一方向炭素繊維強化複合材料の混合モード層内疲労き裂進展に及ぼすき裂架橋効果

概要

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The growth behavior of intralaminar fatigue cracks in a unidirectional carbon/epoxy laminate, Toray T300/#2500, was studied under mixed-mode loading with a ratio of mode II stress intensity factor (SIF) to mode I SIF equal to 2.50. Under a constant value of the applied SIF range, ΔK_<Iap>, the crack propagation rate decreased with the crack extension because of crack-tip shielding by crack bridging. For each value of ΔK_<Iap>, the relationship between the crack propagation rate, da/dN, and the crack extension, Δa, was expressed by the following equation: log(da/dN)=log V_0-Δa log V_1, where V_0 and V_1 are functions of the applied SIF value. The value of V_0 which is the crack propagation rate without crack bridging was approximated by a power law function of the crack-tip value of the SIF range, ΔK_<Itip>. On the basis of the power law relationship, a method for evaluating the shielding SIF range, ΔK_<Ibridge>, was proposed. ΔK_<Ibridge> monotonically increased with the crack extension. Futhermore, ΔK_<Ibridge> for a small ΔK_<Iap> value was higher than that for a large ΔK_<Iap> value when compared to the same amount of crack extension.
1992-11-25