European Journal of Mechanics A-Solids最新文献

In this study, the free vibration analysis and multi-objective robust optimization of three-dimensional pyramidal truss core sandwich plates with interval uncertain parameters are fulfilled. The numerical model for free vibration of the plate is derived by combining the three-dimensional elasticity theory and Rayleigh-Ritz method, and the validity of the model is illustrated by numerical results. On this basis, considering various uncertainties within the plate, a new uncertainty-propagation analysis method is constructed by integrating the numerical model, interval-analysis model, kriging model and optimization. The one-dimensional and multi-source uncertainty-propagation analysis of the fundamental frequency is finished using this method, and the accuracy is proved by comparing with Monte Carlo simulation results. Meanwhile, to minimize the effects of uncertainties on the performance of plates at the design stage, an objective multi-objective robust optimization model with the objectives of maximizing the fundamental frequency and minimizing the robustness factor is established. Finally, an improved pelican optimization algorithm is proposed by introducing the improved opposition-based learning strategy, tracking strategy with step control and convergence strategy. And the Pareto front and corresponding design schemes applicable to different working environments are obtained without repeating the optimization.

The connection between macroscopic deformation and microscopic chain stretch is a key element in constitutive models for rubber-like materials that are based on the statistical mechanics of polymer chains. A new micro-macro chain stretch relation is proposed, using the Irving–Kirkwood–Noll procedure to construct a Cauchy stress tensor from forces along polymer chains. This construction assumes that the deformed polymer network remains approximately isotropic for low to moderate macroscopic stretches, a starting point recently adopted in the literature to propose a non-affine micro-macro chain stretch relation (Amores et al., 2021). Requiring the constructed Cauchy stress to be consistent with the stress tensor derived from the strain energy density results in a new chain stretch relation involving the exponential function. A hybrid chain stretch relation combining the new chain stretch with the well-known affine relation is then proposed to account for the whole range of stretches in experimental datasets. Comparison of the model predictions to experimental data in the literature shows that the two new micro-macro chain stretch relations in this work result in two-parameter constitutive models that outperform those based on existing chain stretches with no increase in the number of fitting parameters used.

Contact modeling is considered a critical step in analyzing the impact resistance of a structure. The classic Hertzian model has been widely used for semi-infinite plane contacts. However, for cases where local indentation and structure deformation are of the same magnitude, the global deformation of the structure cannot often be ignored. In addition, the impact body not only causes the overall bending deformation of the structure but also triggers the propagation of bending waves. This is not considered by the previously published classic contact models. This work proposes an impact contact model for laminated structures, taking a laminated plate as an illustrative example. The coupling effects of local indentation, bending wave propagation, and overall deformation of the component are taken into account. The relation between the contact force and indentation is derived in explicit form by using Laplace transform approach. The contact force and indentation time history curves are given to discuss the influence of bending wave propagation on the impact response of the members. The results show that dissipation significantly affects the impact response of the laminates. It may overestimate the impact resistance of structures due to ignoring this effect. The instantaneous velocity and deformation of the plate at the time of detachment of the impactor have a significant effect on the post-impact vibration.

When the projectile penetrates a hard target at a high speed, the fuze system inside the projectile will inevitably withstand high impact load, and thus encapsulating protection is necessary to prevent the internal electronic components to fail. However, currently encapsulating materials are usually homogeneous and lack sufficient flexibility to resist complex impact loads. Carbon nanotubes (CNTs) reinforced gradient materials exhibit excellent toughness and buffer effect while it has not been applied in encapsulating protection of fuze system. Therefore, this article establishes a simplified projectile body system with different CNT gradient types in the fuze encapsulation and investigates the protective performance of the gradient encapsulating materials for printed circuit boards (PCBs) in fuze system during impact process. Firstly, homogeneous CNT reinforced epoxy matrix composite materials with different concentrations are prepared and 0.7 wt% CNT content is found to have highest quasi-static strength and dynamic strength. Next, a finite element model for a gradient encapsulating composite plate with a PCB is established, and its material model and relevant settings are verified by drop-weight impact experiments. Finally, a simplified projectile model with gradient encapsulated fuze system impacting concrete panel is established and the protective effects of different axial and radial gradient types on the internal circuit system of the fuze are studied. The research results show that the protective performance of gradient materials is superior to that of homogeneous materials. Specifically, the failure speed and overload acceleration of the PCB in axial gradient material “V-L" (the CNT content gradually decreases from the head to the tail of the projectile) have increased from 400 m/s to 500 m/s and 42500 g–65000 g compared to homogeneous materials, respectively. The failure speed and overload acceleration of the PCB in radial gradient material “O–R" (the CNT content gradually increases from the exterior to the interior of the projectile) have increased from 400 m/s to 460 m/s and 42500 g–50000 g compared to homogeneous materials, respectively. This gradient encapsulating structure proposed in this article serves for the design of encapsulating protection of fuze systems.

This study addresses the complexity of buckling behavior in cylindrical shells subjected to non-uniform wind loading, emphasizing the significant impact of geometric parameters on buckling patterns. Cylinders with varying aspect ratios exhibit distinct linear and nonlinear buckling behaviors, complicating the determination of the most detrimental structural imperfections across different geometries. Notably, imperfections affecting stocky cylinders may be less impactful for slender ones. This paper introduced equations for calculating linear critical pressures under wind loading, followed by an extensive numerical analysis assessing the imperfection sensitivity in anchored cylindrical shells of uniform thickness with diverse aspect ratios. Two types of geometric imperfections were employed to assess their influence on the nonlinear buckling strength of cylinders with varying geometries. Results demonstrate that eigenmode imperfections predominantly compromise the buckling strength of stocky cylinders, whereas nonlinear incremental mode imperfections significantly influence the nonlinear critical pressures of intermediate-length and slender cylinders. Consequently, empirical expressions have been formulated to calculate the imperfection reduction factor, offering a precise evaluation of nonlinear buckling pressures in imperfect cylinders under wind loading.

The lotus petiole in nature is characterized by its porous structure and high bending resistance. Inspired by this, in this paper, random sampling of lotus petiole was carried out to clarify the porous distribution pattern of lotus petiole in cross section. On this basis, the original structures with 12 and 13 wells (Os-12w, Os-13w) were constructed, and equal mass hollow circular tube (Emhct) was also designed for comparison. Based on the experimentally verified finite element models, Os-12w, Os-13w and Emhct were comparatively analyzed. In addition, comparisons were made with five other bionic circular structures Compared to the rest of the structures, Os-13w performs better in all comprehensive properties. The bending and traction in the core region of the bionic structure caused the surrounding structures to join in the buckling earlier, creating a global crushing trend. More interestingly, further bending and traction in the core region creates a negative Poisson's ratio phenomenon. In addition, the results of the parametric study show that the optimum loading angle of Os-12w is between 60° and 90°, and the proper adjustment of its core cross-section characteristics can improve the mechanical properties of the structure. This study provides some reference for the development of thin-walled porous structures under radial loading conditions.

Piezoelectric materials are widely used in surface acoustic wave devices. Many piezoelectric materials themselves have viscoelastic properties, and their surface wave characteristics, especially the attenuation characteristics still needs to be explored. This article proposes a Legendre-Laguerre orthogonal polynomial method to solve the Rayleigh wave problems in a viscoelastic piezoelectric half space with a covering layer. The proposed method compensates for the inherent shortcomings of traditional Laguerre polynomials in solving layered half spaces: the normal stress and electric displacement are discontinuous. The correctness of the method was verified through literature comparison and finite element simulation. At the same time, by utilizing the orthogonality of the Legendre-Laguerre polynomial, the integral analytical formula encountered in the solution process is derived, which improves the computational efficiency by more than ten times. Through the analysis and discussion of the dispersion and attenuation curves, it is found that the piezoelectric effect can suppress the attenuation of Rayleigh waves; the piezoelectric and viscous properties of the covering layer mainly affect attenuation at high frequencies, while those of the half space layer mainly affect attenuation at low frequencies of high-order modes.

A thermo-chemo-mechanically coupled theoretical framework is proposed to describe the calcium-magnesium-alumina-silicate (CMAS) corrosion process during the cooling process. A phase-field fracture model is developed to investigate the effect of cooling temperature and CMAS concentration on the degree of corrosion reaction, the stress evolution and the crack initiation and propagation. σ₁₁ concentrates in the region beneath the overlay of CMAS and σ₂₂ appears at the interface between top ceramic coating (TC) and bond coating (BC). The higher stress concentration of σ₁₁ and σ₂₂ contribute to the formation of both vertical and transverse cracks. Transverse cracks first emerge at the interface between TC and BC in the edge region, followed by the formation of vertical cracks in the CMAS-coated region. Vertical cracks propagate to the interface and deflect into transverse cracks. The transverse cracks at the interface further propagate and merge, ultimately leading to the coating delamination. The higher initial cooling temperature and CMAS concentration contribute to the accelerated development of vertical cracking and the increase of the quantity and length of transverse and vertical cracks. The model provides a significant advantage in predicting the failure of TBCs during the cooling stage of CMAS corrosion.

Tensile properties and low cycle fatigue behavior of 316LN austenitic stainless steel were investigated after varied thermal aging durations at 773 K up to 30000 h. After thermal aging for 30000 h, the material exhibits remarkable degradations in both the yield stress and ultimate tensile strength at room temperature and 623 K, and there is a significant decrease in cyclic hardening level at 623 K. These facts indicate that the long-term thermal aging treatment induces softening of this material, which results in the decrease of plastic strain energy density under low cycle fatigue test and the prolongation of fatigue life. From the observation of microstructures, it is found that in the aged material, there existed differences in dislocation structure, the increase of grain size, the transformation of second phase distribution, and the decrease of grain boundaries, which are the significant reasons for the decreasing of cyclic hardening. By introducing the evolution of grain size and thermal aging effect, a modified visco-plasticity constitutive model based on the Ohno-Wang Ⅱ kinematic hardening rule is proposed and successfully used to predict the cyclic behavior of virgin and thermal aged material at both room and elevated temperatures.