Guozheng Kang

Southwest Jiaotong University · Department of Mechanics and Engineering

Introducing twin boundaries (TBs) and nanoprecipitates has emerged as a highly effective approach for enhancing the mechanical properties of metallic materials. In this paper, the dislocation-precipitate and dislocation-TB interaction models were incorporated into the three-dimensional discrete dislocation dynamics (3D-DDD) framework. The effect of...

This paper investigates the effect of hydrogen on the transformation ratcheting of NiTi shape memory alloy (SMA) wires in the experimental and theoretical aspects. In the aspect of experiments, the NiTi SMA orthodontic wires are hydrogen charged by the electrochemical charging method at room temperature with varying charging durations and charging...

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...

A three‐dimensional non‐isothermal phase field model of polycrystalline NiTi shape memory alloy (SMA) was established based on the Ginzburg–Landau's theory, which considered the interaction between crack growth and martensite transformation (MT). Then, the crack propagation of polycrystalline NiTi SMA and its dependence on the system's grain size a...

The pursuit of enhancing strength and toughness remains a critical endeavor in the field of structural materials. This study explores two distinct strategies to overcome the traditional strength-toughness trade-off. Specifically, we manipulate the chemical composition and short-range order (SRO) of the NiCoCr medium-entropy alloy, which has shown r...

梯度晶粒结构金属材料的微观结构以空间级变的晶粒尺寸分布为特征，呈现出比均匀多晶材料更优越的强度-韧性组合。与几何必需位错（GND）相关的随动硬化被认为是梯度晶粒金属的主要强化机制。然而，GND的精确运动学和背应力场的相关性质仍不清楚，这限制了对其变形机制的理解。在这项工作中，我们建立了一个考虑位错与晶界交互作用的非局域晶体塑性模型。非局部特征是通过引入位错流动项来实现，可以模拟由于位错-晶界交互作用而导致的位错的空间重新分布。滑移系统上的非局部性质使其能够直接研究由变形异质性引起的应变梯度效应，且GND密度的空间变化产生的背应力在模型中引入了一个明确的内禀长度尺度。此外，位错与晶界之间的相互作用导致晶界附近位错塞积的形成，这是研究多晶晶粒尺寸效应的关键。对具有不同晶粒尺寸的多晶进行有限元模拟...

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...

A crystal plasticity coupled twinning phase field (CP-TPF) model was developed to investigate the plastic deformation of magnesium (Mg) single crystal. Three types of slip systems, i.e., basal, prismatic, and pyramidal slip ones were considered in the crystal plasticity model, while the crystalline, gradient, and elastic energies were considered in...

The large scatter in high-cycle fatigue (HCF) life poses significant challenges to safe and reliable in-service assessment of additively manufactured metal components. Previous investigations have indicated that inherent manufacturing defects are a critical factor affecting the fatigue performance of the components, and the HCF life is significantl...

Discrete dislocation dynamics (DDD) simulations reveal the evolution of dislocation structures and the interaction of dislocations. This study investigated the compression behavior of single-crystal copper micropillars using few-shot machine learning with data provided by DDD simulations. Two types of features are considered: external features comp...

High-entropy alloys (HEAs), composed of multiple constituent elements with concentrations ranging from 5% to 35%, have been considered ideal solid solution of multi-principal elements. However, recent experimental and computational studies have demonstrated that complex enthalpic interactions among constituents lead to a wide variety of local chemi...

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...

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...

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-...

This paper presents a novel mesoscopic damage model to characterize the low-cycle fatigue damage evolution of an extruded AZ31 magnesium (Mg) alloy, taking into account the effect of twinning. The damage caused by the slip bands (SBs)–twin boundaries (TBs) and SBs–grain boundaries (GBs) interactions is treated based on the Tanaka–Mura model and the...

Fabric‐based materials have demonstrated promise for high‐performance wearable applications but are currently restricted by their deficient mechanical properties. Here, this work leverages the design freedom offered by additive manufacturing and a novel interlocking pattern to for the first time fabricate a dual‐faced chain mail structure consistin...

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...

Gradient grained metals whose microstructure is characterized by a spatially graded grain size distribution show a better strength-ductility combination than their homogeneous counterparts. Kinematic hardening associated with geometrically necessary dislocations (GNDs) is considered to be a dominant strengthening mechanism in gradient grained metal...

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...

Dual-phase high-entropy alloys (DP-HEAs) have been proved to be a kind of promising materials that exhibit a combination of excellent strength and ductility. Previous studies have emphasized the effect of interface and phase volume fraction on mechanical performance in DP-HEAs. However, the deformation mechanisms such as interplays between dislocat...

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...

In this work, cyclic tension-unloading tests with different peak strains (10%-18%) in the temperature range from 313K to 393K are performed to investigate the effects of temperature and loading level on the cyclic deformation behavior of NiTi shape memory alloy (SMA) wires. Experimental results demonstrate that the superelasticity degradation occur...

Cracking from a fine equiaxed zone (FQZ), often just tens of microns across, plagues the welding of 7000 series aluminum alloys. Using a multiscale correlative methodology, from the millimeter scale to the nanoscale, we shed light on the strengthening mechanisms and the resulting intergranular failure at the FQZ. We show that intergranular AlCuMg p...

The interaction between dislocations and twin boundaries plays an important role in the plastic deformation of high-entropy alloys (HEAs), in which deformation twinning mechanisms are highly active. However, research concerning the twinning-induced strengthening in HEAs is lacking, especially atomistic studies. Therefore, molecular dynamics (MD) si...

In the present work, a 3D discrete dislocation dynamics (DDD) method was used to explore the indentation size effect (ISE) in the nanoindentation of single crystals. The distribution of geometrically necessary dislocation (GND) underneath the indent obtained from the DDD simulations was compared with that in experiments. The results show that the G...

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...

1: A gradient nano-grained polycrystal model with dislocation-penetrable grain boundaries was constructed within a discrete dislocation dynamics framework. 2: The mechanisms of synergetic strengthening in gradient nano-grained aluminum were systematically investigated from the view of dislocation dynamics. 3: The distribution of geometrically neces...

Gradient nano-grained (GNG) metals have shown a better strength-ductility combination compared to their homogeneous counterparts. In this paper, the mechanical properties and the related deformation mechanisms of GNG aluminum were investigated using three-dimensional multiscale discrete dislocation dynamics (DDD). GNG polycrystalline models and uni...

The rate-dependent multiaxial fatigue life of PA6 is investigated by conducting a series of stress-controlled multiaxial fatigue tests involving the ratchetting. Based on the obtained experimental results and the critical plane approach, a semi-empirical life-prediction model is proposed, in which the effects of loading path, stress level, and stre...

Based on the Ginzburg-Landau’s theory, a two-dimensional phase field model coupling martensite transformation/reorientation (MT/MR) and crack behavior was established. The crack propagation of single crystal NiTi shape memory alloy (SMA) and its dependence on the system’s crystalline orientation and temperature was studied by the phase filed simula...

To assess the residual life of railway truck heavy couplers made of cast steel with initial defects, a testing campaign has been carried out to determine high cycle fatigue strength, fatigue crack growth rate, threshold, and fracture toughness. The numerical model of a damaged No.17 heavy-haul coupler is established, by fully considering the assemb...

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...

The transformation-induced plasticity (TRIP) steel has an excellent synergy between strength and ductility and is widely used in industry. Cyclic loading is often seen in its industrial application. Therefore, it is of great significance to study cyclic plastic behavior of the TRIP steel. The TRIP steel's cyclic shear behavior and microstructure ev...

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...

By newly introducing a grain boundary energy, a grain size (GS) dependent and thermo-mechanically coupled phase field model was proposed to investigate the elastocaloric effect (eCE) of NiTi shape memory alloys (SMAs), and discuss the effects of GS, texture, gradient-nanograin and bimodal grain structures as well as geometric gradient on the eCE th...

The internal length scale (ILS) is a dominant parameter in strain gradient plasticity (SGP) theories, which helps to successfully explain the size effect of metals at the microscale. However, the ILS is usually introduced into strain gradient frameworks for dimensional consistency and is model-dependent. Even now, its physical meaning, connection w...

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...

Macroscopic experimental observations on the non-proportional multiaxial ratchetting of extruded AZ31 Mg alloy is firstly summarized, and corresponding microscopic investigations are conducted by electron backscatter diffraction (EBSD) technology on the Mg alloy before and after the multiaxial ratchetting. Then, a constitutive model was developed i...

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...

Recent experimental results show that apparent magneto-elastocaloric effect can be induced in the magnetostrictive-shape memory alloy composite system under an ultra-low magnetic field. In this paper, a multiscale theoretical model is constructed to predict the magneto-thermo-mechanically coupled response of such a composite system by considering t...

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...