Acta Mechanica Solida Sinica最新文献

The dynamic deformation behaviors of aluminum alloy sheets often differ from the quasi-static ones. Here, a dynamic biaxial tensile experiment of cruciform specimens has been proposed with electromagnetically actuated punch. A notched cruciform specimen was adopted to obtain heterogeneous deformation covering from equal-biaxial tensile to uniaxial tensile strain path. The inverse identification was used to determine the parameters of Hill48 and YLD2000-2D anisotropic yield functions for 5052-O aluminum alloy sheet. The YLD2000-2D anisotropic yield function was validated by comparison of the simulated and experimental principal strains. By comparison with the anisotropic yield functions under quasi-static loading conditions, the anisotropic yielding behaviors of 5052-O aluminum alloy sheet are alleviated under dynamic loading conditions.

This paper presents a novel fully edge-based smoothed finite element method for free vibration analysis of functionally graded plates, incorporating a quasi-weak form of smoothed integral within an edge-based finite element method framework. Employing first-order shear deformation plate theory, the present method accounts for transverse shear strain and rotary inertia effects while addressing exponentially graded material properties along the plate thickness. The formulation integrates a three-node Mindlin plate element (MIN3) with a shear stabilization technique to prevent shear locking. The quasi-weak form of smoothed integral necessitates the evaluation of indefinite integrals for shape functions, effectively tacking domain integrals related to the shape functions without partial derivatives. By applying both quasi-weak form of smoothed integral and strain smoothing technique, all domain integrals in stiffness and mass matrices are converted into boundary integrals over smoothing domains. Therefore, isoparametric mapping and computing of Jacobian matrix are completely eliminated throughout the solution process. The natural frequencies obtained using the present method are in good agreement with those reported in the literature, highlighting the versatility of the present method for free vibration analysis of functionally graded plates. Notably, the present method demonstrates advantages in eliminating shear locking and reducing sensitivity to mesh distortion.

The recovery stress of materials has a great potential application in the field of road crack self-repair, composite material self-repair, and so on. Taking into account the diversity of practical application environments, the recovery stresses of constrained shape memory alloy (SMA) materials in the initial state of austenite and twinned martensite are given respectively in this paper. As for the experimental research, the austenitic SMA is loaded and constrained. The recovery stresses at different stages are observed by increasing the temperature. In terms of the theoretical research, constitutive models with the initial state of austenite and martensite are established respectively based on the one-dimensional macroscopic phenomenon theoretical model and constraints of SMA. These constitutive models can describe the relationship between recovery stress and volume fraction of martensite under temperature loading with different pre-strains. The theoretical model and experimental data in this paper can provide specific support for the practical engineering application of SMA recovery stress.

Fluid-conveying pipes have been widely used in diverse engineering fields, particularly in aerospace systems, nuclear power plants, oil transportation infrastructure, and biomedical devices. The recent advancements in 3D printing and materials science have increased research interest in the stability and vibration characteristics of slender pipes fabricated from hard magnetic soft (HMS) materials for magnetic control applications. Although several theoretical investigations have been conducted on magnetically controlled cantilevered fluid-conveying pipes, the understanding of their dynamical behavior in vascular environments remains incomplete. In this study, we investigate the buckling and dynamical behaviors of an HMS pipe under the combined effects of an applied magnetic field and nonlinear distributed spring constraints. By solving the nonlinear governing equation, natural frequencies, critical flow velocities, buckling displacements, and dynamic responses of the HMS pipe conveying fluid are obtained. The analysis reveals that the addition of distributed spring constraints leads to a substantial reduction in both buckling and dynamic displacements of the pipe system. Under constant magnetic field conditions, the pipe exhibits static deformation characteristics even when exposed to flow velocities exceeding the critical threshold for buckling instability. When subjected to an alternating magnetic field, the pipe system exhibits periodic oscillatory behavior across a wide range of flow velocities. This periodic response is characterized by displacement variations that show direct correlation with changes in the magnetic declination angle. Notably, nonlinear resonance phenomena associated with the first-mode natural frequency can occur even when the flow velocity is below the threshold for buckling instability. These results demonstrate that both magnetic field strength and declination angle offer a possible means for adjusting the stability, buckling behavior, and dynamic response of an HMS pipe.

Based on the linear elasticity theory of quasicrystals, this study addresses two defect problems in two-dimensional piezoelectric quasicrystals: rigid inclusions and holes. Using the Stroh formalism, Green’s function solutions are obtained for these defects under concentrated and uniformly distributed forces. Numerical examples are presented to analyze the mechanical behavior when loads are applied at various positions, including the center, outside, on the boundary, and at infinity of the elliptical defect. The study emphasizes the significant impact of the phonon line force on the distribution of key physical quantities. Results show that elliptical defects significantly disrupt multiple physical fields, leading to substantial variations in displacement and potential at the hole boundaries and pronounced stress concentrations. The stress in the phason field near the elliptical defect boundary exhibits complex variations under loading conditions, and the piezoelectric effect becomes more pronounced. These findings provide critical guidance for designing quasicrystal-based smart materials with controlled defect responses.

This paper proposes a state-of-the-art three-dimensional Voronoi cell finite element method (3D VCFEM) aimed at investigating the mechanical properties of particle-reinforced composites (PRCs) in space under different microstructural properties. Firstly, the modified residual energy generalized function of 3D VCFEM was proposed by applying the hybrid stress element method, and the element format of the 3D Voronoi element was constructed. On this basis, the interaction between the matrix and the inclusions was considered, and the higher-order stress function including the interaction stress term was constructed. Secondly, to solve the difficulty of integrating easily due to the complexity and irregularity of the integration region in space, Delaunay tetrahedra were introduced within the 3D Voronoi element for mesh refinement. It simplified the integration process. Finally, to verify the accuracy and efficiency of the 3D VCFEM model, comparative models of 3D VCFENM and FEM were established for analysis and discussion. The stress field and strain field were compared and analyzed for the first time. An example was also given for the presence of a large number of randomly distributed inclusion particles. The results showed that under the same accuracy, 3D VCFEM had the advantages of convenient mesh delineation and high computational efficiency compared with FEM, which provided a new way of thinking to analyze the actual PCRs.

Long-duration vehicles in near space have achieved great success; however, the non-destructive testing (NDT) methods for the envelope materials of such long-duration vehicles remain blank. In this paper, we propose the air-coupled ultrasonic NDT method theoretically. In the theoretical analysis process, the envelope material is simplified as an orthogonal sandwich structure. To calculate the displacement and stress fields of each medium, the state vectors are established and the transfer matrices of the material from the upper interface to the lower interface are obtained by using boundary conditions. Then, linear equations about the amplitude of reflected and transmitted waves are derived by combining the coupling boundary conditions of air and solid. The effects of incident angles, inflation of the envelope material, and debonding of the interfaces on the transmission coefficients are considered. The results show that the air-coupled ultrasonic NDT of the envelope material can be carried out in the pre-inflated state. Finally, a method for identifying interface debonding is proposed based on judging transmission coefficients within a certain frequency range.

In this paper, the free vibration and stationary stochastic response of functionally graded (FG) rectangular plates with varying thickness in supersonic flow and thermal environment are analyzed. Two types of material property variations of FG plates with varying thickness are considered: the variation along the direction perpendicular to the mid-surface and that along the direction perpendicular to the bottom surface. Considering the effects of aerodynamic pressure and thermal load, the governing equations of motion of FG plates with varying thickness are derived using Hamilton’s principle within the framework of first-order shear deformation theory. A meshfree Jacobi radial point interpolation (Jacobi-RPI) shape function is constructed by combining the Jacobi polynomials and radial basis to approximate the displacement components of the plate. The accuracy and reliability of the present approach are confirmed through sufficient comparisons with numerical results from the published literature and the finite element software ABAQUS. Finally, the effects of different parameters on the free vibration and stationary stochastic response of FG plates are investigated.

The purpose of this paper is to make an assessment on the performance of a fiber reinforced plastic (FRP) helmet-head system subjected to ballistic impact. Firstly, a finite element (FE) model for the human head is developed. Constitutive models for each component of the head are determined and, in particular, strain rate effects of the compact bone of the skull and the hyperelastic property of the scalp are taken into account for the first time. Secondly, an FE model for Kevlar fiber reinforced plastic (KFRP) helmet is constructed based on the personal armor system for ground troops (PASGT) helmet. Recently developed dynamic constitutive models for metals and FRP laminates are employed for full metal jacketed (FMJ) bullet and the KFRP helmet. Finally, both the head and the helmet models are validated against available test data. Furthermore, the effects of various factors such as padding system, impact position, and projectile type on the ballistic performance of the helmet-head system have been systematically investigated with special attention being paid to the severity of head injury. It is found that the performance of the helmet with OA foam is advantageous over that of the helmet with strap-netting in head injury prevention. It is also found that a lower velocity (358 m/s) FMJ bullet poses more threats to head injury than a higher velocity (610 m/s) fragment-simulating projectile for the PASGT helmet-head system.

In order to realize the automatic recognition and classification of cracks with different depths, in this study, several deep convolutional neural networks including AlexNet, ResNet, and DenseNet were employed to identify and classify cracks at different depths and in various materials. An analysis process for the automatic classification of crack damage was presented. The image dataset used for model training was obtained from scanning experiments on aluminum and titanium alloy plates using an ultrasonic phased-array flaw detector. All models were trained and validated with the dataset; the proposed models were compared using classification precision and loss values. The results show that the automatic recognition and classification of crack depth can be realized by using the deep learning algorithm to analyze the ultrasonic phased array images, and the classification precision of DenseNet is the highest. The problem that ultrasonic damage identification relies on manual experience is solved.