On integral equation approaches to the mechanics of fibre-crack interaction

The paper examines the problem of a penny-shaped crack which is formed by the development of a crack in both the fibre and the matrix of a composite consisting of an isolated elastic fibre located in an elastic matrix of infinite extent. The composite region is subjected to a uniform strain field in the direction of the fibre. The paper presents two integral-equation based approaches for the analysis of the problem. The first approach considers the formulation of the complete integral equations governing the associated elasticity problem for a two material region. The second approach considers the boundary integral equation formulation of the problem. Both methods entail the numerical solution of the governing integral equations. The solutions to these integral equations are used to evaluate the stress intensity factor at the boundary of the penny-shaped crack.     

SiCp/2024复合材料的氢脆敏感性研究

在浸泡、阴极极化、阴极极化同时迭加拉伸变形、添加As₂O₃毒化剂等常见致氢条件下,通过慢应变速率拉伸试验研究了SiC_p/2024复合材料的力学性能,考察了断口形貌.测定了该材料在按几种常用充氢条件充氢后的氢含量.发现虽然强烈阴极极化使材料力学性能下降,但其原因在于阴极极化引起的碱性腐蚀,与氢脆无关.获得了不同于前人研究的新结论:在本文试验条件下SiC_p/2024材料不发生氢脆,也不发生不可逆氢损伤,其原因与该材料难以充入氢有关.     

Thermomechanical stress fields in high-temperature fibrous composites. I: Unidirectional laminates

This two-part paper presents a closed-form procedure for evaluation of estimates of local thermomechanical stress fields in two-phase fibrous composites and laminates. The first part is concerned with a unidirectional elastic laminate subjected to uniform mechanical loads and to uniform changes in temperature. Both phases are assumed to be elastic, with temperature-dependent moduli and expansion coefficients; the solution reflects the influence of thermomechanical interactions. Exact solutions are not possible for any real system, because the local geometry is not known in detail. Instead, estimates of the fields are found from a modified Mori-Tanaka approximation. Examples are presented for two SiC/Ti---Al---Nb composites. Local stresses of interest are found after cooling from fabrication to room temperature. The presence of local yielding, and the influence of coupling terms on the local stress magnitudes are examined. Extension of the results to laminated plates is presented in Part II (Dvorak, G.J., Chen, T. & Teply, J., Composites Science and Technology, 43 (1992) 359–368, this issue).     

金属－橡胶硫化粘接过程中分子取向行为的间接证据

对金属－橡胶热硫化粘接复合体的剥离行为进行了研究，同一粘接试样的双向１８０°剥离试验显示出了巨大的差异。本文分析了弹性材料在硫化过程中的分子行为，并提出了相应的新假设，认为这是由于金属－橡胶在硫化粘接过程中分子取向交联行为所致。这种双向１８０°剥离破坏现象可被看作是金属－橡胶硫化粘接过程中分子取向行为的间接证据。     

T_C≥400°C高温PTC陶瓷的研制

利用国产原料，采用传统的陶瓷材料制备工艺，研制了居里温度ＴＣ≥４００°Ｃ的高温ＰＴＣ陶瓷，制成了居里温度ＴＣ＝４１２°Ｃ，电阻Ｒ≤１０３Ω，ｌｇ（Ｒｍａｘ／Ｒｍｉｎ）＝４的高性能ＰＴＣ热敏陶瓷材料     

颗粒类型对颗粒增强铝基复合材料性能的影响

本文对粉末冶金法制备的ＳｉＣ和ＴｉＣ颗粒增强铝基复合材料进行了研究。试验表明，在颗粒含量相同、尺寸相当的条件下，ＴｉＣ增强Ａｌ基复合材料的强度和模量均低于ＳｉＣ增强Ａｌ基复合材料，但其屈强比却明显高于ＳｉＣ增强Ａｌ基复合材料。高温长时间等温处理对ＴｉＣ颗粒增强纯Ａｌ复合材料的强度没有明显的影响。     

聚吡咯导电材料合成方法的进展

本文对聚吡咯及聚吡咯导电复合物的合成方法进行了综述。     

非对称复合材料层板在面内载荷作用下的非线性横向变形或屈曲

本文利用广义富里叶级数法对非对称复合材料层板在面内载荷作用下的非线性横向变形或屈曲问题进行了分析。文中主要研究了四边简支边界条件下,非对称层板的铺层方式和面内载荷形式对横向变形的影响。通过求解非线性控制方程得到了层板的载荷—挠度曲线或特殊情况下的后屈曲平衡曲线。计算结果表明,对于大多数非对称复合材料层板在面内载荷作用下所产生的是横向变形问题,而不是分叉屈曲问题。     

气相处理对碳纤维表面及其复合材料性能的影响

本文对气相表面处理碳纤维的新工艺进行了系统研究。处理后的碳纤维强度、模量不下降,且其表面能、表面化学官能团含量明显增加;表面微晶结构变小,与环氧树脂复合后,层间剪切强度(LLSS)提高47%左右。本文还对复合材料断口的形态结构进行了分析,说明这种表面处理方法能有效改善碳纤维增强环氧树脂复合材料(CFRP)的界面粘结。     

关于不确定的对称组合系统的稳定化控制器与观测器的设计

本文研究了不确定的对称组合系统的稳定化控制器与观测器的设计问题，给出一种设计稳定化控制器与观测器的方法，在这种设计方法中，使给定的带有不确定性的对称组合系统稳定的状态反馈增益矩阵和观测器增益矩阵可由低阶代数Ｒｉｃｃａｔｉ方程的解导出。