Search Results (55)

This study presents a predictive method for the fatigue behavior of Ti-6Al-4V based on a crystal plasticity finite element (CPFE) model. A thermally activated constitutive model is calibrated using experimental cyclic stress–strain data. The calibrated model simulates the macroscopic cyclic response and grain-scale deformation heterogeneity. By analyzing the simulated micromechanical fields, a scalar fatigue indicator parameter (FIP) is defined based on the accumulated inelastic work. The predictive capability of this FIP is validated against experimental data at multiple stress levels, demonstrating its effectiveness for microstructure-sensitive fatigue assessment. Full article

Existing macroscopic finite element models for electron beam welding (EBW) typically assume isotropic material behavior, often failing to accurately predict residual stresses induced by strong crystallographic textures. To address this limitation, this study established a sequential dual-scale coupled numerical model bridging micro-texture to macro-mechanics by combining the crystal plasticity finite element method (CPFEM) with thermal-elastic-plastic theory. Representative volume elements (RVEs) incorporating α and β dual-phase characteristics were constructed based on electron backscatter diffraction (EBSD) data from the TA15 weld cross-section. Through simulated tensile and shear calculations on the RVEs, homogenized orthotropic stiffness matrices and Hill yield constitutive parameters were derived and mapped onto the macroscopic model. Simulation results indicate that the proposed model maintains the prediction error for molten pool morphology within 16.3%, while effectively correcting the stress overestimation inherent in isotropic models. Specifically, it adjusts the peak longitudinal residual stress at the weld center from 800 MPa to approximately 350 MPa, significantly reducing the anomalous “M-shaped” stress distribution. By successfully capturing shear stress components, this work provides a high-fidelity computational approach for predicting complex stress states in welded joints, offering critical insights for structural integrity assessment. Full article

Inverse pole figure mapping is a common orientation visualization method used in electron backscatter diffraction (EBSD) software to display crystal orientations. Although this technique has been routinely used in commercial EBSD software, the coloring algorithm employed to map the orientation and construct the color key (standard stereographic triangle) has not been reported in the literature. This paper presents a simple algorithm to color the standard stereographic triangles of the 11 Laue groups by mapping the Maxwell color triangle to the curved standard stereographic triangles using nonlinear shape functions commonly employed in finite element methods. Detailed procedures are given to illustrate how the mapping is performed and how it is used to construct inverse pole figure maps from Euler angles. Color coding of the seven different standard stereographic triangles is demonstrated using a computer program written in C++. It is shown that the simple color-coding algorithm presented in this paper can be conveniently utilized to display orientation data in inverse pole figure maps, which is a critical part of designing customized EBSD software. It also provides a method to adjust the color center within the curved triangles to more uniformly distribute the color, which is not available in commercial EBSD software. The algorithm can also be used to design orientation representation software for other applications, e.g., crystal plasticity simulations, where representation of orientation data is also a routine task. Full article

This study proposes a data-driven framework for predicting forming limit diagrams (FLDs) of AA7075-T6 aluminum sheets under various temperatures and strain rates. To overcome the limitations of costly and time-consuming experiments, a hybrid dataset combining experimental results and virtual data from rate-dependent crystal plasticity finite element (CPFE) simulations coupled with the Marciniak–Kuczyński (M–K) model was developed. Several machine learning (ML) models—including linear regression (LR), random forest regression (RFR), support vector regression (SVR), Gaussian process regression (GPR), and multilayer perceptron (MLP)—were trained to predict FLDs. The nonlinear dependence of the FLD on temperature and strain rate was accurately captured by the ML models, with nonlinear algorithms demonstrating notably improved predictive performance. The proposed approach offers an efficient, accurate, and cost-effective method for FLD prediction and supports data-driven process design in lightweight alloy forming. Full article

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using advanced processing techniques such as laser welding, electron beam melting, and controlled cooling, which induce spatial gradients in grain size and optimize material properties by overcoming the traditional strength–ductility trade-off. In this study, a deep learning-based inversion framework combining Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks is proposed to efficiently predict key constitutive parameters, such as the initial critical resolved shear stress and hardening modulus, in alloy gradient-grained structures. The model integrates spatial features extracted from strain-field sequences and grain morphology images with temporal features from loading sequences, providing a comprehensive solution for path-dependent mechanical behavior modeling. Trained on high-fidelity Crystal Plasticity Finite Element Method (CPFEM) simulation data, the proposed framework demonstrates high prediction accuracy for the constitutive parameters. The model achieves an error margin of less than 5%. This work highlights the potential of deep learning techniques for the efficient and physically consistent identification of constitutive parameters in alloy gradient-grained structures, offering valuable insights for alloy design and optimization. Full article

The Nonlinear Twist Extrusion (NLTE) method, a novel severe plastic deformation (SPD) technique, aims to enhance grain refinement and achieve a more uniform plastic strain distribution. Grain size and its uniform distribution strongly influence the physical properties of metals. Therefore, predicting texture evolution during processing is essential for optimizing forming parameters and improving material performance. In this study, a rate-dependent crystal plasticity formulation is implemented in an explicit framework in Abaqus finite element software, based on a finite strain approach with multiplicative decomposition of the deformation gradient. Crystal plasticity finite element (CPFEM) simulations are conducted on single-crystal copper under boundary conditions representing the NLTE process. The influence of dynamic friction coefficients on texture evolution is systematically investigated, and the results are compared with experimental observations. The study provides new insights into deformation mechanisms during NLTE and highlights the strong correlation between texture development and forming parameters. Full article

This study examines the mechanical, thermal, and electrical properties of copper tool electrodes processed via Equal Channel Angular Pressing (ECAP), with a specific focus on their performance in Electrical Discharge Machining (EDM) applications. A novel Crystal Plasticity Finite Element Method (CPFEM) framework is employed to model anisotropic slip behavior and microscale deformation mechanisms. The primary objective is to elucidate how initial crystallographic orientation influences hardness, thermal conductivity, and electrical conductivity. Simulations are performed on single-crystal copper for three representative Face Centered Cubic (FCC) orientations. Using an explicit CPFEM model, the study examines texture evolution and deformation heterogeneity during the ECAP process of single-crystal copper. The results indicate that the <100> single-crystal orientation exhibits the highest Taylor factor and the most homogeneous distribution of plastic equivalent strain (PEEQ), suggesting enhanced resistance to plastic flow. In contrast, the <111> single-crystal orientation displays localized deformation and reduced hardening. A decreasing Taylor factor correlates with more uniform slip, which improves both electrical and thermal conductivity, as well as machinability, by minimizing dislocation-related resistance. These findings make a novel contribution to the field by highlighting the critical role of crystallographic orientation in governing slip activity and deformation pathways, which directly impact thermal wear resistance and the fabrication efficiency of ECAP-processed copper electrodes in EDM. Full article

CoCrFeNiMn high entropy alloy (HEA) fabricated via laser-based powder bed fusion (PBF-LB/M) exhibits exceptional mechanical properties, including high strength, better ductility than titanium alloy, and superior corrosion resistance. This study simulates the intergranular fracture behavior of PBF-LB/M CoCrFeNiMn HEA under tensile loading by embedding cohesive elements with damage mechanisms into polycrystalline representative volume elements based on the crystal plasticity finite element method. The simulation results show good agreement with reported experimental stress–strain curves, demonstrating that the crystal plastic constitutive model combined with the cohesive constitutive model can accurately describe both the macroscopic response behavior and fracture failure behavior of the CoCrFeNiMn HEA. Furthermore, this work investigates the mechanical properties of the HEA in different tensile directions, the improvement of anisotropy through columnar-to-equiaxed grain transition, and the effect of texture strength on crack initiation and propagation. The results show that the polycrystalline CoCrFeNiMn HEA exhibits anisotropic mechanical properties: simulated yield strengths (YSs) are 436.9 MPa (in the scanning direction) and 484.7 MPa (in the building direction), tensile strengths (TSs) reach 639 MPa and 702.5 MPa, and elongations (ELs) are 10.6% and 21.8%, respectively. After equiaxed grain formation, the EL in the scanning direction increased from 10.6% to 17.2%, while the EL in the building direction decreased from 21.8% to 20.3%. Concurrently, the anisotropy coefficients of YS, TS, and EL decreased by 1.8%, 2.2%, and 36.1%, respectively. The cracks initiate at stress concentrations and subsequently propagate along grain boundaries until final fracture. Variations in texture strength significantly influence the crack initiation location and propagation path in the CoCrFeNiMn HEA. Full article

Addressing the limitations of traditional fatigue life prediction methods, which rely on extensive experimental data and incur high costs, and given the current absence of studies that employ deformation inhomogeneity parameters to construct fatigue-indicator parameter (FIP) for predicting low-cycle fatigue (LCF) life of metals in hydrogen environments, this study firstly explores how hydrogen pre-charging influences the LCF behavior of hot-rolled ribbed bar grade 400 (HRB400) steel via experimental and crystal plasticity simulation, and focus on the relationship between the fatigue life and the evolution of microscale deformation inhomogeneity. The experimental results indicate that hydrogen charging causes alterations in cyclic hysteresis, an expansion of the elastic range of the stabilized hysteresis loop, and a significant reduction in LCF life. Secondly, a novel FIP was developed within the crystal plasticity finite element method (CPFEM) framework to predict the LCF life of HRB400 steel under hydrogen influence. This FIP incorporates three internal variables: hydrogen embrittlement index, axial strain variation coefficient, and macroscopic stress ratio. These variables collectively account for the hydrogen charging effects and stress peak impacts on the microscale deformation inhomogeneity. The LCF life of hydrogen-charged HRB400 steel can be predicted using this new FIP. We performed fatigue testing under only one loading condition to measure the corresponding fatigue life and determine the FIP critical value. This helped predict fatigue life under different cyclic loading conditions for the same hydrogen-charged material. We compared the experimental data to validate the novel FIP to accurately predict the LCF life of hydrogen-charged HRB400 steel. The error between the predicted results and the measured results is limited to a factor of two. Full article

In this study, aluminum single crystals with a {1 0 0} <0 0 1> (Cube) orientation were rolled under two conditions: with external constraints imposed by an external aluminum frame (3DRC) and without external constraints (3DR). The crystal plasticity finite element method (CPFEM) was used to simulate texture evolution, and the results corresponded well with experimental observations. The minor discrepancies observed were primarily attributed to the idealized conditions in the simulation. The results demonstrate that in the 3DR model, crystal orientations predominantly rotate around the transverse direction (TD), with non-TD rotations playing a secondary role. In contrast, the 3DRC model exhibits similar rotation patterns to 3DR at lower reductions, but at higher reductions, non-TD rotations become comparable to TD rotations. This difference results in more concentrated orientations in 3DR and more dispersed orientations in 3DRC. Additionally, analysis reveals that external constraints cause deformation behavior to deviate from the plane strain condition rather than move closer to it. The presence of external constraints alters stress and strain states, modifying the activation of slip systems and crystal rotations, leading to significant variations in slip activity, shear strain, and crystal rotation along TD. Full article

Nickel-based superalloys are widely utilized in critical hot-end components, such as aeroengine turbine blades, owing to their exceptional high-temperature strength, creep resistance, and oxidation resistance. During service, these components are frequently subjected to complex localized loading, leading to non-uniform plastic deformation and microstructure evolution within the material. Combining nanoindentation experiments with the crystal plasticity finite element method (CPFEM), this study systematically investigates the effects of loading rate and crystal orientation on the elastoplastic deformation of DD6 alloy under spherical indenter loading. The results indicate that the maximum indentation depth increases and hardness decreases with prolonged loading time, exhibiting a significant strain rate strengthening effect. The CPFEM model incorporating dislocation density effectively simulates the nonlinear characteristics of the nanoindentation process and elucidates the evolution of dislocation density and slip system strength with indentation depth. At low loading rates, both dislocation density and slip system strength increase with loading time. Significant differences in mechanical behavior are observed across different crystal orientations, which correspond to the extent of lattice rotation during texture evolution. For the [111] orientation, crystal rotation is concentrated and highly regular, while the [001] orientation shows uniform texture evolution. This demonstrates that anisotropy governs the deformation mechanism through differential slip system activation and texture evolution. Full article

Aluminum (Al) alloys exhibit exceptional mechanical properties, seeing widespread use in various industrial fields. Here, we use a multiscale simulation method combining phase field method, dislocation dynamics, and crystal plasticity finite element method to reveal the evolution law of precipitates, the interaction mechanism between dislocations and precipitates, and the grain-level creep deformation mechanism in 7A09 Al alloy under creep loading. The phase field method indicates that Al alloys tend to form fewer but larger precipitates during the creep process, under the dominant effect of stress-assisted Ostwald ripening. The dynamic equilibrium process of precipitate is not only controlled by classical diffusion mechanisms, but also closely related to the local strain field induced by dislocations and the elastic interaction between precipitates. Dislocation dynamics simulations indicate that the appearance of multiple dislocation loops around the precipitate during the creep process is the main dislocation creep deformation mechanism. A crystal plasticity finite element model is established based on experimental characterization to investigate the macroscopic creep mechanism. The dislocation climb is hindered by grain boundaries during creep, and high-density dislocation bands are formed around specific grains, promoting non-uniform plastic strain and leading to strong strain gradients. This work provides fundamental insights into understanding creep behavior and deformation mechanism of Al alloy for deep-sea environments. Full article

Selective Laser Melting (SLM) of 316L stainless steel exhibits great potential prospects for engineering applications due to its high strength, high forming freedom, and low material waste. However, due to the unique processing technology of additive manufacturing, challenges related to the microstructure and differences in the mechanical properties of the formed parts are inevitable. To investigate the influence of building direction and grain boundary strength on the fracture parameters of SLM 316L stainless steel, electron backscatter diffraction (EBSD) experiments were conducted to characterize the microstructure of SLM 316L stainless-steel specimens. A representative volume element (RVE) model reflecting the microstructure of SLM 316L stainless steel was established based on a combination of the crystal plastic finite element method (CPFEM) and UMAT subroutine technology. The crystal plasticity parameters were determined by comparing the results of tensile tests. Cohesive elements were employed and inserted at the grain boundaries of the polycrystalline RVE to simulate the intergranular fracture behavior of SLM 316L stainless steel under uniaxial tensile loading. The damage and fracture mechanisms of the material at the microscale were analyzed. The simulated tensile stress–strain curves were in good agreement with the experimental results; hence, the combined CPFEM model is suitable for characterizing the mechanical response and fracture behavior of the SLM 316L stainless steel. The results revealed that cracks initiate at stress concentration sites and propagate along grain boundaries with increasing external load, ultimately leading to rupture. Additionally, the building direction influences the location of microcracks and their propagation significantly. Full article

Compared with powder metallurgy, centrifugal casting, jet molding, and other technologies, Laser Melting Deposition (LMD) stands out as an advanced additive manufacturing technology that provides substantial advantages in the melt forming of functional gradient materials and composites. However, when high-temperature and high-speed laser energy is applied, the resulting materials are susceptible to porosity, which restricts their extensive use in fatigue-sensitive applications such as turbine engine blades, engine connecting rods, gears, and suspension system components. Since fatigue cracks generally originate near pore defects or at stress concentration points, it is crucial to investigate evaluation methods for pore defects and stress concentration in LMD applications. This study examines the effect of pore defects on stress concentration in LMD-manufactured AlSi10Mg using the crystal plasticity finite element method and proposes a stress concentration coefficient characterization approach that considers pore size, morphology, and location. The simulation results indicate a competitive mechanism between pores and grains, where the larger entity dominates. Regarding the influence of aspect ratio on stress concentration, as the aspect ratio decreases along the stress direction, the stress concentration increases significantly. When pores are just emerging from the surface (s/r = 1), the stress concentration caused by the pore reaches its maximum, posing the highest risk of material failure. To assess the extent to which the aspect ratio, position, and size of pores affect stress concentration, a statistical correlation analysis of these variables was conducted. Full article

Cracks due to stress corrosion cracking in stainless steels are becoming a problem not only in boiling water reactors but also in pressurized water reactor nuclear plants. Stress improvement measures have been implemented mainly for large-bore welded piping, but in the case of small-bore welded piping, post-welding stress improvement measures are often not possible due to dimensional restrictions, etc. Therefore, knowing the actual welding residual stresses of small-bore welded piping regardless of reactor type is essential for the safe and stable operation of nuclear power stations, but there are only a limited number of examples of measuring the residual stresses. In this study, austenitic stainless steel pipes with an outer diameter of 100 mm and a wall thickness of 11.1 mm were butt-welded. The residual stresses were measured by the strain scanning method using neutrons. Furthermore, to obtain detailed residual stresses near the penetration bead where the maximum stress is generated, the residual stresses near the inner surface of the weld were measured using the double-exposure method (DEM) with hard X-rays of synchrotron radiation. A method using a cross-correlation algorithm was proposed to determine the accurate diffraction angle from the complex diffraction patterns from the coarse grains, dendritic structures, and plastic zones. A quantum beam hybrid method (QBHM) was proposed that uses the circumferential residual stresses obtained by neutrons and the residual stresses obtained by the double-exposure method in a complementary use. The residual stress map of welded piping measured using the QBHM showed an area where the axial tensile residual stress exists from the neighborhood of the penetration bead toward the inside of the welded metal. This result could explain the occurrence of stress corrosion cracking in the butt-welded piping. A finite element analysis of the same butt-welded piping was performed and its results were compared. There is also a difference between the simulation results of residual stress using the finite element method and the measurement results using the QBHM. This difference is because the measured residual stress map also includes the effect of the stress of each crystal grain based on elastic anisotropy, that is, residual micro-stress. Full article