炭素繊維強化エポキシ積層板の混合モードI+II繰返し荷重による層間疲労き裂進展挙動

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Mixed-mode propagation behavior of interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates. T800H/# 3631. Mixed-mode fatigue tests were conducted by the mixed-mode bending method under a stress ratio of R=0.2. The mixed-mode ratio, G_I/G_<II>, was 0.030,0.19,0.57 and 1.37. When the crack propagation rate da/dN, was correlated to the maximum value of the total energy release rate, G_<max>, the propagation rate increased as the G_I/G_<II> value increased. For each mixed-mode ratio, the crack propagation rate was given by a power function of the maximum value of the energy release rate in the region of rates above 10^<-9>m/cycle. The exponent of the power function decreased as the G_I/G_<II> value decreased. Below da/dN=10^<-9>m/cycle, there exists the threshold for fatigue crack propagation. At the threshold, the relation between the mode I and mode II components of the maximum energy release rate, G_<Imax> and G_<IImaxth>, is given by the following equation : G_<Imax>/G_<Imaxth>+G_<IImax>/G_<IImaxth>=1,where G_<Imaxth> and G_<IImaxth> are the threshold values of the maximum energy release rate for pure mode I and pure mode II loadings.
1999-08-25