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In this present work, a damage-coupled cyclic plasticity model has been developed for more accurate ratcheting–fatigue life estimation under strain and stress controlled ratcheting. Ratcheting–fatigue damage behavior under uniaxial multistep strain-controlled ratcheting shows that the incremental mean ratcheting strain deteriorates the elastic slopes cycle by cycle, by means of ratcheting damage. Severe ratcheting strain accumulation rate has been observed in tertiary region under uniaxial stress controlled ratcheting. The proposed damage-coupled model has been constructed which incorporates both fatigue damage and damaging effect of the accumulated mean plastic strain. The proposed model incorporates a critical fatigue damage parameter which can predict effects of early fatigue crack nucleation due to combined ratcheting and fatigue damages. The performance of the proposed damage-coupled model has been investigated in the present study based on the critical fatigue damage parameter. The proposed model is calibrated on experimental data of SA333 Gr. 6 carbon steel and SA508 Gr. 3 steel. The proposed formulations have been applied in user material subroutine UMAT of finite element software, ABAQUS. The proposed model has been validated by comparing predicted ratcheting behavior with experiments for the two different steels. All the predicted number of cycles to failure are located within 0.5 times error band. The proposed damage-coupled model has demonstrated excellent capabilities of predicting ratcheting–fatigue life under cyclic loading with ratcheting damage. [ABSTRACT FROM AUTHOR]

Ratcheting analysis for cantilever beams subjected to the thermomechanical loads is presented using the finite element method. The cantilever beam is constrained along the vertical direction, and plane stress conditions are assumed according to the bilinear isotropic hardening model. Two points are considered to obtain areas of ratcheting by using linear extrapolation. The results and output diagrams for ratcheting with elastic-perfect plastic behavior are illustrated. It was revealed that the beam behaves elastically after the first considerable plastic strain, which is seen in two shakedown regimes. The numerical results are verified with known and analytical results in the literature. The results indicate a strong correlation between the outcomes from the cyclic ANSYS Parametric Design Language (APDL) model and Bree's analytical predictions. This consistency between the finite element analysis and the analytical solutions underscores the potential of finite element analysis as a powerful tool for addressing complex engineering challenges, offering a reliable and robust alternative to traditional analytical methods. [ABSTRACT FROM AUTHOR]

The operation of a fuel cell poses significant problems related to local current density and the failure rate of components. The issue results from high flow resistance and stresses that guarantee the tightness of the stack. Low flow resistance allows the stack to be used in Hybrid Energy Storage. This study shows that the selection of the best variant of the channel shape in a fuel cell should be based on more than just observing electrochemical performance. Increasing the current density flux can lead to faster component degradation. Older material degradation models based on the strain tensor will only accurately identify some risks. Thanks to the use of Perzyna's viscoplastic model, it was possible to protect the fuel cell from premature failure. Earlier studies did not indicate how the changes in the shape introduced, improving the electrochemical properties, impacted the component's service life during cyclic loads. [Display omitted] • Sinusoidal channels showed a higher power density than the parallel channel. • The sinusoidal wave generates an additional convective mass flux. • The shape canal change did not affect the time to mixed-type fracture. • The use of Perzyna's model showed a cyclical increase in strain energy. • The cyclic increase in plastic strain describes the ratcheting phenomenon. [ABSTRACT FROM AUTHOR]

The deformation of a straight pipeline segment under stepwise cyclic loading by internal pressure is investigated. The tests were carried out on a pneumohydraulic bench, allowing one to determine the strength and durability characteristics of full-scale pressure vessels and pipeline elements under conditions close to operational ones. The pipe element was loaded with stress control. The asymmetric loading regime was a sequence of three types of cycles at a constant stress amplitude with a step change in the mean stress after stabilizing the strain rate. The load level corresponded to the lowcycle fatigue region with distinctive elastoplastic strain of the material. The experiment aimed to obtain diagrams of ratcheting (cyclic creep) of the pipe under the action of a biaxial proportional load from internal pressure (pulsating cycle) depending on the change in the mean stress of the cycle. It is shown that for a pipe element, similar to laboratory specimens, an increase in the load level (compared to that applied at the previous stage) enhances the effect of ratcheting in the circular direction. In contrast, a return to the initial lower level eliminates this effect. Unlike laboratory specimens, the accumulation of ratcheting strains in the pipe element during the first 20 cycles is uneven. A steady-state rate of strain accumulation is observed after reaching 40 loading cycles. An increase in the accumulated plastic strains of the ratcheting in the circular direction with an increase in loading cycles significantly affects the initial distribution of strains in the axial direction. [ABSTRACT FROM AUTHOR]

Low-amplitude repetitive drained loading may hinder the long-term performance of engineered and natural systems. This study examines the volumetric and shear response of a uniform quarzitic sand subjected to repetitive drained simple shear loading under constant vertical stress while tracking the evolution of the secant stiffness and the small-strain shear modulus. We explore the effects of initial density, initial shear stress and cyclic shear stress amplitude to identify criteria that can be used to anticipate asymptotic volumetric and shear states. We analyze experimental results in reference to the sand response under monotonic simple shear loading. All specimens evolved toward some asymptotic terminal void ratio eT when subjected to simple shear cycles. Contractive specimens exhibited unceasing shear strain accumulation and ratcheting when the normalized shear stress exceeded τ*=(τo+Δτ)/τult>0.85 ; on the other hand, dense-dilative specimens exhibited ratcheting only when the normalized shear stress exceeded τ*=(τo+Δτ)/τult>1.25. The small-strain Gmax and the secant Gpp shear moduli increased during repetitive shear cycles to reflect early fabric changes followed by abrasion/fretting among enduring contacts. Results obtained in this study allow us to propose simple guidelines to predict the asymptotic shear and volumetric response of uniform sands subjected to repetitive simple shear loading for first-order engineering analyses. [ABSTRACT FROM AUTHOR]

A long-time dynamic for granular materials arising in the hypoplastic theory of Kolymbas type is investigated. It is assumed that the granular hardness allows exponential degradation, which leads to the densification of material states. The governing system for a rate-independent strain under stress control is described by implicit differential equations. Its analytical solution for arbitrary inhomogeneous coefficients is constructed in closed form. Under cyclic loading by periodic pressure, finite ratcheting for the void ratio is derived in explicit form, which converges to a limiting periodic process (attractor) when the number of cycles tends to infinity. [ABSTRACT FROM AUTHOR]

• R atcheting behaviour of Co-Cr laser cladding alloy Stellite 21 was investigated under uniaxial cyclic loading. • Ratcheting behaviour of R260 used in tram crossings was studied under uniaxial and biaxial cyclic loading. • Stellite 21 showed superior mechanical properties and ratcheting performance compared to R260. • Both Stellite 21 and R260 exhibited initial cyclic hardening followed by stabilized ratcheting. Laser cladding holds the promise to repair damaged rails, including flange tip lift crossings (FTLC) in tram rails. In order to further understand the effectiveness of laser cladding against rail damage, this study investigated the ratcheting behaviour of the laser cladding alloy Stellite 21, used in FTLC repairs, in comparison to the currently used rail steel grade R260. Experimental studies were conducted under uniaxial and biaxial stress-controlled cyclic loads. The study found that under identical uniaxial stress conditions, Stellite 21 exhibits superior ratcheting behaviour compared to R260 steel. Various mean stresses and stress amplitudes were also studied, revealing that increases in mean stresses or stress amplitudes resulted in higher ratcheting strains and ratcheting strain rates. Additionally, biaxial compression-torsion cyclic loading tests were performed on the R260 to replicate real-life stress conditions. The results indicated that the direction of plastic strain accumulation depended on the direction of the applied non-zero mean stress. The findings from this study are essential for calibration of parameters of cyclic plasticity models, which can be used to simulate ratcheting performance of laser-cladded FTLCs under in-service conditions for the prediction of fatigue crack initiation life and maintenance requirements of flange tip lift crossings. [ABSTRACT FROM AUTHOR]

Microalloyed steels have emerged to replace conventional plain-carbon steels to achieve longer wheel life on Chinese railroads. In this work, with the aim of preventing spalling, a mechanism that consists of ratcheting and shakedown theory correlated with steel properties is systematically investigated. Mechanical and ratcheting tests were carried out for microalloyed wheel steel to which vanadium was added in the range of 0–0.15 wt.% and the results were compared with that obtained for conventional plain-carbon wheel steel. The microstructure and precipitation were characterized via microscopy. As a result, the grain size was not obviously refined, and the pearlite lamellar spacing decreased from 148 nm to 131 nm in microalloyed wheel steel. Moreover, an increase in the number of vanadium carbide precipitates was observed, which were mainly dispersed and uneven, and precipitated in the pro-eutectoid ferrite region, in contrast to the observation of lower precipitation in the pearlite. It has been found that vanadium addition can lead to an increase in yield strength by precipitation strengthening, with no reduction or increase in tensile strength, elongation or hardness. The ratcheting strain rate for microalloyed wheel steel was determined to be lower than that for plain-carbon wheel steel via asymmetrical cyclic stressing tests. An increase in the pro-eutectoid ferrite content leads to beneficial wear, which can diminish spalling and surface-initiated RCF. [ABSTRACT FROM AUTHOR]

This study uses experimental and numerical methods to examine the impact of average fatigue force, amplitude fatigue force, and internal pressure on the ratcheting behavior of SS316L concentric and eccentric reducers. The material of the samples was first verified through mechanical analyses. Subsequently, the samples were fatigue tested at controlled force and room temperature (25 °C), and strain reading was done at the critical points of the samples by the digital image correlation (DIC) method. Numerical simulations with Abaqus software were conducted to validate the experimental results, confirming the experimental tests' accuracy with an acceptable margin of error. Finally, after ensuring the reliability of the numerical results, the influence of the changes in the parameters mentioned above was numerically investigated. It was observed that as these variables increase, the ratcheting strain also increases in the axial and circumferential directions, with greater sensitivity to the increase in average force and amplitude force. • The ratcheting behavior of concentric and eccentric reducers was investigated. • Ratcheting was sensitive to internal pressure, amplitude force, and mean force. • The DIC method was able to measure the strains on the reducers with high accuracy. • The Chaboche hardening model could well predict the ratcheting behavior of reducers. [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]

The stiffness and hysteretic response due to mechanical and thermo‐mechanical cycling have been studied in plasma‐sprayed yttria‐stabilized zirconia (YSZ). Mechanical cycling of free‐standing cantilevers of YSZ shows that the progressive decrease in stiffness is accompanied by monotonic increase in hysteretic energy dissipation per cycle and a permanent ratcheting displacement of ∼20 nm/cycle. Below a critical stress, it varies from coating to coating, ratcheting accompanied by a slow decrease in stiffness does not lead to failure even after ∼1000 cycles. In contrast, at higher stresses, the rates of ratcheting and decrease in stiffness increase rapidly, leading to the nucleation of macrocracks that lead to fracture failure. Prior thermal cycling of coatings on Inconel substrate up to 700°C, which induced an estimated cyclic thermal stress of ∼35 MPa, led to a pronounced reduction in stiffness and mechanical cycling life. During bending, damage accumulates in the tension side of the cantilever and the volume going through the compression cycle remains relatively undamaged. [ABSTRACT FROM AUTHOR]

The cyclic uniaxial stress-controlled ratcheting behaviour of GH3536 formed by selective laser melting (SLM) was tested at 800 °C. The effects of different stress rates and building orientations of 0°, 45° and 90° were investigated. Results present that the ratcheting behaviour of SLM GH3536 at 800 °C exhibits significant stress rate dependence. Moreover, the accumulated ratcheting strain increasing with increasing the stress amplitude and stress rate. It is noted that the building orientation angle of the specimen has an important influence on the mechanical performance. The 45° specimen in the experimental conditions has the greatest low cycle fatigue life. The ratcheting evolution over the whole cyclic load history can be divided into three stages. The relationship between steady ratcheting strain range and low cycle fatigue life was established. [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]

In this study, a combination of Chaboche's nonlinear kinematic hardening model and Lemaitre's anisotropic continuum damage mechanics (CDM) model is used to predict ratcheting strain of different loading paths. The fictitious continuum domain is considered, and the consistent relations are developed between real and fictitious materials. The return mapping algorithm is developed to obtain the plastic strain of different loading paths. Non-proportional loading paths are simulated by the combined model. The ratcheting strain of the stress-strain controlled loading paths is obtained numerically and compared with the experimental results of the cyclic loading tests of Corona et al. [ABSTRACT FROM AUTHOR]

We are exploring the idea of data pruning via hyperreduction modeling. The main novelty of this paper is a lossy data compression/decompression approach for ploycrystalline data, which is based on a hyperreduction scheme that preserves data driven modeling capabilities after compression. We assume to know a mechanical model whose equations are satisfied by the data. It is shown that the proposed reconstruction of the data performs an oblique projection of selected original data. This is achieved by the solution of reduced mechanical equations. High resolution crystal plasticity finite element simulations demand computational and storage resources that are unusual, especially in cases where hundreds of grains are interacting under cyclic loading. The development of image-based modeling via computed tomography highlights the problem of long-term storage of simulation data by using data pruning. The present paper focuses on modeling cyclic strain-ratcheting as an example of numerical modeling that the proposed algorithm preserves. The size of the remaining sampled data can be user-defined, depending on the needs concerning storage space. The relevance of the pruned data is tested afterwards for statistics on the predicted strain, as if full finite element data were available. The proposed method is compared to the Gappy POD method, when no additional modeling step is expected after data pruning. [ABSTRACT FROM AUTHOR]

This study assesses the performance of a memory surface constitutive model (SANISAND-MS) in capturing vertical cyclic loading on a suction bucket foundation in sand. The model has been calibrated against drained cyclic triaxial responses and validated against corresponding centrifuge experiments on suction buckets. The model was found to satisfactorily capture the effects of increasing accumulated strain with increasing mean stress level and reducing density. The performance of the model was further investigated through a parametric study on suction buckets at different mean stress levels, densities and loading sequences. The insights gained from investigating the strain and stress responses, along with the movement of the memory surface, reveal that the model can satisfactorily capture the strain accumulation and ratcheting effects under different load histories. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the whole-life ratcheting behavior of sintered copper joints with consideration of the effects of stress rate, stress amplitude, mean stress, maximum stress, and stress ratio. Deformation of joints under cyclic load was measured by a noncontact displacement detecting system. In these joints, ratcheting strain and ratcheting strain rate were found to be sensitive to loading factors. For example, strain decreased as mean stress and stress amplitude decreased, and also as stress ratio and stress rate increased. Meanwhile, larger stress amplitude or mean stress reduced ratcheting fatigue life, while increasing stress ratio and stress rate increased fatigue life. The results indicate the modified Goodman model accounting for the effects of mean stress can usefully predict the ratcheting fatigue life of sintered copper joints at room temperature. [ABSTRACT FROM AUTHOR]

In the current study, the effect of several parameters on the ratcheting response of tubes under cyclic axial loading is studied. Experimental and numerical approaches have been used to provide a comparison between the ratcheting behaviour of tubes under small amplitude wrinkles and subsequent persistent cycles of axial stress ranges. The ratcheting experiments in the tube specimens have also been numerically simulated with nonlinear isotropic/kinematic hardening model (combined hardening rule). It was found that, when appropriate hardening properties (from the material testing results) are considered, the numerical model was producing results reasonably close to those from the experiments. The model has then been used to study effects from some key parameters on the ratcheting response and the progressive plastic failure of tubes. Parameters such as the initial strain, the stress range and the mean stress for the cyclic load, the loading regime, and the material hardening properties have been examined. [ABSTRACT FROM AUTHOR]

A series of experiments subjected to uniaxial and non-proportionally multiaxial cyclic loadings were performed to investigate the ratcheting responses of SA508 Gr.3 steel at room and elevated temperatures. The influences of different stress levels and nonproportional loading paths on the damage-coupled ratcheting responses were discussed. From experimental results, cyclic softening characteristic and dynamic strain aging can be observed under cyclic loadings. Moreover, the steel exhibits an obvious nonproportional path-dependence of the damage evolution under multiaxial loading paths. To numerically simulate the ratcheting responses under uniaxial and multiaxial loadings with the extended cyclic plastic model, the damage-coupled variable was introduced into the classic isotropic and nonlinear kinematic hardening rules. Corresponding material parameters could be calibrated from experimental data, and comparisons between experimental and simulated results were performed to validate the proposed model. [ABSTRACT FROM AUTHOR]

The second part of the study presents development of the Dirac delta functions framework to modelling of cyclic hardening and softening of material during cyclic loading conditions for the investigated in Part I low carbon S355J2 steel. A new criterion of plastic strain range change is formulated. This provides more certainty in the cyclic plasticity modelling framework compared to classical plastic strain memorization modelling. Two hardening parameters from the developed kinematic hardening rule are written as functions of both plastic strain range and previously accumulated plastic strain. This representation of hardening parameters is able to accurately match experimental results with different types of loading programs including random loading conditions and considering initial monotonic behaviour with yield plateau deformation. Ratcheting behaviour is simulated by the developed cyclic plasticity framework by considering an approximated form of the Dirac delta function for modelling the deviation effect and introducing an additional supersurface for better prediction of ratcheting rate. The proposed cyclic plasticity model requires up to 21 material constants, depending on application. A clear and straightforward calibration procedure, where sets of material constants are determined for each plasticity phenomenon considered, is presented. Application of the model to different materials under various tension-compression and non-proportional axial-torsion cycles shows very close agreement with test results. • New criteria of plastic strain range change provides more certainty in the cyclic plasticity modelling framework. • Approximated form of Dirac delta function simulates the stress deviation effect during the ratcheting phenomenon. • Global and local hardening accurately describe cyclic hardening/softening at various loading programs. • New kinematic hardening model closely matches test results under various cyclic loading programs. [ABSTRACT FROM AUTHOR]

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This paper presents an analytical methodology for calibration of the Hyperplastic Accelerated Ratcheting Model (HARM, Houlsby et al., 2017 [3]), based on a closed-form expression for the accumulation of ratcheting strain with cyclic history. The proposed method requires the fit of one test response and of a few continuous cyclic tests. The initial motivation for this work is the calibration of models for the design of piles subjected to long-term cyclic lateral loading, and the test results from Abadie et al. (2018, 2015) [1,2] are used for calibration and proofing of the model. Nevertheless, the method is applicable to other problems of similar behaviour. [ABSTRACT FROM AUTHOR]

In this paper, molecular dynamics (MD) simulation-based study of deformation behavior of ultrafine-grained nanocrystalline nickel under asymmetric cyclic loading having stress ratios (R) such as − 0.2, − 0.4 and − 0.6 for different temperatures, viz. 100, 300 and 500 K, has been performed using embedded atom method potential. The predicted ratcheting strain by MD simulation for nanocrystalline Ni varies from 15 to 30%. A significant increase in ratcheting strain has been observed with the increase in temperature. It has been observed that the number of vacancies increases, and the number of clusters decreases with the increase in temperature. Slight reduction in crystallinity is identified at the middle of the each loading cycle from the performed cluster analysis. Zigzag pattern of dislocation density has been observed and leads to the decrease in dislocation density with the increase in temperature. Stress ratio does not show any significant effect on the number of vacancies, clusters and dislocation density on structural evolution during the asymmetric cyclic loading. Slight change in the grain rotation has been observed with the increase in temperature, and there is almost no change in the final texture evolved. From the post-tensile tests, ultimate tensile strength that remains same may be due to constant average dislocation density. [ABSTRACT FROM AUTHOR]

In the present investigation in-plane anisotropy in tensile and ratcheting behavior of cold rolled and annealed commercially pure titanium plate has been studied. Flat tensile and fatigue test specimen oriented at 0, 45, and 90 degree to the rolling direction from the rolling direction-transverse direction (RD-TD) plane of the plate has been machined out. Specimens with loading axis at 0, 45 and 90 degree to RD have been designated as 0T, 45T and 90T for tensile and 0R, 45R and 90R for fatigue. Owing to initial TD split basal texture of as received plate, 0T sample has crystallographic direction {1010} -{1120} aligned with loading axis. It shows lowest yield strength but highest ductility in monotonic tension. Although ultimate tensile strength (UTS) and strain to failure of samples 45T and 90T are similar, the former has significantly lower yield strength than the latter, indicating different strainhardening behavior due to different slip/twin activity. On the other hand, 0R sample exhibits longer ratcheting life while 90R sample accumulates highest ratcheting strain. This has been attributed to the formation of intersecting multi-variant twins, which increases fatigue crack propagation resistance during cyclic deformation of 0R sample. Viscoplastic self-consistent (VPSC) simulations of one-cycle tension-compression-reload tension indicate alternating activity of pyramidal slip and extension twinning with loading cycle. The detwinning of extension twin during compression cycle induces cross slip activity, which causes rapid accumulation of strain leading to early fatigue failure of 45R and 90R sample. [ABSTRACT FROM AUTHOR]

This paper presents a multi-temporal formulation for simulating elastoplastic solids under cyclic loading. We leverage the proper generalized decomposition (PGD) to decompose the displacements into multiple time scales, separating the spatial and intra-cyclic dependence from the inter-cyclic variation. In contrast with the standard incremental approach, which solves the (non-linear and computationally intensive) mechanical balance equations at every time step, the proposed PGD approach allows the mechanical balance equations to be solved exclusively for the small-time intra-cyclic response, while the large-time inter-cyclic response is described by simple scalar algebraic equations. Numerical simulations exhibiting complex cyclic responses, including a 2D problem and an application to a monopile foundation, demonstrate that PGD solutions with a limited number of space–time degrees of freedom may be obtained numerically, only requiring a few modes to accurately capture the reference response. [ABSTRACT FROM AUTHOR]

The present paper proposes a kinematic hardening model with a memory surface to more accurately reproduce cyclic hardening and the behaviour of saturated granular soils subjected to cyclic loads. The new cyclic hardening law offers improved accuracy in predicting soil ratcheting in drained conditions and failures due to liquefaction in undrained conditions. Simulating these two aspects has been challenging due to issues such as significant loss of accuracy and numerical instability, particularly under extended (or a large number of) cyclic loads. To deal with the challenge, in addition to the novel theoretical framework, we also developed a robust sub-stepping algorithm based on an explicit stress integration scheme with automatic error control. The proposed model is compared with several existing models and its performance is evaluated by conducting sensitivity analyses and performing validations against a wide range of laboratory test results. [ABSTRACT FROM AUTHOR]

In case of cyclic loading, strain may accumulate due to a ratcheting mechanism until the state of shakedown is possibly achieved. Design Codes frequently require strain limits to be satisfied at the end of the specified lifetime of the structure. In addition, the strain range is required for performing fatigue analyses in case of plastic shakedown. However, little guidance is usually provided by Design Codes on how the accumulated strains and strain ranges are to be calculated, and some of the guidelines implemented in Design Codes are not well founded and may therefore be misleading. This is, for example, true for the ASME B&PV Code, Section III. Of course, strains and strain ranges can be determined by means of incremental elastic-plastic analyses, which require to go step-by-step through many cycles of a given load histogram until the state of shakedown is reached. This is rather costly in terms of engineering time and numerical effort. As an alternative, simplified methods can be adopted, e.g. the Simplified Theory of Plastic Zones (STPZ) as used in the present paper. Being a direct method, effects from load history are disregarded. The theory is described shortly and illustrated by some examples. It is shown that the Simplified Theory of Plastic Zones is well suited to provide reasonable estimates of strains accumulated in the state of elastic and plastic shakedown at the cost of few linear elastic analyses. [ABSTRACT FROM AUTHOR]

This paper presents a macroscopic constitutive model that is able to reproduce the uniaxial transformation ratcheting behaviors of the superelastic shape memory alloy (SMA) undergoing cyclic loading. A cosine-type phase transformation equation with the initial martensite evolution coefficient that helps to predict the residual martensite accumulation and the nonlinear features of the hysteresis loop with a small number of material parameters is established to describe the phase transformation behaviors of the SMA undergoing cyclic loading. The proposed model simultaneously takes into account the evolution of transformation-induced plastic strain during cyclic loading. The applied loading level and asymmetric tensile and compressive behavior of the SMA on transformation ratcheting are also considered in the proposed model. The evolutions of transformation ratcheting, transformation-induced plastic strain, and transformation stresses are constructed as the function of the accumulated residual martensite volume fraction. The simulated results are compared with the experimental results to show the validity of the proposed model in transformation ratcheting. [ABSTRACT FROM AUTHOR]

Abstract Ratcheting and low cycle fatigue are failure mechanisms observed in components subjected to cyclic temperature and mechanical loads. Ratcheting is a global failure mechanism which leads to an incremental plastic collapse of the component whereas low cycle fatigue is a localized mechanism which leads to crack initiation. It is exacerbated by grooves, notches and changes in the geometry of the component. To estimate the remaining life of the component and predict its failure mechanism, it is important to understand how it responds to various combinations of cyclic loads. This paper includes investigation of the ratchet limit and the plastic strain range, which is associated with the low cycle fatigue, of a circumferential butt-welded pipe by using the ratchet analysis method which includes Direct Steady Cycle Analysis (DSCA) within the Linear Matching Method Framework (LMMF). The pipe is subjected to a constant internal pressure and a cyclic thermal load. The investigation is carried out by varying 1) material properties of the weld metal (WM); 2) ratio of inner radius to wall thickness; 3) weld geometry. Within the specified ranges, yield stress and the ratio of inner radius to wall thickness affect the ratchet limit curve. The cyclic thermal load plays a crucial role compared to the internal pressure in influencing the ratchet limit curve. It is observed that the pipe experiences thermal ratcheting at lower yield stress values of the WM. The results obtained are combined to create a limit load envelope, which can be used for the design of welded pipes within the specified ranges. [ABSTRACT FROM AUTHOR]

Ratcheting and creep of reinforced graphite sheet with stainless steel insert (RGSWSSI) are tested under cyclic stress‐controlled compression by a self‐designed clamp from 500°C to 600°C. The effects of insert type, temperature, stress amplitude, stress rate, creep, and loading sequence are considered. Results present that ratcheting deformations for RGSWSSI with 316‐L stainless steel tanged and bonded insert approach to each other and show little rate dependence, while they slightly increase with the increment of stress amplitude and temperature. Moreover, obvious ratcheting effect takes place under cyclic pulsating loads with the peak stress of 32 MPa at 500°C or higher. The accumulated deformations of RGSWSSI under small stress amplitude only increase during about the first 25 cycles and then always turn to shakedown. It can also be estimated by the corresponding static creep strain in practical engineering with good accuracy at high temperature. This work provides important data and understanding of RGSWSSI under harsh fluctuating loads. Highlights: Accumulated deformations of 5 different types of RGSWSSI are tested under cyclic compression from 500°C to 600°C.The ratcheting strain, compressive moduli, and creep of RGSWSSI are stressed.The effects of insert type, temperature, stress amplitude, stress rate, creep, and loading sequence are considered.The specimens with tanged insert and bonded insert have very similar mechanical feature under the same load. [ABSTRACT FROM AUTHOR]

The phenomenon of ratcheting occurs under the influence of non-zero mean stress during cyclic loading; it singificantly reduces the low cycle fatigue life of engineering structures. The present investigation deals with a detailed comparison on the estimation of dislocation densities in the 42CrMo4 steel induced by ratcheting using two different methods, i.e. X-ray diffraction (XRD) profile analysis and hardness. The dislocation densities in the ratcheted specimens were assessed using XRD profile analysis following the modified Williamson-Hall method as well as hardness measurements following the modified Nix and Gao model. The results showed that dislocation density increased in the ratcheted specimens as compared to the unratcheted ones and increase in accumulation of ratcheting strain was correlated with the increase in dislocation densities in the ratcheted specimens. It was established that both hardness and X-ray diffraction profile analysis methods can very effectively be used to assess the dislocation densities in the ratcheted specimens. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed for specifying the parameters of the exponential hereditary function kernels of the endochronic theory of plasticity to describe the ratcheting (cyclic creep) effect of metallic materials under stress-controlled complex non-proportional loading. The method involves the dependence of the difference of plastic moduli on the ratcheting rate on the steady-state portion of the cyclic stress-strain curve. The plastic moduli are determined at the points where the maximum stresses act in different half-cycles of asymmetric loading. It is believed that the greater the difference of plastic moduli towards the mean stress in the cycle, the greater the strain increment in each cycle of loading. The statements of our previously proposed approach were used to determine the rate of plastic strain accumulation at the steady-state stage of deformation under biaxial loading. This approach, based on the data of uniaxial experiments under cyclic asymmetric loading in tension-compression and reversed torsion with the known value of the cycle nonproportionality parameter, is developed to analyze the cyclic loading paths with equal mean and amplitude von Mises stress values. With some simplifications, the expression is proposed to determine the parameters of the exponential kernel of the hereditary function depending on the cyclic path geometry and the known ratcheting rate for the basic loading path. Similar values for the exponential kernel parameters of the hereditary function are obtained in terms of the difference of plastic moduli by using a simpler bilinear model of elastoplastic deformation. The obtained values of the hereditary function parameters were used to simulate the ratcheting effect under uniaxial and biaxial cyclic loading. The loading programs and data of experiments were taken from the literature. The results of simulation have shown that the parameters of the constitutive equations for cyclic plasticity obtained with this method allow one to describe satisfactorily the kinetics of the stress-strain state of metallic materials subjected to biaxial non-proportional loading under cyclic creep. [ABSTRACT FROM AUTHOR]

Uniaxial ratcheting behavior of an automotive-grade dual-phase steel sheet of 1.6 mm thickness has been investigated through engineering stress-controlled asymmetric cyclic loading experiments in the elastoplastic regime at ambient temperature (~ 28°C). Experiments have been performed keeping mean stress, stress amplitude or maximum stress constant. The effect of stress combinations on ratcheting deformation has been rationalized in terms of plastic strain amplitudes, both in loading and in unloading directions. It is found that for all stress combinations the steady-state ratcheting rate follows a perfect power relationship. Scanning electron fractography reveals that failure under asymmetric cyclic loading conditions occurs in a ductile manner through the formation of voids as it happens under tensile loading. [ABSTRACT FROM AUTHOR]

The present paper aims to perform an experimental and theoretical study regarding the inelastic deformation progressive accumulation observed in a polyvinylidene fluoride (PVDF) specimen machined from flexible pipe internal pressure sheaths under cyclic load-unload tensile tests and in monotonic tensile tests. Experiments show that the elastic mechanical behaviour is not rate-dependent because the Young's modulus does not suffer a considerable variation with change in the strain rate. However, the strain hardening induced by the plastic deformation is strongly rate-dependent. Hence, the mechanical behaviour of this polymer is not elasto-plastic or viscoelastic, but elasto-viscoplastic. Also, the kinematic hardening strongly increases with growth of accumulated inelastic strain, making it much more significant than the isotropic hardening. This paper proposes an elasto-viscoplastic mechanical model capable of describing the cyclic and monotonic inelastic behaviour for an arbitrary loading history. The kinenatic hardening observed for this PVDF makes it possible to identify experimentally all material parameters that arise in the model by performing load-unload tests using flat specimens, eliminating buckling problems and the need to control eventual misalignment in the universal test machine grips. Good agreement was noted when comparing the theoretical results with experiments. [ABSTRACT FROM AUTHOR]

The ratcheting behavior refers to the progressive accumulation of strains resulting from the cyclic loading applied to the specimens. Nowadays, much attention has been devoted to ratcheting pipelines. Hence, the ratcheting behavior of the SS316L U-shaped pipe subjected to internal pressure and cyclic bending force is investigated here. The experiments use the Servo-hydraulic device of Zwick/Roell Amsler HB 100. The local strains at the internal, external, and lateral bending points are specified using the pipe strain gauges. Then, the effect of the internal pressure, average force, and force amplitude on the ratcheting strains are examined and compared. The numerical simulation also employs the Abaqus software and the isotropic/kinematic nonlinear hardening model. It was revealed that ratcheting strain in the axial direction is more critical than in the pipe's peripheral direction. The effect of amplitude and average pressure on thin-wall the ratcheting behavior of thin-wall pipe in the axial direction during four thousand cycles are investigated. According to the observed results, increasing amplitude and average bending force while the internal pressure is constant increases the ratcheting strain. Besides, the variation of the force amplitude affects the ratcheting strain more significantly than the variation of the average force. In order to validate the obtained results, a careful comparison was made between the numerical and experimental results, and a good agreement was observed between them. Notably, the novelty of this study lies in the comprehensive analysis of the ratcheting behavior of the SS316L U-shaped pipe conducted here. • Proposing a framework for examining the ratcheting effect empirically and numerically. • The ratcheting strain in the axial direction is more critical than in the pipe's peripheral direction. • Examining the effect of amplitude and average pressure on thin-wall the ratcheting. • Investigating the behavior of thin-wall pipe in the axial direction during four thousand cycles. • Increasing amplitude and average bending force while the internal pressure is constant. [ABSTRACT FROM AUTHOR]

AISI H13 hot-work tool steel is extensively used as tool material for the aluminum extrusion process and its working temperature is about 500 °C. It is essential to model cyclic responses and conduct lifetime prediction of H13 reasonably for optimization of the tools. In this study, uniaxial tests are conducted to investigate mechanical properties of H13. It can be observed that the material shows significant rate-dependence and obvious cyclic softening effects. In addition, the evolution of ratcheting obviously has three stages: gradually decreasing stage, approximately constant stage, and rapidly increasing stage. Considering above-mentioned characteristics, a modified visco-plastic constitutive model is proposed to describe the cyclic plasticity responses in the whole lifetime by a combination of modified A-F kinematic hardening rule and a new proposed isotropic hardening rule. Furthermore, its lifetime is predicted by involving a failure criterion with the critical size of yield surface. Accelerated ratcheting phenomena and peak stress reduction in failure phase are simulated reasonably. In addition, the simulation results of cyclic responses give a good estimation of plastic deformation under cyclic loading conditions. All in all, the comparisons of simulation and experimental results indicate that the proposed constitutive model predicts mechanical properties, as well as lifetime reasonably. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation-based studies of tensile test and structural evolution of Cu-5 at.% Zr alloy under asymmetric cyclic loading (i.e., ratcheting behavior) considering various stress ratios such as − 0.2, − 0.4 and − 0.6 for different temperatures, viz.≈ 100, 300 and 500 K have been performed using embedded atom model Finnis-Sinclair potential. According to obtained stress-strain response from MD calculation, Cu-5 at.% Zr alloy specimen is pristine in nature as sudden drop in stress just after yield stress and subsequent elastic type deformation are observed for this alloy. Predicted ratcheting strain by MD simulation for Cu-5 at.% Zr alloy varies from 4.5 to 5%. Significant increase in ratcheting strain has been observed with the increase in temperature. Slight reduction in crystallinity is identified at the middle of the each loading cycle from the performed radial distribution function analysis and cluster analysis. [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]

The present paper is concerned with the experimental and theoretical investigation of the progressive accumulation of inelastic deformation observed in cyclic tension tests performed on a particular polyamide. The elastic properties are not strongly affected by the strain rate, but the strain hardening induced by the plastic deformation is rate-dependent. Thus, the material behaviour is elasto-viscoplastic rather than viscoelastic or elasto-plastic. For the polymer studied in this paper, the kinematic hardening is much more significant than the isotropic hardening, and a negative plastic strain rate may occur even with a positive stress. The kinematic hardening is strongly dependent, not only on the accumulated plastic strain, but also on the loading rate. An elasto-viscoplastic mechanical model able to describe the cyclic inelastic behaviour for an arbitrary loading history is proposed. All parameters that arise in the theory are identified experimentally. The preliminary theoretical results concerning the modelling of cyclic load-unload tests are in good agreement with the experiments. [ABSTRACT FROM AUTHOR]

This paper is concerned with the ratcheting prediction for steels. The yield surface evolution is integrated in the elastoplasticity analysis by a new proposed model. First, the new proposed model of Distortional Yield Surface (DYS) is developed and then ratcheting under different uniaxial and multiaxial cyclic loadings is investigated. The capabilities of the DYS model is assessed by using the results of various stress-controlled and strain-controlled tests under uniaxial loading condition and the cyclic uniaxial experimental results of Hassan and Kyriakides (1994a). In addition, the model prediction under multi-steps uniaxial loadings is also studied. Effects of DYS consideration in different uniaxial loadings are shown. Strain or stress controlled tests and combined stress-strain control experimental tests (Hassan and Kyriakides, 1994b) are used to be modeled by the present distortional yield surface approach. The biaxial experiments on CS 1018 thin-walled tubes (Hassan and Kyriakides, 1994b) are chosen to be compared with the present model results. With the incorporation of DYS, The new proposed model shows better prediction of uniaxial and multiaxial ratchetting in all ranges of experimentally tested parameters. [ABSTRACT FROM AUTHOR]

• The loading history variable is established to record stress history variation. • An improved kinematic hardening rule is developed to simulate ratcheting effect. • A new plastic strain surface is proposed for the evolution of yield stress. • The proposed model can well describe the ratcheting during uniaxial loading. In this paper, an elastoplastic constitutive model is developed to describe the effect of loading history on the ratcheting. The loading history variable is introduced to record stress history variation during cyclic loading, such as equivalent peak stress and equivalent stress amplitude. Based on Ohno-Wang model, an improved kinematic hardening rule is proposed to simulate the ratcheting effect by establishing the nonlinear evolution equation of ratcheting parameter. A new memory evanescence term is introduced to the plastic strain range memory surface. The evanescence term is activated to describe the difference of yield stress evolution during ratcheting and strain-controlled cyclic loading as the plastic strain range radius exceeds a certain threshold. Compared with the experiments and existing models, the results show that the proposed model can better capture the ratcheting effect with loading history. [Display omitted] [ABSTRACT FROM AUTHOR]

Accurate simulation of foundation response subjected to repeated loading require reliable sand constitutive models to reproduce realistic sand cyclic behaviour. Many elastoplastic constitutive models adopted the hypoelasticity law, which results in physically inaccurate strain accumulation prediction of soil when subjected to elastic cyclic loading. To address this issue, the existing elastoplastic bounding surface model SANISAND-MS has been upgraded with a hyperelastic formulation that is derived from the Helmholtz free energy function. The complete form of the derived nonlinear elasticity functions enhanced by stress induced anisotropy is presented in this work. The calibration of the upgraded SANISAND-MS is briefly discussed. It is demonstrated that the hyperelastic formulation with volumetric-deviatoric coupling: (1) guarantees no accumulation of elastic strain upon elastic cyclic loading, and (2) captures the stress-induced anisotropy of sand under reverse loading. This upgraded SANISAND-MS model with a physical adaptation and thermodynamically consistent elasticity law can predict strain accumulation accurately and is physically appropriate. Moreover, the upgraded SANISAND-MS is suitable for simulating problems with high-cyclic loads and is able to be used in boundary value problem simulations in areas including offshore engineering and railway engineering. [ABSTRACT FROM AUTHOR]

• Ratcheting tests for 880-grade rail steel are carried out under uniaxial asymmetric cyclic stressing. • Efficacy of existing stress-based models in predicting cyclic life for ratcheting cases is analysed. • A novel stress-based model has been developed, and its effectiveness has been examined. • The applicability of the proposed model is also investigated for different materials. This work explores a comparative analysis to verify the applicability of the existing stress-based model to predict life under ratcheting for pearlitic rail steel. The walker model is the most accurate of the available models, but its application is limited owing to the intricacy involved and the experimental reliance on its constant (γ) assessment. As a consequence, a novel stress-based life prediction model is proposed in this study. The applicability of the different models, and the proposed one, is described using equivalent stress amplitude vs life plot, stress deviation plot, error distribution box plots, and probability density function plots. [ABSTRACT FROM AUTHOR]

In this work, the crack tip strain localization in a face centered cubic single crystal subject to both monotonic and cyclic loading was investigated. The effect of constraint was implemented using T-stress and strain accumulation was studied for both isotropic and anisotropic elastic cases with the appropriate application of remote displacement fields in plane strain. Modified boundary layer simulations were performed using the crystal plasticity finite element framework. The consideration of elastic anisotropy amplified the effect of constraint level on stress and plastic strain fields near the crack tip indicating the importance of its use in fracture simulations. In addition, to understand the cyclic stress and strain behavior in the vicinity of the crack tip, combined isotropic and kinematic hardening laws were incorporated, and their effect on the evolution of yield curves and plastic strain accumulation were investigated. With zero-tension cyclic load, the evolution of plastic strain and Kirchhoff stress components showed differences in magnitudes between isotropic and anisotropic elastic cases. Furthermore, under cyclic loading, ratcheting was observed along the localized slip bands, which was shown to be affected by T-stress as well as elastic anisotropy. Negative T-stress increased the accumulation of plastic strain with number of cycles, which was further amplified in the case of elastic anisotropy. Finally, in all the cyclic loading simulations, the plastic strain accumulation was higher near the $$55^0 $$ slip band. [ABSTRACT FROM AUTHOR]

Pseudoelastic NiTi based shape memory alloys (SMA) wires have a good potential in civil engineering applications and often used as dampers in anti-seismic or cable structures when a rate varied cyclic loadings is applied. In accordance with these applications, an experimental characterization of NiTi wires under strain- and stress-controlled cyclic loadings at various strain rates is presented. Based on these loadings, it is shown that the stress–strain response of the material evolves up to a complete stabilization with the increase of the number of cycles. This evolution is accompanied with the degeneration of pseudoelasticity and transformation ratcheting in the case of strain- and stress-controlled mode, respectively. Also, it was found that the cyclic deformation of pseudoelastic NiTi SMA is significantly rate dependent. [ABSTRACT FROM AUTHOR]

Residual deformations due to sustained and cyclic loading, acting on full-scale reinforced soil-retaining walls, could lead to an unacceptable serviceability limit state. In the present study, the writers carried out an extensive experimental programme comprising several monotonic and multistage tensile tests on a high-density polyethylene (HDPE) uniaxial extruded geogrid. Based on analysis of the test results, a combined empirical model has been developed that can predict the tensile behaviour of a specific HDPE geogrid subject to cyclic tensile loading. The paper presents the results and analyses of the effect of cyclic tensile loading histories (varying pre-stress tensile load, frequency, amplitude and number of cycles) on those parameters that are characteristic of hysteresis loops (i.e. the maximum and residual strains cumulated during each cyclic loading, tensile stiffness and area of the hysteresis loops). The results show that the average strain rate and the loading time affect the material's tensile response, as well as the combination of pre-stress tensile load and loading amplitude. The writers also investigated the difference between the load-strain relations for the monotonic test and those for the multistage tests, and concluded that the effects of cyclic loading histories are not due to material degradation. [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]

This investigation aims to describe the experimental ratcheting life of AISI 304LN stainless steel with a proposed model. A series of stress-controlled low cycle fatigue experiments have been carried out at room temperature under uniaxial loading on the steel up to failure of specimens, under three sets of stress amplitude and mean stress values. Comparison of the theoretically predicted results with the experimental ones is found to be reasonably satisfactory in the fatigue life range of 102–105 cycles. Additionally the proposed stress-based model for predicting ratcheting fatigue life has been critically discussed with reference to some previous models. [ABSTRACT FROM AUTHOR]

The room temperature ratcheting response of equiatomic FCC CoCuFeMnNi high entropy alloy containing Cu-rich nanoclusters in HEA matrix at different mean stress and stress amplitude indicated the critical role of interaction among dislocations as well as dislocations and Cu-rich nanoclusters in determining the deformation response and damage accumulation contributing to final failure. Detailed microstructural investigation using EBSD and TEM capture the evolution of complex defect microstructure for different cyclic loading conditions. Perennial network of Cu-rich nanoclusters transforming into entangled Cu-rich nanofibers during ratcheting was observed in the three-dimensional elemental maps obtained using APT. This can be attributed to shearing of spherical clusters followed with enhanced short-range diffusion contributing to the decoration of dislocation structure formed by cyclic loading with copper atoms. Further, an increase in the concentration of copper in the solid solution matrix contributes to additional solid solution strengthening, compensating for cluster strengthening and leading to a lower steady-state creep rate with better ratcheting performance. Thus, synergistic operation of cluster and solid solution strengthening in improved ratcheting response of CoCuFeMnNi HEA showcases the unique ability of HEAs to offer excellent mechanical properties beyond superior strength-ductility combination. • Cyclic creep strain increases with increasing stress amplitude as well as mean stress. • EBSD and APT instigation for defect and damage evolution in ratcheting. • Increase in intragranular misorientation and GND density contributes to the failure. • Dislocation interaction with solute environment and Cu nanoclusters accelerates damage. [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]