Accumulation Of Plastic Deformation Research Articles

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.

Cumulative buckling deformation of stiffened panel under cyclic loading

In this study, the cumulative buckling deformation process is evaluated for a stiffened panel subjected to two different uniaxial cyclic loading conditions, namely compressive loading only and alternating tensile-compressive loading. The impact of the cyclic load on the ultimate strength of the panel is then estimated. It should be noted that the occurrence of permanent deformations could be simulated by finite element analysis using a suitable model capable of correctly capturing the deformation components. The results show that the structure accumulates a deformation that appears to grow almost linearly therefore, consequently, it is realistic to expect that if a large number of load cycles of this magnitude are imposed, the accumulated plastic deformation can be quite severe. Furthermore, it is found that these residual deformations, caused by an entity of the cyclic load lower than the design limit, affect the tensile strength of the stiffened panel. Finally, the effects on the numerical evaluation of the ultimate strength of the structure are shown.

Subgrains of γ′ phase in a single-crystal superalloy induced by ultrahigh temperature creep

A new type of γ′ phase subgrain has been found in a single-crystal superalloy after exposure to 360 hours of creep at 1200 °C and 60 MPa. This signifies the capacity of dynamic recrystallization (DRX) of γ′ phase, overturning the widely accepted idea that it is incapable of undergoing DRX. The remarkable plasticity of the γ′-precipitate, activated at ultrahigh temperature, is likely due to the slip/rotation and cracking of the γ′-subgrains. Microstructural evidence of the subgrain boundary originating from γ′-shearing dislocations and their associated walls was obtained, which explains the subgrain formation dependence on plastic deformation accumulation. These findings help us understand the γ′-deformation mechanism and guide to improve creep resistance.

The effects of normal load on the dry-sliding, micro-scratch and nanoindentation behaviors of the Zr-based bulk glassy alloys

In this work, the macro-sliding, micro-scratch and nanoindentation behaviors of the Zr55Cu30Al10Ni5 bulk glassy alloy (BGA) were investigated. It was found that the frictional coefficient and wear rate of the BGA in the dry-sliding test increase with the increasing normal load, and the wear mechanism includes abrasive and oxidative wear. The micro-scratch test results show that the plastic deformation of the alloy and the density of shear bands at the edge of scratch scar increase with the increase in normal load. The friction mechanism between the indenter and the BGA shifts from stick-slip friction to ploughing friction and to micro-cutting as the applied normal load elevates. The nanoindentation result reveals that increasing the normal load leads to the plastic deformation accumulation, and the decreasing elastic modulus and hardness, which are related to the increase in the free volume and shear bands during the deformation process.

Fatigue failure of amorphous alloys under cyclic shear deformation

The accumulation of plastic deformation and flow localization in amorphous alloys under periodic shear are investigated using molecular dynamics simulations. We study a well-annealed binary mixture of one million atoms subjected to oscillatory shear deformation with strain amplitudes slightly above a critical value. We find that upon approaching a critical strain amplitude from above, the number of shear cycles until the yielding transition is well described by a power-law function. Remarkably, the potential energy at the end of each cycle as a function of the normalized number of cycles is nearly independent of the strain amplitude, which allows for estimation of the fatigue lifetime at a given strain amplitude. The analysis of nonaffine displacements of atoms elucidates the process of strain localization, including irreversible rearrangements of small clusters until the formation of a system-spanning shear band.

ANALYSIS OF THE STATE OF STRESS AND DEFORMATION OF THE MATERIAL OF THE BILLET WHEN PLANTING BY THE RESOURCE-SAVING METHOD OF STAMPING BY ROLLING

The processes of planting blanks by the rolling stamping method allow for the efficient production of a wide range of high-quality products, but the possibility of material destruction during deformation prevents the expansion of their technological capabilities. Further development of the processes is possible through the development of new technological schemes based on the analysis of deformation kinematics and the appointment of favorable technological parameters, taking into account their influence on the stress-strain state and deformability of the material of the workpieces. In order to widely use the method of assessing the deformability of workpieces, a reliable technique is needed, which provides for the presence of a mathematical model of the trajectory of deformation of material particles in the coordinates "stress state indicator - accumulated plastic deformation before failure." The work uses an approach to finding an analytical representation of the deformation trajectory based on the construction of a differential equation between the components of plastic deformation increments, followed by the solution of this equation and the identification of its parameters based on experimental data. According to the results of the research, the deformation trajectories of the material particles of the peripheral surface of the flange when planting by rolling stamping method were schematically constructed in the coordinates "intensity of deformations - stress state indicator". Based on the built model, damage accumulation can be simulated by changing the values of the model parameters for different materials and deformation paths. An analytical representation of the deformation trajectory in a parametric form was obtained. The advantages of representing the deformation trajectory in the form of parametric equations are the convenience of analyzing these trajectories. The advantage of the model of the trajectory of deformation of material particles in the coordinates "stress state indicator - plastic strain accumulated before failure" is the absence of a material constant in the analytical expression for the stress state, and the consequence is additional convenience of analyzing ratios and selecting the value of the material constant based on experimental data.

Formation mechanism and microstructure evolution of light etched region during rolling contact fatigue in M50 steel

The microstructure evolution and formation mechanism of lighting etched region (LER) during rolling contact fatigue (RCF) in M50 steel are systematically investigated. The results indicates that LER is a kind of microstructure degeneration due to the accumulation of plastic strain. Finite element simulation indicates that, under 5 GPa contact pressure, the equivalent stress at the subsurface exceeds the yield strength of M50 steel and, thus, induces plastic deformation. The dislocation density and fraction of grain boundaries increase in LER and thus the grain size is refined and the micro-hardness increases. The microstructure evolution in LER during RCF is divided into four stages. Stage 1: dislocations and GBs increase significantly, while the micro-hardness remains almost unchanged with the increase of RCF cycles; Stage 2: GBs and micro-hardness increase gradually with the increase of RCF cycles; Stage 3: LAGBs evolve to HAGBs and thus the total length of LAGBs decreases and the total length of HAGBs increases. Dislocation density and micro-hardness both increase with the increase of RCF cycles; Stage 4: dislocations and GBs continue to increase with the increase of RCF cycles due to accumulation of plastic deformation, and the micro-hardness also increases.