Effects of Low Level Temperature Cycle on the Delamination Progress in Quasi-isotropic Laminates

研究了温度对准各向同性层合板[0/45/-45/90]S损伤扩展和强度的影响。在-100℃的低温下，-45℃和90℃层的裂纹密度增加，而在150℃的高温下，层间的分层则是非线性的。应力-应变关系的拐点对应于两种温度下各界面上分层的合并及其向深度方向的扩展。(1)基体裂纹在-45度层中的扩展方向，(2)在-45度层中沿深度方向产生的多个裂纹，(3)在45/-45层之间分层密度的增加，(4)高温下各层边边缘间隙的扩展和(5)高温下0度层中纤维断裂向边缘表面的扩展。研究还发现，在150℃时，聚酰亚胺的纵向杨氏模量比常温下降低了10%，而在-100℃时，纵向与法向之间的剪切弹性模量的增加幅度远远大于其他温度下的弹性模量。针对高温下裂纹尖端附近随时间变化的裂纹，提出了一个新的韧性参数。

Effects of temperature on the damage propagation and strength of quasi-isotropic laminates [0/45/-45/90]s were investigated. Non-linearity is found to be due to the increase of crack density both in -45 and 90 degree layrs at low temperature of -100 in centigrade and due to the delamination at high temperature of 150 in centigrade. The knee point of stress-strain relation corresponds to the coalescence of delaminations in each interface and the their propagation to the depth direction at both temperatures. Other characteristic phenomena are as follows such as (1) the direction of matrix crack propagation in -45 degree layr, (2) the multi cracks generated along the depth-direction in -45 degree layr, (3) the increase of delamination density between 45/-45 layrs, (4) the progress of the gap between side edges of each layr at high temperature and (5) fiber break cross to the edge surface in 0 degree layr at high temperature.Thermo-mechanical constants were obtained in each temperature and the numerical results based on these data explain the above (3). The followings were also found that the longitudinal Young's modulus at 150 degree in centigrade is 10% less than that of room temperature and that the shear modulus between longitudinal and normal increases at -100 degree in centigrade much more than the other moduli.At high temperature a new carbon fiber reinforced polyimide without toxicity was studied to obtain its delamination characteristics. A new toughness parameter is proposed for the crack with time-dependent behavior near the crack tip under high temperature.