Accumulation Of Plastic Deformation Research Articles

Using Poisson’s ratio and acoustic anisotropy parameter to assess damage and accumulated plastic strain during fatigue loading of austenitic steel

The work investigated the effect of fatigue failure on the elastic characteristics of metastable austenitic steel AISI 321: Poisson’s ratio and acoustic anisotropy parameter. The elastic characteristics were calculated using ultrasonic measurements of the propagation time of longitudinal and shear elastic waves. The volume fraction of strain-induced martensite was determined by the eddy current method. Theoretical studies have shown that the main factors influencing Poisson’s ratio are the accumulation of microdamages and changes in phase composition. The change in the acoustic anisotropy parameter is associated with the influence of cyclic deformation on the crystallographic texture of the material matrix and the formation of oriented crystals of strain-induced martensite. Based on the analysis of experimental results, expressions were obtained for calculating damage and relative accumulated plastic deformation based on acoustic measurement data, which are widely used in engineering practice to determine the fatigue life of structural materials.

Molecular dynamics simulation of crack growth in nanocrystalline nickel considering the effect of accumulated plastic deformation

Molecular dynamics simulations are conducted to investigate atomic stress and plastic strain distribution in pre-cracked crystalline nickel, along with microstructure evolution. The plastic strain calculation method is improved by refining neighboring atom selection. A new parameter for measuring plastic strain concentration allows for comparison across different crystallographic directions. The effects of temperature, strain rate, crystallographic direction, loading mode, grain boundary and grain size are evaluated. At elevated temperature, crack tip blunting becomes obvious, and crack propagation decelerates. The crack propagates through void nucleation, growth, and eventual linkage with the original crack. Higher temperature increases the plasticity limit of void nucleation. Strain rates show a positive correlation with plasticity limit but a negative correlation with crack growth rate and final length. Crystallographic direction influences crack propagation, with crystal 100 exhibiting significant crack propagation, while 110 and 111 demonstrating marked resistances to crack propagation. Crystal 100 has the highest plastic deformation concentration near the crack tip. Loading mode affects plastic deformation accumulation. In-plane shear results in less plastic deformation and less obvious crack propagation. In bi-crystals, the relative rotation angle between grains significantly influences crack propagation. X-rotation of the right grain most significantly impedes crack propagation, while y- and z-rotation tend to cause the crack to cross the grain boundary. In polycrystals, plastic deformation accumulation at grain boundaries is significant, with the crack tending to propagate along grain boundaries. Plastic strain and concentration parameter peaks are lower in grain boundaries than in single crystals, indicating weaker stability. The results demonstrate that the failure process of crystalline nickel is intricately linked to the stress and plastic strain distribution around the crack tip. The plastic strain and concentration parameter are more accurate predictors of crack propagation than atomic stress.

Study on the Deformation Behavior of Two Phases during the Low Cycle Fatigue of UNS S32750 Duplex Stainless Steel.

In this paper, the deformation behavior of UNS S32750 (S32750) duplex stainless steel during low cycle fatigue was studied by controlling the number of cycles. The microstructure of the specimens under different cycles was characterized by optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The microhardness of the two phases was measured by a digital microhardness instrument. The results showed that the microhardness of ferrite increases significantly after the first 4000 cycles, while the austenite shows a higher strain hardening rate after fatigue fracture, and the microhardness of ferrite and austenite increases by 23 HV and 87 HV, respectively. The two-phase kernel average misorientation (KAM) diagram showed that the continuous accumulation of plastic deformation easily leads to the initiation of cracks inside the austenite and at the phase boundaries. The evolution of dislocation morphology in the two phases was obviously different. With the increase in cycle number, the dislocation in ferrite gradually transforms from dislocation bundles and a dislocation array to a sub-grain structure, while the dislocation in austenite gradually develops from dipole array to an ordered Taylor lattice network structure.

3D DEM simulations of cyclic loading-induced densification and critical state convergence in granular soils

Granular soils exhibit very complex responses when subjected to cyclic loading. Understanding the cyclic behavior of such materials is not only crucial for engineering applications but also the bottleneck of most of constitutive models. This study employs 3D Discrete Element Method (DEM) simulations to explore the accumulative plastic deformation and the internal fabric evolution within granular soils during cyclic loading. Two novel observations are identified: (1) A distinct and unique linear relationship between post-cyclic loading void ratio e and log (p*/p0) is found independent of the amplitude of cyclic load and the initial stress state prior to cyclic loading, where p* is the mean pressure incorporating cyclic loading stress and p0 is the mean pressure prior to cyclic loading; (2) When resuming drained triaxial loadings after cyclic loadings, we observe that both microstructural and macroscopic variables converge to the same values they would have reached for pure monotonic drained triaxial loadings. This intriguing behavior underscores and extends to more general loading paths the influential and attractive power of the critical state.

An efficient 3D finite element procedure for simulating wheel–rail cyclic contact and ratcheting

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.

Study on rolling contact fatigue crack initiation and propagation in U75V rail treated by laminar plasma

Surface discrete hardening by laminar plasma (HLP) enhances rail wear resistance by rapidly quenching surfaces to form discrete martensitic zones. In comparative field tests on a North China freight railway, HLP-treated U75V rails supported twice the total passing weight before reaching wear limits, compared to untreated rails. However, HLP treatment increases susceptibility to rolling contact fatigue (RCF) cracks, including interface cracks from mechanical differences, impact cracks from wheel-rail contact, deformation cracks from cumulative deformation, and matrix cracks extending from interfaces. The ratchet effect and seesaw mechanism, due to plastic deformation accumulation and quenching area warping, are crucial for crack initiation and propagation. This research advances understanding of HLP-treated rails' tribological behavior, emphasizing the necessity for customized maintenance strategies.

Failure evaluation mechanism of cement sheath sealing integrity under casing eccentricity during multistage fracturing

A microannulus (MA) is the primary reason for sustained casing pressure in multi-stage fractured-shale gas wells. However, the effect of the casing eccentricity on the long horizontal section has not been considered. In this study, a full-scale integrity tester for cement sheaths is adopted to measure the cumulative plastic deformation. Numerical models are applied to evaluate the development of the cumulative plastic deformation and quantify the MA width considering casing centralization and eccentricity in the context of multiple loading and unloading cycles. Subsequently, the influences of the eccentricity distance and angle, cement-sheath mechanical variables, and different well depths on the cumulative sheath plastic deformation and sheath MA development are explored. The research results demonstrate that casing eccentricity significantly increases the cumulative sheath plastic deformation compared with that of the casing-centered condition. Consequently, the risk of sealing integrity failure increases. The accumulated plastic deformation increases when the eccentricity distance increases. In contrast, the initial plastic deformation increases as the eccentricity angle increases. However, the cumulative plastic deformation decreases after a specific loading and unloading cycle count. Affected by the coupled influence of the internal casing pressure and fracturing stages, the width of the MA in the horizontal section increased from the toe to the heel, and the casing eccentricity significantly increased the MA width at each stage, thus increasing the risk of gas channeling. Finally, an engineering case is considered to study the influence of casing eccentricity. The results show that cement slurries that form low and high elastic moduli can be applied to form a cement sheath when the fracturing stage is lower or higher than a specific value, respectively. The results of this study offer theoretical references and engineering support for the integrity control of cement sheath sealing.

Localization patterns emerging in CPTu tests in a saturated natural clay soil

In this work, the mechanics of cone penetration during CPTu tests in Osaka clay, a natural structured silty clay, was investigated with the Particle Finite Element Method (PFEM). To describe the behavior of the soil, the FD_MILAN model, recently proposed by the Authors, was adopted. The model, based on the multiplicative decomposition of the deformation gradient, incorporates a scalar internal variable, the bond strength Pt, to quantify the effects of structure. The macroscopic description of mechanical destructuration effects is provided by the hardening law of Pt, according to which the bond strength decreases monotonically with accumulated plastic deformations. The brittle behavior resulting from the softening process associated to destructuration make the soil quite susceptible to the spontaneous development of strain localization in the form of shear bands. In order to deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws, incorporating a material constant – the characteristic length ℓc – which provides the material with an internal length scale. The objective of this work was to get some insight on the effects of the characteristic length and of the initial degree of structure on: the kinematics of the soil deformation around the advancing cone tip; the evolution of soil structure with accumulated plastic deformations; the excess pore pressure field generated in the soil as a result of the hydro-mechanical coupling between the solid skeleton and the pore water, and the net cone resistance measured at the base of the cone. The results of the PFEM simulations show that the deformations around the piezocone are strongly affected by the characteristic length. For heavily structured soils, when ℓc is relatively small with respect to cone radius, the accumulated plastic deviatoric deformation field is characterized by clearly visible shear bands while, as ℓc increases, the detection of localized deformation regions becomes more difficult, if not impossible. This depends on the fact that, for large values of ℓc, the shear band width may be of comparable size to the cone radius. In all cases, the soil around the advancing piezocone is subjected to a very strong destructuration process, which leads to the complete loss of bond strength in a large region around the cone tip and shaft. As a consequence, the use of conventional Nc values from the literature in the interpretation of the CPTu test performed in heavily structured soils could provide undrained strength values closer to the ultimate undrained shear strength. At the same time, the use of empirical correlation to estimate the yield stress in oedometric conditions would lead to a significant underestimation of the overconsolidation ratio.

Fretting and mechanically-assisted crevice corrosion (MACC) of rail steel U75V with PA66 liner

Strong evidence has been reported on the occurrence of mechanically-assisted crevice corrosion (MACC) between the upper surface of the rail foot and the liner of the fastener, but there is still a lack of attention regarding its effect on materials degradation. A novel testing apparatus was self-developed in this study to simulate the MACC between the rail foot and the liner (disc-on-disc), and a typical rail steel (U75V) and a typical material for the liner (PA66) have been utilized. The fretting regimes, electrochemical behaviors and morphology of the contact surface have been investigated. It has been found that the fretting was mainly controlled by partial slip regime under the condition in this study, and the OCP and anodic current were both increased with increasing fretting frequency and displacement amplitude. The presence of PA66 debris in the form of large spalling particles has been found to inhibit crevice corrosion and relieve the surface damage to some extent. Cracks and local surface collapse were typically noticed on U75V steel which have been ascribed to the accumulation of plastic deformation and the comprehensive effect of fretting wear and corrosion fatigue.

Grouped rubber-sleeved studs–UHPC pocket connections in prefabricated steel–UHPC composite beams: Shear performance under monotonic and cyclic loadings

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams (PSUCBs) with grouped stud–UHPC pocket connections (GSUPCs) are a successful attempt of UHPC in bridge engineering, which offers significant advantages in accelerating on-site construction, enhancing structural performance, and improving environmental benefits. However, the uneven steel–concrete interfacial shear stresses distribution caused by the insufficient deformability of ordinary studs (OSs) in UHPC may result in the premature stud failure in large interfacial slippage regions. To address this issue, rubber-sleeved studs (RSSs) that wrapped rubber-sleeves around the stud roots were introduced to improve ductility and reduce the stiffness of connectors. However, the shear performance of grouped RSSs embedded in UHPC remains unclear, which hinders their application in practices. Against this background, systematic experimental and numerical studies were conducted to investigate the monotonic and cyclic shear performance of grouped RSSs–UHPC pocket connections. The results indicated that wrapping rubber-sleeve could increase the ultimate slip capacity and remained sufficient shear resistance, demonstrating great potentials of grouped RSSs–UHPC pocket connections in PSUCBs. Increasing the rubber-sleeve thicknesses and height effectively improved the ultimate slip capacity and deformation recovery, but led to the significant plastic deformation accumulation and cyclic stiffness degradation. Finally, design recommendation on rubber-sleeve configuration rationalization, ultimate shear resistance and load–slip relationship predictive models were provided.

Rupture Jumping and Seismic Complexity in Models of Earthquake Cycles for Fault Stepovers with Off-Fault Plasticity

ABSTRACT Fault stepovers are prime examples of geometric complexity in natural fault zones that may affect seismic hazard by determining whether an earthquake rupture continues propagating or abruptly stops. However, the long-term pattern of seismicity near-fault stepovers and underlying mechanisms of rupture jumping in the context of earthquake cycles are rarely studied. Leveraging a hybrid numerical scheme combining the finite element and the spectral boundary integral methods, FEBE, we carry out fully dynamic simulations of sequences of earthquakes and aseismic slip for both compressive and tensile stepovers with off-fault plasticity. We consider a rate-and-state friction law for the fault friction and pressure-sensitive Drucker–Prager plasticity for the off-fault bulk response. We observe that the accumulation of plastic deformation, an indication of off-fault damage, is significantly different in the two cases, with more plastic deformation projected in the overlapping region for the tensile stepover. The seismic pattern for a tensile stepover is more complex than for a compressive stepover, and incorporating plasticity also increases complexity, relative to the elastic case. A tensile stepover with off-fault plasticity shows rupture segmentation, temporal clustering, and frequent rupture jumping from one fault to another. These results shed light on possible mechanisms of rupture jumping in fault stepovers as well as the long-term evolution of the fault zone.

Evaluations and enhancements of fatigue crack initiation criteria for steels subjected to large shear deformations

While large accumulated plastic deformations occur in the rail surface layer where rolling contact fatigue cracks initiate, many available Low Cycle Fatigue (LCF) crack initiation criteria focus on small plastic strains. Accordingly, this paper evaluates available fatigue crack initiation criteria for highly shear-deformed R260 steels, reflecting the conditions in the surface layer of rails. Furthermore, modified crack initiation criteria are suggested. The evaluation is based on three different experiments: Large shear strain increments under varying axial loading (predeformation), strain-controlled LCF tests after some predeformation, and axial High Cycle Fatigue (HCF) experiments. For the predeformation, Finite Element (FE) simulations, with a large-strain plasticity model for cyclic and distortional hardening, provide predictions of the local stress and strain histories. A cross-validation procedure is used to assess the accuracy and reliability of both established and modified fatigue crack initiation criteria. The proposed modifications to one of the criteria show an improved fit to the experimental data. However, there is a tendency to overfitting, which can be improved by including more experimental data.

Influence of secondary orientation on [111]-orientated high temperature creep properties of single crystal alloy with a thin-wall structure

Designing single-crystal superalloy blades to thin wall structures produces the secondary orientation which is the perpendicularity orientation of the wall surface, becoming a newly-concerned crucial factor of performance. Here, we have studied the influence of [110] and [112] secondary orientations on 1100 °C/137 MPa creep properties of [111]-orientated single-crystal superalloys. The plastic deformation accumulation and the plastic limit during creep vary with secondary orientations. Our results give microstructural evidence of the change in the slip systems operation and micro-pore growth, and correlate the possible stress state in the thin wall to plastic deformation mechanism, and finally to properties, which can explain such influence. The results show that the activation of slip systems with different secondary orientations is different due to the different shear stress, and this difference of slip systems causes the difference of plastic deformation ability and pore growth and finally affects the creep performance.

Analytical study on the dynamic mechanical behaviours of foam-core sandwich plate under repeated impacts

The foam-core sandwich structures are probably subjected to repeated impact loadings in engineering applications, resulting in structural plastic deformation and accumulative damage. A valuable analytical approach is needed to predict the accumulative plastic deformation of foam-core sandwich structures under repeated impacts. In this paper, an analytical model of the dynamic responses of foam-core sandwich plates under repeated impacts is proposed using the circumscribing yield locus and the inscribing yield locus based on the rigid-perfectly plastic theory. By employing the principle of energy dissipation rate balance, the analytical expressions of structure permanent deformation and peak force are obtained from the iteration of initial conditions. In addition, polyvinyl chloride (PVC) foam has steady chemical properties and corrosion resistance, which can better adapt to the practical environment and meet the needs of structural protection. To validate the proposed analytical model, the repeated impact dynamic mechanical behaviours of PVC foam-core sandwich plates were experimentally and numerically studied. Results show that theoretical results such as the permanent deformation, peak force, and deformation modes of foam-core sandwich plates under repeated impacts are in good agreement with experimental and numerical results. With the increase in impact numbers, the global bending deformation and local indentation deformation of facesheets increase, the PVC foam core layer is constantly being compressed, and the bottom facesheet plays an increasingly important part in the repeated impact energy absorption with a maximum value of 29.20 %.

Analysis of stress mechanism in a new prefabricated SRC composite column

The superior seismic performance of prefabricated steel-concrete composite structures has recently become a major research focus in the earthquake engineering field. This study proposes an off-site precast steel reinforced concrete (PSRC) column base joint. This joint has a high bearing capacity, efficient assembly, and a fuse function for plastic deformation accumulation at the middle connection. Besides, multiple finite element models are built and calibrated based on the test results using ABAQUS. The research discusses the influence of various parameters on failure modes and seismic performance. The results indicated that the failure position is primarily concentrated in the middle connection, whereas the stress distribution differs within the middle connection. The axial compression ratio and the middle connection position height significantly affect the initial stiffness. The bearing capacity is considerably influenced by various parameters, excluding the thickness of the stiffening plate and cover plate. It is recommended to use an optimal axial compression ratio of 0.45 and a shear span ratio between 2.0 and 2.8 while controlling the stiffening and cover plate thicknesses between 10 and 16 mm. The shear mechanism of the PSRC column base joint mainly includes a steel plate shear wall mechanism and a T-shaped steel frame mechanism. The simplified bearing capacity model results for the proposed PSRC column base joint match well with the experimental and FEM results, and the calculation results are good.

INVESTIGATION OF STAMPING BY WRAPPING PROCESSES THROUGH MATERIAL DEFORMATION MODELING ANALYSIS

This scientific article addresses the pressing issue of material deformation modeling in the context of stamping by wrapping processes (SWP). The main challenges in the development of these processes include the likelihood of workpiece failure due to insufficient material plasticity and unfavorable stress-strain states, determined by technological process parameters. Thus, effective SWP process development requires the utilization of material deformation modeling. The article indicates that any material deformation model in plastic deformation processes comprises three main elements: Analytical representation of the curve or surface of boundary plastic deformations during stationary deformation: This element describes how the material's plastic deformation changes during stationary deformation with alterations in the invariant stress state indicators. Mathematical model of the deformation path in coordinates of stress state indicators - accumulated plastic deformation. This model determines the path along which material deformation develops with changing stress state indicators and is dependent on accumulated plastic deformation. Damage accumulation model: This element takes into account accumulated damage in the material and can be used to predict workpiece failure. Specifically, the article analyzes the surface of boundary plastic deformations during stationary cold deformation and employs terminology to describe the dependence of accumulated plastic deformation until failure on invariant stress state indicators. The term "stationary deformation" is used to denote material deformation under unchanged values of these indicators.

Two Contributions to Rolling Contact Fatigue Testing Considering Different Diameters of Rail and Wheel Discs

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.

Collision damage quantification of RC pier columns coupling axial, flexural and shear effects

Reinforcement concrete (RC) pier columns are the main supporting elements of many highway bridges and city viaducts, therefore the health state of a pier column is critical to the safe operation of bridges. Vehicle-pier collision accidents, which occur increasingly frequently, often induce unexpected damage to an impacted pier column, threatening the safety of bridges. It is important to define appropriate damage indices that can be used to effectively assess the conditions of a pier column damaged by a vehicle collision in a quantitative manner. Previous researchers have proposed many types of damage indices to quantify the degree of damage to an RC column. However, the existing damage indices often suffer from limitations such as undefined upper- and lower-bound rules, ignorance of shear deformation, etc. This paper proposes a plasticity-based damage index, which uses the accumulation of plastic deformation to reflect the damage state of an impacted RC pier column. The proposed damage index ranges between 0.0 and 1.0 which can effectively couple axial, flexural and shear deformation of RC sections during vehicle collisions with detailed model validations using experimental data. A detailed parametric study is then conducted which shows that the damage index can very effectively trace the time-history and spatial distribution of damage on an RC pier column during vehicle collisions.

Measurement of bearing capacity of steel road barrier flange via Barkhausen noise emission

This paper reports about the bearing capacity of a steel road barrier flange and its non-destructive assessment via magnetic Barkhausen noise. Bearing capacity was investigated as a function of the variable degree of plastic straining accumulated in the flange. Plastic deformation was developed on the samples cut from the flange and loaded by uniaxial tension under different strain rates in order to model the dynamic behaviour of plastic deformation during the real collisions. The results of experiments demonstrate that the accumulation of plastic deformation expressed in terms of increasing dislocation density, and the corresponding hardness of the matrix, reduces the bearing capacity of the flange expressed in terms of notch toughness. This decrease is only gentle for the lower plastic strain and becomes steeper for higher strains. Barkhausen noise emission also drops down and MBN envelopes are shifted to higher magnetic fields along with increasing plastic straining as a result of increasing opposition of increasing dislocation density against domain walls motion. It was also found that MBN parameters strongly correlate with notch toughness and especially magnetic hardness is very sensitive for determination of the flange state not only under the high strain rates but also under the strong dynamic impacts as those expected in the high angle collisions. The study proposes the methodology in which the used flanges could be approved for their further use.

Effect of primary carbides on rolling contact fatigue behaviors of M50 bearing steel

It is perceived that the fatigue performance of high-strength steel is preponderantly affected by internal defects. Inclusions may be efficaciously controlled and primary carbides have been proved to be the principal type of defects in M50 bearing steels. Primary carbides in service-status M50 were systematically characterized and the rolling contact fatigue (RCF) properties were evaluated under different friction conditions in this work. An innovative method of shakedown analysis was proposed for the first time, extending the shakedown analysis of materials as an integral based on traditional shakedown theory to that of weaker internal defects. By the response of primary carbides, the RCF process was separated into a plastic instability period and an elastic shakedown period. The accumulation of plastic deformation around carbides before shakedown was proposed as the RCF damage parameter, and the influence of primary carbides was studied based on the damage criterion. The competition between surface and internal fatigue initiation was revealed via different friction coefficients. A predictive model for RCF initiation was established, which could predict the critical sizes for disparate types of primary carbides not deleterious to RCF performance, and the critical sizes under typical industrial service condition were reckoned.