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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]

This paper investigates the response of Ottawa sand to cyclic loading using virtual oedometer tests and the level-set discrete element method. We study both the macroscopic and the micromechanical behavior, shedding light on the grain-scale processes behind the cyclic response observed in crushable sand, namely stress relaxation under strain control and ratcheting under stress control. Tests without particle breakage first show that asymmetrical frictional sliding during loading-unloading induces these cyclic-loading effects. Then, tests considering particle breakage reveal more pronounced stress relaxation and ratcheting, which decrease in rate over cycles, accompanied by increased frictional sliding and reduced particle contact forces. It is found that the broken fragments unload the most and promote an enhanced cushioning effect. These micromechanical processes contribute to a decrease in breakage potential as the cycles progress, implying that cyclically loaded materials may become more resistant to breakage when compared to the same material loaded monotonically at the same strain level. These new insights highlight the main contributions of the present work, factoring in real particle shapes from 3D X-ray tomography and notably contributing to the existing literature on the topic, where most studies rely on idealized particle shapes and rarely consider crushable grains. [ABSTRACT FROM AUTHOR]

Abstract Pipelines subjected to thermal or mechanical loads may fail due to plastic strain accumulation which leads to ratcheting. In this research, cyclic plastic behavior and shakedown limit are investigated experimentally and numerically for a defected pressurized pipe under cyclic bending moment. In the numerical model, the combined isotropic/kinematic hardening model based on the Chaboche model is adopted to represent the cyclic plastic flow of the material. The hardening parameters are determined experimentally and used in the finite element (FE) model. A four-point bending test rig is manufactured to test a pressurized API 5L steel pipe under cyclic bending. An elliptical defect is created by machining to depict corrosion pits in pipes. The plastic strains are measured experimentally and the results are used to tune the parameters of the FE model. The shakedown limit of the defected pipe is determined numerically by tracking the critical points behavior and the results are verified experimentally. Furthermore, the plastic work dissipated energy (PWD) is estimated within the defective structure to study the behavior of the pipe. By running this compatible model, it is found that the yield and the shakedown limits are lowered by mean values of 55% and 25% respectively due to the presence of metal loss defect occupying almost half of the pipe thickness.

Fear of escalating input prices in response to retail success is a commonly discussed phenomenon affecting supply chains. Such a ratchet effect arises when a retailer feels compelled to modify its investments to better serve the end customers in order to hide positive prospects and restrain future wholesale price hikes. In a two-period model of supply chain interactions, the authors demonstrate that such an endogenous ratchet effect can have multifaceted reverberations. A retailer fearing price hikes may be tempted to curtail near-term profits to ensure favorable long-term pricing. In response, the supplier can use deep discounts in its initial wholesale prices to convince the retailer to focus on its short-term profits rather than long-term pricing concerns. These deep discounts not only encourage mutually beneficial investments but also alleviate double marginalization inefficiencies along the supply chain. In light of these results, the authors show that a mandatory information disclosure policy to reduce the ratchet effect decreases total channel efficiency compared with no information disclosure, precisely because mandatory disclosure interrupts the healthy tension among supply chain partners. Thus, the model presents a scenario in which ratcheting concerns can create a degree of self-enforcing cooperation that results in socially beneficial responses in supply chains. [ABSTRACT FROM AUTHOR]

This study aims to describe a toughened adhesive's ratcheting–recovery behavior under reversed cyclic load using a viscoelastic–viscoplastic model. As most adhesives are based on synthetic polymers, their tensile and compression response can be different. A series of load–Sunload tests were conducted on bulk adhesives and bonded joints involving tension/compression–shear loads to characterize the initial yield surface. The effect of hydrostatic stress was studied by considering the instantaneous response and yield strength under tensile and compression loads. Given the observed modulus degradation and extensive permanent strain during reversed cyclic tests, time-dependent damage factors were considered for both viscoelastic and viscoplastic responses. The model was implemented in a finite element (FE) code and used to model the shear response to reversed cyclic load with varying frequency. Good agreement between the model and experiment was obtained. The consideration of both hydrostatic stress and damage was required to describe the observed adhesive reversed cyclic response. [ABSTRACT FROM AUTHOR]

Pipelines subjected to thermal or mechanical loads may fail due to plastic strain accumulation which leads to ratcheting. In this research, cyclic plastic behavior and shakedown limit are investigated experimentally and numerically for a defected pressurized pipe under cyclic bending moment. In the numerical model, the combined isotropic/kinematic hardening model based on the Chaboche model is adopted to represent the cyclic plastic flow of the material. The hardening parameters are determined experimentally and used in the finite element (FE) model. A four-point bending test rig is manufactured to test a pressurized API 5L steel pipe under cyclic bending. An elliptical defect is created by machining to depict corrosion pits in pipes. The plastic strains are measured experimentally and the results are used to tune the parameters of the FE model. The shakedown limit of the defected pipe is determined numerically by tracking the critical points behavior and the results are verified experimentally. Furthermore, the plastic work dissipated energy (PWD) is estimated within the defective structure to study the behavior of the pipe. By running this compatible model, it is found that the yield and the shakedown limits are lowered by mean values of 55% and 25% respectively due to the presence of metal loss defect occupying almost half of the pipe thickness. [ABSTRACT FROM AUTHOR]

The diffusion of brake-shoe system has made it necessary to study brake–wheel–rail interactions. This study aims to elucidate this topic with an innovative small-scale test rig, the '4-contact machine'. A test procedure is designed in which an ER7 steel wheel is coupled with a R260 steel rail and two different brake-shoe materials (cast iron and sintered material). The results show that the 4-contact machine reproduces the effects of wheel–rail–brake shoe contact and damage similar to those observed on a railway wheel at the end of its life, highlighting marked differences in behaviour between the two brake materials. [ABSTRACT FROM AUTHOR]

Low cycle fatigue (LCF) and ratcheting experiments were carried out on annealed low-carbon steel at room temperature within a laboratory environment, utilising stress and strain control modes. The annealed low-carbon steel consistently demonstrates a cyclic softening response over its LCF lifespan, across all tested strain amplitudes. Notably, it was observed that ratcheting strain rises while ratcheting life declines with both rising mean stress and stress amplitude. Annealed low-carbon steel, being entirely ferritic and lacking precipitation or substitutional solid solution strengthening or hard phase strengthening, exhibits a restricted ability to withstand or alleviate the accumulation of ratcheting strain, particularly under very low mean stress conditions. In both LCF and ratcheting, significant substructure formation was detected. Nevertheless, there was no discernible difference in substructure formation between LCF and ratcheting when employing electron channelling contrast imaging techniques. The existing mean stress-based fatigue life prediction model has successfully forecasted ratcheting and LCF life within the 102–105 cycles range. A novel approach utilising modulus is introduced to characterise the cyclic hardening/softening behaviour of alloys in stress and strain-controlled experiments. The cyclic hardening model based on modulus effectively captures the responses observed in cyclic hardening/softening during LCF and ratcheting experiments.

Under the framework of the small deformation crystal plasticity theory, a crystal plastic cyclic constitutive model for body-centered cubic (BCC) cyclic softening polycrystalline metals is established. The constitutive model introduces the isotropic softening rule that includes two different mechanisms: namely softening under monotonic deformation and softening under cyclic deformation on each slip system. Meanwhile, a modified Armstrong-Frederick nonlinear kinematic hardening rule is adopted. The appropriate explicit scale transition rule is selected to extend the single crystal constitutive model to the polycrystalline constitutive model. Then the model is used to predict the uniaxial and multiaxial ratcheting deformation of BCC axle steel EA4T to verify the rationality of the proposed model. The simulation results indicate that the newly established crystal plasticity model can not only describe the cyclic softening characteristics of BCC axle steel EA4T well, but also reasonably describe the evolution laws of uniaxial ratcheting and nonproportional multiaxial ratcheting deformation. Moreover, the established crystal plastic cyclic constitutive model can reasonably predict the ratcheting behavior of BCC single crystal as well. [ABSTRACT FROM AUTHOR]

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]

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]

Uniaxial strain‐controlled fatigue tests were carried out on a 304L austenitic stainless‐steel specimens in air at 300°C and in pressurized water reactor (PWR), without or with the application of a mean stress, at different total strain amplitudes. For strain amplitude no less than 0.2%, a deleterious effect of PWR water on fatigue life is observed, associated with the enhancement of both crack initiation and propagation. Besides, the fatigue life is reduced by the application of a mean stress for a fixed strain amplitude in a given environment. In particular, due to the acceleration of crack initiation stage by an enhancement of the plastic strain accumulation, the PWR water effect on fatigue life is re‐activated for strain amplitude below 0.2% in the presence of a mean stress. The fatigue life reduction under mean stress application is mostly related to the maximum stress level and strain amplitude, rather than the generated ratcheting strain. Highlights: The results of strain‐controlled fatigue tests in air and in PWR water are presented.The application of a mean stress affects the fatigue strength in both environments.The effect of environment and mean stress on initiation and propagation is analyzed.A modified SWT equation is proposed. [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]

High-pressure steam pipes inevitably suffered from the reciprocal interaction of high pressure and temperature during a long-period service, causing deformation and cracking. However, only limited studies about abnormal bulging caused by condensed water have been carried out. To study the relationship between bulging and condensed water, bulging tee joints belonging to high-pressure steam pipes were investigated with a macro visual inspection, chemical composition analysis, and metallographic microscopy. According to the analysis of the bulging samples, pearlite spheroidization was found in the abnormal bulging tee joint. The ANSYS FLUENT modeling indicated that the tube wall of bulging tees was continuously subjected to alternating stress, causing the cyclic transformation of the liquid–gas phase inside the tee joint. The results indicate that the stress produced by a condensed water droplet ranges from 532.8 MPa to 59 MPa, continuously exerting pressure on the tube wall of the tee joint. When combined with the variation in the temperature field, the temperature of the severe bulging tee joint and slight bulging tee joint alternates. Further modeling illustrates that the stress generated by the impact of condensed water droplets on the high-temperature tee joints causes a ratcheting effect, which is identified as the main factor contributing to the bulging of the tee joint. Deterioration of the microstructure is considered a secondary mechanism. [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]

This study applies the theory of stochastic control to an environmental project planning to counteract against the sediment starvation problem in river environments. This can be considered as a time‐average inventory problem to time‐discretely control a continuous‐time system driven by a non‐smooth jump process under habit formation disturbing project implementation. The system is modeled such that the sediment storage dynamics are physically consistent with certain experimental results. Further, the habit formation is modeled as simple linear dynamics and serves as a constraint related to the replenishment amount of the sediment. We show that the time‐average control problem is not necessarily ergodic. Consequently, the effective Hamiltonian may become a non‐constant. Thereafter, ratcheting cases as extreme cases of the irreversible habit formation are considered, owing to them being unique exactly solvable non‐ergodic control problems. The optimality equation associated with a regularized and hence well‐defined control problem is verified. Furthermore, a finite difference scheme is examined against the exactly solvable case and then applied to more complicated cases. [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]

This paper presents the interaction system within the mechanical soil processing process, consisting of two large elements, the metal of the tool and the soil. Due to the two main forces acting on the chisel knives—friction and impact with the sandy soil—the wear of these chisel knives was determined. To determine the wear, a stand was used which allowed testing chisel-type knives in laboratory conditions by changing their functional parameters: working depth, angle of the knives to work the soil, working speed, humidity and granulation of the test environment. The present paper presents an application of the Archard-type wear law to the contact between a chisel-type knife and sandy soil (wet and dry sand). The theoretical model regarding the Archard wear coefficient considered three forms of surface damage (shake down, ratcheting and micro-cutting). The sand was considered spherical and rigid and the surface of the knife was flat. The experimental model considered real steel knives with different surface hardness and operation under controlled conditions of sand granulation, humidity, attack angle, depth of penetration and speed of sliding. The theoretical and experimental results highlight the wear behavior of chisel knives (Archard coefficient) in wet and dry sand. [ABSTRACT FROM AUTHOR]

Recent empirical studies point out that the firms do not fully incorporate the managers' past performance when revising future contractual terms. This study offers a theoretical perspective on the firm's executive compensation strategy that supports such latest empirical findings. Using a two-period principal-agent model, we examine firm's compensation schemes with ratchet principle taking into account key factors such as informational rent, capability uncertainty, and performance noise. After characterizing the optimal incentive rates for a given degree of ratcheting, we examine the efficacy of ratcheting contract in executive compensation. We also explore the optimal degree of ratcheting that strikes a fine balance between informational rent and ratchet effect. We find that the capability gap-performance noise ratio plays a critical role in determining the optimal degree of ratcheting. Funding: I. Hwang and M. K. Lim acknowledge support from the Institute of Management Research at Seoul National University. Supplemental Material: The online appendix is available at https://doi.org/10.1287/deca.2023.0467. [ABSTRACT FROM AUTHOR]

The fatigue and creep–fatigue properties of 316SS formed by selective laser melting (SLM) were investigated, considering the effects of different peak stresses, stress rates and peak-holding times on the ratcheting and creep-ratcheting behaviour of SLM 316 SS specimens at different sampling angles (0°, 90°) and high temperatures (550°C, 650°C, 750°C). Results show that the 90° specimens exhibited better fatigue life than that of the 0° specimens. Moreover, the ratcheting evolution can be divided into three stages, but the first stage is very short and the main ratcheting behaviour takes place in the second and third stages. Interestingly, it was found that at stress rates above 10 MPa/s, the ratcheting evolution curves are highly overlapping. Furthermore, the creep–fatigue interaction promotes the evolution of material damage. Besides, creep increases the total strain of 316SS even with a short dwell time (0.5 min). [ABSTRACT FROM AUTHOR]

We study the use of budgets in public organizations with governance shaped by democratic structures. In particular, we examine political variables – electoral cycle, majority government, and ideology – and managerial variables – past performance and peer performance – in the context of city governments. Using data from 170 municipalities over a period of seven years (two electoral cycles), the study documents the simultaneous effect of these two types of variables. We find evidence that budget increases are more pronounced right before and right after elections (political). Furthermore, our findings suggest that ideology affects not only resource allocation decisions but also how municipalities manage the budgeting process; indicating the potential role of ideology in management practices (political). We also find evidence for ratcheting (managerial): the deviation between last period's actual and budgeted performance is associated with upcoming budgets. However, this effect is symmetric, in contrast to the more common asymmetric structure previously documented in for-profit organizations. Relative target setting (managerial) is also present in public organizations and varies with the relative debt level of the city. The findings of this study are also informative to for-profit organizations as they open up their governance to more democratic structures and begin to experience the competing managerial and political logics in interacting with stakeholders. [ABSTRACT FROM AUTHOR]

Structures may predominantly inelastically deform in a single direction during earthquakes and incur greater damage. This behavior is known as seismic ratcheting and can be caused by eccentric gravity loads. Code clauses were introduced in Canada and New Zealand to amplify displacements obtained from static analysis methods to consider seismic ratcheting effects. However, such clauses are based on analyses of reinforced concrete (RC) wall or single‐degree‐of‐freedom (SDOF) structures, and methods to mitigate seismic ratcheting behavior were not explicitly provided. In this study, parametric analyses of steel and RC moment resisting frame buildings were performed to evaluate the adequacy of code clauses, identify parameters which influence seismic ratcheting behavior, and propose methods to mitigate such behavior. It was found that the New Zealand code underestimated the displacement increase for RC buildings, though it was able to envelope the displacement increase for steel buildings while the Canadian code was conservative. Additionally, the displacement increase was found to be sensitive to the building's post‐yield behavior and ground motion properties. However, assumptions of these properties during design may not be reflective of the actual building and seismic conditions, indicating that a reliable estimate of the increase in displacement is difficult to obtain. Instead, employing mitigation measures to reduce seismic ratcheting effects, such as designing to higher seismic demands, adding a secondary structural system to increase the building's post‐elastic stiffness, or providing more balanced lateral strengths after adjusting for eccentric gravity load effects are better measures to counter seismic ratcheting effects caused by eccentric gravity loads. [ABSTRACT FROM AUTHOR]

To mitigate state exposure threats to long-lived instant messaging sessions, ratcheting was introduced, which is used in practice in protocols like Signal. However, existing ratcheting protocols generally come with a high cost. Recently, Caforio et al. proposed pragmatic constructions, which compose a weakly secure 'light' protocol and a strongly secure 'heavy' protocol, in order to achieve so-called ratcheting on-demand. The light protocol they proposed has still a high complexity. In this paper, we propose the lightest possible protocol we could imagine, which essentially encrypts and then hashes the secret key. We prove it secure in the standard model by introducing a new security notion, which relates symmetric encryption with key updates by hashing. Our protocol composes well with the generic transformation techniques by Caforio et al. to offer high security and performance at the same time. In a second step, we propose another protocol based on a newly defined integrated primitive, extending standard one-time authenticated encryption with an additional output block used as a secret key for the next message. We instantiate this primitive firstly from any authenticated encryption with associated data, and then we propose an efficient instantiation using advanced encryption standard (AES) encryption to update the key and AES-Galois/Counter mode of operation to encrypt and decrypt messages. [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]

Polymers in general, and adhesives in particular, can exhibit nonlinear viscoelastic–viscoplastic response. Prior work has shown that this complex behavior can be described using analytical models, which provided good agreement with measured creep and recovery response. Under cyclic loading, however, some adhesives exhibit a temporal response different from what would be expected from their creep behavior. Ratcheting describes the accumulation of deformation from cyclic loading. The failure surfaces of adhesives subjected to creep and cyclic loads provide evidence of failure modes that depend on the loading history, suggesting a cause for the change in temporal response. The following considers two approaches to describe the ratcheting behavior of adhesives. Given the reduced time dependence, the first approach involved a nonlinear viscoelastic–plastic model. The second approach used a nonlinear viscoelastic–viscoplastic model, calibrated from the cyclic response, rather than the creep response. While both models showed good agreement with experiment for long exposure to cyclic loading, only the viscoelastic–viscoplastic model agreed with experiment for both short and long loading histories. [ABSTRACT FROM AUTHOR]

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 Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime. Depending on the level of loading inelastic strains may lead either to failure, due to low cycle fatigue or ratcheting, or to safety, through elastic shakedown. Thus, it is important to estimate the asymptotic stress state of such structures. This state may be determined by cumbersome incremental time-stepping calculations. Direct methods, alternatively, have big computational advantages as they focus on the characteristics of these states and try to establish them, in a direct way, right from the beginning of the calculations. Among the very few such general-purpose direct methods, a powerful direct method which has been called RSDM has appeared in the literature. The method may directly predict any asymptotic state when the exact time history of the loading is known. The advantage of the method is due to the fact that it addresses the physics of the asymptotic cycle and exploits the cyclic nature of its expected residual stress distribution. Based on RSDM a method for the shakedown analysis of structures, called RSDM-S has also been developed. Despite most direct methods for shakedown, RSDM-S does not need an optimization algorithm for its implementation. Both RSDM and RSDM-S may be implemented in any Finite Element Code. A thorough review of both these methods, together with examples of implementation are presented herein.

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]

With no doubts, bulging in delayed coke drums is one of the most common thermo-mechanical damage to that component linked to their design, fabrication, and normal operation. Coke drums are exposed to several cycles of thermal stresses which will initiate cracks, especially in the welds because of low-cycle fatigue. The bulging is affecting the integrity of the delayed coke drum. If left without repair in the long run, it would subsequently form many cracks on both the internal and external surfaces of the bulges. Therefore, and as recognized by many operators in the last ten years to limit the growth and the progression of bulges, the most common repair method used has been automated, weld overlay using consistent parameters. The first outcome of this paper illustrates the impact of overlay repair on bulge growth during normal cycles. On the other hand, some operators decided to shorten the operation cycle after introducing the repair to exceed the production rate. The second outcome of this paper is discussing the impact of this decision on coke drum integrity and how the overlay weld repair withstands the bulge growing during short cycles. [ABSTRACT FROM AUTHOR]

Accurate analysis of plastic strain accumulation under stress-controlled cyclic loading is vital for numerous engineering applications. Typically, models of plastic ratcheting are calibrated against available experimental data. Since actual experiments are not exactly accurate, one should check the identification protocols for pathological dependencies on experimental errors. In this paper, a step-by-step algorithm is presented to estimate the sensitivities of identified material parameters. As a part of the sensitivity analysis method, a new mechanics-based metric in the space of material parameters is proposed especially for ratcheting-related applications. The sensitivity of material parameters to experimental errors is estimated, based on this metric. Moreover, a relation between pathological error sensitivity and overparametrization is established. This relation gives rise to a new criterion of overparametrization. The advantages of the new overparametrization criterion are exposed and its plausibility is checked by alternative criteria, like the consideration of correlation matrices and validation of identified parameters on "unseen" data. For demonstration purposes, the accumulation of irreversible strain in the titanium alloy VT6 (Russian analog of Ti-6Al-4V) is analysed. Three types of phenomenological models of plastic ratcheting are considered. They are the Armstrong-Frederick model as well as the first and the second Ohno-Wang models. Based on real data, a new rule of isotropic hardening is proposed for greater accuracy of simulation. The ability of the sensitivity analysis to determine reliable and unreliable parameters is demonstrated. [ABSTRACT FROM AUTHOR]

Ratcheting deformation in association with bulk texture evolution in HSLA steel is studied in this investigation. The cyclic deformation behaviors and damage modes of the specimens are obtained at room temperature, employing asymmetric stress-controlled tests under various combinations of mean stress and stress amplitudes. Bulk texture measurements of the specimens are done adopting an X-ray diffraction analysis. The results exhibit an increase in strain accumulation from 0.23 to 30.61% associated with a sharp reduction in ratcheting life from 3320 to 880 cycles by the increment in mean stress/stress amplitude. A continuous cyclic softening until the final failure is observed for all the ratcheting tests. It is noticed that variation of mean stress is more detrimental than stress amplitude in controlling strain accumulation while the effect of stress amplitude is more pronounced than mean stress for the reduction of ratcheting life. The fracture surface morphology indicates typical striation formation in the crack propagation region along with overload failure. The bulk texture studies indicate that there is a transition between 'ϒ' fiber and 'ζ' fiber during all loading conditions. The texture intensity is increased from 5.71 to 11.68 with progressive ratcheting strain accumulation. Here also, influence of stress amplitude is more significant than the mean stress. [ABSTRACT FROM AUTHOR]

A methodology considering Chaboche's isotropic‐kinematic hardening (CIKH) model and genetic algorithm optimization technique is examined here to simulate the cyclic‐plastic response for materials exhibiting cyclic hardening or softening behavior. The aim of the present report is to illustrate the inherent potential of this approach by assessing the closeness of fit of the obtained predictions to the experimental results for several materials like Z2CND18.12N, and 25CDV4.11 steels, OFHC copper, and INCONEL718 alloy. The obtained results were further subjected to comparative examinations with the available predictions to demonstrate the adoptability of the suggested methodology for the cyclic hardening or softening materials. This proposed approach provides a single set of CIKH model parameters to replicate the stabilized hysteresis loops and cyclic hardening or softening behavior under symmetric strain‐controlled loading, as well as ratcheting characteristics under asymmetric stress‐controlled cycling, and is thus generalized in nature. [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]

Creep–fatigue interaction occurs in many structural components of high-temperature systems operating under cyclic and steady-state service conditions, such as in nuclear power plants, aerospace, naval, and other industrial applications. Thus, understanding micromechanisms governing high-temperature creep–fatigue behavior is essential for safety and design considerations. In this work, stress-controlled creep–fatigue tests of advanced austenitic stainless steel (Alloy 709) were performed at a 400 MPa stress range and 750 °C with tensile hold times of 0, 60, 600, 1800, and 3600 s, followed by microstructural examinations. The creep–fatigue lifetime of the Alloy 709 was found to decrease with increasing hold time until reaching a saturation level where the number of cycles to failure did not exhibit a significant decrease. Softening behavior was observed at the beginning of the test, possibly due to the recovery of entangled dislocations and de-twining. In addition, hysteresis loops showed ratcheting behavior, although the mean stress was zero during creep–fatigue cycling, which was attributed to activity of partial dislocations. Microstructural examination of the fracture surfaces showed that fatigue failure dominated at small hold times where the cracks initiated at the surface of the sample. Larger creep cracks were found for longer hold times with a lower probability of dimpled cavities, indicating the dominance of creep deformation. The results were compared with other commonly used stainless steels, and plausible reasons for the observed responses were described. [ABSTRACT FROM AUTHOR]