Acta Mechanica Solida Sinica最新文献

Since dielectric elastomers (DEs) exhibit obvious nonlinear visco-hyperelasticity, and remarkable temperature dependence, it is difficult to accurately predict the cyclic deformation of DEs at various temperatures. To address this issue, an improved visco-hyperelastic constitutive model is proposed here to reproduce the complex temperature-dependent cyclic deformation of DEs. In the improved model, the Ogden model is chosen to provide the strain energy density representing the hyper-elastic response, a nonlinear viscosity evolution equation is used to depict the strong viscosity of DEs, and specific temperature-dependent parameters are incorporated to describe the cyclic deformation of DEs at various temperatures. Finally, the prediction capability of the proposed visco-hyperelastic model is validated by reproducing the cyclic deformation of VHB 4910 DE observed in experiments at different temperatures. This study provides a theoretical basis for the rational design of DE devices.

In this paper, a multiscale model is developed for the mass functionally graded (FG) beam-fluid system to investigate its static and dynamic responses based on 3D printed porous beam free vibration tests, which are determined by two aspects. At the microstructural level, the gradient variation is realized by arbitrary distribution of matrix pores, and the effective moduli under specific distribution are obtained using the micromechanics homogenization theory. In the meantime, at the structural level, the mechanical responses of FG porous beams subjected to mass loading are considered in a static fluid environment. Then, the explicit expressions of local finite-element (FE) expressions corresponding to the static and dynamic responses are given in the appendices. The present results are validated against numerical and experimental results from the literature and mechanical tests of 3D printed structures, with good agreement generally obtained, giving credence to the present model. On this basis, a comprehensive parametric study is carried out, with a particular focus on the effects of boundary conditions, fluid density, and slenderness ratio on the bending and vibration of FG beams with several different gradations.

In recent years, the issue of aircraft icing has gained widespread recognition. The breaking and detachment of dynamic ice can pose a threat to flight safety. However, the shedding and fracture mechanisms of dynamic ice are unclear and cannot meet the engineering needs of ice-shedding hazard assessment. Therefore, studying the fracture toughness of ice bodies has extremely important practical significance. To address this issue, this article uses a centrally cracked Brazilian disk (CCBD) specimen to measure the pure mode I toughness and pure mode II fracture toughness of freshwater ice at different loading rates. The mixed-mode (I–II) fracture characteristics of ice are discussed, and the experimental results are compared and analyzed with the theoretical values of the generalized maximum tangential stress (GMTS) criterion considering the influence of T-stress. The results indicated that as the loading rate increases, the pure mode I toughness and pure mode II fracture toughness of freshwater ice decrease, and the fracture toughness of freshwater ice is more sensitive to the loading rate. In terms of fracture criteria, the theoretical value of the ratio of pure mode II fracture toughness to pure mode I fracture toughness based on the GMTS criterion is in good agreement with the experimental value, while the theoretical value based on the maximum tangential stress (MTS) criterion deviates significantly from the experimental value, indicating that the GMTS criterion considering the influence of T-stress can better predict the experimental results.

The mismatch in thermal expansion coefficients between the fiber-rich and resin-rich regions of a shape memory polymer composite (SMPC) laminate, along with the residual strain during SMPC fabrication, results in buckling deformation of the inhomogeneous laminate. This paper presents a macroscopic model for buckling of an inhomogeneous SMPC laminate under initial biaxial prestrains. Both linear and nonlinear buckling analyses are carried out using the energy method. The influences of prestrain biaxiality, temperature, and ply angle on the buckling wavelength, critical buckling prestrain, and buckling amplitude are calculated. The results demonstrate that the critical buckling wavelength of the SMPC laminate is independent of the prestrain, while the amplitude is almost independent of temperature. In addition, the optimal fiber stacking configuration with the maximum critical buckling prestrains of inhomogeneous SMPC laminates is determined by a genetic algorithm.

In this paper, we investigate the existence of strange nonchaotic attractors (SNAs) in a slender rigid rocking block under quasi-periodic forcing with two frequencies. We find that an SNA can exist between a quasi-periodic attractor and a chaotic attractor, or between two chaotic attractors. In particular, we demonstrate that a torus doubling bifurcation of a quasi-periodic attractor can result in SNAs via the fractal route before transforming into chaotic attractors. This phenomenon is rarely reported in quasiperiodically forced discontinuous differential equations and vibro-impact systems. The properties of SNAs are verified by the Lyapunov exponent, rational approximation, phase sensitivity, power spectrum, and separation of nearby trajectories.

Piezoelectric semiconductors (PSCs) find extensive applications in modern smart electronic devices because of their dual properties of being piezoelectric and semiconductive. With the increasing demand for miniaturization of these devices, the performance of their components needs to be carefully designed and optimized, especially when reduced to nanosize. It has been shown that surface elastic properties play a substantial role in the mechanical performance of nanoscale materials and structures. Building on this understanding, the surface elastic effects, encompassing surface residual stress, surface membrane stiffness, and surface bending stiffness, are comprehensively taken into account to explore the electromechanical responses of a PSC nanobeam. Additionally, the flexoelectric effect on their responses is also systematically studied. The results of this work reveal that surface elastic properties predominantly influence mechanical performance, while the flexoelectric effect plays a more dominant role in electric-related quantities at the nanoscale. Notably, the significance of surface bending rigidity, which was often underestimated in the earlier literature, is demonstrated. Furthermore, owing to the flexoelectric effect, the linear distribution of electric potential and charge carriers along the length transforms into a nonlinear pattern. The distributions of electric potential and charge carriers across the cross section are also evidently impacted. Moreover, the size-dependent responses are evaluated. Our findings may provide valuable insights for optimizing electronic devices based on nanoscale PSCs.

With the increasingly widespread application of rubber in many fields, there is a growing demand for quantitative characterization of temperature-dependent mechanical properties in high-temperature service environments. The critical tearing energy is an important criterion for determining whether rubber materials will experience tearing instability, while tear strength is a key parameter for rubber materials to resist tearing. It is necessary to quantitatively characterize their evolution with temperature. Current theoretical research mainly relies on fitting a large amount of experimental data, which is not convenient for engineering applications. Therefore, in this work, a temperature-dependent critical tearing energy model is firstly developed based on the force-heat equivalence energy density principle. This model considers the equivalent relationship between the critical tearing energy required for crack instability propagation and the thermal energy stored in the rubber material. It is demonstrated that our model has higher prediction accuracy when compared to other models. Furthermore, combining with the Griffith fracture theory, temperature-dependent tear strength models applicable to three different crack modes are separately established. These models are validated using experimental data for Mode I opening cracks and Mode III tearing cracks, and good consistency is achieved. Additionally, a quantitative analysis of the influence of elastic modulus on tear strength at different temperatures is conducted. This work provides a reliable way for predicting temperature-dependent tearing instability behavior and offers beneficial suggestions for improving the tear strength of rubber materials at different temperatures.

The elastic adhesive contact of self-affine fractal rough surfaces against a rigid flat is simulated using the finite element method. An array of nonlinear springs, of which the force-separation law obeys the Lennard–Jones potential, is introduced to account for the interfacial adhesion. For fractal rough surfaces, the interfacial interaction is generally attractive for large mean gaps, but turns repulsive as the gap continuously shrinks. The interfacial interactions at the turning point corresponding to the spontaneous contact are shown for various surfaces. For relatively smooth surfaces, the probability density distributions of repulsion and attraction are nearly symmetric. However, for rougher surfaces, the simulation results suggest a uniform distribution for attraction but a monotonously decreasing distribution with a long tail for repulsion. The pull-off force rises with increasing ratio of the work of adhesion to the equilibrium distance, whereas decreases for solids with a higher elastic modulus and a larger surface roughness. The current study will be helpful for understanding the adhesion of various types of rough solids.

Simulations of contact problems involving at least one plastic solid may be costly due to their strong nonlinearity and requirements of stability. In this work, we develop an explicit asynchronous variational integrator (AVI) for inelastic non-frictional contact problems involving a plastic solid. The AVI assigns each element in the mesh an independent time step and updates the solution at the elements and nodes asynchronously. This asynchrony makes the AVI highly efficient in solving such bi-material problems. Taking advantage of the AVI, the constitutive update is locally performed in one element at a time, and contact constraints are also enforced on only one element. The time step of the contact element is subdivided into multiple segments, and the fields are updated accordingly. During a contact event, only one element involving a few degrees of freedom is considered, leading to high efficiency. The proposed formulation is first verified with a pure elastodynamics benchmark and further applied to a contact problem involving an elastoplastic solid with non-associative volumetric hardening. The numerical results indicate that the AVI exhibits excellent energy behaviors and has high computational efficiency.

The electric fatigue load has a significant effect on the crack propagation behavior and failure life of piezoelectric materials and devices. In this paper, an electrical mixed-mode fatigue crack propagation model for piezoelectric materials is proposed based on the piezoelectric J_k-integral theory. The crack initiation, propagation, and life prediction criteria of piezoelectric materials under electric fatigue loading are given by this model, and the finite element simulation model is established to study the electrical mixed-mode crack propagation behavior of piezoelectric structures. Meanwhile, the electrical mixed-mode fatigue crack propagation model is applied to the fatigue crack propagation behavior of a piezoelectric typical defective structure, the crack–hole interference model. The mixed-mode crack propagation, fatigue life, and the interference behavior between the crack and hole at various hole locations of the crack–hole interference model are well recognized by this model. The crack propagation behavior under different electrical load intensities is also considered. The results show that the hole in front of the crack tip inhibits crack propagation to a certain extent, and the strength of electrical load affects the fatigue life of piezoelectric materials and structures. Therefore, the proposed electrical mixed-mode fatigue crack propagation model provides a reference for predicting the mixed-mode fatigue crack propagation behavior and fatigue life of piezoelectric structures under electric fatigue loading.