Effect of dynamic monotonic and cyclic loading on fracture behavior for Japanese carbon steel pipe STS410

Energy Technology Data Exchange (ETDEWEB)

Kinoshita, Kanji; Murayama, Kouichi; Ogata, Hiroyuki [and others

1997-04-01

The fracture behavior for Japanese carbon steel pipe STS410 was examined under dynamic monotonic and cyclic loading through a research program of International Piping Integrity Research Group (EPIRG-2), in order to evaluate the strength of pipe during the seismic event The tensile test and the fracture toughness test were conducted for base metal and TIG weld metal. Three base metal pipe specimens, 1,500mm in length and 6-inch diameter sch.120, were employed for a quasi-static monotonic, a dynamic monotonic and a dynamic cyclic loading pipe fracture tests. One weld joint pipe specimen was also employed for a dynamic cyclic loading test In the dynamic cyclic loading test, the displacement was controlled as applying the fully reversed load (R=-1). The pipe specimens with a circumferential through-wall crack were subjected four point bending load at 300C in air. Japanese STS410 carbon steel pipe material was found to have high toughness under dynamic loading condition through the CT fracture toughness test. As the results of pipe fracture tests, the maximum moment to pipe fracture under dynamic monotonic and cyclic loading condition, could be estimated by plastic collapse criterion and the effect of dynamic monotonic loading and cyclic loading was a little on the maximum moment to pipe fracture of the STS410 carbon steel pipe. The STS410 carbon steel pipe seemed to be less sensitive to dynamic and cyclic loading effects than the A106Gr.B carbon steel pipe evaluated in IPIRG-1 program.

Effect of dynamic monotonic and cyclic loading on fracture behavior for Japanese carbon steel pipe STS410

International Nuclear Information System (INIS)

Kinoshita, Kanji; Murayama, Kouichi; Ogata, Hiroyuki

1997-01-01

The fracture behavior for Japanese carbon steel pipe STS410 was examined under dynamic monotonic and cyclic loading through a research program of International Piping Integrity Research Group (EPIRG-2), in order to evaluate the strength of pipe during the seismic event The tensile test and the fracture toughness test were conducted for base metal and TIG weld metal. Three base metal pipe specimens, 1,500mm in length and 6-inch diameter sch.120, were employed for a quasi-static monotonic, a dynamic monotonic and a dynamic cyclic loading pipe fracture tests. One weld joint pipe specimen was also employed for a dynamic cyclic loading test In the dynamic cyclic loading test, the displacement was controlled as applying the fully reversed load (R=-1). The pipe specimens with a circumferential through-wall crack were subjected four point bending load at 300C in air. Japanese STS410 carbon steel pipe material was found to have high toughness under dynamic loading condition through the CT fracture toughness test. As the results of pipe fracture tests, the maximum moment to pipe fracture under dynamic monotonic and cyclic loading condition, could be estimated by plastic collapse criterion and the effect of dynamic monotonic loading and cyclic loading was a little on the maximum moment to pipe fracture of the STS410 carbon steel pipe. The STS410 carbon steel pipe seemed to be less sensitive to dynamic and cyclic loading effects than the A106Gr.B carbon steel pipe evaluated in IPIRG-1 program

Fatigue damage assessment under multi-axial non-proportional cyclic loading

International Nuclear Information System (INIS)

Mohta, Keshav; Gupta, Suneel K.; Jadhav, P.A.; Bhasin, V.; Vijayan, P.K.

2016-01-01

Detailed fatigue analysis is carried out for class I Nuclear Power Plant (NPP) components to rule out the fatigue failure during their design lifetime. ASME Boiler and Pressure Vessel code Section III NB, has provided two schemes for fatigue assessment, one for fixed principal directions (proportional) loading and the other for varying principal directions (non-proportional) loading conditions. Recent literature on multi-axial fatigue tests has revealed lower fatigue lives under nonproportional loading conditions. In an attempt to understand the loading parameter lowering the fatigue life, a finite element based study has been carried out. Here, fatigue damage in a tube has been correlated with the applied axial to shear strain ratio and phase difference between them. The FE analysis has used Chaboche nonlinear kinematic hardening rule to model material's realistic cyclic plastic deformation behavior. The ASME alternating stress intensity (based on linear elastic FEA) and the plastic strain energy dissipation (based on elastic-plastic FEA) have been considered to assess the per cycle fatigue damage. The study has revealed that ASME criteria predicts lower alternating stress intensity (fatigue damage parameter S alt ) for some cases of non-proportional loading than that predicted for corresponding proportional loading case. However, the actual fatigue damage is higher in non-proportional loading than that in corresponding proportional loading case. Further the fatigue damage of an NPP component under realistic multi-axial cyclic loading conditions has been assessed using some popular critical plane based models vis-à-vis ASME Sec. III criteria. (author)

Simulation of pore pressure accumulation under cyclic loading using Finite Volume Method

DEFF Research Database (Denmark)

Tang, Tian; Hededal, Ole

2014-01-01

This paper presents a finite volume implementation of a porous, nonlinear soil model capable of simulating pore pressure accumulation under cyclic loading. The mathematical formulations are based on modified Biot’s coupled theory by substituting the original elastic constitutive model...... with an advanced elastoplastic model suitable for describing monotonic as well as cyclic loading conditions. The finite volume method is applied to discretize these formulations. The resulting set of coupled nonlinear algebraic equations are then solved by a ’segregated’ solution procedure. An efficient return...

Effect of cyclic block loading on character of deformation and strength of structural materials in plane stressed state

International Nuclear Information System (INIS)

Kul'chitskij, N.M.; Troshchenko, A.V.; Koval'chuk, B.I.; Khamaza, L.A.; Nikolaev, I.A.

1982-01-01

The paper is concerned with choice of conditions for preliminary cyclic block loading, determination of fatigue failure resistance characteristics for various structural materials under regular and selected block loading, investigation of the preliminary cyclic loading effect on regularities of elastoplastic deformation of materials concerned in the biaxial stressed state. Under selected conditions of cyclic block loading the character of damage accumulation is close to the linear law for the materials of high-srength doped steel, and VT6 alloys of concern. These materials in the initial state and after preliminary cyclic loading are anisotropic. Axial direction is characterized by a higher plastic strain resistance for steel and tangential direction - for VT6 alloy. The generalized strain curves for the materials in question are not invariant as to the stressed state type. It is stated that the effect of preliminary unsteady cyclic loading on resistance and general regularities of material deformation in the complex stressed state is insignificant. It is observed that stress-strain properties of the materials tend to vary in the following way: plastic strain resistance of the steel lowers and that of VT6 rises, anisotropy of the materials somehow decreases. The variation in the material anisotropy may be attributed to a decrease in residual stresses resulting from preliminary cyclic loading

Effect of reverse cyclic loading on the fracture resistance curve of nuclear piping material

International Nuclear Information System (INIS)

Weon, Jong Il; Seok, Chang Sung

1999-01-01

Fracture resistance (J-R) curves, which are used for the elastic-plastic fracture mechanics analyses, are known to be dependent on the cyclic loading history. The objective of this paper is to study the effect of reverse cyclic loading on J-R curves in CT specimens. The effect of two parameters was observed on the J-R curves during the reverse cyclic loading. One was the minimum-to-maximum load ratio (R) and the other was the incremental plastic displacement (δ cycle /δ i ), which is related to the amount of crack growth that occurs in a cycle. Fracture resistance test on CT specimens with varying load ratio and incremental plastic displacement were performed. For the SA 516 Gr. 70 steel, the results showed that the J-R curves were decreased with decreasing the load ratio and the incremental plastic displacement. When the load ratio was set to -1, the results of the J-R curves and the J i value were about 40-50 percent of those for the monotonic loading condition. Also on condition that the incremental plastic displacement reached 1/40, the J-R curves and the J i value were about 50-60 percent of those for the incremental plastic displacement of 1/10

Evaluation of the base/subgrade soil under repeated loading : phase II, in-box and ALF cyclic plate load tests.

Science.gov (United States)

2012-03-01

This research study aims at evaluating the performance of base and subgrade soil in flexible pavements under repeated loading test conditions. For this purpose, an indoor cyclic plate load testing equipment was developed and used to conduct a series ...

Response of monopiles under cyclic lateral loading in sand

DEFF Research Database (Denmark)

Nicolai, Giulio; Ibsen, Lars Bo

2015-01-01

Currently the main design guidelines propose to reduce the lateral resistance of offshore piles when accounting for cyclic loading. The present work provides results from laboratory tests in which such reduction has not occurred. The experimental investigation is based on testing a small......-scale monopile model in dense saturated sand. The experimental setup used to carry out the laboratory tests is able to apply thousands of load cycles and static loading to the monopile model. The purpose of the laboratory tests is to investigate the effects of cyclic loading on the lateral resistance...... of the monopile. It is shown that the soil-pile system becomes stiffer and more resistant after applying cyclic loading, depending on the number of cycles....

Testing and modeling of cyclically loaded rock anchors

Directory of Open Access Journals (Sweden)

Joar Tistel

2017-12-01

Full Text Available The Norwegian Public Roads Administration (NPRA is planning for an upgrade of the E39 highway route at the westcoast of Norway. Fixed links shall replace ferries at seven fjord crossings. Wide spans and large depths at the crossings combined with challenging subsea topography and environmental loads call for an extension of existing practice. A variety of bridge concepts are evaluated in the feasibility study. The structures will experience significant loads from deadweight, traffic and environment. Anchoring of these forces is thus one of the challenges met in the project. Large-size subsea rock anchors are considered a viable alternative. These can be used for anchoring of floating structures but also with the purpose of increasing capacity of fixed structures. This paper presents first a thorough study of factors affecting rock anchor bond capacity. Laboratory testing of rock anchors subjected to cyclic loading is thereafter presented. Finally, the paper presents a model predicting the capacity of a rock anchor segment, in terms of a ribbed bar, subjected to a cyclic load history. The research assumes a failure mode occurring in the interface between the rock anchor and the surrounding grout. The constitutive behavior of the bonding interface is investigated for anchors subjected to cyclic one-way tensile loads. The model utilizes the static bond capacity curve as a basis, defining the ultimate bond τbu and the slip s1 at τbu. A limited number of input parameters are required to apply the model. The model defines the bond-slip behavior with the belonging rock anchor capacity depending on the cyclic load level (τmax cy/τbu, the cyclic load ratio (R = τmin cy/τmax cy, and the number of load cycles (N. The constitutive model is intended to model short anchor lengths representing an incremental length of a complete rock anchor.

Cyclic Elastoplastic Performance of Aluminum 7075-T6 Under Strain- and Stress-Controlled Loading

Science.gov (United States)

Agius, Dylan; Wallbrink, Chris; Kourousis, Kyriakos I.

2017-12-01

Elastoplastic investigations of aerospace aluminum are important in the development of an understanding of the possible cyclic transient effects and their contribution to the material performance under cyclic loading. Cyclic plasticity can occur in an aerospace aluminum component or structure depending on the loading conditions and the presence of external and internal discontinuities. Therefore, it is vital that the cyclic transient effects of aerospace aluminum are recognized and understood. This study investigates experimentally the cyclic elastoplastic performance of aluminum 7075-T6 loaded in symmetric strain control, and asymmetric stress and strain control. A combination of cyclic hardening and softening was noticed from high strain amplitude symmetric strain-controlled tests and at low stress amplitude asymmetric stress-controlled tests. From asymmetric strain control results, the extent of mean stress relaxation depended on the size of the strain amplitude. Additionally, saturation of the ratcheting strain (plastic shakedown) was also found to occur during asymmetric stress control tests. The experimental results were further analyzed using published microstructure research from the past two decades to provide added explanation of the micro-mechanism contribution to the cyclic transient behavior.

Failure mechanisms of closed-cell aluminum foam under monotonic and cyclic loading

International Nuclear Information System (INIS)

Amsterdam, E.; De Hosson, J.Th.M.; Onck, P.R.

2006-01-01

This paper concentrates on the differences in failure mechanisms of Alporas closed-cell aluminum foam under either monotonic or cyclic loading. The emphasis lies on aspects of crack nucleation and crack propagation in relation to the microstructure. The cell wall material consists of Al dendrites and an interdendritic network of Al 4 Ca and Al 22 CaTi 2 precipitates. In situ scanning electron microscopy monotonic tensile tests were performed on small samples to study crack nucleation and propagation. Digital image correlation was employed to map the strain in the cell wall on the characteristic microstructural length scale. Monotonic tensile tests and tension-tension fatigue tests were performed on larger samples to observe the overall fracture behavior and crack path in monotonic and cyclic loading. The crack nucleation and propagation path in both loading conditions are revealed and it can be concluded that during monotonic tension cracks nucleate in and propagate partly through the Al 4 Ca interdendritic network, whereas under cyclic loading cracks nucleate and propagate through the Al dendrites

Effectiveness of screw surface coating on the stability of zirconia abutments after cyclic loading.

Science.gov (United States)

Basílio, Mariana de Almeida; Butignon, Luis Eduardo; Arioli Filho, João Neudenir

2012-01-01

Different surface treatments have been developed in attempts to prevent the loosening of abutment screws. The aim of the current study was to compare the effectiveness of titanium alloy screws with tungsten-doped diamond-like carbon (W-DLC) coating and uncoated screws in providing stability to zirconia (ZrO2) ceramic abutments after cyclic loading. Twenty prefabricated ZrO2 ceramic abutments on their respective external-hex implants were divided into two groups of equal size according to the type of screw used: uncoated titanium alloy screw (Ti) or titanium alloy screw with W-DLC coating (W-DLC/Ti). The removal torque value (preload) of the abutment screw was measured before and after loading. Cyclic loading between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants at a frequency of 15 Hz. A target of 0.5 X 106 cycles was defined. Group means were calculated and compared using analysis of variance and the F test (α = .05). Before cyclic loading, the preload for Ti screws was significantly higher than that for W-DLC/Ti screws (P = .021). After cyclic loading, there was no significant difference between them (P = .499). Under the studied conditions, it can be concluded that, after cyclic loading, both abutment screws presented a significant reduction in the mean retained preload and similar effectiveness in maintaining preload.

Degradation forecast for PEMFC cathode-catalysts under cyclic loads

Science.gov (United States)

Moein-Jahromi, M.; Kermani, M. J.; Movahed, S.

2017-08-01

Degradation of Fuel Cell (FC) components under cyclic loads is one of the biggest bottlenecks in FC commercialization. In this paper, a novel experimental based algorithm is presented to predict the Catalyst Layer (CL) performance loss during cyclic load. The algorithm consists of two models namely Models 1 and 2. The Model 1 calculates the Electro-Chemical Surface Area (ECSA) and agglomerate size (e.g. agglomerate radius, rt,agg) for the catalyst layer under cyclic load. The Model 2 is the already-existing model from our earlier studies that computes catalyst performance with fixed structural parameters. Combinations of these two Models predict the CL performance under an arbitrary cyclic load. A set of parametric/sensitivity studies is performed to investigate the effects of operating parameters on the percentage of Voltage Degradation Rate (VDR%) with rank 1 for the most influential one. Amongst the considered parameters (such as: temperature, relative humidity, pressure, minimum and maximum voltage of the cyclic load), the results show that temperature and pressure have the most and the least influences on the VDR%, respectively. So that, increase of temperature from 60 °C to 80 °C leads to over 20% VDR intensification, the VDR will also reduce 1.41% by increasing pressure from 2 atm to 4 atm.

Assessment of burned coal shale properties based on cyclic load

Directory of Open Access Journals (Sweden)

Grygierek Marcin

2018-01-01

Full Text Available Road surfaces that are subjected to cyclic loads generated by vehicle wheels must meet the requirements concerning the durability in the assumed period of use. The durability of the layered pavement construction systems depends on the value and frequency of the load as well as on the mechanical features of its individual layers. Layers of unbound, mechanically stabilized mixtures are a significant aspect of surfaces that are susceptible. Mixtures of this type can be applied both to the subgrade layers as well as to the bottom pavement layers, including the improved course. Considering the cyclic nature of the load on the surface of the entire system, mechanically stabilized layers are subject to continuous, but slow, densification during the period of use, which results in the formation of permanent deformations and so-called structural ruts. Post-mining waste is frequently used in road construction. which is the so-called burned shale that can be used for the bottom layers of the surface and layers of the improved subgrade (soil replacement. This material was the subject of the analysis. The evaluation was based mainly on the results of pilot studies covering cyclic loads of the layer/course made of the so-called red shale. The applied research method was aimed at preliminary assessment of its suitability for the assessment of the behaviour of the disintegrated medium under the conditions of test loads simulating the movement of vehicles.

Assessment of burned coal shale properties based on cyclic load

Science.gov (United States)

Grygierek, Marcin; Kalisz, Piotr; Pacześniowski, Krzysztof; Pytlik, Andrzej; Zięba, Magdalena

2018-04-01

Road surfaces that are subjected to cyclic loads generated by vehicle wheels must meet the requirements concerning the durability in the assumed period of use. The durability of the layered pavement construction systems depends on the value and frequency of the load as well as on the mechanical features of its individual layers. Layers of unbound, mechanically stabilized mixtures are a significant aspect of surfaces that are susceptible. Mixtures of this type can be applied both to the subgrade layers as well as to the bottom pavement layers, including the improved course. Considering the cyclic nature of the load on the surface of the entire system, mechanically stabilized layers are subject to continuous, but slow, densification during the period of use, which results in the formation of permanent deformations and so-called structural ruts. Post-mining waste is frequently used in road construction. which is the so-called burned shale that can be used for the bottom layers of the surface and layers of the improved subgrade (soil replacement). This material was the subject of the analysis. The evaluation was based mainly on the results of pilot studies covering cyclic loads of the layer/course made of the so-called red shale. The applied research method was aimed at preliminary assessment of its suitability for the assessment of the behaviour of the disintegrated medium under the conditions of test loads simulating the movement of vehicles.

Molecular Simulations of Cyclic Loading Behavior of Carbon Nanotubes Using the Atomistic Finite Element Method

Directory of Open Access Journals (Sweden)

Jianfeng Wang

2009-01-01

Full Text Available The potential applications of carbon nanotubes (CNT in many engineered bionanomaterials and electromechanical devices have imposed an urgent need on the understanding of the fatigue behavior and mechanism of CNT under cyclic loading conditions. To date, however, very little work has been done in this field. This paper presents the results of a theoretical study on the behavior of CNT subject to cyclic tensile and compressive loads using quasi-static molecular simulations. The Atomistic Finite Element Method (AFEM has been applied in the study. It is shown that CNT exhibited extreme cyclic loading resistance with yielding strain and strength becoming constant within limited number of loading cycles. Viscoelastic behavior including nonlinear elasticity, hysteresis, preconditioning (stress softening, and large strain have been observed. Chiral symmetry was found to have appreciable effects on the cyclic loading behavior of CNT. Mechanisms of the observed behavior have been revealed by close examination of the intrinsic geometric and mechanical features of tube structure. It was shown that the accumulated residual defect-free morphological deformation was the primary mechanism responsible for the cyclic failure of CNT, while the bond rotating and stretching experienced during loading/unloading played a dominant role on the strength, strain and modulus behavior of CNT.

Centrifuge modelling of a laterally cyclic loaded pile

DEFF Research Database (Denmark)

Klinkvort, Rasmus Tofte; Leth, Caspar Thrane; Hededal, Ole

2010-01-01

A total number of 9 static and 6 cyclic centrifuge tests on laterally loaded piles in very dense, dry sand was erformed. The prototype dimensions of the piles were 1 meter in diameter and penetration depths varying from 6 to 10 meters. The static tests were used to investigate the initial subgrade...... reaction modulus and as a reference for cyclic tests. For the cyclic tests the accumulation of deflections and the change in secant stiffness of the soil from repetitive loading were investigated. From all the tests carried out accumulations of deflections were seen. rom the centrifuge tests it was seen...

Cyclic loading of thick vessels based on the Prager and Armstrong-Frederick kinematic hardening models

International Nuclear Information System (INIS)

Mahbadi, H.; Eslami, M.R.

2006-01-01

The aim of this paper is to relate the type of stress category in cyclic loading to ratcheting or shakedown behaviour of the structure. The kinematic hardening theory of plasticity based on the Prager and Armstrong-Frederick models is used to evaluate the cyclic loading behaviour of thick spherical and cylindrical vessels under load and deformation controlled stresses. It is concluded that kinematic hardening based on the Prager model under load and deformation controlled conditions, excluding creep, results in shakedown or reversed plasticity for spherical and cylindrical vessels with the isotropy assumption of the tension/compression curve. Under an anisotropy assumption of the tension/compression curve, this model predicts ratcheting. On the other hand, the Armstrong-Frederick model predicts ratcheting under load controlled cyclic loading and reversed plasticity for deformation controlled stress. The interesting conclusion is that the Armstrong-Frederick model is well capable to predict the experimental data under the assumed type of stresses, wherever experimental data are available

THE STRENGTH OF REINFORCED CONCRETE BEAM ELEMENTS UNDER CYCLIC ALTERNATING LOADING AND LOW CYCLE LOAD OF CONSTANT SIGN

Directory of Open Access Journals (Sweden)

Semina Yuliya Anatol'evna

2015-09-01

Full Text Available The behavior of reinforced concrete elements under some types of cyclic loads is described in the paper. The main aim of the investigations is research of the stress-strain state and strength of the inclined sections of reinforced concrete beam elements in conditions of systemic impact of constructive factors and the factor of external influence. To spotlight the problem of cyclic loadings three series of tests were conducted by the author. Firstly, the analysis of the tests showed that especially cyclic alternating loading reduces the bearing capacity of reinforced concrete beams and their crack resistance by 20 % due to the fatigue of concrete and reinforcement. Thus the change of load sign creates serious changes of stress-strain state of reinforced concrete beam elements. Low cycle loads of constant sign effect the behavior of the constructions not so adversely. Secondly, based on the experimental data mathematical models of elements’ strength were obtained. These models allow evaluating the impact of each factor on the output parameter not only separately, but also in interaction with each other. Furthermore, the material spotlighted by the author describes stress-strain state of the investigated elements, cracking mechanism, changes of deflection values, the influence of mode cyclic loading during the tests. Since the data on the subject are useful and important to building practice, the ultimate aim of the tests will be working out for improvement of nonlinear calculation models of span reinforced concrete constructions taking into account the impact of these loads, and also there will be the development of engineering calculation techniques of their strength, crack resistance and deformability.

Cyclic deformation and fatigue data for Ti–6Al–4V ELI under variable amplitude loading

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Patricio E. Carrion

2017-08-01

Full Text Available This article presents the strain-based experimental data for Ti–6Al–4V ELI under non-constant amplitude cyclic loading. Uniaxial strain-controlled fatigue experiments were conducted under three different loading conditions, including two-level block loading (i.e. high-low and low-high, periodic overload, and variable amplitude loading. Tests were performed under fully-reversed, and mean strain/stress conditions. For each test conducted, two sets of data were collected; the cyclic stress–strain response (i.e. hysteresis loops in log10 increments, and the peak and valley values of stress and strain for each cycle. Residual fatigue lives are reported for tests with two-level block loading, while for periodic overload and variable amplitude experiments, fatigue lives are reported in terms of number of blocks to failure.

Fracture studies on stainless steel straight pipes under earthquake-type cyclic loading

International Nuclear Information System (INIS)

Raghava, G.; Vishnuvardhan, S.; Gandhi, P.; Vaze, K.K.

2014-01-01

In order to study the crack growth and cyclic fracture behaviour, which are required for realistic assessment of Leak Before Break (LBB) applicability, experimental investigations were carried out on straight pipes under quasi-crystal loading. Totally 13 pipes were tested; three were stainless steel welded (SSW) using conventional shielded metal arc welding (SMAW) technique and the remaining specimens were Narrow Gap Welded (NGW). The fracture tests were carried out under load control, displacement control and combination of the two; the pipes were subjected to different amplitudes of load or load-line displacement (LLD), which were decided based on the response of the pipes under monotonic loading. Cyclic tearing and crack growth studies on eight straight pipes of the same material reported earlier in published literature are also considered for studying the results and understanding the behaviour. Under load control, with almost equal load amplitude, the NGW pipe exhibited improved life in comparison with SMAW pipe when both are subjected to cyclic loading. The crack growth and tearing instability behaviour of the pipes were studied. The same were found to be different for load control, displacement control and combined control tests. Based in the load-controlled experimental results, material specific plot between cyclic load amplitude (as a percentage of maximum load carrying capacity of a specimen under monotonic fracture) and number of cycles to failure was obtained. The results indicate that the piping components subjected to quasi-cyclic loading may fail in very less number of cycles even when the load amplitude is sufficiently below the monotonic fracture/collapse load. These studies will be helpful in designing nuclear power plant (NPP) piping components subjected to earthquake-type cyclic loading. (author)

Constitutive model and electroplastic analysis of structures under cyclic loading

International Nuclear Information System (INIS)

Wang, X.; Lei, Y; Du, Q.

1989-01-01

Many engineering structures in nuclear reactors, thermal power stations, chemical plants and aerospace vehicles are subjected to cyclic mechanic-thermal loading, which is the main cause of structural fatigue failure. Over the past twenty years, designers and researchers have paid great attention to the research on life prediction and elastoplastic analysis of structures under cyclic loading. One of the key problems in elastoplastic analysis is to construct a reasonable constitutive model for cyclic plasticity. In the paper, the constitutive equations are briefly outlined. Then, the model is implemented in a finite element code to predict the response of cyclic loaded structural components such as a double-edge-notched plate, a grooved bar and a nozzle in spherical shell. Numerical results are compared with those from other theories and experiments

Tape cast isotropic, fine-grained tungsten for thermo-cyclic loading applications

Energy Technology Data Exchange (ETDEWEB)

Sommerer, Mathias, E-mail: Mathias.Sommerer@tum.de [Lehrstuhl für Werkstoffkunde und Werkstoffmechanik, Technische Universität München, Boltzmannstr. 15, 85748 Garching (Germany); Li, Muyuan [Max-Planck-Institut für Plasma Physik, Boltzmannstraße 2, 85748 Garching (Germany); Werner, Ewald [Lehrstuhl für Werkstoffkunde und Werkstoffmechanik, Technische Universität München, Boltzmannstr. 15, 85748 Garching (Germany); Dewitz, Hubertus von; Walter, Steffen; Lampenscherf, Stefan [Siemens AG, Corporate Technology, Otto-Hahn-Ring 6, 81730 München (Germany); Arnold, Thomas [Siemens Healthcare GmbH, Henkestr. 127, 91052 Erlangen (Germany)

2016-04-15

Highlights: • The tape casting process for tungsten is described. • A set-up of a HHF test facility for standing anodes is presented. • The thermo-cyclic behavior of tape cast tungsten and a reference is investigated. • The evolution of crack patterns is described in dependency of HHF-loadings. • The surface roughness of X-ray anodes is related to the microstructural evolution. - Abstract: This paper introduces tape casting as a new route for the production of isotropic and fine-grained tungsten components. Microstructural and thermal properties of tape cast tungsten samples are determined. Thermal shock behavior according to the thermo-cyclic loading of standing X-ray anodes is investigated and compared to the behavior of a rolled tungsten grade. The development of surface roughness during the thermal shock loading is discussed in relation to the development of the grain structure and crack pattern. The fine-grained and stable microstructure of the tape cast material exhibits less roughening under such test conditions.

Performance of 3Y-TZP bioceramics under cyclic fatigue loading

Directory of Open Access Journals (Sweden)

Renato Chaves Souza

2008-03-01

Full Text Available In this work, the static mechanical properties and cyclic fatigue life of 3 mol. (% Y2O3-stabilized tetragonal zirconia polycrystalline (3Y-TZP ceramics were investigated. Pre-sintered samples were sintered in air at 1600 °C for 120 minutes, and characterized by X ray diffraction and scanning electronic microscopy. Hardness and fracture toughness were determined by Vicker's indentation method, and Modulus of Rupture was determined by four-point bending testing. Fully dense sintered samples, near to 100% of theoretical density, presented hardness, fracture toughness and bending strength of 13.5 GPa, 8.2 MPa.m½ and 880 MPa, respectively. The cyclic fatigue tests were also realized using four-point bending testing, within a frequency of 25 Hz and stress ratio R of 0.1. The increasing of load stress lead to decreasing of the number of cycles and the run-out specimens number. The tetragonal-monoclinic (t-m ZrO2-transformation observed by X ray diffraction contributes to the increasing of the fatigue life. The 3Y-TZP samples clearly presents a range of loading conditions where cyclic fatigue can be detected.

Effect of Cyclic Loading on Micromotion at the Implant-Abutment Interface.

Science.gov (United States)

Karl, Matthias; Taylor, Thomas D

2016-01-01

Cyclic loading may cause settling of abutments mounted on dental implants, potentially affecting screw joint stability and implant-abutment micromotion. It was the goal of this in vitro study to compare micromotion of implant-abutment assemblies before and after masticatory simulation. Six groups of abutments (n = 5) for a specific tissue-level implant system with an internal octagon were subject to micromotion measurements. The implant-abutment assemblies were loaded in a universal testing machine, and an apparatus and extensometers were used to record displacement. This was done twice, in the condition in which they were received from the abutment manufacturer and after simulated loading (100,000 cycles; 100 N). Statistical analysis was based on analysis of variance, two-sample t tests (Welch tests), and Pearson product moment correlation (α = .05). The mean values for micromotion ranged from 33.15 to 63.41 μm and from 30.03 to 42.40 μm before and after load cycling. The general trend toward reduced micromotion following load cycling was statistically significant only for CAD/CAM zirconia abutments (P = .036) and for one type of clone abutment (P = .012), with no significant correlation between values measured before and after cyclic loading (Pearson product moment correlation; P = .104). While significant differences in micromotion were found prior to load cycling, no significant difference among any of the abutment types tested could be observed afterward (P > .05 in all cases). A quantifiable settling effect at the implant-abutment interface seems to result from cyclic loading, leading to a decrease in micromotion. This effect seems to be more pronounced in low-quality abutments. For the implant system tested in this study, retightening of abutment screws is recommended after an initial period of clinical use.

Small-Scale Testing Rig for Long-Term Cyclically Loaded Monopiles in Cohesionless Soil

DEFF Research Database (Denmark)

Roesen, Hanne Ravn; Ibsen, Lars Bo; Andersen, Lars Vabbersgaard

2012-01-01

, and the period of the cyclic loading. However, the design guidance on these issues is limited. Thus, in order to investigate the pile behaviour for cyclically long-term loaded monopiles, a test setup for small-scale tests in saturated dense cohesionless soil is constructed and presented in here. The cyclic...... loading is applied mechanically by means of a testing rig, where the important input parameters: mean level, amplitude, number of cycles, and period of the loading can be varied. The results from a monotonic and a cyclic loading test on an open-ended aluminium pile with diameter = 100 mm and embedded...... length = 600 mm proves that the test setup is capable of applying the cyclic long-term loading. The plastic deformations during loading depend not only on the loading applied but also of the relative density of the soil and, thus, the tests are carried out with relative densities of 77-88%, i.e. similar...

Micromechanical studies of cyclic creep fracture under stress controlled loading

DEFF Research Database (Denmark)

van der Giessen, Erik; Tvergaard, Viggo

1996-01-01

is based on numerical unit cell analyses for a planar polycrystal model with the grains and grain boundaries modeled individually, in order to investigate the interactions between the mechanisms involved and to account for the build-up of residual stress fields during cycling. The behaviour of a limiting......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...

Modeling of creep-fatigue interaction of zirconium α under cyclic loading at 200 C

International Nuclear Information System (INIS)

Vogel, C.

1996-04-01

The present work deals with mechanical behaviour of zirconium alpha at 200 deg. C and crack initiation prediction methods, particularly when loading conditions lead to interaction of fatigue and creep phenomena. A classical approach used to study interaction between cyclic effects and constant loading effects does not give easy understanding of experimental results. Therefore, a new approach has been developed, which allow to determine a number of cycles for crack initiation for complex structures under large loading conditions. To study influence of fatigue and creep interaction on crack initiation, a model was chosen, using a scalar variable, giving representation of the material deterioration state. The model uses a non linear cumulating effect between the damage corresponding to cyclic loads and the damage correlated to time influence. The model belongs to uncoupled approaches between damage and behaviour, which is described here by a two inelastic deformations model. This mechanical behaviour model is chosen because it allows distinction between a plastic and a viscous part in inelastic flow. Cyclic damage is function of stress amplitude and mean stress. For the peculiar sensitivity of the material to creep, a special parameter bas been defined to be critical toward creep damage. It is the kinematic term associated to state variables describing this type of hardening in the viscous mechanism. (author)

The influence of cyclic loading on gentamicin release from acrylic bone cements

NARCIS (Netherlands)

Hendriks, JGE; Neut, D; Hazenberg, JG; Verkerke, GJ; van Horn, [No Value; van der Mei, HC; Busscher, HJ

Antibiotic-loaded acrylic bone cement is widely used in total joint replacement to reduce infections. Walking results in cyclic loading, which has been suggested to stimulate antibiotic release. The goal of this study is to compare antibiotic release from cyclically loaded bone cement with the

Numerical modeling of centrifuge cyclic lateral pile load experiments

Science.gov (United States)

Gerolymos, Nikos; Escoffier, Sandra; Gazetas, George; Garnier, Jacques

2009-03-01

To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussées. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on reconstituted samples, and well-established empirical correlations. The tests were simulated using a cyclic nonlinear Winkler spring model, which describes the full range of inelastic phenomena, including separation and re-attachment of the pile from and to the soil. The model consists of three mathematical expressions capable of reproducing a wide variety of monotonic and cyclic experimental p-y curves. The physical meaning of key model parameters is graphically explained and related to soil behavior. Comparisons with the centrifuge test results demonstrate the general validity of the model and its ability to capture several features of pile-soil interaction, including: soil plastification at an early stage of loading, “pinching” behavior due to the formation of a relaxation zone around the upper part of the pile, and stiffness and strength changes due to cyclic loading. A comparison of the p-y curves derived from the test results and the proposed model, as well as those from the classical curves of Reese et al. (1974) for sand, is also presented.

The structural behavior of a bolted flanged connection subjected to a cyclic load

International Nuclear Information System (INIS)

Cesari, F.

1981-01-01

In the vessel of BWR nuclear plants, the bolted flanged connection is subjected to a cyclic load, consisting of four steps: the bolt load, the pressure load with decreasing of bolt load, depressurization with increasing bold load, and at the end, unbolting. In the case of rigid, bolted flange, the elastic behavior is essentially correct, but if the height of the flange is decreased, then the stress gradients are so high that the strains move into the plastic range. In addition, the design of pressure vessels is not complete without an appraisal of failure by progressive distortion or stress ratchteing. There is therefore a need for numerical results for the structures subjected to well-known loading. The aim of this paper is to follow the stress and strain of a bolted flange subjected to the cyclic load, progressively varying the height of the flange, so that the maximum stress intensity becomes 3 Ssub(m). The number of cycles was sufficient to verify the conditions of shakedown or ratcheting. The numerical analysis, using finite element technique and the Adina code, is well established and frequently used. (orig.)

A Discrete Element Method Centrifuge Model of Monopile under Cyclic Lateral Loads

OpenAIRE

Nuo Duan; Yi Pik Cheng

2016-01-01

This paper presents the data of a series of two-dimensional Discrete Element Method (DEM) simulations of a large-diameter rigid monopile subjected to cyclic loading under a high gravitational force. At present, monopile foundations are widely used to support the tall and heavy wind turbines, which are also subjected to significant from wind and wave actions. A safe design must address issues such as rotations and changes in soil stiffness subject to these loadings conditions. Design guidance ...

Cyclic loading tests on ceramic breeder pebble bed by discrete element modeling

Energy Technology Data Exchange (ETDEWEB)

Zhang, Hao [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230027 (China); Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China); Guo, Haibing; Shi, Tao [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China); Ye, Minyou [School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230027 (China); Huang, Hongwen, E-mail: hhw@caep.cn [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China); Li, Zhenghong, E-mail: inpcnyb@sina.com [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China); University of Science and Technology of China, Hefei 230027 (China)

2017-05-15

Highlights: • Methods of cyclic loading tests on the pebble beds were developed in DEM. • Size distribution and sphericity of the pebbles were considered for the specimen. • Mechanical responses of the pebble beds under cyclic loading tests were assessed. - Abstract: Complex mechanics and packing instability can be induced by loading operation on ceramic breeder pebble bed for its discrete nature. A numerical approach using discrete element method (DEM) is applied to study the mechanical performance of the ceramic breeder pebble bed under quasi-static and cyclic loads. A preloaded specimen can be made with servo-control mechanism, the quasi-static and dynamic stress-strain performances are studied during the tests. It is found that the normalized normal contact forces under quasi-static loads have the similar distributions, and increase with increasing loads. Furthermore, the relatively low volumetric strain can be absorbed by pebble bed after several loading and unloading cycles, but the peak normal contact force can be extremely high during the first cycle. Cyclic loading with target pressure is recommended for densely packing, irreversible volume reduction gradually increase with cycles, and the normal contact forces decrease with cycles.

Cyclic loading tests on ceramic breeder pebble bed by discrete element modeling

International Nuclear Information System (INIS)

Zhang, Hao; Guo, Haibing; Shi, Tao; Ye, Minyou; Huang, Hongwen; Li, Zhenghong

2017-01-01

Highlights: • Methods of cyclic loading tests on the pebble beds were developed in DEM. • Size distribution and sphericity of the pebbles were considered for the specimen. • Mechanical responses of the pebble beds under cyclic loading tests were assessed. - Abstract: Complex mechanics and packing instability can be induced by loading operation on ceramic breeder pebble bed for its discrete nature. A numerical approach using discrete element method (DEM) is applied to study the mechanical performance of the ceramic breeder pebble bed under quasi-static and cyclic loads. A preloaded specimen can be made with servo-control mechanism, the quasi-static and dynamic stress-strain performances are studied during the tests. It is found that the normalized normal contact forces under quasi-static loads have the similar distributions, and increase with increasing loads. Furthermore, the relatively low volumetric strain can be absorbed by pebble bed after several loading and unloading cycles, but the peak normal contact force can be extremely high during the first cycle. Cyclic loading with target pressure is recommended for densely packing, irreversible volume reduction gradually increase with cycles, and the normal contact forces decrease with cycles.

Cyclic plastic material behavior leading to crack initiation in stainless steel under complex fatigue loading conditions

International Nuclear Information System (INIS)

Facheris, G.

2014-01-01

The improvement of the reliability and of the safety in the design of components belonging to the primary cooling circuit of a light water nuclear reactor is nowadays one of the most important research topics in nuclear industry. One of the most important damage mechanisms leading the crack initiation in this class of components is the low cycle fatigue (LCF) driven by thermal strain fluctuations caused by the complex thermo-mechanical loading conditions typical for the primary circuit (e.g. operating thermal transients, thermal stratification, turbulent mixing of cold and hot water flows, etc.). The cyclic application of the resulting plastic deformation to the steel grades commonly used for the fabrication of piping parts (e.g. austenitic stainless steels) is associated with a continuous evolution of the mechanical response of the material. As an additional complication, the cyclic behavior of stainless steels is influenced by temperature, strain amplitude and cyclic accumulation of inelastic strain (i.e. ratcheting). The accurate prediction of the structural response of components belonging to the primary cooling circuit requires the development of a reliable constitutive model that must be characterized by a reduced complexity to allow its application in an industrial context. In this framework, the main goal of the current dissertation is to formulate, calibrate and implement in a commercial Finite Element code, a constitutive model that is suitable for the stainless stain grade 316L subjected to complex loading conditions. As a first task, a characterization of the mechanical behavior of 316L subjected to uniaxial and multiaxial strain-controlled conditions (including LCF and ratcheting) is carried out performing several tests in the laboratories of the Paul Scherrer Institute (PSI, Villigen, Switzerland) and of Politecnico di Milano (Italy). The uniaxial experiments demonstrate that, prescribing a strain-controlled ratcheting path, a harder material response

Cyclic plastic material behavior leading to crack initiation in stainless steel under complex fatigue loading conditions

Energy Technology Data Exchange (ETDEWEB)

Facheris, G.

2014-07-01

The improvement of the reliability and of the safety in the design of components belonging to the primary cooling circuit of a light water nuclear reactor is nowadays one of the most important research topics in nuclear industry. One of the most important damage mechanisms leading the crack initiation in this class of components is the low cycle fatigue (LCF) driven by thermal strain fluctuations caused by the complex thermo-mechanical loading conditions typical for the primary circuit (e.g. operating thermal transients, thermal stratification, turbulent mixing of cold and hot water flows, etc.). The cyclic application of the resulting plastic deformation to the steel grades commonly used for the fabrication of piping parts (e.g. austenitic stainless steels) is associated with a continuous evolution of the mechanical response of the material. As an additional complication, the cyclic behavior of stainless steels is influenced by temperature, strain amplitude and cyclic accumulation of inelastic strain (i.e. ratcheting). The accurate prediction of the structural response of components belonging to the primary cooling circuit requires the development of a reliable constitutive model that must be characterized by a reduced complexity to allow its application in an industrial context. In this framework, the main goal of the current dissertation is to formulate, calibrate and implement in a commercial Finite Element code, a constitutive model that is suitable for the stainless stain grade 316L subjected to complex loading conditions. As a first task, a characterization of the mechanical behavior of 316L subjected to uniaxial and multiaxial strain-controlled conditions (including LCF and ratcheting) is carried out performing several tests in the laboratories of the Paul Scherrer Institute (PSI, Villigen, Switzerland) and of Politecnico di Milano (Italy). The uniaxial experiments demonstrate that, prescribing a strain-controlled ratcheting path, a harder material response

Fracture toughness of Ti-Al3Ti-Al-Al3Ti laminate composites under static and cyclic loading conditions

Science.gov (United States)

Patselov, A. M.; Gladkovskii, S. V.; Lavrikov, R. D.; Kamantsev, I. S.

2015-10-01

The static and cyclic fracture toughnesses of a Ti-Al3Ti-Al-Al3Ti laminate composite material containing at most 15 vol % intermetallic compound are studied. Composite specimens are prepared by terminating reaction sintering of titanium and aluminum foils under pressure. The fracture of the titanium layers is quasi-cleavage during cyclic crack growth and is ductile during subsequent static loading.

Finite element analysis of the biaxial cyclic tensile loading of the elastoplastic plate with the central hole: asymptotic regimes

Science.gov (United States)

Turkova, Vera; Stepanova, Larisa

2018-03-01

For elastistoplastic structure elements under cyclic loading three types of asymptotic behavior are well known: shakedown, cyclic plasticity or ratcheting. In structure elements operating in real conditions ratcheting must always be excluded since it caused the incremental fracture of structure by means of the accumulation of plastic strains. In the present study results of finite-element (FEM) calculations of the asymptotical behavior of an elastoplastic plate with the central circular and elliptic holes under the biaxial cyclic loading for three different materials are presented. Incremental cyclic loading of the sample with stress concentrator (the central hole) is performed in the multifunctional finite-element package SIMULIA Abaqus. The ranges of loads found for shakedown, cyclic plasticity and ratcheting are presented. The results obtained are generalized and analyzed. Convenient normalization is suggested. The chosen normalization allows us to present all computed results, corresponding to separate materials, within one common curve with minimum scattering of the points. Convenience of the generalized diagram consists in a possibility to find an asymptotical behavior of an inelastic structure for materials for which computer calculations were not made.

A constitutive model for AS4/PEEK thermoplastic composites under cyclic loading

Science.gov (United States)

Rui, Yuting; Sun, C. T.

1990-01-01

Based on the basic and essential features of the elastic-plastic response of the AS4/PEEK thermoplastic composite subjected to off-axis cyclic loadings, a simple rate-independent constitutive model is proposed to describe the orthotropic material behavior for cyclic loadings. A one-parameter memory surface is introduced to distinguish the virgin deformation and the subsequent deformation process and to characterize the loading range effect. Cyclic softening is characterized by the change of generalized plastic modulus. By the vanishing yield surface assumption, a yield criterion is not needed and it is not necessary to consider loading and unloading separately. The model is compared with experimental results and good agreement is obtained.

Thermal and mechanical cyclic loading of thick spherical vessels made of transversely isotropic materials

International Nuclear Information System (INIS)

Komijani, M.; Mahbadi, H.; Eslami, M.R.

2013-01-01

The aim of this paper is to obtain the dependency of the ratcheting, reversed plasticity, or shakedown behavior of spherical vessels made of some anisotropic materials to the stress category of imposed cyclic loading. The Hill anisotropic yield criterion with the kinematic hardening theories of plasticity based on the Prager and Armstrong–Frederick models are used to predict the yield of the vessel and obtain the plastic strains. An iterative numerical method is used to simulate the cyclic loading behavior of the structure. The effect of mean and amplitude of the mechanical and thermal loads on cyclic behavior and ratcheting rate of the vessel is investigated respectively. The ratcheting rate for the vessels made of transversely isotropic material is evaluated for the various ratios of anisotropy. -- Highlights: ► Cyclic loading analysis of anisotropic spheres is assessed. ► Using the Prager model results in ratcheting. ► Armstrong-Frederick model predicts ratcheting for load controlled cyclic loadings. ► The A-F model predicts ratcheting to a stabilized cycle for thermal loadings

Magnetoelastic Demagnetization of Steel under Cyclic Loading

Science.gov (United States)

Muratov, K. R.; Novikov, V. F.; Neradovskii, D. F.; Kazakov, R. Kh.

2018-01-01

Magnetoelastic demagnetization of steel samples under cyclic tensile loads has been analyzed. It has been established that values of residual magnetization that correspond to peak loads are characterized by the power-law dependence on the number of loading cycles. In some cases, in the region of high loads, the qualitative transition to exponential dependence has been observed. Coefficients of the power-law approximation of peak magnetization depend on the value of amplitude load and have specific characteristics in the vicinity of characteristic loads. The ratios of approximated slide load coefficients depending on the load are common for the three considered samples, and there is an outburst in the vicinity of the fatigue limit, which can be used as the basis for developing the rapid nondestructive method for determination of this limit.

Empirical approach based on centrifuge testing for cyclic deformations of laterally loaded piles in sand

DEFF Research Database (Denmark)

Truong, P.; Lehane, B. M.; Zania, Varvara

2018-01-01

A systematic study into the response of monopiles to lateral cyclic loading in medium dense and dense sand was performed in beam and drum centrifuge tests. The centrifuge tests were carried out at different cyclic load and magnitude ratios, while the cyclic load sequence was also varied...

Ratcheting study in pressurized piping components under cyclic loading at room temperature

International Nuclear Information System (INIS)

Ravi Kiran, A.; Agrawal, M.K.; Reddy, G.R.; Vaze, K.K.; Ghosh, A.K.; Kushwaha, H.S.

2006-07-01

The nuclear power plant piping components and systems are often subjected to reversing cyclic loading conditions due to various process transients, seismic and other events. Earlier the design of piping subjected to seismic excitation was based on the principle of plastic collapse. It is believed that during such events, fatigue-ratcheting is likely mode of failure of piping components. The 1995 ASME Boiler and Pressure Vessel code, Section-III, has incorporated the reverse dynamic loading and ratcheting into the code. Experimental and analytical studies are carried out to understand this failure mechanism. The biaxial ratcheting characteristics of SA 333, Gr. 6 steel and SS 304 stainless steel at room temperature are investigated in the present work. Experiments are carried out on straight pipes subjected to internal pressure and cyclic bending load applied in a three point and four point bend test configurations. A shake table test is also carried out on a pressurized elbow by applying sinusoidal base excitation. Analytical simulation of ratcheting in the piping elements is carried out. Chaboche nonlinear kinematic hardening model is used for ratcheting simulation. (author)

Physical Modelling of Cyclic Laterally Loaded Pile in Cohesionless Soil

DEFF Research Database (Denmark)

Hansen, Mette; Wolf, Torben K.; Rasmussen, Kristian L.

Offshore wind turbines are normally founded with large diameter monopiles and placed in rough environments subjected to variable lateral loads from wind and waves. A long-term lateral loading may create rotation (tilt) of the pile by change in the pile-soil system which is critical in the service......Offshore wind turbines are normally founded with large diameter monopiles and placed in rough environments subjected to variable lateral loads from wind and waves. A long-term lateral loading may create rotation (tilt) of the pile by change in the pile-soil system which is critical...... in the serviceability limit state. In this paper small-scale testing of a pile subjected to cyclic, lateral loading is treated in order to investigate the effect of cyclic loading. The test setup, which is an improvement of a previous setup, is described and the first results of testing are compared with previous...

Laboratory Testing of Cyclic Laterally Loaded Pile in Cohesionless Soil

DEFF Research Database (Denmark)

Roesen, Hanne Ravn; Ibsen, Lars Bo; Hansen, Mette

2013-01-01

Offshore wind turbines are normally founded with large diameter monopiles and placed in rough environments subjected to variable lateral loads from wind and waves. A long-term lateral loading may create rotation (tilt) of the pile by change in the pile-soil system which is critical in the service......Offshore wind turbines are normally founded with large diameter monopiles and placed in rough environments subjected to variable lateral loads from wind and waves. A long-term lateral loading may create rotation (tilt) of the pile by change in the pile-soil system which is critical...... in the serviceability limit state. In this paper small-scale testing of a pile subjected to cyclic, lateral loading is treated in order to investigate the effect of cyclic loading. The test setup, which is an improvement of a previous setup, is described and the first results of testing are compared with previous...

Progressive buckling under both constant axial load and cyclic distortion

International Nuclear Information System (INIS)

Clement, G.; Acker, D.; Lebey, J.

1988-09-01

Thin structures submitted to compressive loads must be carefully designed to avoid any risk of ruin by buckling. The aim of this paper is, first, to evidence that the critical buckling load may be notably lowered when cyclic strains are added to the compressive load and, secondly, to propose a practical rule of prevention against the ruin due to the progressive buckling phenomenon. This rule is validated by the results of numerous tests related to the entire range of modes of buckling (i.e. from fully plastic to fully elastic). Practical cases of interest for its use could mainly be those where cyclic thermal stresses are involved

Fatigue analysis of CANFLEX-NU fuel elements subjected to power-cyclic loads

International Nuclear Information System (INIS)

Sim, Ki Seob; Suk, Ho Chun.

1997-08-01

This report describes the fatigue analysis of the CANDU advanced fuel, so-called CANFLEX-NU, subjected to power-cyclic loads more than 1,000. The CANFLEX-NU bundle is composed of 43 elements with natural uranium fuel. As a result, the CANFLEX-NU fuel elements will maintain good integrity under the condition of 1,500 power-cycles. (author). 4 refs., 19 figs

Residual stresses under quasi-static and cyclic loading in shot peened Inconel 718

Energy Technology Data Exchange (ETDEWEB)

Hoffmeister, Juergen; Schulze, Volker [Karlsruhe Institute of Technology (KIT), Karlsruhe (Germany). Inst. for Applied Materials; Hessert, Roland; Koenig, Gerhard [MTU Aero Engines, Munich (Germany)

2012-01-15

The residual stress state induced by shot peening should be taken into account in the dimensioning of turbine components. Understanding the changes in the residual stress state caused by the application of quasi-static and cyclic loads is a prerequisite. In order to describe the residual stress state after quasi-static loading, several different shot peened Inconel 718 specimens were loaded isothermally up to specific tensile loadings. To analyze the residual stress state after cyclic loading, isothermal low cycle fatigue tests were performed. These tests were stopped after a defined number of cycles. Finally, after the specimens had been subjected to different loads, the surface residual stresses and - for special loadings - the residual stress depth distributions were determined experimentally by using X-ray diffraction. The surface - core model was adapted so that the complete residual stress depth distribution after quasi-static and cyclic loading can now be described. (orig.)

Analysis of the kinetics of decohesion process in the conditions of cyclic temperature variations

International Nuclear Information System (INIS)

Zuchowski, R.

1981-01-01

Specimens made of four types of heat-resistant steels were used in the investigation. Various variants of loading process were applied, resulting in thermal fatigue, cyclic creep and isothermal fatigue. Stress or strain variation as well as intensity of acoustic emission were recorded during the tests as a function of time. Cyclic variations of strain or stress amplitude were found to occur one full period covering few to several cycles. Comparing the relative number of acoustic emission impulses with the variation of stress or strain leads to the conclusion that cyclic character of strain or stress variation results from cyclic character of damage cumulation process. This statement is confirmed by the results of material damage degree determination based on specific strain work measurements. Results of investigation testify to the equivalence of action (in terms of energy) of cyclically variable force field at constant temperature and of constant force field in the conditions of cyclic temperature variations. Damage mechanism can be different in each case, because it depends (for a given material) on loading process parameters and in particular - on temperature and stress value. (orig./HP)

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

Science.gov (United States)

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

Science.gov (United States)

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Experimental Investigation on Deformation Failure Characteristics of Crystalline Marble Under Triaxial Cyclic Loading

Science.gov (United States)

Yang, Sheng-Qi; Tian, Wen-Ling; Ranjith, P. G.

2017-11-01

The deformation failure characteristics of marble subjected to triaxial cyclic loading are significant when evaluating the stability and safety of deep excavation damage zones. To date, however, there have been notably few triaxial experimental studies on marble under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic tests was conducted to analyze the mechanical damage characteristics of a marble. The post-peak deformation of the marble changed gradually from strain softening to strain hardening as the confining pressure increased from 0 to 10 MPa. Under uniaxial compression, marble specimens showed brittle failure characteristics with a number axial splitting tensile cracks; in the range of σ 3 = 2.5-7.5 MPa, the marble specimens assumed single shear fracture characteristics with larger fracture angles of about 65°. However, at σ 3 = 10 MPa, the marble specimens showed no obvious shear fracture surfaces. The triaxial cyclic experimental results indicate that in the range of the tested confining pressures, the triaxial strengths of the marble specimens under cyclic loading were approximately equal to those under monotonic loading. With the increase in cycle number, the elastic strains of the marble specimens all increased at first and later decreased, achieving maximum values, but the plastic strains of the marble specimens increased nonlinearly. To evaluate quantitatively the damage extent of the marble under triaxial cyclic loading, a damage variable is defined according to the irreversible deformation for each cycle. The evolutions of the elastic modulus for the marble were characterized by four stages: material strengthening, material degradation, material failure and structure slippage. Based on the experimental results of the marble specimens under complex cyclic loading, the cohesion of the marble decreased linearly, but the internal friction angles did not depend on the damage extent. To describe the peak strength

Cyclic Loading of Growing Tissue in a Bioreactor: Mathematical Model and Asymptotic Analysis

KAUST Repository

Pohlmeyer, J. V.; Cummings, L. J.

2013-01-01

A simplified 2D mathematical model for tissue growth within a cyclically-loaded tissue engineering scaffold is presented and analyzed. Such cyclic loading has the potential to improve yield and functionality of tissue such as bone and cartilage when

Fatigue Performance of SFPSC under Hot-Wet Environments and Cyclic Bending Loads

Directory of Open Access Journals (Sweden)

Shanshan Luo

2018-01-01

Full Text Available A new structural material named “steel fiber polymer structural concrete (SFPSC” with features of both high strength and high toughness was developed by this research group and applied to the bridge superstructures in the hot-wet environments. In order to investigate the fatigue performance and durability of SFPSC under hot-wet environments, the environment and fatigue load uncoupling method and the coupling action of environment and fatigue load were used or developed. Three-point bending fatigue experiments with uncoupling action of environments and cyclic loads were carried out for SFPSC specimens which were pretreated under hot-wet environments, and the experiments with the coupling action of environments and cyclic loads for SFPSC specimens were carried out under hot-wet environments. Then, the effects of hot-wet environments and the experimental methods on the fatigue mechanism of SFPSC material were discussed, and the environmental fatigue equations of SFPSC material under coupling and uncoupling action of hot-wet environments and cyclic bending loads were established. The research results show that the fatigue limits of SFPSC under the coupling action of the environments and cyclic loads were lower about 15%. The proposed fatigue equations could be used to estimate the fatigue lives and fatigue limits of SFPSC material.

The durability of waveguide fibers at cyclic change of loading, temperature and humidity

International Nuclear Information System (INIS)

Karimov, S.N.; Sultonov, U.; Shamsidinov, M.I.

1992-01-01

Present article is devoted to durability of waveguide fibers at cyclic change of loading, temperature and humidity. The mounting scheme and loading of sample is presented. The dependence of glass fiber durability on number of thermal cycles at various humidity rates was considered. The dependence of number of cycles on maximal loading at cyclic temperature change was studied.

Physical Modelling of Bucket Foundation Under Long-Term Cyclic Lateral Loading

DEFF Research Database (Denmark)

Foglia, Aligi; Ibsen, Lars Bo; Andersen, Lars Vabbersgaard

2012-01-01

Offshore wind farms are a promising renewable energy source. The monopod bucket foundation has the potential to become a reliable and cost-effective concept for offshore wind turbines. The bucket foundation must be designed by accounting for the cyclic loading which might endanger the turbine...... functioning. In this article a 1g physical model of bucket foundation under horizontal and moment cyclic loading is described. A testing program including four tests was carried out. Every test was conducted for at least 30000 cycles, each with different loading features. The capability of the model...

Response of stiff piles in sand to long-term cyclic lateral loading

DEFF Research Database (Denmark)

Bakmar, Christian LeBlanc; Houlsby, Guy T.; Byrne, Byron W.

2010-01-01

. To address this, a series of laboratory tests were conducted where a stiff pile in drained sand was subjected to between 8000 and 60000 cycles of combined moment and horizontal loading. A typical design for an offshore wind turbine monopile was used as a basis for the study, to ensure that pile dimensions...... and loading ranges were realistic. A complete non-dimensional framework for stiff piles in sand is presented and applied to interpret the test results. The accumulated rotation was found to be dependent on relative density and was strongly affected by the characteristics of the applied cyclic load. The pile...... stiffness increased with number of cycles, which contrasts with the current methodology where static p - y curves are degraded to account for cyclic loading. Methods are presented to predict the change in stiffness and the accumulated rotation of a stiff pile due to long-term cyclic loading. The use...

Seismic Load Rating Procedure for Welded Steel Frames Oligo-cyclic Fatigue

International Nuclear Information System (INIS)

Ratiu, Mircea D.; Moisidis, Nicolae T.

2004-01-01

A dynamic load rating approach for seismic qualification of cold-formed steel welded frames is presented. Allowable seismic loads are developed from cyclic and monotonic tests of standard cold-formed steel components commonly used for piping and electrical raceway supports. The method permits simplified qualification of all connections of frame components through a single load comparison. Test input consists of rotation/cycles-to-failure data and monotonic moment/rotation data. Cyclic data are statistically evaluated to determine an acceptable maximum seismic rotation for the connection. The allowable seismic load is determined from the corresponding static rotation. Application to seismic qualification procedures is discussed. (authors)

Temperature rise of cyclicly loaded power cables

Energy Technology Data Exchange (ETDEWEB)

Brakelmann, H

1984-09-01

A calculation method for the current ratings of cyclicly loaded power cables is introduced, taking into account optional shapes of the load cycle as well as the drying-out of the soil. The method is based on the Fourier-analysis of the loss cycle, representing an extension of the calculation method of VDE 0298. It is shown, that the ''VDE-method'' gives good results for the thermal resistances, if an ''utility load cycle'' in accordance with VDE 0298 is supposed. Only for cycles deviating essentially from the utility load cycle, the thermal resistances calculated by the ''VDE-method'' may be too great. In these cases the represented method is advantageous and can be processed by the aid of microcomputers.

Experimental Testing of Monopiles in Sand Subjected to One-Way Long-Term Cyclic Lateral Loading

DEFF Research Database (Denmark)

Roesen, Hanne Ravn; Ibsen, Lars Bo; Andersen, Lars Vabbersgaard

2013-01-01

In the offshore wind turbine industry the most widely used foundation type is the monopile. Due to the wave and wind forces the monopile is subjected to a strong cyclic loading with varying amplitude, maximum loading level, and varying loading period. In this paper the soil–pile interaction...... of a monopile in sand subjected to a long-term cyclic lateral loading is investigated by means of small scale tests. The tests are conducted with a mechanical loading rig capable of applying the cyclic loading as a sine signal with varying amplitude, mean loading level, and loading period for more than 60 000...... cycles. The tests are conducted in dense saturated sand. The maximum moment applied in the cyclic tests is varied from 18% to 36% of the ultimate lateral resistance found in a static loading test. The tests reveal that the accumulated rotation can be expressed by use of a power function. Further, static...

Performance of Geosynthetic-Reinforced Soils Under Static and Cyclic Loading

Directory of Open Access Journals (Sweden)

M. Touahmia

2017-04-01

Full Text Available This paper investigates and discusses the composite behavior of geosynthetic reinforced soil mass. It presents the results of a series of large-scale laboratory tests supported by analytical methods to examine the performance of geogrid reinforcement subjected to static and cyclic pullout loading. The testing equipment and procedures used for this investigation are outlined. The results show that geosynthetic reinforcement can mobilize great resistance to static pulling load under high confining pressures. The reinforcement exhibits gradual deformation under cyclic loading showing no sign of imminent pullout failure for all levels of applied loads. In general, the results demonstrate that geosynthetic can be used in situations where loads are non-static, although care will be required in ensuring that appropriate factors of safety are applied to control the resulting deformation. A simplified analytical model for calculating the pulling capacity of geosynthetic reinforcement is proposed.

Mechanical stability of the diamond-like carbon film on nitinol vascular stents under cyclic loading

International Nuclear Information System (INIS)

Kim, Hyun-Jong; Moon, Myoung-Woon; Lee, Kwang-Ryeol; Seok, Hyun-Kwang; Han, Seung-Hee; Ryu, Jae-Woo; Shin, Kyong-Min; Oh, Kyu Hwan

2008-01-01

The mechanical stability of diamond-like carbon (DLC) films coated on nitinol vascular stents was investigated under cyclic loading condition by employing a stent crimping system. DLC films were coated on the vascular stent of a three dimensional structure by using a hybrid ion beam system with rotating jig. The cracking or delamination of the DLC coating occurred dominantly near the hinge connecting the V-shaped segments of the stent where the maximum strain was induced by a cyclic loading of contraction and extension. However the failures were significantly suppressed as the amorphous Si (a-Si) buffer layer thickness increased. Interfacial adhesion strength was estimated from the spalled crack size in the DLC coating for various values of the a-Si buffer layer thickness

Multiaxial elastoplastic cyclic loading of austenitic 316L steel

Czech Academy of Sciences Publication Activity Database

Mazánová, Veronika; Polák, Jaroslav; Škorík, Viktor; Kruml, Tomáš

2017-01-01

Roč. 11, č. 40 (2017), s. 162-169 ISSN 1971-8993 R&D Projects: GA ČR(CZ) GA13-23652S; GA MŠk LM2015069; GA MŠk(CZ) LQ1601; GA ČR GA15-08826S Institutional support: RVO:68081723 Keywords : 316L steel * Crack initiation * Cyclic stress-strain curve * Multiaxial cyclic loading Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis

Damage evolution analysis of coal samples under cyclic loading based on single-link cluster method

Science.gov (United States)

Zhang, Zhibo; Wang, Enyuan; Li, Nan; Li, Xuelong; Wang, Xiaoran; Li, Zhonghui

2018-05-01

In this paper, the acoustic emission (AE) response of coal samples under cyclic loading is measured. The results show that there is good positive relation between AE parameters and stress. The AE signal of coal samples under cyclic loading exhibits an obvious Kaiser Effect. The single-link cluster (SLC) method is applied to analyze the spatial evolution characteristics of AE events and the damage evolution process of coal samples. It is found that a subset scale of the SLC structure becomes smaller and smaller when the number of cyclic loading increases, and there is a negative linear relationship between the subset scale and the degree of damage. The spatial correlation length ξ of an SLC structure is calculated. The results show that ξ fluctuates around a certain value from the second cyclic loading process to the fifth cyclic loading process, but spatial correlation length ξ clearly increases in the sixth loading process. Based on the criterion of microcrack density, the coal sample failure process is the transformation from small-scale damage to large-scale damage, which is the reason for changes in the spatial correlation length. Through a systematic analysis, the SLC method is an effective method to research the damage evolution process of coal samples under cyclic loading, and will provide important reference values for studying coal bursts.

Effect of cyclic loading and retightening on reverse torque value in external and internal implants.

Science.gov (United States)

Cho, Woong-Rae; Huh, Yoon-Hyuk; Park, Chan-Jin; Cho, Lee-Ra

2015-08-01

The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading.

Determination of the critical plane and durability estimation for a multiaxial cyclic loading

Science.gov (United States)

Burago, N. G.; Nikitin, A. D.; Nikitin, I. S.; Yakushev, V. L.

2018-03-01

An analytical procedure is proposed to determine the critical plane orientation according to the Findley criterion for the multiaxial cyclic loading. The cases of in-phase and anti-phase cyclic loading are considered. Calculations of the stress state are carried out for the system of the gas turbine engine compressor disk and blades for flight loading cycles. The formulas obtained are used for estimations of the fatigue durability of this essential element of structure.

Experimental investigation of steel fiber-reinforced concrete beams under cyclic loading

Science.gov (United States)

Ranjbaran, Fariman; Rezayfar, Omid; Mirzababai, Rahmatollah

2018-03-01

An experimental study has been conducted to study the cyclic behavior of reinforced concrete beams in which steel fibers were added to the concrete mix. Seven similar geometrically specimens in full scale were studied under four- point bending test in the form of slow cyclic loading. One sample as a control specimen was made without steel fibers or 0% volume fraction (vf) and six other samples with 1, 2 and 4% vf of steel fibers in twin models. The maximum and ultimate resistance, ductility, degradation of loading and unloading stiffness, absorption and dissipation of energy and equivalent viscous damping were studied in this investigation and the effect of steel fibers on the cyclic behavior was compared with each other. Generally, the addition of steel fibers up to a certain limit value (vf = 2%) improves the cyclic behavior of reinforced concrete beams and results in the increase of maximum strength and ultimate displacement.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

Science.gov (United States)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Cyclic plasticity of an austenitic-ferritic stainless steel under biaxial non proportional loading

International Nuclear Information System (INIS)

Aubin, V.

2001-11-01

Austenitic-ferritic stainless steels are supplied since about 30 years only, so they are yet not well-known. Their behaviour in cyclic plasticity was studied under uniaxial loading but not under multiaxial loading, whereas only a thorough knowledge of the phenomena influencing the mechanical behaviour of a material enables to simulate and predict accurately its behaviour in a structure. This work aims to study and model the behaviour of a duplex stainless steel under cyclic biaxial loading. A three step method was adopted. A set of tension-torsion tests on tubular specimen was first defined. We studied the equivalence between loading directions, and then the influence of loading path and loading history on the stress response of the material. Results showed that duplex stainless steel shows an extra-hardening under non proportional loading and that its behaviour depends on previous loading. Then, in order to analyse the results obtained during this first experimental stage, the yield surface was measured at different times during cyclic loading of the same kind. A very small plastic strain offset (2*10 -5 ) was used in order not to disturb the yield surface measured. The alteration of isotropic and kinematic hardening variables were deduced from these measures. Finally, three phenomenological constitutive laws were identified with the experimental set. We focused our interest on the simulation of stabilized stress levels and on the simulation of the cyclic hardening/softening behaviour. The comparison between experimental and numerical results enabled the testing of the relevance of these models. (authors)

Laboratory experiments of bucket foundations under cyclic loading

DEFF Research Database (Denmark)

Foglia, Aligi; Ibsen, Lars Bo

This report collects information on the experimental campaign concerning bucket foundations under lateral cyclic loading conducted by the authors between 2011 and 2014. The report includes a step by step manual on the test procedures and a number of information and graphs for each experiment...

Literature review on cyclic lateral loading effects of mono-bucket foundations

DEFF Research Database (Denmark)

Kapitanov, Lachezar Rosenov; Duroska, Peter; Quirante, Cesar Antonio Garcia

2016-01-01

and consequently cost-effectiveness compared to other common solutions. The long-term cyclic loading can cause degradation of soil-bucket system stiffness, which yields into accumulated and permanent deformations. Despite of the advantages, there is no standard procedure to design the foundation especially...... calculation is highly demanded at the different design phases. The intention of the current study is to present, review and summarize the existing techniques to assess the effect of cyclic loading on Mono-Bucket foundations while emphasizing the advantage and disadvantage of each of them. Additionally...

Application of SVR with chaotic GASA algorithm in cyclic electric load forecasting

International Nuclear Information System (INIS)

Zhang, Wen Yu; Hong, Wei-Chiang; Dong, Yucheng; Tsai, Gary; Sung, Jing-Tian; Fan, Guo-feng

2012-01-01

The electric load forecasting is complicated, and it sometimes reveals cyclic changes due to cyclic economic activities or climate seasonal nature, such as hourly peak in a working day, weekly peak in a business week, and monthly peak in a demand planned year. Hybridization of support vector regression (SVR) with chaotic sequence and evolutionary algorithms has successfully been applied to improve forecasting accuracy, and to effectively avoid trapping in a local optimum. However, it has not been widely explored to employ SVR-based model to deal with cyclic electric load forecasting. This paper will firstly investigate the potentiality of a novel hybrid algorithm, namely chaotic genetic algorithm-simulated annealing algorithm (CGASA), with an SVR model to improve load forecasting accurate performance. In which, the proposed CGASA employs internal randomness of chaotic iterations to overcome premature local optimum. Secondly, the seasonal mechanism will then be applied to well adjust the cyclic load tendency. Finally, a numerical example from an existed reference is employed to compare the forecasting performance of the proposed SSVRCGASA model. The forecasting results show that the SSVRCGASA model yields more accurate forecasting results than ARIMA and TF-ε-SVR-SA models. -- Highlights: ► Hybridizing the seasonal adjustment mechanism into an SVR model. ► Employing chaotic sequence to improve the premature convergence of genetic algorithm and simulated annealing algorithm. ► Successfully providing significant accurate monthly load demand forecasting.

Deformation mechanisms in cyclic creep and fatigue

International Nuclear Information System (INIS)

Laird, C.

1979-01-01

Service conditions in which static and cyclic loading occur in conjunction are numerous. It is argued that an understanding of cyclic creep and cyclic deformation are necessary both for design and for understanding creep-fatigue fracture. Accordingly a brief, and selective, review of cyclic creep and cyclic deformation at both low and high strain amplitudes is provided. Cyclic loading in conjunction with static loading can lead to creep retardation if cyclic hardening occurs, or creep acceleration if softening occurs. Low strain amplitude cyclic deformation is understood in terms of dislocation loop patch and persistent slip band behavior, high strain deformation in terms of dislocation cell-shuttling models. While interesting advances in these fields have been made in the last few years, the deformation mechanisms are generally poorly understood

Simulation of cyclic stress-strain relation under non proportional loading

International Nuclear Information System (INIS)

Chen, X.; Zhu, Q.X.; Abel, A.

1995-01-01

A series of cyclic constitutive experiments have been conducted on 42 Cr Mo steel on MTS809 machine under tension-torsional loading. Thin-walled tube specimen were used. Two kinds of cruciform strain path have been investigated. The paper suggests a simple method for the calculation of stable cyclic stress and strain values based on a modified endochronic constitutive theory by redefined intrinsic time scale. (author). 6 refs., 3 figs

Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

Directory of Open Access Journals (Sweden)

Jie Chen

2014-01-01

Full Text Available Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

Effects of cyclic shear loads on strength, stiffness and dilation of rock fractures

Directory of Open Access Journals (Sweden)

Thanakorn Kamonphet

2015-12-01

Full Text Available Direct shear tests have been performed to determine the peak and residual shear strengths of fractures in sandstone, granite and limestone under cyclic shear loading. The fractures are artificially made in the laboratory by tension inducing and saw-cut methods. Results indicate that the cyclic shear load can significantly reduce the fracture shear strengths and stiffness. The peak shear strengths rapidly decrease after the first cycle and tend to remain unchanged close to the residual strengths through the tenth cycle. Degradation of the first order asperities largely occurs after the first cycle. The fracture dilation rates gradually decrease from the first through the tenth cycles suggesting that the second order asperities continuously degrade after the first load cycle. The residual shear strengths are lower than the peak shear strengths and higher than those of the smooth fractures. The strength of smooth fracture tends to be independent of cyclic shear loading.

Effect of laser parameters on surface roughness of laser modified tool steel after thermal cyclic loading

Science.gov (United States)

Lau Sheng, Annie; Ismail, Izwan; Nur Aqida, Syarifah

2018-03-01

This study presents the effects of laser parameters on the surface roughness of laser modified tool steel after thermal cyclic loading. Pulse mode Nd:YAG laser was used to perform the laser surface modification process on AISI H13 tool steel samples. Samples were then treated with thermal cyclic loading experiments which involved alternate immersion in molten aluminium (800°C) and water (27°C) for 553 cycles. A full factorial design of experiment (DOE) was developed to perform the investigation. Factors for the DOE are the laser parameter namely overlap rate (η), pulse repetition frequency (f PRF) and peak power (Ppeak ) while the response is the surface roughness after thermal cyclic loading. Results indicate the surface roughness of the laser modified surface after thermal cyclic loading is significantly affected by laser parameter settings.

Small-Scale Testing of Cyclic Laterally Loaded Monopiles in Dense Saturated Sand

DEFF Research Database (Denmark)

Nicolai, Giulio; Ibsen, Lars Bo

2014-01-01

Monopiles are currently the most common foundations for offshore wind turbines, which are subjected to millions of cyclic loads that are still not well interpreted in the design guidelines. The accumulated rotation of the turbine and the change of foundation stiffness due to the long-term cyclic ...

Experimental Investigation and FE Analysis on Constitutive Relationship of High Strength Aluminum Alloy under Cyclic Loading

Directory of Open Access Journals (Sweden)

Yuanqing Wang

2016-01-01

Full Text Available Experiments of 17 high strength aluminum alloy (7A04 specimens were conducted to investigate the constitutive relationship under cyclic loading. The monotonic behavior and hysteretic behavior were focused on and the fracture surface was observed by scanning electron microscope (SEM to investigate the microfailure modes. Based on Ramberg-Osgood model, stress-strain skeleton curves under cyclic loading were fitted. Parameters of combined hardening model including isotropic hardening and kinematic hardening were calibrated from test data according to Chaboche model. The cyclic tests were simulated in finite element software ABAQUS. The test results show that 7A04 aluminum alloy has obvious nonlinearity and ultra-high strength which is over 600 MPa, however, with relatively poor ductility. In the cyclic loading tests, 7A04 aluminum alloy showed cyclic hardening behavior and when the compressive strain was larger than 1%, the stiffness degradation and strength degradation occurred. The simulated curves derived by FE model fitted well with experimental curves which indicates that the parameters of this combined model can be used in accurate calculation of 7A04 high strength aluminum structures under cyclic loading.

A literature study on the effects of cyclic lateral loading of monopiles in cohesionless soils

Energy Technology Data Exchange (ETDEWEB)

Lange Rasmussen, K. [Niras, Aalborg (Denmark); Hansen, Mette; Kirk Wolf, T. [COWI, Kgs. Lyngby, (Denmark); Ibsen, L.B.; Ravn Roesen, H. [Aalborg Univ.. Dept. of Civil Engineering, Aalborg (Denmark)

2013-06-15

Today, monopiles are the most typical foundation for offshore wind turbines. During their lifetime large diameter, stiff piles are subjected to millions of small cyclic loads due to environmental forces. The long-term cyclic loading can change the granular structure of the soil surrounding the pile. This may change the stiffness of the soil-pile system and create an accumulated rotation of the pile. The behaviour of the soil-pile system is very complex and the influence of soil parameters, number of load cycles, and size, amplitude and characteristic of the load are examined, as they all contribute to the rotation and the change in stiffness. The scope of this article is to outline current design methods and the state of the art knowledge within the subject of long-term cyclic, lateral loading of piles. (Author)

Quantitative damage and detwinning analysis of nanotwinned copper foil under cyclic loading

International Nuclear Information System (INIS)

Yoo, Byung-Gil; Boles, Steven T.; Liu, Y.; Zhang, X.; Schwaiger, Ruth; Eberl, Christoph; Kraft, Oliver

2014-01-01

High-purity Cu samples containing parallel columns of highly aligned nanotwins with median spacing of ∼25 nm were subjected to tension–compression cyclic loading by a high-throughput cyclic testing method. The methodology utilizes gradients in surface strain amplitude of a vibrating cantilever: one along the beam axis, with decreasing strain from the fixed to the free end of the beam, and the other through the foil thickness with decreasing strain from the surface to the neutral axis. Systematic microstructural investigations indicate that nanotwins are not stable under cyclic loading and that the applied strain amplitude has a strong influence on the resulting twin structure. In the highly stressed regions the detwinning process produces a twin free microstructure, allowing for subsequent extrusion and crack formation, and introduces fatal defects into structural parts

Short-Term Creep Behavior of CFRP-Reinforced Wood Composites Subjected to Cyclic Loading at Different Climate Conditions

OpenAIRE

Xiaojun Yang; Meng Gong; Ying Hei Chui

2014-01-01

Carbon fiber reinforced plastic (CFRP) was used to adhesively reinforce Chinese fir (Cunninghamia lanceolata) wood specimens. This study examined the flexural static and creep performances of CFPR-reinforced wood composites that had been subjected to changes in moisture and stress levels. The major findings were as follows: 1) the cyclic creep was slightly lower for those specimens subjected to the cyclic stress condition than for those subjected to a constant stress level due to the deflecti...

Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

Science.gov (United States)

Siadat, Hakimeh; Pirmoazen, Salma; Beyabanaki, Elaheh; Alikhasi, Marzieh

2015-07-01

A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

Effect of reverse cyclic loading on the fracture resistance curve in C(T) specimen

International Nuclear Information System (INIS)

Sung Seok, C.; Jin Kim, Y.; Il Weon, J.

1999-01-01

Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, are known to be dependent on the cyclic loading history. The objective of this paper is to investigate the effect of reverse cyclic loading on the J-R curves in C(T) specimens. The effect of two parameters was observed on the J-R curves during the reverse cyclic loading. One was the minimum-to-maximum load ratio (R) and the other was the incremental plastic displacement (δ cycle /δ i ), which is related to the amount of crack growth that occurs in a cycle. Fracture resistance tests on C(T) specimens with varying the load ratio and the incremental plastic displacement were performed, and the test results showed that the J-R curves were decreased with decreasing the load ratio and decreasing the incremental plastic displacement. Direct current potential drop (DCPD) method was used for the detection of crack initiation and crack growth in typical laboratory J-R tests. The values of crack initiation J-integral (J I ) and crack initiation displacement (δ i ) were also obtained by using the DCPD method. (orig.)

The Effect of Cyclic Loading on the Mechanical Performance of Surgical Mesh

Directory of Open Access Journals (Sweden)

Ho Y.C.

2010-06-01

Full Text Available Polymeric meshes in the form of knitted nets are commonly used in the surgical repair of pelvic organ prolapses. Although a number of these prosthetic meshes are commercially available, there is little published data on their mechanical performance, in particular on the change in stiffness under the repeated loading experienced in vivo. In this in vitro study, cyclic tensile loading was applied to rectangular strips of four different commercially available meshes. The applied force and resultant displacement was monitored throughout the tests in order to evaluate the change in stiffness. In addition, each mesh was randomly marked using indelible ink in order to permit the use of threedimensional digital image correlation to evaluate local displacements during the tests. However, the scale and form of the deformation experienced by some of the meshes made correlation difficult so that confirmation of the values of stiffness were only obtained for two meshes. The results demonstrate that all the meshes experience an increase in stiffness during cyclic loading, that in most cases cyclic creep occurs and in some cases large-scale, irreversible reorganisation of the mesh structure occurs after as few as 200 cycles at loads of the order of 10N.

In-situ investigations of structural changes during cyclic loading by high resolution reciprocal space mapping

DEFF Research Database (Denmark)

Diederichs, Annika M.; Thiel, Felix; Lienert, Ulrich

2017-01-01

dislocation structures can be identified using advanced electron microscopy and synchrotron techniques. A detailed characterization of the microstructure during cyclic loading by in-situ monitoring the internal structure within individual grains with high energy x-rays can help to understand and predict...... the materials behavior during cyclic deformation and to improve the material design. While monitoring macroscopic stress and strain during cyclic loading, reciprocal space maps of diffraction peaks from single grains are obtained with high resolution. High Resolution Reciprocal Space Mapping was applied...

Soil Fatigue Due To Cyclically Loaded Foundations

OpenAIRE

Pytlik, Robert Stanislaw

2016-01-01

Cyclic loading on civil structures can lead to a reduction of strength of the used materials. A literature study showed that, in contrast to steel structures and material engineering, there are no design codes or standards for fatigue of foundations and the surrounding ground masses in terms of shear strength reduction. Scientific efforts to study the fatigue behaviour of geomaterials are mainly focused on strain accumulation, while the reduction of shear strength of geomaterials has not been...

Experimental Investigation of Sandstone under Cyclic Loading: Damage Assessment Using Ultrasonic Wave Velocities and Changes in Elastic Modulus

Directory of Open Access Journals (Sweden)

Sen Yang

2018-01-01

Full Text Available This laboratory study investigated the damage evolution of sandstone specimens under two types of cyclic loading by monitoring and analyzing changes in the elastic moduli and the ultrasonic velocities during loading. During low-level cyclic loading, the stiffness degradation method was unable to describe the damage accumulations but the ultrasonic velocity measurements clearly reflected the damage development. A crack density parameter is introduced in order to interpret the changes in the tangential modulus and the ultrasonic velocities. The results show the following. (1 Low-level cyclic loading enhanced the anisotropy of the cracks. This results from the compression of intergranular clay minerals and fatigue failure. (2 Irreversible damage accumulations during cyclic loading with an increasing upper stress limit are the consequence of brittle failure in the sandstone’s microstructure.

Influence of combined impact and cyclic loading on the overall fatigue life of forged steel, EA4T

Energy Technology Data Exchange (ETDEWEB)

Malekzadeh, A.; Hadidi-Moud, S.; Farhangdoost, Kh [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

2017-03-15

The performance of forged steel, EA4T, used in rail industry, under simulated in service conditions, i.e. combined impact - cyclic loading, was investigated through a comprehensive experimental programme. The standard Paris-Erdogan fatigue design curve parameters, m and C, were calibrated to account for the effect of the impact component of loading. A minimum threshold for impact load component, identified in the experiments, was also incorporated in the proposed empirical model. Comparison with experimental findings indicated that this “modified” Fatigue design curve could predict the fatigue life of pre impact loaded specimens with sufficient accuracy. It was therefore suggested that the modified model may be used as a novel design tool for predicting the overall fatigue life of components made of this material under the specified combined impact and fatigue loading conditions.

Cyclic Loading of Growing Tissue in a Bioreactor: Mathematical Model and Asymptotic Analysis

KAUST Repository

Pohlmeyer, J. V.

2013-10-24

A simplified 2D mathematical model for tissue growth within a cyclically-loaded tissue engineering scaffold is presented and analyzed. Such cyclic loading has the potential to improve yield and functionality of tissue such as bone and cartilage when grown on a scaffold within a perfusion bioreactor. The cyclic compression affects the flow of the perfused nutrient, leading to flow properties that are inherently unsteady, though periodic, on a timescale short compared with that of tissue proliferation. A two-timescale analysis based on these well-separated timescales is exploited to derive a closed model for the tissue growth on the long timescale of proliferation. Some sample numerical results are given for the final model, and discussed. © 2013 Society for Mathematical Biology.

Infrared thermographic analysis of shape memory polymer during cyclic loading

International Nuclear Information System (INIS)

Staszczak, Maria; Pieczyska, Elżbieta A; Maj, Michał; Kukla, Dominik; Tobushi, Hisaaki

2016-01-01

In this paper we present the effects of thermomechanical couplings occurring in polyurethane shape memory polymer subjected to cyclic tensile loadings conducted at various strain rates. Stress–strain characteristics were elaborated using a quasistatic testing machine, whereas the specimen temperature changes accompanying the deformation process were obtained with an infrared camera. We demonstrate a tight correlation between the mechanical and thermal results within the initial loading stage. The polymer thermomechanical behaviour in four subsequent loading-unloading cycles and the influence of the strain rate on the stress and the related temperature changes were also examined. In the range of elastic deformation the specimen temperature drops below the initial level due to thermoelastic effect whereas at the higher strains the temperature always increased, due to the dissipative deformation mechanisms. The difference in the characteristics of the specimen temperature has been applied to determine a limit of the polymer reversible deformation and analyzed for various strain rates. It was shown that at the higher strain rates higher values of the stress and temperature changes are obtained, which are related to higher values of the polymer yield points. During the cyclic loading a significant difference between the first and the second cycle was observed. The subsequent loading-unloading cycles demonstrated similar sharply shaped stress and temperature profiles and gradually decrease in values. (paper)

Damage mechanisms in PBT-GF30 under thermo-mechanical cyclic loading

International Nuclear Information System (INIS)

Schaaf, A.; De Monte, M.; Hoffmann, C.; Vormwald, M.; Quaresimin, M.

2014-01-01

The scope of this paper is the investigation of damage mechanisms at microscopic scale on a short glass fiber reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. In addition the principal mechanisms are verified through micro mechanical FE models. In order to investigate the fatigue behavior of the material both isothermal strain controlled fatigue (ISCF) tests at three different temperatures and thermo-mechanical fatigue (TMF) tests were conducted on plain and notched specimens, manufactured by injection molding. The goal of the work is to determine the damage mechanisms occurring under TMF conditions and to compare them with the mechanisms occurring under ISCF. For this reason fracture surfaces of TMF and ISCF samples loaded at different temperature levels were analyzed using scanning electron microscopy. Furthermore, specimens that failed under TMF were examined on microsections revealing insight into both crack initiation and crack propagation. The findings of this investigation give valuable information about the main damage mechanisms of PBT-GF30 under TMF loading and serve as basis for the development of a TMF life estimation methodology

On behaviour of fuel elements subject to combined cyclic thermomechanical loads

International Nuclear Information System (INIS)

Hsu, T.R.

1980-01-01

This paper presents detailed finite element formulations on the kinematic hardening rule of plasticity included in an existing thermoelastoplastic stress analysis code primarily designed to predict the thermomechanical behaviour of nuclear reactor fuel elements. The kinematic hardening rule is considered to be important for structures subject to repeated (or cyclic) loads. The start-up/operation/shut-down and various power excursions in a reactor all can be classified as cyclic loadings. In addition to the shifting of material yield surfaces as usually handled by the kinematic hardening rule, the thermal effect and temperature-dependent material properties have also been included in the present work for the first time. A case study related to an in-reactor experiment on a single fuel element indicated that significantly higher cumulative sheath residual strains after two load cycles was obtained by the present scheme than those calculated by the usual isotropic hardening rule. This observation may alert fuel modellers to select proper hardening rules in their analyses. (orig.)

CISM course on mechanical behaviour of soils under environmentally induced cyclic loads

CERN Document Server

Wood, David; Mechanical Behaviour of Soils Under Environmentally Induced Cyclic Loads

2012-01-01

The book gives a comprehensive description of the mechanical response of soils (granular and cohesive materials) under cyclic loading. It provides the geotechnical engineer with the theoretical and analytical tools necessary for the evaluation of settlements developng with time under cyclic, einvironmentally idncued loads (such as wave motion, wind actions, water table level variation) and their consequences for the serviceability and durability of structures such as the shallow or deep foundations used in offshore engineering, caisson beakwaters, ballast and airport pavements and also to interpret monitoring data, obtained from both natural and artificial slopes and earth embankments, for the purposes of risk assessment and mitigation.

The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading

International Nuclear Information System (INIS)

Nagel, T.; Shao, H.; Roßkopf, C.; Linder, M.; Wörner, A.; Kolditz, O.

2014-01-01

Highlights: • Detailed analysis of cyclic and monotonic loading of thermochemical heat stores. • Fully coupled reactive heat and mass transport. • Reaction kinetics can be simplified in systems limited by heat transport. • Operating lines valid during monotonic and cyclic loading. • Local integral degree of conversion to capture heterogeneous material usage. - Abstract: Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a reactor level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the reactor level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the reactor behaviour. The degree of material usage within the reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes

Determination of the usage factor of components after cyclic loading by means of high-resolution microstructural examination

International Nuclear Information System (INIS)

Seibold, A.; Scheibe, A.; Assmann, H.D.

1991-01-01

Materials subjected to cyclic loading experience a change in the microstructure which may affect the service life. Quantification of the microstructural changes and allocation of the microstructural condition to the corresponding point on the fatigue curve for the component material allows the usage factor to be derived. Taking the low-alloy, fine-grained structural steel 20MnMoNi55 (quenched and tempered structure) as an example, the relationship between microstructure and number of load cycles can be represented in the form of a reference curve. High-resolution examination allows the usage factor to be determined up to η=N/N f ≅0.5 under the given cyclic loading. Only a small specimen volume is required for examination using a transmission electron microscope. It can be taken from the component without affecting the required minimum wall thickness. The location of the specimen must, however, be stipulated, e.g. the location of highest loading according to calculations. When removing the specimen, care must be taken to ensure that the micro-structure is not affected. If these requirements are observed, high-resolution microstructural examination provides a method for checking the usage factor of a component. (orig.)

Bone healing response in cyclically loaded implants: Comparing zero, one, and two loading sessions per day.

Science.gov (United States)

de Barros E Lima Bueno, Renan; Dias, Ana Paula; Ponce, Katia J; Wazen, Rima; Brunski, John B; Nanci, Antonio

2018-05-31

When bone implants are loaded, they are inevitably subjected to displacement relative to bone. Such micromotion generates stress/strain states at the interface that can cause beneficial or detrimental sequels. The objective of this study is to better understand the mechanobiology of bone healing at the tissue-implant interface during repeated loading. Machined screw shaped Ti implants were placed in rat tibiae in a hole slightly bigger than the implant diameter. Implants were held stable by a specially-designed bone plate that permits controlled loading. Three loading regimens were applied, (a) zero loading, (b) one daily loading session of 60 cycles with an axial force of 1.5 N/cycle for 7 days, and (c) two such daily sessions with the same axial force also for 7 days. Finite element analysis was used to characterize the mechanobiological conditions produced by the loading sessions. After 7 days, the implants with surrounding interfacial tissue were harvested and processed for histological, histomorphometric and DNA microarray analyses. Histomorphometric analyses revealed that the group subjected to repeated loading sessions exhibited a significant decrease in bone-implant contact and increase in bone-implant distance, as compared to unloaded implants and those subjected to only one loading session. Gene expression profiles differed during osseointegration between all groups mainly with respect to inflammatory and unidentified gene categories. The results indicate that increasing the daily cyclic loading of implants induces deleterious changes in the bone healing response, most likely due to the accumulation of tissue damage and associated inflammatory reaction at the bone-implant interface. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading.

Science.gov (United States)

Paepoemsin, T; Reichart, P A; Chaijareenont, P; Strietzel, F P; Khongkhunthian, P

2016-01-01

The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer's recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, Pabutment from implant fixture increased immensely after cyclic loading.

Effect of loading history on cyclic stress-strain response

Czech Academy of Sciences Publication Activity Database

Kunz, Ludvík; Lukáš, Petr; Weiss, B.; Melisova, D.

2001-01-01

Roč. 314, 1/2 (2001), s. 1-6 ISSN 0921-5093. [TMS Annual Meeting. Nashville, 12.03.2000-16.03.2000] R&D Projects: GA AV ČR IBS2041001 Institutional research plan: CEZ:AV0Z2041904 Keywords : cyclic plasticity * loading history * mean stress Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.978, year: 2001

Plastic strain accumulation during asymmetric cyclic loading of Zircaloy-2 at room temperature

International Nuclear Information System (INIS)

Rajpurohit, R.S.; Santhi Srinivas, N.C.; Singh, Vakil

2016-01-01

Asymmetric cyclic loading leads to accumulation of cyclic plastic strain and reduces the fatigue life of components. This phenomenon is known as ratcheting fatigue. Zircaloy-2 is a important structural material in nuclear reactors and used as pressure tubes and fuel cladding in pressurized light and heavy water nuclear reactors. Due to power fluctuations, these components experience plastic strain cycles in the reactor and their life is reduced due to strain cycles. Power fluctuations also cause asymmetric straining of the material and leads to accumulation of plastic strain. The present investigation deals with the effect of the magnitude of mean stress, stress amplitude and stress rate on hardening/softening behavior of Zircaloy-2 under asymmetric cyclic loading, at room temperature. It was observed that plastic strain accumulation increased with mean stress and stress amplitude; however, it decreased with stress rate. (author)

Upregulation of matrix synthesis in chondrocyte-seeded agarose following sustained bi-axial cyclic loading

Directory of Open Access Journals (Sweden)

Belinda Pingguan-Murphy

2012-08-01

Full Text Available OBJECTIVES: The promotion of extracellular matrix synthesis by chondrocytes is a requisite part of an effective cartilage tissue engineering strategy. The aim of this in vitro study was to determine the effect of bi-axial cyclic mechanical loading on cell proliferation and the synthesis of glycosaminoglycans by chondrocytes in threedimensional cultures. METHOD: A strain comprising 10% direct compression and 1% compressive shear was applied to bovine chondrocytes seeded in an agarose gel during two 12-hour conditioning periods separated by a 12-hour resting period. RESULTS: The bi-axial-loaded chondrocytes demonstrated a significant increase in glycosaminoglycan synthesis compared with samples exposed to uni-axial or no loading over the same period (p<0.05. The use of a free-swelling recovery period prior to the loading regime resulted in additional glycosaminoglycan production and a significant increase in DNA content (p<0.05, indicating cell proliferation. CONCLUSIONS: These results demonstrate that the use of a bi-axial loading regime results in increased matrix production compared with uni-axial loading.

Modelling the drained response of bucket foundations for offshore wind turbines under general monotonic and cyclic loading

DEFF Research Database (Denmark)

Foglia, Aligi; Gottardi, Guido; Govoni, Laura

2015-01-01

The response of bucket foundations on sand subjected to planar monotonic and cyclic loading is investigated in the paper. Thirteen monotonic and cyclic laboratory tests on a skirted footing model having a 0.3 m diameter and embedment ratio equal to 1 are presented. The loading regime reproduces t...

The resistance of cortical bone tissue to failure under cyclic loading is reduced with alendronate.

Science.gov (United States)

Bajaj, Devendra; Geissler, Joseph R; Allen, Matthew R; Burr, David B; Fritton, J C

2014-07-01

Bisphosphonates are the most prescribed preventative treatment for osteoporosis. However, their long-term use has recently been associated with atypical fractures of cortical bone in patients who present with low-energy induced breaks of unclear pathophysiology. The effects of bisphosphonates on the mechanical properties of cortical bone have been exclusively studied under simple, monotonic, quasi-static loading. This study examined the cyclic fatigue properties of bisphosphonate-treated cortical bone at a level in which tissue damage initiates and is accumulated prior to frank fracture in low-energy situations. Physiologically relevant, dynamic, 4-point bending applied to beams (1.5 mm × 0.5 mm × 10 mm) machined from dog rib (n=12/group) demonstrated mechanical failure and micro-architectural features that were dependent on drug dose (3 groups: 0, 0.2, 1.0mg/kg/day; alendronate [ALN] for 3 years) with cortical bone tissue elastic modulus (initial cycles of loading) reduced by 21% (pbone remodeling, such as the size of osteons (-14%; ALN1.0: 10.5±1.8, VEH: 12.2±1.6, ×10(3) μm2; pbone tissue are altered by high-dose ALN treatment and contribute to reduced mechanical properties under cyclic loading conditions. Copyright © 2014 Elsevier Inc. All rights reserved.

Reliability evaluation of fiber optic sensors exposed to cyclic thermal load

Energy Technology Data Exchange (ETDEWEB)

Kim, Heon Young; Kim, Dong Hoon [Advanced Materials Research Team, Korea Railroad Research Institute, Uiwang (Korea, Republic of); Kim, Dae Hyun [Dept. of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, Seoul (Korea, Republic of)

2016-06-15

Fiber Bragg grating (FBG) sensors are currently the most prevalent sensors because of their unique advantages such as ease of multiplexing and capability of performing absolute measurements. They are applied to various structures for structural health monitoring (SHM). The signal characteristics of FBG sensors under thermal loading should be investigated to enhance the reliability of these sensors, because they are exposed to certain cyclic thermal loads due to temperature changes resulting from change of seasons, when they are applied to structures for SHM. In this study, tests on specimens are conducted in a thermal chamber with temperature changes from - to for 300 cycles. For the specimens, two types of base materials and adhesives that are normally used in the manufacture of packaged FBG sensors are selected. From the test results, it is confirmed that the FBG sensors undergo some degree of compressive strain under cyclic thermal load; this can lead to measurement errors. Hence, a pre-calibration is necessary before applying these sensors to structures for long-term SHM.

Test method research on weakening interface strength of steel - concrete under cyclic loading

Science.gov (United States)

Liu, Ming-wei; Zhang, Fang-hua; Su, Guang-quan

2018-02-01

The mechanical properties of steel - concrete interface under cyclic loading are the key factors affecting the rule of horizontal load transfer, the calculation of bearing capacity and cumulative horizontal deformation. Cyclic shear test is an effective method to study the strength reduction of steel - concrete interface. A test system composed of large repeated direct shear test instrument, hydraulic servo system, data acquisition system, test control software system and so on is independently designed, and a set of test method, including the specimen preparation, the instrument preparation, the loading method and so on, is put forward. By listing a set of test results, the validity of the test method is verified. The test system and the test method based on it provide a reference for the experimental study on mechanical properties of steel - concrete interface.

Quasi-brittle material behavior under cyclic loading: from virtual testing to structural computation

International Nuclear Information System (INIS)

Vassaux, Maxime

2015-01-01

Macroscopic constitutive laws are developed not only because they allow for large-scale computations but also because refine dissipative mechanisms observed at lower scales. Within the framework of this study, the development of such models is carried out in the context of seismic loading, that is to say reverse cyclic loading, applied to the quasi-brittle materials and more precisely, concrete-like materials. Nowadays, robust and predictive macroscopic constitutive laws are still rare because of the complexity of cracking related phenomena. Among the challenges to face, the material parameters identification is far from being the easiest due to the lack of experimental data. Indeed, the difficulties to carry out cyclic tests on concrete-like materials are numerous. To overcome these difficulties, a virtual testing approach based on a refine model is proposed in this study in order to feed continuum models with the missing material parameters. Adopting a microscopic point of view, a representative volume element is seen as a structure. The microscopic model has been developed with the aim to require a minimal number of material parameters which only need basic mechanical tests to be identified. From an existing lattice model developed to deal with monotonic loading, several enhancements have been realized in order to extend its range of applicability, making it capable of dealing with complex multi-axial cyclic loadings. The microscopic model has been validated as a virtual testing machine that is able to help the identification procedure of continuous constitutive laws. This identification approach has been applied on a new constitutive law developed within the framework of isotropic continuum damage mechanics accounting for cyclic related effects. In particular, the concept of regularized unilateral effect has been introduced to describe the progressive crack closure. The macroscopic model has been calibrated with the help from the aforementioned virtual testing

Application of cyclic J-integral to low cycle fatigue crack growth of Japanese carbon steel pipe

Energy Technology Data Exchange (ETDEWEB)

Miura, N.; Fujioka, T.; Kashima, K. [and others

1997-04-01

Piping for LWR power plants is required to satisfy the LBB concept for postulated (not actual) defects. With this in mind, research has so far been conducted on the fatigue crack growth under cyclic loading, and on the ductile crack growth under excessive loading. It is important, however, for the evaluation of the piping structural integrity under seismic loading condition, to understand the fracture behavior under dynamic and cyclic loading conditions, that accompanies large-scale yielding. CRIEPI together with Hitachi have started a collaborative research program on dynamic and/or cyclic fracture of Japanese carbon steel (STS410) pipes in 1991. Fundamental tensile property tests were conducted to examine the effect of strain rate on tensile properties. Cracked pipe fracture tests under some loading conditions were also performed to investigate the effect of dynamic and/or cyclic loading on fracture behavior. Based on the analytical considerations for the above tests, the method to evaluate the failure life for a cracked pipe under cyclic loading was developed and verified. Cyclic J-integral was introduced to predict cyclic crack growth up to failure. This report presents the results of tensile property tests, cracked pipe fracture tests, and failure life analysis. The proposed method was applied to the cracked pipe fracture tests. The effect of dynamic and/or cyclic loading on pipe fracture was also investigated.

Field testing of stiffened deep cement mixing piles under lateral cyclic loading

Science.gov (United States)

Raongjant, Werasak; Jing, Meng

2013-06-01

Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns (SDCM). This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.

Effect of cyclic load on vertical misfit of prefabricated and cast implant single abutment

Directory of Open Access Journals (Sweden)

Rudys Rodolfo de Jesus Tavarez

2011-02-01

Full Text Available OBJECTIVES: The purpose of this in vitro study was to evaluate misfit alterations at the implant/abutment interface of external and internal connection implant systems when subjected to cyclic loading. MATERIAL AND METHODS: Standard metal crowns were fabricated for 5 groups (n=10 of implant/abutment assemblies: Group 1, external hexagon implant and UCLA cast-on premachined abutment; Group 2, internal hexagon implant and premachined abutment; Group 3, internal octagon implant and prefabricated abutment; Group 4, external hexagon implant and UCLA cast-on premachined abutment; and Group 5, external hexagon implant and Ceraone abutment. For groups 1, 2, 3 and 5, the crowns were cemented on the abutments and in group 4 crowns were screwed directly on the implant. The specimens were subjected to 500,000 cycles at 19.1 Hz of frequency and non-axial load of 133 N in a MTS 810 machine. The vertical misfit (μm at the implant/abutment interface was evaluated before (B and after (A application of the cyclic loading. Data were analyzed statistically by using two-away ANOVA and Tukey's post-hoc test (p<0.05. RESULTS: Before loading values showed no difference among groups 2 (4.33±3.13, 3 (4.79±3.43 and 5 (3.86±4.60; between groups 1 (12.88±6.43 and 4 (9.67±3.08, and among groups 2, 3 and 4. However, groups 1 and 4 were significantly different from groups 2, 3 and 5. After loading values of groups 1 (17.28±8.77 and 4 (17.78±10.99 were significantly different from those of groups 2 (4.83±4.50, 3 (8.07±4.31 and 5 (3.81±4.84. There was a significant increase in misfit values of groups 1, 3 and 4 after cyclic loading, but not for groups 2 and 5. CONCLUSIONS: The cyclic loading and type of implant/abutment connection may develop a role on the vertical misfit at the implant/abutment interface.

Effect of intergranular stress on yielding of 316H during room temperature cyclic loading

International Nuclear Information System (INIS)

Al Mamun, Abdullah; Moat, Richard; Bouchard, John; Kelleher, Joe

2016-01-01

Assessment of cyclic deformation is an integral part of nuclear power plant life assessment code, as many of the components in plant go through scheduled and unscheduled cyclic deformation owing to varying thermal and mechanical stresses. In polycrystalline material like 316H, a type of micro stress known as intergranular stress is generated due to elastic and plastic anisotropies during such cyclic loading. In tension-compression loading cycles, these stresses remain in the material as a residual stress upon unloading to zero stress from the tensile/compressive peak or intermediates stresses. The magnitude of these stresses vary depending on the point in the cycle from which it was unloaded from. When the material is re-loaded either in the same or reverse loading direction these residual stresses increase or decrease the effective stress acting in the material and as such the macroscopic yield stress of the material in subsequent cycle is changed significantly. The magnitude of intergranular stresses in many differently oriented grain families can be measured simultaneously using time of flight (ToF) neutron diffraction technique. In this paper, we have used this technique to experimentally study, how these intergranular stresses affect the yield (proof) stress of 316H at room temperature. (author)

Bending cyclic load test for crystalline silicon photovoltaic modules

Science.gov (United States)

Suzuki, Soh; Doi, Takuya; Masuda, Atsushi; Tanahashi, Tadanori

2018-02-01

The failures induced by thermomechanical fatigue within crystalline silicon photovoltaic modules are a common issue that can occur in any climate. In order to understand these failures, we confirmed the effects of compressive or tensile stresses (which were cyclically loaded on photovoltaic cells and cell interconnect ribbons) at subzero, moderate, and high temperatures. We found that cell cracks were induced predominantly at low temperatures, irrespective of the compression or tension applied to the cells, although the orientation of cell cracks was dependent on the stress applied. The fracture of cell interconnect ribbons was caused by cyclical compressive stress at moderate and high temperatures, and this failure was promoted by the elevation of temperature. On the basis of these results, the causes of these failures are comprehensively discussed in relation to the viscoelasticity of the encapsulant.

Life prediction of simple structures subject to cyclic primary and secondary loading resulting in creep and platicity

International Nuclear Information System (INIS)

Otter, N.R.; Jones, R.T.

1979-01-01

High temperature reactors are subject to cyclic mechanical and thermal loadings resulting from start up and shut down operations. The design must therefore guard against structural failure resulting from excessive deformation and creep-fatigue damage. Before any simplified inelastic analysis techniques can be applied, their validity needs to be examined under situations representative of the reactor. For this to be carried out it is necessary to determine the behaviour of components, initially geometrically simple, subject to loadings, cyclic primary and secondary in nature, which result in creep and plasticity. Beam-like structures have been investigated on a finite element basis with the aim of determining how cyclic plasticity, creep enhancement and plastic ratchetting vary in relationship with modified shakedown criteria, magnitude of loading and hold time. (orig.)

Elasto-plastic behavior of pipe subjected to steady axial load and cyclic bending

International Nuclear Information System (INIS)

Yao Yanping; Lu Mingwan; Zhang Xiong

2004-01-01

The elasto-plastic behavior of a pipe subjected to a steady axial force and a cyclic bending moment is studied. By using two parameters c and d, which describe the elasto-plastic interfaces of beam cross-section, the boundary curve equations between various types of elasto-plastic behavior, such as shakedown, plastic fatigue, ratcheting, and plastic collapse, are derived. The results are applicable for beams of any cross-section with two orthogonal axes of symmetry. As a result, the load regime diagram for a pipe is obtained, which gives an intuitive picture of the elasto-plastic behavior of the pipe under a given combination of constant axial load and cyclic bending moment

Microstructural characterisation and constitutive behaviour of alloy RR1000 under fatigue and creep-fatigue loading conditions

International Nuclear Information System (INIS)

Stoecker, C.; Zimmermann, M.; Christ, H.-J.; Zhan, Z.-L.; Cornet, C.; Zhao, L.G.; Hardy, M.C.; Tong, J.

2009-01-01

Mechanical behaviour of a nickel-based superalloy, RR1000, has been investigated at 650 deg. C under cyclic and dwell loading conditions. The microstructural characteristics of the alloy have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the distribution patterns of the dislocations and slip planes have been compared between samples tested under fatigue and creep-fatigue loading conditions. Constitutive behaviour of the alloy was described by a unified constitutive model, where both cyclic plastic and viscoplastic strains were represented by one inelastic strain. The results show that the precipitation state is very stable at 650 deg. C and only minor differences exist in the dislocation arrangements formed under pure fatigue and combined creep and fatigue conditions. Hence, a unified constitutive model seems to be justified in describing and predicting the constitutive behaviour in both cases.

Smart aggregate based damage detection of circular RC columns under cyclic combined loading

International Nuclear Information System (INIS)

Moslehy, Yashar; Belarbi, Abdeldjelil; Mo, Y L; Gu, Haichang; Song, Gangbing

2010-01-01

Structural health monitoring is an important issue for the maintenance of large-scale civil infrastructures, especially for bridge columns. In this paper, an innovative piezoceramic-based approach is developed for the structural health monitoring of reinforced concrete columns. An innovative piezoceramic-based device, the smart aggregate, is utilized as a transducer for the purpose of health monitoring. To investigate the seismic behavior of reinforced concrete (RC) bridge columns, structural health monitoring tests were performed on two bridge columns under combined reversed cyclic loading at the Missouri University of Science and Technology. The proposed smart aggregate based approach successfully evaluated the health status of concrete columns during the loading procedure. Sensor energy plots and 3D normalized sensor energy plots demonstrated that the damage inside attenuated the transmitted energy. The wavelet packet based damage index and sensor history damage index evaluate the damage development in concrete columns under cyclic loading

Determination of babbit mechanical properties based on tin under static and cyclic loading

Science.gov (United States)

Zernin, M. V.

2018-03-01

Based on the results of studies of babbitt on the basis of tin under static loading under three types of stress state, the parameters of the criterion for the equivalence of stressed states were refined and a single diagram of the babbitt deformation was obtained. It is shown that the criterion of equivalence for static loading should contain the first principal stress and stress intensity. With cyclic loading, the first main voltage can be used as a criterion. The stages of development of fatigue cracks are described and it is logical to use a statistical approach to reveal the boundary of the transition from short cracks to macrocracks, based on a significant difference in the characteristics of the dispersion of the crack speeds at these two stages. The results of experimental studies of the cyclic crack resistance of babbitt are presented and the parameters of this boundary are obtained.

Study the Cyclic Plasticity Behavior of 508 LAS under Constant, Variable and Grid-Load-Following Loading Cycles for Fatigue Evaluation of PWR Components

Energy Technology Data Exchange (ETDEWEB)

Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Barua, Bipul [Argonne National Lab. (ANL), Argonne, IL (United States); Soppet, William K. [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

2016-09-01

This report provides an update of an earlier assessment of environmentally assisted fatigue for components in light water reactors. This report is a deliverable in September 2016 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2016 report, we presented a detailed thermal-mechanical stress analysis model for simulating the stress-strain state of a reactor pressure vessel and its nozzles under grid-load-following conditions. In this report, we provide stress-controlled fatigue test data for 508 LAS base metal alloy under different loading amplitudes (constant, variable, and random grid-load-following) and environmental conditions (in air or pressurized water reactor coolant water at 300°C). Also presented is a cyclic plasticity-based analytical model that can simultaneously capture the amplitude and time dependency of the component behavior under fatigue loading. Results related to both amplitude-dependent and amplitude-independent parameters are presented. The validation results for the analytical/mechanistic model are discussed. This report provides guidance for estimating time-dependent, amplitude-independent parameters related to material behavior under different service conditions. The developed mechanistic models and the reported material parameters can be used to conduct more accurate fatigue and ratcheting evaluation of reactor components.

Evolutions of Yang Phase Under Cyclic Condition and Adiabatic Condition

International Nuclear Information System (INIS)

Qian Shangwu; Gu Zhiyu

2005-01-01

There are three non-integrable phases in literatures: Berry phase, Aharonov-Anandan phase, and Yang phase. This article discusses the evolutions of Yang phase under the cyclic condition and the adiabatic condition for the general time-dependent harmonic oscillator, thus reveals the intimate relations between these three non-integrable phases.

Multiaxial fatigue strength of type 316 stainless steel under push–pull, reversed torsion, cyclic inner and outer pressure loading

International Nuclear Information System (INIS)

Morishita, Takahiro; Itoh, Takamoto; Bao, Zhenlong

2016-01-01

Multiaxial fatigue tests under non-proportional loading in which principal directions of stress and strain are changed in a cycle were carried out using a developed multiaxial fatigue testing machine which can load a push–pull and reversed torsion loading with cyclic inner and outer pressure. This paper presents the developed testing machine and experimental results under several multiaxial loading conditions including non-proportional loading. In strain control tests, the failure life is reduced in accordance with increasing inner pressure at each strain path. The failure life can be correlated by von Mises' equivalent stress amplitude relatively well independent of not only inner pressure but also loading path. In load control tests, the failure life is reduced largely by non-proportional loading but the influence of inner and outer pressure on the failure life is relative small.

Strain-hardening behavior and microstructure development in polycrystalline as-cast Mg-Zn-Y alloys with LPSO phase subjected to cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Shiraishi, Kazuma [Department of Materials Science and Engineering, Kumamoto University, 2-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan); Mayama, Tsuyoshi, E-mail: mayama@kumamoto-u.ac.jp [Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan); Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904 (United States); Yamasaki, Michiaki [School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Brisbane, Qld 4072 (Australia); Magnesium Research Center/Department of Materials Science and Engineering, Kumamoto University, 2-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan); Kawamura, Yoshihito [Magnesium Research Center/Department of Materials Science and Engineering, Kumamoto University, 2-39-1, Kurokami, Chuo-ku, Kumamoto 860-8555 (Japan)

2016-08-30

The strain-hardening behavior and microstructural development of polycrystalline as-cast Mg-Zn-Y alloys with various volume fractions of the long-period stacking ordered (LPSO) phase subjected to cyclic loading were experimentally evaluated. For all alloys, cyclic loading tests with a constant strain amplitude of 0.5% for up to 100 cycles showed asymmetric cyclic hardening behavior. That is, the absolute value of the compressive peak stress significantly increased during cyclic loading while the tensile peak stress slightly decreased. With increasing volume fraction of the LPSO phase, the stress amplitude significantly increased. Cyclic loading tests after compressive preloading up to 200 or 250 MPa resulted in a significant increase in the stress amplitude, while a number of kink bands developed during preloading. For the cyclic hardening behavior, the contribution of the increase in kinematic hardening was significant in the alloys with a higher volume fraction of the LPSO phase. Transmission electron microscopy observation of the cyclically deformed Mg{sub 85}Zn{sub 6}Y{sub 9} alloy indicated the formation of a deformation-induced band, where the crystal structure was transformed from 18R-LPSO to hcp-Mg with the exclusion of solute elements.

Study of fatigue resistance for different steel specimens under conditions of combined action of cyclic bending and torsion

International Nuclear Information System (INIS)

Belkin, L.M.; Filimonov, G.N.; Belkin, M.Ya.; Vishnevskij, A.P.; Volkov, I.B.

1986-01-01

VP6 alloy is studied for its relaxation stability and fatigue strength. Results of the study are presented. Tests are carried out on the specimens with smooth working part to study relaxation properties of the material, with thread working part to determine stress relaxation in a loose thread, on the thread joints to study relaxation in the working thread. All the studied members of the thread joint under cyclic loading are shown to obey a common regularity. Characteristics of the relaxation material stability under different values on an average stress cycle are presented. Stress concentration associated with inhomogeneity in distribution of axial tensile stresses in a loose thread and nonuniformity in the working thread. All the studied members of the thread joint under cyclic loading are shown to obey a common regularity. Characteristics of the relaxation material stability under different values on an average stress cycle are presented. Stress concentration associated with inhomogeneity in distribution of axial tensile stresses in a loose thread and nonuniformity in the load on the working thread turns along the nut length are studied for their effect on the stress relaxation in the thread joint. Ultimate longevity of the materials under conditions of cyclic stress relaxation is evaluated allowing for relaxation and fatigue characteristics of the material

Deformation Behavior of Recycled Concrete Aggregate during Cyclic and Dynamic Loading Laboratory Tests

Directory of Open Access Journals (Sweden)

Wojciech Sas

2016-09-01

Full Text Available Recycled concrete aggregate (RCA is a relatively new construction material, whose applications can replace natural aggregates. To do so, extensive studies on its mechanical behavior and deformation characteristics are still necessary. RCA is currently used as a subbase material in the construction of roads, which are subject to high settlements due to traffic loading. The deformation characteristics of RCA must, therefore, be established to find the possible fatigue and damage behavior for this new material. In this article, a series of triaxial cyclic loading and resonant column tests is used to characterize fatigue in RCA as a function of applied deviator stress after long-term cyclic loading. A description of the shakedown phenomenon occurring in the RCA and calculations of its resilient modulus (Mr as a function of fatigue are also presented. Test result analysis with the stress-life method on the Wohler S-N diagram shows the RCA behavior in accordance with the Basquin law.

Modeling of high-strength concrete-filled FRP tube columns under cyclic load

Science.gov (United States)

Ong, Kee-Yen; Ma, Chau-Khun; Apandi, Nazirah Mohd; Awang, Abdullah Zawawi; Omar, Wahid

2018-05-01

The behavior of high-strength concrete (HSC) - filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs) column subjected to cyclic lateral loading is presented in this paper. As the experimental study is costly and time consuming, a finite element analysis (FEA) is chosen for the study. Most of the previous studies have focused on examining the axial load behavior of HSCFFT column instead of seismic behavior. The seismic behavior of HSCFFT columns has been the main interest in the industry. The key objective of this research is to develop a reliable numerical non-linear FEA model to represent the seismic behavior of such column. A FEA model was developed using the Concrete Damaged Plasticity Model (CDPM) available in the finite element software package (ABAQUS). Comparisons between experimental results from previous research and the predicted results were made based on load versus displacement relationships and ultimate strength of the column. The results showed that the column increased in ductility and able to deform to a greater extent with the increase of the FRP confinement ratio. With the increase of confinement ratio, HSCFFT column achieved a higher moment resistance, thus indicated a higher failure strength in the column under cyclic lateral load. It was found that the proposed FEA model can regenerate the experimental results with adequate accuracy.

MONOTONIC AND CYCLIC LOADING SIMULATION OF STRUCTURAL STEELWORK BEAM TO COLUMN BOLTED CONNECTIONS WITH CASTELLATED BEAM

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SAEID ZAHEDI VAHID

2013-08-01

Full Text Available Recently steel extended end plate connections are commonly used in rigid steel frame due to its good ductility and ability for energy dissipation. This connection system is recommended to be widely used in special moment-resisting frame subjected to vertical monotonic and cyclic loads. However improper design of beam to column connection can leads to collapses and fatalities. Therefore extensive study of beam to column connection design must be carried out, particularly when the connection is exposed to cyclic loadings. This paper presents a Finite Element Analysis (FEA approach as an alternative method in studying the behavior of such connections. The performance of castellated beam-column end plate connections up to failure was investigated subjected to monotonic and cyclic loading in vertical and horizontal direction. The study was carried out through a finite element analysis using the multi-purpose software package LUSAS. The effect of arranging the geometry and location of openings were also been investigated.

Evaluation of torque loss in Co-Cr castable abutments after cyclic loading

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Somayeh Zeighami

2018-03-01

Conclusion: Misfit between the castable implant components can cause torque loss before and after cyclic loading. However, it is more appropriate to relate the results of this study to the screw loosening of the above mentioned abutments than judging their clinical performance.

Prediction of elastic-plastic response of structural elements subjected to cyclic loading

International Nuclear Information System (INIS)

El Haddad, M.H.; Samaan, S.

1985-01-01

A simplified elastic-plastic analysis is developed to predict stress strain and force deformation response of structural metallic elements subjected to irregular cyclic loadings. In this analysis a simple elastic-plastic method for predicting the skeleton force deformation curve is developed. In this method, elastic and fully plastic solutions are first obtained for unknown quantities, such as deflection or local strains. Elastic and fully plastic contributions are then combined to obtain an elastic-plastic solution. The skeleton curve is doubled to establish the shape of the hysteresis loop. The complete force deformation response can therefore be simulated through reversal by reversal in accordance with hysteresis looping and material memory. Several examples of structural elements with various cross sections made from various materials and subjected to irregular cyclic loadings, are analysed. A close agreement is obtained between experimental results found in the literature and present predictions. (orig.)

Modeling of Cyclic Strength for the Asphalt Concrete Considering Damage Accumulation

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Alibai Iskakbayev

2017-12-01

Full Text Available The expression is obtained for determination of cyclic tensile strength for asphalt concrete, which considers damage accumulation and history of loading, using the long-term strength curve for asphalt concrete obtained according to the test results of more than 110 samples to failure at stresses from 0.05 to 0.31 MPa and by introduction of damage kernel in this paper. Cyclic strength depends on the stress, parameters of long-term strength, frequency of loading, durations of loading and relax periods, and ratio of loading period to the long-term strength. Evaluation of accuracy for the obtained expression for the cyclic strength has been performed by comparison with the results of a series for experimental tests of asphalt concrete samples at a temperature of 22 °С and cyclic loading conditions. The stress is 0.31 MPa, and the durations of loading and relax periods are 5 and 60 s, respectively. Calculations performed with the obtained expressions at real road conditions (the stress is 0.31 MPa, and the durations of loading and relax periods are 0.1 and 9.9 s respectively showed the possibility of its use for the prediction of fatigue (multicyclic strength of an asphalt concrete pavement for a highway.

Impact of Cyclic Loading on Chloride Diffusivity and Mechanical Performance of RC Beams under Seawater Corrosion

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Sen Pang

2017-01-01

Full Text Available An experimental study was conducted to investigate the impact of cyclic loading on the mechanical performance and chloride diffusivity of RC beams exposed to seawater wet-dry cycles. To induce initial damage to RC beam specimen, cyclic loading controlled by max load and cycles was applied. Then beam specimens underwent 240 wet-dry cycles of seawater. Results show that the chloride content increased as max load and cycle increased. The chloride content at steel surface increased approximatively linearly as average crack width increased. Moreover, the max load had more influence on chloride content at steel surface than cycle. The difference of average chloride diffusion coefficient between tension and compression concrete was little at uncracked position. Average chloride diffusion coefficient increased as crack width increased when crack width was less than 0.11 mm whereas the increasing tendency was weak when crack width exceeded 0.11 mm. The residual yield load and ultimate load of RC beams decreased as max load and cycle increased. Based on univariate analysis of variance, the max load had more adverse effect on yield load and ultimate load than cycle.

Partial alpha-colony fractures and their protrusions during cyclic loading of a titanium alloy

International Nuclear Information System (INIS)

Cameron, D.W.; Hoeppner, D.W.

1984-01-01

In the course of an extended study of the cyclic load response of several gas turbine alloys, a very interesting phenomenon was observed in some specimens of IMI 829. The response documented shows the emergence of loosely-bound sections of material into the notch root of test specimens. The authors have not seen this effect reported by other investigators. The experimental apparatus consists of a scanning electron microscope coupled with a load frame to view the real-time surface response of cyclically loaded specimens. For reference, the specimen geometry is shown, the cross section (A-A) is rectangular, measuring approximately 1mm X 4mm. Normal preparation is to notch one side of the specimen using a jeweller's saw and metallurgically polish and etch one of the flat surfaces for observation. IMI 829 (Ti-5.5Al-3.5Sn-3.0Zr-0.25Mo-1Nb-0.3Si) is a near-alpha titanium alloy, examined here in the beta-annealed condition which displays plate-like alpha colonies with some primary alpha on the prior beta grain boundaries. It can also manifest a Widmanstaetten-type microstructure. Having a nominal grain size of approximately 1mm, the microstructure-specimen size combination allows for an interesting study in pseudo-continua. Although the experiments were predominantly designed to investigate crack-microstructure interactions, the features of interest here were generated within the saw-cut notch root of the specimen. In the process of nucleating a crack in the notch root, three of six specimens developed discontinuities which were not perpendicular to either the loading axis or the observed specimen surface. In two of these three cases, while the crack was progressing across the ligament and downward through the specimen, some sections broke away

Damage propagation in a masonry arch subjected to slow cyclic and dynamic loadings

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J. Toti

2014-07-01

Full Text Available In the present work, the damage propagation of a masonry arch induced by slow cyclic and dynamic loadings is studied. A two-dimensional model of the arch is proposed. A nonlocal damage-plastic constitutive law is adopted to reproduce the hysteretic characteristics of the masonry material, subjected to cyclic static loadings or to harmonic dynamic excitations. In particular, the adopted cohesive model is able to take into account different softening laws in tension and in compression, plastic strains, stiffness recovery and loss due to crack closure and reopening. The latter effect is an unavoidable feature for realistically reproducing hysteretic cycles. In the studied case, an inverse procedure is used to calibrate the model parameters. Then, nonlinear static and dynamic responses of the masonry arch are described together with damage propagation paths.

Cyclic Creep Behavior of Modified 9Cr-1Mo Steel at 600 .deg. C

International Nuclear Information System (INIS)

Kim, Woo Gon; Kim, Dae Whan; Jang, Jin Sung; Park, Jae Young

2012-01-01

Cyclic deformation behavior is important in practice because high-temperature structural components are exposed under the cyclic conditions of repeated loading. In static creep (SC), the response of the material is simple as a static state of monotonic loading. However, in cyclic creep (CC), it is complex as dynamic loading. Cyclic creep data have been rarely reported until now. In particular, it is not understood well whether cyclic creep will accelerate or retard the creep rate compared with static creep, because it is not only the plastic deformation under cyclic loading is drastically different from monotonic loading, but also the cyclic response is dependent on the cycling frequency, stress range, stress ratio, and hold periods of cycling. Therefore, it is necessary to clarify the cyclic creep behavior influencing the creep deformation and fracture process. In this study, a series of cyclic creep tests was carried out using magnitudes of stress range of constant stress ratio (R=0.1) under continuous tension-tension loading cycles at a hold time of 10 minutes. Cyclic curves were monitored and obtained with time variations, and the properties of the cyclic creep tests were compared with those of static creep tests. The fracture microstructures were observed and analyzed

Parameterized Disturbance Observer Based Controller to Reduce Cyclic Loads of Wind Turbine

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Raja M. Imran

2018-05-01

Full Text Available This paper is concerned with bump-less transfer of parameterized disturbance observer based controller with individual pitch control strategy to reduce cyclic loads of wind turbine in full load operation. Cyclic loads are generated due to wind shear and tower shadow effects. Multivariable disturbance observer based linear controllers are designed with objective to reduce output power fluctuation, tower oscillation and drive-train torsion using optimal control theory. Linear parameterized controllers are designed by using a smooth scheduling mechanism between the controllers. The proposed parameterized controller with individual pitch was tested on nonlinear Fatigue, Aerodynamics, Structures, and Turbulence (FAST code model of National Renewable Energy Laboratory (NREL’s 5 MW wind turbine. The closed-loop system performance was assessed by comparing the simulation results of proposed controller with a fixed gain and parameterized controller with collective pitch for full load operation of wind turbine. Simulations are performed with step wind to see the behavior of the system with wind shear and tower shadow effects. Then, turbulent wind is applied to see the smooth transition of the controllers. It can be concluded from the results that the proposed parameterized control shows smooth transition from one controller to another controller. Moreover, 3p and 6p harmonics are well mitigated as compared to fixed gain DOBC and parameterized DOBC with collective pitch.

Ratchetting behavior of primary heat transport (PHT) piping material SA-333 carbon steel subjected to cyclic loads at room temperature

International Nuclear Information System (INIS)

Kulkarni, S.; Desai, Y.M.; Kant, T.; Reddy, G.R.; Gupta, C.; Chakravarthy, J.K.

2004-01-01

Ratchetting behavior of SA-333 Gr. 6 carbon steel used as primary heat transport (PHT) piping material has been investigated with three constitutive models proposed by Armstrong-Frederick, Chaboche and Ohno-Wang involving different hardening rules. Performance of the above mentioned models have been evaluated for a broad set of uniaxial and biaxial loading histories. The uniaxial ratchetting simulations have been performed for a range of stress ratios (R) by imposing different stress amplitudes and mean stress conditions. Numerical simulations indicated significant ratchetting and opening of hysteresis loop for negative stress ratio with constant mean stress. Application of cyclic stress without mean stress (R = -1.0) has been observed to produce negligible ratchet-strain accumulation in the material. Simulation under the biaxial stress condition was based on modeling of an internally pressurized thin walled pipe subjected to cyclic bending load. Numerical results have been validated with the experiments as per simulation conditions. All three models have been found to predict the observed accumulation of circumferential strain with increasing number of cycles. However, the Armstrong Frederick (A-F) model was found to be inadequate in simulating the ratchetting response for both uniaxial as well as biaxial loading cases. The A-F model actually over-predicted the ratchetting strain in comparison with the experimental strain values. On the other hand, results obtained with the Chaboche and the Ohno-Wang models for both the uniaxial as well as biaxial loading histories have been observed to closely simulate the experimental results. The Ohno-Wang model resulted in better simulation for the presents sets of experimental results in comparison with the Chaboche model. It can be concluded that the Ohno-Wang model suited well compared to the Chaboche model for above sets of uniaxial and biaxial loading histories. (authors)

Performance study of Ke factors in simplified elastic plastic fatigue analyses with emphasis on thermal cyclic loading

International Nuclear Information System (INIS)

Lang, Hermann; Rudolph, Juergen; Ziegler, Rainer

2011-01-01

As code-based fully elastic plastic code conforming fatigue analyses are still time consuming, simplified elastic plastic analysis is often applied. This procedure is known to be overly conservative for some conditions due to the applied plastification (penalty) factor K e . As a consequence, less conservative fully elastic plastic fatigue analyses based on non-linear finite element analyses (FEA) or simplified elastic plastic analysis based on more realistic K e factors have to be used for fatigue design. The demand for more realistic K e factors is covered as a requirement of practical fatigue analysis. Different code-based K e procedures are reviewed in this paper with special regard to performance under thermal cyclic loading conditions. Other approximation formulae such as those by Neuber, Seeger/Beste or Kuehnapfel are not evaluated in this context because of their applicability to mechanical loading excluding thermal cyclic loading conditions typical for power plant operation. Besides the current code-based K e corrections, the ASME Code Case N-779 (e.g. Adam's proposal) and its modification in ASME Section VIII is considered. Comparison of elastic plastic results and results from the Rules for Nuclear Facility Components and Rules for Pressure Vessels reveals a considerable overestimation of usage factor in the case of ASME III and KTA 3201.2 for the examined examples. Usage factors according to RCC-M, Adams (ASME Code Case N-779), ASME VIII (alternative) and EN 13445-3 are essentially comparable and less conservative for these examples. The K v correction as well as the applied yield criterion (Tresca or von Mises) essentially influence the quality of the more advanced plasticity corrections (e.g. ASME Code Case N-779 and RCC-M). Hence, new proposals are based on a refined K v correction.

Efficient cycle jumping techniques for the modelling of materials and structures under cyclic mechanical and thermal loading

International Nuclear Information System (INIS)

Dunne, F.P.E.; Hayhurst, D.R.

1994-01-01

Highly efficient cycle jumping algorithms have been developed for the calculation of stress and damage histories for both cyclic mechanical and cycle thermal loading. The techniques have been shown to be suitable for cyclic plasticity; creep-cyclic plasticity interaction; and creep dominated material behaviour. The cycle jumping algorithms have been validated by comparison of the predictions made using both the cycle jumping technique, and the full calculation involving the integration of the equations around all cycles. Excellent agreement has been achieved, and significant reductions in computer processing time of up to 90% have been obtained by using the cycle jumping technique. A further cycle jumping technique has been developed for full component analysis, using a viscoplastic damage finite element solver, which enables stress redistribution to be modelled. The behaviour and lifetime of a slag tap component has been predicted when subjected to cyclic thermal loading. Cyclic plasticity damage and micro-crack initiation is predicted to occur at the water cooling duct after 2.974 cycles, with damage and micro-crack evolution arresting after 60.000. (author). 18 refs., 13 figs., 4 photos

Evaluation and visualization of multiaxial fatigue behavior under random non-proportional loading condition

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Takahiro Morishita

2017-07-01

Full Text Available In cyclic multiaxial stress/strain condition under nonproportional loading in which principal direction of stress/strain are changed in a cycle, it becomes difficult to analyze stress/strain ranges because of complexity of multiaxial stress/strain states depending on time in cycles. In order to evaluate stress/strain simply and suitably under non-proportional loading, Itoh and Sakane have proposed a method called as IS-method and a strain parameter for life evaluation under non-proportional loading NP. In the method, 6-components of stress/strain are converted to an equivalent stress/strain indicating the amplitude and the direction of principal stress/strain as a function of time as well as an intensity of loading nonproportionality fNP. Based on IS-method, the authors also have developed a tool which enables to analyze multiaxial stress/strain condition with the nonproportionality of loading history and evaluate failure life under nonproportional multiaxial loading. The tool indicates the analyzed results on monitor and users can understand visually not only variation of the stress/strain conditions but also non-proportionality during the cycle, which helps the design of material strength.

Mercury embrittlement of Cu-Al alloys under cyclic loading

Science.gov (United States)

Regan, T. M.; Stoloff, N. S.

1977-01-01

The effect of mercury on the room temperature, high cycle fatigue properties of three alloys: Cu-5.5 pct Al, Cu-7.3 pct Al, and Cu-6.3 pct Al-2.5 pct Fe has been determined. Severe embrittlement under cyclic loading in mercury is associated with rapid crack propagation in the presence of the liquid metal. A pronounced grain size effect is noted under mercury, while fatigue properties in air are insensitive to grain size. The fatigue results are discussed in relation to theories of adsorption-induced liquid metal embrittlement.

Graft tendon slippage with metallic and bioabsorbable interference screws under cyclic load: a biomechanical study in a porcine model

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Ari Digiácomo Ocampo Moré

Full Text Available Introduction The rupture of the anterior cruciate ligament (ACL is the most common type of knee injury. Reconstructive surgery is the ‘gold standard’ treatment. During the immediate post-operative period, the fixation of the graft is entirely dependent on the ability of the grafted implant to be secured inside the bone tunnel under the cyclical loads associated with daily tasks. Poor fixation can lead to graft slippage, thus impairing the healing and integration of the graft. The aim of this study was to evaluate the biomechanical performance of tendon graft fixation devices with metallic and bioabsorbable interference screws. Methods Twenty ACL reconstructions were carried out in porcine tibias using deep flexor tendons to fix 9 × 20 mm metallic (n=10 and PLLA 70/30 bioabsorbable screws (n=10. To verify the ability of a construct to resist immediate postoperative (PO rehabilitation protocols for immediate load bearing, a cyclic loading test was applied with 50-250 N of tensile force at 1 Hz for 1000 cycles, and the displacement was measured at 10, 50, 100, 500 and 1000 load cycles to quantify the slippage of the graft during the test. After the cyclic loading test, a single-cycle load-to-failure test was applied. Results The slippage of the graft using metallic screws did not differ (P = 0.616 from that observed when using bioabsorbable screws. Conclusion The results obtained in this experiment indicate that metallic screws may promote a similar amount of graft slippage during low cyclic loading as bioabsorbable screws. Additionally, there was no difference in the biomechanical performance of these two types of screws during high failure loads.

Chaboche-based cyclic material hardening models for 316 SS–316 SS weld under in-air and pressurized water reactor water conditions

Energy Technology Data Exchange (ETDEWEB)

Mohanty, Subhasish, E-mail: smohanty@anl.gov; Soppet, William K.; Majumdar, Saurindranath; Natesan, Krishnamurti

2016-08-15

Highlights: • 316 SS–316 SS weld cyclically harden/soften while undergoing fatigue loading. • Cyclic hardening/softening creates cycle dependent stress-strain curves. • This necessitate to estimate the cycle dependence of material properties. • Cyclic evolution of Chaboche parameters are estimated under different conditions. - Abstract: This paper discusses a material hardening models for welds made from 316 stainless steel (SS) to 316 SS. The model parameters were estimated from the strain-versus-stress curves obtained from tensile and fatigue tests conducted under different conditions (air at room temperature, air at 300 °C, and primary loop water conditions for a pressurized water reactor). These data were used to check the fatigue cycle dependency of the material hardening parameters (yield stress, parameters related to Chaboche-based linear and nonlinear kinematic hardening models, etc.). The details of the experimental results, material hardening models, and associated calculated results are published in an Argonne report (ANL/LWRS-15/2). This paper summarizes the reported material parameters for 316 SS–316 SS welds and their dependency on fatigue cycles and other test conditions.

On estimation of reliability for pipe lines of heat power plants under cyclic loading

International Nuclear Information System (INIS)

Verezemskij, V.G.

1986-01-01

One of the possible methods to obtain a quantitative estimate of the reliability for pipe lines of the welded heat power plants under cyclic loading due to heating-cooling and due to vibration is considered. Reliability estimate is carried out for a common case of loading by simultaneous cycles with different amplitudes and loading asymmetry. It is shown that scattering of the breaking number of cycles for the metal of welds may perceptibly decrease reliability of the welded pipe line

Strain evolution after fiber failure in a single-fiber metal matrix composite under cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Hanan, Jay C. [Department of Materials Science, California Institute of Technology, Pasadena, CA 91125 (United States)]. E-mail: jay.hanan@okstate.edu; Mahesh, Sivasambu [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Uestuendag, Ersan [Department of Materials Science, California Institute of Technology, Pasadena, CA 91125 (United States)]. E-mail: ersan@caltech.edu; Beyerlein, Irene J. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Swift, Geoffrey A. [Department of Materials Science, California Institute of Technology, Pasadena, CA 91125 (United States); Clausen, Bjorn [Department of Materials Science, California Institute of Technology, Pasadena, CA 91125 (United States); Brown, Donald W. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Bourke, Mark A.M. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2005-06-15

The evolution of in situ elastic strain with cyclic tensile loading in each phase of a single Al{sub 2}O{sub 3}-fiber/aluminum-matrix composite was studied using neutron diffraction (ND). An analytical model appropriate for metal matrix composites (MMCs) was developed to connect the measured axial strain evolution in each phase with the possible micromechanical events that could occur during loading at room temperature: fiber fracture, interfacial slipping, and matrix plastic deformation. Model interpretation showed that the elastic strain evolution in the fiber and matrix was governed by fiber fracture and interface slipping and not by plastic deformation of the matrix, whereas the macroscopic stress-strain response of the composite was influenced by all three. The combined single-fiber composite model and ND experiment introduces a new and quick engineering approach for qualifying the micromechanical response in MMCs due to cyclic loading and fiber fracture.

Strain evolution after fiber failure in a single-fiber metal matrix composite under cyclic loading

International Nuclear Information System (INIS)

Hanan, Jay C.; Mahesh, Sivasambu; Uestuendag, Ersan; Beyerlein, Irene J.; Swift, Geoffrey A.; Clausen, Bjorn; Brown, Donald W.; Bourke, Mark A.M.

2005-01-01

The evolution of in situ elastic strain with cyclic tensile loading in each phase of a single Al 2 O 3 -fiber/aluminum-matrix composite was studied using neutron diffraction (ND). An analytical model appropriate for metal matrix composites (MMCs) was developed to connect the measured axial strain evolution in each phase with the possible micromechanical events that could occur during loading at room temperature: fiber fracture, interfacial slipping, and matrix plastic deformation. Model interpretation showed that the elastic strain evolution in the fiber and matrix was governed by fiber fracture and interface slipping and not by plastic deformation of the matrix, whereas the macroscopic stress-strain response of the composite was influenced by all three. The combined single-fiber composite model and ND experiment introduces a new and quick engineering approach for qualifying the micromechanical response in MMCs due to cyclic loading and fiber fracture

Mechanical Behavior of Red Sandstone under Incremental Uniaxial Cyclical Compressive and Tensile Loading

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Baoyun Zhao

2017-01-01

Full Text Available Uniaxial experiments were carried out on red sandstone specimens to investigate their short-term and creep mechanical behavior under incremental cyclic compressive and tensile loading. First, based on the results of short-term uniaxial incremental cyclic compressive and tensile loading experiments, deformation characteristics and energy dissipation were analyzed. The results show that the stress-strain curve of red sandstone has an obvious memory effect in the compressive and tensile loading stages. The strains at peak stresses and residual strains increase with the cycle number. Energy dissipation, defined as the area of the hysteresis loop in the stress-strain curves, increases nearly in a power function with the cycle number. Creep test of the red sandstone was also conducted. Results show that the creep curve under each compressive or tensile stress level can be divided into decay and steady stages, which cannot be described by the conventional Burgers model. Therefore, an improved Burgers creep model of rock material is constructed through viscoplastic mechanics, which agrees very well with the experimental results and can describe the creep behavior of red sandstone better than the Burgers creep model.

In situ nonlinear ultrasonic technique for monitoring microcracking in concrete subjected to creep and cyclic loading.

Science.gov (United States)

Kim, Gun; Loreto, Giovanni; Kim, Jin-Yeon; Kurtis, Kimberly E; Wall, James J; Jacobs, Laurence J

2018-08-01

This research conducts in situ nonlinear ultrasonic (NLU) measurements for real time monitoring of load-induced damage in concrete. For the in situ measurements on a cylindrical specimen under sustained load, a previously developed second harmonic generation (SHG) technique with non-contact detection is adapted to a cylindrical specimen geometry. This new setup is validated by demonstrating that the measured nonlinear Rayleigh wave signals are equivalent to those in a flat half space, and thus the acoustic nonlinearity parameter, β can be defined and interpreted in the same way. Both the acoustic nonlinearity parameter and strain are measured to quantitatively assess the early-age damage in a set of concrete specimens subjected to either 25 days of creep, or 11 cycles of cyclic loading at room temperature. The experimental results show that the acoustic nonlinearity parameter is sensitive to early-stage microcrack formation under both loading conditions - the measured β can be directly linked to the accumulated microscale damage. This paper demonstrates the potential of NLU for the in situ monitoring of mechanical load-induced microscale damage in concrete components. Copyright © 2018 Elsevier B.V. All rights reserved.

Proper Generalized Decomposition (PGD) for the numerical simulation of polycrystalline aggregates under cyclic loading

Science.gov (United States)

Nasri, Mohamed Aziz; Robert, Camille; Ammar, Amine; El Arem, Saber; Morel, Franck

2018-02-01

The numerical modelling of the behaviour of materials at the microstructural scale has been greatly developed over the last two decades. Unfortunately, conventional resolution methods cannot simulate polycrystalline aggregates beyond tens of loading cycles, and they do not remain quantitative due to the plasticity behaviour. This work presents the development of a numerical solver for the resolution of the Finite Element modelling of polycrystalline aggregates subjected to cyclic mechanical loading. The method is based on two concepts. The first one consists in maintaining a constant stiffness matrix. The second uses a time/space model reduction method. In order to analyse the applicability and the performance of the use of a space-time separated representation, the simulations are carried out on a three-dimensional polycrystalline aggregate under cyclic loading. Different numbers of elements per grain and two time increments per cycle are investigated. The results show a significant CPU time saving while maintaining good precision. Moreover, increasing the number of elements and the number of time increments per cycle, the model reduction method is faster than the standard solver.

Crack density and electrical resistance in indium-tin-oxide/polymer thin films under cyclic loading

KAUST Repository

Mora Cordova, Angel

2014-11-01

Here, we propose a damage model that describes the degradation of the material properties of indium-tin-oxide (ITO) thin films deposited on polymer substrates under cyclic loading. We base this model on our earlier tensile test model and show that the new model is suitable for cyclic loading. After calibration with experimental data, we are able to capture the stress-strain behavior and changes in electrical resistance of ITO thin films. We are also able to predict the crack density using calibrations from our previous model. Finally, we demonstrate the capabilities of our model based on simulations using material properties reported in the literature. Our model is implemented in the commercially available finite element software ABAQUS using a user subroutine UMAT.[Figure not available: see fulltext.].

Behaviour of C-shaped angle shear connectors under monotonic and fully reversed cyclic loading: An experimental study

International Nuclear Information System (INIS)

Shariati, Mahdi; Ramli Sulong, N.H.; Suhatril, Meldi; Shariati, Ali; Arabnejad Khanouki, M.M.; Sinaei, Hamid

2012-01-01

Highlights: ► C-shaped angle connectors show 8.8–33.1% strength degradation under cyclic loading. ► Connector fracture type of failure was experienced in C-shaped angle shear connectors. ► In push-out samples, more cracking was observed in those slabs with longer angles. ► C-shaped angle connectors show good behaviour in terms of the ultimate shear capacity. ► C-shaped angle connectors did not fulfil the requirements for ductility criteria. -- Abstract: This paper presents an evaluation of the structural behaviour of C-shaped angle shear connectors in composite beams, suitable for transferring shear force in composite structures. The results of the experimental programme, including eight push-out tests, are presented and discussed. The results include resistance, strength degradation, ductility, and failure modes of C-shaped angle shear connectors, under monotonic and fully reversed cyclic loading. The results show that connector fracture type of failure was experienced in C-shaped angle connectors and after the failure, more cracking was observed in those slabs with longer angles. On top of that, by comparing the shear resistance of C-shaped angle shear connectors under monotonic and cyclic loading, these connectors showed 8.8–33.1% strength degradation, under fully reversed cyclic loading. Furthermore, it was concluded that the mentioned shear connector shows a proper behaviour, in terms of the ultimate shear capacity, but it does not satisfy the ductility criteria, imposed by the Eurocode 4, to perform a plastic distribution of the shear force between different connectors along the beam length.

Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

Science.gov (United States)

Ghamgosar, M.; Erarslan, N.

2016-03-01

The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

The calculation of dissipated work, elastoplastic cyclic stress and cyclic strain in a structure

International Nuclear Information System (INIS)

Wang Xucheng; Xie Yihuan.

1986-01-01

With the development of the reactor technique, there is being an increasing interest in the calculation of elastoplastic response of a structure to its complex loading. This paper introduces a constitutive relation of a material for discribing unloading property, and uses it in an analysis of a real structure under a cyclic loading. The results, which include cyclic stress, cyclic strain and dissipated work, are meaningful in the researches of the structure behavior under complex loading and of the structural safety

Crack initiation life analysis in notched pipe under cyclic bending loads

International Nuclear Information System (INIS)

Lee, Joon Seong; Kwak, Sang Log; Kim, Young Jin; Park, Youn Won

2001-01-01

In order to improve leak-before-break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but crack initiation cycle was higher than the experimental result

Crack initiation life analysis in notched pipe under cyclic bending loads

International Nuclear Information System (INIS)

Goak, S. R.; Kim, Y. J.; Lee, J. S.; Park, Y. W.

2000-01-01

In order to improve LBB(Leak-Before-Break) methodology, more precisely the crack growth evaluation, a benchmark problem was proposed by the CEA Saclay. The aim of this benchmark analysis was to evaluate the crack growth in a notched pipe under cyclic bending loads. The proposed benchmark analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result

The ratchet–shakedown diagram for a thin pressurised pipe subject to additional axial load and cyclic secondary global bending

International Nuclear Information System (INIS)

Bradford, R.A.W.; Tipping, D.J.

2015-01-01

The ratchet and shakedown boundaries are derived analytically for a thin cylinder composed of elastic-perfectly plastic Tresca material subject to constant internal pressure with capped ends, plus an additional constant axial load, F, and a cycling secondary global bending load. The analytic solution is in good agreement with solutions found using the linear matching method. When F is tensile, ratcheting can occur for sufficiently large cyclic bending loads in which the pipe gets longer and thinner but its diameter remains the same. When F is compressive, ratcheting can occur in which the pipe diameter increases and the pipe gets shorter, but its wall thickness remains the same. When subject to internal pressure and cyclic bending alone (F = 0), no ratcheting is possible, even for arbitrarily large bending loads, despite the presence of the axial pressure load. The reason is that the case with a primary axial membrane stress exactly equal to half the primary hoop membrane stress is equipoised between tensile and compressive axial ratcheting, and hence does not ratchet at all. This remarkable result appears to have escaped previous attention. - Highlights: • A thin cylinder is subject to pressure and cyclic global bending and additional axial load. • Ratchet and shakedown boundaries are derived analytically and using LMM. • Good agreement is found. • No ratcheting occurs for zero additional axial load.

Twinning behavior in the Ti-5at.% Al single crystals during cyclic loading along [0001

International Nuclear Information System (INIS)

Xiao Lin

2005-01-01

Cyclic deformation behavior of Ti-5at.% Al single crystals subjected to pull-push cyclic load along [0001] crystallographic orientation was studied. A higher cyclic stress response was displayed in the Ti-5Al single crystal oriented for [0001] than that oriented for single prism slip. Optical microscopy and transmission electron microscopy examinations show that twinning is a dominant plastic deformation mode in the single crystals during cycling. Trace analysis of prepolished surfaces was used to identify the twin systems primarily responsible for deformation. The major twin type observed was {101-bar 2}, {112-bar 2}, {101-bar 1} and {112-bar 1}. slip was observed in the neighboring region of twins in the fatigued specimens. The activation of multiple twinning systems contributed to the higher cyclic saturation stress in Ti-5Al single crystals oriented for [0001

Performance study of K{sub e} factors in simplified elastic plastic fatigue analyses with emphasis on thermal cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Lang, Hermann, E-mail: hermann.lang@areva.com [AREVA NP GmbH, PEEA-G, Henri-Dunant-Strasse 50, 91058 Erlangen (Germany); Rudolph, Juergen; Ziegler, Rainer [AREVA NP GmbH, PEEA-G, Henri-Dunant-Strasse 50, 91058 Erlangen (Germany)

2011-08-15

As code-based fully elastic plastic code conforming fatigue analyses are still time consuming, simplified elastic plastic analysis is often applied. This procedure is known to be overly conservative for some conditions due to the applied plastification (penalty) factor K{sub e}. As a consequence, less conservative fully elastic plastic fatigue analyses based on non-linear finite element analyses (FEA) or simplified elastic plastic analysis based on more realistic K{sub e} factors have to be used for fatigue design. The demand for more realistic K{sub e} factors is covered as a requirement of practical fatigue analysis. Different code-based K{sub e} procedures are reviewed in this paper with special regard to performance under thermal cyclic loading conditions. Other approximation formulae such as those by Neuber, Seeger/Beste or Kuehnapfel are not evaluated in this context because of their applicability to mechanical loading excluding thermal cyclic loading conditions typical for power plant operation. Besides the current code-based K{sub e} corrections, the ASME Code Case N-779 (e.g. Adam's proposal) and its modification in ASME Section VIII is considered. Comparison of elastic plastic results and results from the Rules for Nuclear Facility Components and Rules for Pressure Vessels reveals a considerable overestimation of usage factor in the case of ASME III and KTA 3201.2 for the examined examples. Usage factors according to RCC-M, Adams (ASME Code Case N-779), ASME VIII (alternative) and EN 13445-3 are essentially comparable and less conservative for these examples. The K{sub v} correction as well as the applied yield criterion (Tresca or von Mises) essentially influence the quality of the more advanced plasticity corrections (e.g. ASME Code Case N-779 and RCC-M). Hence, new proposals are based on a refined K{sub v} correction.

Experimental Comparison of Non-Slender Piles under Static Loading and under Cyclic Loading in Sand

DEFF Research Database (Denmark)

Sørensen, Søren Peder Hyldal; Ibsen, Lars Bo

2012-01-01

An experimental evaluation of the pile behavior of non-slender piles exposed to static and cyclic lateral loading is presented. The tests were conducted in a pressure tank at Aalborg University. This enabled the possibility of applying an overburden pressure to the soil. When conducting small......-scale tests at 1-g the determination of the friction angle and the Young’s modulus of elasticity of the soil are difficult and further these soil parameters varies greatly with depth. These uncertainties were avoided by application of an overburden pressure....

First attempts towards the early detection of fatigued substructures using cyclic-loaded 20 MnMoNi 5 5 steel

International Nuclear Information System (INIS)

Dobmann, G.; Seibold, A.

1992-01-01

Materials subjected to cyclic loading undergo substructural changes which may affect service life. The low alloy, fine-grained structural steel 20 MnMoNi 5 5 is used to demonstrate how substructural changes detected using TEM techniques are a function of the number of cycles undergone. For a given cyclic loading the usage factor η=N/N f =0.5 can be derived. Initial investigations using nondestructive examination methods have indicated that substructural changes and magnetic variables can be correlated. (orig.)

Behaviour of hybrid fibre reinforced concrete beam–column joints under reverse cyclic loads

International Nuclear Information System (INIS)

Ganesan, N.; Indira, P.V.; Sabeena, M.V.

2014-01-01

Highlights: • Developed a high performance hybrid fibre reinforced cementitious composite. • Exterior beam-column joints have been tested under reversed cyclic loading. • Ductility factor, energy dissipation and stiffness degradation have been evaluated. • Contribution to reduce congestion of reinforcement in beam column joints. - Abstract: An experimental investigation was carried out to study the effect of hybrid fibres on the strength and behaviour of High performance concrete beam column joints subjected to reverse cyclic loads. A total of 12 reinforced concrete beams column joints were cast and tested in the present investigation. High performance concrete of M60 grade was designed using the modified ACI method suggested by Aïtcin. Crimped steel fibres and polypropylene fibres were used in hybrid form. The main variables considered were the volume fraction of (i) crimped steel fibres viz. 0.5% (39.25 kg/m 3 ) and 1.0% (78.5 kg/m 3 ) and (ii) polypropylene fibres viz. 0.1% (0.9 kg/m 3 ), 0.15% (1.35 kg/m 3 ), and 0.2% (1.8 kg/m 3 ). Addition of fibres in hybrid form improved many of the engineering properties such as the first crack load, ultimate load and ductility factor of the composite. The combination of 1% (78.5 kg/m 3 ) volume fraction of steel fibres and 0.15% (1.35 kg/m 3 ) volume fraction of polypropylene fibres gave better performance with respect to energy dissipation capacity and stiffness degradation than the other combinations

Toward an MRI-based method to measure non-uniform cartilage deformation: an MRI-cyclic loading apparatus system and steady-state cyclic displacement of articular cartilage under compressive loading.

Science.gov (United States)

Neu, C P; Hull, M L

2003-04-01

Recent magnetic resonance imaging (MRI) techniques have shown potential for measuring non-uniform deformations throughout the volume (i.e. three-dimensional (3D) deformations) in small orthopedic tissues such as articular cartilage. However, to analyze cartilage deformation using MRI techniques, a system is required which can construct images from multiple acquisitions of MRI signals from the cartilage in both the underformed and deformed states. The objectives of the work reported in this article were to 1) design an apparatus that could apply highly repeatable cyclic compressive loads of 400 N and operate in the bore of an MRI scanner, 2) demonstrate that the apparatus and MRI scanner can be successfully integrated to observe 3D deformations in a phantom material, 3) use the apparatus to determine the load cycle necessary to achieve a steady-state deformation response in normal bovine articular cartilage samples using a flat-surfaced and nonporous indentor in unconfined compression. Composed of electronic and pneumatic components, the apparatus regulated pressure to a double-acting pneumatic cylinder so that (1) load-controlled compression cycles were applied to cartilage samples immersed in a saline bath, (2) loading and recovery periods within a cycle varied in time duration, and (3) load magnitude varied so that the stress applied to cartilage samples was within typical physiological ranges. In addition the apparatus allowed gating for MR image acquisition, and operation within the bore of an MRI scanner without creating image artifacts. The apparatus demonstrated high repeatability in load application with a standard deviation of 1.8% of the mean 400 N load applied. When the apparatus was integrated with an MRI scanner programmed with appropriate pulse sequences, images of a phantom material in both the underformed and deformed states were constructed by assembling data acquired through multiple signal acquisitions. Additionally, the number of cycles to reach

Effect of cyclic load on vertical misfit of prefabricated and cast implant single abutment

Science.gov (United States)

DE JESUS TAVAREZ, Rudys Rodolfo; BONACHELA, Wellington Cardoso; XIBLE, Anuar Antônio

2011-01-01

Objective The purpose of this in vitro study was to evaluate misfit alterations at the implant/abutment interface of external and internal connection implant systems when subjected to cyclic loading. Material and Methods Standard metal crowns were fabricated for 5 groups (n=10) of implant/abutment assemblies: Group 1, external hexagon implant and UCLA cast-on premachined abutment; Group 2, internal hexagon implant and premachined abutment; Group 3, internal octagon implant and prefabricated abutment; Group 4, external hexagon implant and UCLA cast-on premachined abutment; and Group 5, external hexagon implant and Ceraone abutment. For groups 1, 2, 3 and 5, the crowns were cemented on the abutments and in group 4 crowns were screwed directly on the implant. The specimens were subjected to 500,000 cycles at 19.1 Hz of frequency and non-axial load of 133 N in a MTS 810 machine. The vertical misfit (μm) at the implant/abutment interface was evaluated before (B) and after (A) application of the cyclic loading. Data were analyzed statistically by using two-away ANOVA and Tukey’s post-hoc test (pabutment connection may develop a role on the vertical misfit at the implant/abutment interface. PMID:21437464

Modeling of creep-fatigue interaction of zirconium {alpha} under cyclic loading at 200 C; Modelisation du comportement et de l`endommagement en fatigue-fluage du zirconium {alpha} a 200C

Energy Technology Data Exchange (ETDEWEB)

Vogel, C.

1996-04-01

The present work deals with mechanical behaviour of zirconium alpha at 200 deg. C and crack initiation prediction methods, particularly when loading conditions lead to interaction of fatigue and creep phenomena. A classical approach used to study interaction between cyclic effects and constant loading effects does not give easy understanding of experimental results. Therefore, a new approach has been developed, which allow to determine a number of cycles for crack initiation for complex structures under large loading conditions. To study influence of fatigue and creep interaction on crack initiation, a model was chosen, using a scalar variable, giving representation of the material deterioration state. The model uses a non linear cumulating effect between the damage corresponding to cyclic loads and the damage correlated to time influence. The model belongs to uncoupled approaches between damage and behaviour, which is described here by a two inelastic deformations model. This mechanical behaviour model is chosen because it allows distinction between a plastic and a viscous part in inelastic flow. Cyclic damage is function of stress amplitude and mean stress. For the peculiar sensitivity of the material to creep, a special parameter bas been defined to be critical toward creep damage. It is the kinematic term associated to state variables describing this type of hardening in the viscous mechanism. (author).

CYCLIC PLASTIC BEHAVIOUR OF UFG COPPER UNDER CONTROLLED STRESS AND STRAIN LOADING

Directory of Open Access Journals (Sweden)

Lucie Navrátilová

2012-01-01

Full Text Available The influence of stress- and strain-controlled loading on microstructure and cyclic plastic behaviour of ultrafine-grained copper prepared by equal channel angular pressing was examined. The stability of microstructure is a characteristic feature for stress-controlled test whereas grain coarsening and development of bimodal structure was observed after plastic strain-controlled tests. An attempt to explain the observed behaviour was made.

Inelastic behavior of materials and structures under monotonic and cyclic loading

CERN Document Server

Brünig, Michael

2015-01-01

This book presents studies on the inelastic behavior of materials and structures under monotonic and cyclic loads. It focuses on the description of new effects like purely thermal cycles or cases of non-trivial damages. The various models are based on different approaches and methods and scaling aspects are taken into account. In addition to purely phenomenological models, the book also presents mechanisms-based approaches. It includes contributions written by leading authors from a host of different countries.

Mechanical behaviors of multi-filament twist superconducting strand under tensile and cyclic loading

Science.gov (United States)

Wang, Xu; Li, Yingxu; Gao, Yuanwen

2016-01-01

The superconducting strand, serving as the basic unit cell of the cable-in-conduit-conductors (CICCs), is a typical multi-filament twist composite which is always subjected to a cyclic loading under the operating condition. Meanwhile, the superconducting material Nb3Sn in the strand is sensitive to strain frequently relating to the performance degradation of the superconductivity. Therefore, a comprehensive study on the mechanical behavior of the strand helps understanding the superconducting performance of the strained Nb3Sn strands. To address this issue, taking the LMI (internal tin) strand as an example, a three-dimensional structural finite element model, named as the Multi-filament twist model, of the strand with the real configuration of the LMI strand is built to study the influences of the plasticity of the component materials, the twist of the filament bundle, the initial thermal residual stress and the breakage and its evolution of the filaments on the mechanical behaviors of the strand. The effective properties of superconducting filament bundle with random filament breakage and its evolution versus strain are obtained based on the damage theory of fiber-reinforced composite materials proposed by Curtin and Zhou. From the calculation results of this model, we find that the occurrence of the hysteresis loop in the cyclic loading curve is determined by the reverse yielding of the elastic-plastic materials in the strand. Both the initial thermal residual stress in the strand and the pitch length of the filaments have significant impacts on the axial and hysteretic behaviors of the strand. The damage of the filaments also affects the axial mechanical behavior of the strand remarkably at large axial strain. The critical current of the strand is calculated by the scaling law with the results of the Multi-filament twist model. The predicted results of the Multi-filament twist model show an acceptable agreement with the experiment.

Fatigue behavior of boxing welded joint under biaxial cyclic loads; 2juku kurikaeshi kajuka ni okeru kakumawashi yosetsu keishu no hiro kyodo

Energy Technology Data Exchange (ETDEWEB)

Takahashi, I.; Takada, A.; Akiyama, S.; Ushijima, M.; Maenaka, H. [Ministry of Transportation, Tokyo (Japan)

1998-12-31

Various forces such as gravity, wave induced force, inertial force etc. compositely act on a ship body from various directions. Therefore, while discussing strength or life of structural elements of ship body, it is necessary to understand the effects of the composite force condition. In this study, fatigue tests of boxing welded joint under rectangular biaxial cyclic loads are performed, the following results are obtained. Even under he biaxial cyclic loads, it is the same as the uniaxial test, the cracks occurred at the boxing weld toes propagate almost in the straight y-direction, but no oblique propagation of the cracks caused by the lad in the y-direction occurs. That the crack at initial stage of the crack progress is improved in y-direction can be illustrated by the facts that the residual stress in x-direction near the toes reaches to the yield stress, and the stress concentration in the welded toes is bigger in x-direction than that in y-direction. But as for prediction of the progress route, a further study including amplitude ratio of the biaxial loads, effects of width of test specimen is necessary. 4 refs., 12 figs., 4 tabs.

Crack propagation behaviour in stainless steel AISI 316L at elevated temperatures under static and cyclic loading

International Nuclear Information System (INIS)

Lange, H.

1991-01-01

Experimental investigations of crack growth under creep and creep-fatigue conditions are presented. The experiments were performed with the austenitic steel AISI 316L, that will be used in fast breeder reactors. A comparison of crack propagation behaviour at temperatures of T = 550deg C and T = 700deg C in common through-thickness cracked specimens and in plates containing surface cracks is carried out by application of several fracture mechanics parameters. The quantitative description of crack initiation times and crack velocities is persued particularly. The propagation rate of one-dimensional cracks under cyclic loading conditions at T = 550deg C is also treated with fracture mechanical methods. The influence of the hold periods on crack speed is discussed. (orig.) [de

History-independent cyclic response of nanotwinned metals

Science.gov (United States)

Pan, Qingsong; Zhou, Haofei; Lu, Qiuhong; Gao, Huajian; Lu, Lei

2017-11-01

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved. Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are unstable (hardening or softening) and history-dependent. Existing rules for fatigue life prediction, such as the linear cumulative damage rule, cannot account for the effect of loading history, and engineering components are often loaded by complex cyclic stresses with variable amplitudes, mean values and frequencies, such as aircraft wings in turbulent air. It is therefore usually extremely challenging to predict cyclic behaviour and fatigue life under a realistic load spectrum. Here, through both atomistic simulations and variable-strain-amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the metal, we report a history-independent and stable cyclic response in bulk copper samples that contain highly oriented nanoscale twins. We demonstrate that this unusual cyclic behaviour is governed by a type of correlated ‘necklace’ dislocation consisting of multiple short component dislocations in adjacent twins, connected like the links of a necklace. Such dislocations are formed in the highly oriented nanotwinned structure under cyclic loading and help to maintain the stability of twin boundaries and the reversible damage, provided that the nanotwins are tilted within about 15 degrees of the loading axis. This cyclic deformation mechanism is distinct from the conventional strain localizing mechanisms associated with irreversible microstructural damage in single-crystal, coarse-grained, ultrafine-grained and nanograined metals.

Assessment of Composite Delamination Self-Healing Under Cyclic Loading

Science.gov (United States)

O'Brien, T. Kevin

2009-01-01

Recently, the promise of self-healing materials for enhanced autonomous durability has been introduced using a micro-encapsulation technique where a polymer based healing agent is encapsulated in thin walled spheres and embedded into a base polymer along with a catalyst phase. For this study, composite skin-stiffener flange debonding specimens were manufactured from composite prepreg containing interleaf layers with a polymer based healing agent encapsulated in thin-walled spheres. Constant amplitude fatigue tests in three-point bending showed the effect of self-healing on the fatigue response of the skin-stiffener flange coupons. After the cycling that created debonding, fatigue tests were held at the mean load for 24 hours. For roughly half the specimens tested, when the cyclic loading was resumed a decrease in compliance (increase in stiffness) was observed, indicating that some healing had occurred. However, with continued cycling, the specimen compliance eventually increased to the original level before the hold, indicating that the damage had returned to its original state. As was noted in a prevoius study conducted with specimens tested under monotonically increasing loads to failure, healing achieved via the micro-encapsulation technique may be limited to the volume of healing agent available relative to the crack volume.

Crack density and electrical resistance in indium-tin-oxide/polymer thin films under cyclic loading

KAUST Repository

Mora Cordova, Angel; Khan, Kamran; El Sayed, Tamer

2014-01-01

Here, we propose a damage model that describes the degradation of the material properties of indium-tin-oxide (ITO) thin films deposited on polymer substrates under cyclic loading. We base this model on our earlier tensile test model and show

Transient hydrogen diffusion analyses coupled with crack-tip plasticity under cyclic loading

International Nuclear Information System (INIS)

Kotake, Hirokazu; Matsumoto, Ryosuke; Taketomi, Shinya; Miyazaki, Noriyuki

2008-01-01

The effect of hydrogen on the material strengths of metals is known as the hydrogen embrittlement, which affects the structural integrity of a hydrogen energy system. In the present paper, we developed a computer program for a transient hydrogen diffusion-elastoplastic coupling analysis by combining an in-house finite element program with a general purpose finite element computer program to analyze hydrogen diffusion. In this program, we use a hypothesis that the hydrogen absorbed in the metal affects the yield stress of the metal. In the present paper, we discuss the effects of the cyclic loading on the hydrogen concentration near the crack tip. An important finding we obtained here is the fact that the hydrogen concentration near the crack tip greatly depends on the loading frequency. This result indicates that the fatigue lives of the components in a hydrogen system depend not only on the number of loading cycles but also on the loading frequency

Acoustic Emission Characteristics of Red Sandstone Specimens Under Uniaxial Cyclic Loading and Unloading Compression

Science.gov (United States)

Meng, Qingbin; Zhang, Mingwei; Han, Lijun; Pu, Hai; Chen, Yanlong

2018-04-01

To explore the acoustic emission (AE) characteristics of rock materials during the deformation and failure process under periodic loads, a uniaxial cyclic loading and unloading compression experiment was conducted based on an MTS 815 rock mechanics test system and an AE21C acoustic emissions test system. The relationships among stress, strain, AE activity, accumulated AE activity and duration for 180 rock specimens under 36 loading and unloading rates were established. The cyclic AE evolutionary laws with rock stress-strain variation at loading and unloading stages were analyzed. The Kaiser and Felicity effects of rock AE activity were disclosed, and the impact of the significant increase in the scale of AE events on the Felicity effect was discussed. It was observed that the AE characteristics are closely related to the stress-strain properties of rock materials and that they are affected by the developmental state and degree of internal microcracks. AE events occur in either the loading or unloading stages if the strain is greater than zero. Evolutionary laws of AE activity agree with changes in rock strain. Strain deformation is accompanied by AE activity, and the density and intensity of AE events directly reflect the damage degree of the rock mass. The Kaiser effect exists in the linear elastic stage of rock material, and the Felicity effect is effective in the plastic yield and post-peak failure stages, which are divided by the elastic yield strength. This study suggests that the stress level needed to determine a significant increase in AE activity was 70% of the i + 1 peak stress. The Felicity ratio of rock specimens decreases with the growth of loading-unloading cycles. The cycle magnitude and variation of the Felicity effect, in which loading and unloading rates play a weak role, are almost consistent.

A boundary element analysis on the influence of Krc and e/d on the performance of cyclically loaded single pile in clay

Directory of Open Access Journals (Sweden)

S. Basack

Full Text Available The environment prevalent in oceans necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action. Such quasi-static load reversal induces deterioration in the strength and stiffness of the soil-pile system, introducing progressive reduction in the bearing capacity associated with increased settlement of the pile foundation. To understand the effect of lateral cyclic load on axial response of single piles in soft clay, a numerical model was previously developed and validated by the author. Using the methodology, further analysis has been carried out to investigate how the variation in relative pilesoil stiffness and eccentricity effects the degradation of axial pile capacity due to the effect of lateral cyclic load. This paper presents a brief description of the methodology, analysis and interpretations of the theoretical results obtained from the further analysis and the relevant conclusions drawn there from.

Evaluation of new composite rigid joint under cyclic loading and its effect on one-floor composite frame

Directory of Open Access Journals (Sweden)

Azadeh Haghighat

2017-08-01

Full Text Available In order to improve the performance of structure against lateral and gravity loads, new systems known as composite systems consisting of the reinforced concrete columns and steel beams (RCS can be used and thereby the advantages of concrete beside steel are acquired. RCS joints can be implemented as either through-beam-type joint or through-column-type joint. In this paper, a concrete joint as standard reference joint and a proposed composite joint through-column‎ with new details were built and tested under cyclic loading. Then, using numerical analysis by finite element method, the behavior of composite joint under cyclic loading has been studied and the behavior and performance of proposed composite joint has been studied by comparing the results with that of concrete joint. The results showed that the joint composition in this way resulted in decreasing of the compressive and tensile damages of concrete and increasing in loading capacity, ductility, stiffness and energy absorption. General results of application of composite joint at the one floor-one span composite frame indicating that lateral loading capacity of frame was increased and the performance of frame was improved.

Settling of abutments into implants and changes in removal torque in five different implant-abutment connections. Part 1: Cyclic loading.

Science.gov (United States)

Kim, Ki-Seong; Han, Jung-Suk; Lim, Young-Jun

2014-01-01

The aim of this study was to evaluate and compare the settling of abutments into implants and the removal torque values (RTVs) before and after cyclic loading. Five different implant-abutment connections were tested: Ext = external butt joint + two-piece abutment; Int-H2 = internal hexagon + two-piece abutment; Int-H1 = internal hexagon + one-piece abutment; Int-O2 = internal octagon + two-piece abutment; and Int-O1 = internal octagon + one-piece abutment. Ten abutments from each group were secured to their corresponding implants (total n = 50). All samples were tested in a universal testing machine with a vertical load of 250 N for 100,000 cycles of 14 Hz. The amount of settling of the abutment into the implant was calculated from the change in the total length of the implant-abutment sample before and after loading, as measured with an electronic digital micrometer. The RTV after cyclic loading was compared to the initial RTV with a digital torque gauge. Statistical analysis was performed at a 5% significance level. A multiple-comparison test showed specific significant differences in settling values in each group after 250 N cyclic loading (Int-H1, Ext abutment type and related to the design characteristics of the implant-abutment connection.

Effect of vibration loading on the fatigue life of part-through notched pipe

International Nuclear Information System (INIS)

Mittal, Rahul; Singh, P.K.; Pukazhendi, D.M.; Bhasin, V.; Vaze, K.K.; Ghosh, A.K.

2011-01-01

A systematic experimental and analytical study has been carried out to investigate the effect of vibration loading on the fatigue life of the piping components. Three Point bend (TPB) specimens machined from the actual pipe have been used for the evaluation of Paris constants by carrying out the experiments under vibration + cyclic and cyclic loading as per the ASTM Standard E647. These constants have been used for the prediction of the fatigue life of the pipe having part-through notch of a/t = 0.25 and aspect ratio (2c/a) of 10. Predicted results have shown the reduction in fatigue life of the notched pipe subjected to vibration + cyclic loading by 50% compared to that of cyclic loading. Predicted results have been validated by carrying out the full-scale pipe (with part-through notch) tests. Notched pipes were subjected to loading conditions such that the initial stress-intensity factor remains same as that of TPB specimen. Experimental results of the full-scale pipe tests under vibration + cyclic loading has shown the reduction in fatigue life by 70% compared to that of cyclic loading. Fractographic examination of the fracture surface of the tested specimens subjected to vibration + cyclic loading have shown higher presence of brittle phases such as martensite (in the form of isolated planar facets) and secondary micro cracks. This could be the reason for the reduction of fatigue life in pipe subjected to vibration + cyclic loading. - Highlights: → Vibration loading affects fatigue crack growth rate. → Crack initiation life depends on crack tip radius. → Crack initiation life depends on the characteristic distance. → Characteristic distance depends on the loading conditions. → Vibration + cyclic load gives lower fatigue life.

Effects of Cyclic Thermal Load on the Signal Characteristics of FBG Sensors Packaged with Epoxy Adhesives

Energy Technology Data Exchange (ETDEWEB)

Kim, Heonyoung; Kang, Donghoon [Korea Railroad Research Institute, Uiwang (Korea, Republic of)

2017-04-15

Fiber optics sensors that have been mainly applied to aerospace areas are now finding applicability in other areas, such as transportation, including railways. Among the sensors, the fiber Bragg grating (FBG) sensors have led to a steep increase due to their properties of absolute measurement and multiplexing capability. Generally, the FBG sensors adhere to structures and sensing modules using adhesives such as an epoxy. However, the measurement errors that occurred when the FBG sensors were used in a long-term application, where they were exposed to environmental thermal load, required calibration. For this reason, the thermal curing of adhesives needs to be investigated to enhance the reliability of the FBG sensor system. This can be done at room temperature through cyclic thermal load tests using four types of specimens. From the test results, it is confirmed that residual compressive strain occurs to the FBG sensors due to an initial cyclic thermal load. In conclusion, signals of the FBG sensors need to be stabilized for applying them to a long-term SHM.

Effect of cyclic loading on microleakage of silorane based composite compared with low shrinkage methacrylate-based composites

Directory of Open Access Journals (Sweden)

Hamid Kermanshah

2016-01-01

Conclusion: Silorane did not provide better marginal seal than the low shrinkage methacrylate-based composites (except Aelite. In addition, cyclic loading did not affect the marginal microleakage of evaluated composite restorations .

Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

Science.gov (United States)

Ren, Huai-Hui; Wang, Xi-Shu

2014-04-01

This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

Behavior of annealed type 316 stainless steel under monotonic and cyclic biaxial loading at room temperature

International Nuclear Information System (INIS)

Ellis, J.R.; Robinson, D.N.; Pugh, C.E.

1978-01-01

This paper addresses the elastic-plastic behavior of type 316 stainless steel, one of the major structural alloys used in liquid-metal fast breeder reactor components. The study was part of a continuing program to develop a structural design technology applicable to advanced reactor systems. Here, behaviour of solution annealed material was examined through biaxial stress experiments conducted at room temperature under radial loadings (√3tau=sigma) in tension-torsion stress space. The effects of both stress limited monotonic loading and strain limited cyclic loading were determined on the size, shape and position of yield loci corresponding to small offset strain (10 microstrain) definition of yield. In the present work, the aim was to determine the extent to which the constitutive laws previously recommended for type 304 stainless steel are applicable to type 316 stainless steel. It was concluded that for the conditions investigated, the inelastic behavior of the two materials are qualitatively similar. Specifically, the von Mises yield criterion provides a reasonable approximation of initial yield behavior and the subsequent hardening behavior, at least under small offset definitions of yield, is to the first order kinematic in nature. (Auth.)

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

Science.gov (United States)

Skorobogatykh, V. N.; Kunavin, S. A.; Prudnikov, D. A.; Shchenkova, I. A.; Bazhenov, A. M.; Zadoinyi, V. A.; Starkovskii, G. L.

2018-02-01

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up-cooling down, opening-closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 103 cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.

Effect of Degeneration on Fluid-Solid Interaction within Intervertebral Disk Under Cyclic Loading - A Meta-Model Analysis of Finite Element Simulations.

Science.gov (United States)

Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

2015-01-01

The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid-fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid-solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid-fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk.

Local cyclic deformation behavior and microstructure of railway wheel materials

International Nuclear Information System (INIS)

Walther, F.; Eifler, D.

2004-01-01

The current investigations concentrate on the relation between the loading and environmental conditions, the local microstructure and the fatigue behavior of highly stressed railway wheel and tire steels. Experiments under stress control and total strain control were performed at ambient temperature with servohydraulic testing systems. Superimposed mean loadings allow an evaluation of cyclic creep and mean stress relaxation effects. Strain, temperature and electrical measuring techniques were used to characterize the cyclic deformation behavior of specimens from different depth positions of the cross-sections of UIC-specified wheel components (UIC: International Railway Union). The measured values show a strong interrelation. The microstructural characterization of the different material conditions was done by light and scanning electron microscopy together with digital image processing

Probabilistic analysis of flaw distribution on structure under cyclic load

International Nuclear Information System (INIS)

Kwak, Sang Log; Choi, Young Hwan; Kim, Hho Jung

2003-01-01

Flaw geometries, applied stress, and material properties are major input variables for the fracture mechanics analysis. Probabilistic approach can be applied for the consideration of uncertainties within these input variables. But probabilistic analysis requires many assumptions due to the lack of initial flaw distributions data. In this study correlations are examined between initial flaw distributions and in-service flaw distributions on structures under cyclic load. For the analysis, LEFM theories and Monte Carlo simulation are applied. Result shows that in-service flaw distributions are determined by initial flaw distributions rather than fatigue crack growth rate. So initial flaw distribution can be derived from in-service flaw distributions

Influence of Hold Time and Stress Ratio on Cyclic Creep Properties Under Controlled Tension Loading Cycles of Grade 91 Steel

International Nuclear Information System (INIS)

Kim, Woo Gon; Park, Jae Young; Jang, Jin Sung; Ekaputra, I Made Wicaksana; Kim, Seon Jin

2017-01-01

Influences of hold time and stress ratio on cyclic creep properties of Grade 91 steel were systemically investigated using a wide range of cyclic creep tests, which were performed with hold times (HTs) of 1 minute, 3 minutes, 5 minutes, 10 minutes, 20 minutes, and 30 minutes and stress ratios (R) of 0.5, 0.8, 0.85, 0.90, and 0.95 under tension loading cycles at 600°C. Under the influence of HT, the rupture time increased to HT = 5 minutes at R = 0.90 and R = 0.95, but there was no influence at R = 0.50, 0.80, and 0.85. The creep rate was constant regardless of an increase in the HT, except for the case of HT = 5 minutes at R = 0.90 and R = 0.95. Under the influence of stress ratio, the rupture time increased with an increase in the stress ratio, but the creep rate decreased. The cyclic creep led to a reduction in the rupture time and an acceleration in the creep rate compared with the case of monotonic creep. Cyclic creep was found to depend dominantly on the stress ratio rather than on the HT. Fracture surfaces displayed transgranular fractures resulting from microvoid coalescence, and the amount of microvoids increased with an increase in the stress ratio. Enhanced coarsening of the precipitates in the cyclic creep test specimens was found under all conditions

Experiment on Behavior of a New Connector Used in Bamboo (Timber Frame Structure under Cyclic Loading

Directory of Open Access Journals (Sweden)

Junwen Zhou

2018-01-01

Full Text Available Connection is an important part of the bamboo and timber structure, and it directly influences the overall structural performance and safety. Based on a comprehensive analysis of the mechanical performance of several wood connections, a new connector for the bamboo (timber frame joint was proposed in this paper. Three full-scale T-type joint specimens were designed to study the mechanical performance under cyclic loading. The thickness of the hollow steel column was different among three specimens. The specimens were loaded under displacement control with a rate of 10 mm per minute until the specimens reach failure. It was observed that the failures of three specimens were caused by the buckling of flanges in the compression and that the steel of connections does not yield. The load-displacement hysteretic curve for three specimens is relatively plump, and the stiffness of connection degenerates with the increasing of cyclic load. The maximum rotation is 0.049 rad, and the energy dissipation coefficient is 1.77. The thickness of the hollow steel column of the connector has significant impact on the energy dissipation capacity and the strength of the connection. A simplified moment-rotation hysteresis model for the joint was proposed.

Reliability prediction for structures under cyclic loads and recurring inspections

Directory of Open Access Journals (Sweden)

Alberto W. S. Mello Jr

2009-06-01

Full Text Available This work presents a methodology for determining the reliability of fracture control plans for structures subjected to cyclic loads. It considers the variability of the parameters involved in the problem, such as initial flaw and crack growth curve. The probability of detection (POD curve of the field non-destructive inspection method and the condition/environment are used as important factors for structural confidence. According to classical damage tolerance analysis (DTA, inspection intervals are based on detectable crack size and crack growth rate. However, all variables have uncertainties, which makes the final result totally stochastic. The material properties, flight loads, engineering tools and even the reliability of inspection methods are subject to uncertainties which can affect significantly the final maintenance schedule. The present methodology incorporates all the uncertainties in a simulation process, such as Monte Carlo, and establishes a relationship between the reliability of the overall maintenance program and the proposed inspection interval, forming a “cascade” chart. Due to the scatter, it also defines the confidence level of the “acceptable” risk. As an example, the damage tolerance analysis (DTA results are presented for the upper cockpit longeron splice bolt of the BAF upgraded F-5EM. In this case, two possibilities of inspection intervals were found: one that can be characterized as remote risk, with a probability of failure (integrity nonsuccess of 1 in 10 million, per flight hour; and other as extremely improbable, with a probability of nonsuccess of 1 in 1 billion, per flight hour, according to aviation standards. These two results are compared with the classical military airplane damage tolerance requirements.

Experimental primers containing synthetic and natural compounds reduce enzymatic activity at the dentin–adhesive interface under cyclic loading

Science.gov (United States)

Sousa, Ana Beatriz Silva; de Mattos Pimenta Vidal, Cristina; Leme-Kraus, Ariene Arcas; de Carvalho Panzeri Pires-de-Souza, Fernanda; Bedran-Russo, Ana K.

2016-01-01

Objective To evaluate the effect of experimental primers (chlorhexidine, enriched mixture of proanthocyanidins and doxycycline) on the adhesive properties and gelatinolytic activity at dentin-resin interfaces of occlusal Class I restorations. Methods The inactivation of enzymes by the experimental primers was assessed by fluorescence assay and gelatin zymography. To assess the adhesive properties, occlusal Class I cavities were prepared in sound human molars, etched with phosphoric acid and restored with one of the primers and an etch-and-rinse adhesive system (Adper Single Bond Plus - 3M ESPE). After the restorative procedures, the specimens were divided into two subgroups (n = 6) consisting of storage in incubation buffer or axial cyclic loading at 50 N and 1,000,000 cycles. Then, the sectioned and sliced specimens were assigned to in situ zymography assay and microtensile bond strength (TBS) test. Results Fluorescence assay and gelatin zymography revealed that the experimental primers inactivated rMMPs. In situ zymography (2-way ANOVA, Tukey, p 0.05). Significance The use of experimental primers impaired the enzymatic activity at the dentin-adhesive interface after cyclic loading and the activity of rMMPs. Cyclic loading did not have a significant effect on the bond strength. PMID:27524231

Fatigue life and cyclic deformation behaviour of quenched and tempered steel AISI 4140 at two-step stress- and total-strain-controlled push-pull loading

Energy Technology Data Exchange (ETDEWEB)

Schulze, V.; Lang, K.H.; Macherauch, E. [Inst. fuer Werkstoffkunde I, Univ. Karlsruhe (Germany)

2003-05-01

The behaviour of steels at multi-step cyclic loading was explored up to now almost exclusively in fatigue-life-oriented investigations. Thus, only few works exist dealing with the cyclic deformation behaviour at two- and multi-step loading. Therefore, the cyclic deformation behaviour at two-step experiments with a single amplitude change (2-block experiments) and with multiple changes between two blocks of certain length and different amplitudes (multi-block experiments) was investigated in this work at the technically important steel AISI 4140 (German grade 42CrMo4). (orig.)

Simulation of reinforced concrete short shear wall subjected to cyclic loading

International Nuclear Information System (INIS)

Parulekar, Y.M.; Reddy, G.R.; Vaze, K.K.; Pegon, P.; Wenzel, H.

2014-01-01

Highlights: • Prediction of the capacity of squat shear wall using tests and analysis. • Modification of model of concrete in the softening part. • Pushover analysis using softened truss theory and FE analysis is performed. • Modified concrete model gives reasonable accurate peak load and displacement. • The ductility, ultimate load and also crack pattern can be accurately predicted. - Abstract: This paper addresses the strength and deformation capacity of stiff squat shear wall subjected to monotonic and pseudo-static cyclic loading using experiments and analysis. Reinforced concrete squat shear walls offer great potential for lateral load resistance and the failure mode of these shear walls is brittle shear mode. Shear strength of these shear walls depend strongly on softening of concrete struts in principal compression direction due to principal tension in other direction. In this work simulation of the behavior of a squat shear wall is accurately predicted by finite element modeling by incorporating the appropriate softening model in the program. Modification of model of concrete in the softening part is suggested and reduction factor given by Vecchio et al. (1994) is used in the model. The accuracy of modeling is confirmed by comparing the simulated response with experimental one. The crack pattern generated from the 3D model is compared with that obtained from experiments. The load deflection for monotonic loads is also obtained using softened truss theory and compared with experimental one

Finite element analysis of beam-to-column joints in steel frames under cyclic loading

Directory of Open Access Journals (Sweden)

Elsayed Mashaly

2011-03-01

Full Text Available The aim of this paper is to present a simple and accurate three-dimensional (3D finite element model (FE capable of predicting the actual behavior of beam-to-column joints in steel frames subjected to lateral loads. The software package ANSYS is used to model the joint. The bolted extended-end-plate connection was chosen as an important type of beam–column joints. The extended-end-plate connection is chosen for its complexity in the analysis and behavior due to the number of connection components and their inheritable non-linear behavior. Two experimental tests in the literature were chosen to verify the finite element model. The results of both the experimental and the proposed finite element were compared. One of these tests was monotonically loaded, whereas the second was cyclically loaded. The finite element model is improved to enhance the defects of the finite element model used. These defects are; the long time need for the analysis and the inability of the contact element type to follow the behavior of moment–rotation curve under cyclic loading. As a contact element, the surface-to-surface element is used instead of node-to-node element to enhance the model. The FE results show good correlation with the experimental one. An attempt to improve a new technique for modeling bolts is conducted. The results show that this technique is supposed to avoid the defects above, give much less elements number and less solution time than the other modeling techniques.

Correlation of Mission Type to Cyclic Loading as a Basis for Agile Military Aircraft Asset Management

NARCIS (Netherlands)

Newcamp, Jeffrey; Verhagen, W.J.C.; Curran, R.

2016-01-01

Military attack aircraft are susceptible to the harmful effects of widespread fatigue damage caused by cyclic loading of structural components, which leads to airframe retirement. Modern structural health monitoring techniques use a multitude of sensors and high data collection rates. Some legacy

Cyclic plasticity models and application in fatigue analysis

Science.gov (United States)

Kalev, I.

1981-01-01

An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.

Steel-reinforced concrete-filled steel tubular columns under axial and lateral cyclic loading

Science.gov (United States)

Farajpourbonab, Ebrahim; Kute, Sunil Y.; Inamdar, Vilas M.

2018-03-01

SRCFT columns are formed by inserting a steel section into a concrete-filled steel tube. These types of columns are named steel-reinforced concrete-filled steel tubular (SRCFT) columns. The current study aims at investigating the various types of reinforcing steel section to improve the strength and hysteresis behavior of SRCFT columns under axial and lateral cyclic loading. To attain this objective, a numerical study has been conducted on a series of composite columns. First, FEM procedure has been verified by the use of available experimental studies. Next, eight composite columns having different types of cross sections were analyzed. For comparison purpose, the base model was a CFT column used as a benchmark specimen. Nevertheless, the other specimens were SRCFT types. The results indicate that reinforcement of a CFT column through this method leads to enhancement in load-carrying capacity, enhancement in lateral drift ratio, ductility, preventing of local buckling in steel shell, and enhancement in energy absorption capacity. Under cyclic displacement history, it was observed that the use of cross-shaped reinforcing steel section causes a higher level of energy dissipation and the moment of inertia of the reinforcing steel sections was found to be the most significant parameter affecting the hysteresis behavior of SRCFT columns.

Fracture mode during cyclic loading of implant-supported single-tooth restorations

DEFF Research Database (Denmark)

Hosseini, Mandana; Kleven, Erik; Gotfredsen, Klaus

2012-01-01

restorations of zirconia abutment-retained crowns with zirconia copings veneered with glass-ceramics (n=8) and feldspathic ceramics (n=8). The control group was composed of 16 metal ceramic restorations of titanium abutment-retained crowns with gold alloy copings veneered with glass (n=8) and feldspathic...... ceramics (n=8). The palatal surfaces of the crowns were exposed to cyclic loading of 800 N with a frequency of 2 Hz, which continued to 4.2 million cycles or until fracture of the copings, abutments, or implants. The number of cycles and the fracture modes were recorded. The fracture modes were analyzed...

Effect of Degeneration on Fluid–Solid Interaction within Intervertebral Disk Under Cyclic Loading – A Meta-Model Analysis of Finite Element Simulations

Science.gov (United States)

Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

2015-01-01

The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid–fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid–solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid–fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk. PMID:25674562

Ratcheting of pressurized piping subjected to seismic loading

International Nuclear Information System (INIS)

Scavuzzo, R.J.; Lam, P.C.; Gau, J.S.

1992-01-01

The ABAQUS finite element code was used to model a pressurized pipe and subjected to cyclic bending loads to investigate ratcheting. A 1-in. schedule 40 pipe was loaded with a slow (static) cyclic load. The pipe internal pressure was varied from 0 to 6000 psi. In this paper, two types of materials were considered: an elastic perfectly plastic and a bilinear elastic-plastic material. Two types of finite elements of the ABAQUS program were compared to analytical solutions to evaluate the element accuracy in the plastic regime. Depending upon loading conditions and specified material properties, three different responses were observed from the finite element analyses: cyclic plasticity, ratcheting of the hoop strain, or shakedown. These analytical results are compared to some experimental measurements

Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading.

Science.gov (United States)

Yan, Zhifeng; Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

2018-03-28

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material's fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11-20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11-20} tensile twins.

Evaluating the damage of steel 09G2S under static and cyclic loading with regard for the level of residual stresses in the metal

Science.gov (United States)

Kuznetsov, A. V.; Kamantsev, I. S.; Zadvorkin, S. M.; Drukarenko, N. A.; Goruleva, L. S.; Veselova, V. E.

2017-12-01

An approach to the estimation of the residual durability of structural elements in view of their initial stress-strain state is proposed. The adequacy of the developed approach is confirmed by experiments on cyclic loading of specimens without pronounced stress concentrators simulating the work of real structural elements under conditions of overshooting the total stresses causing local plastic deformation of the material, with regard for residual stresses.

The behavior of welded joint in steel pipe members under monotonic and cyclic loading

International Nuclear Information System (INIS)

Chang, Kyong-Ho; Jang, Gab-Chul; Shin, Young-Eui; Han, Jung-Guen; Kim, Jong-Min

2006-01-01

Most steel pipe members are joined by welding. The residual stress and weld metal in a welded joint have the influence on the behavior of steel pipes. Therefore, to accurately predict the behavior of steel pipes with a welded joint, the influence of welding residual stress and weld metal on the behavior of steel pipe must be investigated. In this paper, the residual stress of steel pipes with a welded joint was investigated by using a three-dimensional non-steady heat conduction analysis and a three-dimensional thermal elastic-plastic analysis. Based on the results of monotonic and cyclic loading tests, a hysteresis model for weld metal was formulated. The hysteresis model was proposed by the authors and applied to a three-dimensional finite elements analysis. To investigate the influence of a welded joint in steel pipes under monotonic and cyclic loading, three-dimensional finite elements analysis considering the proposed model and residual stress was carried out. The influence of a welded joint on the behavior of steel pipe members was investigated by comparing the analytical result both steel pipe with a welded joint and that without a welded joint

Monitoring of Failure Mechanisms in a Composite Bending Actuator during Cyclic Loading by Acoustic Emission

Science.gov (United States)

Woo, Sung-Choong; Goo, Nam Seo

The objective of this work is to investigate the influence of electromechanical cyclic loading on the performance of a bending piezoelectric composite actuator. We have analyzed the fatigue damage mechanisms in terms of the behavior of the AE event rate. It was found that whether the actuators are subjected to purely electric loading or electromechanical loading, the initial fatigue damage of the bending piezoelectric composite actuator was caused by the transgranular fracture in the PZT ceramic layer; the final failure was caused only in the case of PCAWB under electromechanical loading by a local discharge, which critically affected the performance reduction of the actuators. As the number of cycles increased, a large reduction in displacement performance coincided with a high AE event rate, which was identified via microscopic observations.

Study on Performance of Steel Fiber Concrete Bridge Pier Specimens under Horizontal Cyclic Loading

Directory of Open Access Journals (Sweden)

Baiben Chen

2017-01-01

Full Text Available Because of that steel fiber can effectively prevent the extension and development of small cracks in the concrete, steel fiber reinforced concrete has good toughness and tensile strength. In the application of building materials, steel fiber reinforced concrete is an ideal elastic-plastic material. For the seismic performance, it has advantages. In order to analyze the seismic performance of steel fiber reinforced concrete, 4 piers of the scale model test under horizontal cyclic loading were done. The results showed that failure mode of steel fiber reinforced concrete is better than that of ordinary concrete, and has a large yield moment under the external loads.

Kenaf Fibre Reinforced Polypropylene Composites: Effect of Cyclic Immersion on Tensile Properties

Directory of Open Access Journals (Sweden)

W. H. Haniffah

2015-01-01

Full Text Available This research studied the degradation of tensile properties of kenaf fibre reinforced polypropylene composites due to cyclic immersion into two different solutions, as well as comparison of the developed composites’ tensile properties under continuous and cyclic immersion. Composites with 40% and 60% fibre loadings were immersed in tap water and bleach for 4 cycles. Each cycle consisted of 3 days of immersion and 4 days of conditioning in room temperature (28°C and 55% humidity. The tensile strength and modulus of composites were affected by fibre composition, type of liquid of immersion, and number of cycles. The number of immersion cycles and conditioning caused degradation to tensile strength and modulus of kenaf fibre reinforced polypropylene composites. Continuous and cyclic immersion in bleach caused tensile strength of the composites to differ significantly whereas, for tensile modulus, the difference was insignificant in any immersion and fibre loadings. However, continuous immersion in the bleach reduced the tensile strength of composites more compared to cyclic immersion. These preliminary results suggest further evaluation of the suitability of kenaf fibre reinforced polypropylene composites for potential bathroom application where the composites will be exposed to water/liquid in cyclic manner due to discontinuous usage of bathroom.

Abutments with reduced diameter for both cement and screw retentions: analysis of failure modes and misfit of abutment-crown-connections after cyclic loading.

Science.gov (United States)

Moris, Izabela Cristina Maurício; Faria, Adriana Cláudia Lapria; Ribeiro, Ricardo Faria; Rodrigues, Renata Cristina Silveira

2017-04-01

The aim of this study was to analyze failure modes and misfit of abutments with reduced diameter for both cement and screw retentions after cyclic loading. Forty morse-taper abutment/implant sets of titanium were divided into four groups (N = 10): G4.8S-4.8 abutment with screw-retained crown; G4.8C-4.8 abutment with cemented crown; G3.8S-3.8 abutment with screw-retained crown; and G3.8C-3.8 abutment with cemented crown. Copings were waxed on castable cylinders and cast by oxygen gas flame and injected by centrifugation. After, esthetic veneering ceramic was pressed on these copings for obtaining metalloceramic crowns of upper canine. Cemented crowns were cemented on abutments with provisional cement (Temp Bond NE), and screw-retained crowns were tightened to their abutments with torque recommended by manufacturer (10 N cm). The misfit was measured using a stereomicroscope in a 10× magnification before and after cyclic loading (300,000 cycles). Tests were visually monitored, and failures (decementation, screw loosening and fractures) were registered. Misfit was analyzed by mixed linear model while failure modes by chi-square test (α = 0.05). Cyclic loading affected misfit of 3.8C (P ≤ 0.0001), 3.8S (P = 0.0055) and 4.8C (P = 0.0318), but not of 4.8S (P = 0.1243). No differences were noted between 3.8S with 4.8S before (P = 0.1550) and after (P = 0.9861) cyclic loading, but 3.8C was different from 4.8C only after (P = 0.0015) loading. Comparing different types of retentions at the same diameter abutment, significant difference was noted before and after cyclic loading for 3.8 and 4.8 abutments. Analyzing failure modes, retrievable failures were present at 3.8S and 3.8C groups, while irretrievable were only present at 3.8S. The cyclic loading decreased misfit of cemented and screw-retained crowns on reduced diameter abutments, and misfit of cemented crowns is greater than screw-retained ones. Abutments of reduced diameter failed more than

In-Plane Anisotropy in Mechanical Behavior and Microstructural Evolution of Commercially Pure Titanium in Tensile and Cyclic Loading

Science.gov (United States)

Sinha, Subhasis; Gurao, N. P.

2017-12-01

Tensile and cyclic deformation behavior of three samples oriented at 0, 45, and 90 deg to the rolling direction in the rolling direction-transverse direction (RD-TD) plane of cold-rolled and annealed plate of commercially pure titanium is studied in the present investigation. The sample along the RD (R0) shows the highest strength but lowest ductility in monotonic tension. Although ultimate tensile strength (UTS) and elongation of samples along 45 and 90 deg to the RD (R45 and R90, respectively) are similar, the former has significantly higher yield strength than the latter, indicating different strain-hardening behavior. It is found that the R90 sample exhibits the highest monotonic ductility as well as fatigue life. This is attributed to a higher propensity for twinning in this sample with the presence of multiple variants and twin intersections. Cyclic life is also influenced by the high tendency for detwinning of contraction twins in this orientation. Elastoplastic self-consistent (EPSC) simulations of one-cycle tension-compression load reversal indicate that the activity of pyramidal 〈 c + a〉 slip and extension twinning oscillates during cyclic loading that builds up damage in a cumulative manner, leading to failure in fatigue.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants.

Science.gov (United States)

Mohammed, Hnd Hadi; Lee, Jin-Han; Bae, Ji-Myung; Cho, Hye-Won

2016-02-01

The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Structural analysis of reinforced concrete structures under monotonous and cyclic loadings: numerical aspects

International Nuclear Information System (INIS)

Lepretre, C.; Millard, A.; Nahas, G.

1989-01-01

The structural analysis of reinforced concrete structures is usually performed either by means of simplified methods of strength of materials type i.e. global methods, or by means of detailed methods of continuum mechanics type, i.e. local methods. For this second type, some constitutive models are available for concrete and rebars in a certain number of finite element systems. These models are often validated on simple homogeneous tests. Therefore, it is important to appraise the validity of the results when applying them to the analysis of a reinforced concrete structure, in order to be able to make correct predictions of the actual behaviour, under normal and faulty conditions. For this purpose, some tests have been performed at I.N.S.A. de Lyon on reinforced concrete beams, subjected to monotonous and cyclic loadings, in order to generate reference solutions to be compared with the numerical predictions given by two finite element systems: - CASTEM, developed by C.E.A./.D.E.M.T. - ELEFINI, developed by I.N.S.A. de Lyon

Effect of cyclic load on vertical misfit of prefabricated and cast implant single abutment

OpenAIRE

de Jesus Tavarez, Rudys Rodolfo; Bonachela, Wellington Cardoso; Xible, Anuar Antônio

2011-01-01

OBJECTIVES: The purpose of this in vitro study was to evaluate misfit alterations at the implant/abutment interface of external and internal connection implant systems when subjected to cyclic loading. MATERIAL AND METHODS: Standard metal crowns were fabricated for 5 groups (n=10) of implant/abutment assemblies: Group 1, external hexagon implant and UCLA cast-on premachined abutment; Group 2, internal hexagon implant and premachined abutment; Group 3, internal octagon implant and prefabricate...

Experimental Comparison of Statically and Cyclically Loaded Non-Slender Piles in Sand

DEFF Research Database (Denmark)

Sørensen, Søren Peder Hyldal; Ibsen, Lars Bo

rigid form of motion. The Winkler model approach, employing p-y curves to describe the soil-pile interaction, is often employed as the design method for laterally loaded piles. The p-y curve formulation, currently recommended by the American Petroleum Institute and Det Norske Veritas, is based on tests...... on slender piles with length to diameter ratios larger than ten and outer pile diameters less than two meters. Hence, the pile tests that form the basis of the currently recommended p-y curve formulation are conducted with use of piles that exhibits a flexible behaviour, which is in contrast to the piles...... used as foundation for modern offshore wind energy converters. The aim of the present work is to investigate the pile behaviour for non-slender piles by means of small-scale testing. The pile behaviour is investigated and compared for both static and cyclic loading. When conducting small-scale tests...

Cyclic plasticity of an austenitic-ferritic stainless steel under biaxial non proportional loading; Plasticite cyclique d'un acier inoxydable austeno-ferritique sous chargement biaxial non-proportionnel

Energy Technology Data Exchange (ETDEWEB)

Aubin, V

2001-11-15

Austenitic-ferritic stainless steels are supplied since about 30 years only, so they are yet not well-known. Their behaviour in cyclic plasticity was studied under uniaxial loading but not under multiaxial loading, whereas only a thorough knowledge of the phenomena influencing the mechanical behaviour of a material enables to simulate and predict accurately its behaviour in a structure. This work aims to study and model the behaviour of a duplex stainless steel under cyclic biaxial loading. A three step method was adopted. A set of tension-torsion tests on tubular specimen was first defined. We studied the equivalence between loading directions, and then the influence of loading path and loading history on the stress response of the material. Results showed that duplex stainless steel shows an extra-hardening under non proportional loading and that its behaviour depends on previous loading. Then, in order to analyse the results obtained during this first experimental stage, the yield surface was measured at different times during cyclic loading of the same kind. A very small plastic strain offset (2*10{sup -5}) was used in order not to disturb the yield surface measured. The alteration of isotropic and kinematic hardening variables were deduced from these measures. Finally, three phenomenological constitutive laws were identified with the experimental set. We focused our interest on the simulation of stabilized stress levels and on the simulation of the cyclic hardening/softening behaviour. The comparison between experimental and numerical results enabled the testing of the relevance of these models. (authors)

Tendon Contraction After Cyclic Elongation Is an Age-Dependent Phenomenon: In Vitro and In Vivo Comparisons.

Science.gov (United States)

Lavagnino, Michael; Bedi, Asheesh; Walsh, Christopher P; Sibilsky Enselman, Elizabeth R; Sheibani-Rad, Shahin; Arnoczky, Steven P

2014-06-01

Tendons are viscoelastic tissues that deform (elongate) in response to cyclic loading. However, the ability of a tendon to recover this elongation is unknown. Tendon length significantly increases after in vivo or in vitro cyclic loading, and the ability to return to its original length through a cell-mediated contraction mechanism is an age-dependent phenomenon. Controlled laboratory study. In vitro, rat tail tendon fascicles (RTTfs) from Sprague-Dawley rats of 3 age groups (1, 3, and 12 months) underwent 2% cyclic strain at 0.17 Hz for 2 hours, and the percentages of elongation were determined. After loading, the RTTfs were suspended for 3 days under tissue culture conditions and photographed daily to determine the amount of length contraction. In vivo, healthy male participants (n = 29; age, 19-49 years) had lateral, single-legged weightbearing radiographs taken of the knee at 60° of flexion immediately before, immediately after, and 24 hours after completing eccentric quadriceps loading exercises on the dominant leg to fatigue. Measurements of patellar tendon length were taken from the radiographs, and the percentages of tendon elongation and subsequent contraction were calculated. In vitro, cyclic loading increased the length of all RTTfs, with specimens from younger (1 and 3 months) rats demonstrating significantly greater elongation than those from older (12 months) rats (P = .009). The RTTfs contracted to their original length significantly faster (P fashion, with younger animals contracting faster. In vivo, repetitive eccentric loading exercises significantly increased patellar tendon length (P 30 years). Cyclic tendon loading results in a significant increase in tendon elongation under both in vitro and in vivo conditions. Tendons in both conditions demonstrated an incomplete return to their original length after 24 hours, and the extent of this return was age dependent. The age- and time-dependent contraction of tendons, elongated after repetitive

Evaluation of combined hardening parameters for type 304LN stainless steel under strain-controlled cyclic loading

International Nuclear Information System (INIS)

Kumar, Abhishek; Vishnuvardhan, S.; Raghava, G.

2016-01-01

Low cycle fatigue (LCF) is the primary degradation mechanism affecting coolant piping of pressurized water reactor (PWR) caused by combination of pressure and transient mechanical or thermal loads. In the case of LCF, stresses are high enough for plastic deformation to occur and the fatigue life is correlated with the cyclic plastic strain. Modelling cyclic plastic deformation of a material requires hardening parameters, which have to be obtained from LCF test results. It is customary in low cycle fatigue tests that the strain ranges are kept constant and the stresses are allowed to vary which typically leads to a hysteresis loop that consists of linear and nonlinear parts. In this paper, numerical studies on mechanical behaviour of Type 304LN stainless steel under fully reversed strain-controlled cyclic loading have been carried out. A linear combination of the two hardening types, isotropic and kinematic, governed by a scalar parameter, β (0 ≤β ≤ 1) is used. A value of β=1 indicates a pure isotropic hardening while a value of β=0 indicates pure kinematic hardening. The details of the combined isotropic-kinematic hardening model are also presented. Constitutive relations for the classical von Mises theory along with a bilinear hardening theory have been used. The model is implemented in finite element software ABAQUS using a user subroutine written in FORTRAN, UMAT. An iterative method is adopted to arrive at the model's hardening parameters and the value of β. (author)

Squeeze-Film Lubrication of the Human Ankle Joint Subjected to the Cyclic Loading Encountered in Walking

Czech Academy of Sciences Publication Activity Database

Hlaváček, Miroslav

2005-01-01

Roč. 127, č. 1 (2005), s. 141-147 ISSN 0742-4787 R&D Projects: GA ČR(CZ) GA103/04/0150 Institutional research plan: CEZ:AV0Z20710524 Keywords : cyclic loading * human ankle joint * squeeze-film lubrication * synovial fluid filtration * synovial gel formation Subject RIV: JJ - Other Materials Impact factor: 0.682, year: 2005

Fatigue behaviour of the austenitic steel 1.4550 under mechanical and thermal cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Siegele, D.; Fingerhuth, J.; Varfolomeev, I.; Moroz, S. [Fraunhofer Institute for Mechanics of Materials (IWM), Freiburg (Germany)

2014-07-01

Fatigue behaviour of the austenitic steel 1.4550 (X6CrNiNb18-10) under low-cycle fatigue and high-cycle thermal fatigue was investigated with in two research projects supported by the Federal Ministry of Economic Affairs and Energy and the Ministry of Education and Research. The objectives of the projects were the gain of deep understanding of the damage mechanisms under mechanical and thermal cyclic loading and the development of material models and simulation procedures for an improved lifetime assessment. In comparison to the advanced mechanism based material models engineering computational procedures were proven with respect to their applicability and conservatisms. For thermal cyclic loading, test equipment and technique were developed which allow for cyclic thermal loading with temperature ranges between 1 00 C and 300 C and frequencies between 0.1 and 1 Hz. As a result, tests with a temperature range of 150 C and lower showed no crack formation up to 300,000 cycles. For temperature ranges of 200 C and higher multiple crack patterns were observed with the deepest crack of about 1.3 mm after 1,000,000 cycles, whereas the difference in crack depth between 300,000 and 1,000,000 cycles was negligibly small. To model the fatigue lifetime, the D{sub TMF} damage parameter was applied to the low-cycle fatigue and the thermal, high frequent fatigue tests. For thermal fatigue, the analyses predicted in agreement with the tests crack initiation followed by crack propagation, subsequent retardation and arrest. This behaviour can be explained qualitatively and quantitatively using the methods of linear-elastic fracture mechanics, whereas the consideration of the interaction of multiple cracks is essential to describe the experimentally observed crack retardation. The results for thermal fatigue are in the scatterband of the mechanical p and thermo-mechanical fatigue results and the cycles to failure are 10 times higher than those estimated according to the KTA fatigue

Fatigue crack growth behavior and tearing instability characteristics under cyclic high stress, 2

International Nuclear Information System (INIS)

Mogami, Kazunari; Yamakawa, Jun; Ando, Kotoji; Ogura, Nobukazu

1990-01-01

The J-R curve, fatigue crack growth rate and characteristics of ductile unstable fracture under monotonic and cyclic load were investigated using 1TCT test specimens which were cut out from A508 steel for reactor pressure vessels. All the tests were carried out at 100degc. The main results obtained were as follows. (1) The J-R curve under the cyclic load is not a material constant but is dependent on the test conditions. (2) da/dN from typical fatigue data cannot be extrapolated by ΔJ only if the value of da/dN is above 5x10 -4 mm/cycles. However, it can be extrapolated by using the following equation in which J max is used: da/dN=C{√(ΔJ)/(B-√J max )} m . (3) The J values at instability obtained from the ductile unstable fracture test carried out under the cyclic load of stress ratio R=0, 01 and -1.0 were compared with those from the monotonically increasing load. These J values at instability were almost the same as that for the monotonically increasing load. (author)

Elastic-plastic cyclic deformation of the TEXTOR 94 modified liner under conditions of heating and plasma disruption

International Nuclear Information System (INIS)

Bohn, F.H.; Czymek, G.; Giesen, B.; Bondarchuk, E.; Doinikov, N.; Kozhukhovskaja, N.; Panin, A.

2001-01-01

The present liner of the TEXTOR 94 tokamak installed inside the vacuum vessel represents the thin toroidal shell that is rested on the vessel inner surface. In order to integrate the dynamic ergodic divertor into the tokamak the liner design has been drastically changed. The 120 deg. sector of the liner shell facing the ergodic coils system is removed and some additional holes in the liner are provisioned. This demands a new liner supporting system allowing for the liner thermal expansion and taking the electromagnetic load occurring in the liner during plasma disruption. The cyclic elasto-plastic deformations of the liner caused by the electromagnetic forces and temperature rise have been studied. It is shown that the local plastic deformations occur in the liner elements after the first heating and electromagnetic loading. The most thermal stresses take place in the reinforcing structures around the holes because of the thermal expansion difference of the inconel shell and the steel reinforcements. These stresses are coupled with the bending stress due to the electromagnetic loading. Subsequent repetitive loading does not lead to any significant increment of the plastic deformation. After the materials' hardening the structure cyclically works mostly in the elastic range

Post-examination of helium-cooled tungsten components exposed to DEMO specific cyclic thermal loads

International Nuclear Information System (INIS)

Ritz, G.; Hirai, T.; Linke, J.; Norajitra, P.; Giniyatulin, R.; Singheiser, L.

2009-01-01

A concept of helium-cooled tungsten finger module was developed for the European DEMO divertor. The concept was realized and tested under DEMO specific cyclic thermal loads up to 10 MW/m 2 . The modules were examined carefully before and after loading by metallography and microstructural analyses. While before loading mainly discrete and shallow cracks were found on the tungsten surface due to the manufacturing process, dense crack networks were observed at the loaded surfaces due to the thermal stress. In addition, cracks occurred in the structural, heat sink part and propagated along the grains orientation of the deformed tungsten material. Facilitated by cracking, the molten brazing metal between the tungsten plasma facing material and the W-La 2 O 3 heat sink, that could not withstand the operational temperatures, infiltrated the tungsten components and, due to capillary forces, even reached the plasma facing surface through the cracks. The formed cavity in the brazed layer reduced the heat conduction and the modules were further damaged due to overheating during the applied heat loads. Based on this detailed characterization and possible improvements of the design and of the manufacturing routes are discussed.

High temperature fatigue behaviour of TZM molybdenum alloy under mechanical and thermomechanical cyclic loads

International Nuclear Information System (INIS)

Shi, H.J.; Niu, L.S.; Korn, C.; Pluvinage, G.

2000-01-01

High temperature isothermal mechanical fatigue and in-phase thermomechanical fatigue (TMF) tests in load control were carried out on a molybdenum-based alloy, one of the best known of the refractory alloys, TZM. The stress-strain response and the cyclic life of the material were measured during the tests. The fatigue lives obtained in the in-phase TMF tests are lower than those obtained in the isothermal mechanical tests at the same load amplitude. It appears that an additional damage is produced by the reaction of mechanical stress cycles and temperature cycles in TMF situation. Ratcheting phenomenon occurred during the tests with an increasing creep rate and it was dependent on temperature and load amplitude. A model of lifetime prediction, based on the Woehler-Miner law, was discussed. Damage coefficients that are functions of the maximum temperature and the variation of temperature are introduced in the model so as to evaluate TMF lives in load control. With this method the lifetime prediction gives results corresponding well to experimental data

Fatigue behaviour of core-spun yarns containing filament by means of cyclic dynamic loading

Science.gov (United States)

Esin, S.; Osman, B.

2017-10-01

The behaviour of yarns under dynamic loading is important that leads to understand the growth characteristics which is exposed to repetitive loadings during usage of fabric made from these yarns. Fabric growth is undesirable property that originated from low resilience characteristics of fabric. In this study, the effects of the filament fineness and yarn linear density on fatigue behaviour of rigid-core spun yarns were determined. Cotton covered yarns containing different filament fineness of polyester (PET) draw textured yarns (DTY) (100d/36f, 100d/96f, 100d/144f, 100d/192f and 100d/333f) and yarn linear densities (37 tex, 30 tex, 25 tex and 21 tex) were manufactured by using a modified ring spinning system at the same spinning parameters. Repetitive loads were applied for 25 cycles at levels between 0.1 and 3 N. Dynamic modulus and dynamic strain of yarn samples were analyzed statistically. Results showed that filament fineness and yarn linear density have significance effect on dynamic modulus and dynamic strain after cyclic loading.

Simplified Probabilistic Analysis of Settlement of Cyclically Loaded Soil Stratum by Point Estimate Method

Science.gov (United States)

Przewłócki, Jarosław; Górski, Jarosław; Świdziński, Waldemar

2016-12-01

The paper deals with the probabilistic analysis of the settlement of a non-cohesive soil layer subjected to cyclic loading. Originally, the settlement assessment is based on a deterministic compaction model, which requires integration of a set of differential equations. However, with the use of the Bessel functions, the settlement of a soil stratum can be calculated by a simplified algorithm. The compaction model parameters were determined for soil samples taken from subsoil near the Izmit Bay, Turkey. The computations were performed for various sets of random variables. The point estimate method was applied, and the results were verified by the Monte Carlo method. The outcome leads to a conclusion that can be useful in the prediction of soil settlement under seismic loading.

Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

Energy Technology Data Exchange (ETDEWEB)

Celine Cabet; L. Carroll; R. Wright; R. Madland

2011-05-01

Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

Experimental Studies on the Behavior of a Newly-Developed Type of Self-Insulating Concrete Masonry Shear Wall under in-Plane Cyclic Loading

Directory of Open Access Journals (Sweden)

Abu-Bakre Abdelmoneim Elamin Mohamad

2017-04-01

Full Text Available This study aimed to investigate the inelastic behavior of a newly-developed type of self-insulating concrete masonry shear wall (SCMSW under in-plane cyclic loading. The new masonry system was made from concrete blocks with special configurations to provide a stronger bond between units than ordinary concrete masonry units. A total of six fully-grouted SCMSWs were prepared with different heights (1.59 to 5.78 m and different vertical steel configurations. The developed masonry walls were tested under in-plane cyclic loading and different constant axial load ratios. In addition, the relationship between the amount of axial loading, the amount of the flexural reinforcement and the wall aspect ratios and the nonlinear hysteretic response of the SCMSW was evaluated. The results showed that the lateral load capacity of SCMSW increases with the amount of applied axial load and the amount of vertical reinforcement. However, the lateral load capacity decreases as the wall aspect ratio increases. The existence of the boundary elements at the SCMSW ends increases the ductility and the lateral load capacity. Generally, the SCMSW exhibited predominantly flexural behavior. These results agreed with those reported in previous research for walls constructed with ordinary units.

Simplified Theory of Plastic Zones for cyclic loading and multilinear hardening

International Nuclear Information System (INIS)

Hübel, Hartwig

2015-01-01

The Simplified Theory of Plastic Zones (STPZ) is a direct method based on Zarka's method, primarily developed to estimate post-shakedown quantities of structures under cyclic loading, avoiding incremental analyses through a load histogram. In a different paper the STPZ has previously been shown to provide excellent estimates of the elastic–plastic strain ranges in the state of plastic shakedown as required for fatigue analyses. In the present paper, it is described how the STPZ can be used to predict the strains accumulated through a number of loading cycles due to a ratcheting mechanism, until either elastic or plastic shakedown is achieved, so that strain limits can be satisfied. Thus, a consistent means of estimating both, strain ranges and accumulated strains is provided for structural integrity assessment as required by pressure vessel codes. The computational costs involved typically consist of few linear elastic analyses and some local calculations. Multilinear kinematic hardening and temperature dependent yield stresses are accounted for. The quality of the results and the computational burden involved are demonstrated through four examples. - Highlights: • A method is provided to estimate accumulated elastic–plastic strains. • A consistent method is provided to estimate elastic–plastic strain ranges. • Effect of multilinear kinematic hardening is captured. • Temperature dependent material properties are accounted for. • Few linear elastic analyses required

Effects of cyclic stretch on proliferation of mesenchymal stem cells and their differentiation to smooth muscle cells

International Nuclear Information System (INIS)

Ghazanfari, Samane; Tafazzoli-Shadpour, Mohammad; Shokrgozar, Mohammad Ali

2009-01-01

Bone marrow mesenchymal stem cells (MSCs) are capable of differentiating into a variety of cell types such as vascular smooth muscle cells (SMCs). In this study, we investigated influence of cyclic stretch on proliferation of hMSCs for different loading conditions, alignment of actin filaments, and consequent differentiation to SMCs. Isolated cells from bone marrow were exposed to cyclic stretch utilizing a customized device. Cell proliferation was examined by MTT assay, alignment of actin fibers by a designed image processing code, and cell differentiation by fluorescence staining. Results indicated promoted proliferation of hMSCs by cyclic strain, enhanced by elevated strain amplitude and number of cycles. Such loading regulated smooth muscle α-actin, and reoriented actin fibers. Cyclic stretch led to differentiation of hMSCs to SMCs without addition of growth factor. It was concluded that applying appropriate loading treatment on hMSCs could enhance proliferation capability, and produce functional SMCs for engineered tissues.

Quasi-static characterisation of trained pseudoelastic shape memory alloy wire subjected to cyclic loading: transformation kinetics

DEFF Research Database (Denmark)

Enemark, Søren; Santos, Ilmar

2016-01-01

A kinetic law for constitutive modelling of shape memory alloys is proposed in order to increase model predictability in comparison with experimental data. The proposed law is based on cubic Bézier curves and contains curvature controlling parameters. The kinetic law and also the Duhem–Madelung sub......-loop model are implemented in a state-of-the-art constitutive model based on the framework by Lagoudas and coworkers. The original and modified models are fitted to consistent experimental results from mechanical cyclic loading under isothermal conditions (0–800 MPa, 30–70 °C) of a trained pseudoelastic...... shape memory alloy wire. Quantitative measures of goodness of fit show that both models perform well, but use of the modified model results in 31% reduction of the residual standard deviation compared with the original model (21.4 versus 14.8 MPa) in model calibration and 23% in model validation...

Anti-cyclic regulation of the Ukrainian economy under current conditions of the international markets volatility

Directory of Open Access Journals (Sweden)

Volodymyr Satsyk

2009-04-01

Full Text Available In the article there are considered the theoretical and methodological basis of anti-cyclic regulation of the countries’ economy under conditions of the world economy globalization. It suggests the analysis of practices of implementing of anti-cyclic policy in highly developed states, its defining features and directions under current global financial and economic crisis. There has been researched a practical toolkit of economic cycles diagnostics and cyclic fluctuations of total business activity in Ukraine based on this study. There are suggested recommendations concerning the formation of the effective mechanism of anti-cyclic regulation of the Ukrainian economy.

Loading Conditions and Longitudinal Strength

DEFF Research Database (Denmark)

Sørensen, Herman

1995-01-01

Methods for the calculation of the lightweight of the ship.Loading conditions satisfying draught, trim and intact stability requirements and analysis of the corresponding stillwater longitudinal strength.......Methods for the calculation of the lightweight of the ship.Loading conditions satisfying draught, trim and intact stability requirements and analysis of the corresponding stillwater longitudinal strength....

Density of loose-fill insulation material exposed to cyclic humidity conditions

DEFF Research Database (Denmark)

Rasmussen, Torben Valdbjørn

the granulated loose-fill material is exposed to a climate that is characterised as cyclic humidity conditions (a constant temperature and a relative humidity alternating between two predetermined constant relative humidity levels). A better understanding of the behaviour of granulated loose-fill material...

Methodic aspects of autoclave tests of compact samples on cyclic crack resistance

International Nuclear Information System (INIS)

Pokhmurskij, V.I.; Gnyp, I.P.; Popov, A.A.; Tarasyuk, G.P.; Dutsyak, I.Z.; Timonin, V.M.

1984-01-01

Laboratory autoclave LAKIM-25 was created for investigation of cyclic and static crack resistance of vessel materials of power plants under the conditions close to operation ones. It enables to investigate the cyclic crack resistance of standard samples of up to 25 mm thickness in water at 623 K and 18 MPa. The friction force changes during tests from 6.1 up to 6.4 kN, therefore it is necessary to correct regularly the force of sample loading, recording the s-n diagram on a drum of UMEh-10TM plant. The periodic record of loading diagram coincides with respect to time with the necessity of controlling the change of sample pliability during crack propagation

Propagation of semi-elliptical surface cracks in ferritic and austenitic steel plates under thermal cyclic loading

International Nuclear Information System (INIS)

Bethge, K.

1989-05-01

Theoretical and experimental investigations of crack growth under thermal and thermomechanical fatigue loading are presented. The experiments were performed with a ferritic reactor pressure vessel steel 20 MnMoNi 5 5 and an austenitic stainless steel X6 CrNi 18 11. A plate containing a semi-elliptical surface crack is heated up to a homogeneous temperature and cyclically cooled down by a jet of cold water. On the basis of linear elastic fracture mechanics stress-intensity factors are calculated with the weight function method. The prediction of crack growth under thermal fatigue loading using data from mechanical fatigue tests is compared with the experimental result. (orig.) [de

Cyclic settlement behavior of strip footings resting on reinforced layered sand slope

Directory of Open Access Journals (Sweden)

Mostafa A. El Sawwaf

2012-10-01

Full Text Available The paper presents a study of the behavior of model strip footings supported on a loose sandy slope and subjected to both monotonic and cyclic loads. The effects of the partial replacement of a compacted sand layer and the inclusion of geosynthetic reinforcement were investigated. Different combinations of the initial monotonic loads and the amplitude of cyclic loads were chosen to simulate structures in which loads change cyclically such as machine foundations. The affecting factors including the location of footing relative to the slope crest, the frequency of the cyclic load and the number of load cycles were studied. The cumulative cyclic settlement of the model footing supported on a loose sandy slope, un-reinforced and reinforced replaced sand deposits overlying the loose slope were obtained and compared. Test results indicate that the inclusion of soil reinforcement in the replaced sand not only significantly increases the stability of the sandy slope itself but also decreases much both the monotonic and cumulative cyclic settlements leading to an economic design of the footings. However, the efficiency of the sand–geogrid systems depends on the properties of the cyclic load and the location of the footing relative to the slope crest. Based on the test results, the variation of cumulative settlements with different parameters is presented and discussed.

Multi-scale analysis of behavior and fatigue life of 304L stainless under cyclic loading with pre-hardening

International Nuclear Information System (INIS)

Belattar, A.

2013-01-01

This study investigates the effects of loading history on the cyclic stress-strain curve and fatigue behavior of 304L stainless steel at room temperature. Tension-compression tests were performed on the same specimen under controlled strain, using several loading sequences of increasing or decreasing amplitude. The results showed that fatigue life is significantly reduced by the previous loading history. A previously developed method for determining the effect of prehardening was evaluated. Microstructural analyses were also performed; the microstructures after pre-loading and their evolution during the fatigue cycles were characterized by TEM. The results of these analyses improve our understanding of the macroscopic properties of 304L stainless steel and can help us identify the causes of failure and lifetime reduction. (author)

Effect of Static and Cyclic Loading on Ceramic Laminate Veneers Adhered to Teeth with and Without Aged Composite Restorations

NARCIS (Netherlands)

Gresnigt, Marco M. M.; Ozcan, Mutlu; Kalk, Warner; Galhano, Graziela

2011-01-01

Purpose: Existing composite restorations on teeth are often remade prior to the cementation of fixed dental prostheses. The aim of this study was to evaluate the effect of static and cyclic loading on ceramic laminate veneers adhered to aged resin composite restorations. Materials and Methods:

Validation of a CFD code for Unsteady Flows with cyclic boundary Conditions

International Nuclear Information System (INIS)

Kim, Jong-Tae; Kim, Sang-Baik; Lee, Won-Jae

2006-01-01

Currently Lilac code is under development to analyze thermo-hydraulics of a high-temperature gas-cooled reactor (GCR). Interesting thermo-hydraulic phenomena in a nuclear reactor are usually unsteady and turbulent. The analysis of the unsteady flows by using a three dimension CFD code is time-consuming if the flow domain is very large. Hopefully, flow domains commonly encountered in the nuclear thermo-hydraulics is periodic. So it is better to use the geometrical characteristics in order to reduce the computational resources. To get the benefits from reducing the computation domains especially for the calculations of unsteady flows, the cyclic boundary conditions are implemented in the parallelized CFD code LILAC. In this study, the parallelized cyclic boundary conditions are validated by solving unsteady laminar and turbulent flows past a circular cylinder

On the evolution and modelling of lattice strains during the cyclic loading of TWIP steel

International Nuclear Information System (INIS)

Saleh, Ahmed A.; Pereloma, Elena V.; Clausen, Bjørn; Brown, Donald W.; Tomé, Carlos N.; Gazder, Azdiar A.

2013-01-01

The evolution of lattice strains in fully annealed Fe–24Mn–3Al–2Si–1Ni–0.06C twinning-induced plasticity (TWIP) steel is investigated via in situ neutron diffraction during cyclic (tension–compression) loading between strain limits of ±1%. The pronounced Bauschinger effect observed upon load reversal is accounted for by a combination of the intergranular residual stresses and the intragranular sources of back stress, such as dislocation pile-ups at the intersection of stacking faults. The recently modified elasto-plastic self-consistent (EPSC) model which empirically accounts for both intergranular and intragranular back stresses has been successfully used to simulate the macroscopic stress–strain response and the evolution of the lattice strains. The EPSC model captures the experimentally observed tension–compression asymmetry as it accounts for the directionality of twinning as well as Schmid factor considerations. For the strain limits used in this study, the EPSC model also predicts that the lower flow stress on reverse shear loading reported in earlier Bauschinger-type experiments on TWIP steel is a geometrical or loading path effect

Off-Axis Ratcheting Behavior of Unidirectional Carbon/Epoxy Laminate under Asymmetric Cyclic Loading at High Temperature

Science.gov (United States)

2011-11-01

ply unidirectional carbon/epoxy laminates [0]12 were fabricated from the prepreg tape of P3252-20 (TORAY). They were laid up by hand and cured in...Off-Axis Ratcheting Behavior of Unidirectional Carbon/Epoxy Laminate under Asymmetric Cyclic Loading at High Temperature Takafumi Suzuki 1 and...Development of an engineering model for predicting the off-axis ratcheting behavior of a unidirectional CFRP laminate has been attempted. For this purpose

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

Science.gov (United States)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

STAMINA OF A GASKETED BOLTED FLANGED PIPE JOINT UNDER DYNAMIC LOADING

Directory of Open Access Journals (Sweden)

Muhammad Abid

2016-11-01

Full Text Available Gasketed bolted flange joints are the most critical components in pipelines for their sealing and strength under operating conditions. Most of the work available in literature is under static loading, whereas in industry, cyclic loads are applied due to the vibrating machinery such as motors, pumps, sloshing in offshore applications and in the ships etc. In this study a three dimensional finite element analysis of a gasketed joint is carried out using a spiral wound gasket under bolt up and dynamic operating conditions (internal pressure, axial and bending singly and in combination. The cyclic axial loads are concluded relatively more challenging for both the sealing and strength of the joint. Higher magnitudes of loads and frequencies are also observed more challenging to the joints performance.

Acoustic Emission Analysis of Damage Progression in Thermal Barrier Coatings Under Thermal Cyclic Conditions

Science.gov (United States)

Appleby, Matthew; Zhu, Dongming; Morscher, Gregory

2015-01-01

Damage evolution of electron beam-physical vapor deposited (EBVD-PVD) ZrO2-7 wt.% Y2O3 thermal barrier coatings (TBCs) under thermal cyclic conditions was monitored using an acoustic emission (AE) technique. The coatings were heated using a laser heat flux technique that yields a high reproducibility in thermal loading. Along with AE, real-time thermal conductivity measurements were also taken using infrared thermography. Tests were performed on samples with induced stress concentrations, as well as calcium-magnesium-alumino-silicate (CMAS) exposure, for comparison of damage mechanisms and AE response to the baseline (as-produced) coating. Analysis of acoustic waveforms was used to investigate damage development by comparing when events occurred, AE event frequency, energy content and location. The test results have shown that AE accumulation correlates well with thermal conductivity changes and that AE waveform analysis could be a valuable tool for monitoring coating degradation and provide insight on specific damage mechanisms.

The fracture behavior of an Al-Mg-Si alloy during cyclic fatigue

International Nuclear Information System (INIS)

Azzam, Diya; Menzemer, Craig C.; Srivatsan, T.S.

2010-01-01

In this paper, is presented and discussed the cyclic fracture behavior of the Al-Mg-Si alloy 6063 that is a candidate used in luminaire light poles. The light poles were subject to fatigue deformation. Test sections were taken from the failed region of the light pole and carefully examined in a scanning electron microscope with the objective of rationalizing the macroscopic fracture mode and intrinsic micromechanisms governing fracture under cyclic loading. The fatigue fracture surface of the alloy revealed distinct regions of early microscopic crack growth, stable crack growth and unstable crack growth and overload. An array of fine striations was found covering the regions of early and stable crack growth. Both macroscopic and fine microscopic cracks were found in the region of unstable crack growth. Very few microscopic voids and shallow dimples were evident on the fatigue fracture surface indicative of the limited ductility of the alloy under cyclic loading conditions.

Cyclic behavior of 316L steel predicted by means of finite element computations

International Nuclear Information System (INIS)

Liu, J.; Sauzay, M.; Robertson, C.; Liu, J.

2011-01-01

The cyclic behavior of 316L steels is predicted based on crystalline elastoplastic constitutive laws. Calculations are performed with the finite element software CAST3M, using a polycrystalline mesh where the individual grains are modeled as cubes, having random crystallographic orientations. At the grain scale, the constitutive law parameters are adjusted using single crystal cyclic stress strain curves (CSSCs) from literature. Calculations are performed for different loading conditions (uniaxial tension-compression, biaxial tension-compression and alternated torsion) and a large range of three remote plastic strain amplitudes. We obtained 3 close macroscopic CSSCs. Somewhat lower stresses are obtained in torsion, particularly at high plastic strain amplitude. Our results are in agreement with all the published experimental data. The mean plastic strain is computed in each grain, yielding a particular polycrystalline mean grain plastic strain distribution for each loading condition and remote plastic strain. The plastic strain scatter increases for decreasing macroscopic strains. The number of cycles to the first micro-crack initiation corresponding to the aforesaid plastic strain distributions is then calculated using a surface roughness based initiation criterion. The effect of the different loading conditions is finally discussed. (authors)

Loosening torque of Universal Abutment screws after cyclic loading: influence of tightening technique and screw coating.

Science.gov (United States)

Bacchi, Atais; Regalin, Alexandre; Bhering, Claudia Lopes Brilhante; Alessandretti, Rodrigo; Spazzin, Aloisio Oro

2015-10-01

The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading. Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at 10(6) cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukey's test (5%). The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000). The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.

One-dimensional model of cable-in-conduit superconductors under cyclic loading using artificial neural networks

International Nuclear Information System (INIS)

Lefik, M.; Schrefler, B.A.

2002-01-01

An artificial neural network with two hidden layers is trained to define a mechanical constitutive relation for superconducting cable under transverse cyclic loading. The training is performed using a set of experimental data. The behaviour of the cable is strongly non-linear. Irreversible phenomena result with complicated loops of hysteresis. The performance of the ANN, which is applied as a tool for storage, interpolation and interpretation of experimental data is investigated, both from numerical, as well as from physical viewpoints

A uniaxial cyclic elastoplastic constitutive law with a discrete memory variable

International Nuclear Information System (INIS)

Taheri, S.

1991-01-01

At present, the study on cyclic elastoplastic constitutive laws is focused on nonproportional loading, but for uniaxial loading, some problems still exist. For example, the possibility for a law to describe simultaneously the ratcheting in nonsymmetrical load-controlled test, elastic and plastic shakedown in symmetrical and nonsymmetrical ones. Here a law is presented, which in addition to previous phenomena, describes the cyclic hardening in a pushpull test, the cyclic softening after overloading and also the dependence of cyclic strain-stress curves on the history of loading. These are the usual properties of 316 stainless steel at room temperature. This law uses an internal discrete memory variable: the plastic strain at the last unloading. On the other hand, the choice of all macroscopic variables is justified by a microscopic analysis. This law has been also extended to a three-dimensional case. Regarding the microstructure under cyclic loading, plastic shakedown and ratcheting are discussed. The definition of macroscopic variables taking account of microstructure and uniaxial constitutive law are described. (K.I.)

Effects of air-abrasion pressure on the resin bond strength to zirconia: a combined cyclic loading and thermocycling aging study

Directory of Open Access Journals (Sweden)

Eman Z. Al-Shehri,

2017-06-01

Full Text Available Objectives To determine the combined effect of fatigue cyclic loading and thermocycling (CLTC on the shear bond strength (SBS of a resin cement to zirconia surfaces that were previously air-abraded with aluminum oxide (Al2O3 particles at different pressures. Materials and Methods Seventy-two cuboid zirconia specimens were prepared and randomly assigned to 3 groups according to the air-abrasion pressures (1, 2, and 2.8 bar, and each group was further divided into 2 groups depending on aging parameters (n = 12. Panavia F 2.0 was placed on pre-conditioned zirconia surfaces, and SBS testing was performed either after 24 hours or 10,000 fatigue cycles (cyclic loading and 5,000 thermocycles. Non-contact profilometry was used to measure surface roughness. Failure modes were evaluated under optical and scanning electron microscopy. The data were analyzed using 2-way analysis of variance and χ2 tests (α = 0.05. Results The 2.8 bar group showed significantly higher surface roughness compared to the 1 bar group (p < 0.05. The interaction between pressure and time/cycling was not significant on SBS, and pressure did not have a significant effect either. SBS was significantly higher (p = 0.006 for 24 hours storage compared to CLTC. The 2 bar-CLTC group presented significantly higher percentage of pre-test failure during fatigue compared to the other groups. Mixed-failure mode was more frequent than adhesive failure. Conclusions CLTC significantly decreased the SBS values regardless of the air-abrasion pressure used.

The stiffness change and the increase in the ultimate capacity for a stiff pile resulting from a cyclic loading

DEFF Research Database (Denmark)

Lada, Aleksandra; Ibsen, Lars Bo; Nicolai, Giulio

In the paper the experimental results of small-scale tests on a stiff monopile are presented to outline the change in stiffness during the cyclic loading and the change in the ultimate pile capacity. The results confirm the increase of stiffness and the increase in bearing capacity resulting from...

Damage Accumulation in Cyclically-Loaded Glass-Ceramic Matrix Composites Monitored by Acoustic Emission

Directory of Open Access Journals (Sweden)

D. G. Aggelis

2013-01-01

Full Text Available Barium osumilite (BMAS ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.

Implementation of DSC model and application for analysis of field pile tests under cyclic loading

Science.gov (United States)

Shao, Changming; Desai, Chandra S.

2000-05-01

The disturbed state concept (DSC) model, and a new and simplified procedure for unloading and reloading behavior are implemented in a nonlinear finite element procedure for dynamic analysis for coupled response of saturated porous materials. The DSC model is used to characterize the cyclic behavior of saturated clays and clay-steel interfaces. In the DSC, the relative intact (RI) behavior is characterized by using the hierarchical single surface (HISS) plasticity model; and the fully adjusted (FA) behavior is modeled by using the critical state concept. The DSC model is validated with respect to laboratory triaxial tests for clay and shear tests for clay-steel interfaces. The computer procedure is used to predict field behavior of an instrumented pile subjected to cyclic loading. The predictions provide very good correlation with the field data. They also yield improved results compared to those from a HISS model with anisotropic hardening, partly because the DSC model allows for degradation or softening and interface response.

Performance of an aircraft tire under cyclic braking and of a currently operational antiskid braking system

Science.gov (United States)

Tanner, J. A.

1972-01-01

An experimental investigation was conducted to study the performance of an aircraft tire under cyclic braking conditions and to study the performance of a currently operational aircraft antiskid braking system. Dry, damp, and flooded runway surface conditions were used in the investigation. The results indicated that under cyclic braking conditions the braking and cornering-force friction coefficients may be influenced by fluctuations in the vertical load, flexibility in the wheel support, and the spring coupling between the wheel and the tire-pavement interface. The cornering capability was shown to be negligible at wheel slip ratios well below a locked-wheel skid under all test surface conditions. The maximum available brake-force friction coefficient was shown to be dependent upon the runway surface condition, upon velocity, and, for wet runways, upon tire differences. Moderate reductions in vertical load and brake system pressure did not significantly affect the overall wet-runway performance of the tire.

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

Science.gov (United States)

Gu, Linlin; Ye, Guanlin; Wang, Zhen; Ling, Xianzhang; Zhang, Feng

2017-07-01

In this paper, numerical simulation with soil-water coupling finite element-finite difference (FE-FD) analysis is conducted to investigate the settlement and the excess pore water pressure (EPWP) of a piled-raft foundation due to cyclic high-speed (speed: 300km/h) train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer (No-9 layer) has better effect on reducing the settlement.

Theoretical analysis, infrared and structural investigations of energy dissipation in metals under cyclic loading

International Nuclear Information System (INIS)

Plekhov, O.A.; Saintier, N.; Palin-Luc, T.; Uvarov, S.V.; Naimark, O.B.

2007-01-01

The infrared and structural investigations of energy dissipation processes in metals subjected to cyclic loading have given impetus to the development of a new thermodynamic model with the capability of describing the energy balance under plastic deformation. The model is based on the statistical description of the mesodefect ensemble evolution and its influence on the dissipation ability of the material. Constitutive equations have been formulated for plastic and structural strains, which allow us to describe the stored and dissipated parts of energy under plastic flow. Numerical results indicate that theoretical predictions are in good agreement with the experimentally observed temperature data

Fission gas release behavior of MOX fuels under simulated daily-load-follow operation condition. IFA-554/555 test evaluation with FASTGRASS code

International Nuclear Information System (INIS)

Ikusawa, Yoshihisa; Ozawa, Takayuki

2008-03-01

IFA-554/555 load-follow tests were performed in HALDEN reactor (HBWR) to study the MOX fuel behavior under the daily-load-follow operation condition in the framework of ATR-MOX fuel development in JAEA. IFA-554/555 rig had the instruments of rod inner pressure, fuel center temperature, fuel stack elongation, and cladding elongation. Although the daily-load-follow operation in nuclear power plant is one of the available options for economical improvement, the power change in a short period in this operation causes the change of thermal and mechanical irradiation conditions. In this report, FP gas release behavior of MOX fuel rod was evaluated under the daily-load-follow operation condition with the examination data from IFA-554/555 by using the computation code 'FASTGRASS'. From the computation results of FASTGRASS code which could compute the FP gas release behavior under the transient condition, it could be concluded that FP gas was released due to the relaxation of fuel pellet inner stress and pellet temperature increase, which were caused by the cyclic power change during the daily-load-follow operation. In addition, since the amount of released FP gas decreased during the steady operation after the daily-load-follow, it could be mentioned that the total of FP gas release at the end of life with the daily-load-follow is not so much different from that without the daily-load-follow. (author)

Fatigue mechanisms in an austenitic steel under cyclic loading: Experiments and atomistic simulations

Energy Technology Data Exchange (ETDEWEB)

Soppa, E.A., E-mail: ewa.soppa@mpa.uni-stuttgart.de; Kohler, C., E-mail: christopher.kohler@mpa.uni-stuttgart.de; Roos, E., E-mail: eberhard.roos@mpa.uni-stuttgart.de

2014-03-01

Experimental investigations on the austenitic stainless steel X6CrNiNb18-10 (AISI – 347) and concomitant atomistic simulations of a FeNi nanocrystalline model system have been performed in order to understand the basic mechanisms of fatigue damage under cyclic loading. Using electron backscatter diffraction (EBSD) the influence of deformation induced martensitic transformation and NbC size distribution on the fatigue crack formation has been demonstrated. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∼1 µm sized) differently oriented grains. The atomistic simulations show the role of regions of a high density of stacking faults for the martensitic transformation.

Comparative assessment of cyclic J-R curve determination by different methods in a pressure vessel steel

Energy Technology Data Exchange (ETDEWEB)

Chowdhury, Tamshuk, E-mail: tamshuk@gmail.com [Deep Sea Technologies, National Institute of Ocean Technology, Chennai, 600100 (India); Sivaprasad, S.; Bar, H.N.; Tarafder, S. [Fatigue & Fracture Group, Materials Science and Technology Division, CSIR-National Metallurgical Laboratory, Jamshedpur, 831007 (India); Bandyopadhyay, N.R. [School of Materials Science and Engineering, Indian Institute of Engineering, Science and Technology, Shibpur, Howrah, 711103 (India)

2016-04-15

Cyclic J-R behaviour of a reactor pressure vessel steel using different methods available in literature has been examined to identify the best suitable method for cyclic fracture problems. Crack opening point was determined by moving average method. The η factor was experimentally determined for cyclic loading conditions and found to be similar to that of ASTM value. Analyses showed that adopting a procedure analogous to the ASTM standard for monotonic fracture is reasonable for cyclic fracture problems, and makes the comparison to monotonic fracture results straightforward. - Highlights: • Different methods of cyclic J-R evaluation compared. • A moving average method for closure point proposed. • η factor for cyclic J experimentally validated. • Method 1 is easier, provides a lower bound and direct comparison to monotonic fracture.

Cyclic complex loading of 316 stainless steel: Experiments and calculations

International Nuclear Information System (INIS)

Jacquelin, B.; Hourlier, F.; Dang Van, K.; Stolz, C.

1981-01-01

To test the ability of cyclic constitutive law established by mean of uniaxial test a benchmark is proposed. The calculated results using the model of Chaboche-Cordier-Dang Van are compared with experimental data obtained on cylindrical specimens undergoing simultaneously constant torque and cyclic tension. (orig.)

Rate-dependent response of superelastic Cu–Al–Mn alloy rods to tensile cyclic loads

International Nuclear Information System (INIS)

Araki, Yoshikazu; Maekawa, Nao; Omori, Toshihiro; Sutou, Yuji; Kainuma, Ryosuke; Ishida, Kiyohito

2012-01-01

We report the results of tensile cyclic loading tests conducted to examine the dependence of constitutive relations for superelastic Cu–Al–Mn alloy rods on loading rates. Recently, Cu–Al–Mn alloy rods with diameters up to 8 mm have been developed by the authors, and it has been demonstrated that these rods have excellent superelastic strains of more than 8%, which is comparable to Ni–Ti alloys and far superior to other Cu-based alloys. No information is available, however, on the rate dependence of constitutive relations for Cu–Al–Mn alloys. In this study, we prepare two Cu–Al–Mn alloy rod specimens, whose lengths and diameters are 150 mm and 8 mm, respectively. Their stress–strain relations are examined under the loading frequencies of 0.001, 0.5, and 1 Hz with constant strain amplitude of 4.5%. It was found from the tests that the maximum stress increase in Cu–Al–Mn alloys due to higher loading rate was less than 5%. Thermo-mechanical analysis predicts that stress increase in Cu–Al–Mn alloys is about 1/4 of that in Ni–Ti alloys, which agrees reasonably well with the experimental observations. Such low stress increase is highly desirable in the design of seismic devices such as dampers and isolators. (fast track communication)

Effects of laboratory heating, cyclic pore pressure, and cyclic loading on fracture properties of asphalt mixture.

Science.gov (United States)

2012-04-01

This study involved the identification and evaluation of laboratory conditioning methods and testing protocols considering heat oxidation, moisture, and load that more effectively simulate asphalt mixture aging in the field, and thereby help to prope...

Cyclic stress-strain behaviour under thermomechanical fatigue conditions - Modeling by means of an enhanced multi-component model

Energy Technology Data Exchange (ETDEWEB)

Christ, H J [Institut fuer Werkstofftechnik, Universitaet Siegen, D-57068 Siegen (Germany); Bauer, V, E-mail: hans-juergen.christ@uni-siegen.d [Wieland Werke AG, Graf-Arco Str. 36, D-89072 Ulm (Germany)

2010-07-01

The cyclic stress-strain behaviour of metals and alloys in cyclic saturation can reasonably be described by means of simple multi-component models, such as the model based on a parallel arrangement of elastic-perfectly plastic elements, which was originally proposed by Masing already in 1923. This model concept was applied to thermomechanical fatigue loading of two metallic engineering materials which were found to be rather oppositional with respect to cyclic plastic deformation. One material is an austenitic stainless steel of type AISI304L which shows dynamic strain aging (DSA) and serves as an example for a rather ductile alloy. A dislocation arrangement was found after TMF testing deviating characteristically from the corresponding isothermal microstructures. The second material is a third-generation near-gamma TiAl alloy which is characterized by a very pronounced ductile-to-brittle transition (DBT) within the temperature range of TMF cycling. Isothermal fatigue testing at temperatures below the DBT temperature leads to cyclic hardening, while cyclic softening was found to occur above DBT. The combined effect under TMF leads to a continuously developing mean stress. The experimental observations regarding isothermal and non-isothermal stress-strain behaviour and the correlation to the underlying microstructural processes was used to further develop the TMF multi-composite model in order to accurately predict the TMF stress-strain response by taking the alloy-specific features into account.

Micromechanics of soil responses in cyclic simple shear tests

Directory of Open Access Journals (Sweden)

Cui Liang

2017-01-01

Full Text Available Offshore wind turbine (OWT foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

A comparison of Reactivity Controlled Compression Ignition (RCCI) and Gasoline Compression Ignition (GCI) strategies at high load, low speed conditions

International Nuclear Information System (INIS)

Kavuri, Chaitanya; Paz, Jordan; Kokjohn, Sage L.

2016-01-01

strategy, the longer ignition delay of the gasoline fuel allowed for more air entrainment, causing lower soot emissions while giving reasonable control over combustion. Cyclic variability can be problematic at the load extremes; accordingly, the sensitivity to fluctuations in operating conditions was evaluated. Both strategies were found to be most sensitive to fluctuations in exhaust gas recirculation (EGR) rate. The GCI strategy was more sensitive to small changes in the charge conditions than the RCCI strategy, indicating that cyclic variability may be more problematic for GCI operation.

Inelastic constitutive models for the simulation of a cyclic softening behavior of modified 9Cr-lMo steel at elevated temperatures

International Nuclear Information System (INIS)

Koo, Gyeong Hoi; Lee, Jae Han

2007-01-01

In this paper, the inelastic constitutive models for the simulations of the cyclic softening behavior of the modified 9Cr-1Mo steel, which has a significant cyclic softening characteristic especially in elevated temperature regions, are investigated in detail. To do this, the plastic modulus, which primarily governs the calculation scheme of the plasticity, is formulated for the inelastic constitutive models such as the Armstrong-Frederick model, Chaboche model, and Ohno-Wang model. By implementing the extracted plastic modulus and the consistency conditions into the computer program, the inelastic constitutive parameters are identified to present the best fit of the uniaxial cyclic test data by strain-controlled simulations. From the computer simulations by using the obtained constitutive parameters, it is found that the Armstrong-Frederick model is simple to use but it causes significant overestimated strain results when compared with the Chaboche and the Ohno-Wang models. And from the ratcheting simulation results, it is found that the cyclic softening behavior of the modified 9Cr-1Mo steel can invoke a ratcheting instability when the applied cyclic loads exceed a certain level of the ratchet loading condition

An X-ray diffraction study of microstructural deformation induced by cyclic loading of selected steels

International Nuclear Information System (INIS)

Fourspring, P.M.; Pangborn, R.N.

1996-06-01

X-ray double crystal diffractometry (XRDCD) was used to assess cyclic microstructural deformation in a face centered cubic (fcc) steel (AISI304) and a body centered cubic (bcc) steel (SA508 class 2). The first objective of the investigation was to determine if XRDCD could be used to effectively monitor cyclic microstructural deformation in polycrystalline Fe alloys. A second objective was to study the microstructural deformation induced by cyclic loading of polycrystalline Fe alloys. The approach used in the investigation was to induce fatigue damage in a material and to characterize the resulting microstructural deformation at discrete fractions of the fatigue life of the material. Also, characterization of microstructural deformation was carried out to identify differences in the accumulation of damage from the surface to the bulk, focusing on the following three regions: near surface (0--10 microm), subsurface (10--300 microm), and bulk. Characterization of the subsurface region was performed only on the AISI304 material because of the limited availability of the SA508 material. The results from the XRDCD data indicate a measurable change induced by fatigue from the initial state to subsequent states of both the AISI304 and the SA508 materials. Therefore, the XRDCD technique was shown to be sensitive to the microstructural deformation caused by fatigue in steels; thus, the technique can be used to monitor fatigue damage in steels. In addition, for the AISI304 material, the level of cyclic microstructural deformation in the bulk material was found to be greater than the level in the near surface material. In contrast, previous investigations have shown that the deformation is greater in the near surface than the bulk for Al alloys and bcc Fe alloys

Short analysis of a progressive distorsion problem (tension and cyclic torsion)

International Nuclear Information System (INIS)

Roche, Roland.

1978-06-01

Tests on ratcheting (or progressive distorsion) are in progress in Saclay. A thin tube is subjected to a constant tensile load and to a cyclic twist. The present paper is a short theoretial analysis of that case. A uniform strain and stress field is considered with a constant tensile stress P (primary stress) and a cyclic shearing strain. The shearing strain is known by the corresponding elastic equivalent stress intensity (TRESCA criterion). The cyclic range of the stress intensity is ΔQ (secondary stress range). Are examined the shake down condition and the incremental elongations with different constitutive equations of the material. Special attention is given to perfect plasticity and bilinear kinematic hardening results are presented, but it is believed that these materials mathematical models are simplistic and special experimental tests are proposed [fr

Creep rupture of structures subjected to variable loading and temperature

International Nuclear Information System (INIS)

Wojewodzki, W.

1975-01-01

The aim of the present paper is to show on the basis of equations and the analysis of creep mechanisms the possibilities of a description of the creep behavior of material under variable temperature and loading conditions. Also the influence of cyclic proportional loading and temperature gradient upon the rupture life and strains of a thick cylinder is investigated in detail. The obtained theoretical creep curves coincide with the experimental results for investigated steel in the temperature range from 500 0 C to 575 0 C. The constitutive equations together with the functions determined previously are applied to solve the problem of thick cylinder subjected to cyclic proportional pressure and temperature gradient. Numerical results for the thick steel cylinder are presented both in diagrammatical and tabular form. The obtained new results clearly show the significant influence of temperature gradient, cyclic temperature gradient, and cyclic pressure upon the stress redistribution, the magnitude of deformation, the propagation of the front damage and the rupture life. It was found that small temperature fluctuations at elevated temperature can shorten the rupture life very considerably. The introduced description of the creep rupture behavior of material under variable temperature and loading conditions together with the results for the thick cylinder indicate the possibilities of solutions of practical problems encountered in structural mechanics of reactor technology

Evaluation of trickle-bed air biofilter performance under periodic stressed operating conditions as a function of styrene loading.

Science.gov (United States)

Kim, Daekeun; Cai, Zhangli; Sorial, George A

2005-02-01

Trickle-bed air biofilters (TBABs) are suitable for treating volatile organic compounds (VOCs) at a significantly high practical loading because of their controlled environmental conditions. The application of TBAB for treating styrene-contaminated air under periodic backwashing and cyclical nonuse periods at a styrene loading of 0.64-3.17 kg chemical oxygen demand (COD)/m3 x day was the main focus of this study. Consistent long-term efficient performance of TBAB strongly depended on biomass control. A periodic in situ upflow with nutrient solution under media fluidization, that is, backwashing, was approached in this study. Two different nonuse periods were employed to simulate a shutdown for equipment repair or during weekends and holidays. The first is a starvation period without styrene loading, and the second is a stagnant period, which reflects no flow passing through the biofilter. For styrene loadings up to 1.9 kg COD/m3 x day, removal efficiencies consistently above 99% were achieved by conducting a coordinated biomass control strategy, that is, backwashing for 1 hr once per week. Under cyclical nonuse periods for styrene loadings up to 1.27 kg COD/m3 x day, stable long-term performance of the biofilter was maintained at more than 99% removal without employing backwashing. No substantial impact of nonuse periods on the biofilter performance was revealed. However, a coordinated biomass control by backwashing subsequently was unavoidable for attaining consistently high removal efficiency at a styrene loading of 3.17 kg COD/m3 x day. As styrene loading was increased, reacclimation of the biofilter to reach the 99% removal efficiency following backwashing or the nonuse periods was delayed. After the non-use periods, the response of the biofilter was a strong function of the biomass in the bed. No significant difference between the effects of the two different nonuse periods on TBAB performance was observed during the study period.

[Wear intensity and surface roughness of microhybrid composite and ceramic occlusal veneers on premolars after the thermocycling and cyclic mechanical loading tests].

Science.gov (United States)

Zhang, H Y; Jiang, T; Cheng, M X; Zhang, Y W

2018-02-18

To evaluate the wear intensity and surface roughness of occlusal veneers on premolars made of microhybrid composite resin or two kinds of ceramics in vitro after the thermocycling and cyclic mechanical loading tests. In the study,24 fresh extracted human premolars without root canal treatment were prepared (cusps reduction of 1.5 mm in thickness to simulate middle to severe tooth wear, the inclinations of cusps were 20°). The prepared teeth were restored with occlusal veneers made of three different materials: microhybrid composite, heat-pressed lithium disilicate ceramic and computer-aided design/computer-aided manufacturing (CAD/CAM) lithium disilicate ceramic in the thickness of 1.5 mm. The occlusal veneers were cemented with resin cement. The specimens were fatigued using the thermocycling and cyclic mechanical loading tests after being stored in water for 72 h. The wear of specimens was measured using gypsum replicas and 3D laser scanner before and after the thermocycling and cyclic mechanical loading tests and the mean lost distance (mm) was used to indicate the level of wear. The surfaces of occlusal contact area were observed and the surface roughness was recorded using 3D laser scanning confocal microscope before and after the fatigue test. Differences between the groups were compared using ONE-way ANOVA(Pcomposite group, heat-pressed lithium disilicate ceramic group, and CAD/CAM lithium disilicate ceramic group was (-0.13±0.03) mm, (-0.05±0.01) mm and (-0.05±0.01) mm, the wear of microhybrid composite was significantly higher than the two ceramic groups(Pcomposite was significantly higher than the two ceramic groups(Pcomposite(P=0.005) and CAD/CAM lithium disilicate ceramic (P=0.010). From the view of wear speed, microhybrid composite was significantly higher than the two kinds of ceramics, but it was similar to enamel when the opposing tooth was natural. The surface roughness before the themocycling and cyclic mechanical loading test of microhybrid

Stress recovery and cyclic behaviour of an Fe-Mn-Si shape memory alloy after multiple thermal activation

Science.gov (United States)

Hosseini, E.; Ghafoori, E.; Leinenbach, C.; Motavalli, M.; Holdsworth, S. R.

2018-02-01

The stress recovery and cyclic deformation behaviour of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) shape memory alloy (Fe-SMA) strips, which are often used for pre-stressed strengthening of structural members, were studied. The evolution of recovery stress under different constraint conditions was studied. The results showed that the magnitude of the tensile stress in the Fe-SMA member during thermal activation can have a signification effect on the final recovery stress. The higher the tensile load in the Fe-SMA (e.g., caused by dead load or thermal expansion of parent structure during heating phase), the lower the final recovery stress. Furthermore, this study investigated the cyclic behaviour of the activated SMA followed by a second thermal activation. Although the magnitude of the recovery stress decreased during the cyclic loading, the second thermal activation could retrieve a significant part of the relaxed recovery stress. This observation suggests that the relaxation of recovery stress during cyclic loading is due to a reversible phase transformation-induced deformation (i.e., forward austenite-to-martensite transformation) rather than an irreversible dislocation-induced plasticity. Retrieval of the relaxed recovery stress by the reactivation process has important practical implications as the prestressing loss in pre-stressed civil structures can be simply recovered by reheating of the Fe-SMA elements.

Cyclic life of superalloy IN738LC under in-phase and out-of-phase thermo-mechanical fatigue loading

International Nuclear Information System (INIS)

Chen Hongjun; Wahi, R.P.; Wever, H.

1995-01-01

The cyclic life of IN738LC, a widely used nickel base superalloy for blades in stationary gas turbines, was investigated under thermo-mechanical fatigue loading using a temperature variation range of 1023 to 1223 K, with temperature variation rate in the range of 6 to 15 K/min. Simple thermo-mechanical cycles with linear sequences corresponding to in-phase (IP) and out-of-phase (OP) tests were performed. Both the IP and OP tests were carried out at different constant mechanical strain ranges varied between 0.8 to 2.0% and at a constant mechanical strain rate of 10 -5 s -1 . Thermo-mechanical fatigue lives under both test conditions were compared with each other and with those of isothermal LCF tests at a temperature of 1223 K. The results show that the life under thermo-mechanical fatigue is strongly dependent on the nature of the test, i.e. stress controlled or strain controlled. (orig.)

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

Science.gov (United States)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

Solution of the ratchet-shakedown Bree problem with an extra orthogonal primary load

International Nuclear Information System (INIS)

Bradford, R.A.W.

2015-01-01

The complete shakedown and ratcheting solution is derived analytically for a flat plate subject to unequal biaxial primary membrane stresses and a cyclic secondary bending stress in one in-plane direction (x). The Tresca yield condition and elastic-perfectly plastic behaviour are assumed. It is shown that the results can be expressed in the form of a “universal” ratchet diagram applicable for all magnitudes of orthogonal load. For sufficiently large cyclic bending stresses, tensile ratcheting can occur in the x direction if the x direction primary membrane stress exceeds half that in the orthogonal direction. Conversely, for sufficiently large cyclic bending stresses ratcheting in the x direction will be compressive if the x direction primary membrane stress is less than half that in the orthogonal direction. When the x direction primary membrane stress is exactly half that in the orthogonal direction ratcheting cannot occur however large the cyclic secondary bending stress. - Highlights: • A complete shakedown and ratcheting solution is derived analytically. • The problem is Bree-like but with an extra orthogonal primary load. • The ratchet diagram can be expressed in a form applicable to any orthogonal load. • Tensile ratcheting can occur if the primary load exceeds half the orthogonal load. • Compressive ratcheting can occur for smaller primary loads

Bucket foundations under lateral cyclic loading

DEFF Research Database (Denmark)

Foglia, Aligi

failure envelopes. A jacked installation test is successfully compared with existing models. Tests of bucket foundations under lateral loading applied at different loading rates are analysed. As expected, the bearing capacity of bucket foundations under transient lateral loading increases dramatically...... documents on bearing capacity and installation of bucket foundations are reviewed and the results from the models found in literature are compared to the experimental results obtained in the current study. Monotonic tests of bucket foundations under lateral loading until failure are compared with existing...

Dynamic Strength and Accumulated Plastic Strain Development Laws and Models of the Remolded Red Clay under Long-Term Cyclic Loads: Laboratory Test Results

Directory of Open Access Journals (Sweden)

Li Jian

2015-09-01

Full Text Available The dynamic strength and accumulated plastic strain are two important parameters for evaluating the dynamic response of soil. As a special clay, the remolded red clay is often used as the high speed railway subgrade filling, but studies on its dynamic characteristics are few. For a thorough analysis of the suitability of the remolded red clay as the subgrade filling, a series of long-term cyclic load triaxial test under different load histories are carried out. Considering the influence of compactness, confining pressure, consolidation ratio, vibration frequency and dynamic load to the remolded red clay dynamic property, the tests obtain the development curves of the dynamic strength and accumulated plastic strain under different test conditions. Then, through curve fitting method, two different hyperbolic models respectively for the dynamic strength and accumulated plastic strain are built, which can match the test datum well. By applying the dynamic strength model, the critical dynamic strength of the remolded red clay are gained. Meanwhile, for providing basic datum and reference for relevant projects, all key parameters for the dynamic strength and accumulated plastic strain of the remolded red clay are given in the paper.

Effect of surfaces similarity on contact resistance of fractal rough surfaces under cyclic loading

Science.gov (United States)

Gao, Yuanwen; Liu, Limei; Ta, Wurui; Song, Jihua

2018-03-01

Although numerous studies have shown that contact resistance depends significantly on roughness and fractal dimension, it remains elusive how they affect contact resistance between rough surfaces. The interface similarity index is first proposed to describe the similarity of the contact surfaces, which gives a good indication of the actual contact area between surfaces. We reveal that the surfaces' similarity be an origin of contact resistance variation. The cyclic loading can increase the contact stiffness, and the contact stiffness increases with the increase of the interface similarity index. These findings explain the mechanism of surface roughness and fractal dimension on contact resistance, and also provide reference for the reliability design of the electrical connection.

Thin circular cylinder under axisymmetrical thermal and mechanical loading

International Nuclear Information System (INIS)

Arnaudeau, F.; Zarka, J.; Gerij, J.

1977-01-01

To assess structural integrity of components subjected to cyclic thermal loadings one must look at thermal ratchetting as a possible failure mode. Considering a thin circular cylinder subjected to constant internal pressure and cyclically varying thermal gradient through the thickness Bree, J. Strain Analysis 2 (1967) No.3, obtained a diagram that serves as a foundation for many design rules (e.g.: ASME code). The upper part of the french LMFBR main vessel is subjected to an axisymmetrical axial thermal loading and an axial load (own weight). Operation of the reactor leads to cyclic variations of the axial thermal loading. The question that arises is whether or not the Bree diagram is realistic for such loading conditions. A special purpose computer code (Ratch) was developed to analyse a thin circular cylinder subjected to axisymmetrical mechanical and thermal loadings. The Mendelson's approach of this problem is followed. Classical Kirchoff-Love hypothesis of thin shells is used and a state of plane stress is assumed. Space integrations are performed by Gaussian quadrature in the axial direction and by Simpson's one third rule throughout the thickness. Thermoelastic-plastic constitutive equations are solved with an implicit scheme (Nguyen). Thermovisco-plastic constitutive equations are solved with an explicit time integration scheme (Treanor's algorithm especially fitted). A Bree type diagram is obtained for an axial step of temperature which varies cyclically and a sustained constant axial load. The material behavior is assumed perfectly plastic and creep effect is not considered. Results show that the domain where no ratchetting occurs is reduced when compared with the domain predicted by the Bree diagram

Study on the estimation of safety margin of piping system against seismic loading. 1st report, damage observations of the straight pipes subjected to cyclic load amplitudes of various levels

International Nuclear Information System (INIS)

Nakamura, Izumi; Otani, Akihito; Shiratori, Masaki

2010-01-01

Fatigue failure accompanied by ratchet deformation is well known as one of the failure modes of pressurized pipes under high-level cyclic load. In this research, the process of failure of such pipes was investigated based on the experimental result in which a straight pipe failed by repeatedly increasing cyclic input displacement amplitude in stages. The strain behavior, moment-deflection relationship, and observed damage were compared with the stress level used in the seismic design of the piping system. As a result, no significant damage was observed and the moment-deflection relationship remained almost linear within the primary stress limit of 3S m , although the strain showed elastic-plastic behavior at some measurement points. In the experiment, damage was observed at the applied load levels of approximately 5S m of the primary stress, and 0.15 and more of the fatigue damage index, i.e., the usage factor based on the design. The test results showed that there is a certain time margin before failure occurs to actual piping systems, compared with its designed stress limitation. (author)

Retention Strength after Compressive Cyclic Loading of Five Luting Agents Used in Implant-Supported Prostheses

Directory of Open Access Journals (Sweden)

Angel Alvarez-Arenal

2016-01-01

Full Text Available The purpose of this study was to evaluate and compare the retention strength of five cement types commonly used in implant-retained fixed partial dentures, before and after compressive cyclic loading. In five solid abutments screwed to 5 implant analogs, 50 metal Cr-Ni alloy copings were cemented with five luting agents: resin-modified glass ionomer (RmGI, resin composite (RC, glass ionomer (GI, resin urethane-based (RUB, and compomer cement (CC. Two tensile tests were conducted with a universal testing machine, one after the first luting of the copings and the other after 100,000 cycles of 100 N loading at 0.72 Hz. The one way ANOVA test was applied for the statistical analysis using the post hoc Tukey test when required. Before and after applying the compressive load, RmGI and RC cement types showed the greatest retention strength. After compressive loading, RUB cement showed the highest percentage loss of retention (64.45%. GI cement recorded the lowest retention strength (50.35 N and the resin composite cement recorded the highest (352.02 N. The type of cement influences the retention loss. The clinician should give preference to lower retention strength cement (RUB, CC, and GI if he envisages any complications and a high retention strength one (RmGI, RC for a specific clinical situation.

Evaluation of resilient abutment components on measured strain using dynamic loading conditions.

Science.gov (United States)

Morton, D; Stanford, C M; Aquilino, S A

1998-07-01

Factors that affect transmission of strain from prostheses to bone may affect the long-term success of loaded implants. Current in vitro models are theoretically predictive (finite element modeling) or facsimile (photoelastic) in nature. A more clinically relevant in vitro model for strain evaluation should be investigated. This study attempted: (1) to validate a human cadaver bone model for vitro measurement of cortical bone strain, and (2) to evaluate the effect on cortical strain measurements of a resilient plastic component incorporated within a titanium implant in response to variable dynamic loading. Two IMZ (Interpore International) abutment alternatives were used: the titanium Abutment Complete and the polyoxymethylene Intra-mobile Element. The model system consisted of two implants placed in unfixed human cadaver ulna bone to simulate an implant bound edentulous region. Four biaxial rosette strain gauges simultaneously recorded cortical bone strain immediately mesial and distal to each implant. During experimentation a simulated prosthetic framework supported by either titanium or polyoxymethylene abutments was dynamically loaded 6 min from the terminal abutment along a cantilever extension. Cyclic nominal peak loads were applied with a materials testing machine at 20-N intervals from 20 to 200 N at a crosshead speed of 5 mm/minute. The protocol allowed frequency of load application to vary. A Newtonian linear correlation (r2 > or = 0.98) between load application and strain output was determined for each gauge position except for the terminal gauge located opposite the cantilever. Cortical strains recorded were within reported physiologic ranges involved in bone modeling and remodeling. Further, the polyoxymethylene abutment components did not result in reduction of peak microstrain at any gauge position. The Intra-mobile Element abutments, however, did increase the time required to complete 10 loading cycles when compared with the titanium Abutment

Cyclic plasticity and lifetime of the nickel-based Alloy C-263: Experiments, models and component simulation

Directory of Open Access Journals (Sweden)

Maier G.

2014-01-01

Full Text Available The present work deals with the thermomechanical fatigue and low-cycle fatigue behavior of C-263 in two different material conditions. Microstructural characteristics and fracture modes are investigated with light and electron microscopy. The experimental results indicate that viscoplastic deformations depend on the heat treatment or rather on the current state of the microstructure. The measured data are used to adjust the parameters of a Chaboche type model and a fracture-mechanics based model for fatigue lifetime prediction. The Chaboche model is able to describe the essential phenomena of time and temperature dependent cyclic plasticity including the complex cyclic hardening during thermo-cyclic loading of both material conditions with a unique set of material parameters. This could be achieved by including an additional internal variable into the Chaboche model which accounts for changes in the precipitation microstructure during high temperature loading. Furthermore, the proposed lifetime model is well suited for a common fatigue life prediction of both investigated heats. The deformation and lifetime models are implemented into a user defined material routine. In this work, the material routine is applied for the lifetime prediction of a critical power plant component using the finite element method.

Small-Scale Cyclic Tests on Nonslender Piles Situated in Sand

DEFF Research Database (Denmark)

Sørensen, Søren Peder Hyldal; Ibsen, Lars Bo

In the period from August 2011 till October 2011 a series of small-scale tests on pile foundations has been conducted at Aalborg University. In all the tests, the piles have been exposed to cyclic loading consisting of 20-25 load cycles and all the tests have been conducted in a pressure tank....... The objective of the tests has been to investigate the effect of pile diameter, length to diameter ratio and cyclic loading on the soil response for non-slender piles in sand....

The behaviour of the stiff monopile foundation subjected to the lateral loads

DEFF Research Database (Denmark)

Lada, Aleksandra; Ibsen, Lars Bo; Nicolai, Giulio

The article focuses on the analysis of a large-diameter monopile foundation for offshore wind turbine based on the numerical model results. The case describes the behaviour of a monopile in sand subjected to a lateral loading conditions. The effects of the pile diameter, the length and the load...... eccentricity on the results are investigated. Additionally, the cyclic nature of load is also taken into consideration. The cyclic loading leads to an accumulated rotation, thus the SLS design must ensure that the maximum permanent rotation does not exceed the limit value for a given wind turbine. The approach...... analyzed by LeBlanc et al. [2010] and Lada et al. [2014] is discussed in the way of its use as a preliminary design....

Effect of Repeated Screw Joint Closing and Opening Cycles and Cyclic Loading on Abutment Screw Removal Torque and Screw Thread Morphology: Scanning Electron Microscopy Evaluation.

Science.gov (United States)

Arshad, Mahnaz; Mahgoli, Hosseinali; Payaminia, Leila

To evaluate the effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology using scanning electron microscopy (SEM). Three groups (n = 10 in each group) of implant-abutment-abutment screw assemblies were created. There were also 10 extra abutment screws as new screws in group 3. The abutment screws were tightened to 12 Ncm with an electronic torque meter; then they were removed and removal torque values were recorded. This sequence was repeated 5 times for group 1 and 15 times for groups 2 and 3. The same screws in groups 1 and 2 and the new screws in group 3 were then tightened to 12 Ncm; this was also followed by screw tightening to 30 Ncm and retightening to 30 Ncm 15 minutes later. Removal torque measurements were performed after screws were subjected to cyclic loading (0.5 × 10⁶ cycles; 1 Hz; 75 N). Moreover, the surface topography of one screw from each group before and after cyclic loading was evaluated with SEM and compared with an unused screw. All groups exhibited reduced removal torque values in comparison to insertion torque in each cycle. However, there was a steady trend of torque loss in each group. A comparison of the last cycle of the groups before loading showed significantly greater torque loss value in the 15th cycle of groups 2 and 3 compared with the fifth cycle of group 1 (P abutment is definitively placed.

Damage and fatigue crack growth of Eurofer steel first wall mock-up under cyclic heat flux loads. Part 1: Electron beam irradiation tests

Energy Technology Data Exchange (ETDEWEB)

You, J.H., E-mail: you@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Euratom Association, Boltzmannstr. 2, 85748 Garching (Germany); Höschen, T. [Max-Planck-Institut für Plasmaphysik, Euratom Association, Boltzmannstr. 2, 85748 Garching (Germany); Pintsuk, G. [Forschungszentrum Jülich GmbH, IEK2, Euratom Association, 52425 Jülich (Germany)

2014-04-15

Highlights: • Clear evidence of microscopic damage and crack formation at the notch root in the early stage of the fatigue loading (50–100 load cycles). • Propagation of fatigue crack at the notch root in the course of subsequent cyclic heat-flux loading followed by saturation after roughly 600 load cycles. • No sign of damage on the notch-free surface up to 800 load cycles. • No obvious effect of the pulse time duration on the crack extension. • Slight change in the grain microstructure due to the formation of sub-grain boundaries by plastic deformation. - Abstract: Recently, the idea of bare steel first wall (FW) is drawing attention, where the surface of the steel is to be directly exposed to high heat flux loads. Hence, the thermo-mechanical impacts on the bare steel FW will be different from those of the tungsten-coated one. There are several previous works on the thermal fatigue tests of bare steel FW made of austenitic steel with regard to the ITER application. In the case of reduced-activation steel Eurofer97, a candidate structural material for the DEMO FW, there is no report on high heat flux tests yet. The aim of the present study is to investigate the thermal fatigue behavior of the Eurofer-based bare steel FW under cyclic heat flux loads relevant to DEMO operation. To this end, we conducted a series of electron beam irradiation tests with heat flux load of 3.5 MW/m{sup 2} on water-cooled mock-ups with an engraved thin notch on the surface. It was found that the notch root region exhibited a marked development of damage and fatigue cracks whereas the notch-free surface manifested no sign of crack formation up to 800 load cycles. Results of extensive microscopic investigation are reported.

Inelastic behavior of cold-formed braced walls under monotonic and cyclic loading

Science.gov (United States)

Gerami, Mohsen; Lotfi, Mohsen; Nejat, Roya

2015-06-01

The ever-increasing need for housing generated the search for new and innovative building methods to increase speed and efficiency and enhance quality. One method is the use of light thin steel profiles as load-bearing elements having different solutions for interior and exterior cladding. Due to the increase in CFS construction in low-rise residential structures in the modern construction industry, there is an increased demand for performance inelastic analysis of CFS walls. In this study, the nonlinear behavior of cold-formed steel frames with various bracing arrangements including cross, chevron and k-shape straps was evaluated under cyclic and monotonic loading and using nonlinear finite element analysis methods. In total, 68 frames with different bracing arrangements and different ratios of dimensions were studied. Also, seismic parameters including resistance reduction factor, ductility and force reduction factor due to ductility were evaluated for all samples. On the other hand, the seismic response modification factor was calculated for these systems. It was concluded that the highest response modification factor would be obtained for walls with bilateral cross bracing systems with a value of 3.14. In all samples, on increasing the distance of straps from each other, shear strength increased and shear strength of the wall with bilateral bracing system was 60 % greater than that with lateral bracing system.

Cyclic creep-rupture behavior of three high-temperature alloys.

Science.gov (United States)

Halford, G. R.

1972-01-01

Study of some important characteristics of the cyclic creep-rupture curves for the titanium alloy 6Al-2Sn-4Zr-2Mo at 900 and 1100 F (755 and 865 K), the cobalt-base alloy L-605 at 1180 F (910 K), and for two hardness levels of 316 stainless steel at 1300 F (980 K). The cyclic creep-rupture curve relates tensile stress and tensile time-to-rupture for strain-limited cyclic loading and has been found to be independent of the total strain range and the level of compressive stress employed in the cyclic creep-rupture tests. The cyclic creep-rupture curve was always found to be above and to the right of the conventional (constant load) monotonic creep-rupture curve by factors ranging from 2 to 10 in time-to-rupture. This factor tends to be greatest when the creep ductility is large. Cyclic creep acceleration was observed in every cyclic creep-rupture test conducted. The phenomenon was most pronounced at the highest stress levels and when the tensile and compressive stresses were completely reversed. In general, creep rates were found to be lower in compression than in tension for equal true stresses. The differences, however, were strongly material-dependent.

Cyclical subnormal separation in A-groups

International Nuclear Information System (INIS)

Makarfi, M.U.

1995-12-01

Three main results, concerning A-groups in respect of cyclical subnormal separation as defined in, are presented. It is shown in theorem A that any A-group that is generated by elements of prime order and satisfying the cyclical subnormal separation conditions is metabelian. The two other main results give necessary and sufficient conditions for A-groups, that are split extensions of certain abelian p-groups by a metabelian p'-group, to satisfy the cyclical subnormal separation condition. There is also a result which shows that A-groups with elementary abelian Sylow subgroups are cyclically separated as defined. (author). 7 refs

Characterization of cyclic deformation behaviour of tempered and quenched 42CrMoS4 at single step and variable amplitude loading

International Nuclear Information System (INIS)

Schelp, M.; Eifler, D.

2000-01-01

Cyclic single steps tests were performed on tempered and quenched specimens of the steel 42CrMoS4. Strain, temperature and electrical resistance measurements yielded an empirical prediction of fatigue life according to Coffin, Manson and Morrow. All measured values are based on physical processes and therefore show a strong interaction. A new testing procedure was developed permitting hysteresis measurements to be used for the characterization and description of fatigue behaviour under variable amplitude loading. The basic idea is to combine fatigue tests with any kind of load spectrum with single step tests. This offers the possibility to apply lifetime prediction methods normally used for single step tests for those with random or service loading. (orig.)

The effects of cyclic and dynamic loading on the fracture resistance of nuclear piping steels. Technical report, October 1992--April 1996

Energy Technology Data Exchange (ETDEWEB)

Rudland, D.L.; Brust, F.; Wilkowski, G.M.

1996-12-01

This report presents the results of the material property evaluation efforts performed within Task 3 of the IPIRG-2 Program. Several related investigations were conducted. (1) Quasi-static, cyclic-load compact tension specimen experiments were conducted using parameters similar to those used in IPIRG-1 experiments on 6-inch nominal diameter through-wall-cracked pipes. These experiments were conducted on a TP304 base metal, an A106 Grade B base metal, and their respective submerged-arc welds. The results showed that when using a constant cyclic displacement increment, the compact tension experiments could predict the through-wall-cracked pipe crack initiation toughness, but a different control procedure is needed to reproduce the pipe cyclic crack growth in the compact tension tests. (2) Analyses conducted showed that for 6-inch diameter pipe, the quasi-static, monotonic J-R curve can be used in making cyclic pipe moment predictions; however, sensitivity analyses suggest that the maximum moments decrease slightly from cyclic toughness degradation as the pipe diameter increases. (3) Dynamic stress-strain and compact tension tests were conducted to expand on the existing dynamic database. Results from dynamic moment predictions suggest that the dynamic compact tension J-R and the quasi-static stress-strain curves are the appropriate material properties to use in making dynamic pipe moment predictions.

The effects of cyclic and dynamic loading on the fracture resistance of nuclear piping steels. Technical report, October 1992--April 1996

International Nuclear Information System (INIS)

Rudland, D.L.; Brust, F.; Wilkowski, G.M.

1996-12-01

This report presents the results of the material property evaluation efforts performed within Task 3 of the IPIRG-2 Program. Several related investigations were conducted. (1) Quasi-static, cyclic-load compact tension specimen experiments were conducted using parameters similar to those used in IPIRG-1 experiments on 6-inch nominal diameter through-wall-cracked pipes. These experiments were conducted on a TP304 base metal, an A106 Grade B base metal, and their respective submerged-arc welds. The results showed that when using a constant cyclic displacement increment, the compact tension experiments could predict the through-wall-cracked pipe crack initiation toughness, but a different control procedure is needed to reproduce the pipe cyclic crack growth in the compact tension tests. (2) Analyses conducted showed that for 6-inch diameter pipe, the quasi-static, monotonic J-R curve can be used in making cyclic pipe moment predictions; however, sensitivity analyses suggest that the maximum moments decrease slightly from cyclic toughness degradation as the pipe diameter increases. (3) Dynamic stress-strain and compact tension tests were conducted to expand on the existing dynamic database. Results from dynamic moment predictions suggest that the dynamic compact tension J-R and the quasi-static stress-strain curves are the appropriate material properties to use in making dynamic pipe moment predictions

Influences of cyclic deformation on creep property and creep-fatigue life prediction considering them

International Nuclear Information System (INIS)

Takahashi, Yukio

2009-01-01

Evaluation of creep-fatigue is essential in design and life management of high-temperature components in power generation plants. Cyclic deformation may alter creep property of the materials and its consideration may improve predictability of creep-fatigue failure life. To understand them, creep tests were conducted for the materials subjected to cyclic loading and their creep rupture and deformation behaviors were compared with those of as-received materials. Both 316FR and modified 9Cr-1Mo steel were tested. (1) Creep rupture time and elongation generally tend to decrease with cyclic loading in both materials, and especially elongation of 316FR drastically decreases by being cyclically deformed. (2) Amount of primary creep deformation decreases by cyclic loading and the ways to improve its predictability were developed. (3) Use of creep rupture ductility after cyclic deformation, instead of that of as-received material, brought about clear improvement of life prediction in a modified ductility exhaustion approach. (author)

Investigations On Crack Propagation Under Cyclical Isothermal And Thermo-mechanical Loadings For A Type 304-L Stainless Steel Used For Pressurized Water Reactor

Directory of Open Access Journals (Sweden)

Gourdin Cédric

2018-01-01

Full Text Available The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, the RSE-M Code introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in loadcontrolled conditions. To this end, a device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the thermal cycle, a high frequency induction coil heats the external wall of the tube. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load. Tests have been carried out, and these tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M Code for a significant plasticity.

Cyclic Mechanical Loading Is Essential for Rac1-Mediated Elongation and Remodeling of the Embryonic Mitral Valve.

Science.gov (United States)

Gould, Russell A; Yalcin, Huseyin C; MacKay, Joanna L; Sauls, Kimberly; Norris, Russell; Kumar, Sanjay; Butcher, Jonathan T

2016-01-11

During valvulogenesis, globular endocardial cushions elongate and remodel into highly organized thin fibrous leaflets. Proper regulation of this dynamic process is essential to maintain unidirectional blood flow as the embryonic heart matures. In this study, we tested how mechanosensitive small GTPases, RhoA and Rac1, coordinate atrioventricular valve (AV) differentiation and morphogenesis. RhoA activity and its regulated GTPase-activating protein FilGAP are elevated during early cushion formation but decreased considerably during valve remodeling. In contrast, Rac1 activity was nearly absent in the early cushions but increased substantially as the valve matured. Using gain- and loss-of-function assays, we determined that the RhoA pathway was essential for the contractile myofibroblastic phenotype present in early cushion formation but was surprisingly insufficient to drive matrix compaction during valve maturation. The Rac1 pathway was necessary to induce matrix compaction in vitro through increased cell adhesion, elongation, and stress fiber alignment. Facilitating this process, we found that acute cyclic stretch was a potent activator of RhoA and subsequently downregulated Rac1 activity via FilGAP. On the other hand, chronic cyclic stretch reduced active RhoA and downstream FilGAP, which enabled Rac1 activation. Finally, we used partial atrial ligation experiments to confirm in vivo that altered cyclic mechanical loading augmented or restricted cushion elongation and thinning, directly through potentiation of active Rac1 and active RhoA, respectively. Together, these results demonstrate that cyclic mechanical signaling coordinates the RhoA to Rac1 signaling transition essential for proper embryonic mitral valve remodeling. Copyright © 2016 Elsevier Ltd. All rights reserved.

Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading

Science.gov (United States)

Howser, R. N.; Dhonde, H. B.; Mo, Y. L.

2011-08-01

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity.

Acoustic Emission Assessment of Impending Fracture in a Cyclically Loading Structural Steel

Directory of Open Access Journals (Sweden)

Igor Rastegaev

2016-11-01

Full Text Available Using the advanced acoustic emission (AE technique, we address the problem of early identification of crack initiation and growth in ductile structural steels under cyclic loading. The notched 9MnSi5 steel specimens with weld joints were fatigue tested at room and lower temperatures with concurrent AE measurements. Detection of AE in ductile materials where fatigue crack initiation and propagation is mediated by local dislocation behavior ahead of the notch or crack tip is challenging because of an extremely low amplitude of the AE signal. With account of this issue, two new practically oriented criteria for recognition of different stages of fatigue are proposed on the basis of AE data: (1 a power spectrum-based criterion and (2 a pattern recognition-based criterion utilizing modern clustering algorithms. The applicability of both criteria is verified using obtained AE data. A good correspondence between AE outcomes and experimental observations of the fatigue behavior was obtained and is discussed.

Self-sensing of carbon nanofiber concrete columns subjected to reversed cyclic loading

International Nuclear Information System (INIS)

Howser, R N; Dhonde, H B; Mo, Y L

2011-01-01

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution for preventing such occurrences is the use of structural health monitoring (SHM) technology for concrete structures containing carbon nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of nanocracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain, which can be well utilized for SHM. A series of reinforced concrete (RC) columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity

Evolutive masing model, cyclic plasticity, ageing and memory effects

International Nuclear Information System (INIS)

Sidoroff, F.

1987-01-01

Many models are proposed for the mechanical description of the cyclic behaviour of metals and used for structure analysis under cyclic loading. Such a model must include two basic features: Dissipative behaviour on each cycle (hysteresis loop); evolution of this behaviour during the material's life (cyclic hardening or softening, aging,...). However, if both aspects are present in most existing models, the balance between them may be quite different. Many metallurgical investigations have been performed about the microstructure and its evolution during cyclic loading, and it is desirable to introduce these informations in phenomenological models. The evolutive Masing model has been proposed to combine: the accuracy of hereditary models for the description of hysteresis on each cycle, the versatility of internal variables for the state description and evolution, a sufficient microstructural basis to make the interaction easier with microstructural investigations. The purpose of the present work is to discuss this model and to compare different evolution assumptions with respect to some memory effects (cyclic hardening and softening, multilevel tests, aging). Attention is limited to uniaxial, rate independent elasto-plastic behaviour

Influence of overelastic loading on the stress intensity factor under thermal fatigue conditions

International Nuclear Information System (INIS)

Stamm, H.; Munz, D.

1983-10-01

Thermal shock loading often creates high thermal stresses which may exceed yield strength of the material in a surface layer. In this report the application of the linear elastic ΔK-concept in the case of cyclic thermal loading within the shakedown region is discussed. To this K-factors for an edge crack in a linear elastic - perfectly plastic plate are calculated using the weight function method and are compared with results obtained with the Finite Element Method. It is shown, that rearrangement stresses during plastic flow in the first cycle must be taken into account developing conservative approximation procedures. (orig.) [de

A Novel Repair Method for Radial Tears of the Medial Meniscus: Biomechanical Comparison of Transtibial 2-Tunnel and Double Horizontal Mattress Suture Techniques Under Cyclic Loading.

Science.gov (United States)

Bhatia, Sanjeev; Civitarese, David M; Turnbull, Travis Lee; LaPrade, Christopher M; Nitri, Marco; Wijdicks, Coen A; LaPrade, Robert F

2016-03-01

Complete radial tears of the medial meniscus have been reported to be functionally similar to a total meniscectomy. At present, there is no consensus on an ideal technique for repair of radial midbody tears of the medial meniscus. Prior attempts at repair with double horizontal mattress suture techniques have led to a reportedly high rate of incomplete healing or healing in a nonanatomic (gapped) position, which compromises the ability of the meniscus to withstand hoop stresses. A newly proposed 2-tunnel radial meniscal repair method will result in decreased gapping and increased ultimate failure loads compared with the double horizontal mattress suture repair technique under cyclic loading. Controlled laboratory study. Ten matched pairs of male human cadaveric knees (average age, 58.6 years; range, 48-66 years) were used. A complete radial medial meniscal tear was made at the junction of the posterior one-third and middle third of the meniscus. One knee underwent a horizontal mattress inside-out repair, while the contralateral knee underwent a radial meniscal repair entailing the same technique with a concurrent novel 2-tunnel repair. Specimens were potted and mounted on a universal testing machine. Each specimen was cyclically loaded 1000 times with loads between 5 and 20 N before experiencing a load to failure. Gap distances at the tear site and failure load were measured. The 2-tunnel repairs exhibited a significantly stronger ultimate failure load (median, 196 N; range, 163-212 N) than did the double horizontal mattress suture repairs (median, 106 N; range, 63-229 N) (P = .004). In addition, the 2-tunnel repairs demonstrated decreased gapping at all testing states (P meniscus significantly decrease the ability of the meniscus to dissipate tibiofemoral loads, predisposing patients to early osteoarthritis. Improving the ability to repair medial meniscal radial tears in a way that withstands cyclic loads and heals in an anatomic position could significantly

First wall and blanket stresses induced by cyclic fusion core operations

International Nuclear Information System (INIS)

Bohachevsky, I.O.; Kostoff, R.N.

1981-01-01

An analysis is made of cyclic thermal loads and stresses for the complete range of operating conditions. Two critical components were examined; the solid wall adjacent to the fusion plasma (first wall) and the fuel elements in the high power density region of the blanket. Simple closed form expressions were derived for temperature increases and thermal stresses that may be evaluated conveniently and rapidly and the values compared for different systems

The Investigation of Knitted Materials Bonded Seams Behaviour upon Cyclical Fatigue Loading

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Gita BUSILIENĖ

2017-08-01

Full Text Available In this research uniaxial tension behaviour of PES knitted materials with bonded seams is analysed. The objects of the investigation were two types of knitted materials, having the same fibre composition (93 % PES, 7 % EL, but different in knitting pattern, i. e. plain single jersey and rib 1 × 1. Bonded overlap seams were formed by changing the orientation of knitted materials strips, i. e. parallel/parallel, parallel/bias, parallel/perpendicular, bias/bias and bias/perpendicular. The strips of each knitted material were joined by two types of thermoplastic polyurethane (PU films different in thickness (75 mm and 150 mm. Mechanical characteristics of bonded seams were defined in longitudinal direction. During uniaxial tension such parameters as maximal force Fmax (N and maximal elongation ɛmax (% were recorded from typical tension diagrams. The changes of tested specimens strength and deformation were compared before and after cyclical fatigue tension the conditions of which were 50 cycles up to tension force F equal 24.5 N. The results have shown that changes before and after cyclical fatigue tension are mostly determined by the structure of knitted materials, the orientation of knitted materials strips in bonded seam, but not effected by thermoplastic polyurethane film. These results are opposite compared to the results of biaxial tension of the same type of specimens, which have shown that changes before and after cyclical fatigue punching are mostly determined by the type of thermoplastic film, but not effected by the orientation of knitted materials strips in bonded seams. DOI: http://dx.doi.org/10.5755/j01.ms.23.2.16065

A new pressure chamber to study the biosynthetic response of articular cartilage to mechanical loading.

Science.gov (United States)

Steinmeyer, J; Torzilli, P A; Burton-Wurster, N; Lust, G

1993-01-01

A prototype chamber was used to apply a precise cyclic or static load on articular cartilage explants under sterile conditions. A variable pressure, pneumatic controller was constructed to power the chamber's air cylinder, capable of applying, with a porous load platen, loads of up to 10 MPa at cycles ranging from 0 to 10 Hz. Pig articular cartilage explants were maintained successfully in this chamber for 2 days under cyclic mechanical loading of 0.5 Hz, 0.5 MPa. Explants remained sterile, viable and metabolically active. Cartilage responded to this load with a decreased synthesis of fibronectin and a small but statistically significant elevation in proteoglycan content. Similar but less extensive effects on fibronectin synthesis were observed with the small static load (0.016 MPa) inherent in the design of the chamber.

Dynamic Aftershock Triggering Correlated with Cyclic Loading in the Slip Direction

Science.gov (United States)

Hardebeck, J.

2014-12-01

Dynamic stress changes have been shown to contribute to aftershock triggering, but the physical triggering mechanisms are not fully understood. Some proposed mechanisms are based on dynamic stress loading of the target fault in a direction that encourages earthquake slip (e.g. dynamic Coulomb stress triggering), while other mechanisms are based on fault weakening due to shaking. If dynamic stress loading in the fault slip direction plays a role in aftershock triggering, we would expect to see a relationship between the dynamic stress orientations and the aftershock focal mechanisms. Alternatively, if dynamic stress change triggering functions only through a fault weakening mechanism that is independent of the slip direction of the target fault, no such relationship is expected. I study aftershock sequences of 4 M≥6.7 mainshocks in southern California, and find a small but significant relationship between modeled dynamic stress direction and aftershock focal mechanisms. The mainshock dynamic stress changes have two observed impacts: changing the focal mechanisms in a given location to favor those aligned with the dynamic stress change, and changing the spatial distribution of seismicity to favor locations where the dynamic stress change aligns with the background stress. The aftershock focal mechanisms are significantly more aligned with the dynamic stress changes than the preshock mechanisms for only the first 0.5-1 year following most mainshocks, although for at least 10 years following Hector Mine. Dynamic stress effects on focal mechanisms are best observed at long periods (30-60 sec). Dynamic stress effects are only observed when using metrics based on repeated stress cycling in the same direction, for example considering the dominant stress orientation over the full time series, and not for the peak dynamic stress. These results imply that dynamic aftershock triggering operates at least in part through cyclic loading in the direction of fault slip, although

Cyclic Testing of the 6-Strand Tang and Modified Lim-Tsai Flexor Tendon Repair Techniques.

Science.gov (United States)

Kang, Gavrielle Hui-Ying; Wong, Yoke-Rung; Lim, Rebecca Qian-Ru; Loke, Austin Mun-Kitt; Tay, Shian-Chao

2018-03-01

In this study, we compared the Tang repair technique with the 6-strand modified Lim-Tsai repair technique under cyclic testing conditions. Twenty fresh-frozen porcine flexor tendons were randomized into 2 groups for repair with either the modified Lim-Tsai or the Tang technique using Supramid 4-0 core sutures and Ethilon 6-0 epitendinous running suture. The repaired tendons were subjected to 2 stage cyclic loading. The survival rate and gap formation at the repair site were recorded. Tendons repaired by the Tang technique achieved an 80% survival rate. None of the modified Lim-Tsai repairs survived. The mean gap formed at the end of 1000 cycles was 1.09 mm in the Tang repairs compared with 4.15 mm in the modified Lim-Tsai repairs. The Tang repair is biomechanically stronger than the modified Lim-Tsai repair under cyclic loading. The Tang repair technique may exhibit a higher tolerance for active mobilization after surgery with less propensity for gap formation. Copyright © 2018 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Cyclic deformation behaviour of quenched and tempered 42CrMo4 (AISI 4140) at two-block push-pull-loading; Zum Wechselverformungsverhalten von verguetetem 42CrMo4 bei zweistufiger Zug-Druck-Beanspruchung

Energy Technology Data Exchange (ETDEWEB)

Schulze, V. [Karlsruhe Univ. (T.H.) (Germany). Inst. fuer Werkstoffkunde 1; Lang, K.-H.; Voehringer, O.; Macherauch, E.

1998-11-01

The behaviour of steels in the course of two- and multi-block cyclic loading has been investigated up to now almost exclusively regarding the fatigue life. According to this, only a few papers exist, dealing with the cyclic deformation behaviour at two- and multi-block-push-pull-loading. Therefore, in stress- and total strain-controlled experiments with a single change of the amplitude (two-block-experiments) and multiple changes between two blocks of different lengths and amplitudes (multi-block-experiments) the cyclic deformation processes have been investigated for the quenched and tempered steel grade 42 CrMo 4 (equivalent to AISI 4140). Using the data of stress- and strain-Woehler-curves determined in usual fatigue tests, damages defined according to Miner`s rule were adjoined to the blocks. The Miner-damages at failure observed in the two-block-experiments with changes from high to low amplitudes were smaller than one and at inverse changes of amplitudes larger than one. In contrast to this, in multi-block-experiments no universally valid correlations were observed between the Miner-damages at failure and the test-parameters applied. At all tests cyclic work-softening was observed as in single-step-experiments. However, work-softening processes at high amplitude loadings yield to much larger plastic strain amplitudes after changing to smaller amplitudes than in single-step tests. Contrarily, in multi-block-tests work-softening at higher amplitude loadings reduces with decreasing block-length and increasing portion of the blocks with the smaller amplitude. This is attributed to effects of static strain-ageing. Total-strain-controlled two-block cyclic deformation experiments yield to similar effects as in stress-controlled tests. 18 refs.

Effect of rock joint roughness on its cyclic shear behavior

Directory of Open Access Journals (Sweden)

S.M. Mahdi Niktabar

2017-12-01

Full Text Available Rock joints are often subjected to dynamic loads induced by earthquake and blasting during mining and rock cutting. Hence, cyclic shear load can be induced along the joints and it is important to evaluate the shear behavior of rock joint under this condition. In the present study, synthetic rock joints were prepared with plaster of Paris (PoP. Regular joints were simulated by keeping regular asperity with asperity angles of 15°–15° and 30°–30°, and irregular rock joints which are closer to natural joints were replicated by keeping the asperity angles of 15°–30° and 15°–45°. The sample size and amplitude of roughness were kept the same for both regular and irregular joints which were 298 mm × 298 mm × 125 mm and 5 mm, respectively. Shear test was performed on these joints using a large-scale direct shear testing machine by keeping the frequency and amplitude of shear load under constant cyclic condition with different normal stress values. As expected, the shear strength of rock joints increased with the increases in the asperity angle and normal load during the first cycle of shearing or static load. With the increase of the number of shear cycles, the shear strength decreased for all the asperity angles but the rate of reduction was more in case of high asperity angles. Test results indicated that shear strength of irregular joints was higher than that of regular joints at different cycles of shearing at low normal stress. Shearing and degradation of joint asperities on regular joints were the same between loading and unloading, but different for irregular joints. Shear strength and joint degradation were more significant on the slope of asperity with higher angles on the irregular joint until two angles of asperities became equal during the cycle of shearing and it started behaving like regular joints for subsequent cycles.

Increase of cyclic durability of pressure vessels

International Nuclear Information System (INIS)

Vorona, V.A.; Zvezdin, Yu.I.

1980-01-01

The durability of multilayer pressure vessels under cyclic loading is compared with single-layer vessels. The relative conditional durability is calculated taking into account the assumption on the consequent destruction of layers and viewing a vessel wall as an indefinite plate. It is established that the durability is mainly determined by the number of layers and to a lesser degree depends on the relative size of the defect for the given layer thickness. The advantage of the multilayer vessels is the possibility of selecting layer materials so that to exclude the effect of agressive corrosion media on the strength [ru

In vivo cyclic loading as a potent stimulatory signal for bone formation inside tissue engineering scaffold

Directory of Open Access Journals (Sweden)

A Roshan-Ghias

2010-02-01

Full Text Available In clinical situations, bone defects are often located at load bearing sites. Tissue engineering scaffolds are future bone substitutes and hence they will be subjected to mechanical stimulation. The goal of this study was to test if cyclic loading can be used as stimulatory signal for bone formation in a bone scaffold. Poly(L-lactic acid (PLA/ 5% beta-tricalcium phosphate (beta-TCP scaffolds were implanted in both distal femoral epiphyses of eight rats. Right knees were stimulated (10N, 4Hz, 5 min five times, every two days, starting from the third day after surgery while left knees served as control. Finite element study of the in vivo model showed that the strain applied to the scaffold is similar to physiological strains. Using micro-computed tomography (CT, all knees were scanned five times after the surgery and the related bone parameters of the newly formed bone were quantified. Statistical modeling was used to estimate the evolution of these parameters as a function of time and loading. The results showed that mechanical stimulation had two effects on bone volume (BV: an initial decrease in BV at week 2, and a long-term increase in the rate of bone formation by 28%. At week 13, the BV was then significantly higher in the loaded scaffolds.

Fuel cladding behavior under rapid loading conditions

Science.gov (United States)

Yueh, K.; Karlsson, J.; Stjärnsäter, J.; Schrire, D.; Ledergerber, G.; Munoz-Reja, C.; Hallstadius, L.

2016-02-01

A modified burst test (MBT) was used in an extensive test program to characterize fuel cladding failure behavior under rapid loading conditions. The MBT differs from a normal burst test with the use of a driver tube to simulate the expansion of a fuel pellet, thereby producing a partial strain driven deformation condition similar to that of a fuel pellet expansion in a reactivity insertion accident (RIA). A piston/cylinder assembly was used to pressurize the driver tube. By controlling the speed and distance the piston travels the loading rate and degree of sample deformation could be controlled. The use of a driver tube with a machined gauge section localizes deformation and allows for continuous monitoring of the test sample diameter change at the location of maximum hoop strain, during each test. Cladding samples from five irradiated fuel rods were tested between 296 and 553 K and loading rates from 1.5 to 3.5/s. The test rods included variations of Zircaloy-2 with different liners and ZIRLO, ranging in burn-up from 41 to 74 GWd/MTU. The test results show cladding ductility is strongly temperature and loading rate dependent. Zircaloy-2 cladding ductility degradation due to operational hydrogen pickup started to recover at approximately 358 K for test condition used in the study. This recovery temperature is strongly loading rate dependent. At 373 K, ductility recovery was small for loading rates less than 8 ms equivalent RIA pulse width, but longer than 8 ms the ductility recovery increased exponentially with increasing pulse width, consistent with literature observations of loading rate dependent brittle-to-ductile (BTD) transition temperature. The cladding ductility was also observed to be strongly loading rate/pulse width dependent for BWR cladding below the BTD temperature and Pressurized Water Reactor (PWR) cladding at both 296 and 553 K.

Deformation Mechanisms of Offshore Monopile Foundations Accounting for Cyclic Mobility Effects

DEFF Research Database (Denmark)

Barari, Amin; Bagheri, Mohsen; Rouainia, Mohamed

2017-01-01

Highlights •There has been a huge surge in the construction of marine facilities (e.g., wind turbines) in Europe. •This paper presents some new frameworks for design strategy based on performance measures for cyclic horizontally loaded monopile foundations. •A three-dimensional finite element model...... was developed to investigate the behavior of large-diameter piles. •This model accounts for nonlinear dynamic interactions in offshore platforms under harsh combined moment and horizontal environmental loads. •Magnitude of cyclic loads was found to cause a linear increase in the accumulated rotation....

Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

Science.gov (United States)

Ritchie, R O; Dauskardt, R H; Yu, W K; Brendzel, A M

1990-02-01

Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

A simplified technique for shakedown load determination

International Nuclear Information System (INIS)

Abdalla, H.F.; Younan, M.Y.A.; Megahed, M.M.

2005-01-01

In this paper a simple technique is presented to determine the limit shakedown load of a structure or a component using the finite element method. Through the proposed technique, the limit shakedown load is determined without performing time consuming cyclic loading simulations or iterative elastic techniques. Instead, it is determined by performing only two analyses namely, an elastic analysis and an elastic-plastic analysis. By extracting the results of the two analyses, the limit shakedown load of the structure is determined through the calculation of the residual stresses. The technique is applied and verified using two bench mark shakedown problems namely: the two-bar structure subjected to constant axial force and cyclic thermal loading, and the Bree cylinder subjected to constant internal pressure and cyclic high heat fluxes across its wall. The results of the proposed technique showed very good correlation with the, analytically determined, Bree diagrams of both structures. Moreover, the outcomes of the proposed technique showed very good results in comparison to full cyclic loading elasto-plastic finite element simulations of both structures. (authors)

Crack growth prediction method considering interaction between multiple cracks. Growth of surface cracks of dissimilar size under cyclic tensile and bending load

International Nuclear Information System (INIS)

Kamaya, Masayuki; Miyokawa, Eiichi; Kikuchi, Masanori

2011-01-01

When multiple cracks approach one another, the stress intensity factor is likely to change due to the interaction of the stress field. This causes change in growth rate and shape of cracks. In particular, when cracks are in parallel position to the loading direction, the shape of cracks becomes non-planar. In this study, the complex growth of interacting cracks is evaluated by using the S-Version finite element method, in which local detailed finite element mesh (local mesh) is superposed on coarse finite element model (global mesh) representing the global structure. In order to investigate the effect of interaction on the growth behavior, two parallel surface cracks are subjected to cyclic tensile or bending load. It is shown that the smaller crack is shielded by larger crack due to the interaction and stops growing when the difference in size of two cracks is significant. Based on simulations of various conditions, a procedure and criteria for evaluating crack growth for fitness-for-service assessment is proposed. According to the procedure, the interaction is not necessary to be considered in the crack growth prediction when the difference in size of two cracks exceeds the criterion. (author)

anisotropic crack modelling of reinforced concrete structures with an enhanced kinematics: application to bidimensional elements under cyclic loading

International Nuclear Information System (INIS)

Kishta, Ejona

2016-01-01

Civil engineering buildings, massive and unique, are mostly made of reinforced or prestressed concrete. Sustainability, tightness and safety are the major pillars of a building's performance. Cracking is a major phenomenon which impacts the buildings' behaviour under different loadings in terms of sustainability and structural capacity. Development of numerical models which describe accurately the response of quasi-brittle materials under complex loading remains an important research topic for the scientific community. The objective of this work is the development of a numerical model which represents explicitly cracking of reinforced concrete structures. Concrete and reinforced concrete degradation process, characterised by the appearance of several anisotropic crack families, is described by means of an anisotropic damage model accounting for oriented crack families. The kinematics of this model is enriched with a displacement jump in order to reproduce the development of cracks in the material during loading. This displacement jump is identified as the crack opening. The developed model is validated on simulations of plain concrete structures exhibiting model as well as mixed-mode failure. The performances of the enriched model are shown by the simulation of reinforced concrete structures such as a shear wall submitted to cyclic loading. (author) [fr

Experimental study under uniaxial cyclic behavior at room and high temperature of 316L stainless steel

International Nuclear Information System (INIS)

Kang Guozheng; Gao Qing; Yang Xianjie; Sun Yafang

2001-01-01

An experimental study was carried out of the cyclic properties of 316L stainless steel subjected to uniaxial strain and stress at room and high temperature. The effects of cyclic strain amplitude, temperature and their histories on the cyclic deformation behavior of 316L stainless steel are investigated. And, the influences of stress amplitude, mean stress, temperature and their histories on ratcheting are also analyzed. It is shown that either uniaxial cyclic property under cyclic strain or ratcheting under asymmetric uniaxial cyclic stress depends not only on the current temperature and loading state, but also on the previous temperature and loading history. Some significant results are obtained

Three-dimensional stress and strain around real shape Si particles in cast aluminum alloy under cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Teranishi, Masaki [Department of Nuclear Power & Energy Safety Engineering, University of Fukui (Japan); Kuwazuru, Osamu, E-mail: kuwa@u-fukui.ac.jp [Department of Nuclear Power & Energy Safety Engineering, University of Fukui (Japan); Gennai, Shota [Department of Nuclear Power & Energy Safety Engineering, University of Fukui (Japan); Kobayashi, Masakazu [Department of Mechanical Engineering, Toyohashi University of Technology (Japan); Toda, Hiroyuki [Department of Mechanical Engineering, Kyushu University (Japan)

2016-12-15

The crack initiation mechanism of cast Al-Si-Mg alloy under low-cycle fatigue was addressed by using the synchrotron X-ray computed tomography (CT) and the image-based finite element analysis. The fatigue test and its in situ CT observation were conducted to visualize the crack initiation behavior. In the low-cycle fatigue, the cracking generally started with the voiding by the fracture of silicon particles, and the coalescence of these voids formed the crack. To elucidate the mechanism of silicon particle fracture, the finite element elastic-plastic analyses were performed with regard to twelve silicon particles including the fractured and intact particles detected by the chronological CT observation. By using the image-based modeling technique, the interested particle was embedded in the finite element model along with the surrounding particles as they were in the specimen. The material properties of silicon phase and aluminum matrix were identified by the nanoindentation tests. Ten cycles of loading by the uniform stress which was equivalent to the load in the fatigue test was applied to the finite element model, and the stress, strain and their cyclic response around the silicon particles were simulated. The morphology analysis was also carried out for the interested particles, and the geometrical parameters affecting the particle fracture were examined. By comparing the results of fractured and intact particles, we found that there were some geometrical conditions for the fracture of silicon particles, and a certain magnitude of hydrostatic stress was required to break the particles.

Steel plates and concrete filled composite shear walls related nuclear structural engineering: Experimental study for out-of-plane cyclic loading

International Nuclear Information System (INIS)

Li, Xiaohu; Li, Xiaojun

2017-01-01

Based on the program of CAP1400 nuclear structural engineering, the out-of-plane seismic behavior of steel plate and concrete infill composite shear walls (SCW) was investigated. 6 1/5 scaled specimens were conducted which consist of 5 SCW specimens and 1 reinforced concrete (RC) specimen. The specimens were tested under out-of-plane cyclic loading. The effect of the thickness of steel plate, vertical load and the strength grade of concrete on the out-of-plane seismic behavior of SCW were analyzed. The results show that the thickness of steel plate and vertical load have great influence on the ultimate bearing capacity and lateral stiffness, however, the influence of the strength grade of concrete was little within a certain range. SCW is presented to have a better ultimate capacity and lateral stiffness but have worse ductility in failure stage than that of RC. Based on the experiment, the cracking load of concrete infill SCW was analyzed in theory. The modified calculation formula of the cracking load was made, the calculated results showed good agreement with the test results. The formula can be used as the practical design for the design of cracking loads.

Steel plates and concrete filled composite shear walls related nuclear structural engineering: Experimental study for out-of-plane cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Li, Xiaohu [The College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124 (China); Li, Xiaojun, E-mail: beerli@vip.sina.com [The College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124 (China); Institute of Geophysics, China Earthquake Administration, Beijing 100081 (China)

2017-04-15

Based on the program of CAP1400 nuclear structural engineering, the out-of-plane seismic behavior of steel plate and concrete infill composite shear walls (SCW) was investigated. 6 1/5 scaled specimens were conducted which consist of 5 SCW specimens and 1 reinforced concrete (RC) specimen. The specimens were tested under out-of-plane cyclic loading. The effect of the thickness of steel plate, vertical load and the strength grade of concrete on the out-of-plane seismic behavior of SCW were analyzed. The results show that the thickness of steel plate and vertical load have great influence on the ultimate bearing capacity and lateral stiffness, however, the influence of the strength grade of concrete was little within a certain range. SCW is presented to have a better ultimate capacity and lateral stiffness but have worse ductility in failure stage than that of RC. Based on the experiment, the cracking load of concrete infill SCW was analyzed in theory. The modified calculation formula of the cracking load was made, the calculated results showed good agreement with the test results. The formula can be used as the practical design for the design of cracking loads.

Mechanical Behavior of AZ31B Mg Alloy Sheets under Monotonic and Cyclic Loadings at Room and Moderately Elevated Temperatures

Directory of Open Access Journals (Sweden)

Ngoc-Trung Nguyen

2014-02-01

Full Text Available Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally.

Cyclic AMP in rat pancreatic islets

International Nuclear Information System (INIS)

Grill, V.; Borglund, E.; Cerasi, E.; Uppsala Univ.

1977-01-01

The incorporation of [ 3 H]adenine into cyclic AMP was studied in rat pancreatic islets under varying conditions of labeling. Prolonging the exposure to [ 3 H]adenine progressively augmented the islet cyclic [ 3 H]AMP level. Islets labeled for different periods of time and subsequently incubated (without adenine) in the presence of D-glucose or cholera toxin showed stimulations of intra-islet cyclic [ 3 H]AMP that were proportionate to the levels of radioactive nucleotide present under non-stimulatory conditions. Labeling the islets in a high glucose concentration (27.7 mM) did not modify the nucleotide responses to glucose or cholera toxin. The specific activity of cyclic [ 3 H]AMP, determined by simultaneous assay of cyclic [ 3 H]AMP and total cyclic AMP, was not influenced by glucose or cholera toxin. Glucose had no effect on the specific activity of labeled ATP

Effect of cyclic plastic pre-strain on low cycle fatigue life

International Nuclear Information System (INIS)

Kanno, Satoshi; Nakane, Motoki; Yorikawa, Morio; Takagi, Yoshio

2010-01-01

In order to evaluate structural integrity of nuclear components subjected large seismic load which produce locally plastic strain, low cycle fatigue life was examined using cyclic plastic pre-strained materials of austenitic steel (SUS316, SUS316L, SUS304TP: JIS (Japanese Industrial Standards)) and ferritic steel (SFVQ1A, STS480, STPT410, SFVC2B, SS400: JIS). It was not found that cyclic plastic pre-strain up to range of 16%, 2.5 times affected on low cycle fatigue life. The validity of existing procedure of fatigue life estimation based on usage factor was confirmed when large seismic load brought nuclear materials cyclic plastic strain. (author)

A proposal for evaluation method of crack growth due to cyclic overload for piping materials based on an elastic-plastic fracture mechanics parameter

International Nuclear Information System (INIS)

Yamaguchi, Yoshihito; Katsuyama, Jinya; Onizawa, Kunio; Li, Yinsheng; Sugino, Hideharu

2011-01-01

The magnitude of Niigata-ken Chuetsu-Oki earthquake in 2007 was beyond the assumed one provided in seismic design. Therefore it becomes an important issue to evaluate the crack growth behaviors due to the cyclic overload like large earthquake. Fatigue crack growth is usually evaluated by Paris's law using the range of stress intensity factor (ΔK). However, ΔK is inappropriate in a loading condition beyond small scale yielding. In this study, the crack growth behaviors for piping materials were investigated based on an elastic-plastic fracture mechanics parameter, J-integral. It was indicated that the crack growth due to the cyclic overload beyond small scale yielding could be the sum of fatigue and ductile crack growth. The retardation effect of excessive loading on the crack growth was observed after the loading. The modified Wheeler model using J-integral has been proposed for the prediction of retardation effect. Finally, an evaluation method for crack growth behaviors due to the cyclic overload is suggested. (author)

Pedicle screw anchorage of carbon fiber-reinforced PEEK screws under cyclic loading.

Science.gov (United States)

Lindtner, Richard A; Schmid, Rene; Nydegger, Thomas; Konschake, Marko; Schmoelz, Werner

2018-03-01

Pedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws. In the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm 3  ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm 3  ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from - 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion ("screw toggling") within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles. The nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard

A simplified technique for shakedown limit load determination

International Nuclear Information System (INIS)

Abdalla, Hany F.; Megahed, Mohammad M.; Younan, Maher Y.A.

2007-01-01

In this paper, a simplified technique is presented to determine the shakedown limit load of a structure using the finite element method. The simplified technique determines the shakedown limit load without performing lengthy time consuming full elastic-plastic cyclic loading simulations or conventional iterative elastic techniques. Instead, the shakedown limit load is determined by performing two analyses namely: an elastic analysis and an elastic-plastic analysis. By extracting the results of the two analyses, the shakedown limit load is determined through the calculation of the residual stresses developed within the structure. The simplified technique is applied and verified using two bench mark shakedown problems namely: the two-bar structure subjected to constant axial force and cyclic thermal loading, and the Bree cylinder subjected to constant internal pressure and cyclic high temperature variation across its wall. The results of the simplified technique showed very good correlation with the, analytically determined, Bree diagrams of both structures. In order to gain confidence in the simplified technique, the shakedown limit loads output by the simplified technique are used to perform full elastic-plastic cyclic loading simulations to check for shakedown behavior of both structures

Occlusal loading and cross-linking effects on dentin collagen degradation in physiological conditions.

Science.gov (United States)

Turco, Gianluca; Frassetto, Andrea; Fontanive, Luca; Mazzoni, Annalisa; Cadenaro, Milena; Di Lenarda, Roberto; Tay, Franklin R; Pashley, David H; Breschi, Lorenzo

2016-02-01

This study evaluated the ability of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) to improve the stability of demineralized dentin collagen matrices when subjected to mechanical cycling by means of Chewing Simulation (CS). Demineralized dentin disks were randomly assigned to four groups (N=4): (1) immersion in artificial saliva at 37°C for 30 days; (2) pre-treatment with 0.5 M EDC for 60 s, then stored as in Group 1; (3) CS challenge (50 N occlusal load, 30 s occlusal time plus 30 s with no load, for 30 days); (4) pre-treatment with 0.5 M EDC as in Group 2 and CS challenge as in Group 3. Collagen degradation was evaluated by sampling storage media for ICTP and CTX telopeptides. EDC treated specimens showed no significant telopeptides release, irrespective of the aging method. Cyclic stressing of EDC-untreated specimens caused significantly higher ICTP release at day 1, compared to static storage, while by days 3 and 4, the ICTP release in the cyclic group fell significantly below the static group, and then remained undetectable from 5 to 30 days. CTX release in the cyclic groups, on EDC-untreated control specimens was always lower than in the static group in days 1-4, and then fell to undetectable for 30 days. This study showed that chewing stresses applied to control untreated demineralized dentin increased degradation of collagen in terms of CTX release, while collagen crosslinking agents may prevent dentin collagen degradation, irrespective of simulated occlusal function. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Anterior cement augmentation of adjacent levels after vertebral body replacement leads to superior stability of the corpectomy cage under cyclic loading-a biomechanical investigation.

Science.gov (United States)

Oberkircher, Ludwig; Krüger, Antonio; Hörth, Dominik; Hack, Juliana; Ruchholtz, Steffen; Fleege, Christoph; Rauschmann, Michael; Arabmotlagh, Mohammad

2018-03-01

In the operative treatment of osteoporotic vertebral body fractures, a dorsal stabilization in combination with a corpectomy of the fractured vertebral body might be necessary with respect to the fracture morphology, whereby the osteoporotic bone quality may possibly increase the risk of implant failure. To achieve better stability, it is recommended to use cement-augmented screws for dorsal instrumentation. Besides careful end plate preparation, cement augmentation of the adjacent end plates has also been reported to lead to less reduction loss. The aim of the study was to evaluate biomechanically under cyclic loading whether an additional cement augmentation of the adjacent end plates leads to improved stability of the inserted cage. Methodical cadaver study. Fourteen fresh frozen human thoracic spines with proven osteoporosis were used (T2-T7). After removal of the soft tissues, the spine was embedded in Technovit (Kulzer, Germany). Subsequently, a corpectomy of T5 was performed, leaving the dorsal ligamentary structures intact. After randomization with respect to bone quality, two groups were generated: Dorsal instrumentation (cemented pedicle screws, Medtronic, Minneapolis, MN, USA)+cage implantation (CAPRI Corpectomy Cage, K2M, Leesburg, VA, USA) without additional cementation of the adjacent endplates (Group A) and dorsal instrumentation+cage implantation with additional cement augmentation of the adjacent end plates (Group B). The subsequent axial and cyclic loading was performed at a frequency of 1 Hz, starting at 400 N and increasing the load within 200 N after every 500 cycles up to a maximum of 2,200 N. Load failure was determined when the cages sintered macroscopically into the end plates (implant failure) or when the maximum load was reached. One specimen in Group B could not be clamped appropriately into the test bench for axial loading because of a pronounced scoliotic misalignment and had to be excluded. The mean strength for implant

Experimental study on lateral strength of wall-slab joint subjected to lateral cyclic load

Science.gov (United States)

Masrom, Mohd Asha'ari; Mohamad, Mohd Elfie; Hamid, Nor Hayati Abdul; Yusuff, Amer

2017-10-01

Tunnel form building has been utilised in building construction since 1960 in Malaysia. This method of construction has been applied extensively in the construction of high rise residential house (multistory building) such as condominium and apartment. Most of the tunnel form buildings have been designed according to British standard (BS) whereby there is no provision for seismic loading. The high-rise tunnel form buildings are vulnerable to seismic loading. The connections between slab and shear walls in the tunnel-form building constitute an essential link in the lateral load resisting mechanism. Malaysia is undergoing a shifting process from BS code to Eurocode (EC) for building construction since the country has realised the safety threats of earthquake. Hence, this study is intended to compare the performance of the interior wall slab joint for a tunnel form structure designed based on Euro and British codes. The experiment included a full scale test of the wall slab joint sub-assemblages under reversible lateral cyclic loading. Two sub-assemblage specimens of the wall slab joint were designed and constructed based on both codes. Each specimen was tested using lateral displacement control (drift control). The specimen designed by using Eurocode was found could survive up to 3.0% drift while BS specimen could last to 1.5% drift. The analysis results indicated that the BS specimen was governed by brittle failure modes with Ductility Class Low (DCL) while the EC specimen behaved in a ductile manner with Ductility Class Medium (DCM). The low ductility recorded in BS specimen was resulted from insufficient reinforcement provided in the BS code specimen. Consequently, the BS specimen could not absorb energy efficiently (low energy dissipation) and further sustain under inelastic deformation.

Qualification and post-mortem characterization of tungsten mock-ups exposed to cyclic high heat flux loading

Energy Technology Data Exchange (ETDEWEB)

Pintsuk, G., E-mail: g.pintsuk@fz-juelich.de [Forschungszentrum Jülich GmbH, Euratom Association, D-52425 Jülich (Germany); Bobin-Vastra, I.; Constans, S. [AREVA NP PTCMI-F, Centre Technique, Fusion, F-71200 Le Creusot (France); Gavila, P. [Fusion for Energy, E-08019 Barcelona (Spain); Rödig, M. [Forschungszentrum Jülich GmbH, Euratom Association, D-52425 Jülich (Germany); Riccardi, B. [Fusion for Energy, E-08019 Barcelona (Spain)

2013-10-15

Highlights: • We characterize tungsten mono-block components after exposure to ITER relevant heat loads. • We qualify the manufacturing technology, i.e., hot isostatic pressing and hot radial pressing, and repair technologies. • We determine the microstructural influences, i.e., rod vs. plate material, on the damage evolution. • Needle like microstructures increase the risk of deep crack formation due to a limited fracture strength. -- Abstract: In order to evaluate the option to start the ITER operation with a full tungsten (W) divertor, high heat flux tests were performed in the electron beam facility FE200, Le Creusot, France. Thereby, in total eight small-scale and three medium-scale monoblock mock-ups produced with different manufacturing technologies and different tungsten grades were exposed to cyclic steady state heat loads. The applied power density ranges from 10 to 20 MW/m{sup 2} with a maximum of 1000 cycles at each particular loading step. Finally, on a reduced number of tiles, critical heat flux tests in the range of 30 MW/m{sup 2} were performed. Besides macroscopic and microscopic images of the loaded surface areas, detailed metallographic analyses were performed in order to characterize the occurring damages, i.e., crack formation, recrystallization, and melting. Thereby, the different joining technologies, i.e., hot radial pressing (HRP) vs. hot isostatic pressing (HIP) of tungsten to the Cu-based cooling tube, were qualified showing a higher stability and reproducibility of the HIP technology also as repair technology. Finally, the material response at the loaded top surface was found to be depending on the material grade, microstructural orientation, and recrystallization state of the material. These damages might be triggered by the application of thermal shock loads during electron beam surface scanning and not by the steady state heat load only. However, the superposition of thermal fatigue loads and thermal shocks as also expected

Fracture Resistance of Ceramic Laminate Veneers Bonded to Teeth with Class V Composite Fillings after Cyclic Loading

Directory of Open Access Journals (Sweden)

Leyla Sadighpour

2018-01-01

Full Text Available Purpose. Porcelain laminate veneers (PLVs are sometimes required to be used for teeth with composite fillings. This study examined the fracture strength of PLVs bonded to the teeth restored with different sizes of class V composite fillings. Materials and Methods. Thirty-six maxillary central incisors were divided into three groups (n=12: intact teeth (control and teeth with class V composite fillings of one-third or two-thirds of the crown height (small or large group, resp.. PLVs were made by using IPS e.max and bonded with a resin cement (RelyX Unicem. Fracture resistance (N was measured after cyclic loading (1 × 106 cycles, 1.2 Hz. For statistical analyses, one-way ANOVA and Tukey test were used (α=0.05. Results. There was a significant difference between the mean failure loads of the test groups (P=0.004, with the Tukey-HSD test showing lower failure loads in the large-composite group compared to the control (P=0.02 or small group (P=0.05. The control and small-composite groups achieved comparable results (P>0.05. Conclusions. Failure loads of PLVs bonded to intact teeth and to teeth with small class V composite fillings were not significantly different. However, extensive composite fillings could compromise the bonding of PLVs.

CFD analysis of linear compressors considering load conditions

Science.gov (United States)

Bae, Sanghyun; Oh, Wonsik

2017-08-01

This paper is a study on computational fluid dynamics (CFD) analysis of linear compressor considering load conditions. In the conventional CFD analysis of the linear compressor, the load condition was not considered in the behaviour of the piston. In some papers, behaviour of piston is assumed as sinusoidal motion provided by user defined function (UDF). In the reciprocating type compressor, the stroke of the piston is restrained by the rod, while the stroke of the linear compressor is not restrained, and the stroke changes depending on the load condition. The greater the pressure difference between the discharge refrigerant and the suction refrigerant, the more the centre point of the stroke is pushed backward. And the behaviour of the piston is not a complete sine wave. For this reason, when the load condition changes in the CFD analysis of the linear compressor, it may happen that the ANSYS code is changed or unfortunately the modelling is changed. In addition, a separate analysis or calculation is required to find a stroke that meets the load condition, which may contain errors. In this study, the coupled mechanical equations and electrical equations are solved using the UDF, and the behaviour of the piston is solved considering the pressure difference across the piston. Using the above method, the stroke of the piston with respect to the motor specification of the analytical model can be calculated according to the input voltage, and the piston behaviour can be realized considering the thrust amount due to the pressure difference.

Seismic and Power Generation Performance of U-Shaped Steel Connected PV-Shear Wall under Lateral Cyclic Loading

Directory of Open Access Journals (Sweden)

Hongmei Zhang

2014-01-01

Full Text Available BIPV is now widely used in office and residential buildings, but its seismic performance still remained vague especially when the photovoltaic (PV modules are installed on high-rise building facades. A new form of reinforced concrete shear wall integrated with photovoltaic module is proposed in this paper, aiming to apply PV module to the facades of high-rise buildings. In this new form, the PV module is integrated with the reinforced concrete wall by U-shaped steel connectors through embedded steel plates. The lateral cyclic loading test is executed to investigate the seismic behavior and the electric and thermal performance with different drift angles. The seismic behavior, including failure pattern, lateral force-top displacement relationship, and deformation capacity, was investigated. The power generation and temperature variation on the back of the PV module and both sides of the shear wall were also tested. Two main results are demonstrated through the experiment: (1 the U-shaped steel connectors provide enough deformation capacity for the compatibility of the PV module to the shear wall during the whole cyclic test; (2 the electricity generation capacity is effective and stable during this seismic simulation test.

Synthesis and characterization of cyclic polystyrene using copper-catalyzed alkyne-azide cycloaddition coupling - evaluation of physical properties and optimization of cyclization conditions

Science.gov (United States)

Elupula, Ravinder

Polymers with a cyclic topology exhibit a range of unique and potentially useful physical properties, including reduced rates of degradation and increased rates of diffusion in bulk relative to linear analogs. However the synthesis of high purity cyclic polymers, and verification of their structural purity remains challenging. The copper-catalyzed azide-alkyne "click" cyclization route toward cyclic polymers has been used widely, due to its synthetic ease and its compatibility with diverse polymer backbones. Yet unoptimized click cyclization conditions have been observed to generate oligomeric byproducts. In order to optimize these cyclization conditions, and to better understand the structure of the higher molecular weight oligomers, these impurities have been isolated by size exclusion chromatography (SEC) and characterized by mass spectrometry (MS). Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-ToF) MS is a particularly valuable characterization tool and was used to determine that the high molecular weight impurities are predominantly cyclic oligomers. It should also be noted that the rapid analysis and small analyte requirements of this MS technique make it particularly attractive as a general tool for elucidating polymer architecture. Ability to tailor the physical properties of polymers by changing the architecture alone has garnered a lot of attention over the past few decades. Compared to their linear analogues, these novel polymer architectures behave completely different in nanoscale regime. Cyclic polymers are especially intriguing since we can compare the differences in the physical properties with that of the linear chains. One of the major physical property changes are T g-confinement effect. Using ATRP and "click chemistry" we have produced highly pure cyclic PS (c-PS) with number-average molecular weight (MW) of 3.4 kg/mol and 9.1 kg/mol. Bulk glass transition temperatures for c-PS were weakly depended on MWs

Biaxial loading effects on the growth of cracks

International Nuclear Information System (INIS)

Brown, M.W.; Miller, K.J.; Walker, T.J.

1983-01-01

Fatigue crack growth under different biaxial stress states is considered for both small scale yielding and high bulk stress conditions. Analytical and elastic finite element results are compared favourably alongside experimental results on a AISI 316 stainless steel at both room and elevated temperatures. Differences in crack growth rates are compared against different crack tip cyclic plastic zone sizes for various degrees of mixed mode loading, thereby overcoming the limitations of the Paris Law and LEFM. The usefulness of the approach is indicated for studies in the behaviour of materials subjected to thermal shock. Where steep temperature gradients are introduced due to rapid thermal transients, high strains are produced which propagate fatigue cracks under cyclic conditions. Since stress gradients are generally associated with thermal shock situations, the cracks grow through a plastically deformed region near the surface into an elastic region. A unified approach to fatigue behaviour, encompassing both linear elastic and elastic-plastic fracture mechanics, will enable analysis of thermal shock situations. The approach to crack propagation developed here shows that cyclic growth rates are a function of a severe strain zone size in which local stresses exceed the tensile strength, i.e. monotonic instability. The effects of stress biaxiality and mixed mode loading are included in the analysis, which may be extended to general yielding situations. (orig.)

Micromechanics of intergranular creep failure under cyclic loading

DEFF Research Database (Denmark)

van der Giessen, Erik; Tvergaard, Viggo

1996-01-01

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....... The analyses provide some new understanding that helps to explain the sometimes peculiar behaviour under balanced cyclic creep. Copyright (C) 1996 Acta Metallurgica Inc....

Investigations on the lifetime behaviour of a P23 pipe under fatigue loading

Energy Technology Data Exchange (ETDEWEB)

Friedmann, V.; Hartrott, P. von [Fraunhofer IWM, Freiburg (Germany)

2008-07-01

The performance of girth welds on new P23 low chromium steel pipes under cyclic loading at 450 C was investigated. The loading conditions were chosen to be representative for bore crack initiation and growth observed in main steam lines fabricated of 0.5Cr0.5Mo0.25V (CrMoV) steel. The microstructure of the base material and weldments was analysed. A lifetime model, initially set up for the prediction of thermo-cyclic loading, is used to predict the isothermal component behaviour. It is based on a Chaboche-type deformation model and the DTMF crack growth model. The failure mechanism of two component tests was compared to the model assumptions and the component lifetimes and failure locations are compared to the model predictions. (orig.)

Influence of pores on crack initiation in monotonic tensile and cyclic loadings in lost foam casting A319 alloy by using 3D in-situ analysis

International Nuclear Information System (INIS)

Wang, Long; Limodin, Nathalie; El Bartali, Ahmed; Witz, Jean-François; Seghir, Rian; Buffiere, Jean-Yves; Charkaluk, Eric

2016-01-01

Lost Foam Casting (LFC) process is replacing the conventional gravity Die Casting (DC) process in automotive industry for the purpose of geometry optimization, cost reduction and consumption control. However, due to lower cooling rate, LFC produces in a coarser microstructure that reduces fatigue life. In order to study the influence of the casting microstructure of LFC Al-Si alloy on damage micromechanisms under monotonic tensile loading and Low Cycle Fatigue (LCF) at room temperature, an experimental protocol based on the three dimensional (3D) in-situ analysis has been set up and validated. This paper focuses on the influence of pores on crack initiation in monotonic and cyclic tensile loadings. X-ray Computed Tomography (CT) allowed the microstructure of material being characterized in 3D and damage evolution being followed in-situ also in 3D. Experimental and numerical mechanical fields were obtained by using Digital Volume Correlation (DVC) technique and Finite Element Method (FEM) simulation respectively. Pores were shown to have an important influence on strain localization as large pores generate enough strain localization zones for crack initiation both in monotonic tensile and cyclic loadings.

Influence of pores on crack initiation in monotonic tensile and cyclic loadings in lost foam casting A319 alloy by using 3D in-situ analysis

Energy Technology Data Exchange (ETDEWEB)

Wang, Long, E-mail: longwang_calt@163.com [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France); Limodin, Nathalie; El Bartali, Ahmed; Witz, Jean-François; Seghir, Rian [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France); Buffiere, Jean-Yves [Laboratoire Matériaux, Ingénierie et Sciences (MATEIS), CNRS UMR5510, INSA-Lyon, 20 Av. Albert Einstein, 69621 Villeurbanne (France); Charkaluk, Eric [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France)

2016-09-15

Lost Foam Casting (LFC) process is replacing the conventional gravity Die Casting (DC) process in automotive industry for the purpose of geometry optimization, cost reduction and consumption control. However, due to lower cooling rate, LFC produces in a coarser microstructure that reduces fatigue life. In order to study the influence of the casting microstructure of LFC Al-Si alloy on damage micromechanisms under monotonic tensile loading and Low Cycle Fatigue (LCF) at room temperature, an experimental protocol based on the three dimensional (3D) in-situ analysis has been set up and validated. This paper focuses on the influence of pores on crack initiation in monotonic and cyclic tensile loadings. X-ray Computed Tomography (CT) allowed the microstructure of material being characterized in 3D and damage evolution being followed in-situ also in 3D. Experimental and numerical mechanical fields were obtained by using Digital Volume Correlation (DVC) technique and Finite Element Method (FEM) simulation respectively. Pores were shown to have an important influence on strain localization as large pores generate enough strain localization zones for crack initiation both in monotonic tensile and cyclic loadings.

Safety assessment of reactor components under complex multiaxial cyclic loading. Final report; Sicherheitsbewertung kerntechnischer Komponenten bei komplexer, mehrachsiger Schwingbeanspruchung. Abschlussbericht

Energy Technology Data Exchange (ETDEWEB)

Fesich, Thomas M.; Herter, Karl-Heinz; Schuler, Xaver

2012-12-15

Objective of the project was the experimental assurance of investigations on the theoretical basis of multiaxial fatigue loading. The review of the applicability of existing hypotheses, as well as the extension of the corresponding data base was carried out by experimental studies in fatigue tests under complex multiaxial loading for a ferritic and austenitic material. To investigate the influence of complex multiaxial stress conditions on the fatigue behavior, in this project notched cylindrical specimens were examined under alternating tensile/pressure loading and alternating torsional loading. Through the notch in the notched section inhomogeneous, multiaxial stress states are generated. By uniaxial alternating tests on unnotched specimens and a further series of tests on unnotched specimens under alternating torsional loading an evaluation of the impact and influence of the notch of stress on fatigue behavior was possible. A series of experiments with superimposition of alternating torsional and alternating tensile/pressure loading permits verification of the effect of phase-shifted stress and rotating principal coordinate system. All experiments were performed at room temperature. As part of the research project, the experimental results with the ferritic and austenitic materials were evaluated in terms of material behavior (hardening or softening) under cyclic loading. These were to uniaxial alternating tensile/pressure tests, alternating torsional tests (unnotched cylindrical specimens), alternating tensile/pressure tests on notched cylindrical specimens, alternating torsional tests on notched cylindrical specimens, alternating tensiontorsion tests with complex proportional stresses on unnotched cylindrical specimens (superimposition of normal and shear stress components), as well as alternating tension-torsion tests with complex non-proportional strain on unnotched cylindrical specimens (superimposition of normal and shear stress components with 90 phase

Comparative Study of Phase Transformation in Single-Crystal Germanium during Single and Cyclic Nanoindentation

Directory of Open Access Journals (Sweden)

Koji Kosai

2017-11-01

Full Text Available Single-crystal germanium is a semiconductor material which shows complicated phase transformation under high pressure. In this study, new insight into the phase transformation of diamond-cubic germanium (dc-Ge was attempted by controlled cyclic nanoindentation combined with Raman spectroscopic analysis. Phase transformation from dc-Ge to rhombohedral phase (r8-Ge was experimentally confirmed for both single and cyclic nanoindentation under high loading/unloading rates. However, compared to single indentation, double cyclic indentation with a low holding load between the cycles caused more frequent phase transformation events. Double cyclic indentation caused more stress in Ge than single indentation and increased the possibility of phase transformation. With increase in the holding load, the number of phase transformation events decreased and finally became less than that under single indentation. This phenomenon was possibly caused by defect nucleation and shear accumulation during the holding process, which were promoted by a high holding load. The defect nucleation suppressed the phase transformation from dc-Ge to r8-Ge, and shear accumulation led to another phase transformation pathway, respectively. A high holding load promoted these two phenomena, and thus decreased the possibility of phase transformation from dc-Ge to r8-Ge.

Thermal conductivity of a graphite bipolar plate (BPP) and its thermal contact resistance with fuel cell gas diffusion layers: Effect of compression, PTFE, micro porous layer (MPL), BPP out-of-flatness and cyclic load

Science.gov (United States)

Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid

2015-01-01

This paper reports on measurements of thermal conductivity of a graphite bipolar plate (BPP) as a function of temperature and its thermal contact resistance (TCR) with treated and untreated gas diffusion layers (GDLs). The thermal conductivity of the BPP decreases with temperature and its thermal contact resistance with GDLs, which has been overlooked in the literature, is found to be dominant over a relatively wide range of compression. The effects of PTFE loading, micro porous layer (MPL), compression, and BPP out-of-flatness are also investigated experimentally. It is found that high PTFE loadings, MPL and even small BPP out-of-flatness increase the BPP-GDL thermal contact resistance dramatically. The paper also presents the effect of cyclic load on the total resistance of a GDL-BPP assembly, which sheds light on the behavior of these materials under operating conditions in polymer electrolyte membrane fuel cells.

Mechanical and thermo-mechanical response of a lead-core bearing device subjected to different loading conditions

Directory of Open Access Journals (Sweden)

Zhelyazov Todor

2018-01-01

Full Text Available The contribution is focused on the numerical modelling, simulation and analysis of a lead-core bearing device for passive seismic isolation. An accurate finite element model of a lead-core bearing device is presented. The model is designed to analyse both mechanical and thermo-mechanical responses of the seismic isolator to different loading conditions. Specifically, the mechanical behaviour in a typical identification test is simulated. The response of the lead-core bearing device to circular sinusoidal paths is analysed. The obtained shear displacement – shear force relationship is compared to experimental data found in literature sources. The hypothesis that heating of the lead-core during cyclic loading affects the degrading phenomena in the bearing device is taken into account. Constitutive laws are defined for each material: lead, rubber and steel. Both predefined constitutive laws (in the used general–purpose finite element code and semi-analytical procedures aimed at a more accurate modelling of the constitutive relations are tested. The results obtained by finite element analysis are to be further used to calibrate a macroscopic model of the lead-core bearing device seen as a single-degree-of-freedom mechanical system.

Low-cycle fatigue and cyclic deformation behavior of Type 16-8-2 weld metal at elevated temperature

International Nuclear Information System (INIS)

Raske, D.T.

1977-01-01

The low-cycle fatigue behavior of Type 16-8-2 stainless steel ASA weld metal at 593 0 C was investigated, and the results are compared with existing data for Type 316 stainless steel base metal. Tests were conducted under axial strain control and at a constant axial strain rate of 4 x 10 -3 s -1 for continuous cyclic loadings as well as hold times at peak tensile strain. Uniform-gauge specimens were machined longitudinally from the surface and root areas of 25.4-mm-thick welded plate and tested in the as-welded condition. Results indicate that the low-cycle fatigue resistance of this weld metal is somewhat better than that of the base metal for continuous-cycling conditions and significantly better for tension hold-time tests. This is attributed to the fine duplex delta ferrite-austenite microstructure in the weld metal. The initial monotonic tensile properties and the cyclic stress-strain behavior of this material were also determined. Because the cyclic changes in mechanical properties are strain-history dependent, a unique cyclic stress-strain curve does not exist for this material

Effect of crack closing and cyclic fracture toughness evaluation of structural alloys

International Nuclear Information System (INIS)

Romaniv, O.N.; Nikiforchin, G.N.; Andrusiv, B.N.

1983-01-01

Mechanisms of crack closing (CC), methods of its evalution as well as CC effect on cyclic fracture toughness of structural alloys are considered based on literature and experimental datas several CC mechanisms are suggested. It is noted that evaluation of fatigue crack closing is exercised, mainly, experimentally, though analytical methods of its determination are also suggested. Experimental Methods may be divided in two main groups. The first one comprises techniques based on direct determination of strains and displacements, the second one includes methods based on physical methods of investigations. High importance of CC effect accountancy in investigation of growth kinetics and machanism of corrosion-fatigue cracks in structural materials is noted. Besides, it should be taken into account that cyclic loading changes electrochemical conditions in the apex of corrosion crack

Observations on bucket foundations under cyclic loading in dense saturated sand

DEFF Research Database (Denmark)

Foglia, Aligi; Ibsen, Lars Bo; Nicolai, Giulio

2014-01-01

Offshore wind farms will play a significant role in the European energy supply of the coming years. Today, one of the main challenges faced by the offshore wind market is to reduce the cost of turbine foundations. The monopod bucket foundation is a possible solution to this problem. The long......-term cyclic response of this foundation is not fully understood. In this article, a single gravity physical model is described, an experimental campaign is presented and the observed results are discussed. The aim of the study is to explore the general pattern of response of the foundation under cyclic...

Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

Energy Technology Data Exchange (ETDEWEB)

Utz, S.; Soppa, E.; Silcher, H.; Kohler, C. [Stuttgart Univ. (Germany). Materials Testing Inst.

2013-07-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

International Nuclear Information System (INIS)

Utz, S.; Soppa, E.; Silcher, H.; Kohler, C.

2013-01-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

Mechanical Stimulation of Adipose-Derived Stem Cells for Functional Tissue Engineering of the Musculoskeletal System via Cyclic Hydrostatic Pressure, Simulated Microgravity, and Cyclic Tensile Strain.

Science.gov (United States)

Nordberg, Rachel C; Bodle, Josie C; Loboa, Elizabeth G

2018-01-01

It is critical that human adipose stem cell (hASC) tissue-engineering therapies possess appropriate mechanical properties in order to restore function of the load bearing tissues of the musculoskeletal system. In an effort to elucidate the hASC response to mechanical stimulation and develop mechanically robust tissue engineered constructs, recent research has utilized a variety of mechanical loading paradigms including cyclic tensile strain, cyclic hydrostatic pressure, and mechanical unloading in simulated microgravity. This chapter describes methods for applying these mechanical stimuli to hASC to direct differentiation for functional tissue engineering of the musculoskeletal system.

Multiaxial ratcheting behavior of zirconium alloy tubes under combined cyclic axial load and internal pressure

Energy Technology Data Exchange (ETDEWEB)

Chen, G.; Zhang, X. [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); Li, D.H. [Hunan Taohuajiang Nuclear Power Co., Ltd, Yiyang, 413000 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Z., E-mail: zhe.zhang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

2017-06-15

In this study, a series of uniaxial and multiaxial ratcheting tests were conducted at room temperature on zirconium alloy tubes. The experimental results showed that for uniaxial symmetrical cyclic test, the axial ratcheting strain ɛ{sub x} did not accumulate obviously in initial stage, but gradually increased up to 1% with increasing stress amplitude σ{sub xa}. For multiaxial ratcheting tests, the zirconium alloy tube was highly sensitive to both the axial stress amplitude σ{sub xa} and the internal pressure p{sub i}. The hoop ratcheting strain ɛ{sub θ} increased continuously with the increase of axial stress amplitude, whereas the evolution of axial ratcheting strain ɛ{sub x} was related to the axial stress amplitude. The internal pressure restricted the ratcheting accumulation in the axial direction, but promoted the hoop ratcheting strain on the contrary. The prior loading history greatly restrained the ratcheting behavior of subsequent cycling with a small internal pressure. - Highlights: •Uniaxial and multiaxial ratcheting behavior of the zirconium alloy tubes are investigated at room temperature. •The ratcheting depends greatly on the stress amplitude or internal pressure. •The interaction between the axial and hoop ratcheting mechanisms is greatly dependent on the internal pressure level. •The ratcheting is influenced significantly by the loading history of internal pressure.

Multiaxial ratcheting behavior of zirconium alloy tubes under combined cyclic axial load and internal pressure

International Nuclear Information System (INIS)

Chen, G.; Zhang, X.; Xu, D.K.; Li, D.H.; Chen, X.; Zhang, Z.

2017-01-01

In this study, a series of uniaxial and multiaxial ratcheting tests were conducted at room temperature on zirconium alloy tubes. The experimental results showed that for uniaxial symmetrical cyclic test, the axial ratcheting strain ɛ x did not accumulate obviously in initial stage, but gradually increased up to 1% with increasing stress amplitude σ xa . For multiaxial ratcheting tests, the zirconium alloy tube was highly sensitive to both the axial stress amplitude σ xa and the internal pressure p i . The hoop ratcheting strain ɛ θ increased continuously with the increase of axial stress amplitude, whereas the evolution of axial ratcheting strain ɛ x was related to the axial stress amplitude. The internal pressure restricted the ratcheting accumulation in the axial direction, but promoted the hoop ratcheting strain on the contrary. The prior loading history greatly restrained the ratcheting behavior of subsequent cycling with a small internal pressure. - Highlights: •Uniaxial and multiaxial ratcheting behavior of the zirconium alloy tubes are investigated at room temperature. •The ratcheting depends greatly on the stress amplitude or internal pressure. •The interaction between the axial and hoop ratcheting mechanisms is greatly dependent on the internal pressure level. •The ratcheting is influenced significantly by the loading history of internal pressure.

A failure estimation method of steel pipe elbows under in-plane cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Jeon, Bub Gyu; Kim, Sung Wan; Choi, Hyoung Suk; Park, Dong Uk [Seismic Simulation Tester Center, Pusan National University, Yangsan (Korea, Republic of); Kim, Nam Sik [Dept. of Civil and Environmental Engineering, Pusan National University, Busan (Korea, Republic of)

2017-02-15

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

A Failure Estimation Method of Steel Pipe Elbows under In-plane Cyclic Loading

Directory of Open Access Journals (Sweden)

Bub-Gyu Jeon

2017-02-01

Full Text Available The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

A failure estimation method of steel pipe elbows under in-plane cyclic loading

International Nuclear Information System (INIS)

Jeon, Bub Gyu; Kim, Sung Wan; Choi, Hyoung Suk; Park, Dong Uk; Kim, Nam Sik

2017-01-01

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation

A biomechanical comparison of 2 transosseous-equivalent double-row rotator cuff repair techniques using bioabsorbable anchors: cyclic loading and failure behavior.

Science.gov (United States)

Spang, Jeffrey T; Buchmann, Stefan; Brucker, Peter U; Kouloumentas, Panos; Obst, Tobias; Schröder, Manuel; Burgkart, Rainer; Imhoff, Andreas B

2009-08-01

A novel double-row configuration was compared with a traditional double-row configuration for rotator cuff repair. In 10 matched-pair sheep shoulders in vitro repair was performed with either a double-row technique with corkscrew suture anchors for the medial row and insertion anchors for the lateral row (group A) or a double-row technique with a new tape-like suture material with insertion anchors for both the medial and lateral rows (group B). Each specimen underwent cyclic loading from 10 to 150 N for 100 cycles, followed by unidirectional failure testing. Gap formation and strain within the repair area for the first and last cycles were analyzed with a video digitizing system, and stiffness and failure load were determined from the load-elongation curve. The results were similar for the 2 repair types. There was no significant difference between the ultimate failure loads of the 2 techniques (421 +/- 150 N in group A and 408 +/- 66 N in group B, P = .31) or the stiffness of the 2 techniques (84 +/- 26 N/mm in group A and 99 +/- 20 N/mm in group B, P = .07). In addition, gap formation was not different between the repair types. Strain over the repair area was also not different between the repair types. Both tested rotator cuff repair techniques had high failure loads, limited gap formation, and acceptable strain patterns. No significant difference was found between the novel and conventional double-row repair types. Two double-row techniques-one with corkscrew suture anchors for the medial row and insertion anchors for the lateral row and one with insertion anchors for both the medial and lateral rows-provided excellent biomechanical profiles at time 0 for double-row repairs in a sheep model. Although the sheep model may not directly correspond to in vivo conditions, all-insertion anchor double-row constructs are worthy of further investigation.

Numerical Analysis of Carbon Fiber Reinforced Plastic (CFRP Shear Walls and Steel Strips under Cyclic Loads Using Finite Element Method

Directory of Open Access Journals (Sweden)

N. Askarizadeh

2017-12-01

Full Text Available Reinforced concrete shear walls are the main elements of resistance against lateral loads in reinforced concrete structures. These walls should not only provide sufficient resistance but also provide sufficient ductility in order to avoid brittle fracture, particularly under strong seismic loads. However, many reinforced concrete shear walls need to be stabilized and reinforced due to various reasons such as changes in requirements of seismic regulations, weaknesses in design and execution, passage of time, damaging environmental factors, patch of rebar in plastic hinges and in some cases failures and weaknesses caused by previous earthquakes or explosion loads. Recently, Fiber Reinforced Polymer (FRP components have been extensively and successfully used in seismic improvement. This study reinforces FRP reinforced concrete shear walls and steel strips. CFRP and steel strips are evaluated by different yield and ultimate strength. Numerical and experimental studies are done on walls with scale 1/2. These walls are exposed to cyclic loading. Hysteresis curves of force, drift and strain of FRP strips are reviewed in order to compare results of numerical work and laboratory results. Both numerical and laboratory results show that CFRP and steel strips increase resistance, capacity and ductility of the structure.

Numerical simulation of lead devices for seismic isolation and vibration control on their damping characteristics. Development of lead material model under cyclic large deformation

International Nuclear Information System (INIS)

Matsuda, Akihiro; Yabana, Shuichi; Borst, Rene de

2004-01-01

In order to predict the mechanical properties of lead devices for seismic isolation and vibration control, especially damping behavior under cyclic loading using numerical simulation, cyclic shear loading tests and uniaxial tensile loading tests were performed, and a new material model was proposed with the use of the both test results. Until now, it has been difficult to evaluate mechanical properties of lead material under cyclic loading by uniaxial tensile loading test because local deformations appeared with the small tensile strain. Our shear cyclic loading tests for lead material enabled practical evaluation of its mechanical properties under cyclic large strain which makes it difficult to apply uniaxial test. The proposed material model was implemented into a finite element program, and it was applied to numerical simulation of mechanical properties of lead dampers and rubber bearings with a lead plug. The numerical simulations and the corresponding laboratory loading tests showed good agreement, which proved the applicability of the proposed model. (author)

Cyclic and Fatigue Behaviour of Rock Materials: Review, Interpretation and Research Perspectives

Science.gov (United States)

Cerfontaine, B.; Collin, F.

2018-02-01

The purpose of this paper is to provide a comprehensive state of the art of fatigue and cyclic loading of natural rock materials. Papers published in the literature are classified and listed in order to ease bibliographical review, to gather data (sometimes contradictory) on classical experimental results and to analyse the main interpretation concepts. Their advantages and limitations are discussed, and perspectives for further work are highlighted. The first section summarises and defines the different experimental set-ups (type of loading, type of experiment) already applied to cyclic/fatigue investigation of rock materials. The papers are then listed based on these different definitions. Typical results are highlighted in next section. Fatigue/cyclic loading mainly results in accumulation of plastic deformation and/or damage cycle after cycle. A sample cyclically loaded at constant amplitude finally leads to failure even if the peak load is lower than its monotonic strength. This subcritical crack is due to a diffuse microfracturing and decohesion of the rock structure. The third section reviews and comments the concepts used to interpret the results. The fatigue limit and S- N curves are the most common concepts used to describe fatigue experiments. Results published from all papers are gathered into a single figure to highlight the tendency. Predicting the monotonic peak strength of a sample is found to be critical in order to compute accurate S- N curves. Finally, open questions are listed to provide a state of the art of grey areas in the understanding of fatigue mechanisms and challenges for the future.

Dislocation structure evolution in 304L stainless steel and weld joint during cyclic plastic deformation

Energy Technology Data Exchange (ETDEWEB)

Wang, Hao; Jing, Hongyang; Zhao, Lei; Han, Yongdian; Lv, Xiaoqing [School of Materials Science and Engineering, Tianjin University, Tianjin 300072 (China); Tianjin Key Laboratory of Advanced Joining Technology, Tianjin 300072 (China); Xu, Lianyong, E-mail: xulianyong@tju.edu.cn [School of Materials Science and Engineering, Tianjin University, Tianjin 300072 (China); Tianjin Key Laboratory of Advanced Joining Technology, Tianjin 300072 (China)

2017-04-06

Dislocation structures and their evolution of 304L stainless steel and weld metal made with ER308L stainless steel welding wire subjected to uniaxial symmetric strain-controlled loading and stress-controlled ratcheting loading were observed by transmission electron microscopy (TEM). The correlation between the cyclic response and the dislocation structure has been studied. The experiment results show that the cyclic behaviour of base metal and weld metal are different. The cyclic behaviour of the base metal consists of primary hardening, slight softening and secondary hardening, while the weld metal shows a short hardening within several cycles followed by the cyclic softening behaviour. The microscopic observations indicate that in base metal, the dislocation structures evolve from low density patterns to those with higher dislocation density during both strain cycling and ratcheting deformation. However, the dislocation structures of weld metal change oppositely form initial complicated structures to simple patterns and the dislocation density gradually decrease. The dislocation evolution presented during the strain cycling and ratcheting deformation is summarized, which can qualitatively explain the cyclic behaviour and the uniaxial ratcheting behaviour of two materials. Moreover, the dislocation evolution in the two types of tests is compared, which shows that the mean stress has an effect on the rate of dislocation evolution during the cyclic loading.

Forecasting the condition of petroleum impregnated load bearing ...

African Journals Online (AJOL)

Petroleum products (PP) used in industrial processes systematically fall on the load-bearing CRC structures and gradually impregnate therein. Currently, available guidelines for the assessment of technical condition and reliability of load-bearing CRC structures do not fully take into account the effect of viscosity of PP that ...

Low-Load Space Conditioning Needs Assessment

Energy Technology Data Exchange (ETDEWEB)

Puttagunta, Srikanth [Consortium for Advanced Residential Buildings (CARB), Norwalk, CT (United States)

2015-05-19

Heating, ventilating, and air-conditioning (HVAC) equipment must be right-sized to ensure energy performance and comfort. With limited low-load options in the HVAC market, many new-construction housing units are being fitted with oversized equipment that creates system efficiency, comfort, and cost penalties. To bridge the gap between currently available HVAC equipment that is oversized or inefficient and the rising demand for low-load HVAC equipment in the marketplace, HVAC equipment manufacturers need to be fully aware of the needs of the multifamily building and attached single-family (duplex and townhouse) home market. Over the past decade, Steven Winter Associates, Inc. (SWA) has provided certification and consulting services for hundreds of housing projects and has accrued a large pool of data that describe multifamily and attached single-family home characteristics. The U.S. Department of Energy’s Building America research team Consortium for Advanced Residential Buildings (CARB) compiled and analyzed these data to outline the characteristics of low-load dwellings such as the heating and cooling design loads.

Short bursts of cyclic mechanical compression modulate tissue formation in a 3D hybrid scaffold.

Science.gov (United States)

Brunelli, M; Perrault, C M; Lacroix, D

2017-07-01

Among the cues affecting cells behaviour, mechanical stimuli are known to have a key role in tissue formation and mineralization of bone cells. While soft scaffolds are better at mimicking the extracellular environment, they cannot withstand the high loads required to be efficient substitutes for bone in vivo. We propose a 3D hybrid scaffold combining the load-bearing capabilities of polycaprolactone (PCL) and the ECM-like chemistry of collagen gel to support the dynamic mechanical differentiation of human embryonic mesodermal progenitor cells (hES-MPs). In this study, hES-MPs were cultured in vitro and a BOSE Bioreactor was employed to induce cells differentiation by mechanical stimulation. From day 6, samples were compressed by applying a 5% strain ramp followed by peak-to-peak 1% strain sinewaves at 1Hz for 15min. Three different conditions were tested: unloaded (U), loaded from day 6 to day 10 (L1) and loaded as L1 and from day 16 to day 20 (L2). Cell viability, DNA content and osteocalcin expression were tested. Samples were further stained with 1% osmium tetroxide in order to investigate tissue growth and mineral deposition by micro-computed tomography (µCT). Tissue growth involved volumes either inside or outside samples at day 21 for L1, suggesting cyclic stimulation is a trigger for delayed proliferative response of cells. Cyclic load also had a role in the mineralization process preventing mineral deposition when applied at the early stage of culture. Conversely, cyclic load during the late stage of culture on pre-compressed samples induced mineral formation. This study shows that short bursts of compression applied at different stages of culture have contrasting effects on the ability of hES-MPs to induce tissue formation and mineral deposition. The results pave the way for a new approach using mechanical stimulation in the development of engineered in vitro tissue as replacement for large bone fractures. Copyright © 2017 Elsevier Ltd. All rights

Experimental Investigation of the Influence of Joint Geometric Configurations on the Mechanical Properties of Intermittent Jointed Rock Models Under Cyclic Uniaxial Compression

Science.gov (United States)

Liu, Yi; Dai, Feng; Fan, Pengxian; Xu, Nuwen; Dong, Lu

2017-06-01

Intermittent joints in rock mass are quite sensitive to cyclic loading conditions. Understanding the fatigue mechanical properties of jointed rocks is beneficial for rational design and stability analysis of rock engineering projects. This study experimentally investigated the influences of joint geometry (i.e., dip angle, persistency, density and spacing) on the fatigue mechanism of synthetic jointed rock models. Our results revealed that the stress-strain curve of jointed rock under cyclic loadings is dominated by its curve under monotonic uniaxial loadings; the terminal strain in fatigue curve is equal to the post-peak strain corresponding to the maximum cyclic stress in the monotonic stress-strain curve. The four joint geometrical parameters studied significantly affect the fatigue properties of jointed rocks, including the irreversible strains, the fatigue deformation modulus, the energy evolution, the damage variable and the crack coalescence patterns. The higher the values of the geometrical parameters, the lower the elastic energy stores in this jointed rock, the higher the fatigue damage accumulates in the first few cycles, and the lower the fatigue life. The elastic energy has certain storage limitation, at which the fatigue failure occurs. Two basic micro-cracks, i.e., tensile wing crack and shear crack, are observed in cyclic loading and unloading tests, which are controlled principally by joint dip angle and persistency. In general, shear cracks only occur in the jointed rock with higher dip angle or higher persistency, and the jointed rock is characterized by lower fatigue strength, larger damage variable and lower fatigue life.

Cyclic electron flow provides acclimatory plasticity for the photosynthetic machinery under various environmental conditions and developmental stages

Directory of Open Access Journals (Sweden)

Marjaana eSuorsa

2015-09-01

Full Text Available Photosynthetic electron flow operates in two modes, linear and cyclic. In cyclic electron flow (CEF, electrons are recycled around photosystem I. As a result, a transthylakoid proton gradient (ΔpH is generated, leading to the production of ATP without concomitant production of NADPH, thus increasing the ATP/NADPH ratio within the chloroplast. At least two routes for CEF exist: a PGR5-PGRL1–and a chloroplast NDH-like complex mediated pathway. This review focuses on recent findings concerning the characteristics of both CEF routes in higher plants, with special emphasis paid on the crucial role of CEF in under challenging environmental conditions and developmental stages.

The effect of cyclic and dynamic loads on carbon steel pipe

International Nuclear Information System (INIS)

Rudland, D.L.; Scott, P.M.; Wilkowski, G.M.

1996-02-01

This report presents the results of four 152-mm (6-inch) diameter, unpressurized, circumferential through-wall-cracked, dynamic pipe experiments fabricated from STS410 carbon steel pipe manufactured in Japan. For three of these experiments, the through-wall crack was in the base metal. The displacement histories applied to these experiments were a quasi-static monotonic, dynamic monotonic, and dynamic, cyclic (R = -1) history. The through-wall crack for the third experiment was in a tungsten-inert-gas weld, fabricated in Japan, joining two lengths of STS410 pipe. The displacement history for this experiment was the same history applied to the dynamic, cyclic base metal experiment. The test temperature for each experiment was 300 C (572 F). The objective of these experiments was to compare a Japanese carbon steel pipe material with US pipe material, to ascertain whether this Japanese steel was as sensitive to dynamic and cyclic effects as US carbon steel pipe. In support of these pipe experiments, quasi-static and dynamic, tensile and fracture toughness tests were conducted. An analysis effort was performed that involved comparing experimental crack initiation and maximum moments with predictions based on available fracture prediction models, and calculating J-R curves for the pipe experiments using the η-factor method

Cyclic mechanical behavior of 316L: Uniaxial LCF and strain-controlled ratcheting tests

International Nuclear Information System (INIS)

Facheris, G.; Janssens, K.G.F.

2013-01-01

Highlights: ► Characterization of cyclic plastic deformation behavior of plate and tubular 316L. ► Strain-controlled ratcheting response between room temperature and 200 °C. ► Isotropic cyclic hardening is dependent on the yield criterion used. ► Ratcheting induced hardening mostly affects the kinematic hardening component. ► Ratcheting induced hardening is related to the mean strain and the ratcheting rate. -- Abstract: With the purpose of analyzing the fatigue behavior under loading conditions relevant for the primary cooling circuit of a light water nuclear reactor, a set of uniaxial low cycle fatigue and strain-controlled ratcheting tests (also named ‘cyclic tension tests’) has been performed at room temperature and at 200 °C on specimens manufactured from two different batches of stainless steel grade 316L. The experiments have been repeated varying strain amplitude, cyclic ratcheting rate and ratcheting direction in order to investigate the influence on the cyclic deformation behavior. In strain-controlled ratcheting tests, the stress response is found to be a superposition of two hardening mechanisms: the first one due to the zero mean strain cycling and the second one linked with the monotonic drifting of mean plastic strain. An approach is proposed to distinguish the effect of each mechanism and the influence of the test parameters on the hardening mechanisms is discussed

Cyclic response and early damage evolution in multiaxial cyclic loading of 316L austenitic steel

Czech Academy of Sciences Publication Activity Database

Mazánová, Veronika; Škorík, Viktor; Kruml, Tomáš; Polák, Jaroslav

2017-01-01

Roč. 100, JUL (2017), s. 466-476 ISSN 0142-1123 R&D Projects: GA MŠk LM2015069; GA MŠk(CZ) LQ1601; GA ČR(CZ) GA13-23652S; GA ČR GA15-08826S Institutional support: RVO:68081723 Keywords : 316L steel * Crack initiation * Cyclic plasticity * Damage mechanism * Multiaxial straining Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 2.899, year: 2016

The integrity of CANDU fuel during load following

International Nuclear Information System (INIS)

Tayal, M.; Manzer, A.M.; Sejnoha, R.; Hains, A.J.

1989-08-01

This paper summarizes data and analyses of integrity and of physics of CANDU fuel during load following. Measurements of irradiated fuel show that power cycles do not enhance release of fission gas. Data from research reactors show that the power cycles cause cyclic strains in the sheath. Finite element analyses show that the cyclic strains give highly multiaxial stresses in the sheath. The stresses and the strains are well into the plastic range. The cyclic loads 'use up' some fraction of the sheath's resistance to environmentally-assisted cracking (EAC), depending on the details of the fuel design and of then power cycles. The balance of the sheath's resistance to EAC continues to be available to counteract static loads. Thousands of fuel bundles have experienced many power cycles in research and in commercial reactors. Overall integrity of fuel bundles is well over 99%. Thus, CANDU fuel continues to show good performance in both base-load and load-following reactors

Selecting boundary conditions in physiological strain analysis of the femur: Balanced loads, inertia relief method and follower load.

Science.gov (United States)

Heyland, Mark; Trepczynski, Adam; Duda, Georg N; Zehn, Manfred; Schaser, Klaus-Dieter; Märdian, Sven

2015-12-01

Selection of boundary constraints may influence amount and distribution of loads. The purpose of this study is to analyze the potential of inertia relief and follower load to maintain the effects of musculoskeletal loads even under large deflections in patient specific finite element models of intact or fractured bone compared to empiric boundary constraints which have been shown to lead to physiological displacements and surface strains. The goal is to elucidate the use of boundary conditions in strain analyses of bones. Finite element models of the intact femur and a model of clinically relevant fracture stabilization by locking plate fixation were analyzed with normal walking loading conditions for different boundary conditions, specifically re-balanced loading, inertia relief and follower load. Peak principal cortex surface strains for different boundary conditions are consistent (maximum deviation 13.7%) except for inertia relief without force balancing (maximum deviation 108.4%). Influence of follower load on displacements increases with higher deflection in fracture model (from 3% to 7% for force balanced model). For load balanced models, follower load had only minor influence, though the effect increases strongly with higher deflection. Conventional constraints of fixed nodes in space should be carefully reconsidered because their type and position are challenging to justify and for their potential to introduce relevant non-physiological reaction forces. Inertia relief provides an alternative method which yields physiological strain results. Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.

Numerical optimization of composite hip endoprostheses under different loading conditions

Science.gov (United States)

Blake, T. A.; Davy, D. T.; Saravanos, D. A.; Hopkins, D. A.

1992-01-01

The optimization of composite hip implants was investigated. Emphasis was placed on the effect of shape and material tailoring of the implant to improve the implant-bone interaction. A variety of loading conditions were investigated to better understand the relationship between loading and optimization outcome. Comparisons of the initial and optimal models with more complex 3D finite element models were performed. The results indicate that design improvements made using this method result in similar improvements in the 3D models. Although the optimization outcomes were significantly affected by the choice of loading conditions, certain trends were observed that were independent of the applied loading.

Cyclic creep, mechanical ratchetting and amplitude history dependence of modified 9Cr-1Mo steel and evaluation of unified constitutive models

International Nuclear Information System (INIS)

Tanaka, Eiichi; Yamada, Hiroshi

1993-01-01

The purpose of the present paper is to elucidate inelastic behavior of modified 9Cr-1Mo steel as a candidate material for the next-generation fast breeder reactor and to provide the information for the formulation of a unified constitutive model. For this purpose, cyclic creep, mechanical ratchetting and amplitude history dependence of cyclic hardening were first examined at 550degC. As a result, systematic cyclic creep and mechanical ratchetting behavior were observed under various loading conditions, and little amplitude history dependence was found. Then these results were simulated by three unified constitutive models, i.e. the Chaboche, Bodner-Partom and modified Chaboche models. The simulated results show that these models cannot describe the cyclic creep and mechanical ratchetting behavior with high accuracy, but succeed in describing the inelastic behavior of amplitude variation experiments. (author)

Thermomechanical behavior of different Ni-base superalloys during cyclic loading at elevated temperatures

Directory of Open Access Journals (Sweden)

Huber Daniel

2014-01-01

Full Text Available The material behavior of three Ni-base superalloys (Inconel® 718, Allvac® 718PlusTM and Haynes® 282® during in-phase cyclic mechanical and thermal loading was investigated. Stress controlled thermo-mechanical tests were carried out at temperatures above 700 ∘C and different levels of maximum compressive stress using a Gleeble® 3800 testing system. Microstructure investigations via light optical microscopy (LOM and field emission gun scanning electron microscopy (FEG-SEM as well as numerical precipitation kinetics simulations were performed to interpret the obtained results. For all alloys, the predominant deformation mechanism during deformation up to low plastic strains was identified as dislocation creep. The main softening mechanism causing progressive increase of plastic strain after preceding linear behavior is suggested to be recrystallization facilitated by coarsening of grain boundary precipitates. Furthermore, coarsening and partial transformation of strengthening phases was observed. At all stress levels, Haynes® 282® showed best performance which is attributable to its stable microstructure containing a high phase fraction of small, intermetallic precipitates inside grains and different carbides evenly distributed along grain boundaries.

Eficiencia de los motores de inducción con carga cíclica; Efficiency of Induction Motors with Cyclic Load

Directory of Open Access Journals (Sweden)

Elías de la Rosa Masdueño

2011-02-01

Full Text Available Se propone un nuevo método para determinar la eficiencia de trabajo de los motores de inducción queaccionan cargas cíclicas tales como bombas reciprocantes, martinetes, etc. El método se basa en lasegregación de pérdidas, y la determinación del gráfico de corriente y la energía total del ciclo. Se muestrauna comprobación experimental basada en un método de Monte Carlo.  A new method for finding the working efficiency of the induction motors moving cyclic loads is proposed.This type of loading is frequent in mechanism like piston pumps, hammers, etc. The method is based inthe losses segregation and the determination of the current graphic and the total energy in the cycle. Anexperimental proof based on Monte Carlo method is shown.

Cyclic deformation behavior of steels and light-metal alloys

International Nuclear Information System (INIS)

Walther, Frank; Eifler, Dietmar

2007-01-01

The detailed knowledge of the cyclic deformation behavior of metallic materials is an essential condition for the comprehensive understanding of fatigue mechanisms and a reliable lifetime calculation of cyclically loaded specimens and components. Various steels and light-metal alloys were investigated under stress and strain control on servohydraulic testing systems. In addition to mechanical stress-strain hysteresis measurements, the changes of the specimen temperature and the electrical resistance due to plastic deformation processes were measured. The plasticity-induced martensite formation in metastable austenitic steels was detected in situ with a ferritescope sensor. As advanced magnetic measuring technique giant-magneto-resistance sensors in combination with an universal eddy-current equipment were used for the on-line monitoring of fatigue processes. Due to their direct dependence on microstructural changes, all physical values show a clear interaction with the actual fatigue state. The results of the plastic strain, thermometric, electric and magnetic measuring techniques were presented versus the number of cycles as well as in Morrow and Coffin-Manson plots. The microstructures were characterized by scanning electron microscopy

Cyclic deformation behavior of steels and light-metal alloys

Energy Technology Data Exchange (ETDEWEB)

Walther, Frank [University of Kaiserslautern, Institute of Materials Science and Engineering, P.O. Box 3049, D-67653 Kaiserslautern (Germany)], E-mail: walther@mv.uni-kl.de; Eifler, Dietmar [University of Kaiserslautern, Institute of Materials Science and Engineering, P.O. Box 3049, D-67653 Kaiserslautern (Germany)

2007-11-15

The detailed knowledge of the cyclic deformation behavior of metallic materials is an essential condition for the comprehensive understanding of fatigue mechanisms and a reliable lifetime calculation of cyclically loaded specimens and components. Various steels and light-metal alloys were investigated under stress and strain control on servohydraulic testing systems. In addition to mechanical stress-strain hysteresis measurements, the changes of the specimen temperature and the electrical resistance due to plastic deformation processes were measured. The plasticity-induced martensite formation in metastable austenitic steels was detected in situ with a ferritescope sensor. As advanced magnetic measuring technique giant-magneto-resistance sensors in combination with an universal eddy-current equipment were used for the on-line monitoring of fatigue processes. Due to their direct dependence on microstructural changes, all physical values show a clear interaction with the actual fatigue state. The results of the plastic strain, thermometric, electric and magnetic measuring techniques were presented versus the number of cycles as well as in Morrow and Coffin-Manson plots. The microstructures were characterized by scanning electron microscopy.

Cyclic strength of metals at impact strain rates

International Nuclear Information System (INIS)

Eleiche, A.M.; El-Kady, M.M.

1987-01-01

Rigorous understanding of the effects of impact loading on the mechanical response of materials and structures is essential for the optimum design and safe operation of many sophisticated engineering systems and components, such as industrial high-energy-rate fabrication processes and nuclear reactor containments. Extensive data are available at present on the dynamic behaviour of most metals in uniaxial tension, compression, torsion and pure shear, when they are subjected to diversified loading conditions, ranging from those characterised by monotonic constant rates, to those involving forward or reverse strain-rate jumps of several orders of magnitude. What appears to be missing in the current material data banks, however, is detailed information concerning the mechanical response under cyclic loading at impact strain rates. Such data are needed for engineering design purposes on one hand, and for the formulation of proper constitutive equations and the accurate modeling of deformation processes on the other. In the present paper, typical stress-strain characteristics at ambient temperature for copper, mild steel and titanium are first exhibited. The application of the unified Bodner-Partom constitutive theory to these data is then presented and discussed. (orig./GL)

Anisotropic yield surfaces in bi-axial cyclic plasticity

International Nuclear Information System (INIS)

Rider, R.J.; Harvey, S.J.; Breckell, T.H.

1985-01-01

Some aspects of the behaviour of yield surfaces and work-hardening surfaces occurring in biaxial cyclic plasticity have been studied experimentally and theoretically. The experimental work consisted of subjecting thin-walled tubular steel specimens to cyclic plastic torsion in the presence of sustained axial loads of various magnitudes. The experimental results show that considerable anisotropy is induced when the cyclic shear strains are dominant. Although the true shapes of yield and work-hardening surfaces can be very complex, a mathematical model is presented which includes both anisotropy and Bauschinger effects. The model is able to qualitatively predict the deformation patterns during a cycle of applied plastic shear strain for a range of sustained axial stresses and also indicate the material response to changes in axial stress. (orig.)

Cyclic mechanical stretch contributes to network development of osteocyte-like cells with morphological change and autophagy promotion but without preferential cell alignment in rat.

Science.gov (United States)

Inaba, Nao; Kuroshima, Shinichiro; Uto, Yusuke; Sasaki, Muneteru; Sawase, Takashi

2017-09-01

Osteocytes play important roles in controlling bone quality as well as preferential alignment of biological apatite c -axis/collagen fibers. However, the relationship between osteocytes and mechanical stress remains unclear due to the difficulty of three-dimensional (3D) culture of osteocytes in vitro . The aim of this study was to investigate the effect of cyclic mechanical stretch on 3D-cultured osteocyte-like cells. Osteocyte-like cells were established using rat calvarial osteoblasts cultured in a 3D culture system. Cyclic mechanical stretch (8% amplitude at a rate of 2 cycles min -1 ) was applied for 24, 48 and 96 consecutive hours. Morphology, cell number and preferential cell alignment were evaluated. Apoptosis- and autophagy-related gene expression levels were measured using quantitative PCR. 3D-cultured osteoblasts became osteocyte-like cells that expressed osteocyte-specific genes such as Dmp1 , Cx43 , Sost , Fgf23 and RANKL , with morphological changes similar to osteocytes. Cell number was significantly decreased in a time-dependent manner under non-loaded conditions, whereas cyclic mechanical stretch significantly prevented decreased cell numbers with increased expression of anti-apoptosis-related genes. Moreover, cyclic mechanical stretch significantly decreased cell size and ellipticity with increased expression of autophagy-related genes, LC3b and atg7 . Interestingly, preferential cell alignment did not occur, irrespective of mechanical stretch. These findings suggest that an anti-apoptotic effect contributes to network development of osteocyte-like cells under loaded condition. Spherical change of osteocyte-like cells induced by mechanical stretch may be associated with autophagy upregulation. Preferential alignment of osteocytes induced by mechanical load in vivo may be partially predetermined before osteoblasts differentiate into osteocytes and embed into bone matrix.

Strain Measurement System Developed for Biaxially Loaded Cruciform Specimens

Science.gov (United States)

Krause, David L.

2000-01-01

A new extensometer system developed at the NASA Glenn Research Center at Lewis Field measures test area strains along two orthogonal axes in flat cruciform specimens. This system incorporates standard axial contact extensometers to provide a cost-effective high-precision instrument. The device was validated for use by extensive testing of a stainless steel specimen, with specimen temperatures ranging from room temperature to 1100 F. In-plane loading conditions included several static biaxial load ratios, plus cyclic loadings of various waveform shapes, frequencies, magnitudes, and durations. The extensometer system measurements were compared with strain gauge data at room temperature and with calculated strain values for elevated-temperature measurements. All testing was performed in house in Glenn's Benchmark Test Facility in-plane biaxial load frame.

Damage accumulation of bovine bone under variable amplitude loads

Directory of Open Access Journals (Sweden)

Abbey M. Campbell

2016-12-01

Full Text Available Stress fractures, a painful injury, are caused by excessive fatigue in bone. This study on damage accumulation in bone sought to determine if the Palmgren-Miner rule (PMR, a well-known linear damage accumulation hypothesis, is predictive of fatigue failure in bone. An electromagnetic shaker apparatus was constructed to conduct cyclic and variable amplitude tests on bovine bone specimens. Three distinct damage regimes were observed following fracture. Fractures due to a low cyclic amplitude loading appeared ductile (4000 μϵ, brittle due to high cyclic amplitude loading (>9000 μϵ, and a combination of ductile and brittle from mid-range cyclic amplitude loading (6500 –6750 μϵ. Brittle and ductile fracture mechanisms were isolated and mixed, in a controlled way, into variable amplitude loading tests. PMR predictions of cycles to failure consistently over-predicted fatigue life when mixing isolated fracture mechanisms. However, PMR was not proven ineffective when used with a single damage mechanism. Keywords: Bone fatigue, Bone fracture, Health system monitoring, Failure prediction

Conditional Stochastic Processes Applied to Wave Load Predictions

DEFF Research Database (Denmark)

Jensen, Jørgen Juncher

2015-01-01

The concept of conditional stochastic processes provides a powerful tool for evaluation and estimation of wave loads on ships and offshore structures. This article first considers conditional waves with a focus on critical wave episodes. Then the inherent uncertainty in the results is illustrated...

Creep fatigue damage under multiaxial conditions

International Nuclear Information System (INIS)

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

1977-01-01

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

A biomechanical comparison of tendon-bone interface motion and cyclic loading between single-row, triple-loaded cuff repairs and double-row, suture-tape cuff repairs using biocomposite anchors.

Science.gov (United States)

Barber, F Alan; Drew, Otis R

2012-09-01

To compare tendon-bone interface motion and cyclic loading in a single-row, triple-loaded anchor repair with a suture-tape, rip-stop, double-row rotator cuff repair. Using 18 human shoulders from 9 matched cadaveric pairs, we created 2 groups of rotator cuff repairs. Group 1 was a double-row, rip-stop, suture-tape construct. Group 2 was a single-row, triple-loaded construct. Before mechanical testing, the supraspinatus footprint was measured with calipers. A superiorly positioned digital camera optically measured the tendon footprint motion during 60° of humeral internal and external rotation. Specimens were secured at a fixed angle not exceeding 45° in reference to the load. After preloading, each sample was cycled between 10 N and 100 N for 200 cycles at 1 Hz, followed by destructive testing at 33 mm/s. A digital camera with tracking software measured the repair displacement at 100 and 200 cycles. Ultimate load and failure mode for each sample were recorded. The exposed anterior footprint border (6.5% ± 6%) and posterior footprint border (0.9% ± 1.7%) in group 1 were statistically less than the exposed anterior footprint border (30.3% ± 17%) and posterior footprint border (29.8% ± 14%) in group 2 (P = .003 and P row rotator cuff repair had greater footprint coverage, less rotational footprint displacement, and a greater mean ultimate failure load than the triple-loaded, single-row repair on mechanical testing. No double-row or single-row constructs showed 5 mm of displacement after the first 100 cycles. The most common failure mode for both constructs was suture tearing through the tendon. Differences in cuff fixation influence rotational tendon movement and may influence postoperative healing. Stronger repair constructs still fail at the suture-tendon interface. Copyright © 2012 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Modelling of cyclic plasticity for austenitic stainless steels 304L, 316L, 316L(N)-IG

Energy Technology Data Exchange (ETDEWEB)

Dalla Palma, Mauro, E-mail: mauro.dallapalma@igi.cnr.it

2016-11-01

Highlights: • Stress-strain amplitudes of cyclic stress strain curves defined by design codes are provided as reference data. • A macroinstruction simulating cyclic plasticity and producing hardening parameters of constitutive models is developed. • Hardening parameters of the nonlinear Chaboche model are provided for stainless steels 316l-N, 316L, 304L at different temperatures. • Ratcheting is simulated by using the produced hardening parameters. - Abstract: The integrity assessment of structures subjected to cyclic loading must be verified with regard to cyclic type damage including time-independent fatigue and progressive deformation or ratcheting. Cyclic damage is verified simulating the material elastic-plastic loop and looking at the accumulated net plastic strain during each cycle at all points of the structure subjected to the complete time history of loadings. This work deals with the development of a numerical model producing the Chaboche hardening parameters starting from stress-strain data produced by testing of materials. Then, the total plastic strain can be simulated using the Chaboche inelastic constitutive model requested for finite element analyses. This is particularly demanding for pressure vessels, pressurised piping, boilers, and mechanical components of nuclear installations made of stainless steels. A design optimisation by iterative analyses is developed to approach the stress-strain test data with the Chaboche model. The parameters treated as design variables are the Chaboche parameters and the objective function to be minimised is a combination of the deviations from test data. The optimiser calls a macroinstruction simulating cyclic loading of a sample for different material temperatures. The numerical model can be used to produce hardening parameters of materials for inelastic finite element verifications of structures with complex joints like elbows subjected to a combination of steady sustained and cyclic loads.

Cyclic operation of power plant; Cyklisk drift av kraftvaermeverk

Energy Technology Data Exchange (ETDEWEB)

Storesund, Jan

2007-12-15

The great majority of power plants are designed for base load operation with a relatively small number of starts and stops per year. Therefore, there has been no need to consider fatigue at design. Over the last few years operation with more frequent starts and stops exists as a consequence of swinging electricity prices that has become common. This involves significantly higher frequency of damages; not least fatigue relates damages, and the number of severe failures in components that never before have had damage problems may increase as well. In the present work the different types of component that may suffer from cyclic operation related damage are gathered by a literature survey and described as follows: - where and how the damages comes up, - constructions that should be avoided, - non-destructive testing (NDT) for damage that may come up under cyclic operation, - calculation and assessment of integrity of critical components - areas where continued research would be valuable. Recommendations have been put together to be used to prevent cyclic operation related damage and to detect it in time. The target group for this study is i) plant owners of plants where cyclic operation is or may be present, ii) researchers in the area, and, iii) inspectors and NDT-operators. There are quite a number of components where cyclic operation has been found to significantly influence the lift time. Some of these components are described in many papers whereas occasional papers have been found for others. The amount of information that is possible to get for a certain component is likely related to its significance for cyclic operation damage. The most frequently reported problem is ligament cracking of high temperature headers. Other components where extensive studies have been done are: wall panels, creep-fatigue loaded welds and turbine components

A cyclic constitutive law for metals with a semi-discrete memory variable for description of ratcheting phenomena

International Nuclear Information System (INIS)

Andrieux, S.; Schoenberger, P.; Taheri, S.

1993-01-01

The study of cyclic elastoplastic constitutive laws is, at the moment, focused on non proportional loadings, but for uniaxial loadings some problems remain, as for example the ability for a law to describe simultaneously ratcheting in non symmetrical load-controlled test, elastic and plastic shakedown in symmetrical and non symmetrical ones. We have proposed in a law with a discrete memory variable which, in addition to previous phenomena, describes the cyclic hardening in a pushpull test, and the cyclic softening after overloading. A modified law has been proposed to take into account the dependence of cyclic strain stress curve on the history of loading. The extension to 3D situations of this law is proposed. The discrete nature of the memory leads to discontinuity problems for some loading paths, a modification is then proposed which uses a differential evolution law. For large enough uniaxial cycles, the uniaxial law is nevertheless recovered. In this paper, an incremental form of the implicit evolution problem is given, and we describe the implementation of this model in the Code Aster - a thermomechanical structural software using the finite element method (f.e.m) developed at Electricite de France. Comparison between experiment and numerical results is given for uniaxial ratcheting, non proportional strain controlled test

Random spectrum loading of dental implants: An alternative approach to functional performance assessment.

Science.gov (United States)

Shemtov-Yona, K; Rittel, D

2016-09-01

The fatigue performance of dental implants is usually assessed on the basis of cyclic S/N curves. This neither provides information on the anticipated service performance of the implant, nor does it allow for detailed comparisons between implants unless a thorough statistical analysis is performed, of the kind not currently required by certification standards. The notion of endurance limit is deemed to be of limited applicability, given unavoidable stress concentrations and random load excursions, that all characterize dental implants and their service conditions. We propose a completely different approach, based on random spectrum loading, as long used in aeronautical design. The implant is randomly loaded by a sequence of loads encompassing all load levels it would endure during its service life. This approach provides a quantitative and comparable estimate of its performance in terms of lifetime, based on the very fact that the implant will fracture sooner or later, instead of defining a fatigue endurance limit of limited practical application. Five commercial monolithic Ti-6Al-4V implants were tested under cyclic, and another 5 under spectrum loading conditions, at room temperature and dry air. The failure modes and fracture planes were identical for all implants. The approach is discussed, including its potential applications, for systematic, straightforward and reliable comparisons of various implant designs and environments, without the need for cumbersome statistical analyses. It is believed that spectrum loading can be considered for the generation of new standardization procedures and design applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of cyclic fatigue stress-biocorrosion on noncarious cervical lesions.

Science.gov (United States)

Grippo, John O; Chaiyabutr, Yada; Kois, John C

2013-08-01

Although there is a high prevalence of noncarious cervical lesions (NCCLs), the etiology of these lesions remains contentious. To evaluate the combined effects of cyclic fatigue stress and biocorrosion activity on NCCLs. Extracted premolar teeth were allocated into four groups (N = 10). Two groups were cyclically fatigue loaded (100 N; 72 cycles per minute; 9,200 cycles) and placed in either hydrochloric acid gel (pH = 0.1) or orange juice (pH = 4). The other two groups were stored in identical chemical solutions without fatigue load. The buccal-lingual width of each tooth was measured before and after testing. The depth of biocorrosion, normalized by the percentage change in buccolingual width, normalized by time (hour) was calculated. The data were analyzed using a two-way analysis of variance and Tukey's HSD multiple comparison test (α = 0.05). Mean (SD) of the depth of biocorrosion values were as follows: teeth receiving fatigue loading with hydrochloric acid gel exposure (1.003%/hour [0.063]) revealed a significantly higher depth of biocorrosion than the fatigue-loaded group with orange juice exposure (0.511%/hour [0.281]) (p biocorrosion than the group with orange juice (0.009%/hour [0.004]) (p biocorrosion than either group without fatigue loading (p biocorrosion had a significant effect on the depth of the NCCLs. In order to manage the destructive NCCLs lesions properly, it is essential to understand the etiology of these lesions. The present study indicated that the combined mechanisms of cyclic fatigue stress and biocorrosion could contribute to the formation of NCCLs. © 2013 Wiley Periodicals, Inc.

Cyclic behavior of low rise concrete shear walls containing recycled coarse and fine aggregates

NARCIS (Netherlands)

Qiao, Qiyun; Cao, Wanlin; Qian, Zhiwei; Li, Xiangyu; Zhang, Wenwen; Liu, Wenchao

2017-01-01

In this study, the cyclic behaviors of low rise concrete shear walls using recycled coarse or fine aggregates were investigated. Eight low rise Recycled Aggregates Concrete (RAC) shear wall specimens were designed and tested under a cyclic loading. The following parameters were varied:

Cyclic completion of the anamorphic universe

Science.gov (United States)

Ijjas, Anna

2018-04-01

Cyclic models of the universe have the advantage of avoiding initial conditions problems related to postulating any sort of beginning in time. To date, the best known viable examples of cyclic models have been ekpyrotic. In this paper, we show that the recently proposed anamorphic scenario can also be made cyclic. The key to the cyclic completion is a classically stable, non-singular bounce. Remarkably, even though the bounce construction was originally developed to connect a period of contraction with a period of expansion both described by Einstein gravity, we show here that it can naturally be modified to connect an ordinary contracting phase described by Einstein gravity with a phase of anamorphic smoothing. The paper will present the basic principles and steps in constructing cyclic anamorphic models.

Creep of concrete under various temperature, moisture, and loading conditions

International Nuclear Information System (INIS)

McDonald, J.E.

1976-01-01

An investigation was conducted to obtain information on the time-dependent deformation behavior of concrete in the presence of temperature, moisture, and loading conditions similar to those encountered in a prestressed concrete reactor vessel (PCRV). Variables included concrete strength, aggregate types, curing history, temperature, and types of loading (uniaxial, hydrostatic, biaxial, and triaxial). There were 66 test conditions for creep tests and 12 test conditions for unloaded or control specimens. Experimental results are presented and discussed. Comparisons are made concerning the effect of the various test conditions on the behavior of concrete, and general conclusions are formulated

An improved Armstrong-Frederick-Type Plasticity Model for Stable Cyclic Stress-Strain Responses Considering Nonproportional Hardening