Qianhua Kan

Southwest Jiaotong University · School of Mechanical Engineering

The thermo-mechanical-chemical coupling effect presents significant challenges in accurately predicting the fatigue life of 316 austenitic stainless steel in high-temperature and high-pressure water environments (referred to hereafter as environmental fatigue). The complexity of environmental fatigue experiments results in limited and dispersed dat...

The shape memory effect (SME) under multiaxial pre-deformation has become a significant problem restricting the development of thermo-induced shape memory polyurethane (TSMPU) in complex service conditions. This study experimentally investigates the multiaxial SME of TSMPU under proportionally and non-proportionally multiaxial loadings. The effects...

大量实验研究表明, 当金属材料非均匀塑性变形的特征长度在微米量级时, 材料力学行为呈现出很强的尺寸效应. 不同于传统塑性理论, 应变梯度塑性理论通过引入内禀长度尺寸可有效地描述因非均匀变形引起的尺寸效应. 高阶应变梯度塑性理论可同时捕捉材料在初始屈服和后续硬化阶段的尺寸效应, 但其有限元实现较为复杂; 低阶应变梯度塑性理论则难以解释消除微结构效应的微尺度金属材料在初始屈服时的尺寸效应. 鉴于此, 本文考虑应力梯度效应, 发展了能够描述整个塑性变形阶段尺寸效应的低阶应变梯度塑性模型, 并通过与实验数据进行对比, 验证了其适用性与有效性. 以细丝扭转为例, 量化了应变梯度和应力梯度效应对细铜丝扭转塑性硬化的贡献, 阐明了细铜丝扭转的几何必需位错密度演化及其空间分布特征. 结果表明, 细铜丝扭转时...

Lattice structures are widely used due to their inherent advantages. With the development of smart devices, there is a growing demand for programmable, adjustable, and reconfigurable performances. However, a significant limitation of traditional lattice structures is that their shape, function, and performance cannot be changed after fabrication. I...

Degraded fatigue performance has been frequently reported for metallic materials at elevated temperatures, which is further deteriorated by reducing the loading frequency due to creep deformation. The evaluation of fatigue life for materials and structures typically relies on a large number of experiments and simulations, which is time-consuming an...

The theoretical investigations of cyclic deformation behavior and deformation mechanism of the rail steels under multiaxial loadings are of great significance to the study of rolling contact fatigue. Based on the classical crystal plasticity framework, a new nonproportional parameter at the mesoscale is proposed, and the isotropic and kinematic har...

As an inherent property of the shape memory polymers (SMPs), relaxation plays a crucial role in their mechanical deformation and shape memory effect (SME). During the shape memory processes, relaxation behavior can be divided into short-, medium-, and long-term mechanisms that collectively contribute to the multiple relaxation mechanisms. In this s...

A three-dimensional discrete dislocation dynamics (DDD) method was used to investigate the effect of residual stress on the stress-strain response of gradient nano-grained (GNG) metals. The GNG polycrystalline model was constructed, and different residual stress distributions were introduced in the DDD framework. The simulation shows that the distr...

A calculation model is developed to solve elasto-plastic partial slip contact problems of graded layer-substrate systems. With the high dependence of contact stress on the local region near the contact spot, the graded layer-substrate system of interest is modeled as a homogeneous half-plane with an embedded, finitely long inclusion. Unlike the con...

The gradient nano-grained (GNG) structures achieve a combination of high strength and ductility compared with homogeneous nano-grained structures. In order to study the mechanical behavior of GNG with extremely small grain size, the systematic tension, compression and cyclic deformation behavior of gradient and homogeneous nano-grained CoCrFeMnNi h...

In this chapter, the thermo-mechanically coupled cyclic deformation features of super-elastic and shape memory NiTi SMAs are experimentally investigated under the stress-controlled uniaxial and multiaxial cyclic loading conditions. The definitions and evolution features of the transformation ratchetting, reorientation ratchetting, and temperature-i...

In this chapter, the phenomenological constitutive models of NiTi SMAs are proposed. Firstly, a generalized plasticity-based phenomenological model is proposed to describe the uniaxial transformation ratchetting of NiTi SMAs at room temperature. Then, by considering the interaction between the martensite transformation and dislocation slipping, a d...

In this chapter, some phase-field models are proposed to investigate the thermo-mechanically coupled cyclic deformation of NiTi SMA single crystal and polycrystalline aggregates by addressing the related microscopic mechanisms. Firstly, the crystal plasticity coupled phase-field model are proposed to simulate the super-elasticity and its cyclic deg...

As an introduction, this chapter introduces the super-elasticity and shape memory effect of SMAs first, and then outlines the significant thermo-mechanical coupling effect under different loading rates and the functional fatigue and structural fatigue under cyclic loads of SMAs, finally briefly addresses the classification of SMAs and the content a...

In this chapter, the crystal plasticity-based constitutive models are proposed to describe the cyclic deformation of NiTi SMAs and its rate-dependence. The proposed models are firstly constructed for single crystals by considering different inelastic deformation mechanisms. Meanwhile, the thermo-mechanical coupling nature of rate-dependent cyclic d...

In this chapter, the molecular dynamics (MD) simulations on the thermo-mechanically coupled cyclic deformation of NiTi SMA single crystal and polycrystalline aggregates are performed, the microscopic mechanisms of the cyclic degradations of super-elasticity and one-way shape memory effect are clarified, which are very useful in constructing related...

In this chapter, the damage evolution law and fatigue life prediction models are proposed for NiTi SMAs by addressing their superelasticity and shape memory effect, respectively. The proposed damage evolution law considered the damage coming from the microcrack orientation, propagation, martensite transformation, and martensite reorientation, and t...

A new approach for solving three-dimensional elasto-plastic wheel-rail normal contact problems is presented, which is used to obtain the normal contact pressure distribution in the wheel-rail contact patch and its interior. First, the potential contact region dispersed by rectangular blocks is given. Then, the normal contact pressure in each block...

Excitation of a pure guided wave with a controllable wavefield is essential in structural health monitoring (SHM). For example, a unidirectional-propagation guided wave can significantly reduce the complexity of signal interpretations by avoiding unwanted reflections. However, few transducers are currently capable of exciting a pure unidirectional-...

Shape memory behavior of thermo-induced shape memory polyurethane (TSMPU) under proportionally multiaxial loading is investigated experimentally. The shape memory effect is discussed under different axial and torsional loading angles. By comparing the equivalent stress-equivalent strain curves under different loading angles, it is found that the di...

In this paper, a two-scale thermo-mechanically coupled constitutive model is established to predict the grain size (GS)- and rate-dependent deformation of nano-crystalline super-elastic NiTi shape memory alloy (SMA). At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains...

Considering the complex service environments that high speed railway axles are subjected to, the fatigue crack growth (FCG) behavior of a structurally gradient axle steel with different pre-crack depths both in air and a corrosive medium was investigated at a frequency of 5 Hz. The results indicated that in the high ΔK region, the FCG rate was dram...

In this work, a new micromechanical constitutive model is constructed for high-temperature shape memory alloys. Different from the classical constitutive models, the microstructural patterns, heterogeneities of stress and strain fields at the microscopic scale are addressed. In the proposed model, three different inelastic deformation mechanisms, i...

Experimental investigations on the mechanical deformations of thermo-induced shape memory polymers (TSMPs) at equilibrium temperatures and shape memory effects at non-equilibrium temperatures are conducted at different strain rates. It is found that the loading history conditions change the glass transition temperature, which is the nature of the c...

The damage evolution of an extruded AZ31 magnesium alloy in uniaxial stress-controlled low cycle fatigue is investigated using a quasi-in-situ method. In the three studied samples, that is, slipping dominated (SD), twinning/detwinning/basal slipping (TDBS), and twinning/detwinning/slipping (TDS), the fractions of slip bands and/or twins keep increa...

The amorphous polymers present remarkable temperature- and rate-dependent deformation behaviors. Based on a combination of the multiple relaxation viscoelastic-viscoplastic model and the three-element viscoelastic model, a constitutive model was constructed to describe the changes in mechanical properties of amorphous polymers from below to above g...

Experimental observations show that the torsional deformation of copper micro-wires exhibits obvious sample and grain size effects. In this work, based on the framework of the cyclic plastic J2 flow rule, an incremental higher-order strain gradient constitutive model is established to describe the size effect observed in the torsional deformation o...

Gradient nano-grained (GNG) metals have shown high synergetic strength and good ductility due to their unique gradient microstructure. In this study, the mechanical behavior of gradient nano-grained metals was investigated by three-dimensional discrete dislocation dynamics. The simulation results show a trend that the successive yielding and gradua...

Based on the cyclic tension-unloading tests with various displacements (40, 60 and 80mm) and at different loading rates (0.3mm/s, 1mm/s and 5mm/s), the thermo-mechanically coupled deformation and temperature evolution of pseudoelastic NiTi shape memory alloy (SMA) helical spring are investigated. Experimental results reveal that the phase transitio...

NiTi shape memory alloys (SMAs) are inevitably in contact with hydrogen in specific service environments, which can degrade their mechanical behaviors. In this work, the effect of hydrogen on the super-elasticity of NiTi SMA orthodontic wires is investigated experimentally and theoretically. Firstly, cathodic hydrogen charging was performed for the...

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...

Materials with shape memory effect (SME) can be used as the actuators of self-deforming structures, but the existing ways to design and select actuators with SME are complicated. In this work, an efficient and easy idea was proposed to select the shape memory polyurethane (SMPU) actuator with different designed shapes and sizes. First, the mechanic...

Conventional shape memory alloys (SMAs) exhibit an approximately linear relationship between the critical stresses of martensite transformation (MT) and ambient temperature (Clausius-Clapeyron relationship). Meanwhile, depending on the sign of entropy difference between the parent and martensite phases, these alloys behavior either a conventional o...

Experimental investigations of Carbide-free bainite (CFB) rail steel under different strain amplitudes are conducted to indicate the cyclic deformation feature and hysteresis loop evolution. A modified yield function with an exponential evolution coefficient is proposed to consider the strength differential effect, and a strain range-dependent coef...

The uniaxial tension, strain-controlled and stress-controlled cyclic deformation experiments of U75VG rail steel at various loading rates were carried out. Experimental results show that the U75VG rail steel shows obvious rate-dependent tension, cyclic softening feature and ratcheting behavior. Moreover, based on the rate-dependent experimental res...

Previous tensile tests showed that the typical coarse-grained (CG) interstitial high entropy alloy (iHEA) with the nominal composition Fe49.5Mn30Co10Cr10C0.5 (at.%) has higher yield stress and better strain hardening at cryogenic conditions compared to that at room temperature. However, the yield stress of the fine-grained (FG) iHEA is little influ...

A novel deep learning approach is established in this work to directly model the highly nonlinear mapping between the complex loading conditions (input) and the multiaxial fatigue life (output). An advanced deep learning mechanism, named as self-attention mechanism, is incorporated in this approach to characterize the effects of complex loading his...

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...

The sliding contact shakedown map composed of elastic shakedown limit and elastic limit is significant to the further optimization of functionally graded (FG) coating parameters. The friction heat induced by the relative sliding velocity of contact pairs can cause thermal stress and changes in contact parameters. Nevertheless, the influence of ther...

Torsional or longitudinal wave-based inspection is an effective method for rapid defect screening in pipes, but it has difficulty to locate the circumferential position of a defect due to the axially symmetric properties of torsional and longitudinal modes. In order to overcome this problem, several flexural-wave-based focusing methods have been pr...

In this study, the effects of grain size and dislocation source properties on the yield stress of ultrafine-grained (UFG) polycrystals were examined using three-dimensional multiscale discrete dislocation dynamics (DDD). A polycrystal model containing multiple grains with randomly distributed orientations was constructed within a multiscale DDD fra...

In this study, the effects of grain size and dislocation source properties on the yield stress of ultrafine-grained (UFG) polycrystals were examined using three-dimensional multiscale discrete dislocation dynamics (DDD). A polycrystal model containing multiple grains with randomly distributed orientations was constructed within a multiscale DDD fra...

A three-dimensional non-isothermal and crystal plasticity based phase field model was proposed to simulate the cyclic deformation of nano-polycrystalline NiTi shape memory alloys (SMAs) reflecting their one-way shape memory effect (OWSME) and stress-assisted two-way effect (SATWSME), and then the microscopic mechanism of the cyclic degradation of s...

Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding...

Systematical microstructure characterization, mechanical testing and constitutive modeling were carried out to quantify the effects of residual stress and grain refinement on tensile properties of Ti-6Al-4V alloy treated by laser shock peening (LSP). Microstructure characterization showed that grain size is refined to nanoscale in the outmost surfa...

In this chapter, the application of cyclic plasticity models to the ratcheting of metallic materials and structures is presented. At first, the experimental observations on the ratcheting of such materials are introduced and the evolution features of ratcheting are summarized. Then, the cyclic plasticity models are further specified by addressing t...

The influences of loading conditions on the shape memory effect (SME) of thermo-induced shape memory polyurethane (TSMPU) are investigated by series of thermo-mechanical deformation experiments. The variables related to mechanical responses and the strain contours are extracted to analyze the SME. It is shown that the recovery ratio gradually decre...

It is well-known that conventional multiaxial fatigue life prediction models are generally limited to specific materials and loading conditions. To remove this limitation, a novel attempt is proposed in this work based on the deep learning (i.e., an improvement of artificial neural network in machine learning approaches, which is powerful to learn...

The elastic shakedown analysis of rolling/sliding contact with friction heat is essential for the safety evaluation of tribological components with a functionally graded (FG) coating. However, the corresponding works are still lacking due to the complexity of thermo-elastic contact stress calculation and residual stress optimization induced by the...

To study the effects of twin boundary and high-entropy on elastic–plastic behavior of high-entropy alloys (HEAs), molecular dynamics (MD) was employed to simulate the nanoindentation on single-crystal CoCrNiFeMn HEA (sc-HEA), twinned CoCrNiFeMn HEA (tw-HEA) bicrystal and twinned Ni (tw-Ni) bicrystal. The deformation behaviors of the three samples w...

The ratcheting performance of a new R400HT rail flash butt weld was numerically evaluated under a typical heavy haul in-service condition. Due to varying mechanical properties across the rail weld, the weld region was divided into 23 zones in the numerical study. A dynamic finite element simulation of wheel–rail weld rolling contact was first carri...

The influences of laser dispersed quenching (LDQ) technology on the rolling contact wear and fatigue of U71Mn rail were investigated numerically. Firstly, based on the improved Abdel Karim-Ohno’s material model, a three-dimensional elasto-plastic model with of LDQ rail was established, and the moving load method was used to apply the equivalent con...

According to the Hertz's contact theory (HCT) and considering the strain hardening of materials, an effective calculation method is proposed for solving the elasto-plastic contact pressure and the contact patch size under arbitrary smooth and continuous contact conditions. Firstly, it is assumed that the outer and inner edges of the contact patch a...

Grain boundaries (GBs) have a significant influence on the mechanical properties of metallic materials. It has been a great challenge to describe dislocation interactions with various GBs. In the present article, a generalized dislocation–GB interaction model was constructed and then implemented in the three-dimensional multiscale discrete dislocat...

Based on the previously developed isothermal phase field model [1], the thermo-mechanical cyclic deformation of polycrystalline super-elastic NiTi shape memory alloy (SMA) was simulated by a newly proposed thermo-mechanical phase filed based finite element method. To ensure the efficiency of numerical simulation, a two-dimensional (2D) phase field...

Based on the Ginzburg-Landau's theory, the free energy function of polycrystalline system was modified by introducing an extra grain boundary energy, and a new two-dimensional phase field model considering the continuous variation of temperature was proposed to investigate the grain size dependent super-elasticity (SE) and shape memory effect (SME)...

The development of high-entropy alloys (HEAs) comprising multiple principal components is an innovative design strategy for metallic materials from the perspective of thermodynamic entropy. However, despite their potential candidacy for engineering applications, the lack of research on the cyclic loading responses as well as constitutive modeling o...

Thermo-mechanical coupling one-way shape memory fatigue experiments of NiTi shape memory alloy (SMA) micro-tubes were carried out in this work, which consisted of both the cyclic mechanical and thermal loading parts. In the mechanical cyclic loading part, different stress levels and stress rates were prescribed, but fixed maximum and minimum temper...

In the framework of continuum damage mechanics, a new damage-coupled cyclic plastic model is proposed to describe the nonlinear evolution of whole-life ratchetting and its dependence on the stress level. The characteristic that the damage evolution rate of U75V heat-treated steel decays in the initial load cycles is considered by introducing a modi...

According to the existing experimental investigation on the ratchetting-fatigue interaction of SUS301L stainless steel butt-welded joint, a new life-prediction model addressing the important role of ratchetting is developed based on the ductility exhaustion theory (DET) and continuum damage mechanics (CDM). The total ductility damage is assumed to...

The traditional Hertz contact theory has been widely used in solving contact problems. However, it is only applicable to the elastic contact, and cannot truly reflect the contact stress distribution and contact radius in the elasto-plastic contact. In this work, based on the Hertz contact theory, a fast solving method is proposed to calculate the c...