Impact Strength of Inhomogeneous Materials

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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.