织物预成型体的可压缩性研究

研究了预定型织物在压实阶段的可压缩性,涉及压缩过程中纤维体积含量的变化特点.结果表明,预定型织物对压缩载荷的响应方式与织物层数及定型剂含量有关,织物层数的增加,相同载荷作用下易于获得较高的纤维体积含量;预定型处理降低了织物的可压缩性,随定型剂含量的增加,最终获得的纤维体积含量表现出下降的趋势;在实验施加的压缩载荷作用下,预定型织物的压实后纤维体积含量趋于一致,与压缩织物的层数关系不明显,但仍然受定型剂含量影响.     

X射线实时成像技术在炭纤维预制体及其复合材料中的应用

炭纤维预制体及其复合材料在制备和使用过程中可能产生不同程度的缺陷,对其进行无损检测非常重要。本工作采用X射线实时成像技术对炭纤维预制体及炭/炭复合材料进行无损检测。结果表明：X射线实时成像技术对炭纤维预制体中可能存在的缺陷和夹杂以及炭/炭复合材料的结构均匀性进行无损检测是有效的。炭纤维预制体中存在锥状断针和局部结构疏松缺陷,采用X射线实时成像技术分析得到的密度分布与取样实测的密度分布结果相吻合,这为炭/炭复合材料制备过程中的无损检测提供了快速、可靠手段。     

热梯度化学气相沉积动力学过程的探讨

主要是关于热梯度化学气相过程中预制体致密机理的探讨。通过对沉积试验的结果分析发现:在热梯度化学气相沉积的大部分阶段,预制体沉积致密的动力学方程符合低分子填充孔隙的动力学方程,即指数形式致密方程,这说明热梯度法致密预制体的过程从本质上来说,仍是受制于裂解产物在预制体上孔隙填充的这一动力学过程的,与文献中提到的常规均热法沉积致密模式是一致的。另外,从机理分析和实验结果的对比中发现:热梯度化学气相沉积能够较大幅度提高预制体致密速率的原因是存在于沉积过程的温度梯度和浓度梯度可以较大幅度提高沉积分子的定向扩散速率,所以提高了预制体的致密速率。但这一沉积速率的加快并不改变预制体的致密模式。     

Analysis of the Edge Effect on Flow Patterns in Liquid Composites Molding

In liquid composites molding, the cutting of the fiber preform is often not sufficiently precise leaving a small clearance between the reinforcement and the mold edges. This clearance creates a preferential flow path for the resin which may disrupt the filling of the mold cavity. Experience has shown that even a small clearance of 1 or 2 mm could have a significant effect, especially if the preform has a high fiber content. A model is thus needed to predict this channeling effect in order to take it into account in computer simulations of the mold filling process.This paper presents a model to describe this phenomenon. The idea is to characterize simultaneously the flow in the channel and through the reinforcement. The model is derived using Navier–Stokes equations in the open channel and Darcy's law in the porous preform. From this model, an equivalent porous medium was defined for which an equivalent permeability tensor can be computed as a function of the channel geometry. Numerical simulations performed with the computer software RTMFLOT developed in our laboratory have shown that in some limit cases, i.e., a large channel (5–6 mm) or for very low porosity reinforcements, the transverse flow from the channel to the preform can be neglected in the model while still obtaining quite a good prediction of the flow edge effect. In other cases, however, namely for a clearance of intermediate size (2–3 mm) which is the most common case in RTM, or for a higher porosity of the reinforcement, the transverse flow from the channel to the rest of the preform must be taken into account. Experimental data to validate the proposed model are also presented.     

新型螺旋焊管飞切机

介绍了一种适合于螺旋焊管生产的新型飞切机的结构和特点。该飞切机采用安装在习切小车中部的顶紧同步机构，氧－乙炔气切割的方式。它的通常使用的夹紧同步，气体切割；夹紧同步，铣刀切断；抱辊同步，气体切割等形式的飞切机比较，其结构简单，造价低，同步精确，成型阻力极小，有较高的经济价值和较好的推广前景。