The precise simulation of three-dimensional fluid-structure interaction (FSI) phenomena has always been a hot topic in computational mechanics. To solve FSI problems, a bidirectional coupling strategy technique between the Smoothed Particle Hydrodynamics (SPH) method and Finite Element Method (FEM) is proposed based on a single-layer particle boundary technique in this paper, enabling efficient three-dimensional coupling between fluid particles and solid elements. Within the proposed SPH-FEM coupling framework, a mapping relationship is constructed between surface meshes and single-layer SPH particles, where the surface meshes share nodes with solid elements to transmit external loads. At the same time, the single-layer particles serve as solid boundaries for the SPH solver. The approach eliminates the need for additional boundary treatments and node arrangements required in conventional SPH-FEM coupling algorithms, significantly improving data exchange efficiency between the SPH and FEM modules. The model introduces a boundary shield algorithm and permits different particle/mesh resolutions at the fluid-structure interface, enabling the simulation of three-dimensional FSI problems with complex geometries. Afterwards, the improved SPH-FEM coupling model is adopted to carry out numerical simulations of typical FSI problems, such as the water impact of a wedge, the deformation of an elastic plate under dam-break flows, the flexible floating body under dam-break flows, and the dynamic response of a flexible ship under waves. The numerical results are compared and verified with reference results, proving the computational accuracy of the SPH-FEM coupling algorithm in the FSI problem and broadening the application prospects of the SPH method in engineering problems.

This paper proposes an explicit phase field shell particle method (PFSPM) for simulating dynamic fracture and fragmentation in thin shell structures. The core innovation lies in seamlessly integrating phase field fracture theory into a locking-free shell particle formulation, thereby creating a method that is both accurate for shell kinematics and robust for complex crack evolution. A novel phase field-guided adaptive particle conversion algorithm is introduced to automatically transform critically damaged shell particles into standard MPM particles. This approach effectively eliminates mesh distortion issues while preserving mass and momentum conservation, enabling the robust simulation of complex fragmentation. The method is validated through dynamic crack branching, Kalthoff-Winkler experiments at different impact velocities, ductile tearing of pre-cracked plates, and fracture in cylindrical shells under various loading conditions, showing excellent agreement with experimental data and reference solutions. Furthermore, high-velocity steel sphere penetration simulations of aluminum plates demonstrate PFSPM’s capability in handling extreme deformation and fragmentation scenarios with complex multi-stage impact processes, confirming the method’s accuracy and potential for engineering applications involving severe shell fracture phenomena.

The manufacture of nanostructures on silicon (Si) has profound implications across diverse disciplines. Previous research has focused mainly on qualitative explanations based solely on evidence from electromagnetic and matter reorganization theories. This study designed experiments and explored the characteristics of nanostructures created by scanning with an ultrafast laser, in which experimental evidence supporting both electromagnetic and matter reorganization theories was simultaneously observed. Four distinct surface morphologies were identified, each with specific formation thresholds: 0.06, 0.09, 0.22, and 0.27 J⋅cm−2. The polycrystalline Si that emerged at the apex of the monocrystalline Si matrix was directly characterized, and the occurrence of SiO2 and α-Si was detailed. The simultaneous and distinct contributions of electromagnetic and reorganization theories were revealed. By examining the relationship between phase transitions and laser features, the conditions under which each mechanism operates were established. This study provides novel insights into the precise control of Si nanostructures, which could revolutionize applications in electronics, photonics, and materials science.

A novel peridynamic (PD) contact model based on a background grid is proposed to study complex contact problems involving crack propagation. The proposed model calculates contact forces at the background grid nodes based on a non-penetration condition, rather than searching for contact pairs between particles. Compared to the traditional penalty-based contact model, the proposed contact model does not need artificially chosen parameters, and it can avoid the penetration between different bodies and eliminate the contact force oscillation, which leads to better performance in the accuracy, robustness and stability during the contact process. Furthermore, we develop the proposed contact model into the self-contact problem with a particle classification method to solve the material surface contact problem. Two kinds of examples under different conditions, including plate rolling problem and collision of two rings/blocks, are studied to verify the proposed model. The contact and fracture behaviors are predicted by the proposed contact model, and the obtained results agree well with those from the analytical solution and numerical results. Furthermore, the energy absorption and ballistic resistance of auxetic metamaterials with complex contact situation are studied with the proposedgrid-based PD contact model. The residual impact velocities of the auxetic metamaterials with different cell geometries are studied, which contributes to insights and guidance to the development of the anti-penetration design of auxetic metamaterials.

Fluid–structure interaction modelling has garnered widespread attention in both academic research and engineering practice. Complex fluid–structure interaction problems involving shock waves, multi-material fluid flows, and structural dynamic fractures pose significant challenges to existing numerical methods. This paper presents a staggered grid multi-material arbitrary Lagrangian–Eulerian particle method, which strongly couples the staggered multi-material arbitrary Lagrangian–Eulerian method with the staggered grid material point method within a unified framework of staggered spatial discretisation and cell-centre quadrature. An auxiliary grid is constructed at the cell centres of the staggered multi-material arbitrary Lagrangian–Eulerian grid to accumulate immersed solid variables. Fluid and solid variables are assembled on the staggered multi-material arbitrary Lagrangian–Eulerian grid via cell-centre quadrature, achieving implicit fluid–structure coupling and establishing a monolithic Lagrangian momentum equation. By combining the advantages of the staggered multi-material arbitrary Lagrangian–Eulerian method and the staggered grid material point method, the staggered grid multi-material arbitrary Lagrangian–Eulerian particle method is effective in solving complex fluid–structure interaction problems involving shock waves, multi-material fluid flows, and structural dynamic fractures. The accuracy and reliability of the staggered grid multi-material arbitrary Lagrangian–Eulerian particle method are verified through several numerical examples.

A novel framework for improving stability of virtual element method (VEM) by the graph neural networks (GNNs) is proposed. As a Galerkin method supporting arbitrary element discretization, VEM has greatly advanced polygonal discretization methods. However, its absence of explicit shape functions has long posed challenges to numerical stability. To overcome this limitation, we propose GNE-VEM—a Graph Neural Networks Enhanced VEM (GNE-VEM) framework for optimizing its stability. GNE-VEM leverages GNNs to adaptively determine the element-wise stabilization terms based on local mesh and geometric information, thereby reducing the dependence on heuristic parameter choices and mitigating artificial numerical errors. Specifically, by extracting the shape features of VEM elements via dimensionless quality metrics, GNE-VEM employs graph convolution for message aggregation and outputs a vector of stability coefficients. The evaluation results demonstrate that GNE-VEM generalizes robustly across mesh resolution, element shape arbitrariness, loads and boundary conditions, achieving higher numerical accuracy than the standard VEM. Furthermore, when applied to other linear elasticity problems, GNE-VEM mitigates the shear locking and volumetric locking inherent in low-order VEM through accurate prediction of high-order strain energy, demonstrating its broad applicability to a range of two-dimensional solid mechanics problems.

A set of wing-body junction configurations with varied maximum thickness (tmax) and streamwise location (xtmax) were constructed from the Rood model and investigated numerically using the improved delayed detached-eddy simulation (IDDES) method with the shear-layer-adaptive (SLA) subgrid scale.The mechanisms by which airfoil thickness parameters influence leading-edge (LE) vortex dynamics and trailing-edge (TE) separation were analyzed. Particular attention was paid to the LE turbulent flow structures, including the horseshoe vortex (HSV), secondary vortex (SV), and recirculation region, as well as their responses to variations in thickness parameters firstly. Furthermore, the interaction and suppression mechanisms between the HSV and the SV systems were elucidated. The results demonstrate that increasing the tmax causes the mean three-dimensional separation point, low-shear line, and HSV structure to shift upstream, thereby enlarging the separation region. Moving the xtmax downstream causes the separation location to move closer to the LE, resulting in a reduction in the LE separation region. In the leading-edge junction region, tmax and xtmax mainly affect the oscillation frequency and range of the HSV system. When the vortex legs of the SV approach those of the HSV, the latter can be more effectively weakened, thereby reducing the extent of TE separation. The adjustments to tmax and xtmax can strengthen the coupling and the energy transfer between the HSV and the SV systems. This enhanced interaction will accelerate vortex dissipation and effectively suppresses TE separation. These findings reveal a geometry-dependent connection between LE vortex system dynamics and TE corner separation in wing-body junction flow.

A novel explicit dual-mesh virtual element particle (DM-VEP) method is proposed, establishing a general numerical framework for three-dimensional extreme deformation problems. This method uniquely integrates a hybrid Lagrangian–Eulerian framework, wherein virtual elements and particles, treated as generalized Lagrangian elements, are seamlessly coupled via an Eulerian background grid. To further enhance the simulation of material fracture or fragmentation, an adaptive conversion method of virtual elements to particles is developed. A background grid-based contact method is introduced for multi-body contact problems. Numerical examples demonstrate the robustness and versatility of the proposed method across a range of complex scenarios. This research highlights the potential of DM-VEP method as a powerful tool for solving intricate engineering problems with extreme deformation.

Previous studies have demonstrated that the virtual stress boundary (VSB) method accurately and efficiently imposes nonconforming Neumann boundary conditions in the material point method (MPM). A key advantage of the VSB method is its ability to impose boundary conditions without requiring explicit knowledge of the boundary's position. This is achieved through a transformation that replaces the original boundary traction with an equivalent virtual stress field. The inclusion of this virtual stress field allows the governing equations to be solved using only volume integrals, which are easily computed in the MPM using a particle-wise quadrature scheme. In this study, the VSB method is extended to accommodate various high-order MPM variations. The updates mainly involve addressing the non-local support domain of high-order shape functions and enhancing quadrature accuracy in filled cells. The accuracy and versatility of the combined high-order MPM and VSB method are demonstrated through numerical examples in 1D, 2D, and 3D.

The Material Point Method (MPM) is a hybrid “mesh-particle” approach for large deformation simulations that avoids the high computational costs and boundary challenges of traditional meshfree particle methods. However, bottlenecks arise when modeling geometrically complex boundaries, especially in three dimensions. In this article, a three-dimensional arbitrary grid material point method (3D-AGMPM) is proposed to construct complex boundaries using polyhedral grid cells. This novel method establishes a unified framework for various cell types. In the particle-to-grid mapping procedure, the 3D-Wachspress basis functions are introduced as shape functions for arbitrary grid cells, while an improved hash-cell based particle localization algorithm is proposed to enhance computational efficiency. Nonlinear frictional boundary conditions are proposed in a trial-correction framework to model the frictional interaction between the body and complex geometric surfaces. In addition, a contact algorithm for polyhedral cells is proposed to handle contacts among multiple bodies within the arbitrary grid. Several benchmarks demonstrate the effectiveness of the proposed 3D-AGMPM for handling problems involving complex geometric boundaries. Furthermore, practical case studies, such as the Wangjiayan landslide, highlight its robustness and potential in addressing large-scale, complex engineering problems. Due to the simple implementation, flexibility, and high efficiency, the proposed 3D-AGMPM shows promise as a powerful tool for solving large deformation problems with geometrically complex boundaries.

This study investigates the undrained behavior and strength degradation of marine clay under cyclic loading, which is critical for assessing the performance of coastal and offshore structures. A series of dynamic triaxial tests were conducted on undisturbed marine clay to analyze the evolution of double amplitude strain, pore water pressure, and the degradation index under varying stress levels. Post-cyclic undrained shear tests were also performed to evaluate strength degradation. The results show that a higher cyclic stress ratio (CSR) accelerates the development of double amplitude strain and pore water pressure, with an inflection point in the double amplitude strain evolution curve at approximately 3 %. The critical CSR ranges from 0.15 to 0.20 for clay at depths of 50-60 m, whereas the clay at depths of 70-80 m exhibits a higher critical CSR ranging from 0.20 to 0.25. The cyclic loading effect leads to a reduction in the undrained shear strength of the soil samples, which shows a strong correlation with post-cyclic pore water pressure and double amplitude strain. These findings provide valuable insights for marine engineering design in clay-rich regions.

A novel finite element particle method (FEPM) is proposed in this paper for modeling extreme deformation problems. In a material domain, regions undergoing small deformation are discretized using elements of the finite element method (FEM), while zones subject to extreme deformation are represented with particles of the material point method (MPM). A background grid, covering the entire computational domain, is employed to solve the momentum equations. To circumvent mesh distortion, distorted elements under extreme deformation are adaptively converted into particles during the simulation. The seamless coupling between elements and particles is naturally achieved through the background grid's single-valued velocity field. Furthermore, a contact method is introduced to handle interactions between distinct material domains. Several numerical examples, including symmetric rod impact, soil collapse, soil collapse with a base, penetration of a plate by a long rod projectile, and penetration of a plate by an explosively formed projectile, are studied using the proposed FEPM. The numerical results exhibit good agreement with published literature data and experimental results, demonstrating the effectiveness of FEPM in simulating extreme deformation scenarios.

Silicon carbide (SiC) is a highly valued material for power semiconductor devices due to its wide bandgap, high thermal conductivity, and high breakdown electric field. However, its high hardness, brittleness, and chemical stability present substantial challenges for efficient and high-quality processing. This study investigated the effects of picosecond laser surface scanning on 4H-SiC to enhance the material removal performance. The research focused on surface morphology, phase transitions, subsurface/interface characteristics, and material removal mechanisms under varying laser parameters. The results demonstrate that the laser thermal effect decom poses 4H-SiC into amorphous silicon (a-Si), disordered carbon, and graphite, forming a resolidified layer containing Si-O and Si-C-O oxides. Crystalline silicon (c-Si) is produced under high fluences or extensive irradiations. The variation in the resolidified layer thickness with changing laser parameters is revealed. A detailed laser-induced subsurface damage model is developed, encompassing a resolidified layer that includes the above decomposition and oxidation products, and a deformed layer formed primarily under laser-induced stress. The presence of the resolidified layer and the deformed layer leads to a decreased elastic recovery rate and an increased scratching depth, exceeding 2.5 times that of the unmodified condition. Enhanced material removal performance is mainly driven by the resolidified layer at low fluence and by the deformed layer at high fluence. When aligning the total of the ablation depth and the resolidified layer thickness with the subsurface damage depth in the original material, excellent polishing performance is achieved. These findings provide critical insights for understanding the phase evolution, subsurface damage mechanisms, and material removal behavior of 4H-SiC, offering valuable guidance for optimizing the laser surface modification parameters to achieve high-efficiency processing. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

GaN is characterized by high electron velocity, high electric field, and excellent thermal conductivity, making it highly relevant across various fields. In this study, an ultrafast laser with a pulse duration of 8 ps and a wavelength of 532 nm was used to explore GaN’s ablation characteristics and its underlying mechanisms. Five distinct structures were identified, including shallow incomplete ablation, deep incomplete ablation, complete ablation with edge breakage, substrate damage, and successful ablation, all of which were linked to specific ablation parameters. Two primary ablation mechanisms were observed: one at low laser fluence, where high decomposition pressure led to ablation, and another at high laser energy, where intense electromagnetic effects directly caused ablation. The main defects identified were stress cracking due to high decomposition pressure and substrate damage resulting from excessive laser energy. The threshold for stress cracking was approximately 0.01 J/cm2, while substrate damage occurred at about 0.25 J/cm2 and increased with the decreasing repetition frequency under the influence of spot overlap. By adjusting the laser parameters, different ablation mechanisms could be employed, enabling the fabrication of microgrooves focused on edge quality and substrate recovery that prioritized cleanliness. This study provides valuable insights into the interaction mechanisms between ultrafast lasers and GaN, offering a new theoretical foundation and practical guidance for achieving precise, low-carbon GaN micro/nano machining.

Single-pass laser welding of thick-walled components provides significant efficiency and cost benefits. However, frequent collapse defects during this process pose a major challenge. This study achieved collapse defect suppression in single-pass laser penetration welding of 20 mm-thick stainless steel through rational control of the spatial energy distribution of the laser beam. Under collapse-prone conditions, the laser beam was focused on the top surface and diverged toward the bottom. Consequently, the beam diameter expanded to 269 %, while the peak power density decreased to 30 %. This caused a wider molten pool at the bottom with reduced surface tension, leading to significant melt loss and overall weld collapse. Moreover, adjusting energy distribution through the material thickness reduced the molten pool width at the bottom by 14.5 % and created a high-temperature zone with a steep internal temperature gradient. This increased the surface tension, which promoted molten pool contraction and effectively reduced melt loss, thereby partially suppressing collapse. Furthermore, the use of a beam with more concentrated energy reduced the molten pool width at the bottom by 40.5 %. The backflow within the molten pool was notably reduced under a fully penetrating keyhole, leading to less melt accumulation and a significant decrease in collapse defects. This study provides new insights and practical strategies for defect control in single-pass laser penetration welding of thick plates.

In the standard material point method (MPM), a Cartesian background grid is typically used to solve equations of motion. This can make imposing boundary conditions a challenging task when the boundary of the material domain does not align with the grid edge, as these nonconforming boundary conditions are difficult to apply directly to the nodes of the Cartesian grid. In this paper, we propose the Arbitrary Grid Material Point Method (AGMPM) to efficiently solve problems involving a nonconforming boundary conditions by converting them into conforming boundary conditions. In the AGMPM, boundaries with arbitrary geometries are constructed by using arbitrary convex polygonal grid cells. The Wachspress coordinates are introduced as the shape functions for these grid cells. To impose boundary conditions on the arbitrary grid, two specific types of boundary conditions are proposed as examples: roller boundary conditions, which are two-sided constraints, and rigid-wall-boundary conditions, which are single-sided constraints. These boundary conditions are extensions of those used in the standard MPM. To improve computational efficiency during the particle-to-mesh mapping, an efficient search algorithm based on the bucket search method is presented. Several numerical examples are studied to verify the proposed AGMPM, demonstrate its potential and flexibility in solving engineering problems, and showcase its improved accuracy compared to the standard MPM when dealing with nonconforming boundary conditions.

A novel staggered grid shell particle method (SGSPM) is proposed in this paper to model the shell structural damage subjected to underwater explosion. The material point method (MPM) is used to model the fluid in underwater explosion, and the solid shell material point method (SSMPM) is adopted to model the shell structures. A staggered grid scheme is employed to eliminate the cell crossing noise and improve the accuracy of fluid simulation, and a conversion algorithm is proposed to handle the dynamic fracture of shell structures. In addition, a local multi-mesh contact method is introduced into the staggered grid scheme for modeling the fluid-structure interaction. Several numerical examples, including full hemispherical shell, penetration of a thin plate, large deformation of a plate subjected to underwater explosion, fragmentation of a plate and structural damage of a ship hull subjected to contact underwater explosion, are studied by the proposed SGSPM, and the numerical results agree well with the data in the literature and experiments.

A novel explicit Dual-Mesh virtual element method (DM-VEM) for two dimensional nonlinear dynamic problems is proposed. The DM-VEM employs an Eulerian background grid to solve the momentum equation of the virtual element method (VEM), which significantly improves the spatial stability and the temporal stability of the VEM. An explicit critical time step formula is first developed for one dimensional problems and then extended to two dimensional problems, which takes the effect of vertex position and neighboring cell interaction into consideration. An efficient Lagrangian multiplier contact method based on the background grid is also proposed to deal with contact phenomena. Several numerical examples are studied to verify the proposed explicit DM-VEM in nonlinear dynamic problems.

A peridynamics-based framework is established for the elastic-plastic ductile fracture analysis. In this frame, a new state-based peridynamic elastic-plastic model is presented using the novel bond extension state forms of yield function and plastic flow rule. The nonlinear energy release rate is computed by the extended peridynamic finite crack extension (PFCE) method, and an energy dissipation rate-based bond failure criterion is proposed for ductile crack growth modeling. Numerical methods for plastic states update and yield function solution are also given. Then, examples of plates with a center hole or a center crack, and compact tension (CT) tests are analyzed by the proposed models, and compared to those from theoretical and FEM solutions. The results demonstrate that the proposed peridynamic models can well capture the characteristics of elastic-plastic deformation and ductile fracture, including the plastic shape and size, energy distributions, nonlinear energy release rate, load-displacement and resistance curves, etc.