复合材料正交迭层板拉伸损伤特征的研究

On Damage Characteristics of Cross-Ply Laminates under Tensile Loading

复合材料迭层板的过早损伤直接影响其设计利用率与使用可靠性。本文报导[0_2/90)2]_s、[90_2/0_2]_s 及[+45_2/-45_2]_s 正交迭层板静拉伸过程损伤特征的研究工作。采用了应力—应变曲线、声发射、X—射线、光学显微镜和扫描电子显微镜等研究方法,通过大量的实验结果,全面地考察了三种正交迭层板的宏观损伤特征,并运用微观分析手段,提出了初始损伤机理。研究了基体韧性与正交板损伤特征的定性关系。韧性增加可以推迟初始损伤产生,阻止损伤扩展,减轻损伤程度,从而可以提高复合材料的设计利用率。

Many scholars have paid much attention to damage of multi-ply laminates in recent years[1-6].The cross-ply stacking sequence studied by most authors is[0_2/90_2]_s.It was pointed out that there are several knees on stress-strain curve of cross-ply laminate[1]and that the knees are related to transverse cracks in the 90° lamina[4].But there is no study on mechanisms of formation of trans- verse crack,nor is there any study on the influence of matrix toughness on damage characteristics.In this paper,in an attempt to overcome the shortcomings just mentioned,the authors,using several different experimental techniques, study the macroscopic and microscopic characteristics of damages and the effect of matrix toughness on damage characteristics for three kinds of cross-ply lam- inates:(0_2/90_2)_3,(90_2/0_2)_s and(+45_2/-45_2)_s.The three contributions of this paper,of which the last two are more important,are as follows: 1.There is only one initial knee instead of several on tensile stress-strain curve for three kinds of cross-ply laminates.After the knee,the slope of the curve decreases continuously.The initial knee and the monotonic decrease of slope are macroscopic appearance of cumulative micro-damages. 2.The modes of damage for cross-ply depend on the stacking sequence and they include transverse crack,longitudinal splitting,oblique crack in 45-degree direction,delaminaton etc.All initial micro-damages are real minute cracks which gradually link up to become comparatively larger cracks(Fig.7).The location where initial damage occurs and the direction in which it propagates are controlled by weak points(Such weak points are discussed in Section Three of the paper)within cross-ply laminates. 3.The toughness of resin matrix plays an important role in effeeting the strain value of initial damage and the characteristics of damage propagation of cross-ply laminates,The adoption of toughened resin as matrix material brings the following advantages:(1)The formation of initial damage is delayed,(2)the propagation of crack is slowed down,(3)delamination is delayed,and(4)the degree of damage is reduced.