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Quick Search     Adv Search 2025 Vol. 46, No. 1 Published: 2025-02-28 1 Intermediately Homogenized Peridynamic Simulation of Sandstone Fracture Behavior under Compression Sandstone is a typical discontinuous and heterogeneous material characterized by a significant presence of pores. Porosity is a crucial factor that influences the complex characteristics of sandstone, notably affecting its compressive strength and deformation parameters. It is of considerable theoretical significance and engineering value to investigate the impact of porosity on the fracture behavior of sandstone under compressive loading. In this paper, we apply both the Intermediately-Homogenized PeriDynamic (IH-PD) model and the Fully-Homogenized PeriDynamic (FH-PD) model to examine the fracture behavior of sandstone containing a single oval flaw subjected to uniaxial compression. The IH-PD model incorporates porosity as pre-existing PD damages, wherein mechanical bonds connected to PD nodes are randomly pre-broken to achieve the desired porosity. The IH-PD model considers the heterogeneous characteristics of sandstone without detailing the explicit geometry of the actual pores. Simulation results from the IH-PD model indicate that both pore size and particle size influence the fracture mode of sandstone under uniaxial compression. A comparative analysis of fracture modes and stress-strain curves from IH-PD simulations, FH-PD simulations, and experimental measurements confirms the accuracy and superiority of the IH-PD model for simulating compressive fracture behavior. The results indicate that only the IH-PD model, which accounts for the inherent heterogeneities of sandstone, can adequately reflect the variations in crack paths caused by changes in pore distribution. Moreover, the IH-PD model successfully reproduces tortuous crack paths, captures transverse cracks in sandstone under compression, and exhibits asymmetric fracture modes, which markedly differ from the FH-PD simulation outcomes. This work employs the IH-PD model to investigate the fracture behavior of sandstone containing a single oval flaw with varying porosity levels under uniaxial compression, elucidating the influence of porosity on the failure modes of sandstone. The findings underscore the significant impact of porosity on the paths, roughness, and tortuosity of cracks. As porosity increases, the cracks exhibit greater tortuosity and roughness, and the symmetry of fracture modes becomes more easily disrupted. 2025 Vol. 46 (1): 1-14 [Abstract] ( 43 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 15 Research on buckling behavior in thin-film finite thickness substrate structures considering the flexoelectric effect Large-area and tunable strain gradients has been shown to be introduced by the inhomogeneous deformation in the wrinkled thin film. The great potential of the wrinkled thin film in the application field of the flexoelectric effect has attracted wide attention. The structure and buckling mode of wrinkled thin films have become the focus of attention. In this paper, an electromechanical coupling model is developed to study the buckling behavior of thin-film and finite thickness substrate structures with flexoelectric effect. Firstly, the influence of flexoelectric effect on the buckling evolution of the thin-film substrate structure is studied by the minimum energy method. Then, two kinds of buckling modes global buckling and local wrinkling are distinguished by changing the structural parameters and flexoelectric coefficient. The results show that the stronger the flexoelectric effect in the film, the more slender the film structure, and the more likely global buckling occurs. The stronger the flexoelectric effect in thin films, the larger the critical strain required for buckling, and the more prominent the influence on the local wrinkling mode. The larger the amplitude of the local wrinkling mode, the smaller the maximum strain in thin films. For the local wrinkling mode, the wrinkle is more sparse and the wrinkle amplitude is larger when the flexoelectric effect is stronger. When the flexoelectric effect is increased to a certain extent, the buckling mode of the thin film changes from local wrinkling mode to global buckling mode. The existence of flexoelectric effect will increase the stiffness of the structure and improve the stretchability of the structure. It is also found that the flexoelectric polarization can be adjusted continuously by compressive strain, and the controllability of flexoelectric effect in wrinkled thin films is important for the generation and control of material polarity. These findings will contribute to the design and application of electromechanical devices on micro and nano scale. 2025 Vol. 46 (1): 15-26 [Abstract] ( 46 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 27 Reliability Evaluation of Electromagnetic-acoustic Integrated Testing Method for Composite Defects Metal structures are widely used in modern industrial fields and various composite defects are probably produced during its manufacture and service. For example, both the surface and bottom of structures emerge defects, which seriously affect the mechanical properties and service life of metal structures. Facing such complex conditions, a single nondestructive testing (NDT) method usually cannot meet all needs. However, two or more targeted NDT methods have the problems of low efficiency and high cost. To solve this problem, a novel electromagnetic-acoustic integrated testing method (PECT-EMAT) is developed, and the detection capability of witch is evaluated according to the theory of probability of detection (POD) in this study. Firstly, the simulation method and experimental system of PECT-EMAT are developed for the aluminum alloy specimen with both surface cracks and bottom thinning defects, respectively, the signal separation method based on spectrum analysis theory is studied. Then, the POD model based on statistics is established and the signal database of composite defects is built. Lastly, the signal database is analyzed statistically and the POD of the composite defects detection is analyzed according to the established POD model to determine the minimum detectable size of the PECT-EMAT hybrid testing method. The results of research shows that: (1) For the composite defects with both surface cracks and bottom thinning defects of metal structures, the proposed PECT-EMAT hybrid testing method can detect the composite defects effectively by signal separation. (2) The PECT signals and EMAT signals separated from the original detection signals have obvious signal characteristics for surface cracks and bottom thinning defects, respectively. Moreover, The signal features database of composite defects can been established through above association relationship. (3) Through POD analysis, it finds that the minimum detectable length of the surface crack is 2.72mm and 2.12mm for simulation and experiment, respectively. Similarly, the minimum detectable length of the bottom thinning defect is 4.13mm and 1.92mm, respectively. Through the verification of the detection ability, this paper provides theoretical basis for the popularization and application of the proposed PECT-EMAT hybrid testing method. More importantly, it affords one type of reliable technical means for the complex defects detection for practical engineering structures. 2025 Vol. 46 (1): 27-38 [Abstract] ( 40 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 39 The Finite Particle Method for Solving Crack Propagation of Three-dimensional Solids Simulating three-dimensional (3D) crack propagation in solid structures poses significant challenges due to the unpredictability of crack paths, complicating both computation and solution strategies. Traditional methods often face difficulties in accurately capturing arbitrary crack propagation during large deformations. The finite particle method (FPM), based on vector mechanics, offers a novel numerical approach for analyzing complex behaviors in solid mechanics. Different from conventional continuum-based methods, FPM discretizes the solid domain into a collection of finite particles, each governed by Newton's second law of motion. This particle-based formulation enables seamless transitions between continuum and non-continuum behavior by dynamically adding or removing particles, providing significant advantages for crack propagation analysis in both static and dynamic scenarios. In this study, the FPM is extended to address the dynamic fracture in 3D solids, focusing on the challenges related to crack initiation, propagation, and branching. The FPM is combined with an extrinsic cohesive zone model (CZM) to capture the complex behavior of fractures, avoiding the need to pre-define crack paths and effectively managing discontinuities caused by crack propagation. A discriminant criterion is developed to identify the onset of crack initiation, and an automated embedding process for cohesive elements is implemented to enable real-time simulation of fracture surfaces. To manage the evolving topologies that arise from crack propagation, we propose a general strategy based on an ergodic search algorithm, which updates the connectivity of the discretized solid model dynamically as cracks evolve. In addition, we develop a GPU-based parallel solver using the CUDA toolkit to significantly accelerate fracture computations. The accuracy and applicability of the proposed method are validated through several numerical examples, including fracture simulations of plates and beams subjected to dynamic loading. The results demonstrate the capability of the method to accurately capture the intricate details of crack initiation, growth, and interaction in 3D solids. This extended FPM approach offers a robust tool for analyzing dynamic fractures in engineering applications, providing a versatile framework for studying delamination, material failure, and structural collapse in both research and practical settings. 2025 Vol. 46 (1): 39-53 [Abstract] ( 47 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 54 Finite Element Simulation of Ductile Damage of Notched Specimens Based on a Neural Network Surrogate Model In service conditions, metallic materials may undergo various types of failure under mechanical loadings, including yielding, fracture, buckling, wear, fatigue, and so on. Among these, fracture is one of the most significant and destructive form of failure. In pure metals and alloys, ductile fracture, characterised by dimples on fracture surface, is commonly observed. From the microscopic point of view, the ductile fracture of metals and alloys is closely associated with the nucleation, propagation, and coalescence of voids. This microscopic failure process is influenced by numerous factors such as stress state, void size, void volume fraction, void shape, temperature, etc. Micromechanics based models developed for ductile damage considering the void evolution, such as the Gurson model and its extensions, usually assume spherical voids. The development of models considering realistic void shape and their evolution is of great challenge. Furthermore, conducting mechanical analyses of ductile failure at the specimen and component scales requires addressing cross-scale problems. To address these issues, the present study firstly constructed representative volume element models incorporating an isolated void of different initial shapes. Finite element simulations were carried out based on the representative volume elements by adopting a J2 plasticity model for the matrix. A systematic analysis was realised to understand the influence of the initial void shape on the stress-strain response and ductile damage. Triaxial tensile and shear loading conditions were considered. Using the numerical data generated by the simulations, a neural network based surrogate model was trained to approximate the stress-strain responses and damage evolution. The surrogate model was shown to be capable of predicting the influence of the initial void shape on ductile damage. Subsequently, a user-defined material subroutine was developed, and incorporated into a commercial finite element code. The impact of the initial void shape on the ductile failure process of notched specimens was simulated. It was found that reduced aspect ratio of the void decreased the damage rate leading to a delayed softening at the specimen level. The present work shows the potential of surrogate model for predicting ductile damage involving complex microstructural features. 2025 Vol. 46 (1): 54-66 [Abstract] ( 36 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 67 Bond-based peridynamics simulation for tensile large deformation and fracture behavior of incompressible Neo-Hookean hyperelastic membrane Two-dimensional(2D) bond-based peridynamics (BBPD) model based on the incompressible Neo-Hookean (NH) constitutive model is studied for the simulation of the tensile large deformation and failure behavior of incompressible hyperelastic membrane. First, the force density vector and micropotential function of PD bond are derived by equating the strain energy density of 2D BBPD model to that of NH hyperelastic constitutive model. The model parameters is found to be related to the ratio of the principal stretches within the neighborhood of PD bond. Then a bond-associated horizon is introduced, and the principal stretches are calculated based on the calculation of the deformation gradient within the horizon. Thus a 2D BBPD model for NH hyperelastic material is established. In order to verify the established 2D BBPD model, the nominal stress-stretch curves of a square hyperelastic membrane under uniaxial tension and biaxial tension with different biaxial tension speed ratios are calculated by using the proposed BBPD model, and compared with the theoretical curves. The deformation and load-displacement curves of a hyperelastic membrane with a central circular hole under uniaxial and biaxial tensile loadings are also calculated, and compared with the FEM predictions. Finally, the deformation and failure processes of the hyperelastic membrane with a central circular hole under different tensile loadings are calculated, and the influence mechanisms of loading conditions on the mechanical properties and failure behavior of NH hyperelastic membrane are analyzed based on the evolution analysis of strain energy density and damage of the material points at the crack tip. It is found that the error of calculation results of the proposed BBPD model is less than 10%. The failure load of the hyperelastic membrane with a central circular hole decreases and the failure displacement increases with the increasing of the biaxial tension speed ratio. Crack bifurcation occurs in the hyperelastic membrane with a central circular hole, and the bifurcation angle of the cracks increases with the increasing of the biaxial tension speed ratio. 2025 Vol. 46 (1): 67-78 [Abstract] ( 50 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 79 Method of High-Order Precise Analysis for the P-Δ Effect in Tall Structures due to Arbitrary Axial Loads Traditional methods for analyzing the P-Δ effect in tall structures often struggle to account for time-varying axial forces, potentially underestimating the impact on structural safety. This paper employs the weak form quadrature element method (QEM) to establish Hermite-type quadrature element models for both distributed mass structural systems and systems with concentrated masses. A high-order, precise analytical method for the P-Δ effect in tall structures is developed. The method is applicable to structural systems with abrupt mass changes and can handle time-varying axial forces induced by arbitrary axial loads. High-precision solutions for the P-Δ effect are provided without requiring iterative calculations, accurately revealing the influence patterns of vertical loads and time-varying axial forces on the characteristics of tall structures. Comparative analysis of three different types of cases verifies the feasibility and accuracy of the proposed method. Numerical analysis results demonstrate that this method achieves high-precision P-Δ effect analysis. For both uniformly distributed mass and systems with concentrated masses, using just one quadrature element yields highly accurate dynamic response results. The computational time required is significantly less than that of traditional P-Δ effect analysis methods while maintaining the same level of accuracy. 2025 Vol. 46 (1): 79-92 [Abstract] ( 35 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 93 In-plane oblique loading impact failure and energy absorption of gradient bimaterial honeycomb structure with negative Poisson's ratio As a typical mechanical metamaterial, the material with negative Poisson's ratio will have the phenomenon of indentation resistance when impacted, which makes the impact resistance of the material significantly improved, and it has the characteristics of light weight and high energy absorption. Most of the previous studies focused on the mechanical properties of honeycomb structures under forward impact, but the study on the dynamic response of multi-cell structures with negative Poisson's ratio, especially those made of double material cells, under inclined load is very limited. However, the structural failure caused by inclined load impact cannot be avoided in engineering practice. In this work, the gradient design of multicellular structures is combined with the inclined load impact to study the energy absorption and crushing deformation modes of the structures. A gradient bimaterial negative Poisson's ratio honeycomb structure based on curved edge concave bimaterial cell is proposed in this paper. By changing the transverse and longitudinal curved bar materials, four kinds of material graded gradient honeycomb structures with positive gradient, negative gradient, symmetrical positive gradient and symmetrical negative gradient honeycomb structures are designed. The dynamic behavior of each gradient structure under in-plane oblique impact loading is studied by numerical method. It is found that the honeycomb structure with negative gradient bimaterial arrangement under oblique collision has the best energy absorption effect. For the bimaterial honeycomb structure with negative gradient, the deformation mode, nominal stress-strain curve and energy absorption effect are discussed in detail at different impact velocities and impact oblique angle. The results show that the impact velocity and impact oblique angle have great influence on the energy absorption effect of the model. No matter at what speed, the smaller the impact oblique angle, the better the energy absorption effect of the honeycomb structure, that is, the crashworthiness of the honeycomb structure decreases with the increase of the impact oblique angle. 2025 Vol. 46 (1): 93-104 [Abstract] ( 37 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 105 A STUDY ON CONSTRAINT-RELATED FRACTURE TOUGHNESS PREDICTION BASED ON RANDOM FOREST ALGORITHM AND DATA ENHANCEMENT STRATEGY In this study, the nuclear power steel A508 was selected, and the prediction ability of K-nearest neighbor regression (KNN), nuclear regression (KR), linear regression (LR) and random forest regression (RF) was investigated. It was found that the prediction effect of the four algorithms on the constraint-related fracture toughness is RF > LR > KNN > KR. Further, based on the RF algorithm, the constraint-related fracture toughness of different specimens under different constraints was predicted, and the data under plane stress and plane strain were added to the data for data enhancement. The results show that by adding data enhancement strategy, the fracture toughness prediction model is further improved, the prediction results are more accurate, and the trained model has better generalization ability. 2025 Vol. 46 (1): 105-116 [Abstract] ( 44 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 117 Multimodal self-sustained motion of circular paper sheets under hot steam Self-sustained motion, as a potent tool for solving complex problems and addressing various challenges, has made notable strides across a variety of disciplines, such as bionics, soft robotics, and engineering, owing to its efficiency, resourcefulness, and flexibility. However, single-mode self-sustained motion is typically applicable only to specific types of tasks in varied environments, lacking adaptability to environmental changes. To address these limitations, this study aims to develop a multi-modal self-sustained system using circular silicone oil paper. The study finds that hot steam drives silicone oil paper to achieve self-sustained motion, thereby constructing a self-sustained system. In this system, a circular silicone oil paper is placed on a surface with steam. Driven by the hot steam, the paper can continuously perform self-sustained oscillation and tumbling on the steam-supported surface. The underlying mechanisms of these two modes are analyzed. A geometric model of the self-sustained motion of a circular silicone oil paper is established. Programming calculations are used to study the relationship between the oscillation frequency and amplitude of the circular silicone oil paper and the temperature of the hot steam as well as structural dimensions. The critical conditions for the transition of motion patterns and phase diagrams are presented, and experimental studies are conducted to verify the validity of the theoretical predictions. The research findings reveal that by adjusting the structural size and steam temperature, the circular silicone oil paper can freely transition between three modes: stationary, self-sustained oscillation, and self-sustained tumbling. The frequency and amplitude of the self-sustained oscillation increase with higher steam temperatures, larger outer diameters, and an increased ratio of inner to outer diameters. The multi-modal self-sustained system developed in this study can better adapt to diverse tasks and environments while reducing costs and energy consumption. Therefore, it holds significant potential for applications in fields such as autonomous robotics, medical devices, waste heat recovery, and thermo-mechanical conversion. 2025 Vol. 46 (1): 117-128 [Abstract] ( 34 ) HTML (1 KB)  PDF   (0 KB)  ( 6 ) 129 Study on Energy Absorption Characteristics of New Negative Poisson’s Ratio Star-shaped Honeycomb Structure The negative Poisson's ratio honeycomb structure has been widely used in the field of impact protection because of its unique mechanical properties and good energy absorption capacity. The evolution of local dynamic stress of negative Poisson's ratio honeycomb structure is closely related to the change of cellular microstructure under dynamic impact. The current research on negative Poisson's ratio structure mainly focuses on improving the energy absorption capacity of the whole structure by designing cells with concave deformation mechanism, ignoring structural optimization of existing models, and the research on other energy absorption mechanisms of rotary deformation is also lacking. In order to further improve the dynamic response of star-shaped honeycomb structures with negative Poisson's ratio under in-plane impact, the rotation characteristics of cells are studied in this paper. On the basis of the traditional star-shaped honeycomb structure, the structure of star-shaped honeycomb is further optimized, and the deformation energy absorption mechanism of star-shaped honeycomb cell is endowed with the coupling idea. Based on the principle of relative density equality, two kinds of rotating star-shaped cellular cells with double negative Poisson's ratio effect were obtained by internal rotation and external rotation: internal star-shaped cellular cells and external star-shaped cellular cells. The energy absorption characteristics of different honeycomb structures under in-plane impact loads were studied by numerical simulation, and the influence of both concave and rotating deformation mechanisms on the energy absorption characteristics of honeycomb structures was investigated. Based on one-dimensional shock wave theory and energy absorption efficiency method, the empirical formulas of dynamic platform stress and dense strain of star-shaped honeycomb are given, and the formulas for calculating relative density of star-shaped honeycomb structures are established. According to the theory of critical velocity, the first critical velocity and second critical velocity of star-shaped honeycomb structure are determined. The dynamic response of the rotating star-shaped honeycomb structure under different impact velocities is studied by explicit dynamic finite element method. The simulation results are compared and analyzed with the evaluation indexes of the model macro and micro deformation modes, platform stress and specific energy absorption. The results show that when the new structures are impacted, their cells first rotate and then recessed, which has a stronger negative Poisson's ratio effect. Under the impact of a medium speed of 20m/s, the platform stress of the internal honeycomb structure is higher and the stress stability of the platform is better. In the platform stage, the stress fluctuation of the external spiral honeycomb structure is more severe, but it has a higher specific absorption energy under the impact of high-speed 120m/s. The results of this paper show the relationship between the concave mechanism and rotation mechanism of star-shaped honeycomb structure and its energy absorption characteristics, which provides a new idea for the optimization of impact dynamic performance of honeycomb structure. 2025 Vol. 46 (1): 129-148 [Abstract] ( 46 ) HTML (1 KB)  PDF   (0 KB)  ( 6 )

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