计及相变微结构演化的形状记忆合金本构描述

基于对NiTi形状记忆合金的实验观察及有限元分析,考虑两相间的应变不协调关系,采用应变修正法建立了计及片层状微结构的本构模型,本模型考虑了两相间的相互约束,及其约束随微结构演化的变化规律.研究了NiTi形状记忆合金微圆管在拉伸和扭转下的响应特性.计算结果与实验结果的对比表明所建本构模型较好地描述了伪弹性响应尤其是较好地描述了拉伸实验过程中的应力跌落现象.     

Atomic-scale simulations for lithium dendrite growth driven by strain gradient

Dendrite formation is a major obstacle, e.g., capacity loss and short circuit, to the next-generation high-energy-density lithium (Li)-metal batteries. The development of successful Li dendrite mitigation strategies is impeded by an insufficient understanding in Li dendrite growth mechanisms. The Li-plating-induced internal stress in Li-metal and its effects on dendrite growth have been widely studied, but the underlying microcosmic mechanism is elusive. In the present study, the role of the plating-induced stress in dendrite formation is analyzed through first-principles calculations and ab initio molecular dynamic (AIMD) simulations. It is shown that the deposited Li forms a stable atomic nanofilm structure on the copper (Cu) substrate, and the adsorption energy of Li atoms increases from the Li-Cu interface to the deposited Li surface, leading to more aggregated Li atoms at the interface. Compared with the pristine Li-metal, the deposited Li in the early stage becomes compacted and suffers the in-plane compressive stress. Interestingly, there is a giant strain gradient distribution from the Li-Cu interface to the deposited Li surface, making the deposited atoms adjacent to the Cu surface tend to press upwards with perturbation and causing the dendrite growth. This provides an insight into the atomicscale origin of Li dendrite growth, and may be useful for suppressing the Li dendrite in Li-metal-based rechargeable batteries.     

功能铁磁材料的变形与断裂的研究进展

综述了近几十年, 特别是近十几年来铁磁材料的力磁耦合变形与断裂行为的研究概况. 传统铁磁弹性问题的研究已经有较长时间的积累, 文献中已有大量的研究结果发表. 近些年 来, 随着智能材料及结构应用与研究的兴起, 功能铁磁材料如稀土超磁致伸缩材料、铁磁相 变材料以及铁磁复合材料等的力学行为越来越受到重视, 人们在功能铁磁材料的变形与断裂 以及铁磁复合材料的有效性质等方面开展了大量的研究工作. 本文在简单介绍了经典铁磁弹 性和传统铁磁结构的力磁性能的研究背景基础上, 结合作者近年来在铁磁材料变形与断裂方 面所开展的工作, 着重评述了功能软铁磁材料在变形与断裂的实验研究,如实验设备和技术, 以及铁磁复合材料细观力学、软铁磁材料、铁磁功能材料的变形与断裂理论等方面的研究进 展, 并指出了需要进一步研究的方向.     

Experimental and theoretical study of the nonlinear response of agiant magnetostrictive rod

In this paper, a magnetomechanical coupling constitutive relation of the giant magnetostrictive material was investigated experimentally and theoretically. A grain-oriented magnetostrictive rod of iron and rare earth was tested under a combined magnetomechanical loading. Two types of experimental curves were obtained, i.e., the magnetostrictive curve of the extensional strain vs the magnetic field, and the curve of the magnetic polarization intensity vs the pre-stress. A new theoretical constitutive model, based on the density of domain switching, is developed. Comparison of the theoretical predictions with the experimental results indicates that this model can capture the main characteristics of the magnetoelastic coupling deformation of a giant magnetostrictive rod. The project supported by the National Natural Science Foundation of China (10025209, 10132010, 10102007)     

The continuation and stability analysis methods for quasi-periodic solutions of nonlinear systems

Nonlinear Dynamics - The continuation and stability analysis methods for quasi-periodic solutions of nonlinear systems are proposed. The proposed continuation method advances the...     

Giant forced volume magnetostriction in polycrystalline Tb0.3Dy0.7Fe1.95 alloys under magnetomechanical loading

The axial and transversal linear magnetostrictions (λ_∥ and λ_⊥) in [1 1 0] oriented polycrystalline Tb_0.3Dy_0.7Fe_1.95 alloys were measured simultaneously under uniaxial magnetomechanical loading to get the forced volume magnetostriction (ω=λ_∥+2λ_⊥). Despite the almost zero ω observed in Terfenol-D single crystals, it reaches up to 1000×10⁻⁶ in polycrystalline Tb_0.3Dy_0.7Fe_1.95 alloys near the saturation magnetic field under a stress above 50 MPa.     

A lattice deformation based model of metallic lattice sandwich plates subjected to impulsive loading

A lattice structure deformation mechanism based theoretical model is developed to predict the dynamic response of square lattice sandwich plates under impulsive loading. The analytical model is established on the basis of the three-stage framework proposed by Fleck and Deshpande (2004). In the first stage, the impulse transmitted from air shock loading to the sandwich plates by fluid-structure interaction is analytically calculated. The lattice core suffers non-uniform compression in the second stage due to the clamped boundary conditions. The structure deformation mechanism is introduced in the lattice core compression and the analytical nominal stress–strain curve of core compression accords well with previous experimental results. In the final stage, the sandwich plate is analyzed as a continuum plate with non-uniform thickness deduced by inconsistent deformation of the front and back sheets.The experiment results of square metallic sandwich plates with tetrahedral lattice core are presented and compared with analytical prediction to validate the theoretical model. Good agreements are found between the predicted and testing results for both the impulse transmitted to the sandwich plates and the maximum deflection of the back face sheet.     

A phase-field study on the oxidation behavior of Ni considering heat conduction

Phase-field modeling approach has been used to study the oxidation behavior of pure Ni when considering heat conduction. In this calculation, the dependence of the coefficient of the Cahn–Hilliard equation Lc on the temperature T was considered. To this end, high-temperature oxidation experiments and phase-field modeling for pure Ni were performed in air under atmospheric pressure at 600,700, and 800?C. The oxidation rate was measured by thermogravimetry and Lc at these temperatures was determined via interactive algorithm. With the Lc-T relationship constructed, oxidation behavior of Ni when considering heat conduction was investigated. The influence of temperature boundaries on the oxidation degree, oxide film thickness, and specific weight gain were discussed. The phase-field modeling approach proposed in this study will give some highlights of the oxidation resistance analysis and cooling measures design of thermal protection materials.     

Effects of high order deformations on the strength of planar lattice materials

Lattice materials have been attractive over the last decade for use as load-carrying structures, energy absorbing elements and heat exchanging structures because of their excellent mechanical properties and multifunctional characters. However, the quantitative analysis accounting for high order deformations upon the collapse of lattice materials, which is important for their applications, has not been reported. An analytical investigation of yield surfaces with respect to the high order deformations was carried out for two typical planar lattice materials： triangular and Kagome lattices separately. The analytical results were validated by the finite element method （FEM） simulations. It was found that the effect of high order deformation on the yield strength increases with the relative density. The bending effect of the Kagome lattice is more obvious than that of the triangular one with the same relative density and stress state. The yield strength of the Kagome lattice calculated by neglecting the bending effect overestimates the result by more than 10% when the relative density is higher than about 11.1%, which may not be ignored in engineering applications. The yielding surfaces of the two lattice materials demonstrated in the paper also confirm the analytical results.