Acta Mechanica最新文献

This paper employs the inclusion-based boundary element method (iBEM) to delve into heat transfer phenomena in composites. Initially, we integrate the heat flow function and ellipsoidal integral into a bounded domain containing multiple ellipsoidal inhomogeneities. The eigen-temperature gradient is utilized to simulate the thermal mismatch between inhomogeneities and the matrix. Subsequently, the temperature field is computed considering boundary heat flux and temperature conditions, eigen-temperature gradient, and virtual heat source acting on inhomogeneities. The eigen-temperature gradient and virtual heat source are then solved using the equivalent heat flow conditions to obtain the steady-state heat conduction results within the bounded domain. Through comprehensive numerical examples, we analyze the temperature distribution within composite and scrutinize the impact of particle shapes, orientations, volume fractions, and thermal conductivity ratios on the effective thermal conductivity of composite. Furthermore, we explore the distinctive properties of functional gradient material. Additionally, a comparison between iBEM and the finite element method is conducted. The findings reveal a progressive enhancement in the thermal conductivity of composite as the particle shape transitions from spherical to fibrous.

The accuracy of flow field prediction relies on the resolution of the flow structures, and numerical simulation of flow field based on high-precision methods is of great significance. To this end, an improved interior penalty discontinuous Galerkin (IPDG) method was adopted in the present study to conduct large eddy simulation (LES). It has been validated that the improved IPDG method can reach a precision of at least fourth order. Moreover, the effects of subgrid-scale models and numerical dissipation in the IPDG-LES framework remain questionable. Therefore, the turbulent flow past a circular cylinder at Re = 3900 has been systematically investigated. Compared with Smagorinsky models with/without a damping function and wall-adapting local eddy viscosity model, the dynamic subgrid model leads to higher accuracy due to the modeling strategy. The effect of numerical dissipation seems perverse, and the discrepancy could be attribute to the generation of aliasing error and resolved viscosity when numerical dissipation is artificially suppressed. In addition, NACA0021 airfoil flow simulation at AOA = 60 deg and Re = 2.7 × 10⁵ has been conducted. The characteristics of the turbulence field and high precision are also well demonstrated under the IPDG-LES framework.

Deformation fields near the tip of a crack in a material with properties depending on the type of stress state are presented for conditions of longitudinal shear. These properties are revealed in rocks, concretes, refractory ceramics, cast iron, structural graphite, some composites, and many other microheterogeneous materials. The behavior of heterogeneity depends on the loading conditions, and as a result, the deformation properties of these materials are stress state-dependent. Moreover, shear and volume deformation processes are interrelated in these materials. Therefore, it is impossible to distinguish between the fields corresponding to shear strain and bulk strain in solids. For the study of stress, strain, and displacement fields at a crack tip, corresponding constitutive equations are used to simulate the dependence of equivalent elastic properties on the type of stress state and to describe the relationship between shear strains and volumetric deformations. The traditional approach based on anti-plane strain hypothesis cannot be used for solving problems under longitudinal shear conditions because shear strains are not independent of bulk strains. Therefore, the corresponding representations for displacements have been proposed. Nonlinear constitutive relations are used, and conditions for a unique solution to the boundary value problem have been shown. The obtained solutions are compared with the known solutions for a linear elastic solid. The opening of crack faces is observed under conditions of out-of-plane shear, and the dependence of the crack opening on the sensitivity of material properties to the stress state is studied.

Piezothermoelasticity and wave interaction studies hold immense significance in designing functional devices ranging from transducers to sensors for a variety of purposes like energy harvesting and structural health monitoring. These applications catalyze interest in this article which addresses the problem of reflection of plane wave at the boundary of piezothermoelastic half-space. Through this study, the effect of impedance parameter on amplitude and energy ratios of the reflected waves is studied. Four wave modes are indicated upon reflection and a linear system of equations is formed to obtain a closed-form expression for amplitude and energy ratios. These equations are solved by suitable mathematical tools leading to expression for amplitude ratios as a function of incidence angle. For a suitable piezothermoelastic medium, the ratios are plotted against incidence angle and the findings are compared for two well-known theories of thermoelasticity, namely, Lord–Shulman (LS theory) and Green–Lindsay (GL theory). The analytical outcomes suggest approximate values of impedance and incidence angle for preferred energy division between reflected waves. It is recognized that adding impedance increases the amplitude of the quasi-longitudinal (qP) wave and decreases that of the quasi-transverse wave, making it suitable for devices that require a more robust qP wave signal detection.

This paper proposes a modified two-dimensional (2-D) shear-lag model considering unidirectional or bidirectional interfacial damage to analyze the stress transfer mechanism of rectangular patch-reinforced composites under tensile load. The semi-analytical solutions for bidirectional normal stresses and interfacial shear stresses are provided, accounting for interfacial orthotropic anisotropy and the stiffness variation in the damage stage. The study examines the influence of material parameters, including the difference in Poisson's ratios between the substrate and patch, thickness ratio, and aspect ratio, on interfacial damage in composite materials. The results show a good agreement between the stress distribution solutions predicted by the proposed 2-D model and finite element results. The model provides an effective solution to the 2-D stress problem in rectangular patch-reinforced composites with interface damage.

In contrast to indentation mechanics of homogeneous materials, insight into the deformation behavior of heterogeneous materials, such as those comprising inclusions and second-phase particles, is relatively limited, especially at length scales comparable to the inclusion size and depth, indentation depth, and indenter radius. Therefore, axisymmetric and plane-strain analyses of the effect of an elastic inclusion on the indentation mechanics of elastic-perfectly plastic half-spaces were performed with the finite element method. Numerical results of the mean contact pressure, equivalent plastic strain, and first principal stress obtained for a range of key geometrical parameters, such as indentation depth, indenter radius, inclusion depth, and inclusion diameter, yielded insight into the development of plasticity and tensile stresses that could lead to subsurface cracking and delamination at the inclusion-matrix interface. Simulations revealed the critical ranges of indentation depth, inclusion size, and inclusion depth yielding deformation and stress fields significantly different from those of homogeneous half-spaces. Specifically, the critical mean contact pressure for instigating plasticity below the contact interface, adjacent to the inclusion-matrix interface, and in the proximity of the contact edge in conjunction with the development of plastic zones and tensile stress bands in the subsurface were analyzed for a wide range of inclusion depth and indentation depth. The present analysis provides a computational framework for developing contact mechanics models for particle-reinforced half-space media.

Optimization has been a field of interest in science and engineering and many metaheuristic algorithms have been developed and applied to various problems. These, however, often require parameter adjustments to achieve a suitable performance. This paper proposes a new framework to improve the performance of metaheuristics, termed Multi-Stage Parameter Adjustment (MSPA), which integrates Metaheuristics, an efficient sampling approach, and Machine Learning. The sampling method utilized here known as Extreme Latin Hypercube Sampling (XLHS) is used to divide parameter spaces into equally probable subspaces, ensuring better coverage due to the continuous nature of variables. These parameters are then improved through a primary optimizer for different numbers of variables using a selected benchmark problem. The resultant data are utilized to train an artificial neural network (ANN). The adjusted metaheuristic algorithm is subsequently employed for structural optimization. In this respect, the input data for the ANN comprise the average of the lower and upper bounds of each subspace and the number of variables, while output data are the optimized values obtained using the Primary Optimizer, which does not require extensive parameter adjustments. To evaluate the efficiency of the proposed framework in comparison with the original version and some other algorithms in the literature, the parameters of Particle Swarm Optimization, chosen for its widespread applicability, are adjusted and tested against some mathematical benchmarks, two engineering, and two truss structural optimization problems. Results demonstrate the efficacy of the presented framework in enhancing the performance of metaheuristic algorithms, particularly in the optimal design of truss structures.

This paper examines the problem of a piezomagnetic right-angle plane with irregular boundaries using the boundary element method. It considers SH waves and line source loads as external forces acting on the piezomagnetic right-angle plane. The effectiveness of the boundary element method is demonstrated through two different numerical examples. Firstly, in the absence of line source loads, the paper analyzes the dynamic characteristics in the first example by employing the image method and Graf addition theorem. Then, it introduces Green’s identities and solves the Green’s function in infinite three-dimensional space. In the second example, the paper investigates the dynamic characteristics when irregular boundaries are subjected to line source loads using the boundary element method. The results elucidate the influence on the dynamic stress concentration factor and magnetic field intensity concentration factor under appropriate conditions. Additionally, the analytical solutions are compared with finite element solutions to validate the accuracy of the conclusions presented in this study.

The converse flexoelectric effect can be applied to control thin-shell structures. In this paper, the vibration control of a conical shell with multiple flexoelectric actuators is studied. In order to investigate the actuation performance of the flexoelectric patch, this study analyzes the electric field gradient, modal forces, and displacement of a conical shell driven by the flexoelectric patch and their relationships with the design parameters. In the physical model, the AFM probe is positioned on the upper surface of the flexoelectric patch to create a high-intensity non-uniform electric field within the flexoelectric actuator. In turn, generates internal stress in the flexoelectric actuator patch through the converse flexoelectric effect. The case study shows that the high-intensity non-uniform electric field generated by the AFM probe has nearly zero contribution to the electric field in areas far from the contact point. As a result, the stress generated by the converse flexoelectric effect primarily concentrates near the AFM probe, with the size and shape of the flexoelectric patches having minimal influence on the actuation. Based on the assumption of small deformation and linear displacement, considering the vibration control of multiple flexoelectric actuators on the truncated conical shell, the lateral displacement results controlled by multiple flexoelectric actuators can be calculated by the superposition principle. When multiple flexoelectric actuators work together, the same flexoelectric actuator in different positions may induce opposite lateral displacements at a specific point on the surface of the truncated conical shell. This can result in the cancellation of vibrational displacements produced by the flexoelectric actuators. Approximate optimal distribution positions for the multi-channel flexoelectric actuators were determined through experimental simulations. In this study, the superior vibration suppression capabilities of multi-channel flexoelectric actuators are highlighted through a comparative analysis with single-channel configurations, demonstrating their effectiveness in controlling complex vibration modes in conical shell structures.