Sample records for subcomponent tensile creep

  1. Influence of relative humidity on tensile and compressive creep of ...

    African Journals Online (AJOL)

    This paper presents an experimental study on the influence of ambient relative humidity on tensile creep of plain concrete amended with Ground Granulated Blast - furnace Slag and compares it with its influence on compressive creep. Tensile and compressive creep tests were carried out on concrete specimens of 34.49 ...

  2. influence of relative humidity on tensile and compressive creep of ...

    African Journals Online (AJOL)


    While creep is as a result of sustained stress, shrinkage is due to hygrometric conditions [1]. According to Neville et al [2], a typical concrete element creeps up to twice its initial strain after a year of loading. Concrete creep can occur in tension and also in compression. The properties of tensile and compressive creep are ...

  3. The Creep Properties of Fine Sandstone under Uniaxial Tensile Stress

    Directory of Open Access Journals (Sweden)

    Jiang Haifei


    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.

  4. Study of creep behaviour in P-doped copper with slow strain rate tensile tests

    Energy Technology Data Exchange (ETDEWEB)

    Xuexing Yao; Sandstroem, Rolf [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Materials Science and Engineering


    Pure copper with addition of phosphorous is planned to be used to construct the canisters for spent nuclear fuel. The copper canisters can be exposed to a creep deformation up to 2-4% at temperatures in services. The ordinary creep strain tests with dead weight loading are generally employed to study the creep behaviour; however, it is reported that an initial plastic deformation of 5-15% takes place when loading the creep specimens at lower temperatures. The slow strain rate tensile test is an alternative to study creep deformation behaviour of materials. Ordinary creep test and slow strain rate tensile test can give the same information in the secondary creep stage. The advantage of the tensile test is that the starting phase is much more controlled than in a creep test. In a tensile test the initial deformation behaviour can be determined and the initial strain of less than 5% can be modelled. In this study slow strain rate tensile tests at strain rate of 10{sup -4}, 10{sup -5}, 10{sup -6}, and 10{sup -7}/s at 75, 125 and 175 degrees C have been performed on P-doped pure Cu to supplement creep data from conventional creep tests. The deformation behaviour has successfully been modelled. It is shown that the slow strain rate tensile tests can be implemented to study the creep deformation behaviours of pure Cu.

  5. Study on the Tensile Creep Behavior of Carbon Nanotubes-Reinforced Sn-58Bi Solder Joints (United States)

    Yang, Li; Liu, Haixiang; Zhang, Yaocheng


    The microstructure and tensile creep behavior of plain Sn-58Bi solder and carbon nanotubes (CNTs)-reinforced composite solder joints were investigated. The stress exponent n under different stresses and the creep activation energy Q c under different temperatures of solder joints were obtained by an empirical equation. The results reveal that the microstructure of the composite solder joint is refined and the tensile creep resistance is improved by CNTs. The improvement of creep behavior is due to the microstructural change of the composite solder joints, since the CNTs could provide more obstacles for dislocation pile-up, which enhances the values of the stress exponent and the creep activation energy. The steady-state tensile creep rates of plain solder and composite solder joints are increased with increasing temperature and applied stress. The tensile creep constitutive equations of plain solder and composite solder joints are written as \\dot{ɛ }_{s1} = 14.94( {σ /G} )^{3.7} \\exp ( { - 81444/RT} ) and \\dot{ɛ }_{s2} = 2.5( {σ /G} )^{4.38} \\exp ( { - 101582/RT} ) , respectively. The tensile creep mechanism of the solder joints is the effects of lattice diffusion determined by dislocation climbing.

  6. Study on the Tensile Creep Behavior of Carbon Nanotubes-Reinforced Sn-58Bi Solder Joints (United States)

    Yang, Li; Liu, Haixiang; Zhang, Yaocheng


    The microstructure and tensile creep behavior of plain Sn-58Bi solder and carbon nanotubes (CNTs)-reinforced composite solder joints were investigated. The stress exponent n under different stresses and the creep activation energy Q c under different temperatures of solder joints were obtained by an empirical equation. The results reveal that the microstructure of the composite solder joint is refined and the tensile creep resistance is improved by CNTs. The improvement of creep behavior is due to the microstructural change of the composite solder joints, since the CNTs could provide more obstacles for dislocation pile-up, which enhances the values of the stress exponent and the creep activation energy. The steady-state tensile creep rates of plain solder and composite solder joints are increased with increasing temperature and applied stress. The tensile creep constitutive equations of plain solder and composite solder joints are written as \\dot{ɛ }_{s1} = 14.94( {σ /G} )^{3.7} \\exp ( { - 81444/RT} ) and \\dot{ɛ }_{s2} = 2.5( {σ /G} )^{4.38} \\exp ( { - 101582/RT} ) , respectively. The tensile creep mechanism of the solder joints is the effects of lattice diffusion determined by dislocation climbing.

  7. Tensile creep performance of a developmental in-situ reinforced silicon nitride

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    Wereszczak, A.A.; Kirkland, T.P.; Lin, H.T.; Ferber, M.K. [Oak Ridge National Lab., TN (United States); Li, C.W.; Goldacker, J.A. [Allied-Signal, Inc., Morristown, NJ (United States)


    The evaluation was done between 1300 and 1425 C in ambient air. Minimum creep rate was evaluated vs tensile stress and temperature, and measured tensile creep performances of two different specimen geometries (buttonhead and dogbone - machined from same billet) were compared. This Si nitride exhibited comparable or better creep resistance than other Si nitrides described in the literature. Measured creep response of the material and lifetime were observed to be geometry dependent; the smaller cross-sectioned dogbone samples exhibited faster creep rates and shorter lives, presumably due to faster oxidation-induced damage in this geometry. The tensile creep rates and lifetimes were found to be well represented by the Monkman- Grant relation between 1350 and 1425 C, with some evidence suggesting stratification of the data for the 1300 C tests and a change in dominant failure mode between 1300 and 1350 C. Lastly, values of the temperature-compensated stress exponent and activation energy for tensile creep were found to decrease by 80 and 75% in compression, respectively, illustrating anisotropic creep behavior in this Si nitride.

  8. Properties of aluminum alloys tensile, creep, and fatigue data at high and low temperatures

    CERN Document Server


    This book compiles more than 300 tables listing typical average properties of a wide range of aluminum alloys. The individual test results were compiled, plotted in various ways, and analyzed. The average values from the tensile and creep tests were then normalized to the published typical room-temperature tensile properties of the respective alloys for easy comparison. This extensive project was done by Alcoa Laboratories over a period of several years. The types of data presented include: Typical Mechanical Properties of Wrought and Cast Aluminum Alloys at Various Temperatures, including tensile properties at subzero temperatures, at temperature after various holding times at the test temperature, and at room temperature after exposure at various temperatures for various holding times; creep rupture strengths for various times at various temperatures; stresses required to generate various amounts of creep in various lengths of time; rotating-beam fatigue strengths; modulus of elasticity as a function of t...

  9. Evaluation and mathematical modeling of asymmetric tensile and compressive creep in aluminum alloy ZL109

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Qing [School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Zhang, Weizheng, E-mail: [School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Liu, Youyi [School of Mechanical Engineering, State University of New York at Stony Brook, NY 11790, US (United States)


    This study investigates the effects of tension/compression asymmetry during creep deformation under different conditions. The asymmetry is found to be dependent on stress and temperature. At high temperatures (350 °C, 70 MPa) or high levels of stress (250 °C, 130 MPa), the ratio between the tensile and compressive creep rates can be as large as 10. This ratio is smaller at lower temperatures (200 °C, 90 MPa) and lower levels of stress (300 °C, 30 MPa). Scanning electron microscopy (SEM) visualization of different microdefects indicates that the size and volume of microcavities are dependent on the level of stress applied. Similarly, transmission electron microscopy (TEM) is used to visualize dislocations and twinning. The differences in microcavity size and volume in tensile and compressive creep appear to be larger under higher temperature and stress, but no difference in dislocation is observed and no twinning crystals are found. Cavity nucleation appears to be the cause of the asymmetry in creep behavior, which is determined by temperature and stress. A new mathematical model for creep is constructed and validated considering the different asymmetric mechanisms of tensile and compressive creep.

  10. The High Temperature Tensile and Creep Behaviors of High Entropy Superalloy. (United States)

    Tsao, Te-Kang; Yeh, An-Chou; Kuo, Chen-Ming; Kakehi, Koji; Murakami, Hideyuki; Yeh, Jien-Wei; Jian, Sheng-Rui


    This article presents the high temperature tensile and creep behaviors of a novel high entropy alloy (HEA). The microstructure of this HEA resembles that of advanced superalloys with a high entropy FCC matrix and L1 2 ordered precipitates, so it is also named as "high entropy superalloy (HESA)". The tensile yield strengths of HESA surpass those of the reported HEAs from room temperature to elevated temperatures; furthermore, its creep resistance at 982 °C can be compared to those of some Ni-based superalloys. Analysis on experimental results indicate that HESA could be strengthened by the low stacking-fault energy of the matrix, high anti-phase boundary energy of the strengthening precipitate, and thermally stable microstructure. Positive misfit between FCC matrix and precipitate has yielded parallel raft microstructure during creep at 982 °C, and the creep curves of HESA were dominated by tertiary creep behavior. To the best of authors' knowledge, this article is the first to present the elevated temperature tensile creep study on full scale specimens of a high entropy alloy, and the potential of HESA for high temperature structural application is discussed.

  11. Multi-scale investigation of tensile creep of ultra-high performance concrete for bridge applications (United States)

    Garas Yanni, Victor Youssef

    Ultra-high performance concrete (UHPC) is relatively a new generation of concretes optimized at the nano and micro-scales to provide superior mechanical and durability properties compared to conventional and high performance concretes. Improvements in UHPC are achieved through: limiting the water-to-cementitious materials ratio (i.e., w/cm ≤ 0.20), optimizing particle packing, eliminating coarse aggregate, using specialized materials, and implementing high temperature and high pressure curing regimes. In addition, and randomly dispersed and short fibers are typically added to enhance the material's tensile and flexural strength, ductility, and toughness. There is a specific interest in using UHPC for precast prestressed bridge girders because it has the potential to reduce maintenance costs associated with steel and conventional concrete girders, replace functionally obsolete or structurally deficient steel girders without increasing the weight or the depth of the girder, and increase bridge durability to between 75 and 100 years. UHPC girder construction differs from that of conventional reinforced concrete in that UHPC may not need transverse reinforcement due to the high tensile and shear strengths of the material. Before bridge designers specify such girders without using shear reinforcement, the long-term tensile performance of the material must be characterized. This multi-scale study provided new data and understanding of the long-term tensile performance of UHPC by assessing the effect of thermal treatment, fiber content, and stress level on the tensile creep in a large-scale study, and by characterizing the fiber-cementitious matrix interface at different curing regimes through nanoindentation and scanning electron microscopy (SEM) in a nano/micro-scale study. Tensile creep of UHPC was more sensitive to investigated parameters than tensile strength. Thermal treatment decreased tensile creep by about 60% after 1 year. Results suggested the possibility of

  12. Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene (United States)

    Zhang, Hanyin; Cai, Linlin; Golub, Michael; Zhang, Yi; Yang, Xuehui; Schlarman, Kate; Zhang, Jing


    Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young's modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 N√ m, the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

  13. Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene (United States)

    Zhang, Hanyin; Cai, Linlin; Golub, Michael; Zhang, Yi; Yang, Xuehui; Schlarman, Kate; Zhang, Jing


    Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young's modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 N√ m , the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

  14. SEM and TEM analyses of microstructural changes in creep degraded and tensile tested CMSX-4 superalloy

    Energy Technology Data Exchange (ETDEWEB)

    Bubiel, B.; Czyrska-Filemonowicz, A. [AGH Univ. of Science and Technology, Krakow (Poland); Nazmy, M. [Alstom (Switzerland) Ltd., Baden (Switzerland); Lapin, J. [Slovak Academy of Sciences, Bratislava (Slovakia). Inst. of Materials and Machine Mechanics


    The effect of creep induced microstructural degradation caused by high temperature creep on mechanical properties of single crystal CMSX-4 superalloy was studied. Creep tests were performed at temperature 1050 C and stress of 68 MPa for 2500 h. Pre-crept specimens were subsequently tensile tested at room temperature (RT) and 950 C. Additionally, as a case study, microstructure of ex-service turbine blades after operation for 12700 hours in industrial gas turbine was investigated. Tensile tests of mini specimens cut from turbine blades were also performed. Microstructural analyses of {gamma}-{gamma}' microstructure were carried out using SEM and TEM. Observed microstructural degradation of both laboratory tested and ex-service CMSX-4 samples showed that morphological changes of {gamma}-{gamma}' microstructure associated with dislocation accumulation at {gamma}/{gamma}' interfaces influence the inhibition of deformation in {gamma} channels, what results in deterioration of CMSX-4 strength and ductility. (orig.)

  15. Non-linearities in tensile creep of concrete at early age

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Anders Boe; Damkilde, Lars


    A meterial model for creep is proposed which takes into consideration some of the couplings in early age concrete. The model is in incremental form and reflect the hydration process where new layers of cement gel are formed in a stress free state. In the present context attention is on non......-linear creep at high stress levels. The parameteres in the model develop in time as a result of hydration. The creep model has been used to analyse the tensile experiments at different stress levels carried out in the HETEK project. The tests were made on dogbone shaped specimen and the test procedure...... is described. Furthermore, compressive creep at high stress levels are fitted....

  16. Tensile-Creep Test Specimen Preparation Practices of Surface Support Liners (United States)

    Guner, Dogukan; Ozturk, Hasan


    Ground support has always been considered as a challenging issue in all underground operations. Many forms of support systems and supporting techniques are available in the mining/tunnelling industry. In the last two decades, a new polymer based material, Thin Spray–on Liner (TSL), has attained a place in the market as an alternative to the current areal ground support systems. Although TSL provides numerous merits and has different application purposes, the knowledge on mechanical properties and performance of this material is still limited. In laboratory studies, since tensile rupture is the most commonly observed failure mechanism in field applications, researchers have generally studied the tensile testing of TSLs with modification of American Society for Testing and Materials (ASTM) D-638 standards. For tensile creep testing, specimen preparation process also follows the ASTM standards. Two different specimen dimension types (Type I, Type IV) are widely preferred in TSL tensile testing that conform to the related standards. Moreover, molding and die cutting are commonly used specimen preparation techniques. In literature, there is a great variability of test results due to the difference in specimen preparation techniques and practices. In this study, a ductile TSL product was tested in order to investigate the effect of both specimen preparation techniques and specimen dimensions under 7-day curing time. As a result, ultimate tensile strength, tensile yield strength, tensile modulus, and elongation at break values were obtained for 4 different test series. It is concluded that Type IV specimens have higher strength values compared to Type I specimens and moulded specimens have lower results than that of prepared by using die cutter. Moreover, specimens prepared by molding techniques have scattered test results. Type IV specimens prepared by die cutter technique are suggested for preparation of tensile test and Type I specimens prepared by die cutter

  17. The effect of sheet processing on the microstructure, tensile, and creep behavior of INCONEL alloy 718 (United States)

    Boehlert, C. J.; Dickmann, D. S.; Eisinger, Ny. N. C.


    The grain size, grain boundary character distribution (GBCD), creep, and tensile behavior of INCONEL alloy 718 (IN 718) were characterized to identify processing-microstructure-property relationships. The alloy was sequentially cold rolled (CR) to 0, 10, 20, 30, 40, 60, and 80 pct followed by annealing at temperatures between 954 °C and 1050 °C and the traditional aging schedule used for this alloy. In addition, this alloy can be superplastically formed (IN 718SPF) to a significantly finer grain size and the corresponding microstructure and mechanical behavior were evaluated. The creep behavior was evaluated in the applied stress (σ a ) range of 300 to 758 MPa and the temperature range of 638 °C to 670 °C. Constant-load tensile creep experiments were used to measure the values of the steady-state creep rate and the consecutive load reduction method was used to determine the values of backstress (σ0). The values for the effective stress exponent and activation energy suggested that the transition between the rate-controlling creep mechanisms was dependent on effective stresses (σ e =σ a σ0) and the transition occurred at σ e ≅ 135 MPa. The 10 to 40 pct CR samples exhibited the greatest 650 °C strength, while IN 718SPF exhibited the greatest room-temperature (RT) tensile strength (>1550 MPa) and ductility (ɛ f >16 pct). After the 954 °C annealing treatment, the 20 pct CR and 30 pct CR microstructures exhibited the most attractive combination of elevated-temperature tensile and creep strength, while the most severely cold-rolled materials exhibited the poorest elevated-temperature properties. After the 1050 °C annealing treatment, the IN 718SPF material exhibited the greatest backstress and best creep resistance. Electron backscattered diffraction was performed to identify the GBCD as a function of CR and annealing. The data indicated that annealing above 1010 °C increased the grain size and resulted in a greater fraction of twin boundaries, which in

  18. Comparison of the Tensile, Creep, and Rupture Strength Properties of Stoichiometric SiC Fibers (United States)

    Yun, H. M.; DiCarlo, J. A.


    Tensile strength, creep strength, and rupture strength properties were measured for the following types of polymer-derived stoichiometric SiC fibers: Hi-Nicalon Type S from Nippon Carbon, Tyranno SA from Ube, and Sylramic from Dow Corning. Also included in this study were an earlier version of the SA fiber plus two recent developmental versions of the Sylramic fiber. The tensile strength measurements were made at room temperature on as-received fibers and on fibers after high-temperature inert exposure. The creep-rupture property data were obtained at 1400 deg C in air as well as, argon. Some fiber types showed strong effects of environment on their strength properties. These results are compared and discussed in terms of underlying mechanisms and implications for ceramic composites.

  19. Effect of prior creep at 1365 K on the room temperature tensile properties of several oxide dispersion strengthened alloys (United States)

    Whittenberger, J. D.


    An experimental study was conducted to determine whether oxide dispersion-strengthened (ODS) Ni-base alloys in wrought bar form are subject to creep degradation effects similar to those found in thin-gage sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and advanced ODS-NiCrAl types; the alloys included microstructures ranging from an essentially perfect single crystal to a structure consisting of very small elongated grains. 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, appearance of dispersoid free bands, grain boundary cavitation, and/or internal oxidation are interpreted as creep degradation effects. The amount of degradation depends on creep strain, and degradation appears to be due to diffusional creep which produces dispersoid free bands around grain boundaries acting as vacancy sources.

  20. Tensile Creep and Stress-rupture Behavior of Polymer Derived Sic Fibers (United States)

    Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.


    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400 C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1 percent creep strengths than as-produced as well as-coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  1. Tensile creep and stress-rupture behavior of polymer derived SiC fibers

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    Yun, H.M.; Goldsby, J.C.; DiCarlo, J.A. [NASA Lewis Research Center, Cleveland, OH (United States)


    Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400{degrees}C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1% creep strengths than as-produced as well as coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

  2. Phase structure and tensile creep of recycled poly(ethylene terephthalate/short glass fibers/impact modifier ternary composites

    Directory of Open Access Journals (Sweden)


    Full Text Available Binary and ternary composites of recycled poly(ethylene terephtalate (rPET, short glass fibres (SGF and/or impact modifier (IM were prepared by melt compounding and injection moulding. SEM images of rPET/IM fracture surfaces indicated that IM particles of about 1–2 µm in diameter were uniformly distributed in the rPET matrix, but with a poor adhesion level. Microphotographs of PET/SGF composites evidenced brittle fracture proceeding through the matrix and strong adhesion between components. In ternary composites SGF were evenly distributed, while IM particles were no longer detectable. Tensile creep of rPET and prepared composites was investigated under short and long term testing conditions at various stress levels. Main part of the tensile creep corresponded to the elastic time-independent component, while the timedependent component was rather limited even at relatively high stresses. While SGF accounted for a significant decrease in the overall creep compliance, the incorporation of IM induced a small decrease in the compliance and a non-linear viscoelastic behavior. In ternary composites, the reinforcing effects of SGF was dominating. Under a constant stress, the logarithm of compliance grew linearly with the logarithm of time. The creep rate, which resulted to be generally very small for all tested materials, was slightly reduced by SGF and increased by IM.

  3. Effect of Normalizing Temperature on Fracture Characteristic of Tensile and Impact Tested Creep Strength-Enhanced Ferritic P92 Steel (United States)

    Saini, N.; Pandey, C.; Mahapatra, M. M.


    The high-temperature Cr-Mo creep strength-enhanced ferritic (CSEF) steels are mainly used in nuclear and thermal power plants. In the present investigation, a systematic study on fracture surface morphologies of tensile and impact tested specimens and mechanical properties of cast and forged (C&F) P92 steel was performed for various heat treatment conditions. The heat treatment was carried out in normalizing temperature range of 950-1150 °C and then tempered to a fixed tempering temperature of 760 °C. The effect of varying normalizing temperatures before and after tempering on microstructure evolution, tensile properties, Vicker's hardness and Charpy toughness was studied. The normalizing temperature before and after tempering was having a noticeable effect on mechanical properties of as-received P92 steel. The fracture surface of impact and tensile tested samples was also studied for various normalizing temperatures with or without tempering. Fracture surface morphology was affected by the presence of secondary phase carbide particles. The fraction area of cleavage facets on the tensile fracture surface was found to be increased with an increase in the normalizing temperature. The fractured tensile specimens were characterized by transgranular ductile dimples, tear ridges and transgranular cleavage facets for various heat treatments. The fracture mode of impact tested samples was more complex. It showed both quasi-cleavage facets and ductile dimple tearing for various normalizing temperatures.

  4. Effect of Normalizing Temperature on Fracture Characteristic of Tensile and Impact Tested Creep Strength-Enhanced Ferritic P92 Steel (United States)

    Saini, N.; Pandey, C.; Mahapatra, M. M.


    The high-temperature Cr-Mo creep strength-enhanced ferritic (CSEF) steels are mainly used in nuclear and thermal power plants. In the present investigation, a systematic study on fracture surface morphologies of tensile and impact tested specimens and mechanical properties of cast and forged (C&F) P92 steel was performed for various heat treatment conditions. The heat treatment was carried out in normalizing temperature range of 950-1150 °C and then tempered to a fixed tempering temperature of 760 °C. The effect of varying normalizing temperatures before and after tempering on microstructure evolution, tensile properties, Vicker's hardness and Charpy toughness was studied. The normalizing temperature before and after tempering was having a noticeable effect on mechanical properties of as-received P92 steel. The fracture surface of impact and tensile tested samples was also studied for various normalizing temperatures with or without tempering. Fracture surface morphology was affected by the presence of secondary phase carbide particles. The fraction area of cleavage facets on the tensile fracture surface was found to be increased with an increase in the normalizing temperature. The fractured tensile specimens were characterized by transgranular ductile dimples, tear ridges and transgranular cleavage facets for various heat treatments. The fracture mode of impact tested samples was more complex. It showed both quasi-cleavage facets and ductile dimple tearing for various normalizing temperatures.

  5. An apparatus for the measurement of tensile creep and contraction ratios in small non-rigid specimens


    Darlington, M. W.; Saunders, D W


    An apparatus is described for precise measurement of creep properties in specimens with gauge lengths down to 1.2 cm. An extensometer has been developed which is supported independently of the specimen and exerts a load on the specimen of less than 5 grams. It can thus be used with small non-rigid specimens. The extensometer will detect strains down to 2 x 10-6. The stability is excellent. An adaptation of the system which allows simultaneous measurement of tensile strain...

  6. Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20High Entropy Alloy. (United States)

    Larianovsky, Natalya; Katz-Demyanetz, Alexander; Eshed, Eyal; Regev, Michael


    This paper examines the microstructure and mechanical properties of Ta 20 Nb 20 Hf 20 Zr 20 Ti 20 . Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current study was to investigate the creep and tensile properties of the material, since the literature review revealed no data whatsoever regarding these properties. The main findings are that the HIP process is responsible for the appearance of a Hexagonal Close Packed (HCP) phase that is dispersed differently in these two castings. The HIP process also led to a considerable increase in the mechanical properties of both materials under compression, with values found to be higher than those reported in the literature. Contrary to the compression properties, both materials were found to be highly brittle under tension, either during room temperature tension tests or creep tests conducted at 282 °C. Fractography yielded brittle fracture without any evidence of plastic deformation prior to fracture.

  7. Analysis of elevated-temperature tensile and creep properties of normalized and tempered 2 1/4 Cr-1 Mo steel

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    Booker, M.K.; Booker, B.L.P.; Swindeman, R.W.


    Tensile and creep data were collected for normalized and tempered 2 1/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These included creep data obtained at temperatures from 427 to 600/sup 0/C (800 to 1112/sup 0/F) and tensile data from room temperature to 550/sup 0/C (1022/sup 0/F). Properties examined included yield strength, ultimate tensile strength, 10/sup 5/-h creep-rupture strength, and 10/sup -5/%/h creep strength. These are the properties used in setting allowable stresses for Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code. The data were analyzed by using lot-centered regression approaches that yielded expressions for the variations in the above properties with loading condition, as well as accounting for lot-to-lot variations in properties. No indications were found of systematic differences in any of the properties examined for data from the different countries. However, the estimated allowable stresses from this investigation fell up to 10% below those currently given for this material in the ASME Code. Several possible reasons were cited for the differences, and we concluded that our results are not overly conservative. On the other hand, there is no direct evidence that the current code allowable stresses are insufficiently conservative, since those stresses rely on factors (such as service experience) other than experimental data.

  8. Effect of heat treatment on elevated temperature tensile and creep properties of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Lin, E-mail:; Shi, Wenchao; Jiang, WenMao; Zhao, Zhe; Shan, Debin


    The light and heavy rare earth elements are added to the magnesium alloys to improve the strengths and the creep resistance. The age hardening behaviors of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy aged at 200, 225 and 250 °C were investigated. Tensile tests and creep tests of the extruded and extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr were carried out at 150–300 °C. The relationship between the microstructure and the properties of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy was studied. The result shows that the extruded Mg–6Gd–4Y–Nd–0.7Zr (contained less than 10 wt% Gd) peak aged at 225 °C for 72 h has the excellent creep resistance and high strengths with the UTS more than 350 MPa from room temperature to 200 °C, which are correlative with the precipitates. The high dense and uniform distribution of β′ phase with good heat stability precipitates inhibiting the dislocation motion contributes to age hardening, accelerates the ageing hardening response and increases the creep resistance. The artificially aged (T5) at low temperature further creep tested and tensile tested at higher temperatures decreases the resistance to the dislocation motion and the grain boundary sliding, resulting in the reduction in creep properties and strengths of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy above 225 °C.

  9. Effects of thermomechanical processing on tensile and long-time creep behavior of Nb-1%Zr-0.1%C sheet

    Energy Technology Data Exchange (ETDEWEB)

    Titran, R.H. [National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center; Uz, M. [Lafayette Coll., Easton, PA (United States)


    Effects of thermomechanical processing on the mechanical properties of Nb-1 wt%Zr-0.1wt.%C, a candidate alloy for use in advanced space power systems, were investigated. Sheet bars were cold rolled into 1-mm thick sheets following single, double, or triple extrusion operations at 1,900 K. All the creep and tensile specimens were given a two-step heat treatment of 1 hr at 1,755 K + 2 hr at 1,475 K prior to testing. Tensile properties were determined at 300 as well as at 1,350 K. Microhardness measurements were made on cold rolled, heat treated, and crept samples. Creep tests were carried out at 1,350 K and 34.5 MPa for times of about 10,000 to 19,000 hr. The results show that the number of extrusions had some effects on both the microhardness and tensile properties. However, the long-time creep behavior of the samples were comparable, and all were found to have adequate properties to meet the design requirements of advanced power system regardless of thermomechanical history. The results are discussed in correlation with processing and microstructure, and further compared to the results obtained from the testing of Nb-1wt.%Zr and Nb-1wt.%Zr-0.06wt.%C alloys.

  10. High temperature tensile and creep properties of a cast AIM and ESR intermetallic alloy based on Fe{sub 3}Al

    Energy Technology Data Exchange (ETDEWEB)

    Baligidad, R.G. [Defence Metallurgical Research Lab., Hyderabad (India); Prakash, U. [Defence Metallurgical Research Lab., Hyderabad (India); Radhakrishna, A. [Defence Metallurgical Research Lab., Hyderabad (India)


    A high carbon intermetallic Fe-16 wt.% A1-1.1 wt.% C alloy based on Fe{sub 3}Al was melted under a flux cover by air induction melting (AIM). The AIM ingots exhibited excellent elevated temperature tensile properties in the temperature range (600-800 C) studied, in contrast to poor properties expected in ingots melted without a flux cover. Subsequent processing of the AIM ingots through electroslag remelting (ESR) resulted in improvement in ductility. However, the AIM ingots exhibited better creep properties because of their coarser gain structure. The presence of large (1.1 wt.%) amount of carbon in the alloy resulted in significant improvement in elevated temperature tensile as well as creep properties over those reported for Fe{sub 3}Al based intermetallic alloys with lower carbon contents. These improvements in mechanical properties are attributed to the extensive precipitation of Fe{sub 3}AlC phase and to the formation of a duplex Fe{sub 3}Al-Fe{sub 3}AlC structure at such high levels of carbon. It is suggested that carbon may be an important alloying addition to Fe{sub 3}Al-based intermetallic alloys. (orig.)

  11. The Influence of Lath, Block and Prior Austenite Grain (PAG Size on the Tensile, Creep and Fatigue Properties of Novel Maraging Steel

    Directory of Open Access Journals (Sweden)

    Thomas Simm


    Full Text Available The influence of martensitic microstructure and prior austenite grain (PAG size on the mechanical properties of novel maraging steel was studied. This was achieved by looking at two different martensitic structures with PAG sizes of approximately 40 µm and 80 µm, produced by hot rolling to different reductions. Two ageing heat-treatments were considered: both heat-treatments consisted of austenisation at 960 °C, then aging at 560 °C for 5 h, but while one was rapidly cooled the other was slow cooled and then extended aged at 480 °C for 64 h. It is shown that for the shorter ageing treatment the smaller PAG size resulted in significant improvements in strength (increase of more than 150 MPa, ductility (four times increase, creep life (almost four times increase in creep life and fatigue life (almost doubled. Whereas, the extended aged sample showed similar changes in the fatigue life, elongation and hardness it displayed yet showed no difference in tensile strength and creep. These results display the complexity of microstructural contributions to mechanical properties in maraging steels.

  12. The Influence of Lath, Block and Prior Austenite Grain (PAG) Size on the Tensile, Creep and Fatigue Properties of Novel Maraging Steel. (United States)

    Simm, Thomas; Sun, Lin; McAdam, Steven; Hill, Paul; Rawson, Martin; Perkins, Karen


    The influence of martensitic microstructure and prior austenite grain (PAG) size on the mechanical properties of novel maraging steel was studied. This was achieved by looking at two different martensitic structures with PAG sizes of approximately 40 µm and 80 µm, produced by hot rolling to different reductions. Two ageing heat-treatments were considered: both heat-treatments consisted of austenisation at 960 °C, then aging at 560 °C for 5 h, but while one was rapidly cooled the other was slow cooled and then extended aged at 480 °C for 64 h. It is shown that for the shorter ageing treatment the smaller PAG size resulted in significant improvements in strength (increase of more than 150 MPa), ductility (four times increase), creep life (almost four times increase in creep life) and fatigue life (almost doubled). Whereas, the extended aged sample showed similar changes in the fatigue life, elongation and hardness it displayed yet showed no difference in tensile strength and creep. These results display the complexity of microstructural contributions to mechanical properties in maraging steels.

  13. Predicting creep strengths and lifetimes of creep resistant engineering alloys (United States)

    Zhao, Yanrong; Yao, Hongpeng; Song, Xinli; Jia, Juan; Xiang, Zhidong


    The physical basis for predicting the long-term creep strengths and lifetimes at application temperatures using creep parameters determined from short-term creep tests is investigated for complex creep resistant engineering alloys. It is shown that the seemingly unpredictable stress and temperature dependence of minimum creep rate of such alloys can be rationalised using an approach based on the new power law creep equation that incorporate the tensile strength. This is demonstrated using the tensile and creep data measured for two completely different types of alloys: steel 11Cr-2W-0.4Mo-1Cu-Nb-V and Ni base superalloy 15Cr-28Co-4Mo-2.5Ti-3Al. For both alloys, the stress exponent n determined does not depend on temperature and activation energy of creep does not depend on stress. Consequently, it becomes possible to use the new power law creep equation in combination with the Monkman-Grant relationship to predict the long term creep rupture strengths and lifetimes and microstructure stability of the two alloys from short term creep test data. The implications of the results for creep mechanism identification and future microstructure analysis are discussed.

  14. Subcomponent testing of trailing edge panels in wind turbine blades

    DEFF Research Database (Denmark)

    Branner, Kim; Berring, Peter; Haselbach, Philipp Ulrich


    This paper proposes a static subcomponent test method designed to check the compressive strength of the trailing edge region in wind turbine blades under a simplified loading. The paper presents numerical simulations using the proposed subcomponent test method and discusses its ability to be used...

  15. Subcomponent testing of trailing edge panels in wind turbine blades

    DEFF Research Database (Denmark)

    Branner, Kim; Berring, Peter; Haselbach, Philipp Ulrich


    This paper proposes a static subcomponent test method designed to check the compressive strength of the trailing edge region in wind turbine blades under a simplified loading. The paper presents numerical simulations using the proposed subcomponent test method and discusses its ability to be used...... for checking the compressive strength of the trailing edge region in wind turbine blades....

  16. Irradiation Creep in Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Ubic, Rick; Butt, Darryl; Windes, William


    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.

  17. Tensile testing

    CERN Document Server


    A complete guide to the uniaxial tensile test, the cornerstone test for determining the mechanical properties of materials: Learn ways to predict material behavior through tensile testing. Learn how to test metals, alloys, composites, ceramics, and plastics to determine strength, ductility and elastic/plastic deformation. A must for laboratory managers, technicians, materials and design engineers, and students involved with uniaxial tensile testing. Tensile Testing , Second Edition begins with an introduction and overview of the test, with clear explanations of how materials properties are determined from test results. Subsequent sections illustrate how knowledge gained through tensile tests, such as tension properties to predict the behavior (including strength, ductility, elastic or plastic deformation, tensile and yield strengths) have resulted in improvements in materals applications. The Second Edition is completely revised and updated. It includes expanded coverage throughout the volume on a variety of ...

  18. 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


    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).

  19. Influence of stress on creep deformation properties of 9-12Cr ferritic creep resistant steels

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, K.; Sawada, K.; Kushima, H. [National Institute for Materials Science (Japan)


    Creep deformation property of 9-12Cr ferritic creep resistant steels was investigated. With decrease in stress, a magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the longterm. A time to 1% total strain was observed in the transient creep stage in the short term regime, however, it shifted to the accelerating creep stage in the long-term regime. Life fraction of the times to 1% creep strain and 1% total strain tended to increase with decrease in stress. Difference in stress dependence of the minimum creep rate was observed in the high- and low-stress regimes with a boundary condition of 50% of 0.2% offset yield stress. Stress dependence of the minimum creep rate in the high stress regime was equivalent to a strain rate dependence of the flow stress evaluated by tensile test, and a magnitude of stress exponent, n, in the high stress regime decreased with increase in temperature from 20 at 550 C to 10 at 700 C. On the other hand, n value in the low stress regime was about 5, and creep deformation in the low stress regime was considered to be controlled by dislocation climb. Creep rupture life was accurately predicted by a region splitting method by considering a change in stress dependence of creep deformation. (orig.)

  20. Seismic Creep (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...

  1. Control of Early Age Concrete. Phase 3: Creep in Concrete

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Anders Boe; Damkilde, Lars; Hansen, Per Freiesleben


    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....

  2. Sintered silver joints via controlled topography of electronic packaging subcomponents (United States)

    Wereszczak, Andrew A.


    Disclosed are sintered silver bonded electronic package subcomponents and methods for making the same. Embodiments of the sintered silver bonded EPSs include topography modification of one or more metal surfaces of semiconductor devices bonded together by the sintered silver joint. The sintered silver bonded EPSs include a first semiconductor device having a first metal surface, the first metal surface having a modified topography that has been chemically etched, grit blasted, uniaxial ground and/or grid sliced connected to a second semiconductor device which may also include a first metal surface with a modified topography, a silver plating layer on the first metal surface of the first semiconductor device and a silver plating layer on the first metal surface of the second semiconductor device and a sintered silver joint between the silver plating layers of the first and second semiconductor devices which bonds the first semiconductor device to the second semiconductor device.

  3. Temporospatial dissociation of Pe subcomponents for perceived and unperceived errors

    Directory of Open Access Journals (Sweden)

    Tanja eEndrass


    Full Text Available Previous research on performance monitoring revealed that errors are followed by an initial fronto-central negative deflection (error-related negativity, ERN and subsequently centro-parietal positivity (error positivity, Pe. It has been shown that error awareness mainly influences the Pe, whereas the ERN seems unaffected by conscious awareness of an error. The aim of the present study was to investigate the relation of ERN and Pe to error awareness in a visual size discrimination task in which errors are not elicited by impulsive responding but by perceptual difficulty. Further, we applied a temporospatial principal component analysis (PCA to examine whether the temporospatial subcomponents of the Pe would differentially relate to error awareness. ERP results were in accordance with earlier studies: a significant error awareness effect was found for the Pe, but not for the ERN. Interestingly, a modulation with error perception on correct trials was found: correct responses considered as incorrect had larger correct-related negativity (CRN and lager Pe amplitudes than correct responses considered as correct. The PCA yielded two relevant spatial factors accounting for the Pe (latency 300 ms. A temporospatial factor displaying a centro-parietal positivity varied significantly with error awareness. Of the two temporospatial factors corresponding to response-related negativities, a factor with central topography varied with response correctness and subjective error perception on correct responses. The PCA results indicate that the error awareness effect is specifically related to the centro-parietal subcomponent of the Pe. Since this component has also been shown to be related to the importance of an error, the present variation with error awareness indicates that this component is sensitive to the salience of an error and that salience secondarily triggers error awareness.

  4. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep (United States)

    Raj, S. V.; Noebe, R. D.


    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.

  5. Creep of chemically vapour deposited SiC fibres (United States)

    Dicarlo, J. A.


    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with negligible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  6. In-situ Creep Testing Capability Development for Advanced Test Reactor

    Energy Technology Data Exchange (ETDEWEB)

    B. G. Kim; J. L. Rempe; D. L. Knudson; K. G. Condie; B. H. Sencer


    Creep is the slow, time-dependent strain that occurs in a material under a constant strees (or load) at high temperature. High temperature is a relative term, dependent on the materials being evaluated. A typical creep curve is shown in Figure 1-1. In a creep test, a constant load is applied to a tensile specimen maintained at a constant temperature. Strain is then measured over a period of time. The slope of the curve, identified in the figure below, is the strain rate of the test during Stage II or the creep rate of the material. Primary creep, Stage I, is a period of decreasing creep rate due to work hardening of the material. Primary creep is a period of primarily transient creep. During this period, deformation takes place and the resistance to creep increases until Stage II, Secondary creep. Stage II creep is a period with a roughly constant creep rate. Stage II is referred to as steady-state creep because a balance is achieved between the work hardening and annealing (thermal softening) processes. Tertiary creep, Stage III, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation; that is, the creep rate increases due to necking of the specimen and the associated increase in local stress.

  7. Experimental investigation of tension and compression creep-ageing behaviour of AA2050 with different initial tempers

    Energy Technology Data Exchange (ETDEWEB)

    Li, Y. [Department of Mechanical Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Shi, Z., E-mail: [Department of Mechanical Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Lin, J.; Yang, Y.-L. [Department of Mechanical Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Huang, B.-M.; Chung, T.-F.; Yang, J.-R. [Department of Material Science and Engineering, National Taiwan University, Taiwan, ROC (China)


    Creep-ageing behaviour of aluminium alloy 2050 with different initial tempers (T34, T84 and as-quenched) has been experimentally investigated under both tension and compression creep-ageing conditions, with different stress levels at 155 °C for 18 h. Corresponding strengthening phenomena have been studied by interrupted creep-ageing tests and subsequent tensile tests. Moreover, the microstructures of some selected specimens after creep-ageing tests have been examined by transmission electron microscopy (TEM) and the precipitation process has been analysed. It has been found that creep strains under tensile stresses are much larger than those under compressive stresses during the tests. A new “double primary creep feature” has been observed in both the as-quenched alloys and the pre-stretched/natural-aged (T34) alloys, in which an intermediate inverse creep stage with an increasing creep strain rate locates between the initial primary+transient steady-state creep stages and the second primary+second steady-state creep stages. While for the alloy with peak-aged initial temper (T84), typical primary and steady-state secondary creep stages are observed during tension creep-ageing tests and little creep strain occurs under compressive stresses of 150 and 175 MPa. The mechanisms for these phenomena are discussed in terms of microstructural interactions among the changing dislocations, solute-matrix bonding and precipitates, and their effects on the creep resistance of the alloy during creep-ageing tests are analysed.

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

    Directory of Open Access Journals (Sweden)

    YE Wenming


    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.

  9. Steady state creep of Ni-8YSZ substrates for application in solid oxide fuel and electrolysis cells (United States)

    Wei, J.; Malzbender, J.


    Steady state creep was characterized for Ni-8YSZ solid oxide fuel/electrolysis cell (SOFC/SOEC) substrate material. Intrinsic and extrinsic factors affecting creep behavior were assessed, such as compositional ratio, porosity and mechanical loading configuration. Mechanical tests were supported by analytical and numerical calculations. The results indicated a diffusion-dominated creep mechanism under both compressive and tensile creep conditions. Creep appeared to be dominated by the ceramic phase. Porosity significantly reduced creep resistance. The activation energy was discussed based on loading configuration, temperature and porosity.

  10. Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites (United States)

    Morscher, Gregory N.; Pujar, Vijay


    Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

  11. Creep Behavior of Poly(lactic acid Based Biocomposites

    Directory of Open Access Journals (Sweden)

    Marco Morreale


    Full Text Available Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C. The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric.

  12. Creep Behavior of Poly(lactic acid) Based Biocomposites. (United States)

    Morreale, Marco; Mistretta, Maria Chiara; Fiore, Vincenzo


    Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric.

  13. Creep Behavior of UFG CP Ti at Room Temperature (United States)

    Luo, Lei; Zhao, Xicheng; Liu, XiaoYan; Yang, Xirong


    Ultra-fine grained commercial purity titanium (UFG CP Ti) is processed by Composite refining process (Equal channel angular pressing (ECAP), cold rolling and rotary swaging) at room temperature. The grain size is refined from 19 μm to 180 nm, and the ultimate tensile strength increase to 870 MPa. Creep tests were carried out on Ultra-fine grained commercial purity titanium with the stresses of 640, 660, 680, 700, 720, 740, 760 MPa at room temperature. Steady state creep rate and stress exponent n at various stresses were calculated for Ultra-fine grained commercial purity titanium, and creep deformation mechanism was also investigated. (With the rise of stress, the steady creep rate increases while the creep time decrease). The steady state creep rate reached maximum 1.416×10-6 s-1 (under) stress of 760 MPa. The stress exponent is 17.3 when the stress was 640 ∼ 700MPa, while the stress exponent is 55.7 when the stress was 700 ∼ 760MPa, UFG CP Ti shows good creep property at room temperature. The creep deformation mechanism of UFG CP Ti is the dislocation creep.

  14. Simultaneous consolidation and creep

    DEFF Research Database (Denmark)

    Krogsbøll, Anette


    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 (consol...... (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....

  15. Tension-Compression Asymmetry of Creep and Unilateral Creep Damage in Aluminum for Isothermal and Nonisothermal Processes (United States)

    Zolochevsky, Alexander; Obataya, Yoichi

    A constitutive model is proposed to describe the damage development in aluminum alloys under creep conditions for both isothermal and nonisothermal processes. Special emphasis is laid on four specific phenomena: tension-compression asymmetry of creep, damage induced anisotropy, unilateral creep damage and damage deactivation. Within the framework of the phenomenological approach in the Continuum Damage Mechanics, the nonlinear tensor constitutive equation for creep deformation and damage evolution equation are proposed to account for different orientation of microcracks in aluminum alloys under tensile and compressive loading types. After a determination of the material parameters in the obtained constitutive equation and damage growth equation, the proposed model is applied to the describing creep behavior of the aluminum alloy under uniaxial nonproportional and multiaxial nonproportional loading for both isothermal and nonisothermal processes.

  16. Through thickness microstructural gradients in 7475 and 2022 creep -Ageformed bend coupons


    Bakavos, D.; Prangnell, P. B.; Bes, B.; Eberl, F.; Gardiner, S.


    In creep-ageforming a material experiences continuously variable bending stresses through its thickness, from tensile to compressive, which are maximum at the surfaces. This can potentially result in through thickness microstructural gradients, due to interactions between the bending stresses, creep, and precipitation occurring during ageing, that can alter a component's performance. The aim of the work reported here was to develop an understanding of these effects in an industrial creep agef...

  17. Parallel ICA identifies sub-components of resting state networks that covary with behavioral indices. (United States)

    Meier, Timothy B; Wildenberg, Joseph C; Liu, Jingyu; Chen, Jiayu; Calhoun, Vince D; Biswal, Bharat B; Meyerand, Mary E; Birn, Rasmus M; Prabhakaran, Vivek


    Parallel Independent Component Analysis (para-ICA) is a multivariate method that can identify complex relationships between different data modalities by simultaneously performing Independent Component Analysis on each data set while finding mutual information between the two data sets. We use para-ICA to test the hypothesis that spatial sub-components of common resting state networks (RSNs) covary with specific behavioral measures. Resting state scans and a battery of behavioral indices were collected from 24 younger adults. Group ICA was performed and common RSNs were identified by spatial correlation to publically available templates. Nine RSNs were identified and para-ICA was run on each network with a matrix of behavioral measures serving as the second data type. Five networks had spatial sub-components that significantly correlated with behavioral components. These included a sub-component of the temporo-parietal attention network that differentially covaried with different trial-types of a sustained attention task, sub-components of default mode networks that covaried with attention and working memory tasks, and a sub-component of the bilateral frontal network that split the left inferior frontal gyrus into three clusters according to its cytoarchitecture that differentially covaried with working memory performance. Additionally, we demonstrate the validity of para-ICA in cases with unbalanced dimensions using simulated data.

  18. Creep in ceramics

    CERN Document Server

    Pelleg, Joshua


    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.

  19. High-performance liquid-chromatographic separation of subcomponents of antimycin-A (United States)

    Abidi, S.L.


    Using a reversed-phase high-performance liquid chromatographic (HPLC) technique, a mixture of antimycins A was separated into eight hitherto unreported subcomponents, Ala, Alb, A2a, A2b, A3a, A3b, A4a, and A4b. Although a base-line resolution of the known four major antimycins Al, A2, A3, and A4 was readily achieved with mobile phases containing acetate buffers, the separation of the new antibiotic subcomponents was highly sensitive to variation in mobile phase conditions. The type and composition of organic modifiers, the nature of buffer salts, and the concentration of added electrolytes had profound effects on capacity factors, separation factors, and peak resolution values. Of the numerous chromatographic systems examined, a mobile phase consisting of methanol-water (70:30) and 0.005 M tetrabutylammonium phosphate at pH 3.0 yielded the most satisfactory results for the separation of the subcomponents. Reversed-phase gradient HPLC separation of the dansylated or methylated antibiotic compounds produced superior chromatographic characteristics and the presence of added electrolytes was not a critical factor for achieving separation. Differences in the chromatographic outcome between homologous and structural isomers were interpretated based on a differential solvophobic interaction rationale. Preparative reversed-phase HPLC under optimal conditions enabled isolation of pure samples of the methylated antimycin subcomponents for use in structural studies.

  20. Creep in metals


    Saarinen, Juho


    Creep is time dependent plastic malformation of solids, that happen in static stress and temperature when threshold values are met. Creep occurs at high temperature, meaning temperature more than 30% of material's absolute melting temperature (this limit is a little lower with plastics, and higher in ceramics). The malformations it causes can lead to rupture, which usually happen in a short time compared to the duration of the whole process. The creep effect itself is known from already t...



    Yu. М. Borisov; I. S. Surovtsev; Yu. B. Potapov


    Problem statement. It is well known that creep is the tendency of a solid material to move slowly or deform permanently under the influence of stresses. The aim of the paper is to study the process of creep in polymer concretes. Results and conclusions. It is shown that creep in polymer concrete occurs according to the same pattern as in many other polymer composites with the elastic core. Equations which indirectly es-tablish the relation between complete deformations of polymer concrete, in...

  2. Survey of creep properties of copper intended for nuclear waste disposal

    Energy Technology Data Exchange (ETDEWEB)

    Andersson-Oestling, Henrik C.M. (Swerea KIMAB AB, Stockholm (Sweden)); Sandstroem, Rolf (Materials Science and Engineering, School of Industrial Engineering and Management, Royal Inst. of Technology (KTH), Stockholm (Sweden))


    Creep in copper for application in canisters for nuclear waste disposal is surveyed. The importance of phosphorus doping to obtain adequate properties is demonstrated experimentally as well as explained theoretically. Creep tests results for electron beam and friction stir welds are compared. The latter type of welds has properties that are close to those of parent metal. The relation between slow strain rate tensile and creep is described. Fundamental constitutive equations are presented that are suitable for finite element modelling. These equations are used to simulate creep deformation in canisters

  3. Healing mechanism of nanocrack in nanocrystalline metals during creep process (United States)

    Meraj, Md.; Pal, Snehanshu


    Molecular dynamics (MD) simulation has been performed to demonstrate the fate of cracks present inside ultrafine-grained (grain size 7 nm) nanocrystalline Ni specimen during creep deformation process. It is observed that internal nanocracks are healed within a few pico-seconds of initial part of creep process even if the constant applied load on the specimen is tensile in nature and acting normal to crack surface in the outward direction. This kind of crack-healing phenomenon can be accounted by the facts such as stress-driven grain boundary migration, grain boundary diffusion and amorphization of specimen as per results obtained from this MD simulation. This MD study also reveals that the presence of nanocrack inside ultrafine-grained NC Ni in fact slightly improves creep properties and such enhancement of the creep properties is intensified as the size of internal crack increases.

  4. Double decomposition: decomposing the variance in subcomponents of male extra-pair reproductive success. (United States)

    Losdat, Sylvain; Arcese, Peter; Reid, Jane M


    1. Extra-pair reproductive success (EPRS) is a key component of male fitness in socially monogamous systems and could cause selection on female extra-pair reproduction if extra-pair offspring (EPO) inherit high value for EPRS from their successful extra-pair fathers. However, EPRS is itself a composite trait that can be fully decomposed into subcomponents of variation, each of which can be further decomposed into genetic and environmental variances. However, such decompositions have not been implemented in wild populations, impeding evolutionary inference. 2. We first show that EPRS can be decomposed into the product of three life-history subcomponents: the number of broods available to a focal male to sire EPO, the male's probability of siring an EPO in an available brood and the number of offspring in available broods. This decomposition of EPRS facilitates estimation from field data because all subcomponents can be quantified from paternity data without need to quantify extra-pair matings. Our decomposition also highlights that the number of available broods, and hence population structure and demography, might contribute substantially to variance in male EPRS and fitness. 3. We then used 20 years of complete genetic paternity and pedigree data from wild song sparrows (Melospiza melodia) to partition variance in each of the three subcomponents of EPRS, and thereby estimate their additive genetic variance and heritability conditioned on effects of male coefficient of inbreeding, age and social status. 4. All three subcomponents of EPRS showed some degree of within-male repeatability, reflecting combined permanent environmental and genetic effects. Number of available broods and offspring per brood showed low additive genetic variances. The estimated additive genetic variance in extra-pair siring probability was larger, although the 95% credible interval still converged towards zero. Siring probability also showed inbreeding depression and increased with male age

  5. Creep in buffer clay

    Energy Technology Data Exchange (ETDEWEB)

    Pusch, R. [Geodevelopment AB, Lund (Sweden); Adey, R. [Computational Mechanics BEASY, Southampton (United Kingdom)


    The study involved characterization of the microstructural arrangement and molecular forcefields in the buffer clay for getting a basis for selecting suitable creep models. It is concluded that the number of particles and wide range of the particle bond spectrum require that stochastical mechanics and thermodynamics will be considered and they are basic to the creep model proposed for predicting creep settlement of the canisters. The influence of the stress level on creep strain of MX-80 clay is not well known but for the buffer creep is approximately proportional to stress. Theoretical considerations suggest a moderate impact for temperatures up to 90 deg C and this is supported by model experiments. It is believed that the assumption of strain being proportional to temperature is conservative. The general performance of the stochastic model can be illustrated in principle by use of visco-elastic rheological models implying a time-related increase in viscosity. The shear-induced creep settlement under constant volume conditions calculated by using the proposed creep model is on the order of 1 mm in ten thousand years and up to a couple of millimeters in one million years. It is much smaller than the consolidation settlement, which is believed to be on the order of 10 mm. The general conclusion is that creep settlement of the canisters is very small and of no significance to the integrity of the buffer itself or of the canisters.

  6. The effectiveness of shearography and digital image correlation for the study of creep in elastomers (United States)

    Benito Pascual-Francisco, Juan; Barragán-Pérez, Omar; Susarrey-Huerta, Orlando; Michtchenko, Alexandre; Martínez-García, Amalia; Israel Farfán-Cabrera, Leonardo


    In this paper, authors present a study of the application of speckle shearing interferometry (shearography) and digital image correlation to measure viscoelasticity in terms of creep compliance of elastomeric materials. The creep tests were performed using two different elastomers (neoprene and EPDM) by applying a constant tensile stress to a specimen during 3 h. First, a shearography setup was implemented to measure directly the in-plane strains produced in the specimens and thus determining creep strains. Secondly, digital image correlation was also used to measure the creep strains in similar creep tests. The results obtained were compared each other to see the effectiveness of each measurement technique for the assessment of this property. It was demonstrated that these techniques can be potentially and successfully applied to the creep analysis of these kind of materials. Moreover, advantages and drawbacks of both measurement methods are discussed.

  7. Creep in amorphous metals

    Directory of Open Access Journals (Sweden)

    Michael E. Kassner


    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.

  8. Creep-constitutive behavior of Sn-3.8Ag-0.7Cu solder using an internal stress approach (United States)

    Rist, Martin A.; Plumbridge, W. J.; Cooper, S.


    The experimental tensile creep deformation of bulk Sn-3.8Ag-0.7Cu solder at temperatures between 263 K and 398 K, covering lifetimes up to 3,500 h, has been rationalized using constitutive equations that incorporate structure-related internal state variables. Primary creep is accounted for using an evolving internal back stress, due to the interaction between the soft matrix phase and a more creep-resistant particle phase. Steady-state creep is incorporated using a conventional power law, modified to include the steady-state value of internal stress. It is demonstrated that the observed behavior is well-fitted using creep constants for pure tin in the modified creep power law. A preliminary analysis of damage-induced tertiary creep is also presented.

  9. The influence of cavitation damage upon high temperature creep under stationary and non-stationary loading conditions. Part III: Creep at steady increasing load and true stress (United States)

    Boček, M.; Hoffmann, M.


    In this paper for ideally plastic materials the influence of high temperature cavitation damage upon creep at steady increasing loads is investigated. The damage function A(t) enters a constitutive equation for plastíc flow through an effective stress σ e. For given loading conditions the latter is derived from the solution of Hart's tensile test equation. In the present paper the case of time linear increase in load ( F = constant) and in true stress ( /.s = constant) is investigated. The creep equations for cavitating as well as for non-cavitating materials are derived and the volume change during creep at /.F = constant are calculated.

  10. Seismic Creep, USA Images (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...

  11. Biaxial Creep Specimen Fabrication

    Energy Technology Data Exchange (ETDEWEB)

    JL Bump; RF Luther


    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.

  12. Verification of creep performance of a ceramic gas turbine blade

    Energy Technology Data Exchange (ETDEWEB)

    Lin, H.T.; Becher, P.F.; Ferber, M.K. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.; Parthasarathy, V. [Solar Turbines Inc., San Diego, CA (United States)


    Tensile creep tests were carried out on a Norton NT164 silicon nitride ceramic turbine blade containing 4 wt. % Y{sub 2}O{sub 3} sintering additive at 1,370 C in air under selected stress levels. The objective of this study was to measure the creep properties of test specimens extracted from a complex shaped ceramic gas turbine blade to verify the response of actual components. The creep results indicated that specimens from both the airfoil and dovetail sections exhibited creep rates that were about 4 to 100 times higher than those obtained from both the buttonhead and dogbone creep specimens machined from the developmental billets fabricated with the same composition and processing procedures. Electron microscopy analyses suggested that high creep rates and short lifetimes observed in specimens extracted from the turbine blade resulted from a higher glassy phase(s) content and smaller number density of elongated grain microstructure. Silicon nitride ceramics with an in-situ reinforced elongated microstructure have been the primary candidates for both advanced automotive and land-based gas turbine engine applications.

  13. Creep Resistant Zinc Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Frank E. Goodwin


    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.

  14. Creep Behavior and Durability of Cracked CMC (United States)

    Bhatt, R. T.; Fox, Dennis; Smith, Craig


    To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

  15. Experimental studies of fiber concrete creep

    Directory of Open Access Journals (Sweden)

    Korneeva Irina


    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.

  16. Topical Problems and Applications of Creep Theory (United States)

    Altenbach, H.


    A historical review of achievements in creep theory is given. Primary attention is focused on the phenomenological approach. Different constitutive equations are discussed for primary and secondary creep as well as for creep with damage. New creep problems are examined

  17. Creep of fibrous composite materials

    DEFF Research Database (Denmark)

    Lilholt, Hans


    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 creep strength of composites. The advantage of combined analyses of several data sets is emphasized and illustrated for some experimental data. The analyses show that it is possible to derive creep equations for the (in situ) properties of the fibres. The experiments treated include model systems...

  18. Theory of cyclic creep of concrete based on Paris law for fatigue growth of subcritical microcracks (United States)

    Bazant, Zdenek P.; Hubler, Mija H.


    Recent investigations prompted by a disaster in Palau revealed that worldwide there are 69 long-span segmental prestressed-concrete box-girder bridges that suffered excessive multi-decade deflections, while many more surely exist. Although the excessive deflections were shown to be caused mainly by obsolescence of design recommendations or codes for static creep, some engineers suspect that cyclic creep might have been a significant additional cause. Many investigators explored the cyclic creep of concrete experimentally, but a rational mathematical model that would be anchored in the microstructure and would allow extrapolation to a 100-year lifetime is lacking. Here it is assumed that the cause of cyclic creep is the fatigue growth of pre-existing microcracks in hydrated cement. The resulting macroscopic strain is calculated by applying fracture mechanics to the microcracks considered as either tensile or, in the form of a crushing band, as compressive. This leads to a mathematical model for cyclic creep in compression, which is verified and calibrated by laboratory test data from the literature. The cyclic creep is shown to be proportional to the time average of stress and to the 4th power of the ratio of the stress amplitude to material strength. The power of 4 is supported by the recent finding that, on the atomistic scale, the Paris law should have the exponent of 2 and that the exponent must increase due to scale bridging. Exponent 4 implies that cyclic creep deflections are enormously sensitive to the relative amplitude of the applied cyclic stress. Calculations of the effects of cyclic creep in six segmental prestressed concrete box girders indicate that, because of self-weight dominance, the effect on deflections absolutely negligible for large spans (>150m). For small spans (bridges upward deflections. However, the cyclic creep is shown to cause in bridges with medium and small spans (<80m) a significant residual tensile strain which can produce

  19. Micromechanics of intergranular creep failure under cyclic loading

    DEFF Research Database (Denmark)

    van der Giessen, Erik; Tvergaard, Viggo


    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...

  20. Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments. (United States)

    Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard


    Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

  1. Modeling of Different Fiber Type and Content SiC/SiC Minicomposites Creep Behavior (United States)

    Almansour, Amjad S.; Morscher, Gregory N.


    Silicon Carbide based Ceramic Matrix Composites (CMCs) are attractive materials for use in high-temperature applications in the aerospace and nuclear industries. However, creep damage mechanism in CMCs is the most dominant mechanism at elevated temperatures. Consequently, the tensile creep behavior of Hi-Nicalon, Hi-Nicalon Type S SiC fibers and Chemical vapor infiltrated Silicon Carbide matrix (CVI-SiC) were characterized and creep parameters were extracted from creep experiments. Some fiber creep tests were performed in inert environment at 1200 C on individual fibers. Creep behavior of different fiber content pristine and precracked Hi-Nicalon and Hi-Nicalon Type S reinforced minicomposites with BN interphases and CVI-SiC matrix were then modelled using the creep data found in this study and the literature and compared with creep experiments results for the pristine and precracked Hi-Nicalon and Hi-Nicalon Type S minicomposites. Finally, the effects of load-sharing and matrix cracking on CMC creep behavior will be discussed.

  2. Modification and Performance Evaluation of a Low Cost Electro-Mechanically Operated Creep Testing Machine

    Directory of Open Access Journals (Sweden)

    John J. MOMOH


    Full Text Available Existing mechanically operated tensile and creep testing machine was modified to a low cost, electro-mechanically operated creep testing machine capable of determining the creep properties of aluminum, lead and thermoplastic materials as a function of applied stress, time and temperature. The modification of the testing machine was necessitated by having an electro-mechanically operated creep testing machine as a demonstration model ideal for use and laboratory demonstrations, which will provide an economical means of performing standard creep experiments. The experimental result is a more comprehensive understanding of the laboratory experience, as the technology behind the creep testing machine, the test methodology and the response of materials loaded during experiment are explored. The machine provides a low cost solution for Mechanics of Materials laboratories interested in creep testing experiment and demonstration but not capable of funding the acquisition of commercially available creep testing machines. Creep curves of strain versus time on a thermoplastic material were plotted at a stress level of 1.95MPa, 3.25MPa and 4.55MPa and temperature of 20oC, 40oC and 60oC respectively. The machine is satisfactory since it is always ready for operation at any given time.

  3. Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels (United States)

    Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry


    As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

  4. Development of Creep Resistant Mg-Al-Sr Alloys (United States)

    Pekguleryuz, Mihriban O.; Baril, Eric

    There have been attempts since in the 70's to develop creep resistant magnesium diecasting alloys for automotive applications such as automatic-transmission case and engine components. The earliest die casting alloys developed as a result of these activities were the Mg-Al- RE and Mg-Al-Si systems (AE and AS alloys). The shortcomings of these two alloy systems related to high cost or borderline properties have led to renewed activity in the 90's in the development of magnesium alloys with improved elevaied-temperature properties. This paper presents the development of a new family of creep-resistant Mg alloys based on the Mg-Al-Sr system. Creep resistance, the tensile yield strength and the bolt-load-retention of these alloys at 150°C and 175°C show improvement over Mg-Al-RE and Mg-Al-Si system. The microstructure of the alloys is characterized by Al-Sr-(Mg) containing intermetallic second phases. The absence of the Mg17Al12 phase in the microstructure, either creep-induced or as-cast, is one of the factors that contribute to improved creep-resistance of these alloys over the Mg-Al based diecasting alloys. Furthermore, the alloys exhibit better salt-spray corrosion resistance (0.09-0.15mg/cm2/day) than other commercial magnesium diecasting alloys such as AM60B, AS41, AE42 and the aluminum diecasting alloy A380.

  5. Plastic displacement estimates in creep crack growth testing

    Energy Technology Data Exchange (ETDEWEB)

    Huh, Nam Su [University of Stuttgart, Stuttgart (Germany); Kim, Yun Jae [Korea University, Seoul (Korea, Republic of); Yoon, Kee Bong [Chungang University, Seoul (Korea, Republic of)


    The ASTM test standard recommends the use of the compact tension specimen for creep crack growth rates measurement. In the creep crack growth rate test, the displacement rate due to creep is obtained by subtracting the contribution of elastic and plastic components from the total load line displacement rate based on displacement partitioning method for determining C{sup *}-integral, which involves Ramberg-Osgood (R-O) fitting procedures. This paper investigates the effect of the R-O fitting procedures on plastic displacement rate estimates in creep crack growth testing, via detailed two-dimensional and three-dimensional finite element analyses of the standard compact tension specimen. Four different R-O fitting procedures are considered; (I) fitting the entire true stress-strain data up to the ultimate tensile strength, (II) fitting the true stress-strain data from 0.1% strain to 0.8 of the true ultimate strain, (III) fitting the true stress-strain data only up to 5% strain, and (IV) fitting the engineering stress-strain data. It is found that the last two procedures provide reasonably accurate plastic displacement rates and thus should be recommended in creep crack growth testing. Moreover, several advantages of fitting the engineering stress-strain data over fitting the true stress-strain data only up to 5% strain are discussed.

  6. Laser-Interferometric Creep Rate Spectroscopy of Polymers (United States)

    Bershtein, Vladimir A.; Yakushev, Pavel N.

    Laser-interferometric creep rate meter (LICRM) and creep rate spectroscopy (CRS), as an original high-resolution method for discrete relaxation spectrometry and thermal analysis, were developed in the authors' Materials Dynamics Laboratory at Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint-Petersburg). In the last few decades they have been successfully applied to solving various problems of polymer physics and materials science, especially being combined with DSC, structural, and other techniques. CRS involves measuring ultra-precisely a creep rate at small tensile or compressive stress, typically much lower than the yield stress, as a function of temperature, over the range from 100 to 800 K. LICRM setup allows one to register precisely creep rates on the basis of deformation increment of 150-300 nm. The survey describes this method and summarizes the results of numerous studies performed with the LICRM setup and CRS technique for different bulk polymeric materials, films, or thin fibers. This approach provided new experimental possibilities superior in resolution and sensitivity compared to the conventional relaxation spectrometry techniques. Among such possibilities are discrete analysis of dynamics; creep on submicro-, micro- and meso-scales; revealing relations between stepwise microplasticity and morphology; kinetic information on creep at any temperature and deformation; polymer dynamics at interfaces; analysis of microplasticity, relaxations, and phase transitions in brittle materials; using creep rate spectra for non-destructive prediction of temperature anomalies in mechanical behavior of materials, etc. Considerable attention has been paid to combined CRS/DSC analysis of the peculiarities of segmental dynamics, nanoscale dynamic, and compositional heterogeneity in different kinds of complex polymer systems and nanocomposites.

  7. Creep of timber joints

    NARCIS (Netherlands)

    Van de Kuilen, J.W.G.


    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

  8. Analysis of indentation creep (United States)

    Don S. Stone; Joseph E. Jakes; Jonathan Puthoff; Abdelmageed A. Elmustafa


    Finite element analysis is used to simulate cone indentation creep in materials across a wide range of hardness, strain rate sensitivity, and work-hardening exponent. Modeling reveals that the commonly held assumption of the hardness strain rate sensitivity (mΗ) equaling the flow stress strain rate sensitivity (mσ...

  9. Creep behaviour and creep mechanisms of normal and healing ligaments (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

  10. Separation and Localisation of P300 Sources and Their Subcomponents Using Constrained Blind Source Separation (United States)

    Spyrou, Loukianos; Jing, Min; Sanei, Saeid; Sumich, Alex


    Separation and localisation of P300 sources and their constituent subcomponents for both visual and audio stimulations is investigated in this paper. An effective constrained blind source separation (CBSS) algorithm is developed for this purpose. The algorithm is an extension of the Infomax BSS system for which a measure of distance between a carefully measured P300 and the estimated sources is used as a constraint. During separation, the proposed CBSS method attempts to extract the corresponding P300 signals. The locations of the corresponding sources are then estimated with some indeterminancy in the results. It can be seen that the locations of the sources change for a schizophrenic patient. The experimental results verify the statistical significance of the method and its potential application in the diagnosis and monitoring of schizophrenia.

  11. Miniature fiber optic loop subcomponent for compact sensors and dense routing (United States)

    Gillham, Frederick J.; Stowe, David W.; Ouellette, Thomas R.; Pryshlak, Adrian P.


    Fiber optic data links and embedded sensors, such as Fabry- Perot and Mach-Zehnders, are important elements in smart structure architectures. Unfortunately, one problem with optical fiber is the inherent limit through which fibers and cables can be looped. A revolutionary, patented technology has been developed which overcomes this problem. Based on processing the fiber into low loss miniature bends, it permits routing the fiber to difficult areas, and minimizing the size of sensors and components. The minimum bend diameter for singlemode fiber is typically over two inches in diameter, to avoid light attenuation and limit stresses which could prematurely break the fiber. With the new miniature bend technology, bend diameters as small as 1 mm are readily achieved. One embodiment is a sub-component with standard singlemode fiber formed into a 180 degree bend and packaged in a glass tube only 1.5 mm OD X 8 mm long, Figure 1. Measured insertion loss is less than 0.2 dB from 1260 nm to 1680 nm. A final processing step which anneals the fiber into the eventual curvature, reduces the internal stress, thereby resulting in long life expectancy with robust immunity to external loading. This paper addresses the optical and physical performance of the sub-component. Particular attention is paid to attenuation spectra, polarization dependent loss, reflectance, thermal cycle, damp heat, and shock tests. Applications are presented which employs the bend technology. Concatenating right angle bends into a 'wire harness' demonstrates the ability to route fiber through a smart engine or satellite structure. Miniature optical coils are proposed for sensors and expansion joints.

  12. Effect of creep-aging on precipitates of 7075 aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Y.C., E-mail: [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083 (China); State Key Laboratory of Material Processing and Die and Mould Technology, Wuhan 430074 (China); Jiang, Yu-Qiang; Chen, Xiao-Min; Wen, Dong-Xu [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083 (China); Zhou, Hua-Min [State Key Laboratory of Material Processing and Die and Mould Technology, Wuhan 430074 (China)


    The creep-aging behaviors of 7075 aluminum alloy are studied by uniaxial tensile creep experiments under elevated temperatures. The effects of creep-aging temperature and applied stress on the precipitates of 7075-T651 aluminum alloy are investigated using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Results show that (1) coarse insoluble precipitates (Al{sub 7}Cu{sub 2}Fe and Mg{sub 2}Si) and intermediate precipitates (Al{sub 18}Mg{sub 3}Cr{sub 2} and Al{sub 3}Zr) are found in the aluminum matrix, and the effects of creep-aging treatment on these precipitates are not obvious; (2) the main aging precipitates are η′ and η phases, and the amount of aging precipitates increase with the increase of creep-aging temperature and applied stress; (3) with the increase of creep-aging temperature and applied stress, the precipitates are discontinuously distributed on the grain boundary, and the width of precipitate free zone increases with the increase of creep-aging temperature and applied stress and (4) compared with the microstructure in the traditional stress-free aged sample, the creep-aging process can refine the precipitates and narrow the width of the precipitate free zone.

  13. 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)


    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.)

  14. 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)


    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.

  15. A creep rupture model accounting for cavitation at sliding grain boundaries

    NARCIS (Netherlands)

    Giessen, Erik van der; Tvergaard, Viggo


    An axisymmetric cell model analysis is used to study creep failure by grain boundary cavitation at facets normal to the maximum principal tensile stress, taking into account the influence of cavitation and sliding at adjacent inclined grain boundaries. It is found that the interaction between the

  16. Documentation for the viscoplastic and creep program

    DEFF Research Database (Denmark)

    Bellini, Anna


    The purpose of this document is to summarize the work done in the workpackage 4 of the IDEAL (Integrated Development Routes for Optimized Cast Aluminium Components) project, financed by the EU in frame work 6 and born in collaboration with the automobile and foundry industries. The objective...... of the stress-strain behavior of aluminum at high temperature. As an example, the analysis of several tests performed at various temperatures and strain rates on a particular aluminum alloy, is presented as well. Furthermore, the one dimensional code developed during this project is illustrated and a 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...

  17. Application of speckle shearing interferometry to the evaluation of creep strain in elastomers (United States)

    Pascual-Francisco, Juan Benito; Michtchenko, Alexandre; Susarrey-Huerta, Orlando; Barragán-Pérez, Omar; Ortiz-Gonzáles, Antonio de Jesús


    In this paper, authors present a new application of speckle shearing interferometry (shearography) to a phenomenon known as creep compliance, which is an important mechanical property of viscoelastic materials. Two different sealing elastomers were tested in a short-term creep experiment, applying a constant tensile stress to a specimen. An experimental in-plane shearography setup was implemented to measure directly the in-plane creep strains produced in the tested object. In order to show the effectiveness of shearography for the assessment of this mechanical property, results were compared to that obtained with an equipment of Digital Image Correlation (DIC). It was demonstrated that shearography can be potentially and successfully applied to the creep analysis of these kind of materials. Finally, advantages and limitations of this measurement method are discussed.

  18. Effect of boron addition and ESR process on the creep properties of type 316L(N) stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, W. K.; Kim, D. H.; Jang, J. S.; Kook, I. H.; Ryu, W. S. [KAERI, Taejon (Korea, Republic of)


    The effects of B-addition and ESR(electroslag remelting) process on the creep properties of 316L(N) stainless steel were investigated at 550 deg C in air. High temperature tensile strength for three heats was similar, but creep rupture time of B-doped and ESR-processed 316L(N) steels increased significantly in comparison with B-undoped steels. Also, the creep rupture elongation increased and minimum creep rate decreased inversely. Cross section of crept specimen showed the typical wedge cracks regardless of B-addition or ESR. The size and spacing of grain boundary cavitation in B-doped and ESR-processed steels were smaller than those of B-undoped steels. It was concluded that 0.0025% boron addition increases creep rupture time by delaying the onset of the tertiary stage due to suppression of grain boundary cavitation and wedge cracking.

  19. Finite Element Modeling of Thermo Creep Processes Using Runge-Kutta Method

    Directory of Open Access Journals (Sweden)

    Yu. I. Dimitrienko


    Full Text Available Thermo creep deformations for most heat-resistant alloys, as a rule, nonlinearly depend on stresses and are practically non- reversible. Therefore, to calculate the properties of these materials the theory of plastic flow is most widely used. Finite-element computations of a stress-strain state of structures with account of thermo creep deformations up to now are performed using main commercial software, including ANSYS package. However, in most cases to solve nonlinear creep equations, one should apply explicit or implicit methods based on the Euler method of approximation of time-derivatives. The Euler method is sufficiently efficient in terms of random access memory in computations, however this method is cumbersome in computation time and does not always provide a required accuracy for creep deformation computations.The paper offers a finite-element algorithm to solve a three-dimensional problem of thermo creep based on the Runge-Kutta finite-difference schemes of different orders with respect to time. It shows a numerical test example to solve the problem on the thermo creep of a beam under tensile loading. The computed results demonstrate that using the Runge-Kutta method with increasing accuracy order allows us to obtain a more accurate solution (with increasing accuracy order by 1 a relative error decreases, approximately, by an order too. The developed algorithm proves to be efficient enough and can be recommended for solving the more complicated problems of thermo creep of structures.

  20. Material modelling and its application to creep-age forming of aluminium alloy 7B04

    Directory of Open Access Journals (Sweden)

    Lam Aaron C.L.


    Full Text Available Creep-ageing behaviour of aluminium alloy 7B04-T651 at 115 °C under a range of tensile stress levels has been experimentally investigated and numerically modelled for creep-age forming (CAF applications. Creep strain, yield strength evolution and precipitate growth of creep-aged specimens were investigated. The alloy was modelled using a set of unified constitutive equations, which captures its creep deformation and takes into account yield strength contributions from three creep-age hardening mechanisms. Applications of the present work are demonstrated by implementing the determined material model into a commercial finite element analysis solver to analyse CAF operations carried out in a novel flexible CAF tool. Stress relaxation, yield strength, precipitate size and springback were predicted for the creep-age formed plates. The predicted springback were further quantified and compared with experimental measurements and a good agreement of 2.5% deviation was achieved. This material model now enables further investigations of 7B04 under various CAF scenarios to be conducted inexpensively via computational modelling.

  1. Preconsolidation Pressure and Creep Settlements

    DEFF Research Database (Denmark)

    Thorsen, Grete


    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....

  2. Nanogranular origin of concrete creep (United States)

    Vandamme, Matthieu; Ulm, Franz-Josef


    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

  3. Reassembling Surveillance Creep

    DEFF Research Database (Denmark)

    Bøge, Ask Risom; Lauritsen, Peter


    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 developm......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...

  4. Creep behaviour of a polymer-based underground support liner (United States)

    Guner, Dogukan; Ozturk, Hasan


    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.

  5. Mechanical Properties, Short Time Creep, and Fatigue of an Austenitic Steel

    Directory of Open Access Journals (Sweden)

    Josip Brnic


    Full Text Available The correct choice of a material in the process of structural design is the most important task. This study deals with determining and analyzing the mechanical properties of the material, and the material resistance to short-time creep and fatigue. The material under consideration in this investigation is austenitic stainless steel X6CrNiTi18-10. The results presenting ultimate tensile strength and 0.2 offset yield strength at room and elevated temperatures are displayed in the form of engineering stress-strain diagrams. Besides, the creep behavior of the steel is presented in the form of creep curves. The material is consequently considered to be creep resistant at temperatures of 400 °C and 500 °C when subjected to a stress which is less than 0.9 of the yield strength at the mentioned temperatures. Even when the applied stress at a temperature of 600 °C is less than 0.5 of the yield strength, the steel may be considered as resistant to creep. Cyclic tensile fatigue tests were carried out at stress ratio R = 0.25 using a servo-pulser machine and the results were recorded. The analysis shows that the stress level of 434.33 MPa can be adopted as a fatigue limit. The impact energy was also determined and the fracture toughness assessed.

  6. Analog Experiments on Tensile Strength of Dusty and Cometary Matter (United States)

    Musiolik, Grzegorz; de Beule, Caroline; Wurm, Gerhard


    The tensile strength of small dusty bodies in the solar system is determined by the interaction between the composing grains. In the transition regime between small and sticky dust (μm) and non cohesive large grains (mm), particles still stick to each other but are easily separated. In laboratory experiments we find that thermal creep gas flow at low ambient pressure generates an overpressure sufficient to overcome the tensile strength. For the first time it allows a direct measurement of the tensile strength of individual, very small (sub)-mm aggregates which consist of only tens of grains in the (sub)-mm size range. We traced the disintegration of aggregates by optical imaging in ground based as well as microgravity experiments and present first results for basalt, palagonite and vitreous carbon samples with up to a few hundred Pa. These measurements show that low tensile strength can be the result of building loose aggregates with compact (sub)-mm units. This is in favour of a combined cometary formation scenario by aggregation to compact aggreates and gravitational instability of these units.

  7. Statistical characterization of viscoelastic creep compliances of a vinyl ester polymer (United States)

    Simsiriwong, Jutima

    The objective of this study was to develop a model to predict the viscoelastic material functions of a vinyl ester (VE) polymer (Derakane 441-400, Ashland Co.,) with variations in its material properties. Short-term tensile creep/creep recovery experiments were conducted at two stress levels and at four temperatures below the glass transition temperature of the VE polymer, with 10 replicates for each test configuration. Experimental strains in both the longitudinal and transverse directions were measured using a digital image correlation technique. The measured creep strain versus time responses were subsequently used to determine the creep compliances using the generalized viscoelastic constitutive equation with a Prony series representation. The variation in the creep compliances of Derakane 441-400 was described by formulating the probability density functions (PDFs) and the corresponding cumulative distribution functions (CDFs) of the creep compliances using the two-parameter Weibull and log-normal distributions. The maximum likelihood estimation technique was used to obtain the Weibull shape and its scale parameters and the log-normal location and its scale parameters. The goodness-of-fit of the distributions was determined by performing Kolmogorov-Smirnov (K-S) hypothesis tests. Based on the K-S test results, the Weibull distribution is a better representation of the creep compliances of Derakane 441-400 when compared to the log-normal distribution. Additionally, the Weibull scale and shape parameters of the creep compliance distributions were shown to be time and temperature dependent. Therefore, two-dimensional quadratic Lagrange interpolation functions were used to characterize the Weibull parameters to obtain the PDFs and subsequently the CDFs of the creep compliances for the complete design temperature range during steady state creep. At each test temperature, creep compliance curves were obtained for CDF values of 0.05, 0.50 and 0.95 and compared with

  8. Creep in electronic ceramics

    Energy Technology Data Exchange (ETDEWEB)

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


    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.

  9. Plasticity and creep of metals

    CERN Document Server

    Rusinko, Andrew


    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.

  10. Material modelling for creep-age forming of aluminium alloy 7B04

    Directory of Open Access Journals (Sweden)

    Lam Aaron C.L.


    Full Text Available This paper presents a study on the creep-ageing behaviour of a peak-aged aluminium alloy 7B04 under different tensile loads at 115oC and subsequently modelling it for creep-age forming (CAF applications. Mechanical properties and microstructural evolutions of creep-aged specimens were investigated. The material was modelled using a set of unified constitutive equations, which not only captures the material's creep deformation but also takes into account yield strength contributions from solid solution hardening, age hardening and dislocation hardening during creep-ageing. A possible application of the present work is demonstrated by implementing the determined material model into a commercial finite element analysis solver via a user-defined subroutine for springback prediction of creep-age formed plates. A good agreement is observed between the simulated springback values and experimental results. This material model now enables further investigations of 7B04 under various CAF scenarios to be conducted inexpensively via computational modelling.

  11. Creep in dispersion strengthened aluminium

    Energy Technology Data Exchange (ETDEWEB)

    Orlova, A.; Kucharova, K.; Cadek, J.; Besterci, M.; Slesar, M.


    Results of an investigation of creep at 623 and 723 K in two DISPAL type dispersion strengthened aluminium alloys containing nominal concentrations of 2.5 and 10 vol. pct of dispersed Al4C3 and 2.1 and 3.8 vol. pct of Al2O3, respectively, are presented. The dispersoid particles 25-85 nm in diameter are situated predominantly in grain boundaries and to a less extent as clusters inside the grains. Steady state creep rate, which is strongly applied stress dependent, is most probably controlled by lattice diffusion. A threshold stress characterizing the creep can be identified with the Orowan bowing stress for lattice dislocations. It is shown that creep can be described in terms of lattice diffusion controlled climb of Orowan dislocation loops around dispersed particles. A comparison with creep behavior of dispersion strengthened alloys SAP and NOVAMET shows better resistance of DISPAL as compared to these alloys though its creep ductility is relatively low. 27 references.

  12. Contemporary overview of soil creep phenomenon (United States)

    Kaczmarek, Łukasz; Dobak, Paweł


    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.

  13. Low cycle fatigue of 2.25Cr1Mo steel with tensile and compressed hold loading at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Junfeng; Yu, Dunji; Zhao, Zizhen; Zhang, Zhe; Chen, Gang; Chen, Xu, E-mail:


    A series of uniaxial strain-controlled fatigue and creep-fatigue tests of the bainitic 2.25Cr1Mo steel forging were performed at 455 °C in air. Three different hold periods (30 s, 120 s, 300 s) were employed at maximum tensile strain and compressive strain under fully reversed strain cycling. Both tensile and compressive holds significantly reduce the fatigue life. Fatigue life with tensile hold is shorter than that with compressive hold. A close relationship is found between the reduction of fatigue life and the amount of stress relaxation. Microstructural examination by scanning electron microscope reveals that strain hold introduces more crack sources, which can be probably ascribed to the intensified oxidation and the peeling-off of oxide layers. A modified plastic strain energy approach considering stress relaxation effect is proposed to predict the creep-fatigue life, and the predicted lives are in superior agreement with the experimental results.

  14. Microstructure and creep behavior of magnesium-aluminum alloys containing alkaline and rare earth additions (United States)

    Saddock, Nicholas David

    In the past few decades governmental regulation and consumer demands have lead the automotive companies towards vehicle lightweighting. Powertrain components offer significant potential for vehicle weight reductions. Recently, magnesium alloys have shown promise for use in powertrain applications where creep has been a limiting factor. These systems are Mg-Al based, with alkaline earth or rare earth additions. The solidification, microstructure, and creep behavior of a series of Mg-4 Al- 4 X:(Ca, Ce, La, and Sr) alloys and a commercially developed AXJ530 (Mg--5 Al--3 Ca--0.15 Sr) alloy (by wt%) have been investigated. The order of decreasing freezing range of the five alloys was: AX44, AXJ530, AJ44, ALa44 and ACe44. All alloys exhibited a solid solution primary alpha-Mg phase surrounded by an interdendritic region of Mg and intermetallic(s). The primary phase was composed of grains approximately an order of magnitude larger than the cellular structure. All alloys were permanent mold cast directly to creep specimens and AXJ530 specimens were provided in die-cast form. The tensile creep behavior was investigated at 175 °C for stresses ranging from 40 to 100 MPa. The order of decreasing creep resistance was: die-cast AXJ530 and permanent mold cast AXJ530, AX44, AJ44, ALa44 and ACe44. Grain size, solute concentration, and matrix precipitates were the most significant microstructural features that influenced the creep resistance. Decreases in grain size or increases in solute concentration, both Al and the ternary addition, lowered the minimum creep rate. In the Mg-Al-Ca alloys, finely distributed Al2Ca precipitates in the matrix also improved the creep resistance by a factor of ten over the same alloy with coarse precipitates. The morphology of the eutectic region was distinct between alloys but did not contribute to difference in creep behavior. Creep strain distribution for the Mg-Al-Ca alloys developed heterogeneously on the scale of the alpha-Mg grains. As

  15. (Irradiation creep of graphite)

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, C.R.


    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.

  16. Superior high creep resistance of in situ nano-sized TiCx/Al-Cu-Mg composite. (United States)

    Wang, Lei; Qiu, Feng; Zhao, Qinglong; Zha, Min; Jiang, Qichuan


    The tensile creep behavior of Al-Cu-Mg alloy and its composite containing in situ nano-sized TiC x were explored at temperatures of 493 K, 533 K and 573 K with the applied stresses in the range of 40 to 100 MPa. The composite reinforced by nano-sized TiC x particles exhibited excellent creep resistance ability, which was about 4-15 times higher than those of the unreinforced matrix alloy. The stress exponent of 5 was noticed for both Al-Cu-Mg alloy and its composite, which suggested that their creep behavior was related to dislocation climb mechanism. During deformation at elevated temperatures, the enhanced creep resistance of the composite was mainly attributed to two aspects: (a) Orowan strengthening and grain boundary (GB) strengthening induced by nano-sized TiC x particles, (b) θ' and S' precipitates strengthening.

  17. Photooxidation Behavior of a LDPE/Clay Nanocomposite Monitored through Creep Measurements

    Directory of Open Access Journals (Sweden)

    Francesco Paolo La Mantia


    Full Text Available Creep behavior of polymer nanocomposites has not been extensively investigated so far, especially when its effects are combined with those due to photooxidation, which are usually studied in completely independent ways. In this work, the photooxidation behavior of a low density polyethylene/organomodified clay nanocomposite system was monitored by measuring the creep curves obtained while subjecting the sample to the combined action of temperature, tensile stress, and UV radiation. The creep curves of the irradiated samples were found to be lower than those of the non-irradiated ones and progressively diverging, because of the formation of branching and cross-linking due to photooxidation. This was further proved by the decrease of the melt index and the increase of the intrinsic viscosity; at the same time, the formation of carbonyl groups was observed. This behavior was more observable in the nanocomposite sample, because of its faster photooxidation kinetics.

  18. 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 (United States)

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


    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

  19. The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface (United States)

    Waanders, Daan; Janssen, Dennis; Mann, Kenneth A.; Verdonschot, Nico


    The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage, or micro cracks, and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered; ‘only creep’, ‘only damage’ or ‘creep and damage’. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663

  20. 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)


    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

  1. Implementation of creep-fatigue model into finite-element code to assess cooled turbine blade.

    CSIR Research Space (South Africa)

    Dedekind, MO


    Full Text Available power law, Larson-Miller and Robinson's rule approach, while the fatigue model combines Miner's law and the universal slopes method. In both creep and fatigue cases crack initiation was considered as defining the design... range Ae using the method of universal slopes. This method has the advantage of using material data obtainable from simple tensile tests. The equation combines the Coffin-Manson law: z Aep = efN? ''6 (1...

  2. Measurement of expansin activity and plant cell wall creep by using a commercial texture analyzer


    Perini, Mauro A.; Ignacio N. Sin; Martinez, Gustavo Adolfo; Pedro M. Civello


    Background: Expansins play an important role in cell wall metabolism and fruit softening. Determination of expansin activity is a challenging problem since it depends on measuring cell wall properties by using ad hoc extensometers, a fact that has strongly restricted its study. Then, the objective of the work was to adapt a methodology to measure cell wall creep and expansin activity using a commercial texture meter, equipped with miniature tensile grips and an ad hoc cuvette of easy construc...

  3. Creep behavior of a novel Co-Al-W-base single crystal alloy containing Ta and Ti at 982 ∘C

    Directory of Open Access Journals (Sweden)

    Xue Fei


    Full Text Available The tensile creep behavior of a Co-Al-W-base single crystal alloy containing Ta and Ti was investigated at 982 ∘C and 248 MPa. The lattice misfit of experimental alloy was measured to be positive by synchrotron X-ray diffraction at high temperature, and long term heat treatment at 1000 ∘C for 1000 h revealed a γ′ volume fraction of 75% without secondary phases. The creep test indicated that the creep properties of experimental alloy exceeded commercial 1st generation Ni-base single crystal superalloy CMSX-3 with respect to the rupture life. The initial cuboidal γ′ precipitates directionally coarsened parallel to the applied stress axis during the creep process. The stacking faults in {111} planes within γ′ rafts were the primary creep deformation mode by TEM investigation.

  4. Creep Behaviour of Modified Mar-247 Superalloy

    Directory of Open Access Journals (Sweden)

    Cieśla M.


    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.

  5. Harper-Dorn creep in metals

    Energy Technology Data Exchange (ETDEWEB)

    Cadek, J.; Fiala, J.


    The main characteristics of Harper-Dorn (H-D)(1957) creep at homologous temperatures not lower than 0.95 are discussed. Particular attention is given to intermediate temperature H-D creep which, under certain conditions, is controlled by dislocation core diffusion. A mechanism for this kind of creep involving the nonconservative motion of jogs on screw dislocations is suggested. Practical aspects of H-D creep regarding dispersion-strengthened alloys are considered. 31 references.

  6. Creep of service-aged welds


    Sun, Wei


    The creep behaviour of welds in service-aged pipes are studied. The aims of the research have been achieved using analytical, numerical and experimental approaches to the relevant subjects. Several features of the work are presented: (i) a systematic parametric study of the creep of two-material test specimens including a stress singularity analysis, (ii) an impression creep testing method using a rectangular indenter, which can be applied to study the creep properties in welds, and (iii) met...

  7. Demonstration of creep during filtration

    DEFF Research Database (Denmark)

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

    root of time. Even more clearly it is demonstrated by plotting the liquid pressure at the cake piston interface v.s. the relative deformation (to be shown). The phenomenon of a secondary consolidation processes is in short called creep. Provided that the secondary consolidation rate is of the same...... 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...... and the hydraulic resistance before and after the collapse of the solids structure. This has been observed and modelled for dewatering experiments with activated sludge. It will be argued that although a strong resemblance between blinding and creep exists, these two effects may readily be distinguished by virtue...

  8. Study of Creep of Alumina-Forming Austenitic Stainless Steel for High-Temperature Energy Applications (United States)

    Afonina, Natalie Petrovna

    To withstand the high temperature (>700°C) and pressure demands of steam turbines and boilers used for energy applications, metal alloys must be economically viable and have the necessary material properties, such as high-temperature creep strength, oxidation and corrosion resistance, to withstand such conditions. One promising class of alloys potentially capable of withstanding the rigors of aggressive environments, are alumina-forming austenitic stainless steels (AFAs) alloyed with aluminum to improve corrosion and oxidation resistance. The effect of aging on the microstructure, high temperature constant-stress creep behavior and mechanical properties of the AFA-type alloy Fe-20Cr-30Ni-2Nb-5Al (at.%) were investigated in this study. The alloy's microstructural evolution with increased aging time was observed prior to creep testing. As aging time increased, the alloy exhibited increasing quantities of fine Fe2Nb Laves phase dispersions, with a precipitate-free zone appearing in samples with higher aging times. The presence of the L1 2 phase gamma'-Ni3Al precipitate was detected in the alloy's matrix at 760°C. A constant-stress creep rig was designed, built and its operation validated. Constant-stress creep tests were performed at 760°C and 35MPa, and the effects of different aging conditions on creep rate were investigated. Specimens aged for 240 h exhibited the highest creep rate by a factor of 5, with the homogenized sample having the second highest rate. Samples aged for 2.4 h and 24 h exhibited similar low secondary creep rates. Creep tests conducted at 700oC exhibited a significantly lower creep rate compared to those at 760oC. Microstructural analysis was performed on crept samples to explore high temperature straining properties. The quantity and size of Fe2Nb Laves phase and NiAl particles increased in the matrix and on grain boundaries with longer aging time. High temperature tensile tests were performed and compared to room temperature results. The

  9. 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)


    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.

  10. Stress state dependence of in-reactor creep and swelling. Part 2: Experimental results (United States)

    Hall, M. M., Jr.; Flinn, J. E.


    Irradiation creep constitutive equations, which were developed in Part I, are used here to analyze in-reactor creep and swelling data obtained ca. 1977-1979 as part of the US breeder reactor program. The equations were developed according to the principles of incremental continuum plasticity for the purpose of analyzing data obtained from a novel irradiation experiment that was conducted, in part, using Type 304 stainless steel that had been previously irradiated to significant levels of void swelling. Analyses of these data support an earlier observation that all stress states, whether tensile, compressive, shear or mixed, can affect both void swelling and interactions between irradiation creep and swelling. The data were obtained using a set of five unique multiaxial creep-test specimens that were designed and used for the first time in this study. The data analyses demonstrate that the constitutive equations derived in Part I provide an excellent phenomenological representation of the interactive creep and swelling phenomena. These equations provide nuclear power reactor designers and analysts with a first-of-its-kind structural analysis tool for evaluating irradiation damage-dependent distortion of complex structural components having gradients in neutron damage rate, temperature and stress state.

  11. Numerical-graphical method for describing the creep of damaged highly filled polymer materials (United States)

    Bykov, D. L.; Martynova, E. D.; Mel'nikov, V. P.


    A method for describing the creep behavior until fracture of a highly filled polymer material previously damaged in preliminary tests is proposed. The constitutive relations are the relations of nonlinear endochronic theory of aging viscoelastic materials (NETAVEM) [1]. The numerical-graphical method for identifying the functions occurring in NETAVEM, which was proposed in [2] for describing loading processes at a constant strain rate, is used here for the first time in creep theory. We use the results of experiments with undamaged and preliminary damaged specimens under the action of the same constant tensile loads. The creep kernel is determined in experiments with an undamaged specimen. The reduced time function contained in NETAVEM is determined from the position of points corresponding to the same values of strain on the creep curves of the damaged and undamaged specimens. An integral equation is solved to obtain the aging function, and then the viscosity function is determined. The knowledge of all functions contained in the constitutive relations permits solving the creep problem for products manufactured from a highly filled polymer material.

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

    Directory of Open Access Journals (Sweden)

    A. Carofalo


    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.

  13. Calculation of Constrained Stress in Expansive Mortar with a Composite Creep Model

    Directory of Open Access Journals (Sweden)

    Hyeonggil Choi


    Full Text Available The creep phenomenon of hardening cement paste mixed with an expansive additive was modeled by considering the creep performance of hydration products of cement and expansive additive. A new composite model that is appropriate for particle conditions is proposed by considering the balance of the hydration products of cement and expansive additive and the stress redistribution phenomenon of hydration products newly generated by the progress of hydration. The creep of mortar and concrete mixed with the expansive additive was evaluated using a composite model of the paste and aggregate. Under the assumption that the modeled creep deformation is proportional to the stress and the gel volume of the hydration products, which allows the law of superposition to be applied, the distribution stress was predicted by applying the step-by-step method at each time increment. By predicting the maximum tensile stress applied to an inner steel ring through a creep analysis based on the measured deformation of the inner steel ring, it is possible to predict the stress progression with age to some degree.


    Energy Technology Data Exchange (ETDEWEB)

    P. Macheret


    The objective of this calculation is to compare several creep rupture correlations for use in calculating creep strain accrued by the Zircaloy cladding of spent nuclear fuel when it has been emplaced in the repository. These correlations are used to calculate creep strain values that are then compared to a large set of experimentally measured creep strain data, taken from four different research articles, making it possible to determine the best fitting correlation. The scope of the calculation extends to six different creep rupture correlations.

  15. Creep Resistance of VM12 Steel

    Directory of Open Access Journals (Sweden)

    Zieliński A.


    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.

  16. Creep at very low rates

    CSIR Research Space (South Africa)

    Nabarro, FRN


    Full Text Available of these diffusional processes is, therefore, important. First type of diffusional creep (Nabarro-Herring (N-H)): the sources and sinks of vacancies are grain boundaries. The vacancies may diffuse through the bulk of the grain or along the grain boundaries (Coble (C...

  17. Creep Strength of Discontinuous Fibre Composites

    DEFF Research Database (Denmark)

    Pedersen, Ole Bøcker


    A unidirectional, discontinuous fibre composite is considered under conditions of steady state creep in the direction of reinforcement. The composite consists of noncreeping, discontinuous, perfectly aligned, uniformly distributed fibres which are perfectly bonded to a matrix obeying a power...... 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....

  18. Mechanical characterization of stomach tissue under uniaxial tensile action. (United States)

    Jia, Z G; Li, W; Zhou, Z R


    In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue. Copyright © 2015 Elsevier Ltd. All rights reserved.

  19. Aerodynamic Performance of a Compact, High Work-Factor Centrifugal Compressor at the Stage and Subcomponent Level (United States)

    Braunscheidel, Edward P.; Welch, Gerard E.; Skoch, Gary J.; Medic, Gorazd; Sharma, Om P.


    The measured aerodynamic performance of a compact, high work-factor, single-stage centrifugal compressor, comprising an impeller, diffuser, 90deg-bend, and exit guide vane is reported. Performance levels are based on steady-state total-pressure and total-temperature rake and angularity-probe data acquired at key machine rating planes during recent testing at NASA Glenn Research Center. Aerodynamic performance at the stage level is reported for operation between 70 to 105 percent of design corrected speed, with subcomponent (impeller, diffuser, and exit-guide-vane) flow field measurements presented and discussed at the 100 percent design-speed condition. Individual component losses from measurements are compared with pre-test CFD predictions on a limited basis.

  20. Neutron irradiation creep in stainless steel alloys

    Energy Technology Data Exchange (ETDEWEB)

    Schuele, Wolfgang (Commission of the European Union, Institute for Advanced Materials, I-21020 Ispra (Vatican City State, Holy See) (Italy)); Hausen, Hermann (Commission of the European Union, Institute for Advanced Materials, I-21020 Ispra (Vatican City State, Holy See) (Italy))


    Irradiation creep elongations were measured in the HFR at Petten on AMCR steels, on 316 CE-reference steels, and on US-316 and US-PCA steels varying the irradiation temperature between 300 C and 500 C and the stress between 25 and 300 MPa. At the beginning of an irradiation a type of primary'' creep stage is observed for doses up to 3-5 dpa after which dose the secondary'' creep stage begins. The primary'' creep strain decreases in cold-worked steel materials with decreasing stress and decreasing irradiation temperature achieving also negative creep strains depending also on the pre-treatment of the materials. These primary'' creep strains are mainly attributed to volume changes due to the formation of radiation-induced phases, e.g. to the formation of [alpha]-ferrite below about 400 C and of carbides below about 700 C, and not to irradiation creep. The secondary'' creep stage is found for doses larger than 3 to 5 dpa and is attributed mainly to irradiation creep. The irradiation creep rate is almost independent of the irradiation temperature (Q[sub irr]=0.132 eV) and linearly dependent on the stress. The total creep elongations normalized to about 8 dpa are equal for almost every type of steel irradiated in the HFR at Petten or in ORR or in EBR II. The negative creep elongations are more pronounced in PCA- and in AMCR-steels and for this reason the total creep elongation is slightly smaller at 8 dpa for these two steels than for the other steels. ((orig.))

  1. Creep-Fatigue Failure Diagnosis

    Directory of Open Access Journals (Sweden)

    Stuart Holdsworth


    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.

  2. 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


    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.

  3. Creep of parylene-C film

    KAUST Repository

    Lin, Jeffrey Chun-Hui


    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.

  4. Negative creep in nickel base superalloys

    DEFF Research Database (Denmark)

    Dahl, Kristian Vinter; Hald, John


    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 have no practical implications but under certain conditions it may become critical. For bolts and fasteners, which are highly constrained during service, negative creep may lead to dramatically increased stresses and eventually to failure. The article was inspired by a recent failure of Nimonic 80A...... bolts in German gas turbines. As a result of this failure similar bolts from Danish gas turbines of the same type were investigated and it was found that the bolts had experienced negative creep during service....

  5. Standard test methods for conducting creep, creep-rupture, and stress-rupture tests of metallic materials

    CERN Document Server

    American Society for Testing and Materials. Philadelphia


    1.1 These test methods cover the determination of the amount of deformation as a function of time (creep test) and the measurement of the time for fracture to occur when sufficient force is present (rupture test) for materials when under constant tensile forces at constant temperature. It also includes the essential requirements for testing equipment. For information of assistance in determining the desirable number and duration of tests, reference should be made to the product specification. 1.2 These test methods list the information which should be included in reports of tests. The intention is to ensure that all useful and readily available information is transmitted to interested parties. Reports receive special attention for the following reasons: (1) results from different, recognized procedures vary significantly; therefore, identification of methods used is important; (2) later studies to establish important variables are often hampered by the lack of detailed information in published reports; (3) t...

  6. Standard practice for verification of testing frame and specimen alignment under tensile and compressive axial force application

    CERN Document Server

    American Society for Testing and Materials. Philadelphia


    1.1 Included in this practice are methods covering the determination of the amount of bending that occurs during the application of tensile and compressive forces to notched and unnotched test specimens in the elastic range and to plastic strains less than 0.002. These methods are particularly applicable to the force application rates normally used for tension testing, creep testing, and uniaxial fatigue testing.

  7. Standard practice for verification of testing frame and specimen alignment under tensile and compressive axial force application

    CERN Document Server

    American Society for Testing and Materials. Philadelphia


    1.1 Included in this practice are methods covering the determination of the amount of bending that occurs during the application of tensile and compressive forces to notched and unnotched test specimens in the elastic range and to plastic strains less than 0.002. These methods are particularly applicable to the force application rates normally used for tension testing, creep testing, and uniaxial fatigue testing.

  8. Martensitic zirconium alloys: Influence of chemical composition on creep characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Pahutova, M.; Kucharova, K.; Cadek, J. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie)


    Results of an extensive investigation of creep in martensitic zirconium alloys are summarized with the aim to show the influence of chemical composition on the main creep characteristics - the steady state creep rate and the time and strain to fracture. The activation energy of creep and the parameter of stress sensitivity of steady state creep rate are determined and possible creep mechanisms as well as creep strenghtening mechanisms are discussed. The time to fracture tsub(f) is related to the steady state creep rate epsilonsub(s) through the Monkman-Grant relation as modified by Dobes and Milicka. The creep fracture shows features different from those of ''classical'' intergranular cavitation creep fracture. Most probably the creep fracture is controlled by the same deformation mechanism as the creep.

  9. Creep characterization of solder bumps using nanoindentation (United States)

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


    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.

  10. Modelling of Creep and Stress Relaxation Test of a Polypropylene Microfibre by Using Fraction-Exponential Kernel

    Directory of Open Access Journals (Sweden)

    Andrea Sorzia


    Full Text Available A tensile test until breakage and a creep and relaxation test on a polypropylene fibre are carried out and the resulting creep and stress relaxation curves are fit by a model adopting a fraction-exponential kernel in the viscoelastic operator. The models using fraction-exponential functions are simpler than the complex ones obtained from combination of dashpots and springs and, furthermore, are suitable for fitting experimental data with good approximation allowing, at the same time, obtaining inverse Laplace transform in closed form. Therefore, the viscoelastic response of polypropylene fibres can be modelled straightforwardly through analytical methods. Addition of polypropylene fibres greatly improves the tensile strength of composite materials with concrete matrix. The proposed analytical model can be employed for simulating the mechanical behaviour of composite materials with embedded viscoelastic fibres.

  11. Elongation Transducer For Tensile Tests (United States)

    Roberts, Paul W.; Stokes, Thomas R.


    Extensometer transducer measures elongation of tensile-test specimen with negligible distortion of test results. Used in stress-versus-strain tests of small specimens of composite materials. Clamping stress distributed more evenly. Specimen clamped gently between jaw and facing surface of housing. Friction force of load points on conical tips onto specimen depends on compression of spring, adjusted by turning cover on housing. Limp, light nylon-insulated electrical leads impose minimal extraneous loads on measuring elements.

  12. Creep and microstructural processes in a low-alloy 2.25%Cr1.6%W steel (ASTM Grade 23)

    Energy Technology Data Exchange (ETDEWEB)

    Kucharova, K. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno (Czech Republic); Sklenicka, V., E-mail: [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno (Czech Republic); CEITEC — IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno (Czech Republic); Kvapilova, M.; Svoboda, M. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno (Czech Republic); CEITEC — IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, CZ-616 62 Brno (Czech Republic)


    A low-alloy 2.25%Cr1%Mo steel (ASTM Grade 22) has been greatly improved by the substitution of almost all of the 1%Mo by 1.6%W. The improved material has been standardized as P/T23 steel (Fe–2.25Cr–1.6W–0.25V–0.05Nb–0.07C). The present investigation was conducted on T23 steel in an effort to obtain a more complete description and understanding of the role of the microstructural evolution and deformation processes in high-temperature creep. Constant load tensile creep tests were carried out in an argon atmosphere in the temperature range 500–650 °C at stresses ranging from 50 to 400 MPa. It was found that the diffusion in the matrix lattice is the creep-rate controlling process. The results of an extensive transmission electron microscopy (TEM) analysis programme to investigate microstructure evolution as a function of temperature are described and compared with the thermodynamic calculations using the software package Thermo-Calc. The significant creep-strength drop of T23 steel after long-term creep exposures can be explained by the decrease in dislocation hardening, precipitation hardening and solid solution hardening due to the instability of the microstructure at high temperature. - Highlights: • The constant load creep tests of T23 steel were carried out at 500–650 °C. • The stress exponents of the creep rate correspond to power law (dislocation) creep. • Diffusion in the matrix lattice is the creep-rate controlling process. • The microstructure instability is the main creep degradation process in T23 steel.

  13. Longitudinal Mechano-Sorptive Creep Behavior of Chinese Fir in Tension during Moisture Adsorption Processes. (United States)

    Peng, Hui; Lu, Jianxiong; Jiang, Jiali; Cao, Jinzhen


    To provide comprehensive data on creep behaviors at relative humidity (RH) isohume conditions and find the basic characteristics of mechano-sorptive (MS) creep (MSC), the tensile creep behaviors, "viscoelastic creep (VEC)" at equilibrium moisture content and MSC during adsorption process, were performed on Chinese fir in the longitudinal direction under 20%, 40%, 60% and 80% RH (25 °C) and at 1, 1.3, and 1.6 MPa, respectively. The free swelling behavior was also measured, where the climate conditions corresponded with MSC tests. Based on the databases of free swelling, VEC, and MSC, the existence of MS effect was examined, and the application of the rheological model under the assumption of partitioned strain was investigated. The results revealed that both VEC and MSC increased with magnitude of applied stress, and the increasing RH level. Under all RH isohume conditions, the total strain of MSC was greater than that of VEC. The influence of RH level on VEC was attributed to the water plasticization effect, whereas that on MSC was presumed to be the effect of water plasticization and unstable state in the wood cell wall. In addition, the RH level promoted the relaxation behavior in MSC, while it slightly affected the relaxation behavior in VEC. In the future, the rheological model could consider the link between load configuration and the anatomic structural feature of wood.

  14. Creep and stress rupture of oxide dispersion strengthened mechanically alloyed Inconel alloy MA 754 (United States)

    Howson, T. E.; Tien, J. K.; Stulga, J. E.


    The creep and stress rupture behavior of the mechanically alloyed oxide dispersion strengthened nickel-base alloy MA 754 was studied at 760, 982 and 1093 C. Tensile specimens with a fine, highly elongated grain structure, oriented parallel and perpendicular to the longitudinal grain direction were tested at various stresses in air under constant load. It was found that the apparent stress dependence was large, with power law exponents ranging from 19 to 33 over the temperature range studied. The creep activation energy, after correction for the temperature dependence of the elastic modulus, was close to but slightly larger than the activation energy for self diffusion. Rupture was intergranular and the rupture ductility as measured by percentage elongation was generally low, with values ranging from 0.5 to 16 pct. The creep properties are rationalized by describing the creep rates in terms of an effective stress which is the applied stress minus a resisting stress consistent with the alloy microstructure. Values of the resisting stress obtained through a curve fitting procedure are found to be close to the values of the particle by-pass stress for this oxide dispersion strengthened alloy, as calculated from the measured oxide particle distribution.

  15. The Mechanical Properties and Modeling of Creep Behavior of UHMWPE/Nano-HA Composites (United States)

    Li, Fan; Gao, Lilan; Gao, Hong; Cui, Yun


    Composites with different levels of hydroxyapatite (HA) content and ultra-high molecular weight polyethylene (UHMWPE) were prepared in this work. Mechanical properties of the composites were examined here, and to evaluate the effect of HA particles on the time-dependent behavior of the pure matrix, the creep and recovery performance of composites at various stress levels were also researched. As expected, the addition of HA influenced the time-dependent response of the UHMWPE and the effect had a strong dependence on the HA content. The creep and recovery strain of the composites significantly decreased with increasing HA content, and tensile properties were also impaired, which was due to the concentration of HA fillers. The mechanism and effect of HA dispersed into the UHMWPE matrix were examined by scanning electron microscopy. Additionally, since variations in the adjusted parameters revealed the impact of HA on the creep behavior of the UHMWPE matrix, Findley's model was employed. The results indicated that the analytical model was accurate for the prediction of creep of the pure matrix and its composites.

  16. Creep/Stress Rupture Behavior of 3D Woven SiC/SiC Composites with Sylramic-iBN, Super Sylramic-iBN and Hi-Nicalon-S Fibers at 2700F in Air (United States)

    Bhatt, R. T.


    To determine the influence of fiber types on creep durability, 3D SiC/SiC CMCs were fabricated with Sylramic-iBN, super Sylramic-iBN and Hi-Nicalon-S fibers and the composite specimens were then tested under isothermal tensile creep at 14820C at 69, 103 and 138 MPa for up to 300hrs in air. The failed specimens were examined by scanning electron microscopy (SEM) and computed tomography (CT) for fracture mode analysis. The creep data of these composites are compared with those of other SiC/SiC composites in the literature. The results of this study will be presented.

  17. Materials, Manufacturing, and Test Development of a Composite Fan Blade Leading Edge Subcomponent for Improved Impact Resistance (United States)

    Miller, Sandi G.; Handschuh, Katherine; Sinnott, Matthew J.; Kohlman, Lee W.; Roberts, Gary D.; Martin, Richard E.; Ruggeri, Charles R.; Pereira, J. Michael


    Application of polymer matrix composite materials for jet engine fan blades is becoming attractive as an alternative to metallic blades; particularly for large engines where significant weight savings are recognized on moving to a composite structure. However, the weight benefit of the composite is offset by a reduction of aerodynamic efficiency resulting from a necessary increase in blade thickness; relative to the titanium blades. Blade dimensions are largely driven by resistance to damage on bird strike. Further development of the composite material is necessary to allow composite blade designs to approximate the dimensions of a metallic fan blade. The reduction in thickness over the state of the art composite blades is expected to translate into structural weight reduction, improved aerodynamic efficiency, and therefore reduced fuel consumption. This paper presents test article design, subcomponent blade leading edge fabrication, test method development, and initial results from ballistic impact of a gelatin projectile on the leading edge of composite fan blades. The simplified test article geometry was developed to realistically simulate a blade leading edge while decreasing fabrication complexity. Impact data is presented on baseline composite blades and toughened blades; where a considerable improvement to impact resistance was recorded.

  18. Fractal and probability analysis of creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Mengjia; Xu, Jijin, E-mail:; Lu, Hao; Chen, Jieshi; Chen, Junmei; Wei, Xiao


    Graphical abstract: - Highlights: • Statistical and fractal analysis is applied to study the creep fracture surface. • The tensile residual stresses promote the initiation of creep crack. • The fractal dimension of a mixed mode fracture surface shows a wavy variation. • The fractal dimension increases with increasing intergranular fracture percentage. • Height coordinates of intergranular fracture surface fit Gaussian distribution. - Abstract: In order to clarify creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses, creep crack tests were carried out on the tension creep specimens, in which the residual stresses were generated by local remelting and cooling. Residual stresses in the specimens were measured using Synchrotron X-ray diffraction techniques. The fracture surface of the creep specimen was analyzed using statistical methods and fractal analysis. The relation between fractal dimension of the fracture surface and fracture mode of the creep specimen was discussed. Due to different fracture mechanisms, the probability density functions of the height coordinates vary with the intergranular crack percentage. Good fitting was found between Gaussian distribution and the probability function of height coordinates of the high percentage intergranular crack surface.

  19. Making Ice Creep in the Classroom (United States)

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


    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.

  20. Towards self-healing creep resistant steels

    NARCIS (Netherlands)

    Van der Zwaag, S.; Zhang, S.; Fang, H.; Bruck, E.; Van Dijk, N.H.


    We report the main findings of our work on the behaviour of binary Fe-Cu and Fe-Au model alloys designed to explore routes to create new creep resistant steels having an in-built ability to autonomously fill creep induced porosity at grain boundaries. The alloying elements were selected on the basis

  1. Harper-Dorn creep of zirconium alpha

    Energy Technology Data Exchange (ETDEWEB)

    Fiala, J.; Novotny, J.; Cadek, J. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie)


    Harper-Dorn (H-D) creep in zirconium-alpha has been investigated at homologous temperatures 0.35 to 0.48 (773 to 1023 K) and stresses ranging from 4 x 10/sup -6/ to 9 x 10/sup -5/ G (G is the shear modulus) by the helicoid specimen technique. It has been shown that H-D creep takes place at intercept grain sizes larger than about 125, while at smaller grain sizes Coble creep operates under the same external conditions. The H-D creep is most probably dislocation core diffusion controlled. A threshold stress for steady state creep has been detected increasing with decreasing temperature. The existence of threshold stress has been qualitatively accounted for by high dislocation density (approx. 10/sup 12/ m/sup -2/) in the specimens tested. The nonconservative motion of jogs on screw dislocations dependent on dislocation core diffusion has been suggested as the creep rate controlling mechanism. The energy of jog formation has been estimated to which a mean distance between jogs, approx. 5b, corresponds at 1000 K, where b is the Burgers vector. Also the observed transient creep has been briefly discussed. The transient component of the creep strain cannot be accounted for exclusively by inelastic bowing out of links of dislocation network.

  2. Finite Element and Experimental Studies of Creep Crack Initiation of RENE-95 Superalloy. (United States)


    confined only to a local area. Another evidence to this statement is the result on creep fracture in *. circumferential U-notched specimens of Nimonic 8DA...Fracture in Nimonic 80A under Triaxial Tensile Stressing", IUTAM Symposium on Creep of Structures, iw ed. by Hayhurst and Ponter, pp. 406-421, 1981. [8...0.06 282 Air 115 115.3 Same as 4 16 2 0.06 376 Air 2.2 2.7 17 2 0.06 358 Mr 0.5 0.7 18 2 0.06 *39 Air 9.3 9.7 19 2 0.06 329 Air .3.6 3.8 20 2 0.06 320

  3. Tensile creep and recovery of Norway spruce influenced by temperature and moisture

    DEFF Research Database (Denmark)

    Engelund, Emil Tang; Salmén, Lennart


    of these two climatic factors on TDMB of wood. It was found that the mechanical response of wood tissue is the sum of responses from both tracheids and middle lamella, with only the previous being reversible. The effect of moisture and temperature differed in that the latter affected the elastic and time...

  4. Creep resistant high temperature martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

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


    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 C.

  5. Creep resistant high temperature martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

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


    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 C.

  6. 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)


    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.

  7. 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)


    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)

  8. Creep damage and hardness properties for 9Cr steel by SP-creep test technique

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Seung Se; Yu, Hyo Sun; Kwon, Il Hyun; Chung, Se Hee [Chonbuk National Univ., Jeonju (Korea, Republic of); Lyu, Dae Young; Kim, Jeong Ki [Jeonju Technical College, Jeonju (Korea, Republic of)


    It has recently been raised main issue how solve the problem of insufficient energy. One of the solution is to increase the thermal efficiency of power generation system. For the purpose of high efficiency, it is necessary to increase the steam temperature and pressure. So, the use of modified 9{approx}12%Cr steel having superior creep rupture strength and oxidation resistance is required to endure such severe environment. The evaluation of creep properties of those heat resistance material is very important to secure the reliability of high temperature and pressure structural components. Since creep properties are determined by microstructural change such as carbide precipitation and coarsening. It is certain that there are some relationship between creep properties and hardness affected by microstructure. In this study, SP-creep ruptured test for newly developed 9Cr steel being used as boiler valve material was performed, and creep properties of the material were evaluated. Also, hardness test were performed and hardness results were related to the creep properties such as LMP and creep strength to verify the availability of SP-creep test as creep test method.

  9. Comparison of creep crack growth rates on the base and welded metals of modified 9Cr-1Mo steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Yun, Song Nam; Kim, Yong Wan; Kim, Sung Ho [KAERI, Daejeon (Korea, Republic of); Park, Jae Young; Kim, Seon Jin [Pukyong National Univ., Busan (Korea, Republic of)


    This paper is to compare Creep Crack Growth Rates (CCGR) on the Base Metal (BM) and Welded Metal (WM) of modified 9Cr-1Mo steel for Gen-IV reactors. Welded specimens were prepared by Shielded Metal Arc Weld (SMAW) method. To obtain material properties for the BM and welded metal, a series of creep and tensile tests was conducted at 600 .deg. C, and CCG tests was also performed using 1/2'' compact tension specimens under different applied loads at 600 .deg. C. Their CCGR behaviors were analyzed by using the empirical equation of the da/dt vs. C{sup *} parameter and compared, respectively. It appeared that, for a given value of C{sup *}, the rate of creep propagation was about 2.0 times faster than in the WM than the BM. This reason is that a creep rate in the WM was largely attributed when compared with that in the BM. From this result, it can be utilized for assessing the rate of creep propagation on the BM and WM of the G91 steel.


    Energy Technology Data Exchange (ETDEWEB)

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


    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.

  11. Seismological Studies for Tensile Faults

    Directory of Open Access Journals (Sweden)

    Gwo-Bin Ou


    Full Text Available A shear slip fault, an equivalence of a double couple source, has often been assumed to be a kinematic source model in ground motion simulation. Estimation of seismic moment based on the shear slip model indicates the size of an earthquake. However, if the dislocation of the hanging wall relative to the footwall includes not only a shear slip tangent to the fault plane but also expansion and compression normal to the fault plane, the radiating seismic waves will feature differences from those out of the shear slip fault. Taking account of the effects resulting from expansion and compression to a fault plane, we can resolve the tension and pressure axes as well as the fault plane solution more exactly from ground motions than previously, and can evaluate how far a fault zone opens or contracts during a developing rupture. In addition to a tensile angle and Poisson¡¦s ratio for the medium, a tensile fault with five degrees of freedom has been extended from the shear slip fault with only three degrees of freedom, strike, dip, and slip.

  12. Development of improved low-strain creep strength in Cabot alloy R-41 sheet. [nickel base sheet alloy for reentry shielding (United States)

    Rothman, M. F.


    The feasibility of improving the low-strain creep properties of a thin gauge nickel base sheet alloy through modified heat treatment or through development of a preferred crystal-lographic texture was investigated. The basic approach taken to improve the creep strength of the material by heat treatment was to increase grain size by raising the solution treatment temperature for the alloy to the range of 1420 K to 1475 K (2100 F to 2200 F). The key technical issue involved was maintenance of adequate tensile ductility following the solutioning of M6C primary carbides during the higher temperature solution treatment. The approach to improve creep properties by developing a sheet texture involved varying both annealing temperatures and the amount of prior cold work. Results identified a heat treatment for alloy R-14 sheet which yields a substantial creep-life advantage at temperatures above 1090 K (1500 F) when compared with material given the standard heat treatment. At the same time, this treatment provides reasonable tensile ductility over the entire temperature range of interest. The mechanical properties of the material given the new heat treatment are compared with those for material given the standard heat treatment. Attempts to improve creep strength by developing a sheet texture were unsuccessful.

  13. The influence of grain boundary structure on diffusional creep

    DEFF Research Database (Denmark)

    Thorsen, Peter Anker; Bilde-Sørensen, Jørgen


    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...

  14. Capsule development and utilization for material irradiation tests; study on the in-pile creep measuring method of zirconium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Yong; Lee, Byung Kee; Lee, Jong Jea; Kim, Chang Sik; Kim, B. Hun; Cho, I. Sik [Sunmoon University, Asan (Korea)


    The final objective of this project is to obtain a design and fabrication technology of an in-pile creep test machine of zirconium alloys. First, design concepts of the in-pile creep test machines of various foreign countries were reviewed and a preliminary design of the equipment was carried. Second, the mock-up of the in-pile creep test machine was fabricated based on the preliminary design. The mock-up consisted of upper and lower grips, a yoke, a pressure chamber including a bellows, a push rod and LVDT. Each part was made of 304 L stainless steel. The average surface roughness of the parts was 1.0-14.7 {mu}m. The mock-up precisely determined an extension of a specimen by gas pressure. Finally, in-pile creep capsule was designed, fabricated and modified. High pure aluminum blocks were put in the capsule. Considering heat transfer coefficients of helium and nitrogen gases, the cooling efficiency is about 4 .deg. C at the condition of 300 .deg. C creep test. Yield strength, ultimate tensile strength and elongation at 300 .deg. C were 335 MPa, 591 MPa, 19.8%, respectively. which were lower than the values at room temperature, 353 MPa, 740 MPa, 12.5%. This study gave an important technology related to design, fabrication and performance tests of the in-pile creep test machine, which is applied to the fabrication of a special capsule and also used for the fundamental data for the fabrication of various in-pile creep capsules. 6 refs., 45 figs., 5 tabs. (Author)

  15. Martensitic stainless steel AISI 420—mechanical properties, creep and fracture toughness (United States)

    Brnic, J.; Turkalj, G.; Canadija, M.; Lanc, D.; Krscanski, S.


    In this paper some experimental results and analyses regarding the behavior of AISI 420 martensitic stainless steel under different environmental conditions are presented. That way, mechanical properties like ultimate tensile strength and 0.2 percent offset yield strength at lowered and elevated temperatures as well as short-time creep behavior for selected stress levels at selected elevated temperatures of mentioned material are shown. The temperature effect on mentioned mechanical properties is also presented. Fracture toughness was calculated on the basis of Charpy impact energy. Experimentally obtained results can be of importance for structure designers.

  16. Trunk proprioception adaptations to creep deformation. (United States)

    Abboud, Jacques; Rousseau, Benjamin; Descarreaux, Martin


    This study aimed at identifying the short-term effect of creep deformation on the trunk repositioning sense. Twenty healthy participants performed two different trunk-repositioning tasks (20° and 30° trunk extension) before and after a prolonged static full trunk flexion of 20 min in order to induce spinal tissue creep. Trunk repositioning error variables, trunk movement time and erector spinae muscle activity were computed and compared between the pre- and post-creep conditions. During the pre-creep condition, significant increases in trunk repositioning errors, as well as trunk movement time, were observed in 30° trunk extension in comparison to 20°. During the post-creep condition, trunk repositioning errors variables were significantly increased only when performing a 20° trunk extension. Erector spinae muscle activity increased in the post-creep condition, while it remained unchanged between trunk repositioning tasks. Trunk repositioning sense seems to be altered in the presence of creep deformation, especially in a small range of motion. Reduction of proprioception acuity may increase the risk of spinal instability, which is closely related to the risk of low back pain or injury.

  17. Creep rupture strength of microalloyed steels

    Energy Technology Data Exchange (ETDEWEB)

    Foldyna, V.; Kubon, Z.; Schellong, T.


    The superior creep resistance of the microalloyed steels compared to the carbon steels originates in the presence of very fine particles of minor phases based on vanadium or niobium. These steels are delivered either after controlled rolling or in the normalized state. The creep strength of these microalloyed steels reaches nearly that of low alloy 0.15C-0.3Mo steel type. The best creep properties are detected in steels after controlled rolling, while after normalizing creep rupture strength slightly decreases, especially in heats alloyed with niobium. This is the result of the microstructure of the steel when in steel with niobium originally fine particles of niobium carbonitride coarsen during normalizing with corresponding changes in their interparticle spacing. When compared the creep rupture strength attained experimentally with the data stated in the standard CSN 41 2025, it is clear that the data stated in the standard corresponds the creep properties of this steel after normalizing but do not take into account creep properties attained after controlled rolling (normalizing forming). (orig.)

  18. Low-temperature creep of austenitic stainless steels (United States)

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


    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.

  19. Creep of granulated loose-fill insulation

    DEFF Research Database (Denmark)

    Rasmussen, Torben Valdbjørn

    This report presents a proposal for a standardised method for creep tests and the necessary theoretical framework that can be used to describe creep of a granulated loose-fill material. Furthermore results from a round robin test are shown. The round robin test was carried out in collaboration...... 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...

  20. Cake creep during filtration of flocculated manure

    DEFF Research Database (Denmark)

    Christensen, Morten Lykkegaard; Keiding, Kristian

    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...... model. The calculation shows that the specific filter-cake resistance increases by a factor of 3 during the filtration. Thus, the impact of cake creep is significant when organic materials such as manure are filtered....

  1. Kinematic hardening in creep of Zircaloy

    Energy Technology Data Exchange (ETDEWEB)

    Sedláček, Radan, E-mail:; Deuble, Dietmar


    Results of biaxial creep tests with stress changes on Zircaloy-2 tube samples are presented. A Hollomon-type viscoplastic strain hardening model is extended by the Armstrong-Frederic nonlinear kinematic hardening law, resulting in a mixed (i.e. isotropic and kinematic) strain hardening model. The creep tests with stress changes and similar tests published in the literature are simulated by the models. It is shown that introduction of the kinematic strain hardening in the viscoplastic strain hardening model is sufficient to describe the creep transients following stress drops, stress reversals and stress removals.

  2. 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)


    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.)

  3. Transitional Thermal Creep of Early Age Concrete

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Anders Boe; Damkilde, Lars; Freiesleben Hansen, Per


    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...... termed the microprestresses, which reduces the stiffness of the concrete and increase the creep rate. The aging material is modelled in an incremental way reflecting the hydration process in which new layers of cement gel solidifies in a stress free state and add stiffness to the material. Analysis...

  4. Transitional Thermal Creep of Early Age Concrete

    DEFF Research Database (Denmark)

    Hauggaard, A. B.; Damkilde, L.; Hansen, Per Freiesleben


    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...... termed the microprestresses, which reduce the stiffness of the concrete and increase the creep rate. The aging material is modeled in an incremental way reflecting the hydration process in which new layers of cement gel solidify in a stress free state and add stiffness to the material. Analysis...

  5. Slow creep in soft granular packings. (United States)

    Srivastava, Ishan; Fisher, Timothy S


    Transient creep mechanisms in soft granular packings are studied numerically using a constant pressure and constant stress simulation method. Rapid compression followed by slow dilation is predicted on the basis of a logarithmic creep phenomenon. Characteristic scales of creep strain and time exhibit a power-law dependence on jamming pressure, and they diverge at the jamming point. Microscopic analysis indicates the existence of a correlation between rheology and nonaffine fluctuations. Localized regions of large strain appear during creep and grow in magnitude and size at short times. At long times, the spatial structure of highly correlated local deformation becomes time-invariant. Finally, a microscale connection between local rheology and local fluctuations is demonstrated in the form of a linear scaling between granular fluidity and nonaffine velocity.

  6. Constitutive Equations for Damaged Creeping Materials, (United States)


    honorable task, and it has > " been very successfully accomplished by Argon (1982), Ashby , et al. (1979), Cocks and Ashby (1983), Frost and Ashby (1982...8217Creep Cavitation in 304 Stainless Steel,’ ,>I- Acta Metallurgica, Vol. 29, p. 1321. /" [18] Cocks , A.C.F., Ashby , M.F., (1982), ’On Creep Fracture...and many others are very important in engineering practice. A body of modeling efforts has been dominated by simplified mechanistic approaches ( Ashby

  7. Creep fatigue assessment for EUROFER components

    Energy Technology Data Exchange (ETDEWEB)

    Özkan, Furkan, E-mail:; Aktaa, Jarir


    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.

  8. Bone creep can cause progressive vertebral deformity. (United States)

    Pollintine, Phillip; Luo, Jin; Offa-Jones, Ben; Dolan, Patricia; Adams, Michael A


    Vertebral deformities in elderly people are conventionally termed "fractures", but their onset is often insidious, suggesting that time-dependent (creep) processes may also be involved. Creep has been studied in small samples of bone, but nothing is known about creep deformity of whole vertebrae, or how it might be influenced by bone mineral density (BMD). We hypothesise that sustained compressive loading can cause progressive and measurable creep deformity in elderly human vertebrae. 27 thoracolumbar "motion segments" (two vertebrae and the intervening disc and ligaments) were dissected from 20 human cadavers aged 42-91 yrs. A constant compressive force of approximately 1.0 kN was applied to each specimen for either 0.5 h or 2 h, while the anterior, middle and posterior heights of each of the 54 vertebral bodies were measured at 1 Hz using a MacReflex 2D optical tracking system. This located 6 reflective markers attached to the lateral cortex of each vertebral body, with resolution better than 10 microm. Experiments were at laboratory temperature, and polythene film was used to minimise water loss. Volumetric BMD was calculated for each vertebral body, using DXA to measure mineral content, and water immersion for volume. In the 0.5 h tests, creep deformation in the anterior, middle and posterior vertebral cortex averaged 4331, 1629 and 614 micro-strains respectively, where 10,000 micro-strains represents 1% loss in height. Anterior creep strains exceeded posterior (Pspecimens with average BMDfracture.

  9. Creep analysis of silicone for podiatry applications. (United States)

    Janeiro-Arocas, Julia; Tarrío-Saavedra, Javier; López-Beceiro, Jorge; Naya, Salvador; López-Canosa, Adrián; Heredia-García, Nicolás; Artiaga, Ramón


    This work shows an effective methodology to characterize the creep-recovery behavior of silicones before their application in podiatry. The aim is to characterize, model and compare the creep-recovery properties of different types of silicone used in podiatry orthotics. Creep-recovery phenomena of silicones used in podiatry orthotics is characterized by dynamic mechanical analysis (DMA). Silicones provided by Herbitas are compared by observing their viscoelastic properties by Functional Data Analysis (FDA) and nonlinear regression. The relationship between strain and time is modeled by fixed and mixed effects nonlinear regression to compare easily and intuitively podiatry silicones. Functional ANOVA and Kohlrausch-Willians-Watts (KWW) model with fixed and mixed effects allows us to compare different silicones observing the values of fitting parameters and their physical meaning. The differences between silicones are related to the variations of breadth of creep-recovery time distribution and instantaneous deformation-permanent strain. Nevertheless, the mean creep-relaxation time is the same for all the studied silicones. Silicones used in palliative orthoses have higher instantaneous deformation-permanent strain and narrower creep-recovery distribution. The proposed methodology based on DMA, FDA and nonlinear regression is an useful tool to characterize and choose the proper silicone for each podiatry application according to their viscoelastic properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Surfactant effects on soil aggregate tensile strength (United States)

    Little is known regarding a soil aggregate's tensile strength response to surfactants that may be applied to alleviate soil water repellency. Two laboratory investigations were performed to determine surfactant effects on the tensile strength of 1) Ap horizons of nine wettable, agricultural soils co...

  11. Machining technique prevents undercutting in tensile specimens (United States)

    Moscater, R. E.; Royster, D. M.


    Machining technique prevents undercutting at the test section in tensile specimens when machining the four corners of the reduced section. Made with a gradual taper in the test section, the width of the center of the tensile specimen is less than the width at the four corners of the reduced section.

  12. Unexpectedly low tensile strength in concrete structures

    NARCIS (Netherlands)

    Siemes, A.J.M.; Han, N.; Visser, J.H.M.


    During an extensive investigation of some 25 concrete bridges and other structures suffering from alkali-silica reaction it has been found that the uniaxial tensile strength of the concrete was extremely low in relation to both the compressive strength and the splitting tensile strength. It is known

  13. Influence of Boron on the Creep Behavior and the Microstructure of Particle Reinforced Aluminum Matrix Composites

    Directory of Open Access Journals (Sweden)

    Steve Siebeck


    Full Text Available The reinforcement of aluminum alloys with particles leads to the enhancement of their mechanical properties at room temperature. However, the creep behavior at elevated temperatures is often negatively influenced. This raises the question of how it is possible to influence the creep behavior of this type of material. Within this paper, selected creep and tensile tests demonstrate the beneficial effects of boron on the properties of precipitation-hardenable aluminum matrix composites (AMCs. The focus is on the underlying microstructure behind this effect. For this purpose, boron was added to AMCs by means of mechanical alloying. Comparatively higher boron contents than in steel are investigated in order to be able to record their influence on the microstructure including the formation of potential new phases as well as possible. While the newly formed phase Al3BC can be reliably detected by X-ray diffraction (XRD, it is difficult to obtain information about the phase distribution by means of scanning electron microscopy (SEM and scanning transmission electron microscopy (STEM investigations. An important contribution to this is finally provided by the investigation using Raman microscopy. Thus, the homogeneous distribution of finely scaled Al3BC particles is detectable, which allows conclusions about the microstructure/property relationship.

  14. Transient Liquid Phase Bonding Single-Crystal Superalloys with Orientation Deviations: Creep Properties (United States)

    Sheng, Naicheng; Liu, Jide; Jin, Tao; Sun, Xiaofeng; Hu, Zhuangqi


    Superalloys single crystals with various orientation deviations were bonded using transient liquid phase bonding method, then the creep properties of the bonded specimens were tested at 1033 K (760 °C)/780 MPa. It is found that the creep life of the bonded specimens decreases with the increase of the relative orientation deviations. Despite the fracture of the specimens appears on the bonding region, the deformation mechanism changes from specimens with low angle boundary to high angle boundary. In low angle boundary specimens, cleavage originated from the defects grows perpendicularly to the tensile stress and connects through the different slip planes around the cleavage planes. In this case, the deformation proceeds by the dislocations and stacking faults on multi-planes. With increasing orientation deviation, dislocation and stacking faults moved on single plane. As a result, the dislocations interact with the grain boundary and lead to fracture. Based on the present investigation, the orientation of the bonded superalloys single crystal should be controlled so that the introduced grain boundaries are relatively small and exhibit higher creep strength.

  15. Creep-fatigue interactions in equiaxed and single crystal Ni-base superalloys

    Directory of Open Access Journals (Sweden)

    Vacchieri E.


    Full Text Available Ni-base superalloys are employed as structural materials for the most critical hot gas path components of gas turbines. The current market requirement is to cycle the machine every day, providing energy when it is most needed. It is therefore important to understand how creep and fatigue damages interact in these components. Starting from a significant knowledge base of mechanical and microstructural behaviour established from standard tests of the equiaxed and single crystal superalloys, creep-fatigue tests have been performed to evaluate how the two damage conditions develop together. The creep-fatigue testing conditions represent the maximum temperature and strain at the critical locations in real components, while the position of hold-time has been varied from tensile to compressive to understand the effect on reduction in crack initiation endurance with respect to standard LCF tests and on the microstructural mechanisms. The experimental test results have been explained in terms of microstructural evolution and they have been correlated to that observed at critical locations in real components.

  16. Post Preloading Creep Properties of Highly Compressible Harbor Marine Sediments

    Directory of Open Access Journals (Sweden)

    Franciscus Xaverius Toha


    Full Text Available A laboratory experimental research in creep behavior of soft clay marine sediments was done to investigate creep strain under reloading. A total of 52 oedometer tests were carried out with 16 slurry sediment samples subjected to cycles of unloading at preload removal pressure and reloading to higher design pressures. Common practice as well as more recent advanced methods of creep deformation analysis were used to refine the predictions. The study indicates that although preloading substantially reduces post construction creep, the analysis is very sensitive to creep indices at slight overconsolidation and the resulting creep may not be negligible at previously established limits of primary to secondary compression ratios.

  17. Effect of solute interactions in columbium /Nb/ on creep strength (United States)

    Klein, M. J.; Metcalfe, A. G.


    The creep strength of 17 ternary columbium (Nb)-base alloys was determined using an abbreviated measuring technique, and the results were analyzed to identify the contributions of solute interactions to creep strength. Isostrength creep diagrams and an interaction strengthening parameter, ST, were used to present and analyze data. It was shown that the isostrength creep diagram can be used to estimate the creep strength of untested alloys and to identify compositions with the most economical use of alloy elements. Positive values of ST were found for most alloys, showing that interaction strengthening makes an important contribution to the creep strength of these ternary alloys.

  18. A Creep Model for High-Density Snow (United States)


    modifies Mellor and Smith’s creep model for dense snow to conform to the more general creep power law form (Glen’s creep law for ice is a special case of...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...Glen’s creep law for ice , Glen 1955). From this, I for- mulated a general model that is the basis for both the primary and second- ary creep models


    Directory of Open Access Journals (Sweden)

    David Budiono


    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.

  20. The investigation of expanded polystyrene creep behaviour

    Directory of Open Access Journals (Sweden)

    Zhukov Aleksey


    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.

  1. Time dependence of mesoscopic strain distribution for triaxial woven carbon-fiber-reinforced polymer under creep loading measured by digital image correlation (United States)

    Koyanagi, Jun; Nagayama, Hideo; Yoneyama, Satoru; Aoki, Takahira


    This paper presents the time dependence of the mesoscopic strain of a triaxial woven carbon-fiber-reinforced polymer under creep loading measured using digital image correlation (DIC). Two types of DIC techniques were employed for the measurement: conventional subset DIC and mesh DIC. Static tensile and creep tests were carried out, and the time dependence of the mesoscopic strain distribution was investigated by applying these techniques. The ultimate failure of this material is dominated by inter-bundle decohesion caused by relative rigid rotation and relating shear stress. Therefore, these were focused on in the present study. During the creep tests, the fiber directional strain, shear strain, and rotation were monitored using the DIC, and the mechanism for the increase in the specimen's macro-strain over time was investigated based on the results obtained by the DIC measurement.

  2. Improved creep strength and creep ductility of type 347 austenitic stainless steel through the self-healing effect of boron for creep cavitation (United States)

    Laha, K.; Kyono, J.; Sasaki, T.; Kishimoto, S.; Shinya, N.


    Composition of type 347 austenitic stainless steel was modified with the addition of boron and cerium. An improvement of creep strength coupled with creep ductility of the steel was observed with boron and cerium additions. The observation of enhanced precipitation of carbonitrides in boron-containing steel over that of boron-free steel may in part contribute to the increase in creep strength. Both grain boundary sliding and nucleation and growth of intergranular creep cavities were found to be suppressed in steel-containing boron. This results in an increase in creep strength and creep ductility. Auger electron spectroscopic analysis of the chemistry of creep cavity surfaces (exposed by breaking the creep-exposed steel specimen at liquid nitrogen temperature under impact loading) revealed the segregation of elemental boron on the creep cavity surface. Boron segregation, on the creep cavity surface in the absence of sulfur contamination, suppressed the cavity growth and provided the steel with a self-healing effect for creep cavitation. Cerium additions enabled boron to segregate on the cavity surface by effectively removing the traces of free sulfur in the matrix by the formation of ceriumoxysulfide (Ce2O2S).

  3. Analysis of Superheater Work Under Creep Conditions

    Directory of Open Access Journals (Sweden)

    Piotr Duda


    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.

  4. Comparison of creep deformation rates during load and strain controlled multi-step creep ageing tests on AA7050 (United States)

    Zheng, Jinghua; Davies, Catrin M.; Lin, Jianguo


    In this work, the constant load and constant strain controlled creep behaviour of a precipitation hardenable aluminium alloy 7050 during a two-step ageing treatment have been experimentally studied. The two-step temperature treatment is strictly in accordance with the T74 ageing temperature profile (120 °C × 6 h+ 177 °C × 7 h) for 7050 alloys. It has been found that at 120 °C creep strain generation was extremely small, whilst at 177 °C significant creep strains were developed for both the load and strain controlled creep tests. The samples during the load controlled creep ageing tests reached the tertiary creep regime under a constant stress of 230 MPa within 14 h, while remained in the secondary creep regime under stresses ranging from 150 - 215 MPa for this time. The strain controlled creep ageing tests can prevent the samples from reaching their tertiary creep regimes through reducing the initial high stresses (up to 320 MPa) to a stress lower than 230 MPa during the tests. The creep strain rates obtained from strain controlled creep ageing tests are found smaller than the minimum creep strain rates from load controlled creep tests. The steady state stress exponent n was found ˜3.3 for load controlled creep ageing tests. Similar n values was obtained for strain controlled creep ageing tests when stress is larger than 200 MPa, while this value jumped to ˜15 when stresses reduced to < 200 MPa. All these findings suggest that load and strain controlled creep exhibit different behaviours and thus a proper calibration is required if using the constant load creep data to simulate the constant strain stress relaxation curves under the same ageing conditions.

  5. 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)


    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.)

  6. Studies of Grain Boundaries in Materials Subjected to Diffusional Creep

    DEFF Research Database (Denmark)

    Nørbygaard, Thomas

    Grain boundaries in crystalline Cu(2%Ni) creep specimens have been studied by use of scanning and transmission electron microscopy in order to establish the mechanism of deformation. Creep rate measurements and dependencies were found to fit reasonably well with the model for diffusional creep......) with the activity displayed during diffusional creep testing. It was found that boundaries with low deviation from perfect Σ did not contribute macroscopically to the creep strain. A resist deposition procedure was examined to improve the reference surface grid so as to allow determination of the grain boundary...... plane by use of simple stereomicroscopy directly on the surface. The etched pattern deteriorated heav-ily during creep testing, supposedly because of dislocation creep, due to exces-sive creep stress. Grain boundaries have been studied and characterised by TEM providing an insight into the diversity...

  7. 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))


    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

  8. Creep Properties of Walikukun (Schouthenia ovata Timber Beams

    Directory of Open Access Journals (Sweden)

    Ali Awaludin


    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.

  9. Creep events and creep noise in gravitational-wave interferometers: basic formalism and stationary limit

    CERN Document Server

    Levin, Yuri


    In gravitational-wave interferometers, test masses are suspended on thin fibers which experience considerable tension stress. Sudden microscopic stress release in a suspension fiber, which I call a 'creep event', would excite motion of the test mass that would be coupled to the interferometer's readout. The random test-mass motion due to a time-sequence of creep events is referred to as 'creep noise'. In this paper I present an elasto-dynamic calculation for the test-mass motion due to a creep event. I show that within a simple suspension model, the main coupling to the optical readout occurs via a combination of a "dc" horizontal displacement of the test mass, and excitation of the violin and pendulum modes, and not, as was thought previously, via lengthening of the fiber. When the creep events occur sufficiently frequently and their statistics is time-independent, the creep noise can be well-approximated by a stationary Gaussian random process. I derive the functional form of the creep noise spectral densit...

  10. Finite Element Modelling for Tensile Behaviour of Thermally Bonded Nonwoven Fabric

    Directory of Open Access Journals (Sweden)

    Gao Xiaoping


    Full Text Available A nonwoven fabric has been widely used in geotextile engineering in recent years; its tensile strength is an important behaviour. Since the fibre distributions in nonwoven fabrics are random and discontinuous, the unit-cell model of a nonwoven fabric cannot be developed to simulate its tensile behaviour. This article presents our research on using finite element method (FEM to study the tensile behaviour of a nonwoven fabric in macro-scale based on the classical laminate composite theory. The laminate orientation was considered with orientation distribution function of fibres, which has been obtained by analysing the data acquired from scanning electron microscopy with Hough Transform. The FE model of a nonwoven fabric was developed using ABAQUS software; the required engineering constants of a nonwoven fabric were obtained from experimental data. Finally, the nonwoven specimens were stretched along with machine direction and cross direction. The experimental stress-strain curves were compared with the results of FE simulations. The approximate agreement proves the validity of an FE model, which could be used to precisely simulate the stress relaxation, strain creep, bending and shear property of a nonwoven fabric.

  11. Influence of the phase composition of refractory materials on creep


    Terzić A.; Pavlović Lj.; Milutinović-Nikolić A.


    In this paper, the relationship between the creeping effect and mineralogical characteristics of the applied binding phase for various refractory materials (high-alumina materials, with high or low impurity content, tar bonded either magnesite or dolomite materials and silicate bonded chrom-magnesite materials) is presented. The mechanism of creeping is analyzed and the activation energy for creep for each investigated material is obtained and discussed. All investigated materials are creep s...

  12. Creep motion of a model frictional system. (United States)

    Blanc, Baptiste; Pugnaloni, Luis A; Géminard, Jean-Christophe


    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 effects, 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.

  13. Creep turns linear in narrow ferromagnetic nanostrips. (United States)

    Leliaert, Jonathan; Van de Wiele, Ben; Vansteenkiste, Arne; Laurson, Lasse; Durin, Gianfranco; Dupré, Luc; Van Waeyenberge, Bartel


    The motion of domain walls in magnetic materials is a typical example of a creep process, usually characterised by a stretched exponential velocity-force relation. By performing large-scale micromagnetic simulations, and analyzing an extended 1D model which takes the effects of finite temperatures and material defects into account, we show that this creep scaling law breaks down in sufficiently narrow ferromagnetic strips. Our analysis of current-driven transverse domain wall motion in disordered Permalloy nanostrips reveals instead a creep regime with a linear dependence of the domain wall velocity on the applied field or current density. This originates from the essentially point-like nature of domain walls moving in narrow, line- like disordered nanostrips. An analogous linear relation is found also by analyzing existing experimental data on field-driven domain wall motion in perpendicularly magnetised media.

  14. Development of creep resistant magnesium diecasting alloys

    Energy Technology Data Exchange (ETDEWEB)

    Pekguleryuz, M.O. [Noranda Technol. Center, Que. (Canada)


    The most economic use of magnesium in the automotive industry presently is in diecast applications because of the high productivity of the diecasting process that upsets the relatively high cost of the magnesium metal. The current commercial magnesium alloys developed for diecasting applications fall into two classes. The first group is based on the Mg-Al system and the Mg-Al-Zn systems. These alloys have been developed for good room temperature strength and/or ductility but do not exhibit good creep resistance. The second group of alloys has been developed for improved elevated-temperature performance and are based on the Mg-Al-RE and Mg-Al-Si systems. These second group alloys offer either borderline improvement in creep resistance (Mg-Al-Si) or have cost or other disadvantages despite the good creep resistance (Mg- Al-RE).

  15. Creep motion of a model frictional system

    CERN Document Server

    Blanc, Baptiste; Géminard, Jean-Christophe


    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.

  16. Comparison of the Characteristics of Solid Type and Annular Type Nuclear Fuels Using Thermoelastic-Plastic-Creep FEM

    Directory of Open Access Journals (Sweden)

    Young-Doo Kwon


    Full Text Available The purpose of this study is to compare the characteristics of two types of nuclear fuel using the finite element program of thermoelastic-plastic-creep analysis. The analyzed fuel rods are of two types, solid and annular ones, and their thermomechanical characteristics are compared. Thermoelastic-plastic-creep analyses were made using an in-house finite element analysis program that adopts the “effective-stress-function” algorithm. The temperature-dependent material properties, which were obtained from the experiments for actual nuclear reactors, are adopted. The effects of type of fuel systems are revealed in both stresses and temperature distributions. The maximum tensile and compressive hoop stress of pellet and cladding are monitored to evaluate the mechanical behavior, and the maximum temperature is used to evaluate the thermal behavior. Although the annular type of fuel has certain disadvantage, it would be used very effectively or safely in future nuclear power plants.

  17. Production response of lambs receiving creep feed while grazing ...

    African Journals Online (AJOL)

    Department of Agriculture (Western Cape)

    analysis of variance with treatment (creep feed or no creep feed) and birth status (single and twins) as main factors. Provision a ... At both locations, birth status had no effect on the production parameters for ewes or lambs. Keywords: Creep ... supplementation are of vital importance (De Villiers, 1991; Brand et al., 1999).

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

    NARCIS (Netherlands)

    Giessen, E. van der; Tvergaard, V.


    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

  19. Thermal activated grain boundary creep in polycrystalline copper ...

    African Journals Online (AJOL)

    Creep deformation in metals and alloys at intermediate temperatures and low stresses are attributed to power-law and diffusion mechanisms. ... By superposition of the rate equations, the net strain rate is determined as the sum of three independent creep mechanisms of Cobble diffusion creep, gra-in boundary sliding and ...

  20. Modelling of creep damage development in ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

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


    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.

  1. Nanoindentation creep versus bulk compressive creep of dental resin-composites. (United States)

    El-Safty, S; Silikas, N; Akhtar, R; Watts, D C


    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

  2. Fatigue creep damage at the cement-bone interface: an experimental and a micro-mechanical finite element study (United States)

    Waanders, Daan; Janssen, Dennis; Miller, Mark A.; Mann, Kenneth A.; Verdonschot, Nico


    The goal of this study was to quantify the micromechanics of the cement-bone interface under tensile fatigue loading using finite element analysis (FEA) and to understand the underlying mechanisms that play a role in the fatigue behavior of this interface. Laboratory cement-bone specimens were subjected to a tensile fatigue load, while local displacements and crack growth on the specimen's surface were monitored. FEA models were created from these specimens based upon micro-computed tomography data. To accurately model interfacial gaps at the interface between the bone and cement, a custom-written erosion algorithm was applied to the bone model. A fatigue load was simulated in the FEA models while monitoring the local displacements and crack propagation. The results showed the FEA models were able to capture the general experimental creep damage behavior and creep stages of the interface. Consistent with the experiments, the majority of the deformation took place at the contact interface. Additionally, the FEA models predicted fatigue crack patterns similar to experimental findings. Experimental surface cracks correlated moderately with FEA surface cracks (r2=0.43), but did not correlate with the simulated crack volume fraction (r2=0.06). Although there was no relationship between experimental surface cracks and experimental creep damage displacement (r2=0.07), there was a strong relationship between the FEA crack volume fraction and the FEA creep damage displacement (r2=0.76). This study shows the additional value of FEA of the cement-bone interface relative to experimental studies and can therefore be used to optimize its mechanical properties. PMID:19682690

  3. 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


    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.)

  4. 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: [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)


    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.

  5. Influence of the phase composition of refractory materials on creep

    Directory of Open Access Journals (Sweden)

    Terzić A.


    Full Text Available In this paper, the relationship between the creeping effect and mineralogical characteristics of the applied binding phase for various refractory materials (high-alumina materials, with high or low impurity content, tar bonded either magnesite or dolomite materials and silicate bonded chrom-magnesite materials is presented. The mechanism of creeping is analyzed and the activation energy for creep for each investigated material is obtained and discussed. All investigated materials are creep sensitive under investigated conditions and have similar activation energies for creep except high-alumina refractories with a low impurity content.

  6. Making High-Tensile-Strength Amalgam Components (United States)

    Grugel, Richard


    Structural components made of amalgams can be made to have tensile strengths much greater than previously known to be possible. Amalgams, perhaps best known for their use in dental fillings, have several useful attributes, including room-temperature fabrication, corrosion resistance, dimensional stability, and high compressive strength. However, the range of applications of amalgams has been limited by their very small tensile strengths. Now, it has been discovered that the tensile strength of an amalgam depends critically on the sizes and shapes of the particles from which it is made and, consequently, the tensile strength can be greatly increased through suitable choice of the particles. Heretofore, the powder particles used to make amalgams have been, variously, in the form of micron-sized spheroids or flakes. The tensile reinforcement contributed by the spheroids and flakes is minimal because fracture paths simply go around these particles. However, if spheroids or flakes are replaced by strands having greater lengths, then tensile reinforcement can be increased significantly. The feasibility of this concept was shown in an experiment in which electrical copper wires, serving as demonstration substitutes for copper powder particles, were triturated with gallium by use of a mortar and pestle and the resulting amalgam was compressed into a mold. The tensile strength of the amalgam specimen was then measured and found to be greater than 10(exp 4) psi (greater than about 69 MPa). Much remains to be done to optimize the properties of amalgams for various applications through suitable choice of starting constituents and modification of the trituration and molding processes. The choice of wire size and composition are expected to be especially important. Perusal of phase diagrams of metal mixtures could give insight that would enable choices of solid and liquid metal constituents. Finally, whereas heretofore, only binary alloys have been considered for amalgams

  7. Creep in generation IV nuclear applications

    Energy Technology Data Exchange (ETDEWEB)

    Rissanen, L. (VTT Technical Research Centre of Finland, Espoo (Finland))


    Nuclear power has an important role in fulfilling the world's growing energy needs and reducing the carbon dioxide emission. Six new, innovative nuclear energy systems have been identified and selected for further development by the international Generation Four International Forum (GIF). These generation four (Gen IV) nuclear energy systems include a variety of reactor, energy conversion and fuel cycle technologies. The successful development and deployment of these largely depend on the performance and reliability of the available structural materials. These potential materials need to sustain their mechanical properties up to high temperatures, high neutron doses and corrosive environments of the new or enhanced types of coolants. Current knowledge on material properties, material-coolant interaction and especially material degradation processes in these new environments are limited. This paper gives an overview of the Gen IV material issues with special emphasis on European design of supercritical light water reactor concept high performance light water reactor (HPLWR). The challenges for the structural materials and the components most likely to suffer from creep and creep-irradiation are highlighted. Some results from relatively short term creep testing in supercritical water are presented for AISI 316NG, 347H and 1.4970 steels. The 1.4970 steel was superior in creep and oxidation resistance (orig.)

  8. Polycrystal creep in the microplastic stress range (United States)

    Dudarev, E. F.; Pochivalova, G. P.


    A microcreep theory has been developed for polycrystalline materials, which incorporates the microplastic strain in the aggregate on static loading. Experiments have been performed on the creep laws for polycrystalline metals and alloys, and it is found that the theory fits the experiments. The mobile-dislocation density decreases during microcreep.

  9. Creep measurements on curing epoxy systems

    DEFF Research Database (Denmark)

    Kammer, Charlotte; Szabo, Peter


    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....

  10. Steady-state creep in the mantle

    Directory of Open Access Journals (Sweden)



    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.

  11. Time constant of logarithmic creep and relaxation

    CSIR Research Space (South Africa)

    Nabarro, FRN


    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...

  12. Significance of primary irradiation creep in graphite

    CSIR Research Space (South Africa)

    Erasmus, C


    Full Text Available of Nuclear Materials, vol. 436(1-3), pp 167-174 Significance of primary irradiation creep in graphite Christiaan Erasmus a,⇑, Schalk Kok b, Michael P. Hindley a a Pebble Bed Modular Reactor (Proprietary) Limited, PO Box 9396, Centurion 0046, South...

  13. Martensite zirconium alloys: effect of chemical composition on creep characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Pahutova, M.; Cadek, J. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie)


    The results of an extensive investigation of creep and creep fracture characteristics of martensitic zirconium alloys are summarized and briefly discussed. It is shown that at the temperature 773 K and the applied stress 100 MPa alloying with a properly chosen combination of tin and molybdenum makes it possible to reduce the steady state creep rate of alpha zirconium by seven orders of magnitude. The fracture in creep of martensitic zirconium alloys hardly has features typical of an intercrystalline creep fracture. Most probably, the creep fracture of martensitic zirconium alloys is controlled by the same deformation mechanism as the creep itself. From the point of view of application of martensitic zirconium alloys at temperatures 720 to 770 K their considerable disadvantage consists in that that at creep rates considered for engineering practice the steady state creep rate depends on the applied stress linearly. This suggests the Nabarro-Herring creep as the rate controlling mechanism. Consequently, any further significant reduction in the creep rate and/or increase in the time till fracture requires a considerable reduction in the applied stress.

  14. Nonlinear creep damage constitutive model for soft rocks (United States)

    Liu, H. Z.; Xie, H. Q.; He, J. D.; Xiao, M. L.; Zhuo, L.


    In some existing nonlinear creep damage models, it may be less rigorous to directly introduce a damage variable into the creep equation when the damage variable of the viscous component is a function of time or strain. In this paper, we adopt the Kachanov creep damage rate and introduce a damage variable into a rheological differential constitutive equation to derive an analytical integral solution for the creep damage equation of the Bingham model. We also propose a new nonlinear viscous component which reflects nonlinear properties related to the axial stress of soft rock in the steady-state creep stage. Furthermore, we build an improved Nishihara model by using this new component in series with the correctional Nishihara damage model that describes the accelerating creep, and deduce the rheological constitutive relation of the improved model. Based on superposition principle, we obtain the damage creep equation for conditions of both uniaxial and triaxial compression stress, and study the method for determining the model parameters. Finally, this paper presents the laboratory test results performed on mica-quartz schist in parallel with, or vertical to the schistosity direction, and applies the improved Nishihara model to the parameter identification of mica-quartz schist. Using a comparative analysis with test data, results show that the improved model has a superior ability to reflect the creep properties of soft rock in the decelerating creep stage, the steady-state creep stage, and particularly within the accelerating creep stage, in comparison with the traditional Nishihara model.

  15. 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)


    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.

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


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


    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...

  17. Soil creep and historic landscape changes (United States)

    Lucke, Bernhard


    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.

  18. Finite element creep buckling analysis of circular cylindrical shell under axial compression taking account of creep damage (United States)

    Hagihara, Seiya; Miyazaki, Noriyuki


    Cylindrical shells are utilized as structural elements of nuclear power plants, heat exchangers or pressure vessels, which are operated under elevated temperature. Creep buckling is one of the failure modes of structures at elevated temperature. In some experiments conducted by other authors, axially compressive cylindrical shells with a large ratio of radius to thickness were observed to buckle with circumferential waves. It is observed that the circumferential waves occur due to bifurcation buckling. But, the critical time and the minimum loading for bifurcation buckling obtained from calculations of finite element analyses are not in very good agreement with those of the experiments. One of the reasons for the disagreement is considered to be that the creep constitutive equations employed in many previous analyses represent the steady creep. The creep phenomena usually have primary creep period, steady creep one and tertiary creep one. A creep strain - time relation through the three periods can be simulated by using a constitutive equation based on creep damage mechanics. In the present analysis, we analyzed the bifurcation creep buckling of circular cylindrical shells subjected to axial compression by the use of the finite element method taking account of the creep damage mechanics proposeol by of Kachanov-Rabotonov.

  19. Influence of dispersoids on the creep behavior of dispersion strengthened aluminum materials

    Directory of Open Access Journals (Sweden)

    Carreño, F.


    Full Text Available The creep behavior of a rapidly solidified Al-6.5%Fe-0.6%V-1.3%Si dispersion strengthened material containing 16 volume % of dispersoids has been studied by means of tensile tests at high temperatures from 483 to 821 K. The imposed strain rates ranged from 2.5∙10-6 to 10-2s-1. The microstructure was very fine, consisting of submicron grains and small hard round-shaped dispersoids of about 54 nm. The creep behavior was characterized by high apparent stress exponents and high activation energies that are not accurately predicted by models from the literature. Therefore, a creep equation is developed to describe the creep behavior of the studied aluminum dispersion strengthened material and other materials with similar microstructures. The proposed equation is a generalization of conventional slip creep equations without the use of a threshold stress.

    Se estudió el comportamiento en fluencia del material solidificado rápidamente Al-6,5%Fe-0,6%V-1,3%Si, reforzado por dispersión que contenía una fracción de volumen de dispersoides de 16 %, mediante ensayos de tracción a altas temperaturas desde 483 a 821 K. Las velocidades de deformación impuestas variaron desde 2,5∙10-6 to 10-2s-1. La microestructura, que era muy fina, estaba formada por granos submicrométricos y pequeños dispersoides redondeados y duros de unos 54 nm. El comportamiento en fluencia se caracterizó por altos exponentes de la tensión aparente y altas energías de activación aparentes que no se predicen con exactitud por modelos de la literatura. Por ello, se ha desarrollado una ecuación de fluencia que describe el comportamiento del material de base aluminio reforzado por dispersión y de otros materiales de microestructura similar. La ecuación propuesta es una generalización de ecuaciones de fluencia convencionales por movimiento de dislocaciones y no emplea una tensión umbral.

  20. Creep of Posidonia Shale at Elevated Pressure and Temperature (United States)

    Rybacki, E.; Herrmann, J.; Wirth, R.; Dresen, G.


    The economic production of gas and oil from shales requires repeated hydraulic fracturing operations to stimulate these tight reservoir rocks. Besides simple depletion, the often observed decay of production rate with time may arise from creep-induced fracture closure. We examined experimentally the creep behavior of an immature carbonate-rich Posidonia shale, subjected to constant stress conditions at temperatures between 50 and 200 °C and confining pressures of 50-200 MPa, simulating elevated in situ depth conditions. Samples showed transient creep in the semibrittle regime with high deformation rates at high differential stress, high temperature and low confinement. Strain was mainly accommodated by deformation of the weak organic matter and phyllosilicates and by pore space reduction. The primary decelerating creep phase observed at relatively low stress can be described by an empirical power law relation between strain and time, where the fitted parameters vary with temperature, pressure and stress. Our results suggest that healing of hydraulic fractures at low stresses by creep-induced proppant embedment is unlikely within a creep period of several years. At higher differential stress, as may be expected in situ at contact areas due to stress concentrations, the shale showed secondary creep, followed by tertiary creep until failure. In this regime, microcrack propagation and coalescence may be assisted by stress corrosion. Secondary creep rates were also described by a power law, predicting faster fracture closure rates than for primary creep, likely contributing to production rate decline. Comparison of our data with published primary creep data on other shales suggests that the long-term creep behavior of shales can be correlated with their brittleness estimated from composition. Low creep strain is supported by a high fraction of strong minerals that can build up a load-bearing framework.

  1. Incremental sheet forming analyzed by tensile tests

    NARCIS (Netherlands)

    Emmens, W.C.; van den Boogaard, Antonius H.; Shirvani, B


    To study material behaviour under conditions encountered in ISF operations tensile tests have been carried out on material taken from the walls of pyramidal products. The shape of the stress-strain curves depend on orientation. Tests in the direction of punch movement show an overshoot indicating a

  2. Magnetoactive elastomeric composites: Cure, tensile, electrical and ...

    Indian Academy of Sciences (India)

    Cure characteristics, mechanical, electrical and magnetic properties were experimentally determined for different volume fractions of magnetoactive filler. The cure time decreases sharply for initial filler loading and the decrease is marginal for additional loading of filler. The tensile strength and modulus at 100% strain was ...

  3. Transformation-Induced Creep and Creep Recovery of Shape Memory Alloy. (United States)

    Takeda, Kohei; Tobushi, Hisaaki; Pieczyska, Elzbieta A


    If the shape memory alloy is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of shape memory alloy elements, these deformation properties are important since the deflection of shape memory alloy elements can change under constant stress. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the shape memory alloy. During loading under constant stress rate, temperature increases due to the stress-induced martensitic transformation. If stress is held constant during the martensitic transformation stage in the loading process, temperature decreases and the condition for the progress of the martensitic transformation is satisfied, resulting in the transformation-induced creep deformation. If stress is held constant during the reverse transformation stage in the unloading process, creep recovery appears due to the reverse transformation. The details for these thermomechanical properties are investigated experimentally for TiNi shape memory alloy, which is most widely used in practical applications. The volume fraction of the martensitic phase increases in proportion to an increase in creep strain.

  4. Room temperature creep-fatigue response of selected copper alloys for high heat flux applications

    DEFF Research Database (Denmark)

    Li, M.; Singh, B.N.; Stubbins, J.F.


    Two copper alloys, dispersion-strengthened CuAl25 and precipitation-hardened CuCrZr, were examined under fatigue and fatigue with hold time loading conditions. Tests were carried out at room temperature and hold times were imposed at maximum tensile and maximum compressive strains. It was found...... that hold times could be damaging even at room temperature, well below temperatures typically associated with creep. Hold times resulted in shorter fatigue lives in the high cycle fatigue, long life regime (i.e., at low strain amplitudes) than those of materials tested under the same conditions without hold...... times. The influence of hold times on fatigue life in the low cycle fatigue, short life regime (i.e., at high strain amplitudes) was minimal. When hold time effects were observed, fatigue lives were reduced with hold times as short as two seconds. Appreciable stress relaxation was observed during...

  5. The Creep of Laminated Synthetic Resin Plastics (United States)

    Perkuhn, H


    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.

  6. Ultrasonic study of elastic creep in piezoceramics. (United States)

    Tsaplev, V M; Konovalov, R S


    Ultrasonic method and experimental setup for study the elastic creep of piezoelectric materials are described. The results of experimental studies of time behavior of the Young's modulus and the internal friction are presented as well as the longitudinal and transversal piezomoduli and the electromechanical coupling factor. Four compositions of piezoelectric ceramics both soft and hard, based on BaTiO 3 and PZT, were compressed for a long time (0÷10 7 s) by significant static loads (0÷120MPa). The possible physical mechanisms that cause the creep are briefly considered. The concept of a spectrum of activation energies of the corresponding processes is introduced. The upper and the lower boundaries of the relaxation times spectrum were measured and corresponding activation energies were found. Copyright © 2017 Elsevier B.V. All rights reserved.

  7. Transient effects in friction fractal asperity creep

    CERN Document Server

    Goedecke, Andreas


    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...

  8. Revisiting Creeping Competences in the EU

    DEFF Research Database (Denmark)

    Citi, Manuele


    The literature on European integration has documented several cases of creeping competences in the EU. None of these studies, however, has fully clarified the conditions under which this phenomenon takes place, nor provided any testable hypotheses on its empirical dynamics. This paper studies one...... 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....... 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...

  9. Creep of zirconia/nickel composites

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Rodriguez, A.; Bravo-Leon, A.; Dominguez-Rodriguez, A.; Jimenez-Melendo, M. [Dept. de Fisica de la Materia Condensada, Univ. de Sevilla, Sevilla (Spain)


    The creep properties of wet-processed 3 mol% Y{sub 2}O{sub 3}-stabilized ZrO{sub 2}/Ni composites (20 and 40 vol% of nickel content) have been studied by compressive constant load tests in the temperature range 900 C-1250 C under argon atmosphere. The microstructural characterization of these cermets has been performed using scanning and transmission electron microscopy. The composites consist of nickel particles (1 {mu}m in size) uniformly distributed throughout a fine-grained zirconia matrix (0.13 {mu}m in size). The mechanical and microstructural results indicate that the overall creep behavior of the cermets is controlled primarily by the zirconia matrix; metal additions increase the ductility of the material. (orig.)

  10. Effect of discrete fibre reinforcement on soil tensile strength

    Directory of Open Access Journals (Sweden)

    Jian Li


    Full Text Available The tensile behaviour of soil plays a significantly important role in various engineering applications. Compacted soils used in geotechnical constructions such as dams and clayey liners in waste containment facilities can suffer from cracking due to tensile failure. In order to increase soil tensile strength, discrete fibre reinforcement technique was proposed. An innovative tensile apparatus was developed to determine the tensile strength characteristics of fibre reinforced soil. The effects of fibre content, dry density and water content on the tensile strength were studied. The results indicate that the developed test apparatus was applicable in determining tensile strength of soils. Fibre inclusion can significantly increase soil tensile strength and soil tensile failure ductility. The tensile strength basically increases with increasing fibre content. As the fibre content increases from 0% to 0.2%, the tensile strength increases by 65.7%. The tensile strength of fibre reinforced soil increases with increasing dry density and decreases with decreasing water content. For instance, the tensile strength at a dry density of 1.7 Mg/m3 is 2.8 times higher than that at 1.4 Mg/m3. It decreases by 30% as the water content increases from 14.5% to 20.5%. Furthermore, it is observed that the tensile strength of fibre reinforced soil is dominated by fibre pull-out resistance, depending on the interfacial mechanical interaction between fibre surface and soil matrix.

  11. The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep (United States)

    Xu, Lili; Renner, Jörg; Herwegh, Marco; Evans, Brian


    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

  12. Creep behaviour of macro glass fibre reinforced concrete beams (United States)

    Löber, P.; Heiden, B.; Holschemacher, K.


    This paper aims to present a creep study on structural concrete reinforced with macro glass fibres and wants to contribute to the understanding of creep behaviour of fibre reinforced concrete (FRC). Fibre reinforced concrete beams have been subjected to bending and tested in cracked state under defined stress levels. Therefore, a four-point-bending test setup was chosen and the creep period was 372d. The aim was to determine creep coefficients and to test residual strength values afterwards. Results show a dependence of residual strength and applied stress level. It turned out, that the beams failed due to tertiary creep at stress levels between 65 and 70% of residual crack load at 0.5 mm pre-crack deflection. Nevertheless, all remaining specimens showed increased loads after creep period. Finally, the evaluation is conducted in comparison to other fibre types.

  13. Creep stresses in a spherical shell under steady state temperature (United States)

    Verma, Gaurav; Rana, Puneet


    The paper investigates the problem of creep of a spherical structure under the influence of steady state temperature. The problem of creep in spherical shell is solved by using the concept of generalized strain measures and transition hypothesis given by Seth. The problem has reduced to non-linear differential equation for creep transition. This paper deals with the non-linear behaviour of spherical shell under thermal condition. The spherical shell structures are easily vulnerable to creep, shrinkage and thermal effects; a thorough understanding of their time-dependent behaviour has been fully established. The paper aims to provide thermal creep analysis to enhance the effective design and long life of shells, and a theoretical model is developed for calculating creep stresses and strains in a spherical shell with purpose. Results obtained for the problem are depicted graphically.

  14. Pure climb creep mechanism drives flow in Earth's lower mantle. (United States)

    Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Gouriet, Karine; Hirel, Pierre; Kraych, Antoine; Ritterbex, Sebastian


    At high pressure prevailing in the lower mantle, lattice friction opposed to dislocation glide becomes very high, as reported in recent experimental and theoretical studies. We examine the consequences of this high resistance to plastic shear exhibited by ringwoodite and bridgmanite on creep mechanisms under mantle conditions. To evaluate the consequences of this effect, we model dislocation creep by dislocation dynamics. The calculation yields to an original dominant creep behavior for lower mantle silicates where strain is produced by dislocation climb, which is very different from what can be activated under high stresses under laboratory conditions. This mechanism, named pure climb creep, is grain-size-insensitive and produces no crystal preferred orientation. In comparison to the previous considered diffusion creep mechanism, it is also a more efficient strain-producing mechanism for grain sizes larger than ca. 0.1 mm. The specificities of pure climb creep well match the seismic anisotropy observed of Earth's lower mantle.

  15. Creep and Viscoelastic Behaviour of Human Dentin

    Directory of Open Access Journals (Sweden)



    Full Text Available Statement of Problem: Biomechanics of the human dentition is inherently complex.Purpose: The aim of this study is to investigate, in vitro, the creep and the recovery of dentin under static uniaxial compressive stress conditions.Materials and Methods: Specimens of cylindrical morphology were prepared from recently extracted non-carious lower molar teeth, such that the average tubule orientation was axial. Slides of mid- coronal dentin (parallel surfaces, height 1.8 mm were sectionedwith a slow speed diamond saw and then cut into cylindrical discs. Specimens were stored at 4ºC for 24h to restabilize water content. Creep data were then measured by LVDT axially in water for periods of 2h load + 2h recovery on 4 separate groups (n=6: at two stresses (10 & 18 MPa and at two temperatures: 37 & 60ºC. Maximum creep strain, permanent set,strain recovery and initial compressive modulus were reported.Results: Compliance values were also calculated and slight non-linearity found at 60ºC.Two-way ANOVA was performed on results. Dentin exhibited a linear viscoelastic response under 'clinical' compressive stress levels , with a maximum strain ~ 1% and highrecoverability: permanent set<0.3%.Conclusion: This established a performance standard for viscoelastic stability of restorative biomaterials, replacing human dentin.

  16. 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


    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 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 C. Alloys having improved creep resistance are also disclosed.

  17. Steady-State Creep of Asphalt Concrete

    Directory of Open Access Journals (Sweden)

    Alibai Iskakbayev


    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.

  18. Creep Deformation by Dislocation Movement in Waspaloy. (United States)

    Whittaker, Mark; Harrison, Will; Deen, Christopher; Rae, Cathie; Williams, Steve


    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.

  19. Elevated temperature strength, aging response and creep of aluminum matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Bhagat, R.B.; Amateau, M.F.; House, M.B.; Meinert, K.C.; Nisson, P. (Pennsylvania State University, State College (United States))


    The effect of reinforcement on the high-temperature performance of aluminum matrix composites was investigated using samples of 6061 aluminum alloy reinforced with planar-random graphite fibers, SiC whiskers, or alumina particles, which were aged at 150 and 200 C for up to 500 hrs. As indicated by the results of microhardness tests, all specimens exhibited accelerated aging response, with the response depending on the characteristics of the reinforcement. Both the graphite-fiber- and SiC-whisker-reinforced composites showed a substantially increased strengths over that of the wrought 6061 Al at all temperatures. The graphite-fiber- and the SiC-whisker-reinforced composites were found to retain their tensile strength and stiffness in the overaged condition of the matrix. The whisker-reinforced composite showed significant resistance to creep at temperatures between 232 and 350 C under stresses of up to 100 MPa, while the particulate composite had a moderate increase in creep resistance. 51 refs.


    Directory of Open Access Journals (Sweden)

    Ján Micheľ


    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.

  1. Analysis of Simple Creep Stress Calculation Methods for Creep Life Assessment

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Jun Min; Lee, Han Sang; Kim, Yun Jae [Korea Univ., Daejeon (Korea, Republic of)


    Creep analysis takes much more time than elastic or elastic-plastic analysis. In this study, we conducted elastic and elastic-plastic analysis and compared the results with creep analysis results. In the elastic analysis, we used primary stress, which can be classified by the Mα-tangent method and stress intensities recommended in the ASME code. In the elastic-plastic analysis, we calculated the parameters recommended in the R5 code. For the FE models, a bending load, uniaxial load, and biaxial load were applied to the cross shaped welded plate, and a bending load and internal pressure were applied to the elbow pipe. To investigate the element size sensitivity, we conducted FE analysis for various element sizes for the cases where bending load was applied to the cross shaped welded plate. There was no significant difference between the creep.

  2. Degradation of mechanical properties of CrMo creep resistant steel operating under conditions of creep

    Directory of Open Access Journals (Sweden)

    J. Michel


    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.

  3. Comparison of creep of the cement pastes included fly ash

    Directory of Open Access Journals (Sweden)

    Padevět Pavel


    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.

  4. Stability of MC Carbide Particles Size in Creep Resisting Steels

    Directory of Open Access Journals (Sweden)

    Vodopivec, F.


    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.

  5. Multi-axial Creep and the LICON Methodology for Accelerated Creep Testing

    Energy Technology Data Exchange (ETDEWEB)

    Bowyer, William H. [Meadow End Farm, Farnham (United Kingdom)


    The copper-Iron canister for disposal of nuclear waste in the Swedish Programme has a design life exceeding 100,000 years. Whilst the operating temperature (100 deg C max.) and operating stress (50 MPa max.) are modest, the very long design life does require that the likely creep performance of the canister should be investigated. Many studies have been carried out by SKB but these have all involved very short duration tests at relatively high stresses. The process of predicting canister creep life by extrapolation of data from such tests has been challenged for two main reasons. The first is that the deformation and failure mechanisms in the tests employed are different from the mechanism expected under service conditions and the second is that the extrapolation is extreme. It has been recognised that there is usually scope for some increase in test temperatures and stresses which will accelerate the development of creep damage without compromising the use of extrapolation for life prediction. Cane demonstrated that in steels designed for high temperature and pressure applications, conditions of multi-axial stressing could lead to increases or decreases in the rate of damage accumulation without changing the damage mechanism. This provided a third method for accelerating creep testing which has been implemented as the LICON method. This report aims to explain the background to the LICON method and its application to the case of the copper canister. It seems likely that the method could be used to improve our knowledge of the creep resistance of the copper canister. Multiplication factors that may be achieved by the technique could be increased by attention to specimen design but an extensive and targeted programme of data collection on creep of copper would still be needed to implement the method to best advantage.

  6. Creep strengthening in a discontinuous SiC-Al composite

    Energy Technology Data Exchange (ETDEWEB)

    Park, K.T.; Mohamed, F.A. [Univ. of California, Irvine, CA (United States)


    High-temperature strengthening mechanisms in discontinuous metal matrix composites were examined by performing a close comparison between the creep behavior of 30 vol pct SiC-6061 Al and that of its matrix alloy, 6061 Al. Both materials were prepared by powder metallurgy techniques. The experimental data show that the creep behavior of the composite is similar to that of the alloy in regard to the high apparent stress exponent and its variation with the applied stress and the strong temperature dependence of creep rate. By contrast, the data reveal that there are two main differences in creep behavior between the composite and the alloy: the creep rates of the composite are more than one order of magnitude slower than those of the alloy, and the activation energy for creep in the composite is higher than that in the alloy. Analysis of the experimental data indicates that these similarities and differences in creep behavior can be explained in terms of two independent strengthening processes that are related to (a) the existence of a temperature-dependent threshold stress for creep, {tau}{sub 0}, in both materials and (b) the occurrence of temperature dependent load transfer from the creeping matrix (6061 Al) to the reinforcement (SiC).

  7. A Study of the Creep Effect in Loudspeaker Suspension

    DEFF Research Database (Denmark)

    Agerkvist, Finn T.; Thorborg, Knud; Tinggaard, Carsten


    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...

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

    DEFF Research Database (Denmark)

    van der Giessen, Erik; Tvergaard, Viggo


    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...... case with a facet-site microcrack yields important insight for damage accumulation under balanced loading. Under unbalanced loading, the time-average accumulation of creep cavitation gives rise to macroscopic ratchetting, while its rate is demonstrated to depend subtly on material and loading...

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

    DEFF Research Database (Denmark)

    Hald, John


    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....

  10. Deformation and fracture in one-dimensional creep problems (United States)

    Kovrizhnykh, A. M.; Kovrizhnykh, S. A.


    It is assumed that irreversible deformation is a result of shearing in certain planes. In perpendicular directions to these planes, normal strain undergoes change that is proportional to the associated shear. This approach allows accounting for growth of fractures and pores in the background of increasing creep strains without using Kachanov–Rabotnov’s kinetic equation for development of damage. Material begins failing when maximum shear creep strain reaches critical value, which initiates drop in shear strength. Using the model based on the maximum shear stress and the exponential law, the authors solve problems on deformation and failure of an elastic–creeping body at the stages of unstable and stable creep.

  11. Prediction of creep lives of copper under repository conditions

    Energy Technology Data Exchange (ETDEWEB)

    Bowyer, W.H


    Results from short-term creep tests on three materials based on Oxygen Free (OF) copper have been published in connection with the canister development programme. It is necessary to extrapolate from these results to predict the creep lives which might be expected from these materials under repository conditions. OF copper is a commercial grade of copper which is specified with a limit of 350ppm. impurities. The three materials tested have been identified as OF1 which is the standard grade, OF2 which corresponds to the standard grade with a reduced level of sulphur and OFP which was similar to OF2 except it included an addition of 50 ppm. of phosphorus. The sulphur levels in OF1 and OF2 were 10ppm. and 6ppm. respectively. The models for prediction of steady state creep rates by Frost and Ashby, and for prediction of Creep lives by Cocks and Ashby have been used together with published data from creep tests to predict the life of the copper canister under repository conditions. The key features of the fracture model are; 1. Fracture occurs by nucleation, growth and linking of internal voids. 2. Nucleation occurs very early in creep life. 3. Nucleation may be in grain boundaries or grain interiors. 4. Diffusion or plastic processes may support growth of voids. It predicts that; 1. When diffusion dominates void growth, (diffusion control) voids are restricted to grain boundaries. 2. When plastic processes dominate void growth (power law creep control) voids may be in grain boundaries or grain interiors. 3. At low creep stresses (where initially diffusion creep dominates) void growth is initially diffusion controlled (inter-granular). 4. At higher creep stresses (where power law creep dominates) void growth is initially under power law control. 5. When, in diffusion controlled creep, the void area increases to a critical value the effective increase in stress (owing to the reduction in load bearing area) causes a transition to power law creep controlled void growth

  12. Power-law creep from discrete dislocation dynamics. (United States)

    Keralavarma, Shyam M; Cagin, T; Arsenlis, A; Benzerga, A Amine


    We report two-dimensional discrete dislocation dynamics simulations of combined dislocation glide and climb leading to "power-law" creep in a model aluminum crystal. The approach fully accounts for matter transport due to vacancy diffusion and its coupling with dislocation motion. The existence of quasiequilibrium or jammed states under the applied creep stresses enables observations of diffusion and climb over time scales relevant to power-law creep. The predictions for the creep rates and stress exponents fall within experimental ranges, indicating that the underlying physics is well captured.

  13. 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)


    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.

  14. On High-Temperature Materials: A Case on Creep and Oxidation of a Fully Austenitic Heat-Resistant Superalloy Stainless Steel Sheet

    Directory of Open Access Journals (Sweden)

    A. Kanni Raj


    Full Text Available The creep behavior of AISI 310S stainless steel taken from SAIL’s Salem stainless steel plant has been investigated by constant load tensile creep test at the temperatures of 973, 1023, and 1073 K and loads of 66.6, 74.8, 86.6, and 94.8 MPa. It exhibits steady-state creep behavior in most test conditions. The double logarithm plot of rupture life and applied stress yielded straight lines at all the three test temperatures indicating that power-law creep due to dislocation climb is the operating mechanism of creep deformation. Linear relationship was obtained for plots of logarithm of rupture life against inverse temperature obeying Arrhenius type of temperature dependence with activation energy of 340 kJ/mol. The stress-rupture data yielded a master curve of Larson-Miller parameter. The plot of Monkman-Grant relationship is typical indicating that rupture is controlled by growth of grain boundary cavities. The metallographic examination of crept samples revealed formation of grain boundary voids and cracks leading to intergranular creep fracture. Deformation twins and carbide precipitates were also observed. Oxidation tests were also carried out isothermally at 973 K, 1023 K, and 1073 K in dry air. The plots of mass gain versus square root time were linear at all the three test temperatures obeying parabolic kinetics of oxidation. It was found that scales are well adherent to the substrate. The plot of parabolic rate constant and inverse temperature was linear giving an activation energy value of 210 kJ/mol. The metallographic examination of an oxidized sample reveals duplex types of scales. Finally, rupture properties are compared with that of AISI 600 iron-based superalloy and oxidation weight gain analysis with surface nanocrystalline AISI 310S stainless steel to analyze quantitatively its behavior.

  15. 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


    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.

  16. Características das carcaças de cordeiros lactentes terminados em creep feeding e creep grazing


    Ribeiro, Ticiany Maria Dias; Costa, Ciniro [UNESP; Monteiro, Alda Lúcia Gomes; Piazzetta, Hugo von Linsingen; Silva, Marina Gabriela Berchiol da [UNESP; Silva, Cláudio José Araujo da; Prado, Odilei Rogério; Fernades, Maria Angela Machado; Meirelles, Paulo Roberto de Lima


    The work was developed in Sheep and Goat Production Laboratory of UFPR to evaluate the sucking lambs systems of production in pasture, supplemented in creep feeding or creep grazing. It was evaluated in vivo and carcass characteristic and non-carcass components of Suffolk lambs. Three systems of production were studied: (1) lambs kept with their dams in ryegrass (Lolium multiflorum) until slaughter; (2) lambs kept with their dams in the same pasture but lambs supplemented in creep feeding (2%...

  17. Tensile Instability in a Thick Elastic Body (United States)

    Overvelde, Johannes; Dykstra, David; de Rooij, Rijk; Bertoldi, Katia

    A range of instabilities can occur in soft bodies that undergo large deformation. While most of them arise under compressive forces, it has previously been shown analytically that a tensile instability can occur in an elastic block subjected to equitriaxial tension. Guided by this result, we conducted centimeter-scale experiments on thick elastomeric samples under generalized plane strain conditions and observed for the first time this elastic tensile instability. We found that equibiaxial stretching leads to the formation of a wavy pattern, as regions of the sample alternatively flatten and extend in the out-of-plane direction. Our work uncovers a new type of instability that can be triggered in elastic bodies, enlarging the design space for smart structures that harness instabilities to enhance their functionality.

  18. Relation between incremental lines and tensile strength of coronal dentin. (United States)

    Inoue, Toshiko; Saito, Makoto; Yamamoto, Masato; Nishimura, Fumio; Miyazaki, Takashi


    In one aspect, this study examined the tensile strength of coronal dentin, as a function of the location of incremental lines, in two types of teeth: human molar versus bovine incisor. In another aspect, tensile strength in coronal dentin was examined with tensile loading in two different orientations to the incremental lines: parallel versus perpendicular. There were four experimental groups in this study: HPa, human molar dentin with tensile orientation parallel to the incremental lines; HPe, human molar dentin with tensile orientation perpendicular to the incremental lines; BPa, bovine incisor dentin with tensile orientation parallel to the incremental lines; BPe, bovine incisor dentin with tensile orientation perpendicular to the incremental lines. Tensile strengths of the parallel group (HPa and BPa) were significantly higher (pdentin. However, there were no differences in anisotropy effect between the two tooth types.

  19. Tensile properties of structural fibre reinforced concrete (United States)

    Tipka, M.; Vašková, J.


    The paper deals with the comparison of several loading tests, which are using for determination of tensile strength of cementitious composites. The paper describes several test methods, their advantages, disadvantages and possible outputs. In the experimental program several recipes of concrete and fibre reinforced concrete were tested in splitting test, 3-point and 4-point bending tests and in 2 variants of axial tension test. Tension strength ratios and conversion factors between loading tests were determined for each recipe, based on test results.

  20. Determining tensile properties of sweetgum veneer flakes (United States)

    E.W. Price


    Rotary-cut 8weetgum veneer flakes measuring 3 inchee along the grain, 3/8 inch wide, and 0.015 inch thick, were stressed in tension parallel to the grain at gage lengths from 0.00 to 1.25 inchee for unpressed control and at 0.75 inch gage length for flakes pressed in a flakeboard mat. The control flakes had an average tensile strength of 9,400 psi for the smaller age...

  1. Creep of trabecular bone from the human proximal tibia

    Energy Technology Data Exchange (ETDEWEB)

    Novitskaya, Ekaterina, E-mail: [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)


    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.

  2. Some Tensile Properties of Unsaturated Polyester Resin Reinforced ...

    African Journals Online (AJOL)

    Tensile samples of 165 ×19.5 × 3.2 mm3 prepared using ASTM D638 Standard were tested in a Hounsfield (Monsato) testing unit. Results showed that tensile strength, percentage elongation and tensile toughness at fracture increased as the volume fractions of carbon black nanoparticles increased from 1% to 5% in both ...

  3. The clinical utility of the auditory P300 latency subcomponent event-related potential in preclinical diagnosis of patients with mild cognitive impairment and Alzheimer's disease. (United States)

    Howe, Aaron S; Bani-Fatemi, Ali; De Luca, Vincenzo


    The present meta-analysis investigated the clinical utility of the auditory P300 latency event-related potential in differentiating patients with Alzheimer's disease (AD), patients with mild cognitive impairment (MCI), and unaffected controls. Effect size estimates were computed from mean P300 latency measurements at midline electrodes between patients and unaffected controls using the random effects restricted maximum likelihood model. The effects of clinical and ERP/EEG methological variables were assessed in a moderator analysis. P300 latency was found to be significantly prolonged in patients with AD (and MCI) compared to unaffected controls. Shortened P300 latencies were observed when comparing patients with MCI to patients with AD. Clinically relevant differences in P300 latency effect sizes were associated with mean age, interstimulus interval, stimulus difference, target frequency, reference electrode, and sampling rate. The meta-analytic findings provide robust statistical evidence for the use of the auditory P300 latency subcomponent as a biological marker of prodromal AD. Copyright © 2014 Elsevier Inc. All rights reserved.

  4. 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)


    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.)

  5. 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)


    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

  6. Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep (United States)

    Simpson, R.W.; Lienkaemper, J.J.; Galehouse, J.S.


    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.

  7. Failure by Creep Cracking and Creep Fatigue Interaction in Nickel Base Superalloys. (United States)


    cumulative creep uamage may not be the primary failure mode in superalloys at temperatures encountered by - disks in gas- turbine engines. We believe that the...oxidation, are discussed. *Riuume Les gaz peuvent diffuser le long d’un joint de grains et oxyder des impuretcs ou des precipits. Dans les alliages de

  8. Creep, fatigue and creep-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels (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

  9. Accelerated Creep Testing of High Strength Aramid Webbing (United States)

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


    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.

  10. 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)


    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.

  11. Power series like relation of power law and coupled creep ...

    African Journals Online (AJOL)

    When a solid deforms at high temperature its microstructure may in some sense be altered- holes and cracks may nucleate and grow inside the solid by various mechanism controlled by diffusion and by power law creep or by a combination of these mechanisms. Considering a coupled diffusion power law creep mechanism ...

  12. Some numerical approaches of creep, thermal shock, damage and ...

    Indian Academy of Sciences (India)

    Some numerical approaches of creep, thermal shock, damage and delayed failure of ceramics and refractories ... Ceramic; refractories; creep; thermal stock; damage; delayed failure; numerical simulation. Abstract. Numerical simulation is now very often used to predict the behaviour of components in service conditions.

  13. Accelerated creep of Ni-YSZ anodes during reduction

    DEFF Research Database (Denmark)

    Frandsen, Henrik Lund; Greco, Fabio; Ni, De Wei


    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...

  14. Out-of-pile creep behavior of uranium carbide (United States)

    Wright, T. R.; Seltzer, M. S.


    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.

  15. Development of a technique for testing of tensile properties with miniature size specimens for metal additive manufacturing (United States)

    Dongare, Sujitkumar

    The study of mechanical properties of metals provides a basis to decide on the capability of a particular metal for a task and also to make predictions about its life. The concepts of stress, strain and strength of materials are employed in practically every engineering discipline. Mechanical properties such as stiffness, yield strength, tensile strength, ductility, toughness, impact resistance, creep resistance, fatigue resistance and others, influence the design, fabrication and service life of equipment. Therefore, more than one property is considered for the material selection process for an application. For complete understanding of any material and its feasibility for a particular application, inter-related mechanical properties have to be measured. Unfortunately, these properties cannot be measured in any single test. However, the tensile test can be used to measure a number of the most commonly used mechanical properties. Extensive research has already been performed in this area. Standards have been developed and established regarding the size of test specimens, testing procedures and process parameters. This thesis discusses the development of a testing procedure for non-standard tensile tests for evaluation of material properties. Miniature test specimens similar to the standard ASTM E8 were designed and used for testing. The tests were mainly conducted on the baseline material for aerospace industry i.e. Ti-6Al-4V.

  16. Uniaxial creep behavior of nanostructured, solution and dispersion hardened V-1.4Y-7W-9Mo-0.7TiC with different grain sizes

    Energy Technology Data Exchange (ETDEWEB)

    Sakamoto, T. [Department of Materials Science and Biotechnology, Ehime University, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Kurishita, H., E-mail: [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Furuno, T. [Department of Materials Science and Biotechnology, Ehime University, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Nagasaka, T. [Fusion Engineering Research Center, National Institute for Fusion Science (NIFS), Oroshi-cho 322-6, Toki, Gifu 292 (Japan); Kobayashi, S.; Nakai, K. [Department of Materials Science and Biotechnology, Ehime University, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Matsuo, S.; Arakawa, H. [International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nishimura, A.; Muroga, T. [Fusion Engineering Research Center, National Institute for Fusion Science (NIFS), Oroshi-cho 322-6, Toki, Gifu 292 (Japan)


    Highlights: {yields} The major concern for nanostructured V is poor creep resistance due to grain boundary sliding. {yields} Significant enhancement of creep resistance in nanostructured V has been achieved using V-1.4Y-7W-9Mo-0.7TiC. {yields} The enhancement owes to solute W and Mo, dispersoids of Y{sub 2}O{sub 3} and TiC and grain size (GS) adjustment. {yields} The creep life of V-1.4Y-7W-9Mo-0.7TiC increases by a factor 30 by increasing GS from 0.6 to 2.2 {mu}m. {yields} The creep life for 2.2 {mu}m GS is two orders longer than that of primary candidate V-4Cr-4Ti (GS: {approx}18 {mu}m). - Abstract: Nanostructured vanadium (V) alloys are expected to exhibit high performance under neutron irradiation environments. However, their ultra-fine or refined grains cause significant decrease in flow stress at high temperatures due to grain boundary sliding (GBS), which is the major concern for their high-temperature structural applications such as future fusion reactors. The contribution of GBS to plastic deformation is known to depend strongly on grain size (GS) and may give more significant influence on long-time creep test results than on short-time tensile test results. In order to improve the creep resistance through elucidation of the effect of GS on the uniaxial creep behavior of nanostructured V alloys, a solution and dispersion hardened V alloy, V-1.4Y-7W-9Mo-0.7TiC (in wt%), with GSs from 0.58 to 2.16 {mu}m was developed by mechanical alloying and HIP processes, followed by annealing at 1473-1773 K, and creep tested at 1073 K and 250 MPa in vacuum. It is shown that the creep resistance of V-1.4Y-7W-9Mo-0.7TiC increases monotonically with GS: The creep life for the alloy with 2.16 {mu}m in GS is as long as 114 h, which is longer by factors of 2-30 than those for the other finer grained alloys and by two orders than that for coarse-grained V-4Cr-4Ti (Nifs heat2, GS: 17.8 {mu}m) that is a primary candidate material for fusion reactor structural applications. The

  17. Creep deformation and rupture behavior of CLAM steel at 823 K and 873 K

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Boyu [Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Huang, Bo, E-mail: [Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Li, Chunjing; Liu, Shaojun; Xu, Gang [Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Zhao, Yanyun; Huang, Qunying [Key Laboratory of Neutronics and Radiation Safety, Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230027 (China)


    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-dot{sub 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.

  18. Tracing Thermal Creep Through Granular Media (United States)

    Steinpilz, Tobias; Teiser, Jens; Koester, Marc; Schywek, Mathias; Wurm, Gerhard


    A temperature gradient within a granular medium at low ambient pressure drives a gas flow through the medium by thermal creep. We measured the resulting air flow for a sample of glass beads with particle diameters between 290 μ m and 420 μ m for random close packing. Ambient pressure was varied between 1 Pa and 1000 Pa. The gas flow was quantified by means of tracer particles during parabolic flights. The flow varies systematically with pressure between 0.2 cm/s and 6 cm/s. The measured flow velocities are in quantitative agreement to model calculations that treat the granular medium as a collection of linear capillaries.

  19. Determination of the Creep Parameters of Linear Viscoelastic Materials

    Directory of Open Access Journals (Sweden)

    Alibay Iskakbayev


    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.

  20. On creep behavior in powder metallurgy 6061 Al

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed, F.A. [Univ. of California, Irvine, CA (United States)


    There has been a considerable interest in studying the creep characteristics of powder metallurgy (PM) Al alloys such as PM 6061 Al and PM 2124 Al. First, these alloys have been used as matrices in the development of discontinuous SiC-Al composites which have been under consideration as attractive materials for high temperature applications. Second, creep data on these alloys can be used not only to characterize the elevated temperature mechanical behavior of SiC-Al composites in terms of deformation mechanisms but also to provide a close comparison between the creep strength of a composite and its unreinforced matrix alloy. Such a comparison under similar experimental conditions may determine whether the composite is more creep resistant than the alloy. The purpose of this note is to examine the experimental results reported for PM 6061 Al in the light of the advances that have been made in rationalizing the creep behavior of Al-based solid-solution alloys.

  1. Experimental Research on Creep Characteristics of Nansha Soft Soil

    Directory of Open Access Journals (Sweden)

    Qingzi Luo


    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.

  2. Small Punch Creep Test in a 316 Austenitic Stainless Steel (United States)

    Saucedo-Muñoz, Maribel L.; Komazaki, Ken-Icbi; Ortiz-Mariscal, Arturo; Lopez-Hirata, Victor M.

    The small punch creep test was used to evaluate the creep behavior of a 316 type austenitic stainless steel at temperatures of 650, 675 and 700 °C and loads from 199 to 512 N using a creep tester with a specimen size of 10 x 10 x 0.3 mm under an argon atmosphere. The small punch creep curves shows the three stages found in the creep curves of the conventional uniaxial test. The time to rupture decreases as the testing temperature and load increase. The secondary stage is also reduced with the increase in test load. An intergranular ductile fracture mode was observed at a testing temperature of 700 °C, while intergranular brittle mode at 650 °C which is associated with the absence of abundant precipitation at 650 °C.

  3. Effect of uniaxiai ratcheting on subsequent creep deformation (United States)

    Sasaki, Katsuhiko; Ishikawa, Hiromasa


    Experimental observation and numerical simulation are conducted to clarify the effect of viscosity on deformation of materials. First, creep tests after the primary uniaxial ratcheting are carded out using Type 304 stainless steel. Specimens are subjected to cyclic tension-unloading with step and triangular waves during 20000 seconds as the primary ratcheting. After the ratcheting the subsequent creep test at the maximum stress is conducted during 20000 seconds. The experimental results show that the values of the subsequent creep strain after the ratcheting depend on the wave type and the time period of the ratcheting. The shorter time period of the ratcheting leads to the larger subsequent creep strain. Numerical simulations are also carried out using the constitutive model based on dislocation density [Estrin et al.]. As a result, the equivalent value of the ratcheting strain to creep strain is found out from the simulations and experiments.

  4. Experimental Research on Creep Characteristics of Nansha Soft Soil (United States)

    Luo, Qingzi; Chen, Xiaoping


    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 C a/C c 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. PMID:24526925

  5. Creep-caused fracture of PbSn solder joint (United States)

    Meng, M.; Wang, Z. B.; Wang, X.; Chen, Y.


    This paper analyzes two failure cases of creep-caused fracture of PbSn solder joint, including the joint between the wire and solder cup in the connector and the joint between the integrated circuit (IC) pins and the printed circuit board (PCB). The environment conditions, for the creep of PbSn solder joint is demonstrated, including the temperature and stress level. The stress origin and fracture morphology are summarized based on the failure analysis. Besides, the developing process of creep-caused fracture is explained. The paper comprehensively clarifies the creep mechanism of PbSn solder and consequently provides significant guidance for the reliable electronic assembly to avoid the creep-caused damage.

  6. 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


    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Wu Rui; Sandstroem, Rolf


    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.

  8. 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.


    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

  9. Thermal, creep-recovery and viscoelastic behavior of high density polyethylene/hydroxyapatite nano particles for bone substitutes: effects of gamma radiation. (United States)

    Alothman, Othman Y; Fouad, H; Al-Zahrani, S M; Eshra, Ayman; Al Rez, Mohammed Fayez; Ansari, S G


    High Density Polyethylene (HDPE) is one of the most often used polymers in biomedical applications. The limitations of HDPE are its visco-elastic behavior, low modulus and poor bioactivity. To improve HDPE properties, HA nanoparticles can be added to form polymer composite that can be used as alternatives to metals for bone substitutes and orthopaedic implant applications. In our previous work (BioMedical Engineering OnLine 2013), different ratios of HDPE/HA nanocomposites were prepared using melt blending in a co-rotating intermeshing twin screw extruder. The accelerated aging effects on the tensile properties and torsional viscoelastic behavior (storage modulus (G') and Loss modulus (G")) at 80°C of irradiated and non-irradiated HDPE/HA was investigated. Also the thermal behavior of HDPE/HA were studied. In this study, the effects of gamma irradiation on the tensile viscoelastic behavior (storage modulus (E') and Loss modulus (E")) at 25°C examined for HDPE/HA nanocomposites at different frequencies using Dynamic Mechanical Analysis (DMA). The DMA was also used to analyze creep-recovery and relaxation properties of the nanocomposites. To analyze the thermal behavior of the HDPE/HA nanocomposite, Differential Scanning Calorimetry (DSC) was used. The microscopic examination of the cryogenically fractured surface revealed a reasonable distribution of HA nanoparticles in the HDPE matrix. The DMA showed that the tensile storage and loss modulus increases with increasing the HA nanoparticles ratio and the test frequency. The creep-recovery behavior improves with increasing the HA nanoparticle content. Finally, the results indicated that the crystallinity, viscoelastic, creep recovery and relaxation behavior of HDPE nanocomposite improved due to gamma irradiation. Based on the experimental results, it is found that prepared HDPE nanocomposite properties improved due to the addition of HA nanoparticles and irradiation. So, the prepared HDPE/HA nanocomposite appears to

  10. Stability of germanene under tensile strain

    KAUST Repository

    Kaloni, Thaneshwor P.


    The stability of germanene under biaxial tensile strain and the accompanying modifications of the electronic properties are studied by density functional theory. The phonon spectrum shows that up to 16% strain the germanene lattice is stable, where the Dirac cone shifts towards higher energy and hole-doped Dirac states are achieved. The latter is due to weakening of the Ge-Ge bonds and reduction of the s-p hybridization. Our calculated Grüneisen parameter shows a similar dependence on the strain as reported for silicene (which is different from that of graphene). © 2013 Elsevier B.V. All rights reserved.

  11. Tensile Fabrics Enhance Architecture Around the World (United States)


    Using a remarkable fabric originally developed to protect Apollo astronauts, Birdair Inc. of Amherst, New York, has crafted highly durable, safe, environmentally friendly, and architecturally stunning tensile membrane roofs for over 900 landmark structures around the world. Travelers in airports, sports fans at stadiums, and shoppers in malls have all experienced the benefits of the Teflon-coated fiberglass fabric that has enabled Birdair to grow from a small company established in its founder?s kitchen in 1955 to a multimillion-dollar specialty contractor today.

  12. The effect of cold rolling on the grain boundary character and creep rupture properties of INCONEL alloy 718

    Energy Technology Data Exchange (ETDEWEB)

    Boehlert, C.J. [Alfred Univ., School of Ceramic Engineering and Materials Science, Alfred, NY (United States); Civelekoglu, S. [Alfred Univ., School of Ceramic Engineering and Materials Science, Alfred, NY (United States); Eisinger, N.; Smith, G.; Crum, J. [Special Metals Corp., Huntington (United States)


    In order to evaluate the effects of sheet processing on the grain boundary character distribution (GBCD) of INCONEL trademark alloy 718 (IN 718), electron backscattered diffraction (EBSD) mapping was performed on samples cold rolled between 0-40%. Increased cold rolling increased the fraction of low-angle boundaries at the expense of the coincident site lattice boundaries. The tensile-creep rupture life (T{sub r}) and elongation-to-failure ({epsilon}{sub f}) were evaluated at 649 C and 758 MPa, and the data indicated that increased cold rolling significantly increased both the T{sub r} and {epsilon}{sub f} values. In addition the GBCD and room-temperature (RT) tensile properties were evaluated for superplastically formed INCONEL trademark alloy 718 (IN 718SPF). The tensile results indicated the exceptional strength of the fine-grained IN 718SPF material, however the GBCD parameters were intermediate to those of the 10% and 20% cold rolled IN 718 materials. (orig.)

  13. Subcomponent vaccine based on CTA1-DD adjuvant with incorporated UreB class II peptides stimulates protective Helicobacter pylori immunity. (United States)

    Nedrud, John G; Bagheri, Nayer; Schön, Karin; Xin, Wei; Bergroth, Hilda; Eliasson, Dubravka Grdic; Lycke, Nils Y


    A mucosal vaccine against Helicobacter pylori infection could help prevent gastric cancers and peptic ulcers. While previous attempts to develop such a vaccine have largely failed because of the requirement for safe and effective adjuvants or large amounts of well defined antigens, we have taken a unique approach to combining our strong mucosal CTA1-DD adjuvant with selected peptides from urease B (UreB). The protective efficacy of the selected peptides together with cholera toxin (CT) was first confirmed. However, CT is a strong adjuvant that unfortunately is precluded from clinical use because of its toxicity. To circumvent this problem we have developed a derivative of CT, the CTA1-DD adjuvant, that has been found safe in non-human primates and equally effective compared to CT when used intranasally. We genetically fused the selected peptides into the CTA1-DD plasmid and found after intranasal immunizations of Balb/c mice using purified CTA1-DD with 3 copies of an H. pylori urease T cell epitope (CTA1-UreB3T-DD) that significant protection was stimulated against a live challenge infection. Protection was, however, weaker than with the gold standard, bacterial lysate+CT, but considering that we only used a single epitope in nanomolar amounts the results convey optimism. Protection was associated with enhanced Th1 and Th17 immunity, but immunizations in IL-17A-deficient mice revealed that IL-17 may not be essential for protection. Taken together, we have provided evidence for the rational design of an effective mucosal subcomponent vaccine against H. pylori infection based on well selected protective epitopes from relevant antigens incorporated into the CTA1-DD adjuvant platform.

  14. 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


    The subsection ASME NH high temperature design procedure does not admit crack-like defects into the structural components. The US NRC identified the lack of treatment of crack growth within NH as a limitation of the code and thus this effort was undertaken. This effort is broken into two parts. Part 1, summarized here, involved examining all high temperature creep-fatigue crack growth codes being used today and from these, the task objective was to choose a methodology that is appropriate for possible implementation within NH. The second part of this task, which has just started, is to develop design rules for possible implementation within NH. This second part is a challenge since all codes require step-by-step analysis procedures to be undertaken in order to assess the crack growth and life of the component. Simple rules for design do not exist in any code at present. The codes examined in this effort included R5, RCC-MR (A16), BS 7910, API 579, and ATK (and some lesser known codes). There are several reasons that the capability for assessing cracks in high temperature nuclear components is desirable. These include: (1) Some components that are part of GEN IV reactors may have geometries that have sharp corners - which are essentially cracks. Design of these components within the traditional ASME NH procedure is quite challenging. It is natural to ensure adequate life design by modeling these features as cracks within a creep-fatigue crack growth procedure. (2) Workmanship flaws in welds sometimes occur and are accepted in some ASME code sections. It can be convenient to consider these as flaws when making a design life assessment. (3) Non-destructive Evaluation (NDE) and inspection methods after fabrication are limited in the size of the crack or flaw that can be detected. It is often convenient to perform a life assessment using a flaw of a size that represents the maximum size that can elude detection. (4) Flaws that are observed using in-service detection

  15. 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)


    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.

  16. Ground Motions Due to Earthquakes on Creeping Faults (United States)

    Harris, R.; Abrahamson, N. A.


    We investigate the peak ground motions from the largest well-recorded earthquakes on creeping strike-slip faults in active-tectonic continental regions. Our goal is to evaluate if the strong ground motions from earthquakes on creeping faults are smaller than the strong ground motions from earthquakes on locked faults. Smaller ground motions might be expected from earthquakes on creeping faults if the fault sections that strongly radiate energy are surrounded by patches of fault that predominantly absorb energy. For our study we used the ground motion data available in the PEER NGA-West2 database, and the ground motion prediction equations that were developed from the PEER NGA-West2 dataset. We analyzed data for the eleven largest well-recorded creeping-fault earthquakes, that ranged in magnitude from M5.0-6.5. Our findings are that these earthquakes produced peak ground motions that are statistically indistinguishable from the peak ground motions produced by similar-magnitude earthquakes on locked faults. These findings may be implemented in earthquake hazard estimates for moderate-size earthquakes in creeping-fault regions. Further investigation is necessary to determine if this result will also apply to larger earthquakes on creeping faults. Please also see: Harris, R.A., and N.A. Abrahamson (2014), Strong ground motions generated by earthquakes on creeping faults, Geophysical Research Letters, vol. 41, doi:10.1002/2014GL060228.

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

  18. Induced creep and creep/fatigue of a nickel-base superalloy at ambient temperatures (United States)

    Chen, G. L.; Fritzemeier, L. G.; Xie, X.; Tien, J. K.


    The stress controlled fatigue of Nimonic*115, a typical γ’-strengthened nickel-base superalloy, was studied at ambient temperature, using a trapezoidal wave form at 1 Hz, with stresses chosen to produce failure in the lO4 to lO4 cycle range. In tests with maximum stress greater than the proportional limit, most of the fatigue damage occurs within the first few test cycles. Much of this strain is accumulated under static load and is therefore identified as creep strain. Transmission electron microscopy shows that these creep strains occur in slip bands which disrupt the ordered γ’ precipitates. Strain is found to follow a logarithmic time dependence, which suggests a low activation energy mechanism.

  19. Improved methods of creep-fatigue life assessment of components

    Energy Technology Data Exchange (ETDEWEB)

    Scholz, Alfred; Berger, Christina [Inst. fuer Werkstoffkunde (IfW), Technische Univ. Darmstadt (Germany)


    The improvement of life assessment methods contributes to a reduction of efforts at design and an effective long term operation of high temperature components, reduces technical risk and increases high economical advantages. Creep-fatigue at multi-stage loading, covering cold start, warm start and hot start cycles in typical loading sequences e.g. for medium loaded power plants, was investigated here. At hold times creep and stress relaxation, respectively, lead to an acceleration of crack initiation. Creep fatigue life time can be calculated by a modified damage accumulation rule, which considers the fatigue fraction rule for fatigue damage and the life fraction rule for creep damage. Mean stress effects, internal stress and interaction effects of creep and fatigue are considered. Along with the generation of advanced creep data, fatigue data and creep fatigue data as well scatter band analyses are necessary in order to generate design curves and lower bound properties inclusive. Besides, in order to improve lifing methods the enhancement of modelling activities for deformation and life time are important. For verification purposes, complex experiments at variable creep conditions as well as at creep fatigue interaction under multi-stage loading are of interest. Generally, the development of methods to transfer uniaxial material properties to multiaxial loading situations is a current challenge. For specific design purposes, a constitutive material model is introduced which is implemented as an user subroutine for Finite Element applications due to start-up and shut-down phases of components. Identification of material parameters have been performed by Neural Networks. (orig.)

  20. 3D discrete dislocation dynamics study of creep behavior in Ni-base single crystal superalloys by a combined dislocation climb and vacancy diffusion model (United States)

    Gao, Siwen; Fivel, Marc; Ma, Anxin; Hartmaier, Alexander


    A three-dimensional (3D) discrete dislocation dynamics (DDD) creep model is developed to investigate creep behavior under uniaxial tensile stress along the crystallographic [001] direction in Ni-base single crystal superalloys, which takes explicitly account of dislocation glide, climb and vacancy diffusion, but neglects phase transformation like rafting of γ‧ precipitates. The vacancy diffusion model takes internal stresses by dislocations and mismatch strains into account and it is coupled to the dislocation dynamics model in a numerically efficient way. This model is helpful for understanding the fundamental creep mechanisms in superalloys and clarifying the effects of dislocation glide and climb on creep deformation. In cases where the precipitate cutting rarely occurs, e.g. due to the high anti-phase boundary energy and the lack of superdislocations, the dislocation glide in the γ matrix and the dislocation climb along the γ/γ‧ interface dominate plastic deformation. The simulation results show that a high temperature or a high stress both promote dislocation motion and multiplication, so as to cause a large creep strain. Dislocation climb accelerated by high temperature only produces a small plastic strain, but relaxes the hardening caused by the filling γ channels and lets dislocations further glide and multiply. The strongest variation of vacancy concentration occurs in the horizontal channels, where more mixed dislocations exit and tend to climb. The increasing internal stresses due to the increasing dislocation density are easily overcome by dislocations under a high external stress that leads to a long-term dislocation glide accompanied by multiplication.

  1. Creep of Two-Phase Microstructures for Microelectronic Applications

    Energy Technology Data Exchange (ETDEWEB)

    Reynolds, Heidi Linch [Univ. of California, Berkeley, CA (United States)


    The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a

  2. Study of cavities in a creep crack growth test specimen


    Jazaeri, H; Bouchard, P. J.; Hutchings, M. T.; Mamun, A. A.; Heenan, R K


    Small Angle Neutron Scattering (SANS) and Scanning Electron Microscopy (SEM) have been used to determine the degree of cavitation damage, of length scale 5-300 nm, associated with a creep crack grown in a compact tension specimen cut from a Type 316H stainless steel weldment. The specimen was supplied by EDF Energy as part of an extensive study of creep crack growth in the heat affected zone of reactor components. The creep crack propagates along a line 1.5 mm away from, and parallel to, the ...

  3. Power law creep of polycarbonate by Berkovich nanoindentation (United States)

    Gao, Chenghui; Liu, Ming


    Power-law creep of polycarbonate was investigated by Berkovich indentation under three different conditions at room temperature, namely: constant displacement rate condition, constant displacement loading condition, and constant ratio of loading rate over load condition. Only the data during the loading process were analysed, and the experiments under different loading conditions gave consistent results that accorded well with theoretical prediction by dimensional analysis of indentation of power-law creep material. Material constants were characterized by curve fitting of the experimental results with theoretical equations, and the power law exponent for the power-law creep relation was found to be about 0.138 for the notably soft polycarbonate.

  4. Low-temperature creep of a carburized steel (United States)

    Neu, R. W.; Sehitoglu, Huseyin


    The low-temperature creep behavior of carburized 4320 steel with retained austenite contents of 35 and 14 pct and two uncarburized 4320 steels was investigated. The temperature range in the experiments was from 70 °C to 195 °C. The creep rate obeyed a logarithmic law when the stress level was below or near the proportional limit. A kinetic model is presented which de-scribes the low-temperature creep behavior of this steel under different stress and temperature conditions. The techniques for determining the constants in the model are given.

  5. Grain size, stress and creep in polycrystalline solids

    CSIR Research Space (South Africa)

    Nabarro, FRN


    Full Text Available than Nabarro-Herring creep provided that [6] (3) Different modes of creep will operate depending on whether the product L s is or is not large enough for Bardeen?Herring climb sources to operate within or on the surface of the grain. If the line...] interpret this kind of formula in the following way. As diffusional creep occurs, edge dislocations climb along the grain boundaries. Inequal- ity (5) represents the condition that, if these disloca- tions are removed, they can be replaced by new dislo...

  6. Creep of the dispersion-strengthened aluminum alloy IN 9052

    Energy Technology Data Exchange (ETDEWEB)

    Orlova, A.; Kucharova, K.; Cadek, J.


    The creep behavior of IN 9052, an Al-4Mg alloy strengthened by a very fine Al/sub 4/C/sub 3/ dispersion (in addition to a small volume fraction of Al/sub 2/O/sub 3/) is investigated experimentally in the temperature range 623-723 K. It is found that the apparent activation energies of steady-state creep and time to rupture are twice as large as the activation enthalpy of lattice diffusion. Two phenomenological interpretations of the observed creep behavior are proposed and evaluated. 22 references.

  7. The constitutive representation of high-temperature creep damage (United States)

    Chan, K. S.


    The elastic-viscoplastic constitutive equations of Bodner-Partom were applied to modeling creep damage in a high temperature Ni-alloy, B1900 + Hf. Both tertiary creep in bulk materials and creep crack growth in flawed materials were considered. In the latter case, the energy rate line integral was used for characterizing the crack driving force, and the rate of crack extension was computed using a local damage formulation that assumed fracture was controlled by cavitation occurring within the crack-tip process zone. The results of this investigation were used to assess the evolution equation for isotropic damage utilized in the Bodner-Partom constitutive equations.

  8. Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G., E-mail: [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)


    Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

  9. Understanding effects of microstructural inhomogeneity on creep response – New approaches to improve the creep resistance in magnesium alloys

    Directory of Open Access Journals (Sweden)

    Yuanding Huang


    Full Text Available Previous investigations indicate that the creep resistance of magnesium alloys is proportional to the stability of precipitated intermetallic phases at grain boundaries. These stable intermetallic phases were considered to be effective to suppress the deformation by grain boundary sliding, leading to the improvement of creep properties. Based on this point, adding the alloying elements to form the stable intermetallics with high melting point became a popular way to develop the new creep resistant magnesium alloys. The present investigation, however, shows that the creep properties of binary Mg–Sn alloy are still poor even though the addition of Sn possibly results in the precipitation of thermal stable Mg2Sn at grain boundaries. That means other possible mechanisms function to affect the creep response. It is finally found that the poor creep resistance is attributed to the segregation of Sn at dendritic and grain boundaries. Based on this observation, new approaches to improve the creep resistance are suggested for magnesium alloys because most currently magnesium alloys have the commonality with the Mg–Sn alloys.

  10. Dataset of tensile strength development of concrete with manufactured sand

    Directory of Open Access Journals (Sweden)

    Shunbo Zhao


    Full Text Available This article presents 755 groups splitting tensile strength tests data of concrete with manufactured sand (MSC in different curing age ranged from 1 day to 388 days related to the research article “Experimental study on tensile strength development of concrete with manufactured sand” (Zhao et al., 2017 [1]. These data were used to evaluate the precision of the prediction formulas of tensile strength of MSC, and can be applied as dataset for further studies.

  11. Tensile Strength of Water Exposed to Pressure Pulses

    DEFF Research Database (Denmark)

    Andersen, Anders Peter; Mørch, Knud Aage


    at an extended water-solid interface by imposing a tensile stress pulse which easily causes cavitation. Next, a compressive pulse of duration ~1 ms and a peak intensity of a few bar is imposed prior to the tensile stress pulse. A dramatic increase of the tensile strength is observed immediately after...... the compressive pulse, but the effect is shortlived. We presume that diffusion of non-condensable gas from the cavitation nuclei into the liquid at compression, and back again later, is responsible for the changes of tensile strength....

  12. Tensile-stressed microelectromechanical apparatus and micromirrors formed therefrom (United States)

    Fleming, James G [Albuquerque, NM


    A microelectromechanical (MEM) apparatus is disclosed which includes one or more tensile-stressed actuators that are coupled through flexures to a stage on a substrate. The tensile-stressed actuators, which can be formed from tensile-stressed tungsten or silicon nitride, initially raise the stage above the substrate without any applied electrical voltage, and can then be used to control the height or tilt angle of the stage. An electrostatic actuator can also be used in combination with each tensile-stressed actuator. The MEM apparatus has applications for forming piston micromirrors or tiltable micromirrors and independently addressable arrays of such devices.

  13. Composite Analysis of Concrete - Creep, Relaxation and Eigenstrain/stress

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang


    approach.The model is successfully justified comparing predicted results with recent experimental data obtained in tests made at the Danish Technological Institute and at the Technical University of Denmark on creep, relaxation, and shrinkage of very young concretes (hours) - and also with experimental...... results on creep, shrinkage, and internal stresses caused by drying shrinkage reported in the literature on the mechanical behavior of mature concretes.Shrinkage (autogeneous or drying) of mortar and concrete and associated internal stress states are examples of analysis made in this report......A composite-rheological model of concrete is presented by which consistent predictions of creep, relaxation, and internal stresses can be made from known concrete composition, age at loading, and climatic conditions. No other existing "creep prediction method" offers these possibilities in one...

  14. Microstructural evolution and creep of Fe-Al-Ta alloys

    Energy Technology Data Exchange (ETDEWEB)

    Prokopcakova, Petra; Svec, Martin [Technical University of Liberec (Czech Republic). Dept. of Material Science; Palm, Martin [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany). Structure and Nano-/Micromechanics of Materials


    The microstructural evolution in Fe-Al-Ta alloys containing 23 - 31 at.% Al and 1.5 - 2.2 at.% Ta has been studied in the temperature range 650 - 750 C by annealing for 1, 10, 100 and 1 000 h. The experiments confirm that in this temperature range the precipitation of the stable hexagonal C14 Laves phase is preceded by formation of coherent, metastable L2{sub 1} Heusler phase precipitates within the Fe-Al matrix. However, precipitates of C14 are observed after much shorter annealing times than previously assumed. Creep strength increases substantially with increasing Al content of the alloys because the solid solubility for Ta in the Fe-Al matrix increases with increasing Al content and solid-solution hardening contributes substantially to the observed high creep strength. It may therefore be that the microstructural changes during creep have no noticeable effect on creep strength.

  15. Behaviour of Epoxy Silica Nanocomposites Under Static and Creep Loading (United States)

    Constantinescu, Dan Mihai; Picu, Radu Catalin; Sandu, Marin; Apostol, Dragos Alexandru; Sandu, Adriana; Baciu, Florin


    Specific manufacturing technologies were applied for the fabrication of epoxy-based nanocomposites with silica nanoparticles. For dispersing the fillers in the epoxy resin special equipment such as a shear mixer and a high energy sonicator with temperature control were used. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%.. The obtained nanocomposites were subjected to monotonic uniaxial and creep loading at room temperature. The static mechanical properties were not significantly improved regardless the filler percentage and type of epoxy resin. Under creep loading, by increasing the stress level, the nanocomposite with 0.1 wt% silica creeps less than all other materials. Also the creep rate is reduced by adding silica nanofillers.

  16. Creep and Shrinkage of High Strength Concretes: an Experimental Analysis

    Directory of Open Access Journals (Sweden)

    Berenice Martins Toralles carbonari


    Full Text Available The creep and shrinkage behaviour of high strength silica fume concretes is significantly different from that of conventional concretes. In order to represent the proper time-dependent response of the material in structural analysis and design, these aspects should be adequately quantified. This paper discusses an experimental setup that is able to determine the creep and shrinkage of concrete from the time of placing. It also compares different gages that can be used for measuring the strains. The method is applied to five different concretes in the laboratory under controlled environmental conditions. The phenomena that are quantified can be classified as basic shrinkage, drying shrinkage, basic creep and drying creep. The relative importance of these mechanisms in high strength concrete will also be presented.

  17. Study on the creep and recovery behaviors of ferrofluids (United States)

    Li, Zhenkun; Li, Decai; Hao, Du; Cheng, Yanhong


    The creep and recovery behaviors of lubrication oil based ferrofluids of different particle concentration were systematically investigated to understand the viscoelasticity of ferrofluids. The influence of stress level, magnetic field strength and temperature on creep and recovery behaviors of ferrofliuids was studied experimentally and the microscopic mechanisms behind the rheological phenomenon were discussed. Linear viscoelasticity theory and generalized Burgers models were employed to analyze the experimental results. The experimental results demonstrate that the ferrofluids exhibits unique creep and recovery properties significantly different from other stimuli responsive materials both in the linear and nonlinear viscoelastic region. Furthermore, structures larger than single chains are supposed to be responsible for many experimental results, including the extended relaxation process in recovery phase and the nonlinear increasing trend of creep strain with magnetic field strength and temperature. These findings contribute to a better understanding of the microscopic mechanism of magnetorheology of ferrofluids and also provide guidance for many practical applications.

  18. Geometrical versus rheological transient creep closure in a salt cavern (United States)

    Bérest, Pierre; Karimi-Jafari, Mehdi; Brouard, Benoît


    An in-situ test performed in a brine-filled cavern proves that, when brine pressure decreases rapidly, the creep closure rate increases drastically. Conversely, a rapid pressure increase leads to ;reverse; creep closure: cavern volume increases, even when, at cavern depth, fluid pressure is lower than geostatic pressure. It is tempting to explain these two phenomena by transient salt creep, a characteristic feature of salt rheological behavior commonly observed during laboratory creep tests. In fact, computations performed on an idealized cylindrical cavern excavated from a Norton-Hoff rock mass (a constitutive law that includes no transient component) prove that these two phenomena are, at least partly, of a structural nature: their origin is in the slow redistribution of stresses following any pressure change.

  19. Microstructure evolution of CLAM steel during creep at 923K (United States)

    Ye, S.; Zhao, F.; Huang, F.; He, J.; Wang, J. L.


    The microstructure change of CLAM steel during creep testing process was investigated at the temperature of 923K with different stress. The results show that the fragmentation and polygonization of martensite lath, as well as the degeneration of dislocation structure are the main factors to deteriorate the creep performance. The stability of MX precipitates in CLAM steel during high temperature creep is good, but the amount and size of M23C6 precipitates are increased. The Laves phase was not found in all samples, which may be due to the experimental temperature is close to the dissolution temperature of Laves phase. The higher temperature accelerates the microstructure evolution of CLAM steel, which results in the degradation of creep properties.

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

    National Research Council Canada - National Science Library

    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


    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...

  1. Reference diameter in calculations of creep strain for steam pipelines

    Directory of Open Access Journals (Sweden)

    Łopata Stanisław


    Full Text Available Recommended methods of the operational safety assessment of high-pressure steam pipelines include periodic testing that enables determination of creep strain and the creep rate. The accuracy with which the two quantities are determined depends, among others, on the control of the testing conditions and on the assumed reference diameter. The analysis conducted herein concerns the impact of the reference diameter on the results characterizing the creep phenomenon in the pipeline elements (straight sections and bends. In this respect, the initial ovality of the pipeline cross-section is an important parameter. The calculations are made using own results obtained from many years of the steam pipeline creep testing, including tests performed after the expiry of the computational service life.

  2. NASALIFE - Component Fatigue and Creep Life Prediction Program (United States)

    Gyekenyesi, John Z.; Murthy, Pappu L. N.; Mital, Subodh K.


    NASALIFE is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although the primary focus was for CMC components, the underlying methodologies are equally applicable to other material systems as well. The program references empirical data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method or a peak counting type method. Lastly, damage due to cyclic loading and creep is combined with Minor's Rule to determine damage due to cyclic loading, damage due to creep, and the total damage per mission and the number of potential missions the component can provide before failure.

  3. Porosity Evolution in a Creeping Single Crystal (Preprint) (United States)


    mechanism. Our analyses focus on the role of stress state on deformation and void growth in ductile single crystals in the dislocation creep regime. We also...orientation effects on void growth and coalescence in fcc single crystals . International Journal of Plasticity, 22, 921-942. [27] Kysar J.W., Gan Y.X...AFRL-RX-WP-TP-2012-0373 POROSITY EVOLUTION IN A CREEPING SINGLE CRYSTAL (PREPRINT) A. Srivastava and A. Needleman University of North

  4. Experimental Study on the Porosity Creep Properties of Broken Limestone

    Directory of Open Access Journals (Sweden)

    Li Shun-cai


    Full Text Available In the underground engineering, the long-term stability of the surrounding rocks (especially the broken rocks containing water and the ground settlement resulted from the seepage-creep coupling above goaf have been the important research subjects concerning the deep mining. For the broken rock, its porosity is an important structural parameter determining its creep properties, and the porosity change rate is more superior to describe the creep characteristics compared with the strain change rate at a certain direction. In this paper, MTS815.02 Rock Mechanics Test System is used to carry out the creep experiments on water-saturated broken limestone, and then the time curves of porosity and of the porosity change rate are obtained. By regression, we have got the relation equation between the porosity change rate with the instant porosity and the stress level during the creep. The study indicates that when the stress retains a constant level, the relation between the porosity change rate and the instant porosity can be fitted with a cubical polynomial. The obtained creep relation equation between the porosity change rate and the instant porosity and the instant stress provides a necessary state equation for studying the coupling between the seepage and the creep of the broken rock. Furthermore, the seepage in the broken rock has been verified to satisfy the Forchheimer’s non-Darcy flow according to our previous studies, and its seepage properties, k, β and ca can all be expressed respectively as the polynomial of the porosity, so, by combining with these three state equations we have obtained the four essential state equations for solving the coupling problems of the seepage and the creep for the broken rocks.

  5. Creep and crack growth of zircon and mullite base materials

    Energy Technology Data Exchange (ETDEWEB)

    Carbonneau, X.; Olagnon, C.; Fantozzi, G. [INSA, Villeurbanne (France). GEMPPM


    The creep and crack propagation properties of mullite and zircon ceramics were compared. In the investigated temperature range, mullite presents a simple crack propagation of a unique macrocracks, although a change of mechanism is observed at 1200 C. The zircon material present a rather more complex crack propagation, with multicracking and branching, due to a significant crack healing. The creep behaviours also appeared as different for both materials. The mullite creep curves present only two stages, even when fracture occurs, while a tertiary regime is observed in the case of zircon. The results show that grain boundary sliding is the main deformation mechanism for the two different materials. In fact, they exhibit similar overall real behaviours with a different characteristic temperature. At low stress, the minimum creep rate can be considered as a stationary creep, but at a higher stress, generalised or localised damage interfere, leading to a higher apparent stationary creep exponent. Sub-critical crack growth and deformation act as parallel mechanisms for mullite, while the interaction is more complex in zircon where crack healing induce multi-cracking. (orig.) 9 refs.

  6. Denuded Zones, Diffusional Creep, and Grain Boundary Sliding

    Energy Technology Data Exchange (ETDEWEB)

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


    The appearance of denuded zones following low stress creep in particle-containing crystalline materials is both a microstructural prediction and observation often cited as irrefutable evidence for the Nabarro-Herring mechanism of diffusional creep. The denuded zones are predicted to be at grain boundaries that are orthogonal to the direction of the applied stress. Furthermore, their dimensions should account for the accumulated plastic flow. In the present paper, the evidence for such denuded zones is critically examined. These zones have been observed during creep of magnesium, aluminum, and nickel-base alloys. The investigation casts serious doubts on the apparently compelling evidence for the link between denuded zones and diffusional creep. Specifically, denuded zones are clearly observed under conditions that are explicitly not diffusional creep. Additionally, the denuded zones are often found in directions that are not orthogonal to the applied stress. Other mechanisms that can account for the observations of denuded zones are discussed. It is proposed that grain boundary sliding accommodated by slip is the rate-controlling process in the stress range where denuded zones have been observed. It is likely that the denuded zones are created by dissolution of precipitates at grain boundaries that are simultaneously sliding and migrating during creep.

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

    Directory of Open Access Journals (Sweden)

    Zakaria Abdallah


    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.

  8. ANSYS Creep-Fatigue Assessment tool for EUROFER97 components

    Directory of Open Access Journals (Sweden)

    M. Mahler


    Full Text Available The damage caused by creep-fatigue is an important factor for materials at high temperatures. For in-vessel components of fusion reactors the material EUROFER97 is a candidate for structural application where it is subjected to irradiation and cyclic thermo-mechanical loads. To be able to evaluate fusion reactor components reliably, creep-fatigue damage has to be taken into account. In the frame of Engineering Data and Design Integration (EDDI in EUROfusion Technology Work Programme rapid and easy design evaluation is very important to predict the critical regions under typical fusion reactor loading conditions. The presented Creep-Fatigue Assessment (CFA tool is based on the creep-fatigue rules in ASME Boiler Pressure Vessel Code (BPVC Section 3 Division 1 Subsection NH which was adapted to the material EUROFER97 and developed for ANSYS. The CFA tool uses the local stress, maximum elastic strain range and temperature from the elastic analysis of the component performed with ANSYS. For the assessment design fatigue and stress to rupture curves of EUROFER97 as well as isochronous stress vs. strain curves determined by a constitutive model considering irradiation influence are used to deal with creep-fatigue damage. As a result allowable number of cycles based on creep-fatigue damage interaction under given hold times and irradiation rates is obtained. This tool can be coupled with ANSYS MAPDL and ANSYS Workbench utilizing MAPDL script files.

  9. High temperature creep of refractory bricks. Final report

    Energy Technology Data Exchange (ETDEWEB)

    McGee, T.D. [Ames Lab., IA (United States)


    The uniaxial compressive creep of the 13 high chromia-commercial refractories that are candidate materials for lining coal gasification vessels was studied using stresses from 50 to 1500 psi (0.34 MPa to 10.3 MPa) and temperature from 1900{degrees}F to 2600{degrees}F (1038{degrees} to 1427{degrees}C). The regimes to stress and temperature in which creep was active varied widely, depending on impurities and microstructure, not chromia content, and was active at lower stresses and temperatures than would be expected from hot strength data. The creep was always primary, going through steady state to failure as a transient phase. One specimen with a liquid phase at temperature gave a longer steady-state region. The primary creep time exponent varied from 0.4 to nearly one. It was smaller at low stresses and temperatures, but was often a linear function of stress. Activation enthalpies were less for refractories containing a significant liquid phase at temperature, and were in the range expected for cation diffusion. Current theoretical models to not fit these systems. Two models are suggested to explain the primary creep regime. More research to correlate primary creep with microstructure is needed.

  10. Creep in jointed rock masses. State of knowledge

    Energy Technology Data Exchange (ETDEWEB)

    Glamheden, Rune (Golder Associates AB (Sweden)); Hoekmark, Harald (Clay Technology AB, Lund (Sweden))


    To describe creep behaviour in hard rock masses in a physically realistic way, elaborate models including various combinations of dash pots, spring elements and sliders would be needed. According to our knowledge, there are at present no numerical tools available that can handle such a creep model. In addition, there are no records over sufficient long time periods of tunnel convergence in crystalline rock that could be used to determine or calibrate values for the model parameters. A possible method to perform bounding estimates of creep movements around openings in a repository may be to use distinct element codes with standard built-in elasto-plastic models. By locally reducing the fracture shear strength near the underground openings a relaxation of fracture shear loads is reached. The accumulated displacements may then represent the maximum possible effects of creep that can take place in a jointed rock mass without reference to the actual time it takes to reach the displacements. Estimates based on results from analyses where all shear stresses are allowed to disappear completely will, however, be over-conservative. To be able to set up and analyse reasonably realistic numerical models with the proposed method, further assumptions regarding the creep movements and the creep region around the opening have to be made. The purpose of this report is to present support for such assumptions as found in the literature.

  11. Creep behavior of tantalum alloy T-222 at 1365 to 1700 K (United States)

    Titran, R. H.


    High vacuum creep tests on the tantalum T-222 alloy at 0.42 to 0.52 T sub m show that the major portion of the creep curves, up to at least 1 percent strain, can be best described by an increasing creep rate, with strain varying linearly with time. Correlation and extrapolation of the creep curves on the basis of increasing creep rates results in more accurate engineering design data than would use of approximated linear rates. Based on increasing creep rates, the stress for 1 percent strain in 10,000 hours for T-222 is about four times greater than for the Ta-10W alloy. Increasing the grain size results in increased creep strength. Thermal aging prior to testing caused precipitation of the hexagonal close packed (Hf,Ta) sub 2 C, which initially increased creep strength. However, this dimetal carbide was converted during creep testing to face-centered cubic (Hf,Ta)C.

  12. Manuals of SORE, the creep fatigue damage calculation program, and the post program of the creep fatigue damage calculation program

    Energy Technology Data Exchange (ETDEWEB)

    Tanabe, Hiroaki [Japan Nuclear Cycle Development Inst., Tsuruga, Fukuki (Japan). Tsuruga Head Office; Sago, Hiromi [Mitsubishi Heavy Industries Ltd., Tokyo (Japan)


    This report includes the Manuals of 'the Structural Integrity Oriented Reliability Assessment System for 'MONJU' (SORE)', 'the creep fatigue damage calculation program using planning operation data' and 'the post program of the creep fatigue damage calculation program using planning operation data'. These programs were developed for the purpose of assisting the preservation management during the 'MONJU' plant employment period from an operation start. (author)

  13. Evaluation of Permanent Deformation of CRM-Reinforced SMA and Its Correlation with Dynamic Stiffness and Dynamic Creep

    Directory of Open Access Journals (Sweden)

    Nuha Salim Mashaan


    Full Text Available Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM, in stone mastic asphalt (SMA 20 performance. The virgin bitumen (80/100 penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness, dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture.

  14. Evaluation of permanent deformation of CRM-reinforced SMA and its correlation with dynamic stiffness and dynamic creep. (United States)

    Mashaan, Nuha Salim; Karim, Mohamed Rehan


    Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM)), in stone mastic asphalt (SMA 20) performance. The virgin bitumen (80/100) penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness), dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture.

  15. Ply tensile properties of banana stem and banana bunch fibres

    African Journals Online (AJOL)


    Mar 1, 2012 ... surface after tensile test indicated a ductile failure of the material with appreciable plastic deformation. Keywords: lamina, natural fibre, banana fibre, natural rubber, tensile properties, fracture surface, angle ply. 1. Introduction. Most governments all over the world are now very conscious of their environment.

  16. New Scanning Electron Microscope Used for Cryogenic Tensile Testing

    CERN Multimedia

    Maximilien Brice


    At CERN engineering department's installation for cryogenic tensile testing, the new scanning electron microscope (SEM) allows for detailed optical observations to be carried out. Using the SEM, surface coatings and tensile properties of materials can investigated in order to better understand how they behave under different conditions.

  17. Effect of alcoholic treated MWCNT on tensile behavior of epoxy ...

    African Journals Online (AJOL)

    Tensile strength, Young's modulus, and Elongation are found to be effectively improved with the addition of alcoholic functionalized MWCNT in epoxy matrix. Increased tensile strength and elastic modulus of epoxy composites loaded with the alcoholic functionalized MWCNT are observed through experimental studies.

  18. Hybrid filler composition optimization for tensile strength of jute fibre ...

    Indian Academy of Sciences (India)

    The effect of weight content of bagasse fibre, carbon black and calcium carbonate on tensile strength of pultruded GFRP composite is evaluated and the optimum hybrid filler composition for maximizing the tensile strength is determined. Different compositions of hybrid filler are prepared by mixing three fillers using Taguchi ...

  19. Vacuum fused deposition modelling system to improve tensile ...

    African Journals Online (AJOL)

    The results obtained show an improvement of 12.83 % of tensile strength compared to the standard specimen. This paper concludes that the low pressure environment is useful in reducing the heat loss due to convection of air, hence directly improves the specimen's tensile strength. Keywords: additive manufacturing; fused ...

  20. Sterilization effects on tensile strength of non-conventional suture ...

    African Journals Online (AJOL)

    An experiment was carried out to determine the tensile strength of embroidery, braiding, cobbler's thread and nylon mono-filament fishing line (NMFL) use as non-conventional suture material. Their tensile strength were determined pre- sterilization using various calibrated weights (50gm, 100gm, 500gm).

  1. some tensile properties of unsaturated polyester resin reinforced wi

    African Journals Online (AJOL)

    Dr Obe

    and tensile toughness at fracture increased as the volume fractions of carbon black nanoparticles ... pharmaceuticals, biomedical, energy, sports ... applications. 2.0 OBJECTIVE OF THE STUDY. The objective of this work was to investigate the monotonic tensile properties of carbon black reinforced polyester, especially at ...

  2. Effect of Temperature on the Tensile Strength and Thermoelectric ...

    African Journals Online (AJOL)

    The tensile strength and thermoelectric e.m.f. values of 6063 aluminum alloy quenched at different temperatures from 2500C to 6000C were investigated. The result empirically confirmed that a perfect correlation exists between the tensile strength and thermoelectric e.m.f. values with concurrent minimum temperature ...

  3. Tensile behaviour of polyethylene and poly(p-xylylene) fibres

    NARCIS (Netherlands)

    van der Werff, Harm


    This thesis deals with the tensile behaviour of fibres prepared from high molecular weight polymers.The tensile strength of a polymeric fibre is in general much lower than the corresponding theoretical value. In case of ultra-high molecular weight polyethylene (UHMWPE), fibres can be prepared by

  4. Stress-deformed state of cylindrical specimens during indirect tensile strength testing

    Directory of Open Access Journals (Sweden)

    Levan Japaridze


    Full Text Available In this study, the interaction between cylindrical specimen made of homogeneous, isotropic, and linearly elastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed that the specimen is diametrically compressed by elliptic normal contact stresses. The frictional contact stresses between the specimen and platens are neglected. The analytical solution starts from the contact problem of the loading jaws of any curvature and cylindrical specimen. The contact width, corresponding loading angle (2θ0, and elliptical stresses obtained through solution of the contact problems are used as boundary conditions for a cylindrical specimen. The problem of the theory of elasticity for a cylinder is solved using Muskhelishvili's method. In this method, the displacements and stresses are represented in terms of two analytical functions of a complex variable. In the main approaches, the nonlinear interaction between the loading bearing blocks and the specimen as well as the curvature of their surfaces and the elastic parameters of their materials are taken into account. Numerical examples are solved using MATLAB to demonstrate the influence of deformability, curvature of the specimen and platens on the distribution of the normal contact stresses as well as on the tensile and compressive stresses acting across the loaded diameter. Derived equations also allow calculating the modulus of elasticity, total deformation modulus and creep parameters of the specimen material based on the experimental data of radial contraction of the specimen.

  5. Comprehensive Creep and Thermophysical Performance of Refractory Materials

    Energy Technology Data Exchange (ETDEWEB)

    Ferber, M.K.; Wereszczak, A.; Hemrick, J.A.


    Furnace designers and refractory engineers recognize that optimized furnace superstructure design and refractory selection are needed as glass production furnaces are continually striving toward greater output and efficiencies. Harsher operating conditions test refractories to the limit, while changing production technology (such as the conversion to oxy-fuel from traditional air-fuel firing) can alter the way the materials perform [1-3]. Refractories for both oxy- and air-fuel fired furnace superstructures (see Fig. 1) are subjected to high temperatures that may cause them to creep excessively or subside during service if the refractory material is not creep resistant, or if it is subjected to high stress, or both. Furnace designers can ensure that superstructure structural integrity is maintained if the creep behavior of the refractory material is well understood and well represented by appropriate engineering creep models. Several issues limit the abilities of furnace designers to (1) choose the optimum refractory for their applications, (2) optimize the engineering design, or (3) predict the service mechanical integrity of their furnace superstructures. Published engineering creep data are essentially nonexistent for almost all commercially available refractories used for glass furnace superstructures. The limited data that do exist are supplied by the various refractory suppliers. Unfortunately, the suppliers generally have different ways of conducting their mechanical testing, and they interpret and report their data differently. This inconsistency makes it hard for furnace designers to draw fair comparisons between competing grades of candidate refractories. Furthermore, the refractory suppliers' data are often not available in a form that can be readily used for furnace design or for the prediction and design of long-term structural integrity of furnace superstructures. As a consequence, the U.S. Department of Energy (DOE) Industrial Technology Program

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

    Directory of Open Access Journals (Sweden)

    Saucedo-Muñoz, Maribel L.


    Full Text Available 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 °C. The small punch test was carried out using a creep tester with a specimen size of 10×10×0.3 mm at 650, 675 and 700 °C 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.El ensayo de termofluencia por indentación se utilizó para evaluar el comportamiento a la termofluencia en un acero inoxidable austenítico 316. Este ensayo se realizó en una máquina de indentación con muestras de 10×10×0,3 mm a temperaturas de 650, 675 y 700 °C con cargas de 199 a 512 N. Las curvas de termofluencia del ensayo mostraron las tres etapas características observadas en el ensayo convencional de tensión. Asimismo, las principales relaciones de termofluencia entre parámetros como velocidad de termofluencia, esfuerzo, tiempo de ruptura y temperatura se observaron en los parámetros correspondientes al ensayo de indentación, lo que permitió caracterizar el comportamiento de termofluencia en este acero. El mecanismo y la energía de activación del proceso de deformación en la termofluencia corresponden al deslizamiento de los límites de grano y la difusión a través de los mismos, respectivamente, lo cual causó la fractura intergranular en las muestras ensayadas.

  7. Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep. (United States)

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


    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

  8. Evaluation of the Permanent Deformations and Aging Conditions of Batu Pahat Soft Clay-Modified Asphalt Mixture by Using a Dynamic Creep Test

    Directory of Open Access Journals (Sweden)

    Al Allam A. M.


    Full Text Available This study aimed to evaluate the permanent deformation and aging conditions of BatuPahat soft clay–modified asphalt mixture, also called BatuPahat soft clay (BPSC particles; these particles are used in powder form as an additive to hot-mix asphalt mixture. In this experiment, five percentage compositions of BPSC (0%, 2%, 4%, 6%, and 8% by weight of bitumen were used. A novel design was established to modify the hot-mix asphalt by using the Superpave method for each additive ratio. Several laboratory tests evaluating different properties, such as indirect tensile strength, resilient stiffness modulus, and dynamic creep, was conducted to assess the performance of the samples mixed through the Superpave method. In the resilient modulus test, fatigue and rutting resistance were reduced by the BPSC particles. The added BPSC particles increased the indirect tensile strength. Among the mixtures, 4% BPSC particles yielded the highest performance. In the dynamic creep test, 4% BPSC particles added to the unaged and short-term aged specimens also showed the highest performance. Based on these results, our conclusion is that the BPSC particles can alleviate the permanent deformation (rutting of roads.

  9. Super long-term creep tests of advanced HP and IP rotor steels

    Energy Technology Data Exchange (ETDEWEB)

    Tchizhik, A.A. [The Polzunov Central Boiler and Turbine Institute, Department the Fatigue Life of Materials for Power Plans Equipment, St. Petersburg (Russian Federation)


    A creep model has been developed for predicting the long-term creep behavior, in excess of 200,000 h for advanced materials.The new creep theory is based on a continuum microdamage model and is used to calculate the fields of stress and strain and wedge and cavities damage in critical components of steam and gas turbines. The application of this new model increases the reliability and service life of modern turbines. The accuracy of the model to predict long - term creep behavior, creep ductility was verified using the data bank of super long-term creep tests of advanced materials. (orig.) 12 refs.

  10. Creep Deformation and Fracture Processes in OF and OFP Copper

    Energy Technology Data Exchange (ETDEWEB)

    Bowyer, William H. [Meadow End Farm, Farnham (United Kingdom)


    The literature on creep processes in many materials, including copper, has been thoroughly reviewed and complemented by Ashby and co-workers. They have provided physical models which describe the deformation and fracture processes with good qualitative and quantitative agreement with experimental data for many cases. A description of the deformation and fracture models is provided and the relevant equations are included in the appendices. Published data from the canister development programme has been compared with the predictions from the models. The purpose was to improve our understanding of (1) a reported benefit to creep performance which arises from additions of 50 ppm phosphorus to oxygen free (OF) copper, and (2) an observed transition from brittle to ductile failure in OF copper. The models adequately describe the general variations in the observed creep behaviour of the experimental materials. Steady state creep rates for OF copper are observed to be up to one order of magnitude higher than the model predicts for pure copper across a wide range of temperatures and stresses in the power law and power law breakdown regimes. For OF copper with 50ppm of phosphorus added (OFP copper), observed steady state creep rates in the power law breakdown regime are up to one order of magnitude lower than the model predicts for pure copper. Creep lives in the experimental OFP material are also higher than creep lives for OF material under similar conditions. The lower creep deformation rates and the longer creep lives of OFP material are attributed the known effects of phosphorus on recovery in copper. The model predicts that the same mechanism will improve creep lives under repository conditions. It is suggested that the factor of improvement under repository conditions will be less than the factor which is observed in the power law breakdown regime. Predicted creep lives, based on measured steady state creep rates and stress exponents ('n' values) are in good

  11. AGC 2 Irradiation Creep Strain Data Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Windes, William E. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Rohrbaugh, David T. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Swank, W. David [Idaho National Lab. (INL), Idaho Falls, ID (United States)


    The Advanced Reactor Technologies Graphite Research and Development Program is conducting an extensive graphite irradiation experiment to provide data for licensing of a high temperature reactor (HTR) design. In past applications, graphite has been used effectively as a structural and moderator material in both research and commercial high temperature gas cooled reactor designs. Nuclear graphite H-451, used previously in the United States for nuclear reactor graphite components, is no longer available. New nuclear graphite grades have been developed and are considered suitable candidates for new HTR reactor designs. To support the design and licensing of HTR core components within a commercial reactor, a complete properties database must be developed for these current grades of graphite. Quantitative data on in service material performance are required for the physical, mechanical, and thermal properties of each graphite grade, with a specific emphasis on data accounting for the life limiting effects of irradiation creep on key physical properties of the HTR candidate graphite grades. Further details on the research and development activities and associated rationale required to qualify nuclear grade graphite for use within the HTR are documented in the graphite technology research and development plan.

  12. Quantification of Permafrost Creep by Remote Sensing (United States)

    Roer, I.; Kaeaeb, A.


    Rockglaciers and frozen talus slopes are distinct landforms representing the occurrence of permafrost conditions in high mountain environments. The interpretation of ongoing permafrost creep and its reaction times is still limited due to the complex setting of interrelating processes within the system. Therefore, a detailed monitoring of rockglaciers and frozen talus slopes seems advisable to better understand the system as well as to assess possible consequences like rockfall hazards or debris-flow starting zones. In this context, remote sensing techniques are increasingly important. High accuracy techniques and data with high spatial and temporal resolution are required for the quantification of rockglacier movement. Digital Terrain Models (DTMs) derived from optical stereo, synthetic aperture radar (SAR) or laser scanning data are the most important data sets for the quantification of permafrost-related mass movements. Correlation image analysis of multitemporal orthophotos allow for the quantification of horizontal displacements, while vertical changes in landform geometry are computed by DTM comparisons. In the European Alps the movement of rockglaciers is monitored over a period of several decades by the combined application of remote sensing and geodetic methods. The resulting kinematics (horizontal and vertical displacements) as well as spatio-temporal variations thereof are considered in terms of rheology. The distinct changes in process rates or landform failures - probably related to permafrost degradation - are analysed in combination with data on surface and subsurface temperatures and internal structures (e.g., ice content, unfrozen water content).

  13. Proposition of Improved Methodology in Creep Life Extrapolation

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo Gon; Park, Jae Young; Jang, Jin Sung [KAERI, Daejeon (Korea, Republic of)


    To design SFRs for a 60-year operation, it is desirable to have the experimental creep-rupture data for Gr. 91 steel close to 20 y, or at least rupture lives significantly higher than 10{sup 5} h. This requirement arises from the fact that, for the creep design, a factor of 3 times for extrapolation is considered to be appropriate. However, obtaining experimental data close to 20 y would be expensive and also take considerable time. Therefore, reliable creep life extrapolation techniques become necessary for a safe design life of 60 y. In addition, it is appropriate to obtain experimental longterm creep-rupture data in the range 10{sup 5} ∼ 2x10{sup 5} h to improve the reliability of extrapolation. In the present investigation, a new function of a hyperbolic sine ('sinh') form for a master curve in time-temperature parameter (TTP) methods, was proposed to accurately extrapolate the long-term creep rupture stress of Gr. 91 steel. Constant values used for each parametric equation were optimized on the basis of the creep rupture data. Average stress values predicted for up to 60 y were evaluated and compared with those of French Nuclear Design Code, RCC-MRx. The results showed that the master curve of the 'sinh' function was a wider acceptance with good flexibility in the low stress ranges beyond the experimental data. It was clarified clarified that the 'sinh' function was reasonable in creep life extrapolation compared with polynomial forms, which have been used conventionally until now.

  14. Creep-induced anisotropy in covalent adaptable network polymers. (United States)

    Hanzon, Drew W; He, Xu; Yang, Hua; Shi, Qian; Yu, Kai


    Anisotropic polymers with aligned macromolecule chains exhibit directional strengthening of mechanical and physical properties. However, manipulating the orientation of polymer chains in a fully cured thermoset is almost impossible due to its permanently crosslinked nature. In this paper, we demonstrate that rearrangeable networks with bond exchange reactions (BERs) can be utilized to tailor the anisotropic mechanical properties of thermosetting polymers. When a constant force is maintained at BER activated temperatures, the malleable thermoset creeps in the direction of stress, and macromolecule chains align themselves in the same direction. The aligned polymer chains result in an anisotropic network with a stiffer mechanical behavior in the direction of creep, while with a more compliant behavior in the transverse direction. The degree of network anisotropy is proportional to the amount of creep strain. A multi-length scale constitutive model is developed to study the creep-induced anisotropy of thermosetting polymers. The model connects the micro-scale BER kinetics, orientation of polymer chains, and directional mechanical properties of network polymers. Without any fitting parameters, it is able to predict the evolution of creep strain at different temperatures and anisotropic stress-strain behaviors of CANs after creep. Predictions on the chain orientation are verified by molecular dynamics (MD) simulation. Based on parametric studies, it is shown that the influences of creep time and temperature on the network anisotropy can be generalized into a single parameter, and the evolution of directional modulus follows an Arrhenius type time-temperature superposition principle (TTSP). The presented work provides a facile approach to transform isotropic thermosets into anisotropic ones using simple heating, and their directional properties can be readily tailored by the processing conditions.

  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)


    A model for the plastic deformation and creep of copper has been developed. It is based on the principle that the strain rate response to stress is dependent on the microstructural state of the material. The specific microstructural state variables used in the model are the dislocation density and the vacancy concentration. The model has been used to study the relation between minimum or stationary creep rate and stress at different temperatures. It was noted that when creep tests at constant stress were simulated no so called power law breakdown was observed while simulations of creep tests at constant load showed a power law breakdown behaviour similar to that observed in the experimental constant load creep tests. This indicates that the power law breakdown behaviour observed in creep tests of copper may be an experimental artefact of constant load creep testing rather than a true physical phenomenon. More specifically power law creep behaviour was evaluated at 75, 100 and 150 deg C where experimental data is inaccessible within a reasonable time scale. With access to the power-law creep relations at low temperature it is possible to make an estimate of the creep life of the copper canister based on the theory for void-growth controlled creep fracture by Cocks and Ashby.

  16. Effect of matrix hardness on the creep properties of a 12CrMoVNb steel

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.S.; Yu, J. [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering


    Using a creep-ductile 12CrMoVNb steel, constant-load creep tests were conducted in air at 650 C, and the effects of matrix hardness on the creep properties were investigated. Specimens with a matrix hardness (Rc) of 30, 25, and 20 were prepared using different tempering conditions. The creep behaviors were well described by the power-law creep equation, with the stress exponents of strain rate (n) and rupture time ({chi}) decreasing with matrix hardness. Rupture-time analyses showed that creep rupture occurred by the nucleation of creep cavities on second-phase particles and growth by creep flow of the surrounding matrix. A hardness decrease tends to lower the rupture time and increase the strain rate ({dot {var_epsilon}}), and the effect of hardness was quite distinct at high applied stresses due to the short creep times, but not so at low applied stresses due to elongated creep times. After 10{sup 4} hours, there were almost no effects. The hardness decrease during the creep test was more severe for the specimens with higher hardness and was also more severe in the gage section than in the head section, the latter due to the stress-assisted diffusion in the coarsening of carbides. Microstructural examinations showed that subgrain boundaries grew during creep, and equiaxed carbide particles coarsened during the creep test, the rates of coarsening being greater for specimens with a higher hardness.

  17. Extreme creep resistance in a microstructurally stable nanocrystalline alloy (United States)

    Darling, K. A.; Rajagopalan, M.; Komarasamy, M.; Bhatia, M. A.; Hornbuckle, B. C.; Mishra, R. S.; Solanki, K. N.


    Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation. Here we show that nanocrystalline copper-tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10-6 per second—six to eight orders of magnitude lower than most nanocrystalline metals—at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of

  18. Extreme creep resistance in a microstructurally stable nanocrystalline alloy. (United States)

    Darling, K A; Rajagopalan, M; Komarasamy, M; Bhatia, M A; Hornbuckle, B C; Mishra, R S; Solanki, K N


    Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation. Here we show that nanocrystalline copper-tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10(-6) per second-six to eight orders of magnitude lower than most nanocrystalline metals-at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of

  19. On-and-off dynamics of a creeping frictional system. (United States)

    Blanc, Baptiste; Géminard, Jean-Christophe; Pugnaloni, Luis A


    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 rest length of the springs, we induce the reptation of the chain. Decreasing the amplitude of the perturbation below a critical value, we observe an intermittent creep regime characterized by alternated periods of reptation (flowing state) and rest (quiescent state). A further decrease of the perturbation leads to the disappearance of the reptation. The width of the transition region between the continuous creep and the full stop (i.e., the range of excitation amplitudes where the intermittent creep is observed) is shown to depend on the difference between the static (μ(s)) and the dynamic (μ(d)) friction coefficients. For μ(s) = μ(d) the intermittent creep is not observed. Studying the statistical features of the intermittent creep regime for any given perturbation amplitude, we find that the time the system resides in each state (flowing or quiescent) suggests that: i) reptation events are uncorrelated, and ii) rest events are history dependent. We show that this latter history dependence is consistent with the aging of the stress state inside the chain of sliders during the quiescent periods.


    Directory of Open Access Journals (Sweden)

    Najat J. Saleh


    Full Text Available Inpresent work tubular –shaped fiber reinforced composites were manufactured byusing two types of resins ( Epoxy and unsaturated polyester and separatelyreinforced with glass, carbon and kevlar-49 fibers (filament and woven roving,hybrid reinforcement composites of these fibers were also prepared. The fiberswere wet wound on a mandrel using a purposely designed winding machine,developed by modifying an ordinary lathe, in winding angle of 55° for filament. A creep test was made of either the fulltube or specimens taken from it. Creep was found to increase upon reinforcementin accordance to the rule of mixture and mainly decided by the type of singleor hybridized fibers. The creep behavior, showed that the observed strain tendsto appear much faster at higher temperature as compared with that exhibited atroom temperate. The creep rate also found to be depending on fiber type, matrixtype, and the fiber /matrix bonding. The creep energy calculated fromexperimental observations was found to exhibit highest value for hybridizedreinforcement.

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

    CERN Document Server

    American Society for Testing and Materials. Philadelphia


    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...

  2. Understanding the mechanisms of amorphous creep through molecular simulation. (United States)

    Cao, Penghui; Short, Michael P; Yip, Sidney


    Molecular processes of creep in metallic glass thin films are simulated at experimental timescales using a metadynamics-based atomistic method. Space-time evolutions of the atomic strains and nonaffine atom displacements are analyzed to reveal details of the atomic-level deformation and flow processes of amorphous creep in response to stress and thermal activations. From the simulation results, resolved spatially on the nanoscale and temporally over time increments of fractions of a second, we derive a mechanistic explanation of the well-known variation of creep rate with stress. We also construct a deformation map delineating the predominant regimes of diffusional creep at low stress and high temperature and deformational creep at high stress. Our findings validate the relevance of two original models of the mechanisms of amorphous plasticity: one focusing on atomic diffusion via free volume and the other focusing on stress-induced shear deformation. These processes are found to be nonlinearly coupled through dynamically heterogeneous fluctuations that characterize the slow dynamics of systems out of equilibrium.

  3. Creep Behaviour of Fly Ash-Based Geopolymer Concrete

    Directory of Open Access Journals (Sweden)

    Wallah S.E.


    Full Text Available Fly ash-based geopolymer concrete is manufactured using fly ash as its source material and does not use Portland cement at all. Beside fly ash, alkaline solution is also utilized to make geopolymer paste which binds the aggregates to form geopolymer concrete. This paper presents the study of creep behaviour of fly ash-based geopolymer concrete. Four series of specimens with various compressive strengths were prepared to study its creep behaviour for the duration of test up to one year. The test method followed the procedures applied for Ordinary Portland Cement (OPC concrete. Test results show that fly ash-based geopolymer concrete undergoes low creep which is generally less than that of OPC concrete. After one year of loading, the results for specific creep of fly ash-based geopolymer concrete in this study ranges from 15 to 29 microstrain for concrete compressive strength 67–40 MPa respectively. From the test results, it is also found out that the creep coefficient of fly ash-based geopolymer concrete is about half of that predicted using Gilbert’s Method for OPC concrete.

  4. Cumulative creep damage for unidirectional composites under step loading (United States)

    Guedes, Rui Miranda


    The creep lifetime prediction of unidirectional composite materials under step loading, based on constant loading durability diagram, is analyzed for the two-step creep loading condition. For this purpose different nonlinear cumulative-damage laws are revisited and applied to predict creep lifetime. One possible approach to accounting for damage accumulation is provided by the continuum-damage mechanics (CDM). However, the CDM lifetime expression obtained for constant loading condition presents some drawbacks. Specifically, the upper stress range is not accommodated by CDM form. A modification of CDM is proposed, forcing the CDM to capture the short-term creep failure. It is proven that this modified CDM (MCDM) does not yield the same predictions as the Linear Cumulative-damage law (Miner's law). Predictions obtained from the nonlinear cumulative-damage laws are compared against synthetic lifetime generated by a micromechanical model that simulates unidirectional composites under two-step creep loading condition. Comparable deviations from Miner's law are obtained by the nonlinear cumulative-damage laws.

  5. Creep-resistant, cobalt-free alloys for high temperature, liquid-salt heat exchanger systems

    Energy Technology Data Exchange (ETDEWEB)

    Holcomb, David E; Muralidharan, Govindarajan; Wilson, Dane F.


    An essentially Fe- and Co-free alloy is composed essentially of, in terms of weight percent: 6.0 to 7.5 Cr, 0 to 0.15 Al, 0.5 to 0.85 Mn, 11 to 19.5 Mo, 0.03 to 4.5 Ta, 0.01 to 9 W, 0.03 to 0.08 C, 0 to 1 Re, 0 to 1 Ru, 0 to 0.001 B, 0.0005 to 0.005 N, balance Ni, the alloy being characterized by, at C., a yield strength of at least 25 Ksi, a tensile strength of at least 38 Ksi, a creep rupture life at 12 Ksi of at least 25 hours, and a corrosion rate, expressed in weight loss [g/(cm.sup.2 sec)]10.sup.-11 during a 1000 hour immersion in liquid FLiNaK at C., in the range of 3 to 10.

  6. Creep Tests and Modeling Based on Continuum Damage Mechanics for T91 and T92 Steels (United States)

    Pan, J. P.; Tu, S. H.; Zhu, X. W.; Tan, L. J.; Hu, B.; Wang, Q.


    9-11%Cr ferritic steels play an important role in high-temperature and high-pressure boilers of advanced power plants. In this paper, a continuum damage mechanics (CDM)-based creep model was proposed to study the creep behavior of T91 and T92 steels at high temperatures. Long-time creep tests were performed for both steels under different conditions. The creep rupture data and creep curves obtained from creep tests were captured well by theoretical calculation based on the CDM model over a long creep time. It is shown that the developed model is able to predict creep data for the two ferritic steels accurately up to tens of thousands of hours.

  7. Creep simulation of adhesively bonded joints using modified generalized time hardening model

    Energy Technology Data Exchange (ETDEWEB)

    Sadigh, Mohammad Ali Saeimi [Azarbaijan Shahid Madani University, Tabriz (Iran, Islamic Republic of)


    Creep behavior of double lap adhesively bonded joints was investigated using experimental tests and numerical analysis. Firstly, uniaxial creep tests were carried out to obtain the creep characteristics and constitutive parameters of the adhesive at different stress and temperature levels. Generalized time hardening model was used to predict the creep behavior of the adhesive. This model was modified to simulate the creep behavior at different stress and temperature levels. Secondly, the developed model was used to simulate the creep behavior of bonded joints using finite element based numerical analysis. Creep deformations of the joints were measured experimentally and good agreement was observed in comparison with the results obtained using numerical simulation. Afterward, stress redistribution due to the creep along the adhesively bonded joint was obtained numerically. It was observed that temperature level had a significant effect on the stress redistribution along the adhesive thickness.

  8. Nuclear Energy Research Initiative Program (NERI) Quarterly Progress Report; New Design Equations for Swelling and Irradiation Creep in Generation IV Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Wolfer, W G; Surh, M P; Garner, F A; Chrzan, D C; Schaldach, C; Sturgeon, J B


    The objectives of this research project are to significantly extend the theoretical foundation and the modeling of radiation-induced microstructural changes in structural materials used in Generation IV nuclear reactors, and to derive from these microstructure models the constitutive laws for void swelling, irradiation creep and stress-induced swelling, as well as changes in mechanical properties. The need for the proposed research is based on three major developments and advances over the past two decades. First, new experimental discoveries have been made on void swelling and irradiation creep which invalidate previous theoretical models and empirical constitutive laws for swelling and irradiation creep. Second, recent advances in computational methods and power make it now possible to model the complex processes of microstructure evolution over long-term neutron exposures. Third, it is now required that radiation-induced changes in structural materials over extended lifetimes be predicted and incorporated in the design of Generation IV reactors. Our approach to modeling and data analysis is a dual one in accord with both the objectives to simulate the evolution of the microstructure and to develop design equations for macroscopic properties. Validation of the models through data analysis is therefore carried out at both the microscopic and the macroscopic levels. For the microstructure models, we utilize the transmission electron microscopy results from steels irradiated in reactors and from model materials irradiated by neutrons as well as ion bombardments. The macroscopic constitutive laws will be tested and validated by analyzing density data, irradiation creep data, diameter changes of fuel elements, and post-irradiation tensile data. Validation of both microstructure models and macroscopic constitutive laws is a more stringent test of the internal consistency of the underlying science for radiation effects in structural materials for nuclear reactors.

  9. High temperature tensile properties of V-4Cr-4Ti

    Energy Technology Data Exchange (ETDEWEB)

    Zinkle, S.J.; Rowcliffe, A.F.; Stevens, C.O. [Oak Ridge National Lab., TN (United States)


    Tensile tests have been performed on V-4Cr-4Ti at 750 and 800 C in order to extend the data base beyond the current limit of 700 C. From comparison with previous measurements, the yield strength is nearly constant and tensile elongations decrease slightly with increasing temperature between 300 and 800 C. The ultimate strength exhibits an apparent maximum near 600 C (attributable to dynamic strain aging) but adequate strength is maintained up to 800 C. The reduction in area measured on tensile specimens remained high ({approximately}80%) for test temperatures up to 800 C, in contrast to previous reported results.

  10. Tensile-stressed microelectromechanical apparatus and tiltable micromirrors formed therefrom (United States)

    Fleming, James G.


    A microelectromechanical (MEM) apparatus is disclosed which includes a pair of tensile-stressed actuators suspending a platform above a substrate to tilt the platform relative to the substrate. A tensile stress built into the actuators initially tilts the platform when a sacrificial material used in fabrication of the MEM apparatus is removed. Further tilting of the platform can occur with a change in the ambient temperature about the MEM apparatus, or by applying a voltage to one or both of the tensile-stressed actuators. The MEM apparatus can be used to form a tiltable micromirror or an array of such devices, and also has applications for thermal management within satellites.

  11. Elevated Temperature Tensile Tests on DU–10Mo Rolled Foils

    Energy Technology Data Exchange (ETDEWEB)

    Schulthess, Jason [Idaho National Lab. (INL), Idaho Falls, ID (United States)


    Tensile mechanical properties for uranium-10 wt.% molybdenum (U–10Mo) foils are required to support modeling and qualification of new monolithic fuel plate designs. It is expected that depleted uranium-10 wt% Mo (DU–10Mo) mechanical behavior is representative of the low enriched U–10Mo to be used in the actual fuel plates, therefore DU-10Mo was studied to simplify material processing, handling, and testing requirements. In this report, tensile testing of DU-10Mo fuel foils prepared using four different thermomechanical processing treatments were conducted to assess the impact of foil fabrication history on resultant tensile properties.

  12. Effect of normalizing temperature on microstructural stability and mechanical properties of creep strength enhanced ferritic P91 steel

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, C.; Giri, A.; Mahapatra, M.M.


    Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied. - Highlights: • SEM-EDS analysis of P91 steel precipitates present at grain boundary and grain interior were carried out. • For constant tempering time effect of normalizing temperature on precipitate size, particle-to particle distance, and grain size were carried out. • Effect of normalizing temperature on tensile strength, yield strength, hardness, % elongation and % reduction of area of P91 steel were studied. • For constant tempering time effect of normalizing temperature on room temperature impact toughness of P91 steel were studied. Fracture surface after impact testing were also characterized by using SEM. • Fracture surface after room temperature tensile testing were also characterized by using SEM to study the effect of normalizing temperature on fracture surface.

  13. 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


    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

  14. Effects of segregation of primary alloying elements on the creep response in magnesium alloys

    DEFF Research Database (Denmark)

    Huang, Y.D.; Dieringa, H.; Hort, N.


    The segregation of primary alloying elements deteriorates the high temperature creep resistance of magnesium alloys. Annealing at high temperatures alleviating their segregations can improve the creep resistance. Present investigation on the effect of segregation of primary alloying elements...... on the creep response may provide some useful information about how to improve the creep resistance of magnesium alloys in the future. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved....

  15. Creep of SiC Hot-Pressed with Al, B, and C

    Energy Technology Data Exchange (ETDEWEB)

    Sixta, Mark Eldon [Univ. of California, Berkeley, CA (United States)


    The creep of a high strength, high toughness SiC, sintered with Al, B, and C was investigated. For elevated temperature applications, the time-dependent deformation, creep response, must be fully characterized for candidate materials. The mechanisms responsible for high temperature deformation in ABC-SiC were evaluated. The creep response was compared to materials that have glassy grain boundary phases but do not have interlocked grains. The creep mechanisms were assessed.

  16. Physical-Mechanism Exploration of the Low-Cycle Unified Creep-Fatigue Formulation


    Dan Liu; Dirk John Pons


    Background—Creep-fatigue behavior is identified as the incorporated effects of fatigue and creep. One class of constitutive-based models attempts to evaluate creep and fatigue separately, but the interaction of fatigue and creep is neglected. Other models treat the damage as a single component, but the complex numerical structures that result are inconvenient for engineering application. The models derived through a curve-fitting method avoid these problems. However, the method of curving fit...

  17. In-situ electron microscopy studies on the tensile deformation mechanisms in aluminium 5083 alloy

    CSIR Research Space (South Africa)

    Motsi, G


    Full Text Available In this study tensile deformation mechanisms of aluminium alloy 5083 were investigated under observations made from SEM equipped with a tensile stage. Observations during tensile testing revealed a sequence of surface deformation events...

  18. Constitutive Modeling of High Temperature Uniaxial Creep-Fatigue and Creep-Ratcheting Responses of Alloy 617

    Energy Technology Data Exchange (ETDEWEB)

    P.G. Pritchard; L.J. Carroll; T. Hassan


    Inconel Alloy 617 is a high temperature creep and corrosion resistant alloy and is a leading candidate for use in Intermediate Heat Exchangers (IHX) of the Next Generation Nuclear Plants (NGNP). The IHX of the NGNP is expected to experience operating temperatures in the range of 800 degrees - 950 degrees C, which is in the creep regime of Alloy 617. A broad set of uniaxial, low-cycle fatigue, fatigue-creep, ratcheting, and ratcheting-creep experiments are conducted in order to study the fatigue and ratcheting responses, and their interactions with the creep response at high temperatures. A unified constitutive model developed at North Carolina State University is used to simulate these experimental responses. The model is developed based on the Chaboche viscoplastic model framework. It includes cyclic hardening/softening, strain rate dependence, strain range dependence, static and dynamic recovery modeling features. For simulation of the alloy 617 responses, new techniques of model parameter determination are developed for optimized simulations. This paper compares the experimental responses and model simulations for demonstrating the strengths and shortcomings of the model.


    Directory of Open Access Journals (Sweden)

    Hana Staneková


    Full Text Available The effect of long-term creep exposure on the microstructure stability of a new cast air-hardenable intermetallic alloy with nominal chemical composition Ti-46Al-8Ta (at .% was studied. Constat load creep test were performed at the temperature 750°C and at applied stress 250 MPa up to 3479,3 h. The initial gama(TiAl + alpha2(Ti3Al microstructure of the alloy is unstable and transforms to alpha2 + gama + tau type. During creep the formation of cavities along the lamellar colony and grain boundaries is observed. The specimens fail by the growth and coalescence of such cavities with intergranular type of fracture.

  20. Time of creep fracture of axisymmetrically loaded structures (United States)

    Banshchikova, I. A.; Lubashevskaya, I. V.


    A stress-strain state and a time duration up to fracture are calculated with allowance for two-stage behavior of a rotating disk under creep conditions. The duration of the stages is investigated depending on the choice of the version of the creep kinetic theory and the geometric dimensions of the disk. The first stage is the accumulation of damage and the beginning of fracture in some area of the body, where the accumulated damage reaches a critical value. The second stage is the spread of the fracture front and the complete destruction of the body. A calculation method has been developed which reduces the solution of the unsteady-state creep problem to the solution of an analogous steady-state problem.

  1. Standard test method for creep-fatigue testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia


    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 ...

  2. Creep Burst Testing of a Woven Inflatable Module (United States)

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


    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. 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)


    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.

  4. Thermomechanical fatigue, oxidation, and Creep: Part II. Life prediction (United States)

    Neu, R. W.; Sehitoglu, Huseyin


    A life prediction model is developed for crack nucleation and early crack growth based on fatigue, environment (oxidation), and creep damage. The model handles different strain-temperature phasings (i.e., in-phase and out-of-phase thermomechanical fatigue, isothermal fatigue, and others, including nonproportional phasings). Fatigue life predictions compare favorably with experiments in 1070 steel for a wide range of test conditions and strain-temperature phasings. An oxide growth (oxide damage) model is based on the repeated microrupture process of oxide observed from microscopic measurements. A creep damage expression, which is stress-based, is coupled with a unified constitutive equation. A set of interrupted tests was performed to provide valuable damage progression information. Tests were performed in air and in helium atmospheres to isolate creep damage from oxidation damage.

  5. Microstructural Effects on Creep-Fatigue Life of Alloy 709

    Energy Technology Data Exchange (ETDEWEB)

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


    Creep-fatigue tests were performed on plates of Alloy 709 from various heats and processing conditions, but often with inhomogeneous microstructures. After testing, metallographic analysis was performed and the specimens were generally found to either have a uniform grain size or a bimodal grain size distribution with either isolated or groups (bands) of large grains. Creep-fatigue life was characterized with respect to the length of the grain boundary perpendicular to the stress axis, and it was found that large grains (>400 μm) tended to be detrimental to creep-fatigue life, with the exception of elongated (parallel to the stress axis) grains and some specimens that underwent additional annealing.

  6. Salt creep and wicking counteract hydrophobic organic structures (United States)

    Burkhardt, Juergen


    The hydrophobic nature of many biological and edaphic surfaces prevents wetting and water movement. Already small amounts of salts and other hygroscopic material (e.g. by aerosol deposition to leaf surfaces) may change this situation. Salts attract minute amounts of liquid water to the surface and may dynamically expand on the original surface by creeping (evaporation-driven extension of crystals). Creeping is governed by fluctuations of relative humidity and increases with time. Under high, almost saturated concentrations of the salt solutions, ions from the chaotropic side of the Hofmeister series creep most efficiently. Once established, continuous salt connections may act to channel small water flows along the surface. They may act as wicks if water is removed from one side by evaporation. Stomata may in this way become 'leaky' by the leaf surface accumulation of hygroscopic aerosols.

  7. Probability based high temperature engineering creep and structural fire resistance

    CERN Document Server

    Razdolsky, Leo


    This volume on structural fire resistance is for aerospace, structural, and fire prevention engineers; architects, and educators. It bridges the gap between prescriptive- and performance-based methods and simplifies very complex and comprehensive computer analyses to the point that the structural fire resistance and high temperature creep deformations will have a simple, approximate analytical expression that can be used in structural analysis and design. The book emphasizes methods of the theory of engineering creep (stress-strain diagrams) and mathematical operations quite distinct from those of solid mechanics absent high-temperature creep deformations, in particular the classical theory of elasticity and structural engineering. Dr. Razdolsky’s previous books focused on methods of computing the ultimate structural design load to the different fire scenarios. The current work is devoted to the computing of the estimated ultimate resistance of the structure taking into account the effect of high temperatur...

  8. Power-law creep and residual stresses in carbopol microgels (United States)

    Lidon, Pierre; Manneville, Sebastien

    We report on the interplay between creep and residual stresses in carbopol microgels. When a constant shear stress σ is applied below the yield stress σc, the strain is shown to increase as a power law of time, γ (t) =γ0 +(t / τ) α , with and exponent α ~= 0 . 38 that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some characteristic value of about σc / 10 , the microgels experience a more complex creep behavior that we link to the existence of residual stresses and to weak aging of the system after preshear. The influence of the preshear protocol, of boundary conditions and of microgel concentration on residual stresses is investigated. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.

  9. Creep Behavior of ABS Polymer in Temperature-Humidity Conditions (United States)

    An, Teagen; Selvaraj, Ramya; Hong, Seokmoo; Kim, Naksoo


    Acrylonitrile-Butadiene-Styrene (ABS), also known as a thermoplastic polymer, is extensively utilized for manufacturing home appliances products as it possess impressive mechanical properties, such as, resistance and toughness. However, the aforementioned properties are affected by operating temperature and atmosphere humidity due to the viscoelasticity property of an ABS polymer material. Moreover, the prediction of optimum working conditions are the little challenging task as it influences the final properties of product. This present study aims to develop the finite element (FE) models for predicting the creep behavior of an ABS polymeric material. In addition, the material constants, which represent the creep properties of an ABS polymer material, were predicted with the help of an interpolation function. Furthermore, a comparative study has been made with experiment and simulation results to verify the accuracy of developed FE model. The results showed that the predicted value from FE model could agree well with experimental data as well it can replicate the actual creep behavior flawlessly.

  10. Creep of thermoplastic polyurethane reinforced with ozone functionalized carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Z. Zhang


    Full Text Available This work focused on the mechanical behavior, especially creep resistance, of thermoplastic polyurethane (TPU filled with ozone-treated multi-walled carbon nanotubes (MWCNTs. It was found that the ozone functionalization of MWCNTs could improve their dispersion and interfacial adhesion to the TPU matrix as proved by scanning electron microscope and Raman spectrometer. It finally contributed to the enhancement of Young’s modulus and yield strength of TPU/MWCNT composites. Moreover, the creep resistance and recovery of MWCNT/TPU composites revealed a significant improvement by incorporating ozone functionalized MWCNTs. The strong interaction between the modified MWCNTs and TPU matrix would enhance the interfacial bonding and facilitate the load transfer, resulting in low creep strain and unrecovered strain.

  11. Effect of fine {gamma}' precipitation on non-isothermal creep and creep-fatigue behaviour of nickel base superalloy MC2

    Energy Technology Data Exchange (ETDEWEB)

    Le Graverend, J.-B., E-mail: [Office National d' Etudes et de Recherches Aerospatiales, 29 avenue de la Division Leclerc, BP 72, 92322 Chatillon (France); Institut Pprime CNRS-ENSMA-Universite de Poitiers, Departement Physique et Mecanique des Materiaux, ENSMA-Teleport 2, 1 avenue Clement Ader, BP 40109, F86961 FUTUROSCOPE CHASSENEUIL cedex (France); Cormier, J.; Jouiad, M. [Institut Pprime CNRS-ENSMA-Universite de Poitiers, Departement Physique et Mecanique des Materiaux, ENSMA-Teleport 2, 1 avenue Clement Ader, BP 40109, F86961 FUTUROSCOPE CHASSENEUIL cedex (France); Gallerneau, F.; Paulmier, P. [Office National d' Etudes et de Recherches Aerospatiales, 29 avenue de la Division Leclerc, BP 72, 92322 Chatillon (France); Hamon, F. [Institut Pprime CNRS-ENSMA-Universite de Poitiers, Departement Physique et Mecanique des Materiaux, ENSMA-Teleport 2, 1 avenue Clement Ader, BP 40109, F86961 FUTUROSCOPE CHASSENEUIL cedex (France)


    A novel technique, combining on the one hand creep-fatigue tests with an overheating and creep tests with thermal cycling in the other hand, performed on {gamma}/{gamma}' nickel base single crystal superalloy MC2 have led to an increased understanding of fine {gamma}' precipitation and its strengthening effect. Both creep and creep-fatigue tests were conducted at 1050 deg. C with 1200 deg. C overheating for creep-fatigue experiments and with repeated overheatings at 1100 deg. C and 1150 deg. C for creep. The resulting microstructures of these experiments were examined using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It appears, both on creep or creep-fatigue, once an overheating is experienced a fine {gamma}' precipitation occurs in {gamma} matrix. These precipitates seem to have a transient strengthening effect on the mechanical properties. For the creep-fatigue experiments a decrease of the plastic strain rate was measured at once after the temperature peak. In the case of the creep tests under thermal cycling, no extra deformation induced by the overheating at 1100 deg. C was recorded. However, overheatings at 1150 deg. C lead to a plastic strain jump which progressively decreases upon thermal cycling, due to the formation of fine {gamma}' precipitates. Furthermore, the {gamma}' fine particles seem to have a hardening effect that vanishes once they dissolve.

  12. 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)


    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.

  13. Does light attract piglets to the creep area? (United States)

    Larsen, M L V; Pedersen, L J


    Hypothermia, experienced by piglets, has been related to piglet deaths and high and early use of a heated creep area is considered important to prevent hypothermia. The aims of the present study were to investigate how a newly invented radiant heat source, eHeat, would affect piglets' use of the creep area and whether light in the creep area works as an attractant on piglets. A total of 39 sows, divided between two batches, were randomly distributed to three heat source treatments: (1) standard infrared heat lamp (CONT, n=19), (2) eHeat with light (EL, n=10) and (3) eHeat without light (ENL, n=10). Recordings of piglets' use of the creep area were made as scan sampling every 10 min for 3 h during two periods, one in daylight (0900 to 1200 h) and one in darkness (2100 to 2400 h), on day 1, 2, 3, 7, 14 and 21 postpartum. On the same days, piglets were weighted. Results showed an interaction between treatment and observation period (PPiglets average daily weight gain was not affected by treatment, but was positively correlated with piglets' birth weight and was lower in batch 1 compared with batch 2. Seen from the present results, neither eHeat nor light worked as an attractant on piglets; in contrast, piglets preferred to sleep in the dark and it would therefore be recommended to turn off the light in the creep area during darkness. Heating up the creep area without light can be accomplished by using a radiant heat source such as eHeat in contrast to the normally used light-emitting infrared heat lamp.

  14. Creep feed intake during lactation enhances net absorption in the small intestine after weaning

    NARCIS (Netherlands)

    Kuller, W.I.; Beers-Schreurs, van H.M.G.; Soede, N.M.; Langendijk, P.; Taverne, M.A.M.; Kemp, B.; Verheijden, J.H.M.


    The aim of the study was to measure the effect of creep feeding during lactation on net absorption in the small intestine at 4 days after weaning. Intermittent suckling was used to increase creep feed intake during lactation. Creep feed containing chromic oxide was provided. Based on the colour of

  15. New constraints on upper mantle creep mechanism inferred from silicon grain-boundary diffusion rates (United States)

    Fei, Hongzhan; Koizumi, Sanae; Sakamoto, Naoya; Hashiguchi, Minako; Yurimoto, Hisayoshi; Marquardt, Katharina; Miyajima, Nobuyoshi; Yamazaki, Daisuke; Katsura, Tomoo


    The creep in the Earth's interior is dominated either by diffusion creep which causes Newtonian mantle flow, or by dislocation creep which results in non-Newtonian mantle flow. Although previous deformation studies on olivine claimed a transition from dislocation creep to diffusion creep with depth in the upper mantle, they might misunderstand the creep rates due to experimental difficulties. Since creep in olivine is controlled by silicon diffusion, we measured the silicon grain-boundary diffusion coefficient in well-sintered iron-free olivine aggregates as a function of temperature, pressure, and water content, showing activation energy, activation volume, and water content exponent of 220 ± 30 kJ /mol, 4.0 ± 0.7 cm3 /mol, and 0.26 ± 0.07, respectively. Our results based on Si diffusion in forsterite predict that diffusion creep dominates at low pressures and low temperatures, whereas dislocation creep dominates under high pressure and high temperature conditions. Water has negligible effects on both diffusion and dislocation creep. There is a transition from diffusion creep in the shallow upper mantle to dislocation creep in deeper regions. This explains the seismic anisotropy increases at the Gutenberg discontinuity beneath oceans and at the mid-lithosphere discontinuity beneath continents.

  16. Creep of polycrystalline yttrium aluminum garnet (YAG) at elevated temperature in air and in steam

    Energy Technology Data Exchange (ETDEWEB)

    Armani, C.J. [Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433-7765 (United States); Ruggles-Wrenn, M.B., E-mail: [Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433-7765 (United States); Hay, R.S.; Fair, G.E. [Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433-7817 (United States); Keller, K.A. [UES Inc., Dayton, OH 45432 (United States)


    Compressive creep of high-purity polycrystalline yttrium aluminum garnet (YAG, Y{sub 3}Al{sub 5}O{sub 12}) was investigated at 1300 °C and 50–200 MPa in air and in steam. Compressive creep behavior of silica-doped polycrystalline YAG (Y{sub 3}Al{sub 5}O{sub 12}–0.14 wt% SiO{sub 2}) was also studied. Creep specimens were microstructurally characterized by optical microscopy and TEM before and after creep. Steam slightly increased creep rates of material with grain size less than 1 μm (the undoped YAG), but otherwise had little effect. The flow stress exponent was n≈1 for both SiO{sub 2}-doped YAG and undoped YAG. Creep rates and microstructural observations are consistent with the Nabarro-Herring creep mechanism, with creep rate limited by lattice diffusion of yttrium cations (Y{sup 3+}). Silica-doped YAG had a larger grain size of 2.41 μm and lower creep rates than undoped YAG with 0.92 μm grain size. However, creep rates normalized by grain size for Nabarro-Herring creep were higher in SiO{sub 2}-doped YAG. Possible effects of SiO{sub 2} doping and steam on creep of YAG are discussed.

  17. Biaxial Thermal Creep of Alloy 617 and Alloy 230 for VHTR Applications

    Energy Technology Data Exchange (ETDEWEB)

    Mo, Kun; Lv, Wei; Tung, Hsiao-Ming; Yun, Di; Miao, Yinbin; Lan, Kuan-Che; Stubbins, James F.


    In this study, we employed pressurized creep tubes to investigate the biaxial thermal creep behavior of Inconel 617 (alloy 617) and Haynes 230 (alloy 230). Both alloys are considered to he the primary candidate structural materials for very high-temperature reactors (VITITRs) due to their exceptional high-temperature mechanical properties. The current creep experiments were conducted at 900 degrees C for the effective stress range of 15-35 MPa. For both alloys, complete creep strain development with primary, secondary, and tertiary regimes was observed in all the studied conditions. Tertiary creep was found to he dominant over the entire creep lives of both alloys. With increasing applied creep stress, the fraction of the secondary creep regime decreases. The nucleation, diffusion, and coarsening of creep voids and carbides on grain boundaries were found to be the main reasons for the limited secondary regime and were also found to be the major causes of creep fracture. The creep curves computed using the adjusted creep equation of the form epsilon= cosh 1(1 rt) + P-sigma ntm agree well with the experimental results for both alloys at die temperatures of 850-950 degrees C.

  18. 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)


    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.

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

    Directory of Open Access Journals (Sweden)

    Yingchong Wang


    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.

  20. Nano-scale simulation based study of creep behavior of bimodal nanocrystalline face centered cubic metal. (United States)

    Meraj, Md; Pal, Snehanshu


    In this paper, the creep behavior of nanocrystalline Ni having bimodal grain structure is investigated using molecular dynamics simulation. Analysis of structural evolution during the creep process has also been performed. It is observed that an increase in size of coarse grain causes improvement in creep properties of bimodal nanocrystalline Ni. Influence of bimodality (i.e., size difference between coarse and fine grains) on creep properties are found to be reduced with increasing creep temperature. The dislocation density is observed to decrease exponentially with progress of creep deformation. Grain boundary diffusion controlled creep mechanism is found to be dominant at the primary creep region and the initial part of the secondary creep region. After that shear diffusion transformation mechanism is found to be significantly responsible for deformation as bimodal nanocrystalline Ni transforms to amorphous structure with further progress of the creep process. The presence of , , and  distorted icosahedra has a significant influence on creep rate in the tertiary creep regime according to Voronoi cluster analysis.

  1. Hindsight Bias Doesn't Always Come Easy: Causal Models, Cognitive Effort, and Creeping Determinism (United States)

    Nestler, Steffen; Blank, Hartmut; von Collani, Gernot


    Creeping determinism, a form of hindsight bias, refers to people's hindsight perceptions of events as being determined or inevitable. This article proposes, on the basis of a causal-model theory of creeping determinism, that the underlying processes are effortful, and hence creeping determinism should disappear when individuals lack the cognitive…

  2. On accounting for tempering effect in unsteady creep model for metals

    Directory of Open Access Journals (Sweden)

    Volkov Ivan


    Full Text Available A mathematical model describing processes of nonstationary creep of metals under multiaxial stress state is developed. A phenomenon of reverse creep modeling is considered in more details. The results of numerical modeling of the reverse creep process in variety of structural steels are presented. Obtained numerical results are compared with available results of physical experiments.

  3. A fractional derivative approach to full creep regions in salt rock (United States)

    Zhou, H. W.; Wang, C. P.; Mishnaevsky, L.; Duan, Z. Q.; Ding, J. Y.


    Based on the definition of the constant-viscosity Abel dashpot, a new creep element, referred to as the variable-viscosity Abel dashpot, is proposed to characterize damage growth in salt rock samples during creep tests. Ultrasonic testing is employed to determine a formula of the variable viscosity coefficient, indicating that the change of the variable viscosity coefficient with the time meets a negative exponent law. In addition, by replacing the Newtonian dashpot in the classical Nishihara model with the variable-viscosity Abel dashpot, a damage-mechanism-based creep constitutive model is proposed on the basis of time-based fractional derivative. The analytic solution for the fractional-derivative creep constitutive model is presented. The parameters of the fractional derivative creep model are determined by the Levenberg-Marquardt method on the basis of the experimental results of creep tests on salt rock. Furthermore, a sensitivity study is carried out, showing the effects of stress level, fractional derivative order and viscosity coefficient exponent on creep strain of salt rock. It is indicated that the fractional derivative creep model proposed in the paper provides a precise description of full creep regions in salt rock, i.e., the transient creep region (the primary region), the steady-state creep region (the secondary region) and the accelerated creep region (the tertiary region).

  4. Mechanical properties of graphene nanoribbons under uniaxial tensile strain (United States)

    Yoneyama, Kazufumi; Yamanaka, Ayaka; Okada, Susumu


    Based on the density functional theory with the generalized gradient approximation, we investigated the mechanical properties of graphene nanoribbons in terms of their edge shape under a uniaxial tensile strain. The nanoribbons with armchair and zigzag edges retain their structure under a large tensile strain, while the nanoribbons with chiral edges are fragile against the tensile strain compared with those with armchair and zigzag edges. The fracture started at the cove region, which corresponds to the border between the zigzag and armchair edges for the nanoribbons with chiral edges. For the nanoribbons with armchair edges, the fracture started at one of the cove regions at the edges. In contrast, the fracture started at the inner region of the nanoribbons with zigzag edges. The bond elongation under the tensile strain depends on the mutual arrangement of covalent bonds with respect to the strain direction.

  5. Infliximab treatment reduces tensile strength in intestinal anastomosis

    DEFF Research Database (Denmark)

    Jensen, Jonas Sanberg; Petersen, Nacie Bello; Biagini, Matteo


    :1) to receive either repeated IFX treatment or placebo. On day 15, three separate end-to-end anastomoses were performed on the jejunum. On postoperative day 5, tensile strength and bursting pressure for the anastomoses were tested and histologic changes examined. RESULTS: We found a significantly reduced...... tensile strength in the IFX group (1.94 +/- 0.44 N) compared with the placebo group (3.33 +/- 0.39 N), (P tensile strength and serum values of IFX (coefficient = -0.63; P = 0.003) as well...... as number of sutures in the tested anastomosis (coefficient = 0.51; P = 0.024). The general histologic score was significantly higher in the placebo group (5.00 +/- 1.26 versus 3.31 +/- 1.65, P = 0.03). CONCLUSIONS: Repeated high-dose IFX treatment reduces tensile strength significantly in rabbits...

  6. Creep analysis of fuel plates for the Advanced Neutron Source

    Energy Technology Data Exchange (ETDEWEB)

    Swinson, W.F.; Yahr, G.T.


    The reactor for the planned Advanced Neutron Source will use closely spaced arrays of fuel plates. The plates are thin and will have a core containing enriched uranium silicide fuel clad in aluminum. The heat load caused by the nuclear reactions within the fuel plates will be removed by flowing high-velocity heavy water through narrow channels between the plates. However, the plates will still be at elevated temperatures while in service, and the potential for excessive plate deformation because of creep must be considered. An analysis to include creep for deformation and stresses because of temperature over a given time span has been performed and is reported herein.

  7. Oxidation resistant high creep strength austenitic stainless steel (United States)

    Brady, Michael P.; Pint, Bruce A.; Liu, Chain-Tsuan; Maziasz, Philip J.; Yamamoto, Yukinori; Lu, Zhao P.


    An austenitic stainless steel displaying high temperature oxidation and creep resistance has a composition that includes in weight percent 15 to 21 Ni, 10 to 15 Cr, 2 to 3.5 Al, 0.1 to 1 Nb, and 0.05 to 0.15 C, and that is free of or has very low levels of N, Ti and V. The alloy forms an external continuous alumina protective scale to provide a high oxidation resistance at temperatures of 700 to C. and forms NbC nanocarbides and a stable essentially single phase fcc austenitic matrix microstructure to give high strength and high creep resistance at these temperatures.

  8. A damage model of creep crack growth in polycrystals (United States)

    Thouless, M. D.; Hsueh, C. H.; Evans, A. G.


    Cocks and Ashby (1982) have derived a simplified constrained crack growth model for a polycrystalline material subject to power law creep. A generalized damage mechanism is considered, and it is required that the damage rate be dictated by the creep rate of the material ahead of the crack tip. This premise results in an upper bound constraint. The present investigation is concerned with an extension of the crack growth concepts considered in the model. Attention is given to a mechanism involving diffusive cavitation ahead of the crack in a polycrystalline, linear viscous material. Implications for the resulting crack velocity are also discussed.

  9. Covalent Crosslinking of Carbon Nanotube Materials for Improved Tensile Strength (United States)

    Baker, James S.; Miller, Sandi G.; Williams, Tiffany A.; Meador, Michael A.


    Carbon nanotubes have attracted much interest in recent years due to their exceptional mechanical properties. Currently, the tensile properties of bulk carbon nanotube-based materials (yarns, sheets, etc.) fall far short of those of the individual nanotube elements. The premature failure in these materials under tensile load has been attributed to inter-tube sliding, which requires far less force than that needed to fracture individual nanotubes.1,2 In order for nanotube materials to achieve their full potential, methods are needed to restrict this tube-tube shear and increase inter-tube forces.Our group is examining covalent crosslinking between the nanotubes as a means to increase the tensile properties of carbon nanotube materials. We are working with multi-walled carbon nanotube (MWCNT) sheet and yarn materials obtained from commercial sources. Several routes to functionalize the nanotubes have been examined including nitrene, aryl diazonium, and epoxide chemistries. The functional nanotubes were crosslinked through small molecule or polymeric bridges. Additionally, electron beam irradiation induced crosslinking of the non-functional and functional nanotube materials was conducted. For example, a nanotube sheet material containing approximately 3.5 mol amine functional groups exhibited a tensile strength of 75 MPa and a tensile modulus of 1.16 GPa, compared to 49 MPa and 0.57 GPa, respectively, for the as-received material. Electron beam irradiation (2.2x 1017 ecm2) of the same amine-functional sheet material further increased the tensile strength to 120 MPa and the modulus to 2.61 GPa. This represents approximately a 150 increase in tensile strength and a 360 increase in tensile modulus over the as-received material with only a 25 increase in material mass. Once we have optimized the nanotube crosslinking methods, the performance of these materials in polymer matrix composites will be evaluated.

  10. Ply Tensile Properties of Banana Stem and Banana Bunch Fibres ...

    African Journals Online (AJOL)

    Natural rubber composite lamina reinforced with BSF which were treated with a mixture of NaOH and Na2SO3 had a superior tensile strength of 4.0 MPa and Young's modulus of 147.34MPa over the untreated BSF with tensile strength and Young's Modulus of 3.7MPa and 84.30MPa respectively. Both the treated and ...

  11. Fault creep and strain partitioning in Trinidad-Tobago: Geodetic measurements, models, and origin of creep (United States)

    Geirsson, Halldór; Weber, John; La Femina, Peter; Latchman, Joan L.; Robertson, Richard; Higgins, Machel; Miller, Keith; Churches, Chris; Shaw, Kenton


    We studied active faults in Trinidad and Tobago in the Caribbean-South American (CA-SA) transform plate boundary zone using episodic GPS (eGPS) data from 19 sites and continuous GPS (cGPS) data from 8 sites, then modeling these data using a series of simple screw dislocation models. Our best-fit model for interseismic fault slip requires: 12-15 mm/yr of right-lateral movement and very shallow locking (0.2 ± 0.2 km; essentially creep) across the Central Range Fault (CRF); 3.4 +0.3/-0.2 mm/yr across the Soldado Fault in south Trinidad, and 3.5 +0.3/-0.2 mm/yr of dextral shear on fault(s) between Trinidad and Tobago. The upper-crustal faults in Trinidad show very little seismicity (1954-current from local network) and do not appear to have generated significant historic earthquakes. However, paleoseismic studies indicate that the CRF ruptured between 2710 and 500 yr. B.P. and thus it was recently capable of storing elastic strain. Together, these data suggest spatial and/or temporal fault segmentation on the CRF. The CRF marks a physical boundary between rocks associated with thermogenically generated petroleum and overpressured fluids in south and central Trinidad, from rocks containing only biogenic gas to the north, and a long string of active mud volcanoes align with the trace of the Soldado Fault along Trinidad's south coast. Fluid (oil and gas) overpressure may thus cause the CRF fault creep that we observe and the lack of seismicity, as an alternative or addition to weak mineral phases on the fault.

  12. Present Development Status of Anti-creep Magnesium Rare-Earth Alloys (United States)

    Gui, Yunwei; Li, Quanan; Chen, Xiaoya


    The research status of creep resistance of rare earth magnesium alloy at home and abroad is reviewed, and the mechanism of high temperature creep resistance and the way of improving the creep resistance of magnesium alloy were also discussed. The problems of high temperature resistance and creep resistance of cast magnesium alloy are pointed out, and its future development direction is forecasted. The purpose of this paper is to provide the idea and basis for the development of creep resistant and heat resistant magnesium alloy.

  13. A fractional derivative approach to full creep regions in salt rock

    DEFF Research Database (Denmark)

    Zhou, H. W.; Wang, C. P.; Mishnaevsky, Leon


    on the basis of time-based fractional derivative. The analytic solution for the fractional-derivative creep constitutive model is presented. The parameters of the fractional derivative creep model are determined by the Levenberg–Marquardt method on the basis of the experimental results of creep tests on salt...... rock. Furthermore, a sensitivity study is carried out, showing the effects of stress level, fractional derivative order and viscosity coefficient exponent on creep strain of salt rock. It is indicated that the fractional derivative creep model proposed in the paper provides a precise description...

  14. Creep analysis of boiler tubes by fem | Taye | Zede Journal

    African Journals Online (AJOL)

    In this paper an analysis is developed for the determination of creep deformation of an axisymmetric boiler tubes subjected to axisymmetric loads. The stresses and the permanent strains at a particular time and at the steady state condition, resulting from loading of the tube under constant internal pressure and elevated ...

  15. Creeping Viscous Flow around a Heat-Generating Solid Sphere

    DEFF Research Database (Denmark)

    Krenk, Steen


    The velocity field for creeping viscous flow around a solid sphere due to a spherically symmetric thermal field is determined and a simple thermal generalization of Stokes' formula is obtained. The velocity field due to an instantaneous heat source at the center of the sphere is obtained in close...... form and an application to the storage of heat-generating nuclear waste is discussed....

  16. Mission Creep and Teaching at the Master's University (United States)

    Henderson, Bruce B.


    The accusation of mission creep at master's institutions is not erroneous. It has been occurring for decades. The imitation of the research universities by other institutions is not good for the institutions, for their faculty members, or for the cause of college teaching. Research and scholarship need to be differentiated so that scholarliness,…

  17. Does light attract piglets to the creep area?

    DEFF Research Database (Denmark)

    Larsen, Mona Lilian Vestbjerg; Pedersen, Lene Juul


    Hypothermia, experienced by piglets, has been related to piglet deaths and high and early use of a heated creep area is considered important to prevent hypothermia. The aims of the present study were to investigate how a newly invented radiant heat source, eHeat, would affect piglets' use...... of the creep area and whether light in the creep area works as an attractant on piglets. A total of 39 sows, divided between two batches, were randomly distributed to three heat source treatments: (1) standard infrared heat lamp (CONT, n=19), (2) eHeat with light (EL, n=10) and (3) eHeat without light (ENL, n......=10). Recordings of piglets' use of the creep area were made as scan sampling every 10 min for 3 h during two periods, one in daylight (0900 to 1200 h) and one in darkness (2100 to 2400 h), on day 1, 2, 3, 7, 14 and 21 postpartum. On the same days, piglets were weighted. Results showed an interaction...

  18. Diagnosis of bearing creep in wind turbine gearboxes

    DEFF Research Database (Denmark)

    Skrimpas, Georgios Alexandros; Liu, Zhenyan; Hilmisson, Reynir


    deals with the evaluation of the development of an inner race defect from surface pitting to race axial crack resulting in excessive rotational looseness, also referred to as bearing creep. It is shown that an inner race defect can be identified efficiently at an early stage by employing well known...

  19. Production response of lambs receiving creep feed while grazing ...

    African Journals Online (AJOL)

    The aim of the study was to determine the production responses of lambs receiving either creep feed or not while grazing two different pastures. The production of ewes within each treatment was also recorded. The study was conducted at both the Kromme Rhee and Langgewens Research Farms. At Kromme Rhee, sheep ...

  20. Relating fundamental creep mechanisms in Waspaloy to the Wilshire equations

    Directory of Open Access Journals (Sweden)

    Deen C.


    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, notably those with stresses 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. In particular, the roles of recovery, tertiary gamma prime particles and dislocation foresting are examined, and related back to observations from the Wilshire fits. The virgin (untested material has been forged and heat treated, containing some recrystallised material together with areas of more heavily deformed and recovered material clustered around the grain boundaries. Observations from tests below the 0.2% proof stress show relatively low dislocation densities away from grain boundaries and dislocation movement can be seen to be governed by interactions with the γ′ precipitates. In contrast, above the 0.2% proof stress, TEM observations show a substantially greater density of dislocations. The increased density provides an increment of strength through forest hardening. At stresses above the original yield point, determined by the precipitates, the creep rate is controlled by inter-action with the dislocation forest and results in an apparent activation energy change. 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.

  1. Intermittent flow under constant forcing: Acoustic emission from creep avalanches (United States)

    Salje, Ekhard K. H.; Liu, Hanlong; Jin, Linsen; Jiang, Deyi; Xiao, Yang; Jiang, Xiang


    While avalanches in field driven ferroic systems (e.g., Barkhausen noise), domain switching of martensitic nanostructures, and the collapse of porous materials are well documented, creep avalanches (avalanches under constant forcing) were never observed. Collapse avalanches generate particularly large acoustic emission (AE) signals and were hence chosen to investigate crackling noise under creep conditions. Piezoelectric SiO2 has a strong piezoelectric response even at the nanoscale so that we chose weakly bound SiO2 spheres in natural sandstone as a representative for the study of avalanches under time-independent, constant force. We found highly non-stationary crackling noise with four activity periods, each with power law distributed AE emission. Only the period before the final collapse shows the mean field behavior (ɛ near 1.39), in agreement with previous dynamic measurements at a constant stress rate. All earlier event periods show collapse with larger exponents (ɛ = 1.65). The waiting time exponents are classic with τ near 2.2 and 1.32. Creep data generate power law mixing with "effective" exponents for the full dataset with combinations of mean field and non-mean field regimes. We find close agreement with the predicted time-dependent fiber bound simulations, including events and waiting time distributions. Båth's law holds under creep conditions.

  2. Physical simulations of cavity closure in a creeping material

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, H.J.; Preece, D.S.


    The finite element method has been used extensively to predict the creep closure of underground petroleum storage cavities in rock salt. Even though the numerical modeling requires many simplifying assumptions, the predictions have generally correlated with field data from instrumented wellheads, however, the field data are rather limited. To gain an insight into the behavior of three-dimensional arrays of cavities and to obtain a larger data base for the verification of analytical simulations of creep closure, a series of six centrifuge simulation experiments were performed using a cylindrical block of modeling clay, a creeping material. Three of the simulations were conducted with single, centerline cavities, and three were conducted with a symmetric array of three cavities surrounding a central cavity. The models were subjected to body force loading using a centrifuge. For the single cavity experiments, the models were tested at accelerations of 100, 125 and 150 g's for 2 hours. For the multi-cavity experiments, the simulations were conducted at 100 g's for 3.25 hours. The results are analyzed using dimensional analyses. The analyses illustrate that the centrifuge simulations yield self-consistent simulations of the creep closure of fluid-filled cavities and that the interaction of three-dimensional cavity layouts can be investigated using this technique.

  3. Some numerical approaches of creep, thermal shock, damage and ...

    Indian Academy of Sciences (India)


    Ecole des Mines de Paris – Centre des Matériaux P.M. Fourt, B.P. 87, 91003 EVRY Cedex, France. Abstract. 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.

  4. 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)


    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.

  5. Physical hydrodynamic propulsion model study on creeping viscous ...

    Indian Academy of Sciences (India)

    Physical hydrodynamic propulsion model study on creeping viscous flow through a ciliated porous tube ... Dates. Manuscript received: 7 February 2016; Manuscript revised: 20 July 2016; Accepted: 5 October 2016; Early published: Unedited version published online: Final version published online: 16 February 2017 ...

  6. secondary creep response of hand lay-up grp composites

    African Journals Online (AJOL)

    Dr Obe

    REFERENCES. 1. Andrade, E.N. daC. On the Viscous. Flow of Metal and Allied Phenomena. Proc. Roy Soc(London),A84,1910,P.1. 2. Chen, C.H and Cheng, C.H.,. Micromechanical Modeling of Creep. Behaviour in. Praticle-Reinforced. Silicone - Rubber Composites. Trans. ASME, Vol. 64, December 1997, Pp 781. - 786.

  7. Time to fracture and cavity growth mechanisms in creep

    Energy Technology Data Exchange (ETDEWEB)

    Sklenicka, V.; Saxl, I.; Cadek, J. (Ceskoslovenska Akademie Ved, Brno. Ustav Fyzikalni Metalurgie)


    Stress dependences of time to intergranular fracture in creep of copper, a low alloy CrMoV steel and an austenitic CrNi stainless steel were analysed with the aim of identifying the cavity growth mechanisms. The analysis was based on the theories of diffusional cavity growth and coupled diffusion and power-law creep cavity growth proposed by Edward and Ashby. Both the above processes were found to take place under certain conditions. Pure power-law creep cavity growth has not been observed, in contrast to pure grain boundary sliding growth. Also the intragranular fracture was observed under conditions when the intergranular fracture due to the power-law creep cavity growth would be expected. The agreement of stress dependences of time to fracture derived from the theory with those determined experimentally makes it possible to predict the time to fracture. However, successful prediction depends critically on the correct choice of a number of parameters characterising the properties of the material under consideration, as well as a number of parameters characterising the intergranular damage. The proper choice of the latter parameters is discussed in detail.

  8. Tension and Compression Creep Apparatus for wood-Plastic Composites (United States)

    Scott E. Hamel; John C. Hermanson; Steven M. Cramer


    Design of structural members made of wood-plastic composites (WPC) is not possible without accurate test data for tension and compression. The viscoelastic behavior of these materials means that these data are required for both the quasi-static stress-strain response, and the long-term creep response. Their relative incompressibility causes inherent difficulties in...

  9. Creep behavior of precast segmental box girder bridge (United States)

    Xihua, Dai; Liangfang, Liu; Rong, Xian


    The concrete creep effect is more obvious when the box girder is assembled by segment. It is necessary to consider the influence of the loading value of the section at different time and the different age of concrete at different stages. In this paper, ACI209R-92, CEB-FIP MC90 and B3 and other concrete creep models are compared. The results show that the B3 model has many factors to consider and the calculation accuracy is high. Secondly, this paper discusses the influence of the segmental construction technology on the creep calculation, and puts forward the characteristics of the stress analysis of the segmental box girder. Finally, on the basis of the B3 model of concrete creep, the Midas software is used to establish the calculation model of segmental box girder, and the internal force and deformation of the box girder are calculated. The results show that the internal force and deformation of the box girder is too large due to the poor integrity of the segmental assembling process, which will seriously affect the normal service performance.

  10. secondary creep response of hand lay-up grp composites

    African Journals Online (AJOL)

    Dr Obe

    ABSTRACT. Glass Reinforced Plastics (GRP) composite load bearing components are now in common use, quite often at temperatures above the ambient, where creep behaviour may be significant, as in pressurized industrial containers. This is especially true of those composites produced by the. Hand Lay-Up Contact ...

  11. Finite element analysis of moisture migration, creep, shrinkage and cracking

    NARCIS (Netherlands)

    Zijl, G.P.A.G. van; Borst, R. de; Rots, J.G.


    A finite element formulation is presented for the analysis of moisture migra-tion, creep, shrinkage and cracking in cementitious materials. A one-way coupled approach is followed, where the pore humidity, the driving force for shrinkage, is solved for from a diffusion equation. The evolution of the

  12. Secondary Creep Response of Hand Lay-Up GRP Composites ...

    African Journals Online (AJOL)

    Glass Reinforced Plastics (GRP) composite load bearing components are now in common use, quite often at temperatures above the ambient, where creep behaviour may be significant, as in pressurized industrial containers. This is especially true of those composites produced by the Hand Lay-Up Contact Moulding ...

  13. Mechanical Interferometry Imaging for Creep Modeling of the Cornea


    Yoo, Lawrence; Reed, Jason; Gimzewski, James K; Demer, Joseph L.


    Nanoindentation by magnetic microspheres imaged by optical interferometry permits determination of the viscoelastic properties of fine local regions of each layer of the cornea. This approach provides robust biomechanical data on corneal creep behavior that scales reliably with the magnitude of applied force throughout the tissue.

  14. Shear heating in creeping faults changes the onset of convection (United States)

    Tung, R.; Poulet, T.; Alevizos, S.; Veveakis, E.; Regenauer-Lieb, K.


    The interaction between mechanical deformation of creeping faults and fluid flow in porous media has an important influence on the heat and mass transfer processes in Earth sciences. Creeping faults can act as heat sources due to the effect of shear heating and as such could be expected to alter the conditions for hydrothermal convection. In this work, we provide a finite element-based numerical framework developed to resolve the problem of heat and mass transfer in the presence of creeping faults. This framework extends the analytical approach of the linear stability analysis (LSA) frequently used to determine the bifurcation criterion for onset of convection, allowing us to study compressible cases with the option of complex geometry and/or material inhomogeneities. We demonstrate the impact of creeping faults on the onset of convection and show that shear heating—expressed through its dimensionless group the Gruntfest number Gr—has exponential influence on the critical value of the Lewis number Le (inversely proportional to the Rayleigh number Ra) required for convection: Lec ˜ Lec0 eGr. In this expression, Lec0 is the critical value of Le in the absence of shear heating. This exponential scaling shows that shear heating increases the critical Lewis number and triggers hydrothermal convection at lower permeability than in situations without it. We also show that the effect of shear heating in a fault significantly alters the pattern of convection in and around the fault zone.

  15. 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)


    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.

  16. Prediction of elemental creep. [steady state and cyclic data from regression analysis (United States)

    Davis, J. W.; Rummler, D. R.


    Cyclic and steady-state creep tests were performed to provide data which were used to develop predictive equations. These equations, describing creep as a function of stress, temperature, and time, were developed through the use of a least squares regression analyses computer program for both the steady-state and cyclic data sets. Comparison of the data from the two types of tests, revealed that there was no significant difference between the cyclic and steady-state creep strains for the L-605 sheet under the experimental conditions investigated (for the same total time at load). Attempts to develop a single linear equation describing the combined steady-state and cyclic creep data resulted in standard errors of estimates higher than obtained for the individual data sets. A proposed approach to predict elemental creep in metals uses the cyclic creep equation and a computer program which applies strain and time hardening theories of creep accumulation.

  17. Study on Flexural Creep Parameters of Overlayed Particleboard by Natural and Melaminated Veneers

    Directory of Open Access Journals (Sweden)

    Abdollah Najafi


    Full Text Available In this study, effects of natural and artificial veneer on flexural creep behavior of particleboard was investigated. Particleboard panels were prepared from Pars Neopan industries with 660 kg/m3 density and then overlaid by natural and melamine veneers. Their creep behavior was compared to control particleboard. For evaluating maximum bending load in static flexural test, specimens were cut from panels according to ASTM D 1037 with dimensions of 370×50×16 mm. Then, The flexural creep tests at 20% and 40% of failure bending load was applied to test specimens. Results of flexural tests indicated that the MOR and MOE values of veneered particleboard were highest. Results of creep showed that levels of stresses are effective on all creep parameters, but showed less effect on relative creep. Also, creep parameters less effective on specimens overlaid by natural veneer.

  18. Computation of Effective Steady-State Creep of Porous Ni–YSZ Composites with Reconstructed Microstructures

    DEFF Research Database (Denmark)

    Kwok, Kawai; Jørgensen, Peter Stanley; Frandsen, Henrik Lund


    This paper investigates the effective steady-state creep response of porous Ni–YSZ composites used in solid oxide fuel cell applications by numerical homogenization based on three-dimensional microstructural reconstructions and steadystate creep properties of the constituent phases. The Ni phase...... is found to carry insignificant stress in the composite and has a negligible role in the effective creep behavior. Thus, when determining effective creep, porous Ni–YSZ composites can be regarded as porous YSZ in which the Ni phase is counted as additional porosity. The stress exponents of porous YSZ...... are the same as that of dense YSZ, but the effective creep rate increases by a factor of 8–10 due to porosity. The relationship of creep rate and volume fraction of YSZ computed by numerical homogenization is underestimated by most existing analytical models. The Ramakrishnan–Arunchalam creep model provides...

  19. Effect of Water Fugacity on Creep Strength of Anorthite (United States)

    Rybacki, E.; Gottschalk, M.; Dresen, G.


    High-temperature creep of nominally water-free crustal silicates like quartz or feldspar is significantly affected by the presence of trace amounts of water. For water-saturated rocks the creep rate is expected to depend on water fugacity raised to a power of r. In this study we present first results on the fugacity exponent r and the activation volume V for creep of polycrystalline plagioclase. Fine-grained ( ˜3 μ m) anorthite aggregates were fabricated from a glass-powder by hot-isostatic pressing at 300 MPa pressure and a temperature of 1100oC. To estimate the activation volume, 8 samples were subsequently dried ( ˜ 0.003 wt% H2O) and co-axially deformed at temperatures of 1125-1200oC, pressures between 100 to 400 MPa, and axial stresses between ˜30 to 400 MPa, resulting in axial strain rates of about 7×10-7 - 5×10-4 s-1. Sample deformation at constant load was dominantly accommodated by grain boundary diffusion creep for stresses below about 200 MPa. The resulting creep activation volume is about 24 cm3mol-1. A total of 20 samples were encapsulated in talc setting water activity aH2O = 1. We used Fe, Ni or Cu jackets to buffer oxygen fugacity. Water content of samples after deformation was determined using Fourier-transformed infrared spectroscopy. Absorbance spectra suggest mainly molecular water located dominantly on grain boundaries. The water content is about 0.33 wt% H2O. Wet samples were deformed at temperatures of 1000-1150oC, confining pressures of 100 - 450 MPa, and stresses of ˜10 - 330 MPa, yielding strain rates of about 6×10-7 - 1×10-3 s-1. In comparison to dry samples wet specimens are about 1.5 orders of magnitude weaker. In diffusion creep the fugacity exponent r is estimated to about 0.6. Samples buffered by Cu-CuO are considerably weaker than those deformed using Fe and Ni jackets. Since the strength of (dry) anorthite is independent of oxygen fugacity, our results suggest that hydrogen fugacity also affect the creep strength of wet

  20. Brittle creep, damage, and time to failure in rocks (United States)

    Amitrano, David; Helmstetter, AgnèS.


    We propose a numerical model based on static fatigue laws in order to model the time-dependent damage and deformation of rocks under creep. An empirical relation between time to failure and applied stress is used to simulate the behavior of each element of our finite element model. We review available data on creep experiments in order to study how the material properties and the loading conditions control the failure time. The main parameter that controls the failure time is the applied stress. Two commonly used models, an exponential tf-exp (-bσ/σ0) and a power law function tf-σb' fit the data as well. These time-to-failure laws are used at the scale of each element to simulate its damage as a function of its stress history. An element is damaged by decreasing its Young's modulus to simulate the effect of increasing crack density at smaller scales. Elastic interactions between elements and heterogeneity of the mechanical properties lead to the emergence of a complex macroscopic behavior, which is richer than the elementary one. In particular, we observe primary and tertiary creep regimes associated respectively with a power law decay and increase of the rate of strain, damage event and energy release. Our model produces a power law distribution of damage event sizes, with an average size that increases with time as a power law until macroscopic failure. Damage localization emerges at the transition between primary and tertiary creep, when damage rate starts accelerating. The final state of the simulation shows highly damaged bands, similar to shear bands observed in laboratory experiments. The thickness and the orientation of these bands depend on the applied stress. This model thus reproduces many properties of rock creep, which were previously not modeled simultaneously.

  1. Diffusion Creep of Enstatite at High Pressures Under Hydrous Conditions (United States)

    Zhang, Guinan; Mei, Shenghua; Song, Maoshuang; Kohlstedt, David L.


    Mantle convection and large-scale plate motion depend critically on the nature of the lithosphere-asthenosphere boundary and thus on the viscosity structure of Earth's upper mantle, which is determined by the rheological properties of its constituent minerals. To constrain the flow behavior of orthopyroxene, the second most abundant constituent of the upper mantle, deformation experiments were carried out in triaxial compressive creep on fine-grained ( 6 μm) samples of enstatite at high pressures (3.8-6.3 GPa) and high temperatures (1323-1573 K) using a deformation-DIA apparatus. Based on results from this study, the deformation behavior of enstatite is quantitatively presented in the form of a flow law that describes the dependence of deformation rate on differential stress, water fugacity, temperature, and pressure. Specifically, the creep rate depends approximately linearly on stress, indicating deformation in the diffusion creep regime. A least squares regression fit to our data yielded a flow law for diffusion creep with an activation energy of 200 kJ/mol and an activation volume of 14 × 10-6 m3/mol. The magnitude of the water-weakening effect is similar to that for olivine with a water fugacity exponent of r ≈ 0.7. This strong dependence of viscosity on water fugacity (concentration) indicates that the viscosity of an orthopyroxene-bearing mantle varies from one geological setting to another, depending on the large-scale water distribution. Based on the rheology contrast between olivine and enstatite, we conclude that olivine is weaker than enstatite throughout most of the upper mantle except in some shallow regions in the diffusion creep regime.

  2. 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


    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.)

  3. Analysis of tensile bond strengths using Weibull statistics. (United States)

    Burrow, Michael F; Thomas, David; Swain, Mike V; Tyas, Martin J


    Tensile strength tests of restorative resins bonded to dentin, and the resultant strengths of interfaces between the two, exhibit wide variability. Many variables can affect test results, including specimen preparation and storage, test rig design and experimental technique. However, the more fundamental source of variability, that associated with the brittle nature of the materials, has received little attention. This paper analyzes results from micro-tensile tests on unfilled resins and adhesive bonds between restorative resin composite and dentin in terms of reliability using the Weibull probability of failure method. Results for the tensile strengths of Scotchbond Multipurpose Adhesive (3M) and Clearfil LB Bond (Kuraray) bonding resins showed Weibull moduli (m) of 6.17 (95% confidence interval, 5.25-7.19) and 5.01 (95% confidence interval, 4.23-5.8). Analysis of results for micro-tensile tests on bond strengths to dentin gave moduli between 1.81 (Clearfil Liner Bond 2V) and 4.99 (Gluma One Bond, Kulzer). Material systems with m in this range do not have a well-defined strength. The Weibull approach also enables the size dependence of the strength to be estimated. An example where the bonding area was changed from 3.1 to 1.1 mm diameter is shown. Weibull analysis provides a method for determining the reliability of strength measurements in the analysis of data from bond strength and tensile tests on dental restorative materials.

  4. Capturing tensile size-dependency in polymer nanofiber elasticity. (United States)

    Yuan, Bo; Wang, Jun; Han, Ray P S


    As the name implies, tensile size-dependency refers to the size-dependent response under uniaxial tension. It defers markedly from bending size-dependency in terms of onset and magnitude of the size-dependent response; the former begins earlier but rises to a smaller value than the latter. Experimentally, tensile size-dependent behavior is much harder to capture than its bending counterpart. This is also true in the computational effort; bending size-dependency models are more prevalent and well-developed. Indeed, many have questioned the existence of tensile size-dependency. However, recent experiments seem to support the existence of this phenomenon. Current strain gradient elasticity theories can accurately predict bending size-dependency but are unable to track tensile size-dependency. To rectify this deficiency a higher-order strain gradient elasticity model is constructed by including the second gradient of the strain into the deformation energy. Tensile experiments involving 10 wt% polycaprolactone nanofibers are performed to calibrate and verify our model. The results reveal that for the selected nanofibers, their size-dependency begins when their diameters reduce to 600 nm and below. Further, their characteristic length-scale parameter is found to be 1095.8 nm. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Brittle Creep of Tournemire Shale: Orientation, Temperature and Pressure Dependences (United States)

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


    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

  6. A Miniaturized In Situ Tensile Platform under Microscope

    Directory of Open Access Journals (Sweden)

    Xiaoli Hu


    Full Text Available Aiming at the mechanical testing of three-dimensional specimens with feature size of centimeter level, a miniaturized tensile platform, which presents compatibility with scanning electron microscope (SEM and metallographic microscope, was designed and built. The platform could accurately evaluate the parameters such as elastic modulus, elongation and yield limit, etc. The calibration experiments of load sensor and displacement sensor showed the two kinds of sensors had high linearity. Testing of transmission error and modal parameters showed that the platform presented good following behaviors and separation of resonance region. Comparison tests based on stress-strain curve were carried out between the self-made platform and the commercial tensile instrument (Instron to verify the feasibility of the platform. Furthermore, the in situ tensile experiment under metallographic microscope was carried out on a kind of manganese steel.

  7. Handbook for tensile properties of austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, D. W.; Ryu, W. S.; Jang, J. S.; Kim, S. H.; Kim, W. G.; Chung, M. K.; Han, C. H. [Korea Atomic Energy Research Institute, Taejeon (Korea)


    Database system of nuclear materials has not been developed and the physical and mechanical properties of materials used in nuclear power plant are not summarized systematically in Korea. Although Korea designs nuclear power plant, many materials used in nuclear power plant are imported because we do not have database system of nuclear material yet and it was hard to select a proper material for the structural materials of nuclear power plant. To develop database system of nuclear materials, data of mechanical, corrosion, irradiation properties are needed. Of theses properties, tensile properties are tested and summarized in this report. Tensile properties of stainless steel used in nuclear reactor internal were investigated. Data between Korea Atomic Energy Research Institute and foreign laboratory were compared to determine the precision of the result. To develope database system, materials, chemical composition, heat treatment, manufacturing process, and grain size were classified. Tensile properties were tested and summarized to use input data of database system. 9 figs., 9 tabs. (Author)

  8. Induced martensitic transformation during tensile test in nanostructured bainitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Rivas, L. [Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); University of Kaiserslautern, Materials Testing, Gottlieb - Daimler - Str., 67663 Kaiserslautern (Germany); Garcia-Mateo, C., E-mail: [Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo, 8, 28040 Madrid (Spain); Kuntz, Matthias [Robert Bosch GmbH, Materials and Processing Dept, P.O. Box 300240, Stuttgart (Germany); Sourmail, Thomas [Asco Industries CREAS (Research Centre) Metallurgy, BP 70045, Hagondange Cedex 57301 (France); Caballero, F.G. [Department of Physical Metallurgy, National Center for Metallurgical Research (CENIM-CSIC), Avda. Gregorio del Amo, 8, 28040 Madrid (Spain)


    Retained austenite in nanostructured bainite is able to undergo mechanically induced martensitic transformation. However, the link between transformation and deformation mechanisms involved makes difficult the understanding of the process. In this work, a model has been developed to assess the effect of the external stress itself on the martensite phase transformation. In addition, after a detailed initial microstructural characterization, the martensite fraction evolution during tensile deformation has been obtained by means of X-ray diffraction analyses after interrupted tensile tests in several nanostructured bainitic steels. Experimental results have been compared to the outputs of the model, as a reference. They suggests that stress partitioning between phases upon tensile deformation is promoted by isothermal transformation at lower temperatures.

  9. Tensile-stressed microelectromechanical apparatus and microelectromechanical relay formed therefrom (United States)

    Fleming, James G [Albuquerque, NM


    A microelectromechanical (MEM) apparatus is disclosed which includes a shuttle suspended above a substrate by two or more sets of tensile-stressed beams which are operatively connected to the shuttle and which can comprise tungsten or a silicon nitride/polysilicon composite structure. Initially, the tensile stress in each set of beams is balanced. However, the tensile stress can be unbalanced by heating one or more of the sets of beams; and this can be used to move the shuttle over a distance of up to several tens of microns. The MEM apparatus can be used to form a MEM relay having relatively high contact and opening forces, and with or without a latching capability.

  10. Tensile strength of glulam laminations of Nordic spruce

    DEFF Research Database (Denmark)

    Hoffmeyer, Preben; Bräuner, Lise; Boström, Lars


    Design of glulam according to the European timber code Eurocode 5 is based on the standard document prEN1194 , according to which glulam beam strength is to be established either by full scale testing or by calculation. The calculation must be based on a knowledge of lamination tensile strength....... This knowledge may be obtained either by adopting a general rule that the characteristic tensile strength is sixty percent of the characteristic bending strength, or by performing tensile tests on an adequate number of laminations representative of the whole population. The present paper presents...... an investigation aimed at establishing such an adequate experimental background for the assignment of strength classes for glulam made of visually strength graded laminations from Nordic sawmills. The investigation includes more than 1800 boards (laminations) of Norway spruce (Picea abies) sampled from eight...


    Directory of Open Access Journals (Sweden)

    BRAD Raluca


    Full Text Available An objective approach to select the best fabric for technical and home textiles consists in mechanical properties evaluation. The goal of this study is to analyze the behavior of knitted fabrics undergoing stretch stress. In this respect, three types of 2 colors Rib structure (backstripes jacquard, twillback jacquard and double-layered 3x3 rib fabric have been presented and tested for tensile strength and elongation on three directions. First, the elasticity and the behavior of knitted Rib fabrics were described The fabrics were knitted using 100% PAN yarns with Nm 1/15x2 on a E5 CMS 330 Stoll V-bed knitting machine, and have been tested using INSTROM 5587 Tensile Testing Machine in respect of standards conditions. After a relaxation period, 15 specimens were prepared, being disposed at 0°, 45 and 90 angles to the wale direction on the flat knitted panel. The tensile strength and the elongation values were recorded and mean values were computed. After strength and tensile elongation testing for 3 types of rib based knitted fabrics, one can see that the double layer knit presents the best mechanical behavior, followed by birds-eyebacking 2 colors Jacquard and then back striped Jacquard. For tensile stress in bias direction, the twillbacking Jacquard has a good breakage resistance value due to the higher number of rib sinker loops in structure that are positioned on the same direction with the tensile force. The twillbacking Jacquard structure could be considered as an alternative for the base material for decorative and home textile products.

  12. Laboratory simulation of rockslide creep and hydro-mechanical coupling (United States)

    Agliardi, Federico; Scuderi, Marco M.; Collettini, Cristiano


    Deep-seated rockslides are major threats in mountain areas, evolving over hundreds or thousands of years in changing morpho-climatic settings. They usually exhibit time-dependent displacements with superposed long-term and seasonal creep components, the latter related to hydrologic forcing (e.g. rainfall and snowmelt). Most rockslide deformation usually localizes in one or more shear zones, especially in crystalline anisotropic rocks. Shear zones are made of cataclastic breccia and gouge layers similar to those occurring in tectonic faults zones. While several mathematical models have been proposed to reproduce observed rockslide behaviour, only a few laboratory investigations, mostly limited to the assessment of residual friction properties, have been carried out. Here we present laboratory experiments to characterize the frictional stability and time-dependent slip behaviour of real rockslide shear zones, using a biaxial apparatus within a pressure vessel (BRAVA). In order to compare experimental results with in situ observations, we characterized samples collected by full-core boreholes at a depth of 90m from the shear zones of the 50 Mm3 Spriana rockslide (Central Alps, Italy). The rockslide is characterised by long-term evolution after the Last Glacial Maximum, over a century of documented activity and over 25 years of deformation and hydrological monitoring. The rockslide creeps at slow rates of 0.4-3 cm/yr and undergoes order-of-magnitude acceleration stages correlated with groundwater fluctuations. We performed the experiments on 5x5cm samples of phyllosilicate-rich gouge under stress conditions characteristic of the sampled shear zones. We designed experiments in order to evaluate: 1) shear zone strength and permeability; 2) rate- and state- frictional properties for shear displacement rates (0.1-500 microns/s) covering the range of real rockslide slow-to-fast transition; 3) shear zone creep and hydro-mechanical coupling behaviour in response to pore

  13. Delamination analysis of tapered laminated composites under tensile loading (United States)

    Armanios, Erian A.; Parnas, Levend


    A study was conducted to analyze tapered composite laminates under tensile loading. A tapered construction made of S2/SP250 glass/epoxy laminate was used to achieve a thickness reduction using three consecutive dropped plies over a distance of 60 ply thicknesses. The principle of minimum complementary potential energy was used to determine interlaminar stresses. The interlaminar peel stress distribution shows a higher tensile intensity at the taper/thin portion juncture. The total strain energy release rate is determined using a simplified membrane model. Results are compared with a finite element simulation.

  14. Physical-Mechanism Exploration of the Low-Cycle Unified Creep-Fatigue Formulation

    Directory of Open Access Journals (Sweden)

    Dan Liu


    Full Text Available Background—Creep-fatigue behavior is identified as the incorporated effects of fatigue and creep. One class of constitutive-based models attempts to evaluate creep and fatigue separately, but the interaction of fatigue and creep is neglected. Other models treat the damage as a single component, but the complex numerical structures that result are inconvenient for engineering application. The models derived through a curve-fitting method avoid these problems. However, the method of curving fitting cannot translate the numerical formulation to underlying physical mechanisms. Need—Therefore, there is a need to develop a new creep-fatigue formulation for metal that accommodates all relevant variables and where the relationships between them are consistent with physical mechanisms of fatigue and creep. Method—In the present work, the main dependencies and relationships for the unified creep-fatigue equation were presented through exploring what the literature says about the mechanisms. Outcomes—This shows that temperature, cyclic time and grain size have significant influences on creep-fatigue behavior, and the relationships between them (such as linear relation, logarithmical relation and power-law relation are consistent with phenomena of diffusion creep and crack growth. Significantly, the numerical form of “1 − x” is presented to show the consumption of creep effect on fatigue capacity, and the introduction of the reference condition gives the threshold of creep effect. Originality—By this means, the unified creep-fatigue equation is linked to physical phenomena, where the influence of different dependencies on creep fatigue was explored and relationships shown in this equation were investigated in a microstructural level. Particularly, a physical explanation of the grain-size exponent via consideration of crack-growth planes was proposed.


    Directory of Open Access Journals (Sweden)

    Cláudio José Araújo da Silva1, 2, 3, 4, 3,


    Full Text Available The objective of this study was to evaluate the influence of creep feeding and creep grazing on the pasture characteristics and on performance and productivity of sheep. Three systems of lambs production on Tifton 85 (Cynodon spp. pastures oversown with Italian ryegrass (Lolium multiflorum Lam were studied: lambs with dams until slaughter without supplementation (1; lambs with dams until slaughter fed concentrate in creep feeders at 2% (2; and lambs with dams until slaughter and supplemented with white clover (Trifolium repens in creep grazing system ad libitum (3. The characteristics of the pasture did not differ (P>0.05 among the systems. Individual lamb growth was higher with creep feeding (307g/day and creep grazing (274g/day compared to no supplemented systems (204g/day; p<0.05. Animal productivity per area on supplemented treatments (2.4 kg BW/ha/day was significantly greater than no supplemented one (1.8kg BW/ha/day; p<0.05. White clover showed to be a particularly good supplement for raising lambs on pastures. It may be concluded that systems of feeding lambs in creep feeding and creep grazing yielded favorable productivity mainly if there is forage deficit in spring.

  16. Investigation of the rate-controlling mechanism(s) for high temperature creep and the relationship between creep and melting by use of high pressure as a variable

    Energy Technology Data Exchange (ETDEWEB)


    Using high pressure as a variable, the rate-controlling mechanism for high temperature creep and the relationship between creep and melting is investigated for silicon and nickel. An apparatus is used in which the samples are heated to melting point and subjected to 1 to 3 GigaPascal pressure. The stress behavior of the materials are then studied.

  17. 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)


    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.)

  18. Creep-to-rupture of the steel P92 at 650 °C in oxygen-controlled stagnant lead in comparison to air (United States)

    Yurechko, Mariya; Schroer, Carsten; Skrypnik, Aleksandr; Wedemeyer, Olaf; Konys, Jürgen


    Creep-to-rupture experiments were performed on 9%-Cr ferritic-martensitic steel P92 in the CRISLA facility. The specimens of P92 were examined at 650 °C and static tensile stress between 75 and 325 MPa in both stagnant lead with 10-6 mass% dissolved oxygen and air. The steel showed an insignificant difference in time-to-rupture, tR, and ductile fracture in both environments at >100 MPa, corresponding to tR oxidation in the different environments were studied using metallographic techniques. The Laves phase that forms during thermal aging at 650 °C was found along prior austenite grain boundaries and martensite laths already after relatively short testing time, along with chromium carbides that are already present in the as-received condition of the steel.

  19. Interaction between particle precipitation and creep behavior in the NI-base Alloy 617B: Microstructural observations and constitutive material model

    Energy Technology Data Exchange (ETDEWEB)

    Haan, J., E-mail:; Bezold, A., E-mail:; Broeckmann, C., E-mail:


    The creep behavior of the Ni-base Alloy 617B was analyzed at 725 °C with the focus on microstructural changes during temperature and stress exposure. High resolution electron microscopy of crept specimens reveals the precipitation behavior of secondary phases such as Cr-rich M{sub 23}C{sub 6}-carbides and the γ'-phase. Physical models are used to describe the Ostwald coarsening of the γ' particles and the evolution of the yield strength of the alloy. Together with the results from hot tensile tests and hardness measurements, a constitutive model for Alloy 617B has been developed. This model takes account of precipitation strengthening which is consistent with the microstructural observations, internal back stress due to dislocation hardening and material damage, all by evolutionary equations.

  20. Detection and analysis of the stored grain insect creeping sound (United States)

    Geng, Senlin; Zhang, Xiuqin; Zhao, Wei


    With the random acoustic source model as the theory model of the stored grain insects creeping, the sounds, of 20 Alphitobius diaperinus Panzer in wheat and 20 Tribolium castaneum Herbst adults in corn, are detected, respectively. By using Matlab, the original sound signals are reproduced and the de-noised signals are obtained. The power spectrums characteristics analysis are made. It is shown that the random acoustic source model is effective for the stored grain insect creeping sound detection, and their power spectrums are all discrete, where the highest frequency is 1600 Hz, the main frequency 205 Hz in the former, and the highest frequency is 800 Hz, the main frequency 350 Hz the latter, which may be used to distinguish different types insects in grain.

  1. In-reactor creep behavior of selected ferritic alloys

    Energy Technology Data Exchange (ETDEWEB)

    Puigh, R.J.; Wire, G.L.


    An experiment was conducted in the Experimental Breeder Reactor-II (EBR-II) to investigate the in-reactor creep behavior of selected ferritic alloys. Pressurized tube creep specimens fabricated from the following ferritic alloys: HT-9, 9Cr-2Mo, and 2-1/4Cr-1Mo, were irradiated in EBR-II to a peak fluence of 2.8 x 10/sup 22/ n/cm/sup 2/ (E > 0.1 MeV) and at irradiation temperatures of 443, 505 and 572/sup 0/C. Each alloy had four specimens with midwall hoop stresses of 0, 50, 75 and 100 MPa at each irradiation temperature. Measurements of the zero-stressed specimens indicate that none of the ferritic alloys are exhibiting evidence for swelling or phase transformations at these irradiation temperatures and at a fluence of 2.8 x 10/sup 22/ n/cm/sup 2/ (E > 0.1 MeV).

  2. Spatiotemporal Patterns in Ultraslow Domain Wall Creep Dynamics. (United States)

    Ferrero, Ezequiel E; Foini, Laura; Giamarchi, Thierry; Kolton, Alejandro B; Rosso, Alberto


    In the presence of impurities, ferromagnetic and ferroelectric domain walls slide only above a finite external field. Close to this depinning threshold, they proceed by large and abrupt jumps called avalanches, while, at much smaller fields, these interfaces creep by thermal activation. In this Letter, we develop a novel numerical technique that captures the ultraslow creep regime over huge time scales. We point out the existence of activated events that involve collective reorganizations similar to avalanches, but, at variance with them, display correlated spatiotemporal patterns that resemble the complex sequence of aftershocks observed after a large earthquake. Remarkably, we show that events assemble in independent clusters that display at large scales the same statistics as critical depinning avalanches. We foresee these correlated dynamics being experimentally accessible by magnetooptical imaging of ferromagnetic films.

  3. Creep effects in diffusion bonding of oxygen-free copper

    CERN Document Server

    Moilanen, Antti

    Diffusion is the transport of atoms or particles through the surrounding material. Various microstructural changes in metals are based on the diffusion phenomena. In solid metals the diffusion is closely related to crystallographic defects. In single-component metals the dominant mechanism of diffusion is the vacancy mechanism. Diffusion bonding is a direct technological application of diffusion. It is an advanced solidstate joining process in which the surfaces of two components are brought to contact with each other and heated under a pressing load in a controlled environment. During the process, the contact surfaces are bonded by atomic diffusion across the interface and as a result, one solid piece is formed. The condition of high temperature and low applied stress combined with relatively long process duration enables the creep effects to take place in bonded metals. Furthermore, creep causes unwanted permanent deformations in the bonded components. Some authors suggest that there could be a threshold fo...

  4. Creep test observation of viscoelastic failure of edible fats (United States)

    Vithanage, C. R.; Grimson, M. J.; Smith, B. G.; Wills, P. R.


    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.

  5. Study of the temperature dependence of the uniaxial creep property of similar material of new soft rock (United States)

    Wang, Y. Y.; Wu, Y.; Fan, X. Y.; Zhang, J. L.; Guo, P.; Li, J. G.


    Using the experimental method, the experimental research of creep properties were conducted under different temperature ranging from 10°C to 60°C. The similar material of new soft rock consists of paraffin, which can obtain that the deformation contains the instantaneous elastic deformation and creep deformation through the uniaxial creep experimental results. And thus the increase of temperature has great influence on the creep characteristics of similar soft rock according to the creep curve of similar soft rock at 10°C to 60°C. With the increase of temperature, the slope of the stress-strain curve of similar soft rock is increasing, while the average of the creep modulus is decreasing, which means that the capacity of resist deformation is reduced. Therefore, the creeps law of high-temperature and short-time can be shown the creep phenomenon of low-temperature and long-time, and further shorten the creep experimental cycle.

  6. Status of Centralized Environmental Creep Testing Facility Preparation and Upgrade

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Weiju [ORNL; Battiste, Rick [ORNL


    Because the ASME Codes do not cover environmental issues that are crucial in the design and construction of VHTR system, investigation of long-term impure helium effects on metallurgical stability and properties becomes very important. The present report describes the development of centralized environmental creep testing facility, its close collaborations with the experiments in low velocity helium recirculation loop, important lessons learned, upgrades in system design in FY06, and current status of the development.


    Energy Technology Data Exchange (ETDEWEB)

    C. ZHOU; ET AL


    Micro Raman spectroscopy and classic composite shear-lag models were used to analyze the evolution with time of fiber and matrix strain/stress around fiber breaks in planar model graphite fiber-epoxy matrix composites. Impressive agreements were found between the model predictions and the experimental results. The local matrix creep leads to an increase in the load transfer length around the break under a constant load. This increases the chance of fiber breakage in the neighboring intact fibers.

  8. Optimisation of hardness and tensile strength of friction stir welded ...

    African Journals Online (AJOL)

    DR OKE

    The present work aims to optimize the operating parameters such as rotational speed, welding speed and tool diameter for maximum Hardness and Tensile strength of the friction stir welded joint on AA6061 alloy. Three factors with five level response surface design matrix were developed by using MINITAB14 software ...

  9. Evaluation of tensile strength and fracture behavior of friction welded ...

    Indian Academy of Sciences (India)

    Friction welding; tensile strength; SEM; microhardness. 1. Introduction. Joining of the metals is one of the most essential needs of the industry (Handa & Chawla 2013a). The joining has increasingly been used in the materials technology because of the materials hav- ing different mechanical properties needs to be efficiently ...

  10. Strain distribution during tensile deformation of nanostructured aluminum samples

    DEFF Research Database (Denmark)

    Kidmose, Jacob; Lu, L.; Winther, Grethe


    To optimize the mechanical properties, especially formability, post-process deformation by cold rolling in the range 5–50 % reduction was applied to aluminum sheets produced by accumulative roll bonding to an equivalent strain of 4.8. During tensile testing high resolution maps of the strain...

  11. Evaluation of tensile strength and fracture behavior of friction welded ...

    Indian Academy of Sciences (India)

    In the present study an attempt was made to join austenitic stainless steel (AISI 304) with low alloy steel (AISI 1021) at five different rotational speeds ranging from 800 to 1600 rpm and at as many different axial pressures ranging from 75 MPa to 135 MPa and then determining the strength of the joint by means of tensile ...

  12. Improvement in tensile properties of PVC–montmorillonite ...

    Indian Academy of Sciences (India)

    Abstract. In this paper we present the results exhibiting an improvement in the tensile properties of polyvinyl chlo- ride (PVC)–montmorillonite nanocomposites through uniaxial stretching. The clay was dispersed in PVC matrix with the help of dodecylamine. PVC–montmorillonite nanocomposites films containing varying ...

  13. The post peak response of concrete for dynamic tensile loading

    NARCIS (Netherlands)

    Vegt, I.; Weerheijm, J.


    The mechanical response of concrete is represented in the load-deformation curve which shows the response up to maximum strength as well as the post-peak response up to complete failure. Dynamic tests exhibit an extensive rate effect on the tensile strength beyond loading rates of about 50 GPa/s

  14. Effect of nanoparticles on tensile, impact and fatigue properties of ...

    Indian Academy of Sciences (India)


    the potential energy mgh0 at the top of the pendulum swing before and after the collision would be the same. The greater the energy used in the breaking, the greater the loss of energy and so the lower the height to which the pendulum rises. If the pendulum swings up to a height ... mined by a simple tensile test. Such a ...

  15. Compressive and Tensile Strength of Expanded Polystyrene Beads Concrete


    Subhan, Tengku Fitriani L


    Penelitian ini betujuan untuk mempelajari property dari beton ringan yang mengandung expanded polystyrene beads, yaitu kuat tekan (compressive strength) dan kuat tarik (tensile strength). Property tersebut kemudian dibandingkan dengan beton normal (beton tanpa expanded polystyrene beads) sebagai campuran pengontrol. Hasil penelitian ini menunjukkan bahwa jumlah polystyrene beads yang dimasukkan sebagai campuran beton mempengaruhi property beton; yaitu dapat menurunkan kuat tekan beton. Tetapi...

  16. Tensile and Hardness Property Evaluation of Kaolin- Sisal Fibre ...

    African Journals Online (AJOL)

    In this work, the tensile and hardness properties of Kaolin- sisal fibre- epoxy composite were evaluated using standard methods. Epoxy type 3354A with its hardener was mixed in the ratio 2:1. Calcined kaolin particle with average size of 35µm and 3-4mm sisal fibre were added to the epoxy matrix during the composite ...

  17. Tensile Strength of GFRP Reinforcing Bars with Hollow Section

    Directory of Open Access Journals (Sweden)

    Young-Jun You


    Full Text Available Fiber reinforced polymer (FRP has been proposed to replace steel as a reinforcing bar (rebar due to its high tensile strength and noncorrosive material properties. One obstacle in using FRP rebars is high price. Generally FRP is more expensive than conventional steel rebar. There are mainly two ways to reduce the cost. For example, one is making the price of each composition cost of FRP rebar (e.g., fibers, resin, etc. lower than steel rebar. Another is making an optimized design for cross section and reducing the material cost. The former approach is not easy because the steel price is very low in comparison with component materials of FRP. For the latter approach, the cost could be cut down by reducing the material cost. Therefore, an idea of making hollow section over the cross section of FRP rebar was proposed in this study by optimizing the cross section design with acceptable tensile performance in comparison with steel rebar. In this study, glass reinforced polymer (GFRP rebars with hollow section and 19 mm of outer diameter were manufactured and tested to evaluate the tensile performance in accordance with the hollowness ratio. From the test results, it was observed that the tensile strength decreased almost linearly with increase of hollowness ratio and the elastic modulus decreased nonlinearly.

  18. Positron lifetime analysis of dislocations arising from tensile strain

    DEFF Research Database (Denmark)

    Petersen, K.; Repin, I.A.; Trumpy, Georg


    Aluminium single crystal samples were treated by uniaxial tensile strain. Positron lifetime studies carried out at different dislocation densities and in a wide temperature range give information about the mechanism of positron trapping, as well as trapping rates, binding energy and the development...

  19. Concrete under Impact Loading, Tensile Strength and Bond

    NARCIS (Netherlands)

    Reinhardt, H.W.


    Uniaxial impact tensile tests on plain concrete were carried out with the aid of Split Hopkinson Bar equipment with stress rates of up to 60000 N/mm2. s. Various concrete mixes were investigated under. dry and wet conditions. All the concretes showed an increase in strength with increasing stress

  20. Regional Variation in the Microscopy and Tensile Strength of the ...

    African Journals Online (AJOL)

    The linea alba (LA), a midline tendinous structure formed by the interlocking anterior abdominal wall aponeurotic fibers, acts as a passive tensile band that prevents sagging of the lower abdomen. The microstructure and the strength of these fibres would thus be expected to reflect on the forces that act on the linea alba.