一方向強化AS4/PEEK積層板の高温疲労層間はく離き裂伝ぱに対する繊維架橋によるクラックシールディング効果

概要

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Crack shielding by fiber bridging under high temperature (473K) fatigue conditions was investigated using the Double Cantilever Beam (DCB) specimens of unidirectional AS4/PEEK laminates. Under a constant applied stress-intensity-factor-range, △K_<apply, > the crack propagation rate decreases due to the shielding by fiber bridges between the crack surfaces as the crack extends. After the crack propagates to a few mm long, the propagation rate is saturated at the lower bound. The highest propagation rate can be obtained by extrapolating the propagation rate at the initial slit. The rate is evaluated as the intrinsic value of crack propagation rate having no effect of fiber bridging, and it is correlated well with △K_<apply>. The fact implies that the crack propagation is governed by the intrinsic stress-intensity-factor range at the crack tip, △K_<tip, > which is equal to △K_<apply>-△K_<bridge> where △K_<bridge> is the stress-intensity-factor range carried by fiber bridging. In constant load amplitude tests, the crack propagation rate shows a transition from the upper bound represented by the da/dN-△K_<tip> relation without bridging to the lower one obtained from the constant △K_<apply> tests.
1995-06-15