Impact Strength of Inhomogeneous Materials

本文研究了普通石墨和细化石墨的冲击疲劳强度以及DFRP空心圆柱试样中应变波的传播行为，石墨条试样的结果如下：1）在各S-N图上观察到表观疲劳极限。2）试样长度对冲击疲劳寿命的影响并不明显，这是因为在冲击疲劳过程中，应变脉冲衰减很大; 3）裂纹在主裂纹尖端与小裂纹连接，以锯齿形方式扩展; 4）缺口降低了两个系列的冲击疲劳寿命。随着冲击速度的增加，材料的动弹性常数逐渐减小; 6）残余应变先随冲击次数的增加而显著增加，然后逐渐增加; 7）石墨的细化对提高材料的强度是有效的。通过使用包括与轴成0 °和45 °角的纤维的两种类型的层来制备14个系列的试样。结果表明：1）应变脉冲的传播速度不依赖于层的叠层顺序，可以通过基于混合定律的弹性常数来估计; 2）波的传播效率WTR，在冲击压缩结构中，随着0层层数的增加，WTR增加。3）随着45层层数的增加，WTR增加。4）当冲击压缩作用于静态扭转试件时，在大多数情况下，扭转力矩对波的传播速度影响不明显。不同配置的WTR不同。

Impact fatigue strengths of usual and refined structural graphites and strain wave propagation behavior in DFRP hollow cylindrical specimen were investigated.The results obtained for graphite strip specimens are summarized as follow.1) Apparent fatigue limit was observed on each S-N diagram. This strength corresponded to the knee point on the stress-strain curve.2) The effect of specimen length on the impact fatigue life can not be seen clearly due to the large attenuation in strain pulse during the propagation.3) A crack propagated zig-zag way by linking with small cracks ahead of main crack tip.4) A notch reduced the impact fatigue life for both series.5) Dynamic elastic constant was reduced with increase of impact velocity.6) Residual strain was increased with increase of Pulsated number markedly at first and gradually after that.7) Refinement of graphite is effective to improve the strength.For CFRP, fourteen series of specimen were prepared by using two types of layer including the fibers at angle of 0^ﾟ and 45^ﾟ to the axis. The results were summarized as follows.1) The velocity of a strain pulse does not depend on the order of lamination of layer and can be estimated by using an elastic constant evaluated based on the law of mixture.2) The efficiency of wave transmission, WTR, is increased with increase of number of 0^ﾟ-layer in a configuration for an impact compression.3) The WTR is increased with increase of the number of 45^ﾟ-layer for an impact torsion.4) When impact compression is applied to a specimen under a static torsion, The wave Propagation velocity is not affected clearly by the torsional moment in most cases. The WTR is different for different configuration.