Meshless simulation of crack propagation in multiphase materials

The material body considered in this work consists of multiphases. Digital imaging data are taken as the input to specify the configuration and composition of the specimen. Meshless method is demonstrated as a superior numerical tool to analyze crack initiation and propagation in multiphase material. A fracture criterion, based on the ratio of the opening stress over the material toughness distributed in front of the crack tip, is proposed to determine the direction of crack propagation of mixed mode fracture problem in multiphase material. Numerical results are presented and discussed.     

流体界面稳定性的线化分析及其对界面实际稳定性的预报

本文用边界积分方法导出了多孔介质中流体界面的发展方程,用线化方法导出了界面的稳定性准则,并通过数值实验研究了线化结果对界面实际稳定性的可预报性。     

圆板中摩尔—库仑准则的弯矩表达

在结构塑性极限分析中常使用以内力表示的塑性条件。针对圆板，本文给出了在考虑应变软化时以弯矩表示的摩尔－库仓准则。该准则可应用于岩石，混凝土等材料构成的圆板的极限承载能力分析。     

纤维束增强复合材料细观统计破坏理论

本文分别用剪滞模型和载荷几何局部分配法则分析了纤维束和束中纤维的载荷集中。在此基础上,利用裂纹临界核模型的统计方法,建立了小纤维束(须考虑纤维束的边界影响)和大纤维束增强复合材料的细观统计破坏准则,并用这两个准则研究了纤维束增强复合材料的断裂强度问题,所算得的强度和裂纹临界长度的合理性表明了这两个准则的正确性。     

对智能复合材料单向疲劳失效的研究

对智能复合材料在经受单向拉—拉试验产生的光纤疲劳失效性能进行了研究，对智能复合材料内的光纤方位角分别为０°、４５°、９０°进行了应力—寿命试验．在输入应变能量的基础上提出了疲劳失效准则，这一准则可用于光纤方位角的调整和应力比的分析．     

复杂应力条件下脆性材料的受拉破坏准则

根据脆性材料微粒对之间距离超过特定距离而破坏的微观机理,结合宏细观试验结果指出的绝大多数的破坏颗粒对的方向与σ1的方向之间的夹角都大于0°这一事实,导出了新的脆性材料张破坏准则: σ1 ασ2 βσ3≤[σ],式中系数β与材料的优势角θ(破坏颗粒对的方向与σ1的方向之间的夹角的某种平均) 和泊松比μ有关．同时还指出了经典强度理论由于没有考虑优势角从而导致了它们与宏观实验结果不符．实验结果表明,在张破坏条件下此准则比经典的准则有更高的精度．     

Study of Pressure Sensitive Plastic Flow Behaviour of Gasket Materials

The mechanical behaviour of the materials used as compressible gasket in the ultra high pressure apparatus is investigated. Materials such as pyrophyllite and talc, showing a pressure sensitive plastic flow behaviour were considered and a testing configuration was set up for studying the dependence of their plastic response on the hydrostatic component of the stress tensor, according to the Drucker-Prager criterion. A Finite Element modelling of the test was performed to evaluate the specimen response and the local stress condition, during loading. The Finite Element results were validated by comparison with those of a specific experimental characterisation. A parametric analysis was then carried out, by varying the materials constitutive behaviour, in order to build up a data base of representative curves. In this way an algorithm was developed, with the aim of determining the material constitutive behaviours by the analysis of the experimental data. The proposed procedure was then used to study the mechanical response of different gasket materials.     

工程活动断裂鉴定的时限标准讨论

鉴定工程活动断裂时限标准的制订需考虑科学性与工程安全性原则。活动断裂时限的确定依赖于对构造活动阶段性与重复性的认识 ,通过对中国大陆晚第四纪以来构造变形与断裂活动性特点的综合分析研究 ,得出了晚更新世晚期 (约距今 3万年 ) ,中国大陆发生了一次广泛的构造变动 ,经历这次构造变动后 ,各地的构造变形特征进入了一个新的阶段 ,其总体活动性质与活动强度没有大的改变 ,这一结果是确定工程活动断裂时限的科学基础。从工程安全性考虑 ,在中国大陆将活动断裂的时限定为晚更新世以来活动过的断裂偏于保守 ;定义为全新世以来活动过的断裂又存在较大的风险。而将晚更新世晚期 (约距今 3万年 )作为鉴定活动断裂的时限从科学意义上有其合理性 ,并符合工程安全性需要。但对一些安全性要求极高的重大工程 ,相关活动断裂的鉴定时限以晚更新世 (约距今 12万年 )为宜     

Surface waves in a deformed isotropic hyperelastic material subject to an isotropic internal constraint

An isotropic elastic half-space is prestrained so that two of the principal axes of strain lie in the bounding plane, which itself remains free of traction. The material is subject to an isotropic constraint of arbitrary nature. A surface wave is propagated sinusoidally along the bounding surface in the direction of a principal axis of strain and decays away from the surface. The exact secular equation is derived by a direct method for such a principal surface wave; it is cubic in a quantity whose square is linearly related to the squared wave speed. For the prestrained material, replacing the squared wave speed by zero gives an explicit bifurcation, or stability, criterion. Conditions on the existence and uniqueness of surface waves are given. The bifurcation criterion is derived for specific strain energies in the case of four isotropic constraints: those of incompressibility, Bell, constant area, and Ericksen. In each case investigated, the bifurcation criterion is found to be of a universal nature in that it depends only on the principal stretches, not on the material constants. Some results related to the surface stability of arterial wall mechanics are also presented.     

用三线摆测定物体对非质心轴的转动惯量

对三线摆的线性近似模型和转动惯量计算公式的由来作了简要说明. 分析了三线摆扭振系统 质心偏移对转动惯量测试的影响，给出了扭振系统质心与三线摆中心轴对齐的判别准则和用 三线摆测定物体对非质心轴转动惯量的工程实用方法. 通过工程实例说明了该方法的有效性 与可靠性. 最后讨论了提高转动惯量实测精度的几项具体措施.