacancy concentration gradient across the boundary.

  2. Creep measurements on curing epoxy systems

    DEFF Research Database (Denmark)

    Kammer, Charlotte; Szabo, Peter

    1998-01-01

    The chemical curing of a stoichiometric mixture of the diglycidyl ether of bisphenol A and a 1,3-bis-(aminomethyl)-cyclohexane is studied.Creep experiments are combined with measurements in a Differential Scanning Calorimeter (DSC) to determine the change in bulk viscosity due to network formation....

  3. Creep of granulated loose-fill insulation

    DEFF Research Database (Denmark)

    Rasmussen, Torben Valdbjørn

    with SP-Building Physics in Sweden and VTT Building Technology in Finland. For the round robin test a cellulosic fibre insulation material was used. The proposed standardised method for creep tests and theories are limited to cases when the granulated loose-fill material is exposed to a constant...

  4. Time constant of logarithmic creep and relaxation

    CSIR Research Space (South Africa)

    Nabarro, FRN

    2001-07-15

    Full Text Available of logarithmic creep have been proposed, the work-hardening of a set of barriers to dislocation motion, all having the same activation energy, or the progressive exhaustion of the weaker barriers in a set which has a distribution of activation energies...

  5. Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

    Energy Technology Data Exchange (ETDEWEB)

    Celine Cabet; L. Carroll; R. Wright; R. Madland

    2011-05-01

    Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

  6. Creep properties of aged duplex stainless steels containing [sigma] phase

    Energy Technology Data Exchange (ETDEWEB)

    Shek, C.H.; Wong, K.W.; Lai, J.K.L. (City Univ. of Hong Kong, Kowloon (Hong Kong). Dept. of Physics and Materials Science); Li, D.J. (Department of Materials Engineering, Dalian University of Technology, Dalian 116 024 (China))

    1999-06-30

    The creep properties of a cast of duplex stainless steel were characterized at temperatures 550-800 C under different loading conditions. For fully aged specimens containing [sigma], the stress exponent for creep was close to 3 and the activation energy was 281[+-]9 kJ mol[sup -1]. The results suggested that the creep mechanism in the samples in this investigation was controlled by dislocation movement. Extensive [sigma]/[gamma][sub 2] interfaces introduced during ageing improved the creep resistance of the material and related to a reduction of the creep rate in Stage II creep and an increase in the creep rupture strength of the material. Microstructural studies revealed the dependence of the creep properties on the morphology of the microstructure. Among the aged specimens containing [sigma], the creep strength and ductility were higher for specimens having larger [gamma] grain thickness measured on the longitudinal plane. This characteristic was related to the crack propagation and interconnection of voids within [gamma] matrix during tertiary creep. With appropriate solution treatment, the creep strength of [sigma]-containing steels can be improved to a value exceeding that of type 316 steels. (orig.) 14 refs.

  7. An Overview of Irradiation Creep of Stainless Steels

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Woo Seog [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    This paper reviewed systematically a state-of-art of irradiation creep for stainless steels to provide a background information for performing irradiation creep tests and establishing the creep model for advanced domestic steels effectively. An irradiation creep model of SFR core materials is necessary to apply to the fuel cladding and assembly materials of domestic SFR reactor system. The document of in-reactor irradiation creep has been obtained by investing a long time and large-scale cost using limited experimental research reactors. This paper will provide the knowledge to understand the irradiation creep and to obtain the background information of advanced domestic steels, so that it hopes to practically apply for timely producing the documents of irradiation creep of advanced domestic steels necessary for the national SFR program.

  8. The Potential United Kingdom Energy Gap and Creep Life Prediction Methodologies

    Science.gov (United States)

    Evans, Mark

    2013-01-01

    The United Kingdom faces a looming energy gap with around 20 pct of its generating capacity due for closure in the next 10 to 15 years as a result of plant age and new European legislation on environmental protection and safety at work. A number of solutions exist for this problem including the use of new materials so that new plants can operate at higher temperatures, new technologies related to carbon capture and gasification, development of renewable resources, and less obviously the use of accurate models for predicting creep life. This article reviews, with illustrations, some of the more applicable and successful creep prediction methodologies used by academics and industrialists and highlights how these techniques can help alleviate the looming energy gap. The role that these approaches can play in solving the energy gap is highlighted throughout.

  9. Soil creep and historic landscape changes

    Science.gov (United States)

    Lucke, Bernhard

    2017-04-01

    Many erosion models assume that soil sediments are transported grain-by-grain, and thus calculate loss and deposition according to parameters such as bulk density and average grain size. However, clay-rich soils, such as the widespread Red Mediterranean Soils or Terrae Rossae that are often found near important archaeological sites, can behave differently. This is illustrated by a case study of historic landscape changes in Jordan, where evidence for soil creep as main process of soil movement was found in the context of ancient cemeteries. Due to a dominance of smectites, the Red Mediterranean Soils in this area shrink and form cracks during the dry period. Because of the cracks and underlying limestone karst, they can swallow strong rains without high erosion risk. However, when water-saturated, these soils expand and can start creeping. Buried geoarchaeological features like small water channels on formerly cleared rocks suggest that soils can move a few cm uplslope when wet, and buried graves illustrate that soil creep can create new level surfaces, sealing cavities but not completely filling them. Such processes seem associated with slumping and earth flows as instable rocks might collapse under the weight of a creeping soil. While it is very difficult to measure such processes, landscape archaeology offers at least an indirect approach that could be suited to estimate the scale and impact of soil creep. Analogies with modern rainfalls, including record levels of precipitation during the winter 1991/1992, indicate that similar levels of soil moisture have not been reached during times of modern instrumental rainfall monitoring. This suggests that very strong deluges must have occurred during historical periods, that could potentially cause tremendous damage to modern infrastructure if happening again.

  10. Central oxygen pipeline failure

    African Journals Online (AJOL)

    Anaesthetic and critical care staff play a governing role in the comprehension of a ... complete central oxygen pipeline failure occurred throughout. Tygerberg Hospital. ..... emergency stations and at plant room emergency supply manifolds.

  11. Influence of delta ferrite on mechanical and creep properties of steel P92

    Energy Technology Data Exchange (ETDEWEB)

    Mohyla, Petr [VSB - Technical Univ. of Ostrava (Czech Republic). Faculty of Mechanical Engineering; Kubon, Zdenek [Material and Metallurgical Research Ltd., Ostrava (Czech Republic)

    2010-07-01

    This article presents some new results obtained during research of chromium modified steel P92. This steel is considered the best modified 9-12% Cr steel for the construction of modern power plants with ultra-super-critical steam parameters. High creep rupture strength of steel P92 is characterized by its chemical composition and by microstructure as well. Optimal microstructure of steel P92 is ideally composed of homogeneous martensite and fine dispersion of secondary particles. During the research program one P92 heat with an occurrence of about 20% delta ferrite was produced. The article describes the microstructure of the heat in various modes of heat treatment, as well as the results of mechanical properties tests at room temperature and also creep test results. The results are confronted with properties of other heats that have no delta ferrite. The relevance is on the significant difference while comparing of creep test results. The comparison of results brings conclusions, defining influence of delta ferrite on mechanical and creep properties of P92 steel. (orig.)

  12. EVIDENCE FOR LANDSCAPE LEVEL, POLLEN-MEDIATED GENE FLOW FROM CREEPING BENTGRASS WITH CP4 EPSPS AS A MARKER

    Science.gov (United States)

    In a landscape level study, gene flow via pollen was tracked from multiple source fields of genetically modified (GM) herbicide resistant creeping bentgrass (Agrostis stolonifera L.) to 75 of 138 sentinel plants of A. stolonifera and to 29 of 69 resident populations of Agrostis s...

  13. Creep Crack Growth Behavior of Alloys 617 and 800H in Air and Impure Helium Environments at High Temperatures

    Science.gov (United States)

    Grierson, D. S.; Cao, G.; Brooks, P.; Pezzi, P.; Glaudell, A.; Kuettel, D.; Fischer, G.; Allen, T.; Sridharan, K.; Crone, W. C.

    2016-11-01

    The environmental degradation of intermediate heat exchanger (IHX) materials in impure helium has been identified as an area with major ramifications on the design of very high-temperature reactors (VHTR). It has been reported that in some helium environments, non-ductile failure is a significant failure mode for Alloy 617 with long-term elevated-temperature service. Non-ductile failure of intermediate exchangers can result in catastrophic consequences; unfortunately, the knowledge of creep crack initiation and creep crack growth (CCG) in candidate alloys is limited. Current codes and code cases for the candidate alloys do not provide specific guidelines for effects of impure helium on the high-temperature behavior. The work reported here explores creep crack growth characterization of Alloy 617 and Alloy 800H at elevated temperatures in air and in impure helium environments, providing information on the reliability of these alloys in VHTR for long-term service. Alloy 617 was found to exhibit superior CCG resistance compared to Alloy 800H. For Alloy 617 tested at 973 K (700 °C), a notable increase in the resistance to crack growth was measured in air compared to that measured in the helium environment; CCG results for Alloy 800H suggest that air and helium environments produce similar behavior. Testing of grain boundary-engineered (GBE) Alloy 617 samples revealed that, although the technique produces superior mechanical properties in many respects, the GBE samples exhibited inferior resistance to creep crack growth compared to the other Alloy 617 samples tested under similar conditions. Grain size is noted as a confounding factor in creep crack growth resistance.

  14. Creep Crack Growth Behavior of Alloys 617 and 800H in Air and Impure Helium Environments at High Temperatures

    Science.gov (United States)

    Grierson, D. S.; Cao, G.; Brooks, P.; Pezzi, P.; Glaudell, A.; Kuettel, D.; Fischer, G.; Allen, T.; Sridharan, K.; Crone, W. C.

    2017-03-01

    The environmental degradation of intermediate heat exchanger (IHX) materials in impure helium has been identified as an area with major ramifications on the design of very high-temperature reactors (VHTR). It has been reported that in some helium environments, non-ductile failure is a significant failure mode for Alloy 617 with long-term elevated-temperature service. Non-ductile failure of intermediate exchangers can result in catastrophic consequences; unfortunately, the knowledge of creep crack initiation and creep crack growth (CCG) in candidate alloys is limited. Current codes and code cases for the candidate alloys do not provide specific guidelines for effects of impure helium on the high-temperature behavior. The work reported here explores creep crack growth characterization of Alloy 617 and Alloy 800H at elevated temperatures in air and in impure helium environments, providing information on the reliability of these alloys in VHTR for long-term service. Alloy 617 was found to exhibit superior CCG resistance compared to Alloy 800H. For Alloy 617 tested at 973 K (700 °C), a notable increase in the resistance to crack growth was measured in air compared to that measured in the helium environment; CCG results for Alloy 800H suggest that air and helium environments produce similar behavior. Testing of grain boundary-engineered (GBE) Alloy 617 samples revealed that, although the technique produces superior mechanical properties in many respects, the GBE samples exhibited inferior resistance to creep crack growth compared to the other Alloy 617 samples tested under similar conditions. Grain size is noted as a confounding factor in creep crack growth resistance.

  15. Modelling of degradation processes in creep resistant steels through accelerated creep tests after long-term isothermal ageing

    Energy Technology Data Exchange (ETDEWEB)

    Sklenicka, V.; Kucharova, K.; Svoboda, M.; Kroupa, A.; Kloc, L. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials; Cmakal, J. [UJP PRAHA a.s., Praha-Zbraslav (Czech Republic)

    2010-07-01

    Creep behaviour and degradation of creep properties of creep resistant materials are phenomena of major practical relevance, often limiting the lives of components and structures designed to operate for long periods under stress at elevated and/or high temperatures. Since life expectancy is, in reality, based on the ability of the material to retain its high-temperature creep strength for the projected designed life, methods of creep properties assessment based on microstructural evolution in the material during creep rather than simple parametric extrapolation of short-term creep tests are necessary. In this paper we will try to further clarify the creep-strength degradation of selected advanced creep resistant steels. In order to accelerate some microstructural changes and thus to simulate degradation processes in long-term service, isothermal ageing at 650 C for 10 000 h was applied to P91 and P23 steels in their as-received states. The accelerated tensile creep tests were performed at temperature 600 C in argon atmosphere on all steels both in the as-received state and after long-term isothermal ageing, in an effort to obtain a more complete description of the role of microstructural stability in high temperature creep of these steels. Creep tests were followed by microstructural investigations by means of both transmission and scanning electron microscopy and by the thermodynamic calculations. The applicability of the accelerated creep tests was verified by the theoretical modelling of the phase equilibria at different temperatures. It is suggested that under restructed oxidation due to argon atmosphere microstructural instability is the main detrimental process in the long-term degradation of the creep rupture strength of these steels. (orig.)

  16. Active fault creep variations at Chihshang, Taiwan, revealed by creep meter monitoring, 1998-2001

    Science.gov (United States)

    Lee, Jian-Cheng; Angelier, Jacques; Chu, Hao-Tsu; Hu, Jyr-Ching; Jeng, Fu-Shu; Rau, Ruey-Juin

    2003-11-01

    The daily creep meter data recorded at Chihshang in 1998-2001 are presented. The Chihshang creep meter experiment was set up across the Chihshang thrust fault, the most active segment of the Longitudinal Valley Fault, which is the present-day plate suture between the Eurasian and the Philippine Sea plates in eastern Taiwan. Near-continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates: 16.2 mm at the Tapo site (comprising two connected creep meters) and 15.0 mm at the Chinyuan site (three creep meters straddling parallel fault branches). Four of the five creep meters showed a seasonal variation, with the fault moving steadily during the rainy season from April to October, and remaining quiescent during the rest of the year. The only exception was recorded by the creep meter located on a mélange-composed hillslope, where local gravitational landsliding played an additional role other than tectonic faulting. Through comparison with daily precipitation data, we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault, during the transition period of the dry/wet season. During the observation period from 1998 to 2001, the subsurface seismicity exhibited clusters of microearthquakes on the Chihshang Fault at depths of 10-25 km. Recurrent earthquakes occurred regardless of whether the season was wet or dry, indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface. The accumulated strain on the Chihshang Fault at shallow surface levels was released through creep during the wet season. In addition to these short-term seasonal variations, an apparent decrease in the annual slipping rate on the Chihshang Fault during the last few years deserves further investigation in order to mitigate against seismic hazard.

  17. Survey of creep damage in retired live steam piping; Kartlaeggning av krypskador i utrangerat aangnaet

    Energy Technology Data Exchange (ETDEWEB)

    Storesund, Jan; Pettersson, Anders; Leijonberg, Anders

    2007-12-15

    During the last years a number of creep fractures and cases of creep cracking have been reported in Swedish plants where the service temperature has been below the limit temperature for creep design. Previously, there have been quite few thorough investigations of steam pipe systems which have been in operation below the limit temperature, particularly among those with a significantly lower service temperature. Soedra Cell, Vaeroe has recently scrapped a steam line system from 1972. The operation temperature was 450 deg C i.e. 30 deg C below the limit temperature for the current material, 13 CrMo 4 4. This gives opportunity to map the old pipelines thoroughly with respect to creep damage. Magnetic particle testing (MT) was performed on all accessible welds (13 welds) and on 2 pipe bends. Replica testing was performed on 8 welds and 2 pipe bends. The investigations resulted in: Defect indications in two of the welds. Both of them in conjunction to the one and the same T-joint. The longest defect was approximately 100 mm. In the same weld a 50 mm long indication was found at the opposite side of the weld. The indication in the other weld was small, approximately 1 mm. Replicas showed that all the MT indications were creep cracks, placed in the coarse grained part of the HAZs, close to the fusion boundaries. The retaining part of the replica tests had relatively few positions with creep damage and in these mainly as damage class 2a, separated cavities to a small extent. In some cases creep damage was found in the fine grained and the inter-critical part of the HAZ, where creep cracking often is found in the creep range. Previously, damage observations only have been reported at the fusion lines at service temperatures around 450 deg C. Reheat cracks may be formed at the fusion lines. Their appearance are about the same as service induced creep cracks when formed at temperatures around 450 deg C. It is, therefore, difficult to conclude if the observed cracks are, or

  18. Failure mode analysis for lime/limestone FGD system. Volume III. Plant profiles. Part 1 of 3

    Energy Technology Data Exchange (ETDEWEB)

    Kenney, S.M.; Rosenberg, H.S.; Nilsson, L.I.O.; Oxley, J.H.

    1984-08-01

    This volume contains plant profiles for: Petersburg 3; Hawthorn 3, 4; La Cygne 1; Jeffry 1, 2; Lawrence 4, 5; Green River 1-3; Cane Run 4, 5; Mill Creek 1, 3; Paddy's Run 6; Clay Boswell 4; Milton R. Young 2; Pleasants 1, 2; and Colstrip 1, 2. (DLC)

  19. Common Cause Failure Analysis of Control Rods and Drives in the Swedish and Finnish BWR Plants. Operating Experiences in 1983 - 2003

    Energy Technology Data Exchange (ETDEWEB)

    Mankamo, Tuomas [Avaplan Oy, Espoo (Finland)

    2006-11-15

    substantial time difference and/or spatial distance within the core. The exploration of CCF cases showed that the most prevalent factor in the CCF mechanisms was the time coupling by sequencing maintenance into refueling outages. Essential contributing factors were design changes, deviations or errors in maintenance or new types of replacement parts, accompanied by unexpected influences. An evident positive trend could be observed both for single failures and CCFs . Impact Vectors were used to expresses the conditional failure probability for the various multiplicity in CCF events, linking event analysis to the estimation of CCF model parameters. A reference application was made for the Forsmark 1 and 2 plant. The Common Load Model was used as parametric CCF model, which proved to be a practicable approach. This method provides a consistent handling of failure combinations and workable extension to evaluate localized dependence between adjacent control rod and drives. Also international experience and reference information were surveyed. The developed methods and collected data are utilized in the ongoing PSA updates for the Swedish BWRs and Olkiluoto 1 and 2. Review - within the project a detailed and project extern review has been performed, covering also the older CCF events. This do now guarantee that the CCF data for the control rods and drives in Swedish and Finnish BWR:s during the observation period 1983 - 2003, now can be judged as quality assured. The scope of this project was limited to collection, analysis and classification of CCF data, and reference application using the industry average of pooled data. It has not been the scope of this project to perform more comprehensive probabilistic studies on e.g., positive learning trends, impact of plant specific design details or different amount of failing control rods at different operational conditions in the reactor vessel and with different safety and support systems in operation. It has either been the scope to

  20. Creep testing of nodular iron at ambient and elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Martinsson, Aasa; Andersson-Oestling, Henrik C.M.; Seitisleam, Facredin; Wu, Rui; Sandstroem, Rolf (Swerea KIMAB AB, Stockholm (Sweden))

    2010-12-15

    The creep strain at room temperature, 100 and 125 deg C has been investigated for the ferritic nodular cast iron insert intended for use as the load-bearing part of canisters for long term disposal of spent nuclear fuel. The microstructure consisted of ferrite, graphite nodules of different sizes, compacted graphite and pearlite. Creep tests have been performed for up to 41,000 h. The specimens were cut out from material taken from two genuine inserts, I30 and I55. After creep testing, the specimens from the 100 deg C tests were hardness tested and a metallographic examination was performed. Creep strains at all temperatures appear to be logarithmic, and accumulation of creep strain diminishes with time. The time dependence of the creep strain is consistent to the W-model for primary creep. During the loading plastic strains up to 1% appeared. The maximum recorded creep strain after the loading phase was 0.025%. This makes the creep strains technically insignificant. Acoustic emission recordings during the loading of the room temperature tests showed no sounds or other evidence of microcracking during the loading phase. There is no evidence that the hardness or the graphite microstructure changed during the creep tests

  1. Influence of phosphorus on the creep ductility of copper

    Energy Technology Data Exchange (ETDEWEB)

    Sandström, Rolf, E-mail: rsand@kth.se [Materials Science and Engineering, KTH, Brinellvägen 23, S-100 44 Stockholm (Sweden); Swerea KIMAB, Box 7074, S-164 07 Kista (Sweden); Wu, Rui [Swerea KIMAB, Box 7074, S-164 07 Kista (Sweden)

    2013-10-15

    Around 1990 it was discovered that pure copper could have extra low creep ductility in the temperature interval 180–250 °C. The material was intended for use in canisters for nuclear waste disposal. Although extra low creep ductility was not observed much below 180 °C and the temperature in the canister will never exceed 100 °C, it was feared that the creep ductility could reach low values at lower temperatures after long term exposure. If 50 ppm phosphorus was added to the copper the low creep ductility disappeared. A creep cavitation model is presented that can quantitatively describe the cavitation behaviour in uniaxial and multiaxial creep tests as well as the observed creep ductility for copper with and without phosphorus. A so-called double ledge model has been introduced that demonstrates why the nucleation rate of creep cavities is often proportional to the creep rate. The phosphorus agglomerates at the grain boundaries and limits their local deformation and thereby reduces the formation and growth of cavities. This explains why extra low creep ductility does not occur in phosphorus alloyed copper.

  2. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Bimal K. Kad

    2005-11-23

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in crossrolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to

  3. Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yanli [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jetter, Robert I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Baird, Seth T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pu, Chao [Univ. of Tennessee, Knoxville, TN (United States); Sham, Sam [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2015-06-22

    For the temperature range of 990-950C, Alloy 617 is a candidate IHX structural material for high temperature gas reactors (HTGRs) because of its high temperature creep properties. Also, its superior strength over a broad temperature range also offers advantages for certain component applications. In order for the designers to be able to use Alloy 617 for these high temperature components, Alloy 617 has to be approved for use in Section III (the nuclear section) of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. A plan has been developed to propose a Code Case for use of Alloy 617 at elevated temperature in Section III of the ASME Code by September 2015. There has not been a new high temperature material approved for use in Section III for almost 20 years. The Alloy 617 Code Case effort would lead the way to establish a path for Code qualification of new high temperature materials of interest to other advanced SMRs. Creep-fatigue at elevated temperatures is the most damaging structural failure mode. In the past 40 years significant efforts have been devoted to the elevated temperature Code rule development in Section III, Subsection NH* of the ASME Boiler and Pressure Vessel Code, to ascertain conservative structural designs to prevent creep-fatigue failure. The current Subsection NH creep-fatigue procedure was established by the steps of (1) analytically obtaining a detailed stress-strain history, (2) comparing the stress and strain components to cyclic test results deconstructed into stress and strain quantities, and (3) recombining the results to obtain a damage function in the form of the so-called creep-fatigue damage-diagram. The deconstruction and recombination present difficulties in evaluation of test data and determination of cyclic damage in design. The uncertainties in these steps lead to the use of overly conservative design factors in the current creep-fatigue procedure. In addition, and of major significance to the

  4. Cake creep during filtration of flocculated manure

    DEFF Research Database (Denmark)

    Christensen, Morten Lykkegaard; Keiding, Kristian

    the distribution of N and P on the fields. Filtration is a useful method for such a separation. Furthermore, chemicals can be added to flocculate the solids and thereby increase the filterability i.e. the specific filter-cake resistance can be reduced from 1015 m/kg to 1011 m/kg. Both the amount of added chemicals......, and the mixing procedure affect the result, and lab-scale experiments are often used to study how these pre-treatments influence the filtration process. However, the existing mathematical filtration models are based on filtration of inorganic particles and cannot simulate the filtration data obtained when manure...... that the discrepancy between the filtration theory and the observed filtration behaviour is due to a time-dependent collapse of the formed cake (creep). This can also explain the observed behaviour when flocculated manure is filtered. The filtration data can be simulated if cake creep is adopted in the filtration...

  5. Transient effects in friction fractal asperity creep

    CERN Document Server

    Goedecke, Andreas

    2013-01-01

    Transient friction effects determine the behavior of a wide class of mechatronic systems. Classic examples are squealing brakes, stiction in robotic arms, or stick-slip in linear drives. To properly design and understand mechatronic systems of this type, good quantitative models of transient friction effects are of primary interest. The theory developed in this book approaches this problem bottom-up, by deriving the behavior of macroscopic friction surfaces from the microscopic surface physics. The model is based on two assumptions: First, rough surfaces are inherently fractal, exhibiting roughness on a wide range of scales. Second, transient friction effects are caused by creep enlargement of the real area of contact between two bodies. This work demonstrates the results of extensive Finite Element analyses of the creep behavior of surface asperities, and proposes a generalized multi-scale area iteration for calculating the time-dependent real contact between two bodies. The toolset is then demonstrated both...

  6. The Creep of Laminated Synthetic Resin Plastics

    Science.gov (United States)

    Perkuhn, H

    1941-01-01

    The long-time loading strength of a number of laminated synthetic resin plastics was ascertained and the effect of molding pressure and resin content determined. The best value was observed with a 30 to 40 percent resin content. The long-time loading strength also increases with increasing molding pressure up to 250 kg/cm(exp 2); a further rise in pressure affords no further substantial improvement. The creep strength is defined as the load which in the hundredth hour of loading produces a rate of elongation of 5 X 10(exp -4) percent per hour. The creep strength values of different materials were determined and tabulated. The effect of humidity during long-term tests is pointed out.

  7. Very slow creep tests on salt samples

    Directory of Open Access Journals (Sweden)

    de Greef V.

    2010-06-01

    Full Text Available Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (σ = 0.02 to 0.1 MPa . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations were measured through special displacement sensors with a resolution of ∆ε = 10-8. Strain rates as small as έ = 7 × 10-13s-1 were measured. These tests allow rock-sample creep to be investigated at very small strain rates. The tests also prove that extrapolation of constitutive laws at very small rates is often incorrect.

  8. Failures during Load-Frequency Control Maneuvers in an Upgraded Hydropower Plant: Causes, Identification of Causes and Solution Proposals

    Directory of Open Access Journals (Sweden)

    Juan I. Pérez-Díaz

    2015-09-01

    Full Text Available The objective of this paper is to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level of a real hydropower plant during secondary load-frequency control (LFC maneuvers, after the replacement of the turbine runner, and to propose solutions that allow the power plant to continue providing secondary LFC in a safe and reliable manner. For this purpose, a simulation model has been developed and calibrated from data gathered during several on-site tests. Two different solutions are proposed in order to cope with the observed problem: using a state-dependent load change rate limiter or modifying the hydro turbine governor gains; the turbine governor remains the same as before the runner replacement. The proposed solutions are tested against a set of realistic secondary LFC signals by means of simulations and compared to each other as a function of the probability that the surge tank water level descends below a minimum safe level and the quality of the secondary LFC response. The results presented in the paper demonstrate the validity of the methodology proposed to determine the state-dependent ramp limit, as well as its effectiveness to prevent the surge tank drawdown and to provide clear insight into the trade-off between response quality and power plant safety.

  9. The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep

    Science.gov (United States)

    Xu, Lili; Renner, Jörg; Herwegh, Marco; Evans, Brian

    2009-03-01

    We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2-30 h) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in high-magnesian calcite aggregates with Mg content ranging from 0.5 to 17 mol%. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 μm, increased with time at temperature, and decreased with increasing Mg content (>3.0 mol%). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5-17.0 mol% Mg, respectively. We deformed samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium deformation apparatus. The deformation tests took place at between 700 and 800°C and at strain rates between 10-6 and 10-3 s-1. After deformation to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The deformation data indicated a transition in mechanism from diffusion creep to dislocation creep. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, ( n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and temperature, the stress at

  10. Application of Failure Mode and Effect Analysis (FMEA) and cause and effect analysis in conjunction with ISO 22000 to a snails (Helix aspersa) processing plant; A case study.

    Science.gov (United States)

    Arvanitoyannis, Ioannis S; Varzakas, Theodoros H

    2009-08-01

    Failure Mode and Effect Analysis (FMEA) has been applied for the risk assessment of snails manufacturing. A tentative approach of FMEA application to the snails industry was attempted in conjunction with ISO 22000. Preliminary Hazard Analysis was used to analyze and predict the occurring failure modes in a food chain system (snails processing plant), based on the functions, characteristics, and/or interactions of the ingredients or the processes, upon which the system depends. Critical Control points have been identified and implemented in the cause and effect diagram (also known as Ishikawa, tree diagram, and fishbone diagram). In this work a comparison of ISO22000 analysis with HACCP is carried out over snails processing and packaging. However, the main emphasis was put on the quantification of risk assessment by determining the RPN per identified processing hazard. Sterilization of tins, bioaccumulation of heavy metals, packaging of shells and poisonous mushrooms, were the processes identified as the ones with the highest RPN (280, 240, 147, 144, respectively) and corrective actions were undertaken. Following the application of corrective actions, a second calculation of RPN values was carried out leading to considerably lower values (below the upper acceptable limit of 130). It is noteworthy that the application of Ishikawa (Cause and Effect or Tree diagram) led to converging results thus corroborating the validity of conclusions derived from risk assessment and FMEA. Therefore, the incorporation of FMEA analysis within the ISO22000 system of a snails processing industry is considered imperative.

  11. Shark skin effect in creeping films

    CERN Document Server

    Scholle, M

    2006-01-01

    If a body in a stream is provided with small ridges aligned in the local flow direction, a remarkable drag reduction can be reached under turbulent flow conditions. This surprising phenomenon is called the 'shark skin effect'. We demonstrate, that a reduction of resistance can also be reached in creeping flows if the ridges are aligned perpendicular to the flow direction. We especially consider in gravity-driven film flows the effect of the bottom topography on the mean transport velocity.

  12. Zinc alloy enhances strength and creep resistance

    Energy Technology Data Exchange (ETDEWEB)

    Machler, M. [Fisher Gauge Ltd., Peterborough, Ontario (Canada). Fishercast Div.

    1996-10-01

    A family of high-performance ternary zinc-copper-aluminum alloys has been developed that provides higher strength, hardness, and creep resistance than the traditional zinc-aluminum alloys Zamak 3, Zamak 5, and ZA-8. Designated ACuZinc, mechanical properties comparable to those of more expensive materials make it suitable for high-load applications and those at elevated temperatures. This article describes the alloy`s composition, properties, and historical development.

  13. Creep Rupture of the Simulated HAZ of T92 Steel Compared to that of a T91 Steel

    Directory of Open Access Journals (Sweden)

    Yu-Quan Peng

    2017-02-01

    Full Text Available The increased thermal efficiency of fossil power plants calls for the development of advanced creep-resistant alloy steels like T92. In this study, microstructures found in the heat-affected zone (HAZ of a T92 steel weld were simulated to evaluate their creep-rupture-life at elevated temperatures. An infrared heating system was used to heat the samples to 860 °C (around AC1, 900 °C (slightly below AC3, and 940 °C (moderately above AC3 for one minute, before cooling to room temperature. The simulated specimens were then subjected to a conventional post-weld heat treatment (PWHT at 750 °C for two hours, where both the 900 °C and 940 °C simulated specimens had fine grain sizes. In the as-treated condition, the 900 °C simulated specimen consisted of fine lath martensite, ferrite subgrains, and undissolved carbides, while residual carbides and fresh martensite were found in the 940 °C simulated specimen. The results of short-term creep tests indicated that the creep resistance of the 900 °C and 940 °C simulated specimens was poorer than that of the 860 °C simulated specimens and the base metal. Moreover, simulated T92 steel samples had higher creep strength than the T91 counterpart specimens.

  14. Creep Deformation by Dislocation Movement in Waspaloy

    Directory of Open Access Journals (Sweden)

    Mark Whittaker

    2017-01-01

    Full Text Available Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention paid to comparing tests performed above and below the yield stress. This paper highlights how the dislocation structures vary throughout creep and proposes a dislocation mechanism theory for creep in Waspaloy. Activation energies are calculated through approaches developed in the use of the recently formulated Wilshire Equations, and are found to differ above and below the yield stress. Low activation energies are found to be related to dislocation interaction with γ′ precipitates below the yield stress. However, significantly increased dislocation densities at stresses above yield cause an increase in the activation energy values as forest hardening becomes the primary mechanism controlling dislocation movement. It is proposed that the activation energy change is related to the stress increment provided by work hardening, as can be observed from Ti, Ni and steel results.

  15. Steady-State Creep of Asphalt Concrete

    Directory of Open Access Journals (Sweden)

    Alibai Iskakbayev

    2017-02-01

    Full Text Available This paper reports the experimental investigation of the steady-state creep process for fine-grained asphalt concrete at a temperature of 20 ± 2 °С and under stress from 0.055 to 0.311 MPa under direct tension and was found to occur at a constant rate. The experimental results also determined the start, the end point, and the duration of the steady-state creep process. The dependence of these factors, in addition to the steady-state creep rate and viscosity of the asphalt concrete on stress is satisfactorily described by a power function. Furthermore, it showed that stress has a great impact on the specific characteristics of asphalt concrete: stress variation by one order causes their variation by 3–4.5 orders. The described relations are formulated for the steady-state of asphalt concrete in a complex stressed condition. The dependence is determined between stress intensity and strain rate intensity.

  16. Experimental studies of fiber concrete creep

    Directory of Open Access Journals (Sweden)

    Korneeva Irina

    2017-01-01

    Full Text Available The results of two-stage experimental studies of the strength and deformation characteristics of fibrous concrete reinforced with steel fiber. In the experiments we used steel fiber with bent ends, which practically does not form "hedgehogs", which allows to achieve an even distribution of the fiber by volume. At the first stage, the cube and prismatic strength, deformability at central compression, a number of special characteristics are determined: water absorption, frost resistance, abrasion; the optimal percentage of fiber reinforcement and the maximum size of the coarse aggregate fraction were selected. Fiber reinforcement led to an increase in the strength of concrete at compression by 1,35 times and an increase in the tensile strength at bending by 3,4 times. At the second stage, the creep of fibrous concrete and plain concrete of similar composition at different stress levels was researched. Creep curves are plotted. It is shown that the use of fiber reinforcement leads to a decrease in creep strain by 21 to 30 percent, depending on the stress level.

  17. Magnetic field annealing for improved creep resistance

    Energy Technology Data Exchange (ETDEWEB)

    Brady, Michael P.; Ludtka, Gail M.; Ludtka, Gerard M.; Muralidharan, Govindarajan; Nicholson, Don M.; Rios, Orlando; Yamamoto, Yukinori

    2015-12-22

    The method provides heat-resistant chromia- or alumina-forming Fe-, Fe(Ni), Ni(Fe), or Ni-based alloys having improved creep resistance. A precursor is provided containing preselected constituents of a chromia- or alumina-forming Fe-, Fe(Ni), Ni(Fe), or Ni-based alloy, at least one of the constituents for forming a nanoscale precipitate MaXb where M is Cr, Nb, Ti, V, Zr, or Hf, individually and in combination, and X is C, N, O, B, individually and in combination, a=1 to 23 and b=1 to 6. The precursor is annealed at a temperature of 1000-1500.degree. C. for 1-48 h in the presence of a magnetic field of at least 5 Tesla to enhance supersaturation of the M.sub.aX.sub.b constituents in the annealed precursor. This forms nanoscale M.sub.aX.sub.b precipitates for improved creep resistance when the alloy is used at service temperatures of 500-1000.degree. C. Alloys having improved creep resistance are also disclosed.

  18. Creep Test of Polymer-matrix 3-D Braided Composites

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The long-term creep behavior of polymer-matrix 3-D braided composites was studied by using the tensile creep test method, and the effect of braiding structure, braiding angle and fiber volume fraction were discussed. The creep curve appears as expected, and can be defimed two phases,namely, the primary phase and the secondary phase. For each sample, strain increases with time rapidly, and then the strain rate decreases and appears to approach a constant rate of change (steady-state creep). The experiment results show that the creep resistant properties are improved while the braiding angle decreases or the fiber volume fraction increases, and that the five-directional braiding structure offers better creep resistant properties than the fourdirectional braiding structure.

  19. A Comparison of Creep Rupture Strength of Ferritic/Austenitic Dissimilar Weld Joints of Different Grades of Cr-Mo Ferritic Steels

    Science.gov (United States)

    Laha, K.; Chandravathi, K. S.; Parameswaran, P.; Goyal, Sunil; Mathew, M. D.

    2012-04-01

    Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.

  20. Degradation of mechanical properties of CrMo creep resistant steel operating under conditions of creep

    Directory of Open Access Journals (Sweden)

    J. Michel

    2012-01-01

    Full Text Available Mechanical properties of a steam tube made of CrMo creep resistant steel are analysed in this contribution after up to 2,6•105 hours service life in creep conditions at temperature 530 °C and calculated stress level in the tube wall 46,5 MPa. During service life there were in the steel gradual micro structure changes, fi rst pearlite spheroidization, precipitation, coaugulation and precipitate coarsening. Nevertheless the strength and deformation properties of the steel (Re, Rm, A5, Z, and the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2,1•105 hours in service. The steam tube is now in service more than 2,6•105 h.

  1. MICROSTRUCTURE AND MECHANICAL PROPERTIES DEGRADATION OF CrMo CREEP RESISTANT STEEL OPERATING UNDER CREEP CONDITIONS

    Directory of Open Access Journals (Sweden)

    Ján Micheľ

    2011-07-01

    Full Text Available In this contribution microstructure degradation of a steam tube is analysed. The tube is made of CrMo creep resistant steel and was in service under creep conditions at temperature 530°C and calculated stress level in the tube wall 46.5 MPa. During service life in the steel gradual micro structure changes were observed, first pearlite spheroidization, precipitation, coagulation and precipitate coarsening. Despite the fact that there were evident changes in the micro structure the strength and deformation properties of the steel (Re, Rm, A5, Z, the resistance to brittle fracture and the creep strength limit, were near to unchanged after 2.1x10 5 hours in service. The steam tube is now in service more than 2.6x10 5 h.

  2. Amazonian and neotropical plant communities on glacial time-scales: The failure of the aridity and refuge hypotheses

    Science.gov (United States)

    Colinvaux, P. A.; De Oliveira, P. E.; Bush, M. B.

    2000-01-01

    Plants respond to Pleistocene climatic change as species, not as associations or biomes. This has been demonstrated unequivocally by paleobotanical data for temperate latitudes. In the far richer vegetations of the tropics species populations also fluctuated independently in response to climatic forcing, from their longlasting glacial states to the patterns of brief interglacials like the present and back again. We use pollen data to reconstruct the vegetation of the Amazon basin in oxygen isotope stages 3 and 2 of the last glaciation in order to measure how the plant populations of the Amazon responded to the global warming at the onset of the Holocene. We find that plant communities of the neotropics vent copious pollen to lake sediments and that this pollen yields powerful signals for community composition. Three continuous sedimentary records reaching through oxygen isotope stage 2 are available from the Amazon lowlands, those from Carajas, Lake Pata and marine deposits off the mouth of the Amazon River. All three records yield pollen histories of remarkable constancy and stability. By comparing them with deposits of equal antiquity from the cerrado (savanna) of central Brazil, we show that most of the Amazon lowlands remained under forest throughout a glacial cycle. This forest was never fragmented by open vegetation as postulated by the refugia hypothesis. Instead the intact forest of glacial times included significant populations of plants that are now montane, suggesting that the global warming of the early Holocene resulted in the expulsion of heat intolerant plants from the lowland forest. Pollen data from the Amazonian flank of the Andes and from Pacific Panama provide evidence that populations of these heat intolerant plants survive the heat of interglacials in part by maintaining large populations at cooler montane altitudes. Our conclusion that the Amazon lowlands were forested in glacial times specifically refutes the hypothesis of Amazonian glacial

  3. Brittle and semibrittle creep in a low porosity carbonate rock

    Science.gov (United States)

    Nicolas, Aurélien; Fortin, Jérôme; Regnet, Jean-Baptiste; Dimanov, Alexandre; Guéguen, Yves

    2016-04-01

    The mechanical behavior of limestones at room temperature is brittle at low confining pressure and becomes semi-brittle with the increase of the confining pressure. The brittle behavior is characterized by a macroscopic dilatancy due to crack propagation, leading to a stress drop when cracks coalesce at failure. The semi-brittle behavior is characterized by diffuse deformation due to intra-crystalline plasticity (dislocation movements and twinning) and microcracking. The aim of this work is to examine the influence of pore fluid and time on the mechanical behavior. Constant strain rate triaxial deformation experiments and stress-stepping creep experiments were performed on white Tavel limestone (porosity 14.7%). Elastic wave velocity evolutions were recorded during each experiment and inverted to crack densities. Constant strain rate triaxial experiments were performed for confining pressure in the range of 5-90 MPa. For Pc≤55 MPa our results show that the behavior is brittle. In this regime, water-saturation decreases the differential stress at the onset of crack propagation and enhances macroscopic dilatancy. For Pc≥70 MPa, the behavior is semi-brittle. Inelastic compaction is due to intra-crystalline plasticity and micro-cracking. However, in this regime, our results show that water-saturation has no clear effect at the onset of inelastic compaction. Stress stepping creep experiments were performed in a range of confining pressures crossing the brittle-ductile transition. In the brittle regime, the time-dependent axial deformation is coupled with dilatancy and a decrease of elastic wave velocities, which is characteristic of crack propagation and/or nucleation. In the semi-brittle regime, the first steps are inelastic compactant because of plastic pore collapse. But, following stress steps are dilatant because of crack nucleation and/or propagation. However, our results show that the axial strain rate is always controlled by plastic phenomena, until the last

  4. Viscous Creep in Dry Unconsolidated Gulf of Mexico Shale

    Science.gov (United States)

    Chang, C.; Zoback, M. D.

    2002-12-01

    We conducted laboratory experiments to investigate creep characteristics of dry unconsolidated shale recovered from the pathfinder well, Gulf of Mexico (GOM). We subjected jacketed cylindrical specimens (25.4 mm diameter) to hydrostatic pressure that increased from 10 to 50 MPa in steps of 5 MPa. We kept the pressure constant in each step for at least 6 hours and measured axial and lateral strains (provided by LVDTs) and ultrasonic velocities (provided by seismic-wave transducers). The dry shale exhibited pronounced creep strain at all pressure levels, indicating that the dry frame of the shale possesses an intrinsic viscous property. Interestingly, the creep behavior of the shale is different above and below 30 MPa confining pressure. Above 30 MPa, the amount of creep strain in 6 hours is nearly constant with equal pressurization steps, indicating a linear viscous rheology. Below 30 MPa, the amount of creep increases linearly as pressure is raised in constant incremental steps, suggesting that the creep deformation accelerates as pressure increases within this pressure range. Thus, the general creep behavior of the GOM shale is characterized by a bilinear dependence on pressure magnitude. This creep characteristic is quite different from that observed in unconsolidated reservoir sands (Hagin and Zoback, 2002), which exhibited nearly constant amount of creep regardless of the pressure magnitude for equal increasing steps of pressure. The shale exhibits a lack of creep (and nearly negligible strain recovery) when unloaded, suggesting that the creep strain is irrecoverable and can be considered viscoplastic deformation. SEM observations show that the major mechanism of compaction of the dry shale appears to be packing of clay and a progressive collapse of pore (void) spaces. Creep compaction is considerably more significant than compaction that occurs instantaneously, indicating that the process of shale compaction is largely time-dependent.

  5. Stability of MC Carbide Particles Size in Creep Resisting Steels

    Directory of Open Access Journals (Sweden)

    Vodopivec, F.

    2006-01-01

    Full Text Available Theoretical analysis of the dependence microstructure creep rate. Discussion on the effects of carbide particles size and their distribution on the base of accelerated creep tests on a steel X20CrMoV121 tempered at 800 °C. Analysis of the stability of carbide particles size in terms of free energy of formation of the compound. Explanation of the different effect of VC and NbC particles on accelerated creep rate.

  6. Control of Early Age Concrete. Phase 3: Creep in Concrete

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Anders Boe; Damkilde, Lars; Hansen, Per Freiesleben

    1997-01-01

    The mechanical properties of the "Road Directorate Concrete" at early ages are studied. Creep in tension at 24 and 72 maturity hours are measured on dogbone shaped specimens. The development of tensile modulus of elasticity and strength are measured with a method developed here. The results...... are compared to compression values and splitting strengths. It is found that the properties of creep in tension are similar to the properties in compression. Further the influence form temperature on creep is found to be significant....

  7. Comparison of creep of the cement pastes included fly ash

    Directory of Open Access Journals (Sweden)

    Padevět Pavel

    2017-01-01

    Full Text Available The paper is devoted to comparison of creep of cement pastes containing fly ash admixture. The size of creep in time depends on the amount of components of the cement paste. Attention is paid to the content of classical fly ash in cement paste and its impact on the size of creep. The moisture of cement pastes is distinguished because it significantly affects the rheological properties of the material.

  8. Quantification of creep-induced damaging processes in structural components under multiaxial stress; Quantifizierung der Kriechschaedigungsentwicklung in mehrachsig beanspruchten Bauteilen

    Energy Technology Data Exchange (ETDEWEB)

    Maile, K.; Purper, H.; Theofel, H.; Gaudig, W.

    1996-12-31

    Based on results obtained by research projects examining the deformation performance and failure of heat-resistant steels under long-term creep, the contribution explains the different damaging effects of multiaxial or uniaxial stress with regard to cree-induced damage. (orig./RHM) [Deutsch] Anhand von Ergebnissen durchgefuehrter Forschungsvorhaben, die sich mit dem Verformungs- und Versagensverhalten von warmfesten Staehlen im Zeitstandbereich befassen, wurden die Unterschiede zwischen mehr- und einachsiger Beanspruchung im Hinblick auf die Kriechschaedigungsentwicklung herausgestellt. (orig./RHM)

  9. Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement.

    Science.gov (United States)

    Jeffers, Jonathan R T; Browne, Martin; Taylor, Mark

    2005-09-01

    The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure; at 20 MPa specimens failed between 2 x 10(3) and 2 x 10(4) load cycles, while at 7 MPa specimens failed from 3 x 10(5) load cycles but others were still intact after 3 x 10(6) load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications.

  10. Undetected latent failures of safety-related systems. Preliminary survey of events in nuclear power plants 1980-1997

    Energy Technology Data Exchange (ETDEWEB)

    Lydell, B. [RSA Technologies, Vista, CA (United States)

    1998-03-01

    This report summarizes results and insights from a preliminary survey of events involving undetected, latent failures of safety-related systems. The survey was limited to events where mispositioned equipment (e.g., valves, switches) remained undetected, thus rendering standby equipment or systems unavailable for short or long time periods. Typically, these events were symptoms of underlying latent errors (e.g., design errors, procedure errors, unanalyzed safety conditions) and programmatic errors. The preliminary survey identified well over 300 events. Of these, 95 events are documented in this report. Events involving mispositioned equipment are commonplace. Most events are discovered soon after occurrence, however. But as evidenced by the survey results, some events remained undetected beyond several shift changes. The recommendations developed by the survey emphasize the importance of applying modern root cause analysis techniques to the event analysis to ensure that the causes and implications of occurred events are fully understood. 7 refs, 4 tabs, 3 figs. Also available at the SKI Home page: //www.ski.se.

  11. A Study of the Creep Effect in Loudspeaker Suspension

    DEFF Research Database (Denmark)

    Agerkvist, Finn T.; Thorborg, Knud; Tinggaard, Carsten

    2008-01-01

    This paper investigates the creep effect, the visco elastic behaviour of loudspeaker suspension parts, which can be observed as an increase in displacement far below the resonance frequency. The creep effect means that the suspension cannot be modelled as a simple spring. The need for an accurate...... creep model is even larger as the validity of loudspeaker models are now sought extended far into the nonlinear domain of the loudspeaker. Different creep models are investigated and implemented both in simple lumped parameter models as well as time domain non-linear models, the simulation results...

  12. Shear creep characteristics and constitutive model of limestone

    Institute of Scientific and Technical Information of China (English)

    Yu Mei; Mao Xianbiao; Hu Xinyu

    2016-01-01

    The characters of limestone in weak interlayer of a high rocky slope in Xuzhou, China, are studied by shear static test and shear creep test. The results show that limestone specimens have attenuation creep properties and constant rate creep properties, almost have no accelerated creep properties. The exponen-tial type empirical formula is selected to fit creep grading curves by polynomial regression analysis method, and the square sums of the fitting results residual are in the order of 10-7. Then grade creep curves at every shear loads are set up. Combining creep rate-time curve, the creep properties of limestone are analyzed. As the physical meaning of component model is clearer, the Poytin–Thomson model is set up. Through the least square method, the optimal parameters of Poytin–Thomson model are obtained, and the sums of squared residuals belong to 10-3 order of magnitude, which can meet the accuracy requirements of engineering calculation. So the Poytin–Thomson model can reflect the shear creep char-acteristics of limestone very well.

  13. Contribution to irradiation creep arising from gas-driven bubbles

    Energy Technology Data Exchange (ETDEWEB)

    Woo, C.H. [Hong Kong Polytechnic Univ., Kowloon (Hong Kong); Garner, F.A. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    In a previous paper the relationship was defined between void swelling and irradiation creep arising from the interaction of the SIPA and SIG creep-driven deformation and swelling-driven deformation was highly interactive in nature, and that the two contributions could not be independently calculated and then considered as directly additive. This model could be used to explain the recent experimental observation that the creep-swelling coupling coefficient was not a constant as previously assumed, but declined continuously as the swelling rate increased. Such a model thereby explained the creep-disappearance and creep-damping anomalies observed in conditions where significant void swelling occurred before substantial creep deformation developed. At lower irradiation temperatures and high helium/hydrogen generation rates, such as found in light water cooled reactors and some fusion concepts, gas-filled cavities that have not yet exceeded the critical radius for bubble-void conversion should also exert an influence on irradiation creep. In this paper the original concept is adapted to include such conditions, and its predictions then compared with available data. It is shown that a measurable increase in the creep rate is expected compared to the rate found in low gas-generating environments. The creep rate is directly related to the gas generation rate and thereby to the neutron flux and spectrum.

  14. Probabilistic models for creep-fatigue in a steel alloy

    Science.gov (United States)

    Ibisoglu, Fatmagul

    In high temperature components subjected to long term cyclic operation, simultaneous creep and fatigue damage occur. A new methodology for creep-fatigue life assessment has been adopted without the need to separate creep and fatigue damage or expended life. Probabilistic models, described by hold times in tension and total strain range at temperature, have been derived based on the creep rupture behavior of a steel alloy. These models have been validated with the observed creep-fatigue life of the material with a scatter band close to a factor of 2. Uncertainties of the creep-fatigue model parameters have been estimated with WinBUGS which is an open source Bayesian analysis software tool that uses Markov Chain Monte Carlo method to fit statistical models. Secondly, creep deformation in stress relaxation data has been analyzed. Well performing creep equations have been validated with the observed data. The creep model with the highest goodness of fit among the validated models has been used to estimate probability of exceedance at 0.6% strain level for the steel alloy.

  15. Estimation of transient creep C(t)-integrals for SE(B) specimen under elastic-plastic creep

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Sang; Je, Jin Ho; Kim, Dong Jun; Kim, Yun Jae [Dept. of Mechanical Engineering, Korea University, Seoul (Korea, Republic of)

    2015-09-15

    In this paper, we estimate the time-dependent C(t) integrals under elastic-plastic-creep conditions. Finite-element (FE) transient creep analyses have been performed for single-edge-notched-bend (SEB) specimens. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step load. We consider both the same stress exponent and different stress exponents in the power-law creep and plasticity to elastic-plastic-creep behavior. To estimate the C(t) integrals, we compare the FE analysis results with those obtained using formulas. In this paper, we propose a modified equation to predict the C(t) integrals for the case of creep exponents that are different from the plastic exponent.

  16. Estimation of transient creep crack-tip stress fields for SE(B) specimen under elastic-plastic-creep conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Han Sang; Je, Jin Ho; Kim, Dong Jun; Kim, Yun Jae [Dept. of Mechanical Engineering, Korea University, Seoul (Korea, Republic of)

    2015-10-15

    This paper estimates the time-dependent crack-tip stress fields under elastic-plastic-creep conditions. We perform Finite-Element (FE) transient creep analyses for a Single-Edge-notched-Bend (SEB) specimen. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step-load. We consider both the same stress exponent and different stress exponent in the power-law creep and plasticity to determine the elastic-plastic-creep behaviour. To estimation of the crack-tip stress fields, we compare FE analysis results with those obtained numerically formulas. In addition, we propose a new equation to predict the crack-tip stress fields when the creep exponent is different from the plastic exponent.

  17. Recovery of creep properties of the nickel-base superalloy nimonic 105

    CSIR Research Space (South Africa)

    Girdwood, RB

    1996-01-01

    Full Text Available -crept samples and creep recovery quantitatively assessed. Microstructural damage occurring during the creep of Nimonic 105 was studied. Creep strength is lost by the coarsening of the precipitate and grain boundary carbides. The Theta Projection Concept relates...

  18. Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design

    Science.gov (United States)

    Annigeri, Ravindra

    Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of

  19. Influence of weld structure on cross-weld creep behavior in P23 steel

    Energy Technology Data Exchange (ETDEWEB)

    Allen, D.J.; Degnan, C.C. [E.ON Engineering (United Kingdom); Brett, S.J. [RWE npower (United Kingdom); Buchanan, L.W. [Doosan Babcock (United Kingdom)

    2010-07-01

    A thick section pipe weld in low alloy steel P23 has been characterised by cross-weld creep rupture testing at a range of stresses, together with all-weld-metal and parent material testing, under the auspices of the UK High Temperature Power Plant Forum. The results generally show that the weld metal can be weak when tested in the transverse (cross-weld) orientation, and can fail with limited overall ductility by cracking in the zone of refined weld metal beneath the fusion boundary of the superposed weld bead. However, one specimen showed a much superior performance, which could be understood in terms of its locally more creep resistant weld macrostructure. The implications for P23 performance and weld manufacture are discussed. (orig.)

  20. Collect Available Creep-Fatigue Data and Study Existing Creep-Fatigue Evaluation Procedures for Grade 91 and Hastelloy XR

    Energy Technology Data Exchange (ETDEWEB)

    Tai Asayama; Yukio Tachibana

    2007-09-30

    This report describes the results of investigation on Task 5 of DOE/ASME Materials Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 5 is to collect available creep-fatigue data and study existing creep-fatigue evaluation procedures for Grade 91 steel and Hastelloy XR. Part I of this report is devoted to Grade 91 steel. Existing creep-fatigue data were collected (Appendix A) and analyzed from the viewpoints of establishing a creep-fatigue procedure for VHTR design. A fair amount of creep-fatigue data has been obtained and creep-fatigue phenomena have been clarified to develop design standards mainly for fast breeder reactors. Following this, existing creep-fatigue procedures were studied and it was clarified that the creep-fatigue evaluation procedure of the ASME-NH has a lot of conservatisms and they were analyzed in detail from the viewpoints of the evaluation of creep damage of material. Based on the above studies, suggestions to improve the ASME-NH procedure along with necessary research and development items were presented. Part II of this report is devoted to Hastelloy XR. Existing creep-fatigue data used for development of the high temperature structural design guideline for High Temperature Gas-cooled Reactor (HTGR) were collected. Creep-fatigue evaluation procedure in the design guideline and its application to design of the intermediate heat exchanger (IHX) for High Temperature Engineering Test Reactor (HTTR) was described. Finally, some necessary research and development items in relation to creep-fatigue evaluation for Gen IV and VHTR reactors were presented.

  1. Monitoring for vertical creep in concrete in two silos at Wivenhoe pumped storage hydro power station

    Energy Technology Data Exchange (ETDEWEB)

    Harris, M.W. [Queensland Univ. of Technology, Brisbane (Australia). School of Surveying

    1996-12-31

    The need for structural monitoring is generated by expected or unexpected (newly discovered in the life of the structure) behaviour. Due to the long vertical driveshafts involved at Wivenhoe the phenomenon of `concrete creep` which, if it is occurring, could contribute to shaft misalignment and unscheduled bearing wear or failure, was used as a motivation to establish a vertical monitoring system. The particular system developed for this site is traceable, replaceable, expandable and inexpensive. Measurements are obtained by precise levelling and the use of specially calibrated vertically suspended tapes. The analysis of the vertical loops is performed using constrained variance estimation and `robust` inter-epoch comparison. (orig.)

  2. Analysis of Accelerometer Data from a Woven Inflatable Creep Burst Test

    Science.gov (United States)

    James, George H.; Grygier, Michael; Selig, Molly M.

    2015-01-01

    Accelerometers were used to montor an inflatable test article during a creep test to failure. The test article experienced impulse events that were classified based on the response of the sensors and their time-dependent manifestation. These impulse events required specialized techniques to process the structural dynamics data. However, certain phenomena were defined as worthy of additional study. An assessment of one phenomena (a frequency near 1000Hz) showed a time dependent frequency and an amplitude that increased significantly near the end of the test. Hence, these observations are expected to drive future understanding of and utility in inflatable space structures.

  3. Development of Bundle Position-Wise Linear Model for Predicting the Pressure Tube Diametral Creep in CANDU Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jae Yong [Korea Electric Power Corporation Research Institute, Daejeon (Korea, Republic of); Na, Man Gyun [Chosun University, Gwangju (Korea, Republic of)

    2011-08-15

    Diametral creep of the pressure tube (PT) is one of the principal aging mechanisms governing the heat transfer and hydraulic degradation of a heat transport system. PT diametral creep leads to diametral expansion that affects the thermal hydraulic characteristics of the coolant channels and the critical heat flux. Therefore, it is essential to predict the PT diametral creep in CANDU reactors, which is caused mainly by fast neutron irradiation, reactor coolant temperature and so forth. The currently used PT diametral creep prediction model considers the complex interactions between the effects of temperature and fast neutron flux on the deformation of PT zirconium alloys. The model assumes that long-term steady-state deformation consists of separable, additive components from thermal creep, irradiation creep and irradiation growth. This is a mechanistic model based on measured data. However, this model has high prediction uncertainty. Recently, a statistical error modeling method was developed using plant inspection data from the Bruce B CANDU reactor. The aim of this study was to develop a bundle position-wise linear model (BPLM) to predict PT diametral creep employing previously measured PT diameters and HTS operating conditions. There are twelve bundles in a fuel channel and for each bundle, a linear model was developed by using the dependent variables, such as the fast neutron fluxes and the bundle temperatures. The training data set was selected using the subtractive clustering method. The data of 39 channels that consist of 80 percent of a total of 49 measured channels from Units 2, 3 and 4 were used to develop the BPLM models. The remaining 10 channels' data were used to test the developed BPLM models. The BPLM was optimized by the maximum likelihood estimation method. The developed BPLM to predict PT diametral creep was verified using the operating data gathered from the Units 2,3 and 4 in Korea. Two error components for the BPLM, which are the

  4. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    Energy Technology Data Exchange (ETDEWEB)

    Bimal K. Kad

    2005-06-27

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  5. Creep and creep-rupture behavior of a continuous strand, swirl mat reinforced polymer composite in automotive environments

    Energy Technology Data Exchange (ETDEWEB)

    Ren, W.; Brinkman, C.R. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

    1998-12-31

    Creep and creep-rupture behavior of an isocyanurate based polyurethane matrix with a continuous strand, swirl mat E-glass reinforcement was investigated for automotive applications. The material under stress was exposed to various automobile service environments. Results show that environment has substantial effects on its creep and creep-rupture properties. Proposed design guide lines and stress reduction factors were developed for various automotive environments. These composites are considered candidate structural materials for light weight and fuel efficient automobiles of the future.

  6. Creep rupture behavior of 9Cr–1.8W–0.5Mo–VNb (ASME grade 92) ferritic steel weld joint

    Energy Technology Data Exchange (ETDEWEB)

    Sakthivel, T., E-mail: tsakthivel@igcar.gov.in; Vasudevan, M.; Laha, K., E-mail: laha@igcar.gov.in; Parameswaran, P.; Chandravathi, K.S.; Panneer Selvi, S.; Maduraimuthu, V.; Mathew, M.D.

    2014-01-03

    Creep rupture behavior of 9Cr–1.8W–0.5Mo–VNb (ASME grade 92) ferritic steel weld joint fabricated by activated TIG (A-TIG) welding process have been investigated at 923 K over a stress range of 80–150 MPa. The weld joint was comprise of fusion zone, heat affected zone (HAZ) and base metal. The HAZ consisted of coarse prior-austenite grain (CGHAZ), fine prior-austenite grain (FGHAZ) and intercritical (ICHAZ) regions in an order away from the fusion zone to base metal. A hardness trough was observed at the outer edge of HAZ of the weld joint. TEM investigation revealed the presence of coarse M{sub 23}C{sub 6} precipitates and recovery of martensite lath structure into subgrain in the ICHAZ of the weld joint, leading to the hardness trough. The weld joint exhibited lower creep rupture lives than the base metal at relatively lower stresses. Creep rupture failure location of the weld joint was found to shift with applied stress. At high stresses fracture occurred in the base metal, whereas failure location shifted to FGHAZ at lower stresses with significant decrease in rupture ductility. SEM investigation of the creep ruptured specimens revealed precipitation of Laves phase across the joint, more extensively in the FGHAZ. On creep exposure, the hardness trough was found to shift from the ICHAZ to FGHAZ. Extensive creep cavitation was observed in the FGHAZ and was accompanied with the Laves phase, leading to the premature type IV failure of the steel weld joint at the FGHAZ.

  7. Microstructural Evolution and Creep-Rupture Behavior of Fusion Welds Involving Alloys for Advanced Ultrasupercritical Power Generation

    Science.gov (United States)

    Bechetti, Daniel H., Jr.

    Projections for large increases in the global demand for electric power produced by the burning of fossil fuels, in combination with growing environmental concerns surrounding these fuel sources, have sparked initiatives in the United States, Europe, and Asia aimed at developing a new generation of coal fired power plant, termed Advanced Ultrasupercritical (A-USC). These plants are slated to operate at higher steam temperatures and pressures than current generation plants, and in so doing will offer increased process cycle efficiency and reduced greenhouse gas emissions. Several gamma' precipitation strengthened Ni-based superalloys have been identified as candidates for the hottest sections of these plants, but the microstructural instability and poor creep behavior (compared to wrought products) of fusion welds involving these alloys present significant hurdles to their implementation and a gap in knowledge that must be addressed. In this work, creep testing and in-depth microstructural characterization have been used to provide insight into the long-term performance of these alloys. First, an investigation of the weld metal microstructural evolution as it relates to creep strength reductions in A-USC alloys INCONELRTM 740, NIMONICRTM 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and HaynesRTM 282RTM (Haynes and 282 are registered trademarks of Haynes International) was performed. gamma'-precipitate free zones were identified in two of these three alloys, and their development was linked to the evolution of phases that precipitate at the expense of gamma'. Alloy 282 was shown to avoid precipitate free zone formation because the precipitates that form during long term aging in this alloy are poor in the gamma'-forming elements. Next, the microstructural evolution of INCONELRTM 740H (a compositional variant of alloy 740) during creep was investigated. Gleeble-based interrupted creep and creep-rupture testing was used to

  8. Creep of trabecular bone from the human proximal tibia

    Energy Technology Data Exchange (ETDEWEB)

    Novitskaya, Ekaterina, E-mail: eevdokim@ucsd.edu [Mechanical and Aerospace Engineering, UC, San Diego, La Jolla, CA 92093 (United States); Materials Science and Engineering Program, UC, San Diego, La Jolla, CA 92093 (United States); Zin, Carolyn [Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218 (United States); Chang, Neil; Cory, Esther; Chen, Peter [Departments of Bioengineering and Orthopaedic Surgery, UC, San Diego, La Jolla, CA 92093 (United States); D’Lima, Darryl [Shiley Center for Orthopaedic Research and Education, Scripps Health, La Jolla, CA 92037 (United States); Sah, Robert L. [Materials Science and Engineering Program, UC, San Diego, La Jolla, CA 92093 (United States); Departments of Bioengineering and Orthopaedic Surgery, UC, San Diego, La Jolla, CA 92093 (United States); McKittrick, Joanna [Mechanical and Aerospace Engineering, UC, San Diego, La Jolla, CA 92093 (United States); Materials Science and Engineering Program, UC, San Diego, La Jolla, CA 92093 (United States)

    2014-07-01

    Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for 2 h and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37 °C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (μCT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. - Highlights: • Compressive creep tests of human trabecular bone across the tibia were performed. • The creep rate was found to be inversely proportional to the density of the samples. • μ-computed tomography before and after testing identified regions of deformation. • Bending of the trabeculae was found to be the main deformation mode.

  9. Creep life simulations of EB welded copper overpack

    Energy Technology Data Exchange (ETDEWEB)

    Holmstroem, S.; Laukkanen, A.; Andersson, T. [VTT Technical Research Centre of Finland, Espoo (Finland)

    2013-12-15

    The long term life predictions of copper overpack (sealed by EB welding in Finland) have previously been based on stress estimations that vary over a wide range, typically between 40-100 MPa. These values are usually not based on structural calculation including the EB-weld that increases the complexity of the stress state in the copper overpack. This report will attempt to pinpoint and simulate the stresses and strains developing in the copper overpack during its first decennia of repository service by advanced FEA simulations including the impact of the EB-weld. The main challenge of this work is the extrapolation of the creep strain response of OFP copper to the service relevant loads and temperatures. The uniaxial creep model is translated to a multiaxial constitutive equation form with adequate computational efficiency. The copper overpack strain and stress evolution has been simulated at up to 100 000 years at a conservative constant temperature of 80 deg C with 14 MPa of external pressure. The results indicate rapid creep relaxation in the initial stages after the load has been applied followed by limited creep strain accumulation thereafter. Local elastic-plastic and creep deformation is predicted at the EB weld root with a total strain of below 12 %. The predicted stresses after external loading and short term relaxation are moderate and the impact of weld residual stresses and the lower creep rupture properties of the EB seem not to be detrimental to the predicted long term creep response. The simulation results imply that the most crucial impact on the creep strain accumulation of the copper overpack is related to the OFP copper primary creep properties. The present study predicts sufficiently low creep strains for a 100 000 years canister life with the conservative assumption at a constant temperature of 80 deg C. However a sensitivity study on the impact of primary creep is strongly recommended due to contradicting analysis results from earlier FEA

  10. Creep and Creep Crack Growth Behaviors for SMAW Weldments of Gr. 91 Steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Yin, Song Nan; Park, Ji Yeon; Hong, Sung Deok; Kim, Yong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Jae Young [Pukyong National University, Busan (Korea, Republic of)

    2010-05-15

    High Cr ferritic resistance steels with tempered martensite microstructures posses enhanced creep strength at the elevated temperatures. Those steels as represented by a modified 9Cr-1Mo steel (ASME Grade 91, hereafter Gr.91) are regarded as main structural materials of sodium-cooled fast reactors (SFR) and reactor pressure vessel materials of very high temperature reactors (VHTR). The SFR and VHTR systems are designed during long-term duration reaching 60 years at elevated temperatures and often subjected to non-uniform stress and temperature distribution during service. These conditions may generate localized creep damage and propagate the cracks and ultimately may cause a fracture. A significant portion of its life is spent in crack propagation. Therefore, a creep crack growth rate (CCGR) due to creep damage should be assessed for both the base metal (BM) and welded metal (WM). Enough CCGR data for them should be provided for assessing their structural integrities. However, their CCGR data for the Gr. 91 steels is still insufficient. In this study, the CCGR for the BM and the WM of the Gr. 91 steel was comparatively investigated. A series of the CCG tests were conducted under different applied loads for the BM and the WM at 600 .deg. C. The CCGR was characterized in terms of the C parameter, and their CCG behavior were compared, respectively

  11. Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep

    Science.gov (United States)

    Simpson, R.W.; Lienkaemper, J.J.; Galehouse, J.S.

    2001-01-01

    Variations ill surface creep rate along the Hayward fault are modeled as changes in locking depth using 3D boundary elements. Model creep is driven by screw dislocations at 12 km depth under the Hayward and other regional faults. Inferred depth to locking varies along strike from 4-12 km. (12 km implies no locking.) Our models require locked patches under the central Hayward fault, consistent with a M6.8 earthquake in 1868, but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends. For the northern onshore part of the fault, our models contain 1.4-1.7 times more stored moment than the model of Bu??rgmann et al. [2000]; 45-57% of this stored moment resides in creeping areas. It is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip.

  12. Diffusional creep and creep degradation in the dispersion-strengthened alloy TD-NiCr

    Science.gov (United States)

    Whittenberger, J. D.

    1972-01-01

    Dispersoid-free regions were observed in TD-NiCr (Ni-20Cr-2ThO2) after slow strain rate testing in air from 1145 to 1590 K. Formation of the dispersoid-free regions appears to be the result of diffusional creep. The net effect of this creep is the degradation of TD-NiCr to a duplex microstructure. Degradation is further enhanced by the formation of voids and integranular oxidation in the thoria-free regions. These regions apparently provided sites for void formation and oxide growth since the strength and oxidation resistance of Ni-20Cr is much less than Ni-20Cr-2ThO2. This localized oxidation does not appear to reduce the static load bearing capacity of TD-NiCr since long stress rupture lives were observed even with heavily oxidized microstructures. But this oxidation does significantly reduce the ductility and impact resistance of the material. Dispersoid-free bands and voids were also observed for two other dispersion strengthened alloys, TD-NiCrAl and IN-853. Thus, it appears that diffusional creep is charactertistic of dispersion-strengthened alloys and can play a major role in the creep degradation of these materials.

  13. Boron effects on creep rupture strength of W containing advanced ferritic creep resistant steels

    Energy Technology Data Exchange (ETDEWEB)

    Mito, N.; Hasegawa, Y. [Tohoku Univ., Sendai (Japan)

    2010-07-01

    The creep strength in ferritic creep resistant steels is increased by boron addition. However, the strengthening mechanisms have not yet been studied. This study clarifies the strengthening mechanism of 9% chromium steels with 10{proportional_to}100ppm boron and 0.5{proportional_to}2.0mass% tungsten in the laboratory. The strengthening effect of simultaneous addition of boron and tungsten was analyzed by hardenability, room-temperature strength and creep tests at 650 C. Changes in the microstructure as a result of the addition of boron and tungsten were also examined by optical microscope and transmission electron microscope (TEM). In addition, Alpha-ray Track Etching (ATE) method was used to detect the boron distribution and analyze the mechanisms change in the mechanical properties. Boron addition did not affect room-temperature strength, however, simultaneous addition of boron and tungsten increased room-temperature and high-temperature strength. According to ATE analysis, boron exists at the grain boundary. Therefore, synergistic effects of boron and tungsten on the creep strength suggest the tungsten precipitates stabilization by boron at the grain boundary. (orig.)

  14. Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yanli [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jetter, Robert I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Baird, Seth T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pu, Chao [Univ. of Tennessee, Knoxville, TN (United States); Sham, Sam [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2015-06-22

    For the temperature range of 990-950C, Alloy 617 is a candidate IHX structural material for high temperature gas reactors (HTGRs) because of its high temperature creep properties. Also, its superior strength over a broad temperature range also offers advantages for certain component applications. In order for the designers to be able to use Alloy 617 for these high temperature components, Alloy 617 has to be approved for use in Section III (the nuclear section) of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. A plan has been developed to propose a Code Case for use of Alloy 617 at elevated temperature in Section III of the ASME Code by September 2015. There has not been a new high temperature material approved for use in Section III for almost 20 years. The Alloy 617 Code Case effort would lead the way to establish a path for Code qualification of new high temperature materials of interest to other advanced SMRs. Creep-fatigue at elevated temperatures is the most damaging structural failure mode. In the past 40 years significant efforts have been devoted to the elevated temperature Code rule development in Section III, Subsection NH* of the ASME Boiler and Pressure Vessel Code, to ascertain conservative structural designs to prevent creep-fatigue failure. The current Subsection NH creep-fatigue procedure was established by the steps of (1) analytically obtaining a detailed stress-strain history, (2) comparing the stress and strain components to cyclic test results deconstructed into stress and strain quantities, and (3) recombining the results to obtain a damage function in the form of the so-called creep-fatigue damage-diagram. The deconstruction and recombination present difficulties in evaluation of test data and determination of cyclic damage in design. The uncertainties in these steps lead to the use of overly conservative design factors in the current creep-fatigue procedure. In addition, and of major significance to the

  15. Technique for the residual life assessment of high temperature components based on creep-rupture testing on welded miniature specimens

    Energy Technology Data Exchange (ETDEWEB)

    Garzillo, A.; Guardamagna, C.; Moscotti, L.; Ranzani, L. [Ente Nazionale per l`Energia Elettrica, Milan (Italy)

    1995-06-01

    Following the present trend in the development of advanced methodologies for residual life assessment of high temperature components operating in power plants, particularly in non destructive methods, a testing technique has been set up at ENEL-CRAM based on creep-rupture testa in an argon on welded miniature specimens. Five experimental systems for creep-rupture tests in an argon atmosphere have been set up which include high accuracy systems, vacuum chambers and exrwnsometer devices. With the aim of establishing and validating the suitability of the experimental methodology, creep-rupture and interrupted creep testing programmes have been performed on miniature specimens (2 mm diameter and 10 mm gauge lenght). On the basis of experience gathered by various European research laboratories, a miniature specimen construction procedure has been developed using a laser welding technique for joining threaded heads to sample material. Low alloy ferritic steels, such as virgin 2.25CrlMo, 0.5Cr 0.5Mo 0.25V, and IN 738 superalloy miniature specimens have been investigated and the results, compared with those from standard specimens, show a regular trend in deformation vs time. Additional efforts to provide guidelines for material sampling from each plant component will be required in order to reduce uncertainties in residual life prediction.

  16. Creep, fatigue and creep-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels

    Science.gov (United States)

    Kalyanasundaram, Valliappa

    Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated temperature structural components. Creep-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the creep, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (creep, fatigue and C-F) on grade P91 steel at 625°C in a round-robin (RR) program. Along with 7 creep deformation and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal creep deformation and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625°C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of

  17. Assessment of surface relief and short cracks under cyclic creep in a type 316LN austenitic stainless steel

    Science.gov (United States)

    Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Laha, K.

    2015-12-01

    Formation of surface relief and short cracks under cyclic creep (stress-controlled fatigue) in type 316LN stainless steel was studied at temperatures ranging from ambient to 923 K using scanning electron microscopy technique. The surface topography and crack distribution behaviour under cyclic creep were found to be strong functions of testing temperature due to the difference in strain accumulation. At 823 K, surface relief mainly consisted of fine slip markings due to negligible accumulation of strain as a consequence of dynamic strain ageing (DSA) which led to an increase in the cyclic life. Persistent slip markings (PSM) with distinct extrusions containing minute cracks were seen to prevail in the temperature range 873-923 K, indicating a higher slip activity causing higher strain accumulation in the absence of DSA. Besides, a large number of secondary cracks (both transgranular and intergranular) which were partially accentuated by severe oxidation, were observed. Extensive cavitation-induced grain boundary cracking took place at 923 K, which coalesced with PSM-induced transgranular cracks resulting in failure dominated by creep that in turn led to a drastic reduction in cyclic life. Investigations on the influence of stress rate were also carried out which underlined the presence of DSA at 823 K. At 923 K, lowering the stress rate caused further strengthening of the contribution from creep damage marked by a shift in the damage mechanism from cyclic slip to diffusion.

  18. Study of irradiation creep of vanadium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, H.; Strain, R.V.; Smith, D.L. [Argonne National Lab., IL (United States)] [and others

    1997-08-01

    Thin-wall tubing was produced from the 832665 (500 kg) heat of V-4 wt.% Cr-4 wt.% Ti to study its irradiation creep behavior. The specimens, in the form of pressurized capsules, were irradiated in Advanced Test Reactor and High Flux Isotope Reactor experiments (ATR-A1 and HFIR RB-12J, respectively). The ATR-A1 irradiation has been completed and specimens from it will soon be available for postirradiation examination. The RB-12J irradiation is not yet complete.

  19. Revisiting Creeping Competences in the EU

    DEFF Research Database (Denmark)

    Citi, Manuele

    2014-01-01

    case where secondary legislation was employed to extend a formal treaty-based competence (civilian research and technology policy) to an area that, for historical and strategic reasons, has always been a policy monopoly of national governments: research and technology development policy for security...... and defence. Through the analysis of a large pool of documentary data, I elaborate a set of linked hypotheses about the empirical dynamics of creeping competences, and show how the theory of incomplete contracting is best suited to explain this phenomenon....

  20. Out-of-pile creep behavior of uranium carbide

    Science.gov (United States)

    Wright, T. R.; Seltzer, M. S.

    1974-01-01

    Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi.

  1. Mullite—corundum Refractories with High Creep Resistance

    Institute of Scientific and Technical Information of China (English)

    LIANGYong-be; LINan; 等

    1996-01-01

    Mullite-corundum bricks and kiln furni-ture with high creep resistance and good thermal shock resistance were fabricated based on low cost raw materials,the approaches of introducing some additives and optimisig,chemical composition and partical size were mployed to produce a high temperature matrix phase with high creep resistance and good thermal shock resistance.

  2. Creep behavior of abaca fibre reinforced composite material

    Energy Technology Data Exchange (ETDEWEB)

    Tobias, B.C.; Lieng, V.T. [Victoria Univ. of Technology, Victoria (Australia)

    1996-12-31

    This study investigates the creep behavior of abaca fibre reinforced composite lamina. The optimum proportions of constituents and loading conditions, temperature and stresses, are investigated in terms of creep properties. Lamina with abaca fibre volume fractions of 60, 70 and 80 percent, embedded in polyester resin were fabricated. Creep tests in tension at three temperature levels 20{degrees}C, 100{degrees}C and 120{degrees}C and three constant stress levels of 0. 1 MPa, 0. 13 Mpa and 0. 198 MPa using a Dynamic Mechanical Analyzer (DMA) were performed. The creep curves show standard regions of an ideal creep curve such as primary and secondary creep stage. The results also show that the minimum creep rate of abaca fibre reinforced composite increases with the increase of temperature and applied stress. Plotting the minimum creep rate against stress, depicts the variations of stress exponents which vary from 1.6194 at 20{degrees}C to 0.4576 at 120{degrees}C.

  3. Creep degradation in oxide-dispersion-strengthened alloys

    Science.gov (United States)

    Whittenberger, J. D.

    1977-01-01

    Oxide dispersion strengthened Ni-base alloys in wrought bar form are studied for creep degradation effects similar to those found in thin gage sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and three types of advanced ODS-NiCrAl alloys. Tensile test specimens were exposed to creep at various stress levels at 1365 K and then tensile tested at room temperature. Low residual tensile properties, change in fracture mode, the appearance of dispersoid-free bands, grain boundary cavitation, and internal oxidation in the microstructure were interpreted as creep degradation effects. This work showed that many ODS alloys are subject to creep damage. Degradation of tensile properties occurred after very small amounts of creep strain, ductility being the most sensitive property. All the ODS alloys which were creep damaged possessed a large grain size. Creep damage appears to have been due to diffusional creep which produced dispersoid-free bands around boundaries acting as vacancy sources. Low angle and possibly twin boundaries acted as vacancy sources.

  4. A Comparison of the Irradiation Creep Behavior of Several Graphites

    Energy Technology Data Exchange (ETDEWEB)

    Burchell, Timothy D [ORNL; Windes, Will [Idaho National Laboratory (INL)

    2016-01-01

    Graphite creep strain data from the irradiation creep capsule Advanced Graphite Creep-1 (AGC-1) are reported. This capsule was the first (prototype) of a series of five or six capsules planned as part of the AGC experiment, which was designed to fully characterize the effects of neutron irradiation and the radiation creep behavior of current nuclear graphite. The creep strain data and analysis are reported for the six graphite grades incorporated in the capsule. The AGC-1 capsule was irradiated in the Advanced Test Reactor at Idaho National Laboratory (INL) at approximately 700 C and to a peak dose of 7 dpa (displacements per atom). The specimen s final dose, temperature, and stress conditions have been reported by INL and were used during this analysis. The derived creep coefficients (K) were calculated for each grade and were found to compare well to literature data for the creep coefficient, even under the wide range of AGC-1 specimen temperatures. Comparisons were made between AGC-1 data and historical grade data for creep coefficients.

  5. ON INTEGRITY ASSESSMENT OF AXISYMMETRIC COMPONENTS OPERATING WITHIN CREEP REGIME

    Institute of Scientific and Technical Information of China (English)

    ZARRABI K; LAWRENCE Ng

    2006-01-01

    A multiaxial paradigm for predicting creep damage/lives of components is described. Although in principle the paradigm is general, it is verified using axisymmetric experimental data. It is shown that the proposed paradigm is capable of predicting creep lives with an error of less than 2%. It is also shown that the proposed paradigm is more accurate than the reference stress method.

  6. Creep deformation and rupture behavior of CLAM steel at 823 K and 873 K

    Science.gov (United States)

    Zhong, Boyu; Huang, Bo; Li, Chunjing; Liu, Shaojun; Xu, Gang; Zhao, Yanyun; Huang, Qunying

    2014-12-01

    China Low Activation Martensitic (CLAM) steel is selected as the candidate structural material in Fusion Design Study (FDS) series fusion reactor conceptual designs. The creep property of CLAM steel has been studied in this paper. Creep tests have been carried out at 823 K and 873 K over a stress range of 150-230 MPa. The creep curves showed three creep regimes, primary creep, steady-state creep and tertiary creep. The relationship between minimum creep rate (ε˙min) and the applied stress (σ) could be described by Norton power law, and the stress exponent n was decreased with the increase of the creep temperature. The creep mechanism was analyzed with the fractographes of the rupture specimens which were examined by scanning electron microscopy (SEM). The coarsening of precipitates observed with transmission electron microscope (TEM) indicated the microstructural degradation after creep test.

  7. Effect of misalignment on mechanical behavior of metals in creep. [computer programs

    Science.gov (United States)

    Wu, H. C.

    1979-01-01

    Application of the endochronic theory of viscoplasticity to creep, creep recovery, and stress relaxation at the small strain and short time range produced the following results: (1) The governing constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation were derived by imposing appropriate constraints on the general constitutive equation of the endochronic theory. (2) A set of material constants was found which correlate strain-hardening, creep, creep recovery, and stress relaxation. (3) The theory predicts with reasonable accuracy the creep and creep recovery behaviors at short time. (4) The initial strain history prior to the creep stage affects the subsequent creep significantly. (5) A critical stress was established for creep recovery. A computer program, written for the misalignment problem is reported.

  8. Optimum design of inhomogeneous rotating discs under secondary creep

    Energy Technology Data Exchange (ETDEWEB)

    Farshi, Behrooz [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846 (Iran, Islamic Republic of)], E-mail: Farshi@iust.ac.ir; Bidabadi, Jalal [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846 (Iran, Islamic Republic of)

    2008-07-15

    Rotating discs commonly used in the aerospace industry often operate under high mechanical stresses due to centrifugal forces, while subject to high temperature gradients. High stresses and temperatures lead to creep in such rotating disc applications. This problem is particularly important in turbine discs under continuous operation. Since such discs are subject to secondary creep effects during most of their useful lives, it is important that they be optimized for minimum weight for the steady-state creep stresses. In this investigation, by considering the variable physical properties of the rotating disc materials under a high temperature gradient, a procedure for weight minimization for the steady-state creep stresses is proposed. The method aims to design the disc thickness profile so as to have minimum weight while the equivalent secondary creep stresses of the rotating disc under a high temperature gradient at all points simultaneously approach but do not exceed an allowable stress. An example is given to illustrate the method.

  9. Accelerated creep of Ni-YSZ anodes during reduction

    DEFF Research Database (Denmark)

    Frandsen, Henrik Lund; Greco, Fabio; Ni, De Wei

    2014-01-01

    by the thermomechanical history of the stack (e.g. sintering temperature, time at temperature etc.). During operation the stress state will depend on time as stresses are relaxed by creep processes. Creep has mainly been studied at operating conditions, where the Ni-YSZ anode is in the reduced state and YSZ is the main...... load-carrying component. In this work we report on a new creep-reduction phenomenon observed to take place during the reduction process itself, where stresses are relaxed at a rate much faster (~×104) than during operation where the anode is in fully reduced state. Furthermore, samples exposed...... to a very small tensile stress (0.004 MPa) were observed to expand during reduction, which is in contrast with reports in literature [Ref].The “accelerated” creep has a tremendous impact on the stress field in an operating SOFC stack. Creep experiments, where carried out on NiO-YSZ anode support structures...

  10. Uniaxial tension and tensile creep behaviors of EPS

    Institute of Scientific and Technical Information of China (English)

    康颖安; 李显方; 谭加才

    2008-01-01

    The mechanical behavior of EPS(Expanded polystyrene) with three densities at room temperature and under tension loading was studied.The results show that EPS material is characterized by brittle behavior in the tension tests,and tensile properties of EPS increase with the increase of density.Volume fraction has no a significant effect on the modulus of these foams.The tensile creep strain increases with stress for EPS with same density,indicating that the creep behavior is of the stress dependency.And the creep behavior of EPS exhibits density dependency,which the creep strain decreases with densities for a fixed stress value.Moreover the creep behavior under the constant tension load is well in coincidence with the three-parameter solid model.

  11. Creep in refractory materials; Fluencia en materiales refractarios

    Energy Technology Data Exchange (ETDEWEB)

    Tomba Martinez, A. G.; Luz, A. P.; Pandolfelli, V. C.

    2013-10-01

    Refractory materials are widely used in various industrial fields due to their outstanding properties and performance in aggressive environments. However, although creep resistance is one of the most important properties for the selection of these materials, few researches were carried out focused on the fundamentals and technological understanding of their performance at high temperatures. In this context, this work addresses: 1) the creep mechanisms, 2) the mathematical models proposed for the analysis and to forecast the creep deformation at high temperature, 3) technical procedures and experimental testing, and 4) a critical analysis of some basic and practical aspects considering the literature available on this issue. Based on the collected information, mathematical models (such as the Projection concept) were considered as a powerful tool for the prediction of the refractories creep behavior, helping to identify the main creep mechanisms in these materials and to induce the development of optimized compositions able to attend the end-users requirements. (Author)

  12. Indentation creep in zirconia ceramics under variable loads

    Energy Technology Data Exchange (ETDEWEB)

    Ren, X.J. [School of Engineering, Liverpool John Moores Univ., Liverpool (United Kingdom); Hooper, R.M. [School of Engineering and Computer Science, Univ. of Exeter, Exeter (United Kingdom); Henshall, J.L. [Mechanical and Mfg. Engineering Dept., Nottingham Trent Univ., Nottingham (United Kingdom)

    2005-07-01

    Time dependent deformation at room and elevated temperature is a significant property of zirconia ceramics and has a direct influence on their use. An understanding of this time dependent behaviour is therefore important in predicting the service life of a component. In this work, the indentation creep behaviour of two typical zirconia ceramics - ceria stabilised polycrystalline tetragonal (Ce-TZP) and yttria (6%) stabilized polycrystalline cubic zirconia, YCPZ, have been investigated from room temperature to 600 C. Indentation creep tests with various loads yielded identical creep rate, which indicates that indentation size effect has no significant effect on the indentation creep of zirconia ceramics. Tests with variable loads, using a spring loaded apparatus, exhibited comparable indentation creep rates to that under constant loading. (orig.)

  13. Dislocation-mediated creep process in nanocrystalline Cu

    Institute of Scientific and Technical Information of China (English)

    Mu Jun-Wei; Sun Shi-Cheng; Jiang Zhong-Hao; Lian Jian-She; Jiang Qing

    2013-01-01

    Nanocrystalline Cu with average grain sizes ranging from ~ 24.4 to 131.3 nm were prepared by the electric brushplating technique.Nanoindentation tests were performed within a wide strain rate range,and the creep process of nanocrystalline Cu during the holding period and its relationship to dislocation and twin structures were examined.It was demonstrated that creep strain and creep strain rate are considerably significant for smaller grain sizes and higher loading strain rates,and are far higher than those predicted by the models of Cobble creep and grain boundary sliding.The analysis based on the calculations and experiments reveals that the significant creep deformation arises from the rapid absorption of high density dislocations stored in the loading regime.Our experiments imply that stored dislocations during loading are highly unstable and dislocation activity can proceed and lead to significant post-loading plasticity.

  14. Determination of the Creep Parameters of Linear Viscoelastic Materials

    Directory of Open Access Journals (Sweden)

    Alibay Iskakbayev

    2016-01-01

    Full Text Available Creep process of linear viscoelastic materials is described by the integral equation of Boltzmann-Volterra in which creep kernel is approximated by Rabotnov’s fractional exponential function. The creep equation contains four unknown parameters: α, singularity parameter; β, fading parameter; λ, rheological parameter; and ε0, conditionally instantaneous strain. Two-stage determination method of creep parameters is offered. At the first stage, taking into account weak singularity properties of Abel’s function at the initial moment of loading, parameters ε0 and α are determined. At the second stage, using already known parameters ε0 and α, parameters β and λ are determined. Analytical expressions for calculating these parameters are obtained. An accuracy evaluation of the offered method with using experimentally determined creep strains of material Nylon 6 and asphalt concrete showed its high accuracy.

  15. A New Creep Constitutive Model for 7075 Aluminum Alloy Under Elevated Temperatures

    Science.gov (United States)

    Lin, Y. C.; Jiang, Yu-Qiang; Zhou, Hua-Min; Liu, Guan

    2014-12-01

    Exposure of aluminum alloy to an elastic loading, during "creep-aging forming" or other manufacturing processes at relatively high temperature, may lead to the lasting creep deformation. The creep behaviors of 7075 aluminum alloy are investigated by uniaxial tensile creep experiments over wide ranges of temperature and external stress. The results show that the creep behaviors of the studied aluminum alloy strongly depend on the creep temperature, external stress, and creep time. With the increase of creep temperature and external stress, the creep strain increases quickly. In order to overcome the shortcomings of the Bailey-Norton law and θ projection method, a new constitutive model is proposed to describe the variations of creep strain with time for the studied aluminum alloy. In the proposed model, the dependences of creep strain on the creep temperature, external stress, and creep time are well taken into account. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate description of the creep behaviors of 7075 aluminum alloy. Meanwhile, the obtained stress exponent indicates that the creep process is controlled by the dislocation glide, which is verified by the microstructural observations.

  16. Effects of Cytokinin and Nitrogen on Drought Tolerance of Creeping Bentgrass.

    Science.gov (United States)

    Chang, Zhihui; Liu, Yang; Dong, Hui; Teng, Ke; Han, Liebao; Zhang, Xunzhong

    2016-01-01

    Cytokinin (CK) is a vital plant hormone that controls many aspects of growth and development in plants. Nitrogen (N) is the indispensable macronutrient needed in plants and also one of the most important limiting factors for plant growth. This study was designed to investigate the simultaneous effects of CK and N on the visual turf quality and antioxidant metabolism of drought-stressed creeping bentgrass (Agrostis stolonifera L.). 'PennA-4' creeping bentgrass treated with trans-zeatin riboside at three rates of CK concentrations of 0, 10 and 100 μM (designated by CK0, 10, and 100) and two nitrogen rates with 2.5 and 7.5 kg N·ha-1 every 15 days (designated by low and high N) in a complete factorial arrangement was grown under two soil moisture regimes: well-watered and drought stress. Exogenous CK improved turf quality and delayed leaf wilting under drought stress, especially under high N. The grasses treated with CK10 and CK100 had lower O2- production and H2O2 concentration than those without CK treatment. The CK100 treatment enhanced the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (POD) by 25%, 22%, 17% and 24%, respectively, relative to CK0. Moreover, the activity changes of the antioxidant enzyme isoforms were more significant under high N condition relative to low N condition. Our results demonstrated the beneficial impacts of CK and N on physiological reactions, especially antioxidant metabolism, and foliar application of CK at 10 or 100 μM plus 7.5 kg ha-1 N biweekly may improve drought stress resistance of creeping bentgrass.

  17. Addition of chromic oxide to creep feed as a fecal marker for selection of creep feed-eating suckling pigs

    NARCIS (Netherlands)

    Kuller, W.I.; Beers-Schreurs, van H.M.G.; Soede, N.M.; Taverne, M.A.M.; Kemp, B.; Verheijden, J.H.M.

    2007-01-01

    Objective-To determine whether the addition of chromic oxide (Cr2O3) to creep feed could be used as a visual marker in feces for selection of creep feed-eating suckling pigs. Animals-20 suckling pigs. Procedures-Via syringe, 5 pigs (2 to 3 days old on day 0; 1 pig/treatment) from each of 4 litters

  18. Addition of chromic oxide to creep feed as a fecal marker for selection of creep feed-eating suckling pigs

    NARCIS (Netherlands)

    Kuller, W.I.; Beers-Schreurs, van H.M.G.; Soede, N.M.; Taverne, M.A.M.; Kemp, B.; Verheijden, J.H.M.

    2007-01-01

    Objective-To determine whether the addition of chromic oxide (Cr2O3) to creep feed could be used as a visual marker in feces for selection of creep feed-eating suckling pigs. Animals-20 suckling pigs. Procedures-Via syringe, 5 pigs (2 to 3 days old on day 0; 1 pig/treatment) from each of 4 litters r

  19. Active disturbance rejection control for output force creep characteristics of ionic polymer metal composites

    Science.gov (United States)

    Xiong, Yan; Chen, Yang; Sun, Zhiyong; Hao, Lina; Dong, Jie

    2014-07-01

    Ionic polymer metal composites (IPMCs) are a type of electroactive polymer (EAP) that can be used as both sensors and actuators. An IPMC has enormous potential application in the field of biomimetic robotics, medical devices, and so on. However, an IPMC actuator has a great number of disadvantages, such as creep and time-variation, making it vulnerable to external disturbances. In addition, the complex actuation mechanism makes it difficult to model and the demand of the control algorithm is laborious to implement. In this paper, we obtain a creep model of the IPMC by means of model identification based on the method of creep operator linear superposition. Although the mathematical model is not approximate to the IPMC accurate model, it is accurate enough to be used in MATLAB to prove the control algorithm. A controller based on the active disturbance rejection control (ADRC) method is designed to solve the drawbacks previously given. Because the ADRC controller is separate from the mathematical model of the controlled plant, the control algorithm has the ability to complete disturbance estimation and compensation. Some factors, such as all external disturbances, uncertainty factors, the inaccuracy of the identification model and different kinds of IPMCs, have little effect on controlling the output block force of the IPMC. Furthermore, we use the particle swarm optimization algorithm to adjust ADRC parameters so that the IPMC actuator can approach the desired block force with unknown external disturbances. Simulations and experimental examples validate the effectiveness of the ADRC controller.

  20. Remaining life assessment of a high pressure turbine casing in creep and low cycle service regime

    Directory of Open Access Journals (Sweden)

    Bakić Gordana M.

    2014-01-01

    Full Text Available Thick walled components such as high pressure (HP steam turbine casings operating under high parameter conditions are subjected to a complex stress state. As a result of that stress state, some parts of HP turbine casing undergo to the creep fatigue caused by the combination of thermal fatigue resulted from repeated start/stop operation and the creep which occurs during long-term operation at high temperature and high-pressure. It is well known that domestic thermal power plants have been in use over 100000 h which means that significant cost is required not only for maintenance, but often for renewal of equipment. Based on comprehensive investigation, the results of residual life assessment of one high pressure steam turbine casing, which belongs to the older turbine generation, taking into account simultaneous action of thermal fatigue and creep, are presented in this paper. Also, the critical flaw crack size of HP turbine casing is determined because this parameter has a strong influence on casing integrity and residual life. The results of residual life assessment provide not only a basis for further maintenance, but also estimated time for reparation or renewal.