变振幅振动钻削提高微小孔入钻定位精度的研究

分析了微小孔钻头轴向振动入钻时特殊的动力学行为及其对入钻定位误差的修正作用。首次采用变振幅振动钻削的新方法，用直径为０．２８ｍｍ的高速钢麻花钻对１８Ｃｒ２Ｎｉ４ＷＡ低碳合金钢进行了钻削实验，结果在提高钻头寿命的同时显著提高了微小孔的入钻定位精度，验证了这种新方法新颖优良的工艺效果。     

多孔吸水涤纶断裂机理的研究

以配备有动态拉伸装置的扫描电子显微镜(SEM)对高吸水多孔涤纶的拉伸断裂过程进行了研究,结合纤维的断裂端形态,对微孔的形态、大小和大小分布对其力学性能的影响作了初步探讨。结论为,经不同碱浓度和不同时间处理后的纤维断裂行为是不同的,经短时间处理的纤维以局部剪切屈服为其断裂的主要形式,而长时间处理后的纤维断裂主要发生在其真实截面最小处。在同样的拉伸条件下具有圆形孔洞的纤维有较高的力学性能。     

A finite element analysis of fracture initiation in ductile/brittle periodically layered composites

A near-tip plane strain finite element analysis of a crack terminating at and normal to the interface in a laminate consisting of alternate brittle and ductile layers is conducted under mode-I loading. The studies are carried out for a system representing steel/alumina composite laminate. The Gurson constitutive model, which accounts for the ductile failure mechanisms of microvoid nucleation, growth and coalescence, is employed within the framework of small deformation plasticity theory. Evolution of plastic zone and damage in the ductile layer is monitored with increasing load. High plastic strain localization and microvoid damage accumulation are found to occur along the brittle/ductile interface at the crack-tip. Fracture initiation in the ductile phase is predicted and the conditions for crack renucleation in the brittle layer ahead of the crack are established for the system under consideration. Ductile fracture initiation has been found to occur before plasticity spreads in multiple ductile layers. Effects of material mismatch and yield strength on the plastic zone evolution are briefly discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

含孔橡胶矩形板的单向压缩

在船舶和海洋工程领域,以橡胶材料为代表的超弹性材料应用越来越广泛,故研究橡胶材料的损伤和破坏的力学机理是一个非常现实的重大课题.该文力求通过研究橡胶材料的空穴萌生和增长来了解超弹性材料的损伤和破坏的力学机理.利用高玉臣给出的一类应变能函数分析了含单个微孔橡胶矩形板在受单向压缩作用下生长的有限变形问题.利用不可压缩条件确定了矩形板的变形模式,此变形模式含有2个物理意义完全不一样的参数,其中一个参数可由远场的变形状态确定,另一个参数可用最小势能原理导出变分近似解.进而给出了反映微孔变形的参数与外载间的关系,以及孔边应力分布的解析解.结果显示,高玉臣给出的应变能函数能较好地描述橡胶材料的有限变形特性,含有单个圆柱微孔的三维橡胶矩形板受压与受拉时的力学特性相差较大.     

Effect of crosslinking structure on sorption of CO2 in photocrosslinked PVCA film

The sorption behavior of CO₂ gas in photocrosslinked poly(vinyl cinnamate) film was examined under atmospheric pressure. The sorption isotherm was well described by the Langmuir equation, suggesting that sorption of CO₂ is mainly governed by adsorption in the microvoids. The amount of sorbed CO₂ was significantly affected by the degree of crosslinking. The CO₂ sorption was enhanced at a lower degree of crosslinking but was decreased at a higher degree of crosslinking. The unexpected increase in the amount of adsorbed CO₂ correlated with the increase in the number of microvoids that occurred as a result of the crosslinking reaction. However, further crosslinking led to a decrease in the mean size of the microvoids. The smaller microvoids, in comparison to CO₂ molecules, did not act as adsorption sites, so that the amount of sorbed CO₂ decreased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1744–1750, 2000     

Interface crack interacting with a microvoid in the near-tip process zone

This paper deals with the elastic problem of an interface macrocrack interacting with a near-tip microvoid in the process zone. The `pseudo-traction-edge-dislocation method' (abbreviated PTEDM) proposed by Zhao and Chen (1996) is extended to treat the macrocrack-microvoid interaction problem in bimaterial solids. A system of singular integral equations with Hilbert kernel is reduced and solved numerically, which provides a fundamental understanding of the interaction effect. Numerical results are given for six kinds of bimaterial combinations (Hutchinson, Meer and Rice, 1987). The J-integral analysis is also applied to the interaction problem, and some useful conclusions are presented in detail.     

冻胶法制备超高分子量聚乙烯/SiO2杂化微孔膜研究——稀释剂与SiO2对铸膜液熔融结晶性能的影响

根据界面相分离原理,以矿物油为稀释剂,O2为添加剂,采用冻胶法制备了超高分子量聚乙烯(UHMWPE)膜以及UHMWPE/SiO2杂化微孔膜,讨论了稀释剂以及无机粒子含量对膜熔融结晶性能的影响.结果表明,矿物油作为微孔稀释剂,其加入使微孔膜中UHMWPE熔点降低,结晶度减小.当SiO2与UHMWPE质量比低于8/10时,随SiO2含量增加,UHMWPE熔点变化不显著,熔限增加,结晶温度升高,相对结晶度增大,微晶尺寸减小;当SiO2加入量足够大时,相对结晶度反而减小.随SiO2其含量增加,界面孔增多,膜孔隙率提高,水通量增大,泡点孔径先增大后减小.     

250℃下时间效应对PAN纤维热氧稳定化反应的影响及关联

借用傅里叶变换红外光谱(FT-IR)、元素分析(EA)、X射线衍射(XRD)和示差扫描量热分析(DSC)等手段,对比研究了热氧稳定化过程中250℃下时间效应与两种聚丙烯腈(PAN)共聚纤维及其炭纤维结构和性能之间的关联。研究结果表明,PAN纤维在250℃温区内停留超过9min时,最终热氧稳定化纤维的环化度(RCI)、体密度和芳构化指数(AI)的增加速率开始变小;炭纤维的孔含量(Vp)值与内部微晶的d002值开始增大,微晶排列的规整程度变差,缺陷增多,拉伸强度开始降低。     

微孔型COC/PETG收缩薄膜的制备以及性能研究

利用单向牵伸工艺,在PETG原材料中添加一定比例的COC,制备了45μm的微孔型COC/PETG收缩薄膜。利用SEM、紫外分光光度计、收缩率测试仪、收缩力测试仪、电子拉伸机等分别对薄膜的微孔形貌、结构以及微孔对薄膜收缩行为的影响进行了深入分析。结果显示,20%(质量分数)含量COC的加入使PETG收缩薄膜内部产生了尺寸为3~10μm的微孔,孔隙率可达到25%,微孔的存在一定程度上降低了薄膜的拉伸强度,但大大改善了薄膜纵向的收缩率曲线,降低了薄膜的收缩内应力,并达到了阻隔紫外线的效果。