炭素繊維強化エポキシ積層板の混合モードI+II層間疲労き裂進展に及ぼす応力比の影響

概要

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The stress-ratio effect on the propagation behabior of interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates, T800H/#3631, under mixed mode(I+II)loading. Fatigue tests were conducted under the stress ratios of R=0.2 and 0.5 with several mixed-mode ratios, G_I/G_<II> by using the mixed mode bending method. For each R value, the crack propagation rate, da/dN, was higher for higher G_I/G_<II> ratios at the same value of the maximum total energy release rate, G_<max>. Under a constant value of the G_I/G_<II> ratio, both the maximum load and the load amplitude affect the crack propagation rate. For high propagation rates and high G_I/G_<II> ratios, the crack propagation rate is mainly controlled by the maximum load, while for low propagation rates and low G_I/G_<II> ratios, the contibution of the load amplitude is large. For both R values, the relation between the mode I and II maximum energy release rates, G_<Imax> and G_<IImax> at the fatigue threshold is approximated by the following equation : G_<Imax>/G_<Imaxth>+G_<IImax>/G_<IImaxth>=1, where G_<Imaxth> and G_<IImaxth> are the threshold energy release rates for pure mode I and II loadings and decrease as the R value decreases.
1999-12-15