Cyclic Deformation Characteristics Research Articles

Local ratcheting and stress relaxation at notch root of CP-Ti specimen under cyclic loading: Experiment and simulation

Damage and crack always origin from notch, and it is necessary to understand the local ratcheting and stress relaxation at notch root for commercially pure titanium (CP-Ti). Symmetric strain-controlled cyclic test for smooth CP-Ti specimen is conducted to determine the cyclic constitutive relationship based on the combined hardening model. Asymmetric force-controlled cyclic test combined with Digital Image Correlation (DIC) technology is conducted to reveal local ratcheting strain distribution at notch root of CP-Ti specimen, while the distributions of stress, local stress ratio, and local hysteresis curve at notch root are obtained by finite element (FE) simulation. It is found that plastic zone, local ratcheting and stress relaxation at notch root area change significantly with cyclic load levels. In the low stress amplitude region with the mean nominal stress lower than 87 MPa, the small-scale yield occurs, and the notch root is in a state of plastic shakedown. With the mean nominal stress increasing to 96 MPa in the transition region, the notch root is in a state that exceeds the plastic shakedown limit but the continuous ratcheting progress is not found. In the high stress amplitude region with the mean nominal stress higher than 104 MPa, the plastic zone significantly expends, and the notch root is in a continuous ratcheting progress state, accompanied by stress relaxation. For a specific structural configuration, the local ratcheting at notch root is affected by both the load level and the cyclic deformation characteristics of the material. In the high stress amplitude region, the reverse yield occurs at the notch root during unloading, which promotes continuous ratcheting progress and stress redistribution, resulting in stress relaxation. The higher the load level, the larger the ratcheting strain rate, and the lower the stress relaxation rate.

The Effects of Drainage Conditions on the Cyclic Deformation Characteristics of Over Consolidated Clayey Soil

The Effects of Drainage Conditions on the Cyclic Deformation Characteristics of Over Consolidated Clayey Soil

Monotonic and cyclic properties of silty sand and sandy silt for foundation design of offshore windfarms

This paper presents results of a series of monotonic and cyclic direct simple shear laboratory tests performed on reconstituted samples of two silty sands and one sandy silt. The laboratory program aimed to determine the cyclic shear strength and deformation characteristics of soils to be used in the offshore wind turbine foundation design. Various cyclic contour diagrams including cyclic shear strength and average and cyclic shear strains for different number of cycles were provided. The effect of strain rate for drained monotonic tests and overconsolidation ratio effect on both monotonic and cyclic properties were discussed. This study indicated that the fines content plays an important role in static and cyclic shear strength of silty soils, in addition to mineralogy and coefficient of uniformity.

Statistical Estimation of Resistance to Cyclic Deformation of Structural Steels and Aluminum Alloy

Resistance to cyclic loading is a key property of the material that determines the operational reliability of the structures. When selecting a material for structures operating under low-cycle loading conditions, it is essential to know the cyclic deformation characteristics of the material. Low-cycle strain diagrams are very sensitive to variations in chemical composition, thermal processing technologies, surface hardening, loading conditions, and other factors of the material. The application of probability methods enables the increase in the life characteristics of the structures and the confirmation of the cycle load values at the design phase. Most research papers dealing with statistical descriptions of low-cycle strain properties do not look into the distribution of low-cycle diagram characteristics. The purpose of our paper is to provide a probability assessment of the low-cycle properties of materials extensively used in the automotive and aviation industries, taking into account the statistical assessment of the cyclic elastoplastic strain diagrams or of the parameters of the diagrams. Materials with contrasting cyclic properties were investigated in the paper. The findings of the research allow for a review of durability and life of the structural elements of service facilities subjected to elastoplastic loading by assessing the distribution of low-cycle strain parameters, as well as the allowed distribution limits.

Pseudoelastic deformation in Mo-based refractory multi-principal element alloys

Phase diagrams supported by density functional theory methods can be crucial for designing high-entropy alloys that are subset of multi-principal-element alloys. We present phase and property analysis of quinary (MoW)xZry(TaTi)1-x-y refractory high-entropy alloys from combined Calculation of Phase Diagram (CALPHAD) and density-functional theory results, supplemented by molecular dynamics simulations. Both CALPHAD and density-functional theory analysis of phase stability indicates a Mo-W-rich region of this quinary has a stable single-phase body-centered-cubic structure. We report first quinary composition from Mo-W-Ta-Ti-Zr family of alloy with pseudo-elastic behavior, i.e., hysteresis in stress-strain. Our analysis shows that only Mo-W-rich compositions of Mo-W-Ta-Ti-Zr, i.e., Mo+W≥85at.%, show reproducible hysteresis in stress-strain responsible for pseudo-elastic behavior. The (MoW)85Zr7.5(TaTi)7.5 was down-selected based on temperature-dependent phase diagram analysis and molecular dynamics simulations predicted elastic behavior that reveals twinning-assisted pseudoelastic behavior. While mostly unexplored in body-centered-cubic crystals, twinning is a fundamental deformation mechanism that competes against dislocation slip in crystalline solids. This alloy shows identical cyclic deformation characteristics during uniaxial <100> loading, i.e., the pseudoelasticity is isotropic in loading direction. Additionally, a temperature increase from 77 to 1,500 K enhances the elastic strain recovery in load-unload cycles, offering possibly control to tune the pseudoelastic behavior.

Cyclic behaviour of precast reinforced concrete beam-columns connected with headed bars

This paper evaluates the structural behaviour of precast reinforced concrete (RC) beam-columns connected with novel ribbed headed bars, and compares with conventional anchorage system of development length and partial development length. Additionally, the effect of encasement with expa-mesh and varying spacing of lateral ties in precast RC column is also investigated. Precast RC beam-column joints were subjected to the displacement controlled quasi-static reversed cyclic loading on the beam end and constant axial load on the column. Structural behaviour was assessed with regards to damage pattern, cyclic load capacity, stiffness degradation, deformation characteristics and energy dissipation; and performance assessment carried out in accordance with ACI 374.1–05. Most of the specimens experienced crack at the interface of beam-column joint at yield limit. Ultimate failure was beam rebar rupture along with separation of beam and column, thus forming plastic hinge at the joint, rather than in the beam element. Both headed bar and conventional specimens surpassed their nominal moment strength and design shear force, thus exhibiting satisfactory performance. On the other hand, specimens with partial development length attained their nominal moment strength but failed to reach joint shear. The strength parameters of headed bar specimens were well comparable to that of conventionally detailed specimens and satisfied the acceptance criteria of ACI 374.1–05, which can be considered as a benchmark to adopt the proposed ribbed headed bar system of anchorage for precast RC beam-column joints in light of its certain advantages over conventional anchorage system.

Physical and Mechanical Properties of Granulated Rubber Mixed with Granular Soils—A Literature Review

End-of-life tires (ELTs) represent a great source of readily available, low-cost and sustainable construction materials having excellent engineering properties. Their reuse (in the form of granulated rubber mixed with soils) in large-volume recycling civil (geotechnical) engineering applications would be beneficial and should be encouraged. It is estimated that at present worldwide only less than 10% of ELTs are reused in geotechnical applications, while nearly 40% are recycled as tire-derived fuel. Although many studies have focused on the material characterization of soil-rubber mixtures (SRMs), it appears that the results of such investigations have not been properly compiled and compared, making it difficult to fully understand the potential applicability of SRMs. In an attempt to provide useful insights facilitating the use of SRMs as geotechnical construction materials, this review paper presents a comprehensive review of published research on the engineering properties of granular soils (i.e., mainly sand and gravel) blended with various recycled rubber inclusions. Available experimental data are scrutinized, and the results of the analyses are presented and discussed primarily in terms of effects of rubber content and aspect ratio (ratio of rubber to gravel median particle sizes) on compaction, permeability, strength and compression properties along with dynamic and cyclic deformation characteristics of SRMs. This review paper may help to alleviate the concerns of designers and consumers and encourage and further promote the use of recycled rubber tires on a larger scale in civil engineering projects.

Study on Cyclic Cumulative Deformation Characteristics and the Equivalent Cyclic Creep Model of Soft Clay

Suction caisson foundations can be used to anchor tension leg platforms. The soil at the bottom of the caisson undergoes both unloading and cyclic loading under wind and wave loads. However, the problem of cyclic cumulative deformation of soft clay under unloading has rarely been addressed. So, the strain cumulative deformation and strain softening characteristics of soft clay are studied by cyclic triaxial tests. The test results show that under low static deviator stress ratios and dynamic deviator stress ratios, the soil has a low level of strain accumulation and softening. As the dynamic deviator stress ratios increase, the cumulative cyclic deformation gradually increases, which rapidly develops in the early stage and tends to stabilize in the later stage. Moreover, the softening index gradually increases and is linearly related to the logarithm of the number of cycles. The cyclic cumulative deformation of the soil increases with increases in unloading stress and dynamic deviator stress, showing a creep characteristic of attenuation and then stabilization. Based on the tests, an equivalent cyclic creep model is established to describe the strain accumulation and softening of soil and verified through comparison with the test results. Then, the model is extended to a three-dimension model, and a finite element subroutine is developed for studying the strain cumulative deformation and strain softening characteristics of soft clay.

Pseudoelastic Deformation in Refractory (MoW) &lt;sub&gt;85&lt;/sub&gt; Zr &lt;sub&gt;7.5&lt;/sub&gt;(TaTi) &lt;sub&gt;7.5&lt;/sub&gt; High-Entropy Alloy

Phase diagrams supported by density functional theory methods can be crucial for designing high-entropy alloys that are subset of multi-principal-element alloys. We present phase and property analysis of quinary (MoW)xZry(TaTi)1-x-y refractory high-entropy alloys from combined Calculation of Phase Diagram (CALPHAD) and density-functional theory results, supplemented by molecular dynamics simulations. Both CALPHAD and density-functional theory analysis of phase stability indicates a Mo-W-rich region of this quinary has a stable single-phase body-centered-cubic structure. We report first quinary composition from Mo-W-Ta-Ti-Zr family of alloy with pseudo-elastic behavior, i.e., hysteresis in stress-strain. Our analysis shows that only Mo-W-rich compositions of Mo-W-Ta-Ti-Zr, i.e., Mo+W ≥ 85 at.%, show reproducible hysteresis in stress-strain responsible for pseudo-elastic behavior. The (MoW)85Zr7.5(TaTi)7.5 was down-selected based on temperature-dependent phase diagram analysis and molecular dynamics simulations predicted elastic behavior that reveals twinning-assisted pseudoelastic behavior. While mostly unexplored in body-centered-cubic crystals, twinning is a fundamental deformation mechanism that competes against dislocation slip in crystalline solids. This alloy shows identical cyclic deformation characteristics during uniaxial loading, i.e., the pseudoelasticity is isotropic in loading direction. Additionally, a temperature increase from 77 to 1,500 K enhances the elastic strain recovery in load-unload cycles, offering possibly control to tune the pseudoelastic behavior.

Multi-axial Fatigue of Head-Hardened Pearlitic and Austenitic Manganese Railway Steels: A Comparative Study

Switches and crossings (S&Cs) in rail networks suffer from damage and deformation due to severe loading of their complex geometric shapes. This article presents a comparative study of the cyclic deformation characteristics and fatigue behavior of two typical crossing materials, namely head-hardened pearlitic steel and Hadfield manganese steel, as well as the associated microstructural changes. Both uniaxial and biaxial loadings (proportional and non-proportional) are studied. The pearlitic steel endured more cycles to failure for a given strain amplitude compared to the manganese steel. The cyclic response of manganese steel shows significant hardening whereas softening was observed for the pearlitic steel except under biaxial non-proportional loading. The microstructures developed in the two types of steels after deformation are characterized by optical (OM) and transmission electron microscopy (TEM). TEM micrographs reveal that the deformed microstructure of the pearlitic steel consists of threading dislocations and dislocation tangles in the ferrite lamellae. The microstructures in the manganese steel after the different loadings are composed of dislocation cells with dislocation tangles inside, intersected by straight stacking fault lamellae. The observed microstructures are related to the results of the mechanical test, and the suitability of the steels for use in S&Cs is discussed.

Cyclic deformation characteristics of S355 and S690 steels under different loading protocols

Despite of excellent high strength to self-weight ratios of the S690 steels, when compared with the S355 steels, there is a widespread concern regarding the ductility of the S690 steels. It is generally considered that the ductility of the S690 steels is significantly lower than that of the S355 steels – this is the general understandings the authors attempt to investigate.This paper presents an experimental investigation into cyclic deformation characteristics of both S355 and S690 steels through low-cycle high-strain cyclic tests with two different loading protocols. A detailed account of the results of 32 cyclic tests on both the S355 and the S690 funnel-shaped coupons is presented. Effects of four different target strains and two different loading frequencies are also examined in details. For the ranges of loading protocols, strain amplitudes, and frequencies considered, the hysteretic responses of these coupons of the two steels are compared directly in terms of engineering stress–strain curves based on their nominal diameters. Microstructures of the fractured coupons of the two steels are also identified for comparison.Contrary to the general understandings, it is demonstrated that the high strength S690 steels do have a good ductility under both monotonic and cyclic actions. Moreover, depending on specific loading protocols and target strains, the cyclic deformation characteristics of the S690 steels are demonstrated to be superior to those of the S355 steels in terms of the number of cycles completed prior to failure and their corresponding energy dissipation characteristic under various target strains up to ±10.0%.The findings of this experimental investigation highlight the importance of establishing ductility requirements and cyclic deformation characteristics for the high strength S690 steels in accordance with specifically designed cyclic tests rather than relying solely on conventional monotonic tensile tests.

Effects of Initial Fabric and Shearing Direction on Cyclic Deformation Characteristics of Sand

Effects of Initial Fabric and Shearing Direction on Cyclic Deformation Characteristics of Sand

High-performance full-field crystal plasticity with dislocation-based hardening and slip system back-stress laws: Application to modeling deformation of dual-phase steels

This paper presents a microstructural cell-level crystal plasticity model aimed at predicting elasto-plastic, anisotropic, rate- and temperature-sensitive deformation of polycrystalline aggregates subjected to large plastic strains. The crystallography-based model embeds strain-path aware dislocation-based hardening and slip-system-level kinematic back-stress laws. The crystal-level response is linked to the microstructural cell-level response using an elasto-viscoplastic fast Fourier transform-based (EVPFFT) micromechanical homogenization. The overall model is ported on a high-performance computational platform integrating a graphics processing unit (GPU) to facilitate computationally efficient modeling of high-resolution microstructures. The high-performance multi-level EVPFFT is applied to modeling monotonic and cyclic deformation of dual-phase (DP) steel sheets. To this end, the effective elastic and flow stress behavior under monotonic and cyclic deformation is calculated for several steels: three DP, DP 590, DP 980, and DP 1180, and one martensitic (MS), MS 1700. Crystallographic textures and phase fractions of these steels are characterized using electron microscopy along with electron-backscattered diffraction to initialize the models. A comprehensive set of Young's modulus, Poisson's ratio, and flow stress data is used to calibrate and validate the model. The model parameters for ferrite and martensite are identified using data for two steels and used to predict the behavior of the other two streels. The model captures elasto-plastic monotonic behavior as well as the particularities pertaining to large strain cyclic deformation characteristics such as non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals based on evolving microstructure including the evolution of dislocation density and crystallographic grain reorientation. In addition, it offers insights into the role of back-stress and dislocation annihilation on the cyclic deformation of DP steels.

Cyclic deformation characteristics of the metastable β-type Ti–40Nb alloy

The present study investigates the cyclic deformation behavior of a new metastable β-type Ti–40Nb alloy (wt%) in two different microstructural conditions. Severe cold rolling followed by recrystallization annealing were performed on cast and homogenized Ti–40Nb rods to obtain a single β-phase microstructure at room temperature. Additional aging at 573 K was carried out to generate isothermal ω-phase precipitates in the β-matrix. Fatigue tests at cycles up to 2 × 106 and a stress ratio of R = −1 were realized with samples with electrochemically polished surfaces. EBSD analysis was carried out after the fatigue tests. Furthermore, detailed fractographic investigations as well as TEM analysis were executed. Results revealed significant differences in the cyclic deformation behavior and a higher fatigue strength for the aged condition. Reasons for superior fatigue properties of the aged condition are a pronounced precipitation hardening effect of the ω-phase as well as a complete suppression of stress-induced martensite formation and deformation twinning due to a barrier function of the ω-precipitates. In the vicinity of the fatigue crack tip, where the localized plastic zone dominates the damage evolution, precipitation-depleted channels can be observed. Within these ω-depleted channels dislocations have an increased mobility, allowing highly localized plastic deformation. Signs of other deformation features with increasing distance to the fatigue crack are not observed. EBSD analysis of the recrystallized samples with initial single β-phase showed on the contrary changes in the microstructure caused by the cyclic loading and the high instability of the β-phase. A dominant development of stress-induced α’’-martensite towards a full martensitic microstructure dependent on the applied stress amplitudes and cycles as well as additional isolated {332} <113> twinning were detected.

Cyclic mean stress relaxation behaviour of P91 steel: Experiments and constitutive modeling

In the present study effect of mean strain on cyclic plastic deformation characteristics of P91 steel is experimentally evaluated and compared with results of finite element simulation considering cyclic plasticity models. P91 steels being used in various components in fossil fired and nuclear power plants are subjected to cyclic loading with mean strains/stresses. Symmetrical and asymmetrical strain controlled tests of P91 steel conducted at room temperature revealed cyclic softening nature during the fatigue cycling process. The influence of mean strain imposed showed strong dependence on stress relaxation behavior and fatigue life of P91 steel. Tensile mean stress was found to relax steeply in initial cycles followed by stabilization during the asymmetric strain cycling. A reduction in fatigue life is observed with increase in mean strain for particular strain amplitude. An attempt has also been made to simulate asymmetric strain controlled behavior of P91 steel through cyclic plastic modeling in the framework of rate independent plasticity theory. Ohno-Wang material model is employed to predict the influence of mean strain on stress relaxation behavior of the investigated steel. The simulated results depicted that Ohno-Wang model captures the cyclic plastic deformation behavior of P91 steel reasonably well.

Shakedown analysis of cyclic plastic deformation characteristics of unbound granular materials under moving wheel loads

Cyclic plastic strain behavior of unbound granular materials (UGMs) exhibits significant stress path dependency. Using a customized triaxial apparatus capable of applying stress path loading, a series of laboratory repeated load triaxial (RLT) tests were conducted on two typical UGMs by varying simultaneously the axial stress and the radial stress. Effects of realistic in-situ stress paths due to a passing wheel on cyclic plastic strain behavior of unbound granular base and subbase materials were investigated and quantified. The analyses of experimental results revealed that the accumulated plastic strain responses of both UGMs subjected to different stress path loadings can be described by the shakedown approach. The amount of accumulated permanent strain, permanent strain rate, and resilient strain were used to classify the plastic deformation accumulation patterns of tested materials under moving wheel loads. Finally, the significance of the research findings on pavement analysis and design practices was highlighted to evaluate permanent deformation resistance of UGMs and their suitability for use in rut resistant and stable pavement foundation layers.

Effects of principal stress axis rotation on cyclic deformation characteristics of rail track subgrade materials

The cumulative plastic deformation of rail track subgrade materials under moving wheel loads is a complex problem. The plastic deformation and resilient modulus of subgrade materials subjected to moving wheel loads are a function of Principal Stress Axis Rotation (PSAR). Difficulties associated with the control of PSAR in conservative experimental methods lead to inaccurate estimations of the actual plastic deformation characteristics of rail track subgrade. Therefore, this study modifies a torsional multi-ring shear apparatus to evaluate the deformation characteristics of subgrade materials under moving wheel loads. The performance of this modified apparatus is evaluated by comparing the experimental results with those of small-scale model tests on an asphalt roadbed rail track with sandy subgrade. The evaluation suggests that the modified multi-ring shear apparatus has an excellent capability to estimate the deformation characteristics of rail track subgrade under moving wheel loads. A series of modified multi-ring shear tests is then conducted to investigate the effects of the loading conditions, the subgrade density, and the loading frequency on the deformation of subgrade materials under moving wheel loads. The results of these tests show that cyclic single-point load tests underestimate the actual deformation characteristics of subgrade materials irrespective of the subgrade density and the loading frequency. Furthermore, the ratio between the plastic cumulative deformations obtained from the moving wheel loading and from the cyclic single-point loading, referred to as the “ratio of axial strain” (Rs), is introduced to evaluate the plastic deformation characteristics of rail track subgrade materials under moving wheel loads only, using the results of cyclic single-point loading tests. Finally, an empirical formula is proposed to predict the cyclic plastic deformation of rail track subgrade materials as a function of the number of loading cycles.

Microstructure and fatigue properties of linear friction welded TC4 titanium alloy joints

The welded joints are often subjected to cyclic stresses and high-strain-rate deformation resulting in worrisome fatigue failure. Therefore, it is necessary to evaluate the fatigue resistance and cyclic deformation characteristics of these weldments. Ti–6Al–4V–0.3Fe–0.1C–0.05N–0.015H–0.2O (TC4) titanium alloy joints were produced via linear friction welding and a sound joint was obtained. It was observed that fine subgrains formed in the weld zone where the hardness became higher. The strain ratio had a strong effect on the cyclic deformation characteristics of the joint, with hysteresis loops being different at different strain ratios. However, the difference of fatigue life of the joint was small with varying strain ratios. The stress amplitude of linear friction welded TC4 joint showed essentially cyclic softening until failure at all strain ratios. Fatigue cracks initiated from the near-surface of base metal and propagated by the formation of fatigue striations together with secondary cracks.

Local Deformation Behavior and Cyclic Deformation Characteristics of Functionally-Graded Shape Memory Polymer Foam

Local Deformation Behavior and Cyclic Deformation Characteristics of Functionally-Graded Shape Memory Polymer Foam

Influence of residual thermal stresses on fatigue crack growth life of discontinuous reinforcements in metal matrix composites

AbstractThe fatigue life prediction model based on crack propagation from micro‐structural features is derived and presented for planar and randomly oriented Discontinuous Reinforced Metal Matrix Composites (DRMMCs). The model contains the influence of micro‐structural properties such as aspect ratio, volume fraction of particle/fibre and constraint between particle and the matrix. The effect of residual thermal stresses generated within the matrix during development of composite is considered. The particle/fibre plays a dominant role in the development of the cyclic plastic zone size ahead of the crack tip; moreover, it enhances the cyclic plastic deformation characteristics of DRMMC. The theoretical model‐based evaluations for low cycle fatigue in DRMMCs are within the proximity of the experimental results.