Ratcheting Behavior Research Articles

Ratcheting behavior of non-equiatomic TRIP dual-phase high entropy alloy

Ratcheting behavior of metastable dual-phase (FCC+HCP) Fe50Mn30Co10Cr10 high entropy alloy has been investigated for various combinations of mean stress(σm) and stress amplitude (σa) at ambient temperature. The experimental results show that the accumulation of ratcheting strain and fatigue life primarily depend on the applied mean stress and stress amplitude combination. Detailed microstructure analyses using electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi Diffraction (TKD) revealed the activation of multiple deformation mechanisms, including planar slip, deformation-induced twinning (TWIP), and deformation-induced martensitic phase transformation (TRIP) in both the phases. The synergistic operation of these mechanisms with reverse HCP to FCC transformation at local stress concentration regions in the microstructure promoted cyclic hardening leading to an improved low cycle fatigue behavior of the TRIP DP-HEA under asymmetrical stress-controlled cyclic deformation. In a nutshell, the operation of multiple factors responsible for twinning is unique, providing means to design novel multicomponent alloys.

Ratcheting and low cycle fatigue of nickel-based alloy GH3536 formed by selective laser melting at 800 °C

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

Uniaxial ratcheting behavior and molecular dynamics simulation evaluation of 316LN stainless steel

In this study, a series of uniaxial ratcheting experiments under different mean stresses with a constant stress amplitude were performed on a 316LN stainless steel at room temperature. Meanwhile, molecular dynamics (MD) simulation was carried out to reveal the microstructure evolution mechanism at the initial stage of ratcheting deformation at atomic scale. The results showed that the initial stage of ratcheting deformation could be divided into three stages: the stage of beginning (ratcheting strain growth rate (RSGR, dεr/dN) >0.01%), the stage of decreasing ratcheting rate (RSGR at 0.00001–0.01) and the stage of elastic/plastic shakedown (RSGR <0.00001) based on the changes of ratcheting strain rate. The shakedown ratcheting strain was linearly increased with increase of the mean stress in both MD simulation and experiment. And the ratchet deformation at different stages strongly depended on dislocation evolution. At the stage of beginning, the dislocation originated from coincident site lattice (CSL) boundaries and formed pile-up structures at random angle grain boundaries (RAGBs); while at the stage of decreasing ratcheting rate, the dislocation tangled at CSL grain boundaries or inside the grain, the dislocation density gradually increased and tended to be stable. When the given stress was insufficient to produce more plastic strain, the dislocation density balanced dynamically and the ratchet deformation entered the stage of elastic/plastic shakedown.

Temperature-dependent cyclic plastic deformation of U75VG rail steel: Experiments and simulations

To reveal the temperature-dependent cyclic plastic deformation of U75VG steel, the monotonic tension, strain- and stress-controlled cyclic deformation experiments are carried out at different temperatures. The results show that the U75VG rail steel shows the cyclic softening, cyclic hardening and cyclic softening at 278 K, 573 K and 873 K. Moreover, the U75VG rail steel exhibits obvious ratcheting behavior at differ-ent temperatures, and the ratcheting strain depends on the applied mean stress and stress amplitude. The ratcheting strain is restrained at 573 K due to the influence of dynamic strain aging, while it rapidly increases at 873 K due to increasing the viscos-ity at high temperatures. A temperature-dependent cyclic plastic model is constructed to consider the influence of dynamic strain aging on the cyclic plastic deformation. By comparing the simulation and experimental results, the prediction ability of the proposed model for U75VG rail steel under different temperatures is verified.

Power metallization degradation monitoring on power MOSFETs by means of concurrent degradation processes

An on-chip solution for health monitoring of semiconductor power switches subjected to thermo-mechanical metal fatigue degradation is proposed. The fatigue detection relies on the correlation between the progress of the main failure mechanism, which is critical to the functionality of the device, and a parallel degradation of a non-critical sensing structure using a different mechanism. Both mechanisms are driven by the same cyclic thermo-mechanical load. This study specifically develops a sensing structure for detecting power metallization aging through electrically detectable ratcheting behavior in the routing metal layer underneath. Experiments have been carried out on a dedicated test structure with electrical sensing of the health monitoring structure. Meanwhile, the main degradation progress was observed via scanning electron microscopy in regular intervals. Results show that the proposed approach will reliably work only for detecting degradation driven by repeated high overload events.

Constitutive and damage model for the whole-life uniaxial ratcheting behavior of SAC305

With the wide application of SAC305 solders in electronic packaging, it is important to examine their reliability. In this study, uniaxial ratcheting experiments were carried out on SAC305 solders with varying loading rates, mean stresses, and stress amplitudes at room temperature. Based on the unified creep–plasticity constitutive model applicable to SAC305 solders, a nonlinear continuum damage mechanics model was established to simulate the whole-life ratcheting behavior. The damage variable was extracted from the elastic modulus decline of the unloading section during the cyclic loading process, and its evolution was based on the damage dissipation potential, which was derived from the theory of continuum damage mechanics. In addition, the normalized life was used to correct the evolution of the damage variable. For a more accurate description of their evolution, the energy method was used to modify the damage evolution parameters under different loading conditions. Finally, the uniaxial ratcheting behavior of SAC305 solder could be accurately described by the modified damage-coupled constitutive model under different loading conditions.

The effect of microstructure evolution on the ratchetting-fatigue interaction of carbide-free bainite rail steels under different heat-treatment conditions

Low-cycle fatigue experiments emphasizing the ratchetting are performed on the carbide-free bainitic (CFB) rail steel under different heat-treatment conditions. The effects of microstructure and retained austenite (RA) on the ratchetting-fatigue interaction are investigated through macroscopic and microscopic characterizations. The results indicate that the CFB rail steel exhibits a non-saturated and strain amplitude-dependent cyclic softening feature and shows different ratchetting behaviors and failure modes at various stress levels. Ratchetting promotes the development of stable dislocation substructure and the transformation of blocky RA. The fatigue resistance of 1380 grade CFB steel under the online controlled cooling conditions is better than that of 1280 grade CFB steel under the air-cooling condition.

The ratchetting and retained austenite transformation of medium‐manganese transformation‐induced plasticity steel during asymmetrical cyclic stressing

AbstractThe uniaxial ratchetting behavior and cyclic softening/hardening characteristics of Fe‐0.4C‐7Mn‐3.2Al steel are revealed by cyclic loading experiments. Electron backscattered diffraction (EBSD) and X‐ray diffraction (XRD) analyses have been carried out for assessing retained austenite (RA) transformation during cyclic deformation. Fe‐0.4C‐7Mn‐3.2Al steel exhibits a gradual transition from cyclic stabilization to slight cyclic hardening with increasing strain amplitude. RA transformation is one of the reasons for cyclic hardening. The ratchetting of Fe‐0.4C‐7Mn‐3.2Al steel shows two different characteristics under asymmetrical cyclic stressing. When the stress amplitude is below a certain value, the ratchetting is similar to that of typical cyclic stabilized materials in three stages of deceleration, stabilization and acceleration. However, when the stress amplitude reaches a certain level, the ratchetting evolution accelerates from the beginning to the fracture. The results show that the interaction between transformation‐induced plasticity and ratchetting strain can lead to accelerated accumulation of plastic strain.

Dual Frequency Domain Characteristics of Ratcheting Behavior of Az31b Alloy Under Asymmetrically Stress-Controlled Loading Mode

Dual Frequency Domain Characteristics of Ratcheting Behavior of Az31b Alloy Under Asymmetrically Stress-Controlled Loading Mode

Dynamic Strain Aging-Mediated Temperature Dependence of Ratcheting Behavior in a 316ln Austenitic Stainless Steel

Dynamic Strain Aging-Mediated Temperature Dependence of Ratcheting Behavior in a 316ln Austenitic Stainless Steel

Ratcheting and recovery of adhesively bonded joints under tensile cyclic loading

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

Fatigue performance of friction stir welded weathering mild steels joined below A1 temperature

Hot cracks are prone to occur at the welded joints of weathering steel with high phosphorus contents and drastically reduce the fatigue strength. The present study evaluated the fatigue performance of the weathering steels SMA490AW and SPA-H joined by friction stir welding (FSW) at low temperature (below A1), which can inhibit the segregation of phosphorus. The high-cycle fatigue experiments were conducted on the base metal and welded joint, and the strain distribution was measured by digital image correlation (DIC). The different ratcheting behaviors influenced by the applied maximum stress were analyzed. The S-N curves for the two weathering steels were fitted and compared to the recommended design curves. It is found that the fatigue strength of the welded joints is higher than the design values assessed by nominal stress. The base metal and FSW joints of the weathering steels have almost identical fatigue strength, indicating a favourable weldability. The fatigue fracture of the FSW-joined specimens all occurred in the base metal region due to the high strength of the weld nugget and absence of geometry discontinuities or heat affected zone (HAZ) softening.

Chemo-mechanical analysis of ratcheting deformation in silicon particle electrode under cyclic charging and discharging

Evidences have accumulated that high capacity silicon electrode will expand/shrink dramatically during cyclic charging/discharging operation. In this process, the electrode may undergo elastic-inelastic deformation, and cyclic asymmetric behavior of tension and compression can naturally result in the electrode ratcheting deformation. In this paper, a chemo-mechanical semi-analytical model is established to describe the ratcheting behavior of the silicon particle electrode based on concentration-dependent material properties. The results show that inelastic deformation can reduce the rapid increase of the stresses and further reduce the possibility of surface crack. However, the accumulated irreversible inelastic strain may become one of the important factors for mechanical degradation and even electrode failure. The influence of hydrostatic stress on electrode ratcheting behavior is discussed in detail. It can decrease the concentration gradient and stress level, thereby reducing the inelastic region and ratcheting deformation, which will prolong the predicted lifetime of the electrode. The diffusion coefficient, particle size and the charging rate have also been investigated. The results reveal that ratcheting deformation may be decreased by the high diffusivity, the small particle size and slow charging strategy, which will improve the mechanical stability and capacity of the electrode. Meanwhile, interparticle contact may worsen the ratcheting deformation. Increasing the electrode porosity appropriately can provide space for silicon particles to expand, which may reduce the ratcheting deformation. The present work gives a new explanation for ratcheting deformation in silicon particle electrode and provides a theoretical basis for guiding one in designing next-generation high capacity lithium-ion batteries.

Model Simulation of Creep and Thermal Ratcheting of Engineering Polymers

AbstractIn the present work, the creep response at specific temperatures and stress level of several polymers has been modeled by a viscoelastic model, analyzed in previous works. In particular, the experimental creep results under thermal cycling of polymers used in bolted flange connections, utilized as components of pressure vessel and piping are employed. The analysis is focused on the experimental results for polymeric flange materials like high density polyethylene and three types of gasket materials, namely poly‐tetrafluoroethylene PTFE (expanded e‐ and virgin v‐) and clickable nucleic acid. It has been proved that by the implementation of the model on a simple creep curve at a specific temperature, the model parameters could be evaluated. Hereafter, by imposing a thermal cycling process, two more parameters, associated with thermal ratcheting, could be acquired. It is found that the thermal ratcheting behavior exhibited by the employed materials, could be captured with a good accuracy. Given that the effect of thermal ratcheting on the long‐time performance of polymers in targeted applications is a crucial issue, the research findings in the present work are encouraging for the design of appropriate materials, and the prediction of thermal ratcheting.

Characterization and modeling of the ratcheting behavior of unidirectional off-axis composites

The ratcheting behavior of unidirectional carbon/epoxy composites under cyclic off-axis loading with non-zero average stress was investigated, with a focus on the influence of peak stress (stress ratio R = 0) and fiber orientation. The experimental results show that nonlinear hysteresis and ratcheting behaviors heavily depend on fiber orientation and loading stress. Herein, the evolutionary features of the nonlinear hysteresis behavior and ratcheting deformation of the material are discussed. Furthermore, a creep damage-coupled viscoplastic cyclic constitutive model based on the nonlinear hysteresis behavior and cyclic creep is proposed to simulate the ratcheting behavior of carbon fiber composites under different stress levels and with various fiber orientations. The proposed model can adequately predict the nonlinear response during loading, hysteresis behavior during unloading and reloading, and ratcheting phenomena after a large number of cycles.

Ratcheting Analysis of Steel Plate under Cycling Loading using Dynamic Relaxation Method Experimentally Validated

The present study aimed to introduce a numerical method to study ratcheting strains of rectangular plates. A new numerical analysis was conducted by development of dynamic relaxation method combined with MATLAB software to evaluate the ratcheting behavior of the thin steel plate under mentioned loading condition. In order to verify the results, experimental tests were performed under stress-controlled conditions by a zwick/roell amsler HB100 machine and bending ratcheting of CK45 steel plate at room temperature was studied. Under stress-controlled conditions with non-zero mean stress, ratcheting behavior occurred on thin plate. Moreover, a finite element analysis was carried out by Abaqus using nonlinear isotropic/kinematic (combined) hardening model. The results showed that the rate of ratcheting strain decreased with an increase in cycle number. It was found that the hysteresis loops were wider in experimental method than those of other methods because of more energy dissipation. The numerical results are in a good agreement with the simulation and experimental data. Comparison of errors between these methods obviously demonstrate high accuracy of the new introduced method.

Ratcheting Behavior of Sintered Copper Joints for Electronic Packaging

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

Analysis of dissipation energy and ratchetting behaviors on multiaxial fatigue of adhesively bonded joints

The multiaxial fatigue experiments were conducted on the adhesive bonded hollow cylinder butt-joints under the stress-controlled mode. The effect of loading path, equivalent stress amplitude, equivalent mean stress and period on the multiaxial fatigue behaviors were discussed. The multiaxial fatigue damages of adhesively bonded joints were also analyzed from the evolution of ratchetting and dissipative energy behavior. The results showed that the loading paths had a great influence on dissipated energy and ratchetting strain, and the effects of non-proportional loading path on the ratchetting strain and dissipation energy were greater than that of the proportional loading path. Moreover, the equivalent stress amplitude, equivalent mean stress and period all had some influence on the dissipation energy and equivalent ratchetting strain. In addition, the dissipative energy and the ratchetting strain increased gradually with the number of cycle increase, which resulted in the fatigue life decreases with the increase of equivalent stress amplitude and mean stress, and the decreasing period. The effects of period on the multiaxial fatigue life under the elliptic loading path were insignificant for the adhesive bonding butt-joints.

The effects of kinematic hardening on thermal ratcheting and Bree diagram boundaries

Elastoplastic design of process equipment in petrochemical and power generation industries requires the consideration of thermal ratcheting. Classical Bree diagrams assuming no strain hardening have been the basis in most of today's design Codes and Standards, which can be excessively conservative. In this study, three major kinematic hardening models by Pager, Armstrong and Frederick, and Chaboche are considered for modeling detailed thermal ratcheting behaviors and establishing Bree diagrams. It is found that the linear hardening model by Prager provides a reasonable upper bound ratcheting strain estimation while the perfect plastic assumption by Bree is adequate for the design diagram construction.

Temperature- and time-dependent behavior of Z2CN18.10 stainless steel under uniaxial loading

A series of uniaxial monotonic tensile tests were first conducted on the piping specimens of Z2CN18.10 stainless steel within the temperature range from 20°C to 350°C at different strain rates. The results show an interesting characteristic of the material: it exhibited obvious rate-dependence at room temperature, whereas at 350°C no such significant dependence was observed. Then some tests were performed within the same temperature range to explore the effect of this property on the uniaxial ratcheting behavior of Z2CN18.10 steel. The results reveal that with increasing temperature the ratcheting behavior of the material tended toward shaking-down and became less sensitive to loading rates and peak dwell time. Such temperature-dependent viscoplasticity of the material can presumably be attributed to the dynamic strain aging (DSA) effect, which results in more loss of viscosity of the material as temperature increases.