Acta Mechanica Solida Sinica最新文献

In this work, a three-dimensional crystal-plasticity-based phase-field model considering three kinds of inelastic deformation mechanisms, i.e., martensitic transformation, dislocation slip in austenite, and dislocation slip in martensite, is established to simulate the stress-assisted two-way shape memory effect (SATWSME) of NiTi single crystals and its cyclic degradation. The simulation results show that the ability of the SATWSME of NiTi single crystal increases as increasing the constant stress in the range discussed in this work (10–100 MPa), which is due to the increase of reoriented martensite formed in the cooling process due to the enhanced variant-selection capability of increased constant stress. The martensitic transformation and its reverse in the cyclic process reflecting the SATWSME show more and more obvious localization characteristics, resulting in the accumulation of significantly heterogeneous plastic deformation (mainly caused by the dislocation slip in austenite), which leads to the cyclic degradation of SATWSME. The simulation results and the conclusions drawn from this work are helpful for further understanding the mechanism of functional cyclic degradation of NiTi alloys.

In micro-electro-mechanical systems, interface expansion issues are commonly encountered, and due to their small size, they often exist at the micro- or nano-scale. The influence of the micro-structural effect on interface mechanics cannot be ignored. This paper focuses on studying the impact of micro-structural effect on interface crack propagation. Modified couple stress theory (MCST) is used to study the buckling delamination of ultra-thin film-substrate systems. The equivalent elastic modulus (EEM) and equivalent flexural rigidity (EFR) are derived based on MCST. Substituting EEM and EFR into the classical Kirchhoff plate theory, the governing equations of ultra-thin film-substrate system with micro-structural effect can be obtained. The finite element method (FEM) was used to calculate the critical strain energy release rate for crack extension. Differences between the three theoretical approaches of MCST, classical theory (CT), and FEM were compared. The effects of stress ratio (frac{sigma }{{sigma_{c} }}), initial crack length, film thickness, and micro-structural effect parameters on crack extension were analyzed. The results show that the FEM calculations coincide with the CT calculations. The stress ratio (frac{sigma }{{sigma_{c} }}), initial crack length, film thickness, and micro-structural effect parameters have significantly influence crack extension.

A model of a sandwich magnetorheological elastomer (MRE) beam with a concentrated mass attached to one end is proposed to analyze the resonance characteristics of the cantilever beam-mass resonator. This model of sandwich MRE resonator consists of two types of components: the beam element with two nodes and four degrees of freedom and the beam element with concentrated mass. The effectiveness of this model is verified by comparing its results with existing results and finite element results. Through integrating the metamaterial beam with MRE resonators, a band-gap-adjustable metamaterial beam is proposed and low-frequency vibration suppression is achieved. The results suggest that the band gap of the structure can be effectively adjusted within a wide range by changing the external magnetic field applied to the presented MRE resonators.

Adiabatic shear band (ASB), a typical failure mechanism in a metal at high strain rates, is hardly controllable or predictable to some extent. The development of the microstructure plays a crucial role in its formation. In this paper, the effect of strain rate on the development of microstructure in ASB of titanium alloy TC4 is investigated using hat-shaped specimens with the split-Hopkinson pressure bar device. The results show that the fracture strength of TC4 is significantly dependent on the shear strain rate. The increase in fracture strength from a strain rate of 11,300 s⁻¹ to 24,930 s⁻¹ is much higher than that from 24,930 s⁻¹ to 35,620 s⁻¹, which can be attributed to the effect of strain rate on dislocation evolution. Microstructures in both as-received and deformed states are investigated using various characterization techniques such as electron backscatter diffraction and X-ray diffraction. The region of ASB clearly shows three different microstructural features: random distribution of coarse grains (as received), distribution of elongated grains (transition zone), and distribution of equiaxed nanocrystals (shear-localized zone). The width of ASB increases with the strain rate. The possible reason for this is that the higher the strain rate, the larger the region where dynamic recrystallization (DRX) occurs due to the accumulation of a large number of dislocations. In the middle of ASB, a significant decrease in low-angle grain boundaries (LAGBs) and a large increase in high-angle grain boundaries are observed. The texture of specimens, especially the {11–20} and {10–10} planes, changes significantly during shear deformation at high strain rates. The mechanism of continuous dynamic recrystallization can well explain the formation and evolution of DRX within the ASB.

In this paper, the degradation of mechanical properties of engineering cementitious composites (ECCs) at elevated temperatures and the failure of fiber are considered. A failure model under coupled thermo-mechanical loads for ECC is developed based on bond-based peridynamics. A semi-discrete model is constructed to describe fiber–matrix interactions and simulate thermal failure in ECC. The peridynamic differential operator (PDDO) is utilized for non-local modeling of thermal fluid flow and heat transfer. A multi-rate explicit time integration method is adopted to address thermo-mechanical coupling over different time scales. Model validation is achieved through simulating transient heat transfer in a homogeneous plate, with results aligning with analytical solutions. The damage behavior of a heated ECC plate in a borehole and under a fire scenario is analyzed, providing insights for enhancing fire resistance and high-temperature performance of ECC materials and structures.

Elastic beams resting on an elastic foundation are frequently encountered in civil, mechanical, aeronautical, and other engineering disciplines, and the analysis of static and dynamic deflections is one of the essential requirements related to various applications. The Galerkin method is a classical mathematical method for solving differential equations without a closed-form solution with a wide range of applications in engineering and scientific fields. In this study, a demonstration is presented to solve the nonlinear differential equation by transforming it into a series of nonlinear algebraic equations with the Galerkin method for asymptotic solutions in series, and the nonlinear deformation of beams resting on the nonlinear foundation is successfully solved as an example. The approximate solutions based on trigonometric functions are utilized, and the nonlinear algebraic equations are solved both numerically and iteratively. Although widely used in linear problems, it is worth reminding that the Galerkin method also provides an effective approach in dealing with increasingly complex nonlinear equations in practical applications with the aid of powerful tools for symbolic manipulation of nonlinear algebraic equations.