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Scaled rolling contact fatigue tests, used to practically simulate the wear of the wheel and rail material under laboratory conditions, are typically classified into two categories. Tests in the first category use twin-disc stands, while the second group of test rigs use two discs of different diameters considering the rail disc as the larger one. The latter setup is closer to the real situation, but problems can occur with high contact pressures and tractions. The focus of this paper is on two main contributions. Firstly, a case study based on finite element analysis is presented, allowing the optimization of the specimen geometry for high contact pressures. Accumulated plastic deformation caused by cycling is responsible for abrupt lateral deformation, which requires the use of an appropriate cyclic plasticity model in the finite element analysis. In the second part of the study, two laser profilers are used to measure the dimensions of the specimen in real time during the rolling contact fatigue test. The proposed technique allows the changes in the specimen dimensions to be characterized during the test itself, and therefore does not require the test to be interrupted. By using real-time values of the specimen's dimensional contours, it is possible to calculate an instantaneous value of the slip ratio or the contact path width. [ABSTRACT FROM AUTHOR]

• Destructive contour method for measuring residual stress in rails is presented. • Integrating residual stress into FEA model to assess rail ratcheting behaviours. • Tensile residual stress at railhead accelerates the onset of ratcheting damages. • The redistribution of the residual stress occurs in the first loading cycle. Residual stress from manufacturing significantly impacts rail durability under the conditions of repeated wheel-to-rail contact. Using the destructive contour method, this study assessed the manufacturing-introduced residual stress in a low-alloyed heat-treated heavy haul rail by measuring surface displacements due to stress relaxation after making a cut into the rail. A two-dimensional map showing the longitudinal residual stress distribution was constructed and applied to a quasi-static wheel-rail contact finite element model to explore the potential effect of residual stress on ratcheting behaviours of the rail with practical working conditions. Findings revealed that tensile longitudinal residual stress at the railhead, a result of manufacturing, markedly accelerates the onset of damages driven by the ratcheting mechanism, such as rolling contact fatigue cracks. Additionally, the residual stress redistributes after the first loading cycle due to the plastic deformation under the combined contact stresses and residual stress, and then it stabilizes in subsequent cycles. This research validates the utility of the contour method for mapping residual stresses and demonstrates how manufacturing-induced tensile stress detrimentally impacts ratcheting behaviours in heavy-haul rails, thus enhancing comprehension regarding the influence of residual stress on rail degradation. [ABSTRACT FROM AUTHOR]

Various models for simulating rail ratcheting behaviour were developed to study rolling contact fatigue (RCF) damage in rails. However, limitations remain in terms of the accuracy of wheel–rail contact modelling and computational efficiency of the cyclic loading simulation. This study developed an efficient 3D finite element (FE) procedure to simulate ratcheting in rails subjected to numerous load cycles. The procedure simulates a wheel rolling repeatedly over a rail section with updated stress–strain states, enabling automatically executed cyclic loading simulation given a predefined number of cycles. To ensure the accuracy of the contact modelling, the effect of meshing schemes on subsurface stress distribution was examined. In addition, the FE contact model with the selected meshing scheme, which balances accuracy and computational efficiency, was verified against the widely accepted CONTACT program. Subsequently, a non-linear kinematic hardening (NLKH) steel material was used in the FE model for ratcheting simulations with up to 100 wheel-loading cycles. The rail surface and subsurface stress states were replicated under partial-slip wheel–rail rolling contact conditions with traction coefficients of 0.10, 0.20 and 0.35, respectively. The ratcheting behaviour was extensively analysed in terms of plastic deformation, contact patch evolution, and ratcheting rates. The simulated plastic deformation was found to alter the contact geometry and thus contact stresses, which in turn affect further accumulation of plastic deformation and subsequent ratcheting strains. These findings highlighted the importance of considering the interplay between the rail ratcheting behaviour of the rail and evolving contact conditions for predicting ratcheting and RCF damage in rails. • Develop an efficient, automated and reliable procedure for rail ratcheting simulation. • Verify the FE wheel–rail contact model against the widely accepted CONTACT programme. • Simulate 100 cycles of wheel rolling contacts using non-linear kinematic hardening steel. • Capture the interplay between the rail ratcheting behaviour and contact patch evolution. [ABSTRACT FROM AUTHOR]

Deformation of rectilinear elements of Du 200 pipeline made of 20 steel under cyclic loading with internal pressure has been studied experimentally. Tests were carried out on a pneumohydraulic bench under conditions close to plane stress state, room temperature, and cycle asymmetry under soft loading mode (stress control). Circumferential and axial strains were recorded at three points of a diametrical section located in the middle of the element under study. Two tubular elements were tested at different values of maximum and amplitude stresses based on 100 cycles of loading. Deformation curves (cyclic creep) of tubes in a circular direction have been obtained, the character of which is significantly non-uniform in comparison with deformation of laboratory specimens. It is shown that even a slight increase in maximum (by 4%) and amplitude (by 8%) stresses significantly (up to 50%) increases the cyclic creep strains in the circular direction. Such growth of deformations can be explained by a peculiarity of 20 steel, the deformation diagram of which in the elastoplastic transition area contains a yield point, which determines intensive deformation of the material. Fixed plastic deformations in the axial direction are more than an order smaller than circular ones, and with increasing loading cycles, they change insignificantly and coincide for the two studied tubular elements. [ABSTRACT FROM AUTHOR]

• A coupled diffusion and finite-strain plasticity framework is formulated. • Increased plastic deformation reduces the wrinkling threshold and accelerates instability. • Softening of electrode's Young modulus and yield stress activates wrinkling and ratcheting. • Ratcheting occurs concomitantly with wrinkling in the form of a growing wrinkling amplitude. Lithium-ion batteries (LIBs) often suffer from capacity fading and poor cyclic performance due to mechanical degradation of the solid-electrolyte interphase (SEI). Here we perform numerical simulations and theoretical analysis to elucidate the role of plasticity in wrinkling and ratcheting behaviors of an SEI/electrode system. A coupled diffusion and finite deformation framework is formulated and numerically implemented as a user-element subroutine (UEL) to describe transient lithium diffusion and accompanying elastic–viscoplastic deformation of the electrode. It is found that concentration dependent properties and plastic deformation facilitate wrinkling in such a system. A wrinkled morphology may further lead to ratcheting and related failure under cycling. A phase diagram of four types of cyclic behaviorsis identified in terms of the charging rate and time. Our analysis suggests several potential strategies to avoid wrinkling and ratcheting instabilities, such as charging/discharging the electrode at a sufficiently slow rate, and/or introducing a thick artificial SEI with a pre-tension. [ABSTRACT FROM AUTHOR]

Featured Application: The presented method allows applying the limit analysis of structures and reformulates the method in terms of displacements and permanent strain. In this perspective, it results that the method is stated directly considering the strain rather than the stress. Hence when one calculates the limit load factor, i.e., collapse load limit or shakedown load limit, one obtains the Melan residual strain immediately. The main disadvantage of limit analysis of structure is the uncertainty about the dissipated energy. As a consequence, the limit analysis does not occupy, within the structural analysis practice, the position it deserves. The proposed method, which can be extended to the general Finite Element Method, allows us to calculate the dissipation and to evaluate the permanent displacement compatible with it. It is, in our opinion, a useful tool to assess the structural safety in the masonry building, seismic analysis of frames to support push over and step-by-step approaches. The analogous application concerns the mechanical forecast of structural integrity under severe loads when plastic deformation is expected to occur, and one wants to allow the structure to dissipate extra-energy to prevent hazards. Safety assessment of structures can be obtained employing limit design to overcome uncertainties concerning actual response due to inelastic constitutive behavior and more generally to non-linear structural response and loads' random variability. The limit analysis is used for evaluating the safety of the structures, starting directly from load level without any knowledge of the load history. In the paper, the lower bound calculation is proposed where a new strain-based approach is used that allowed describing the residual stress and displacement in terms of permanent strain. The strategy uses the permanent strain as effective parameters of the procedure so that it is possible to assess the ductility requirements for the complete load program developed till collapse or shakedown. The procedure is compared to experimental results obtained on aluminum beams in shakedown. [ABSTRACT FROM AUTHOR]

Highlights • High cycle fatigue properties of laser powder bed fusion stainless steel 316L. • Effects of build orientation, annealing and hot isostatic pressing. • Roles of defect, microstructure and cyclic plasticity on fatigue failure mechanism. • Stress-based fatigue modelling considering the effects of cyclic plasticity. Abstract Variations in the physical and mechanical properties of parts made by laser power bed fusion (L-PBF) could be affected by the choice of processing or post-processing strategies. This work examined the influence of build orientation and post-processing treatments (annealing or hot isostatic pressing) on the fatigue and fracture behaviours of L-PBF stainless steel 316L in the high cycle fatigue region, i.e. 104–106 cycles. Experimental results show that both factors introduce significant changes in the plastic deformation properties, which affect fatigue strength via the mechanism of fatigue-ratcheting interaction. Cyclic plasticity is characterised by hardening, which promotes mean stress insensitivity and improved fatigue resistance. Fatigue activities, involving the initiation of crack at defects and microstructural heterogeneities, are of greater relevance to the longer life region where the global deformation mode is elastic. As the simultaneous actions of ratcheting and fatigue generate complex nonlinear interactions between the alternating stress amplitude and mean stress, the fatigue properties could not be effectively predicted using traditional stress-based models. A modification to the Goodman relation was proposed to account for the added effects of cyclic plasticity and was demonstrated to produce good agreement with experimental results for both cyclic hardening and softening materials. [ABSTRACT FROM AUTHOR]

The purpose of this research is determining experimentally the characteristics of tension and cyclic plastic behaviours of as‐received and annealed coppers and studying distribution of stress/strain field near the crack tip. Samples made by pure copper were annealed at 420°C for 40 minutes in electric furnace. To determine the properties of the cyclic plastic behaviour, proper tests with symmetric strain‐controlled conditions were performed on standard samples. Chaboche nonlinear hardening model was used to determine the cyclic plastic behaviour of both materials. According to results, annealing process creates isotropic hardening in the copper and also changes its initial kinematic hardening behaviour. Effects of the annealing and hardening on the variations of the stresses and strains around the crack tip were investigated. Also, ratcheting and mean stress relaxations versus number of cycles, inside the plastic region, were studied. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, we investigate the numerical convergence of a set of plasticity models with different kinematic and directional distortional hardening rules under cyclic plastic loading. In particular, we revisit the results presented in Feigenbaum et al. (2012) in order to more robustly check for convergence during the numerical integration procedure, and show that the results presented in the previous work do not converge. We investigate the role of the step-size and numerical scheme on the convergence of these models when predicting ratcheting. By reducing step-sizes and using a forward Euler scheme during numerical integration, converged solutions are obtained. The new converged results lead to new conclusions. Results still suggest that directional distortional hardening can improve ratcheting predictions, however the addition of directional distortional hardening yields less improvements compared to kinematic hardening alone than previously thought. This new conclusion, strongly suggests the need for additional modeling developments in order accurately predict ratcheting strains under a wide variety of cyclic plastic loadings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this article, we propose an approach suitable for modeling isothermal fatigue in amorphous polymers. The theory is formulated in a rate form within continuum mechanics framework without the need to measure damage changes per loading cycles. Using the approach, contribution of ratcheting to fatigue of polycarbonate (PC) was investigated and the results were compared to previous experimental observations. When subjected to uniaxial stress-controlled cyclic loadings, ratcheting deformation apparently occurs and increases with mean stress and amplitude. The development of ratcheting deformation shows an initial growth followed by a decrease to almost a constant growth rate which occupies majority of the total lifetime. Ratcheting behavior under multiaxial stress states was also investigated based on finite element analyses of a dogbone-shaped test specimen. The results show that fatigue damage develops at the sites following closely the localized plastic deformation and increases with ratcheting deformation during cyclic loadings. The results indicate that the ratcheting behavior can be exploited in the evaluation of the entire fatigue lifetime. [ABSTRACT FROM AUTHOR]

Stress- and strain-controlled tests of heat treated high-strength rail steel (Australian Standard AS1085.1) have been performed in order to improve the characterisation of the said material׳s ratcheting and fatigue wear behaviour. The hardness of the rail head material has also been studied and it has been found that hardness reduces considerably below four-millimetres from the rail top surface. Historically, researchers have used test coupons with circular cross-sections to conduct cyclic load tests. Such test coupons, typically five-millimetres in gauge diameter and ten‐millimetres in grip diameter, are usually taken from the rail head sample. When there is considerable variation of material properties over the cross-section it becomes likely that localised properties of the rail material will be missed. In another case from the literature, disks 47 mm in diameter for a twin-disk rolling contact test machine were obtained directly from the rail sample and used to validate ratcheting and rolling contact fatigue wear models. The question arises: How accurate are such tests, especially when large material property gradients exist? In this research paper, the effects of rail sampling location on the ratcheting behaviour of AS1085.1 rail steel were investigated using rectangular-shaped specimens obtained at four different depths to observe their respective cyclic plasticity behaviour. The microstructural features of the test coupons were also analysed, especially the pearlite inter-lamellar spacing which showed strong correlation with both hardness and cyclic plasticity behaviour of the material. This work ultimately provides new data and testing methodology to aid the selection of valid parameters for material constitutive models to better understand rail surface ratcheting and wear. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper presents a new type of experiment focused on investigation of the influence of mean stress and stress amplitude on steady state ratcheting realized in ST52 steel at the Technical University of Ostrava. Therefore, a new cyclic plasticity model based on the AbdelKarim–Ohno kinematic hardening rule, Jiang–Sehitoglu memory surface, and modified Calloch isotropic hardening rule is described. The model allows correct description of the stress–strain behavior of ST52 steel, including ratcheting, non-Masing behavior, and cyclic hardening under proportional as well as non-proportional loading. The model was implemented in the commercial FE code ANSYS using a Fortran subroutine. The results of all simulations focusing on the uniaxial and biaxial ratcheting prediction correspond with experiments very well. The AbdelKarim–Ohno nonlinear kinematic hardening rule in its original form gives an accurate prediction of ratcheting even for the non-proportional loading, when the additional hardening is correctly described by the isotropic hardening rule. [ABSTRACT FROM AUTHOR]

A damage-coupled constitutive model has been built to predict the ratcheting effect and fatigue life of Cu-Nb micro-composite conductor under different loading conditions. The model is rate-independent and has no isotropic hardening effect according to the experiments reported in Part I. The Abdel-Karim-Ohno model (Abdel-Karim and Ohno, 2000) is improved for a better description of the ratcheting effect. Two damage factors D t and D a are respectively defined to be related to the ratcheting strain and accumulative plastic strain. The damage factor D t is coupled to the model to reflect the stress reduction. On the contrary, the damage factor D a is not coupled to the model but still calculated to decide the failure of the conductor. Accordingly, there are three failure criteria for different peak stress levels without considering the ratcheting strain above 5%. When the peak stress is above 758.5 MPa, the failure is decided by the peak stress being equal to the tensile stress corresponding to the ratcheting strain. When the peak stress is between 650 MPa and 758.5 MPa, the failure is caused by the competition between the ratcheting strain and D a whose critical values are respectively 5% and 0.065. When the peak stress is below 650 MPa, failure happens due to D a > 0.065. As a result, the simulated ratcheting effect is more or less overestimated for some loading conditions, which leads to certain deviation between the predicted and experimental fatigue life. Nevertheless, the precision is still reasonable with the fatigue life ranging from 10 2 to 10 5 which is large enough for a further analysis of the fatigue behavior of pulsed magnets where the conductor is applied. [ABSTRACT FROM AUTHOR]

This study intends to characterize numerically the ratcheting behavior of stainless steel pipes subjected to cyclic bending and internal pressure. A cyclic plasticity constitutive model able to simulate the cyclic plastic behavior is first presented in the framework of rate-independent plasticity theory. Validity of the constitutive model is confirmed against the strain- and stress-controlled cyclic loading test data. The verified constitutive model is then applied to parametric studies in which the local (circumferential strain) and global (cross-section diameter change) ratcheting responses of pressurized straight stainless steel pipes under cyclic in-plane bending are scrutinized. The results demonstrate that the shape and degree of the ovalization which occurs during the multiaxial ratcheting are dependent not only on the geometry but also on the applied loads such as the internal pressure and the cyclic in-plane bending. [ABSTRACT FROM AUTHOR]

Knowledge of cyclic plastic deformation response at the fatigue crack tip is crucial to understand the nature of cyclic damage acting on the crack tip. Interaction between crack and defect is equally important to understand the cyclic damage progression at crack tip; however isotropic hardening model was adopted in all existing literatures. Isotropic hardening model is suitable to model only the monotonic plastic zone and unable to model the cyclic/reverse plastic zone. Kinematic hardening model is suitable to model the key cyclic plastic deformation responses like Bauschinger effect, ratcheting, and mean stress relaxation. A non-linear kinematic hardening (Chaboche) model is used in this present investigation to represent the material’s cyclic stress–strain response accurately. Effect of micro-cavity positions (angle and distance from crack tip) and sizes on plastic zones near a crack tip is investigated in this study by two dimensional plane strain finite element model of a compact tension specimen. It is observed that the size and shape of the monotonic and cyclic plastic zones are affected by position and size of the micro-cavity. During asymmetric loading condition, the ratcheting strain accumulation direction is also affected by the position of micro-cavity. [ABSTRACT FROM AUTHOR]

In the process of fluid transportation, polytetrafluoroethylene (PTFE) lined pipe is subject to constant thermal stress caused by constant temperature fluid and alternating thermal stress caused by alternate flow of cold and hot fluid, making it susceptible to progressive plastic strain accumulation, namely the ratcheting. In this paper, cold and hot shock tests of PTFE lined pipe at different temperatures were carried out. Ohno-Wang II model was used to predict the ratcheting of PTFE lined pipe under cyclic temperature loading. The simulation result shows that the ratcheting strains occur in the same position as the test result. The equivalent plastic strain control method was used to determine the ratcheting boundary temperature as 145 °C and 90 °C for PTFE lined pipes under cold and hot shock respectively. The ratcheting boundaries of lined pipe with different PTFE lining thickness were given to obtain the influence of lining thickness on ratcheting boundary. • Thermal shock experiments reveal that significant plastic deformations occur at the flanging of the PTFE lined pipe. • Thermal shock cyclic plasticity analysis was analyzed with the Ohno-Wang II kinematic hardening model. • Determining the constitutive model parameters by a series of uniaxial tensile and uniaxial ratcheting tests. • Thermal shock ratcheting boundary temperature of the PTFE lined pipe was determined. [ABSTRACT FROM AUTHOR]

One of the main failure indications in rolling bearings subjected to rolling contact fatigue (RCF) is premature subsurface cracking accompanied by white etching areas (WEAs). The cracks that are linked with WEAs are called white etching cracks (WECs). The formation mechanisms of WEAs/WECs are still highly debatable according to international state of art. Often SAE 52100 steel is used for bearing rings. Its microstructure consists of a martensitic or bainitic matrix and homogeneously distributed chromium rich cementite precipitations. There are two main hypotheses based on what forms first, the cracks or WEAs (hypothesis 1 & 2 respectively). There are many numerical studies that examine non-metallic inclusions as a source of cracks that leads to WEAs (hypothesis 1), but none that considers carbides as the source of severe plastic deformation subjected to RCF that leads to WEAs and, eventually WECs (hypothesis 2). In this study, the testing was conducted on a ZF-type modified RCF test rig with hydrogen charged samples to reproduce WEAs/WECs formation. Later the influence of the microstructural features of the carbides on the steel matrix, during the formation of WEAs was investigated by microstructural investigations and multiscale finite element modelling. It was found that carbides can contribute to severe local plastic deformation which leads to formation of WEAs. Thus, it also supported the likelihood of hypothesis 2. Additionally, the surface traction and microstructural characteristics of carbides are correlated with the wide range of WEAs formation depths and timescales. • Influence of slip and Hertzian pressure on WEA/WEC failures under diffusible hydrogen. • Microstructural investigations SEM BSE, SE imaging and SEM EBSD measurements: shearing of carbides, WEA/WECs. • Simulation models enable a detailed understanding of the impact of carbides under RCF during formation of WEAs. • Multi-scale simulation model: RCF, Influence of the microstructural features of the carbides, ratcheting effect. • Carbide shearing simulation during formation of WEAs under adiabatic and non-adiabatic conditions. [ABSTRACT FROM AUTHOR]

A version of the endochronic theory of plasticity is developed to describe the stress-strain state under stress-controlled, asymmetric biaxial non-proportional cyclic loading. In order to solve the obtained non-linear system of differential equations, the numerical procedure is proposed and the relevant computational program is developed. The model validity is verified by satisfactory agreement between the calculated and experimental data. [ABSTRACT FROM AUTHOR]

In this paper the framework of a combined Chaboche type kinematic and isotropic hardening model is explained for large deformation with Henky strain description to evaluate strain ratcheting of interference fitted double shear lap joints near the hole based on the works of Montáns et al. [doi: 10.1016/j.mechrescom.2012.03.001 ] and Henann and Anand [doi: 10.1016/j.ijplas.2008.11.008 ]. The described elasto-plasticity formulation is in the context of hyper-elasticity and based on the dual multiplicative decomposition of the deformation gradient into elastic and plastic parts. The decomposition of plastic part into energetic and dissipative part is considered and a new rheological model is suggested for extension of one term Armestrong–Frederick (A–F) model to multi-component A–F (Caboche) model in finite regime. A brief and simple numerical integration scheme is suggested for integrating the presented kinematic hardening. The suggested integration algorithm reduces the complexity of large deformation and for convenience, allows embedding small strain subroutines. To solve the system of nonlinear equations of the constitutive model, the successive substitution method is suggested for simplifying the solution and reducing the computational cost appreciably. In order to avoid non-smooth interaction between the pin and the hole, and also unrealistic plastic deformation, a well-established and an accurate frictional mortar contact formulation is used and combined with the material nonlinearity. The whole numerical formulations are coded in 3D finite element code in FORTRAN programming language and the code is optimized so that it can be efficient for ratcheting simulation over cycles. The approach shows stability and robustness in convergence due to consistent linearization of all contact and internal forces even in the presence of contact, geometry and high material nonlinearity. To evaluate the efficiency and accuracy of the presented formulations, the ratcheting data from simulation is compared with the experimental ratcheting data from strain gauges attached to the studied double shear lap joints. [ABSTRACT FROM AUTHOR]

Part I of this work introduced efficient reduced-order five-dimensional (5D) stress and strain spaces that can be used to predict ratcheting and mean stress relaxation phenomena at a much lower computation cost than in traditional 6D formulations. These 5D spaces were then applied to the qualitative study of uniaxial ratcheting, multiaxial ratcheting, and mean stress relaxation. Several non-linear kinematic (NLK) hardening models have been proposed to capture these effects in incremental plasticity simulations. In this Part II, an incremental plasticity formulation is proposed in the adopted 5D spaces, while its advantages over the classical 6D formulation are discussed. The 5D version of the main NLK models proposed in the literature are presented, which allows the definition of a unified generalized equation. The physical and geometrical interpretation of the hardening, dynamic recovery, and radial return terms from the proposed generalized equation are presented. Several surface translation rules can be represented as a particular case of the proposed model, including the ones by Chaboche (1979), Burlet–Cailletaud (1986), Ohno–Wang (1993), Jiang–Sehitoglu (1996), Bari–Hassan (2001) and Chen–Jiao (2004), among others. The adopted hardening surface representation can be used not only for the studied NLK models, but also to reproduce the Mróz–Garud multi-surface approach. Uniaxial ratcheting, multiaxial ratcheting, and mean stress relaxation experiments with 316L and 1020 steel tubular and cylindrical specimens are conducted to validate the proposed models. [ABSTRACT FROM AUTHOR]

Ratcheting is an accumulation of plastic strain that can influence fatigue lives of structural components due to the premature exhaustion of the material ductility, much earlier than predicted by traditional fatigue crack initiation models. Ratcheting is usually associated with a significant mean stress component in either uniaxial or multiaxial stress-controlled histories. The very same process can induce mean stress relaxation in strain-controlled histories, affecting fatigue lives due to consequent mean or maximum stress effects. Such processes are mainly caused by a local distortion of the yield surface, which would require the use of complex yield functions other than von Mises’ to be properly described. The addition of non-linear terms to the kinematic hardening rules compensates for this requirement, rendering it possible to model ratcheting effects using the von Mises yield function without dealing with distortion. In this two-part work, the formulation of the main non-linear kinematic (NLK) models is unified into a generalized equation, represented using engineering notation in a reduced-order five-dimensional (5D) space that may lower in half the associated computational cost. Part I introduces the proposed 5D stress and strain spaces, which are a scaled version of Ilyushin’s 5D spaces. These 5D spaces are then applied to the qualitative study of uniaxial ratcheting, multiaxial ratcheting, and mean stress relaxation. Part II of this work derives all incremental plasticity equations from the NLK approach in the spaces proposed in Part I, and discusses its advantages over the classical 6D formulation. These NLK models are then used in Part II to quantitatively predict uniaxial ratcheting, multiaxial ratcheting, and mean stress relaxation, validated from experiments with 316L steel cylindrical and tubular specimens. [ABSTRACT FROM AUTHOR]

An existing cyclic plasticity constitutive model is enhanced to simulate low-cycle fatigue and ratcheting responses of 304 stainless steel (SS) under proportional and various nonproportional loading cycles. Nonproportional loading and multiaxial ratcheting parameters, and strain range dependent cyclic hardening/softening modeling features are incorporated into a modified Ohno–Wang model to enhance its uniaxial and multiaxial loading responses. The improved constitutive model is incorporated in the commercial Finite Element Code ABAQUS through its user defined subroutine UMAT and the responses of 304 SS tubular specimen from literature have been simulated. The proposed model has demonstrated good correlation with uniaxial and different types of multiaxial fatigue and ratcheting responses. Two types of multiaxial loading cycles are studied; the first included axial and torsion cycles along different loading paths, and the second included steady internal pressure and axial strain or stress cycles. The axial–torsional loading cycles demonstrated axial and/or shear strain ratcheting, whereas the internal pressure-axial cycles demonstrated axial and/or circumferential strain ratcheting. Complex interactions between ratcheting strains in different directions along with the rate of ratcheting are simulated well by the improved Ohno–Wang model. [ABSTRACT FROM AUTHOR]

A procedure for damage assessment in wheel–rail contact is still an open task: much work has been done for understanding failure mechanisms such as wear, cyclic plasticity and Rolling Contact Fatigue, but only recently the competition between them has been taken into account. In this study, a numerical procedure for damage assessment of railway wheel steels, considering the complex interaction between various failure phenomena that can occur at the loaded region, is proposed. The procedure is based on various damage mechanism models, integrated into an overall simulation method able to take into account their reciprocal influence. The model was applied for characterising a railway wheel steel (ER8 EN13262), through the elaboration of the results of rolling–sliding experiments, determining the plasticity and the wear model constants that can be used for damage assessment of real wheels. The experiments showed that the main damage phenomenon was surface crack formation due to unidirectional plastic flow (ratcheting); in the presence of water these cracks propagated causing very severe damage. A role of manganese sulphides non-metallic inclusions as preferential site for subsurface crack nucleation was observed. A quantitative evaluation of these phenomena was provided. [ABSTRACT FROM AUTHOR]

In the framework of rate-independent plasticity theory, a constitutive model capable of simulating the uniaxial strain cycling and the uniaxial/multiaxial ratcheting responses of a super duplex stainless steel (S32750) which has cyclic hardening characteristics under strain-controlled cyclic loading is derived. In the developed constitutive model, the steady cyclic flow was reflected by the nonlinear evolution of the proposed kinematic hardening rule based on the Chaboche model and the Burlet and Cailletaud model; the cyclic hardening was modeled by the evolution of isotropic hardening; the strain memory effect was also considered through the asymptotic value of the isotropic hardening variable. Verification of the proposed constitutive model was achieved by simulating the uniaxial/multiaxial strain- and stress-controlled cyclic loading tests and comparing the predicted results with the experimental measurements. [ABSTRACT FROM AUTHOR]

This paper proposes methods for assessing Bree-type ratcheting in a cylinder subjected to constant internal pressure and cyclic thermal loading. The proposed methods are elastic analysis-route and elastic–plastic analysis-route. The former is based on the polynomial approximation of the elastic stress distributions for thermal stresses and the reference stress concept for estimating primary stress. The latter elastic–plastic route method is based on the concept of relative elastic core size. The methods proposed were validated by performing elastic–plastic finite element analyses of a smooth cylinder that exhibited Bree-type ratcheting. [ABSTRACT FROM AUTHOR]

Cyclic plastic deformation characteristics of 304LN stainless steel material have been studied with two proposed cyclic plasticity models. Model MM-I has been proposed to improve the simulation of ratcheting phenomenon and model MM-II has the capability to simulate both cyclic hardening and softening characteristics of the material at various strain ranges. In the present paper, strain controlled simulations are performed with constant, increasing and decreasing strain amplitudes to verify the influences of loading schemes on cyclic plasticity behaviors through simulations and experiments. It is observed that the material 304LN exhibits non Masing characteristics under cyclic plastic deformation. The measured deviation from Masing is well established from the simulation as well as from experiment. Simulation result shows that the assumption of only isotropic hardening is unable to explain the hardening or softening characteristics of the material in low cycle fatigue test. The introduction of memory stress based cyclic hardening coefficient and an exponentially varying ratcheting parameter in the recall term of kinematic hardening rule, have resulted in exceptional improvement in the ratcheting simulation with the proposed model, MM-II. Plastic energy, shape and size of the hysteresis loops are additionally used to verify the nature of cyclic plasticity deformations. Ratcheting test and simulation have been performed to estimate the accumulated plastic strain with different mean and amplitude stresses. In the proposed model MM-I, a new proposition is incorporated for yield stress variation based on the memory stress of loading history along with the evolution of ratcheting parameter with an exponential function of plastic strain. These formulations lead to better realization of ratcheting rate in the transient cycles for all loading schemes. Effect of mean stress on the plastic energy is examined by the simulation model, MM-I. Finally, the micro structural investigation from transmission electronic microscopy is used to correlate the macroscopic and microscopic non Masing behavior of the material. [ABSTRACT FROM AUTHOR]

In this research, softening and ratcheting behaviors of SS316L cantilevered cylindrical shells under cyclic bending load were investigated. Experimental tests were carried out by a Servo-Hydraulic INSTRON 8802 machine. Force-control and displacement-control loadings were applied and the effects of displacement amplitude, mean force, loading history and cutout position were examined. Under displacement-control loading, softening behavior was observed due to growth of ovalization and it was shown that as the displacement amplitude increases, softening rate and density of plastic energy increase. Accumulation of the plastic strain or ratcheting phenomenon occurred under force-control loading with nonzero mean force. Increase of the mean force accompanied with an increase in the accumulation of the plastic deformation and its rate. In loading history, it was seen that prior load with higher force amplitude retards the ratcheting behavior and plastic deformation of subsequent load with smaller force amplitude. In addition, due to sensitivity of cutout to the bending moment, as the position of the cutout changes from the middle of shell towards the cantilevered end, the accumulation of the plastic deformation increases. [ABSTRACT FROM AUTHOR]

Abstract: The effect of monotonic and cyclic deformation on the evolution of back stress vis-à-vis Bauschinger effect due to different amounts of unidirectional plastic deformation in annealed OFHC copper has been investigated. It is observed that for the same amount of prestrain the back stress evolution and the corresponding Bauschinger phenomenon depend upon the mode of deformation. It is found that higher back stress develops in case of monotonic deformation as compared to ratcheting deformation for same amount of unidirectional prestrain. It is also found that the effect of stress rate on the change of Bauschinger parameters is comparatively less than the effect of increasing prestrain in both types of deformation. [Copyright &y& Elsevier]

Highlights: [•] Localized ratcheting during RCF is studied at the microstructural scale. [•] The origin of ratcheting near heterogeneous carbide particle is also investigated. [•] During RCF, carbides alter the shear stress cycle, promoting localized ratcheting. [•] A novel method for estimating cyclic hardening parameters is presented. [•] The results presented are also applicable to other heterogeneous materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ratcheting experiments conducted for the first time involving twinning–detwinning in Mg. [•] Long-term ratcheting rate decay identified to follow a power law relationship. [•] Three types of cyclic deformation of Mg identified. [•] Twinning–detwinning found to be a key cyclic hardening mechanism in Mg. [ABSTRACT FROM AUTHOR]

A Frictionally constrained condition implies dependence of friction force on tangential displacement amplitude. The condition may occur due to chemical, physical, and/or me-chanical interaction between the contacting suifaces. The condition, sometimes also referred to as the presliding condition or partial slip condition, is characterized under fretting. Under such conditions, various experimental studies indicate the existence of two distinguishable regions, that is, stick region and slip region. In the present study, fric-tionally constrained conditions are identified and the evolutions of stick-slip regions are investigated in detail. Investigations have been performed on self-mated stainless steel and chromium carbide coated suifaces mated against stainless steel, under both vacuum and ambient conditions. Contact conditions prevailing at the contact interface were iden-tified based on the mechanical responses and were correlated with the surface damage observed. Surface degradation has been obsen'ed in the form of microcracks and mate-rial transfer. Detailed numerical analysis has also been performed in order to understand the energy dissipation and the damage mode involved in the surface or subsurface dam-age. It has been observed that under frictionally constrained conditions, the occurrence of annular slip features are mainly due to the junction growth, resulting from elastic-plastic deformation at the contact interface. Ratcheting has been observed as the govern-ing damage mode under cyclic tangential loading condition. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The integrity assessment of the primary piping components needs to be demonstrated under normal operation cyclic loadings as well as under complex cyclic loadings of extreme magnitude as may come during a severe earthquake event. In order to understand material's cyclic plasticity and fatigue-ratcheting behaviour, systematic experimental and analytical investigations have been carried out on specimens of SA333Gr.6 carbon steel and SS304LN stainless steel. The material specification of SA333Gr.6 is same as used in Primary Heat Transport (PHT) piping of Pressurized Heavy Water Reactors (PHWRs) and material specification of SS304LN steel is same as proposed for Indian Advance Heavy Water Reactor's (AHWR's) Main Heat Transport (MHT) piping. The test program included the tensile, axial fatigue and uniaxial ratcheting tests to establish the material's mechanical properties and cyclic plasticity behavior. The results of these tests have been investigated in details using few popular finite element cyclic plasticity models to understand and quantify the material's cyclic plasticity behavior. The studies revealed the need to modify the Chaboche model to simulate the LCF/cyclic plasticity and ratcheting under different strain/stress amplitudes loading conditions. On accounting for modification, the Chaboche model nicely predicted the LCF and ratcheting response for all the tests. The tests, finite element analyses result and their interpretations have been presented in this paper. [Copyright &y& Elsevier]

Abstract: The present paper is concerned with the experimental investigation of the progressive accumulation of deformation observed in cyclic tension tests performed on an epoxy polymer. The strain rate dependency is almost negligible and the material behaviour is elastic-plastic rather than elastic-viscoplastic or viscoelastic. Under cyclic loading and unloading, this polymer exhibits hysteresis (a phase lag), which leads to dissipation of mechanical energy and to the accumulation of cyclic plastic deformation. It is verified experimentally that this phenomenon is essentially due to kinematic hardening. Preliminary ideas for an elastic-plastic phenomenological model able to describe the plastic cyclic behaviour of this epoxy polymer are also presented. [Copyright &y& Elsevier]

Abstract: This article presents an overview of recent progresses in experimental investigation and finite element analysis (FEA) of ratcheting behavior of pressurized piping. Ratcheting, namely the cyclic accumulation of plastic deformation, occurs when the structures are subjected to a primary load with a secondary cyclic load if the applied loads are high enough to make the structures yield. Typical piping structures including straight pipes, elbow pipes and piping joints have been investigated experimentally under mechanical or thermal cyclic loading. Finite element analyses with several well-developed constitutive models implemented in the commercial software ANSYS and ABAQUS have been conducted to simulate and predict the ratcheting behavior of pressurized piping. Based on such experimental and FEA research, ratcheting boundaries have been determined with the final aim of aiding the safety design and assessment of engineering piping structures. Some suggestions for structure ratcheting study are proposed. [Copyright &y& Elsevier]

Abstract: To determine the nature of damage acting on a fatigue crack-tip, it is mandatory to know the detailed cyclic plastic deformation response. In this work, cyclic plastic deformation response has been studied on a stationary CT specimen crack-tip in an elasto-plastic finite element frame work at selected R-ratios and ΔK. Chaboche kinematic hardening model has been used to describe material behavior. Monotonic and cyclic/reverse plastic zone identified during plane strain finite element analysis. It is noticed that progressive accumulation of permanent strain i.e. ratcheting occurs in the cyclic plastic zone ahead of a fatigue crack-tip. [Copyright &y& Elsevier]

Abstract: Shakedown and ratcheting behaviour is derived for uniaxial primary membrane and thermal bending stresses both cycling strictly in-phase. The complete analytic solution for perfect plasticity is presented, including the shakedown/ratcheting diagram and the ratchet strains or cyclic plastic strains where relevant. This cyclic loading is shown to be considerably more benign than that of the original Bree problem in which the primary membrane stress does not cycle. [Copyright &y& Elsevier]

Abstract: The paper deals with uniaxial ratcheting phenomenon of cyclic plasticity behavior of the materials SA333 carbon Manganese steel. A mechanistic model for the ratcheting phenomenon has been proposed. It is observed that von Mises yield criterion together with Chaboche’s kinematic hardening rules are not sufficient to model ratcheting phenomenon. Other associated phenomena like plastic strain memory surface, back stress memory points and over all the extra hardening behavior have to be incorporated to get a complete material model for ratcheting. The proposed model assembled all these ideas together with von Mises yield criterion and Chabache’s kinematic hardening rule. Low cycle fatigue tests and uniaxial ratcheting tests have been conducted for the materials. The material constants are identified and derived from experimental results. The ratcheting coefficients have been properly calibrated with these material constants. The material model, as mentioned above, for the ratcheting phenomenon has been implemented in an elastic plastic finite element code. The ratcheting results for different stress controlled ratcheting loads have been computed. The good feature of this model is that it reduces to symmetric low cycle fatigue model when loop closes. [Copyright &y& Elsevier]

Abstract: In this study, the yield surface distortion was incorporated in the cyclic plasticity modeling as well as its center movement. The combination of Chaboche’s model and the yield surface distortion model of Baltov was used in a set of uniaxial and multiaxial loadings. The variation of the stress amplitude and the mean stress and different multiaxial loadings such as tension-torsion tests were studied. It was shown that the consideration of the distortion of the yield surface via the distortion parameter and its sign in modeling has an important effect on the plastic strain increment determination and so on the ratcheting rate. The combined model was applied to the experimental results. It was shown that the combination of the nonlinear kinematic hardening model of Chaboche and the yield surface distortion leads to a good estimation of the ratcheting strain increment in different uniaxial and multiaxial tests. [Copyright &y& Elsevier]

Abstract: Cyclic plastic deformation phenomena include the Bauschinger effect, cyclic hardening/softening, strain range effect, loading history memory, ratcheting, mean stress dependent hardening, mean stress relaxation and non-proportional hardening. In this work, different cyclic plastic deformation responses of piping materials (SA333 C–Mn steel and 304LN stainless steel) are experimentally explored. Cyclic hardening/softening is depends upon loading types (i.e. stress/strain controlled), previous loading history and strain/stress range. Pre-straining followed by LCF and mean stress relaxation shows similar kind of material response. Substantial amount of non proportional hardening is observed in SA333 C–Mn steel during 90° out of phase tension-torsion loading. During ratcheting, large amount of permanent strain is accumulated with progression of cycles. Permanent strain accumulation in a particular direction causes cross-sectional area reduction and which results uncontrollable alteration of true stress in engineering stress controlled ratcheting test. In this work, true stress control ratcheting on piping materials has been carried out in laboratory environment. Effects of stress amplitude and mean stress on the ratcheting behaviors are analyzed. A comparison has also been drawn in between the true and engineering stress controlled tests, and massive difference in ratcheting life and strain accumulation is found. [Copyright &y& Elsevier]

Abstract: Under compression, pressurized tubes thick enough to deform plastically buckle into an axisymmetric wrinkling mode. The wrinkle amplitude is initially small but with persistent compression grows inducing a gradual reduction in axial rigidity and eventually causing a limit load instability, which is followed by collapse. The onset of buckling and collapse can be separated by a strain level of a few percent. This work investigates whether a tube that develops small-amplitude wrinkles can be subsequently collapsed by persistent axial cycling. Part I presents the results from a set of experiments on super-duplex tubes with D/t of 28.5 loaded as follows. A tube is pressurized and then compressed into the plastic range to a level that initiates wrinkling. It is then cycled under stress control about a compressive mean stress while the pressure is kept constant. The combined loads cause simultaneous ratcheting in the hoop and axial directions as well as a gradual growth of the wrinkles. At some stage the amplitude of the wrinkles starts to grow exponentially with the number of cycles N leading to localization and collapse. The rate of ratcheting and the number of cycles to collapse depend on the initial compressive pre-strain, the internal pressure, and the stress cycle parameters all of which were varied sufficiently to generate an adequate data base. Interestingly, in all cases collapse was found to occur when the accumulated average strain reached the value at which the tube localizes under monotonic compression. A shell model coupled to a specially calibrated plasticity model that can reproduce the biaxial ratcheting exhibited in the problem are presented in Part II. The model is first evaluated by comparison to the experiments and then used to study parametrically cyclic loading histories seen in buried pipelines. [Copyright &y& Elsevier]

Abstract: Low cycle fatigue, ratcheting and dependence of their deformation response on previous deformation histories are investigated at room temperature laboratory environment for SA333 C–Mn steel. It is noticed that cyclic hardening/softening response of low cycle fatigue is considerably influenced by applied strain amplitude, monotonic pre-straining and high to low step loading sequences. Results indicate that ratcheting under high to low step loading has significant effect on its subsequent ratcheting response. However, ratcheting under low to high step loading has very little effect on successive ratcheting responses. [Copyright &y& Elsevier]

Abstract: Determining the boundary between the shakedown and ratcheting domains (ratchet boundary) for a component using cyclic elastic-plastic analysis is computationally very expensive since it requires a solution over several loading cycles to be repeated several times. A non-cyclic method to identify the ratchet boundary directly without the need for cyclic analysis was recently proposed. The numerical implementation of the non-cyclic method offers the promise to be an attractive alternative to cyclic elastic-plastic analysis since it is simple, and requires considerably less computational effort and computer storage space. Another attractive feature is that the method provides a go/no go criterion for the ratchet boundary, whereas the results of a cyclic elastic-plastic analysis are often difficult to interpret near the ratchet boundary. To explore the performance of the method further, it is applied to a number of configurations that include two-dimensional and three-dimensional effects. [Copyright &y& Elsevier]

BSTRACT [ABSTRACT FROM AUTHOR]

Abstract: 304LN stainless steel samples are tested in room temperature under low cycle fatigue (LCF), ratcheting, pre-ratcheting followed by LCF and tensile, and pre-LCF followed by tensile conditions to understand the deformation behavior and damage evolution during cyclic plastic deformation. It is found that pre-ratcheting have massive detrimental effect on its subsequent LCF life. Systematic alterations in tensile properties are noticed with cyclic plastic damage evolution in this work. Orderly alteration of tensile yield stress with cyclic hardening/softening of the material is also observed. [Copyright &y& Elsevier]

The present study aims to evaluate the capabilities of a class of models that take into account non-linear isotropic and kinematic hardening. The purpose is to predict the behaviour of a 'Bi-tube' structure when submitted to a cyclic thermo-mechanical loading. The first part consists of an overview of the methods of describing different kinematic hardening variables. In the second part, the studied structure and the results of numerical simulation of the models used are presented, with an emphasis on the sensitivity of the analysis with regard to the choice of the element type, using a FE software 'Code-Aster', developed by Electricité de France. This study constitutes a first step in the validation of the models of cyclic behaviour with respect to tests on structures, limited in this first case to Bi-tube structure. The comparison between numerical predictions and the experimental results demonstrates that the model of Taheri seems to be the best adapted to the study of 'Bi-tube' structures because it leads to stabilisation around 1%, which is comparable to the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: Low cycle fatigue experiments have been conducted on 304LN stainless steel in ambient air at room temperature. Uniaxial ratcheting behavior has also been studied on this material and in both engineering and true stress controlling modes. It is shown that material’s cyclic hardening/softening behavior in low cycle fatigue and in ratcheting is dependent not only on material but also on the loading condition. Improvement of ratcheting life and mean stress dependent hardening are observed in the presence of mean stress. A method based on the strain energy density (SED) is used to represent cyclic hardening/softening behavior of the material in this work. The decrease of SED with cycles is an indication that the life in low cycle fatigue and in ratcheting is improved. The SED represents the area of the hysteresis loops. [ABSTRACT FROM AUTHOR]