Compression-after-Impact Strength of Sandwich Panels with Core Crushing Damage

Compression-after-impact (CAI) strength of foam-cored sandwich panels with composite face sheets is investigated experimentally. The low-velocity impact by a semi-spherical (blunt) projectile is considered, producing a damage mainly in a form of core crushing accompanied by a permanent indentation (residual dent) in the face sheet. Instrumentation of the panels by strain gauges and digital speckle photography analysis are used to study the effect of damage on failure mechanisms in the panel. Residual dent growth inwards toward the mid-plane of a sandwich panel followed by a complete separation of the face sheet is identified as the failure mode. CAI strength of sandwich panels is shown to decrease with increasing impact damage size. Destructive sectioning of sandwich panels is used to characterise damage parameters and morphology for implementation in a finite element model. The finite element model that accounts for relevant details of impact damage morphology is developed and proposed for failure analysis and CAI strength predictions of damaged panels demonstrating a good correlation with experimental results.     

Fatigue damage accumulation of cold expanded hole in aluminum alloys subjected to block loading

Fatigue damage accumulation of cold expanded hole in aluminum alloys used in land transportation components was investigated. Tests were carried out using pre-cracked SENT specimens and inserting an expanded hole at the crack tip. The degree of the cold expansion was chosen equal to 4.3%. Tests were performed in two and four block loading under constant amplitude. Two sequences were compared.The increasing and the decreasing magnitude were compared. The experimental results were compared to the damage calculated by the Miner's rule and a new simple fatigue damage indicator. This comparison shows that the ‘model of the damage stress’, which take into account of the loading history, yields a good estimation of the experimental results. Moreover, the error is minimized in comparison to the Miner's model.     

A rate-dependent cohesive model for simulating dynamic crack propagation in brittle materials

Numerical investigations are conducted to simulate high-speed crack propagation in pre-strained PMMA plates. In the simulations, the dynamic material separation is explicitly modeled by cohesive elements incorporating an initially rigid, linear-decaying cohesive law. Initial attempts using a rate-independent cohesive law failed to reproduce available experimental results as numerical crack velocities consistently overestimate experimental observations. As proof of concept, a phenomenological rate-dependent cohesive law, which bases itself on the physics of microcracking, is introduced to modulate the cohesive law with the macroscopic crack velocity. We then generalize this phenomenological approach by establishing a rate-dependent cohesive law, which relates the traction to the effective displacement and rate of change of effective displacement. It is shown that this new model produces numerical results in good agreement with experimental data. The analysis demonstrates that the simulation of high-speed crack propagation in brittle structures necessitates the use of rate-dependent cohesive models, which account for the complicated rate-process of dynamic fracture at the propagating crack tip.     

An elliptical disc anchor in a damage‐susceptible poroelastic medium

A flat rigid elliptical anchorage located in a damage‐susceptible fluid‐saturated poroelastic medium is subjected to an in‐plane load, which induces a pure translation in the plane of the anchor. This paper develops computational estimates for the time‐dependent displacement of the disc anchor for the classical problem that involves Biot consolidation and compares the results with situations where the porous skeleton can experience micro‐mechanical damage that leads to an alteration in both its elasticity and fluid transport characteristics. Copyright © 2005 John Wiley & Sons, Ltd.     

二维无规行走链和自回避行走链的计算机模拟

编写了四位置模型的键长涨落算法 ,表征了二维无规行走模型链 (RW链 )和自回避行走模型链 (SAW链 )的均方末端距和均方半径与聚合度之间的标度关系 ,计算结果与deGennes对此所做的标度分析基本相符。     

我国法律体系建构之思考

建构一个完善的法律体系不仅有利于限制国家公权力对公民私权利的侵蚀,保护公民的权利和自由,也有利于立法的规划和协调,促进法律的实现。要实现建构法律体系的价值,必须从现实主义角度出发,结合公法和私法的划分以及部门法划分来建构法律体系,即先将法律规范分为公法和私法,然后在公法和私法的框架内划分为不同的部门法,而划分部门法的标准就是法律的调整对象——行为关系。     

论当代中国宪政道路上的三次理性选择

随着中国的市场经济日益向纵深发展，建设民主和法治的宪政道路的要求越来越高，依法治国、依法执政、依法行政应运而生，这三个概念有着自己的深刻内涵。他们是当代中国宪政道路上的三次理性选择。     

恒温恒液位系统的动态机理建模与仿真

对恒温恒液位系统进行深入机理分析，根据系统规律建立其动态机理模型。为了使所建模型具有实用性，对模型进行降阶、线性化、增量化及离散化处理，然后进行仿真研究。仿真结果与实际情况的相吻合说明所建模型是有效的，并且该动态机理建模方法是工业系统模型建立时一种易学、有效的方法，具有很好的应用价值。     

钢纤维砼的动态本构关系

在对钢纤维砼冲击动态力学实验研究的基础上,分析了砼材料动态力学行为的应变率敏感的非线性粘弹性和计及损伤的动态本构关系的力学模型和本构特性,从而给出了钢纤维砼的计及损伤演化的率型本构方程,理论预示与实验结果吻合良好。     

高耸塔架结构节点损伤的指标分析与反分析两步诊断法

针对高耸钢塔架结构的损伤特点，建立了具有节点损伤的有限元模型，提出了一种指标分析与反分析两步诊断法：第一步，通过对节点残余力向量指标进行分析来确定结构可能损伤杆件的位置；第二步，把可能损伤的杆件的损伤因子作为设计变量，以损伤前后的杆端应变模态差向量的2范数作为目标函数，应用改进的混合遗传算法进行反分析运算，最终得到具体的损伤节点位置处的损伤程度．通过对一平面塔架结构的数值仿真分析表明，在理论上该方法是可行的．