アルミニウム合金における変動荷重下の疲労裂進展とき裂開閉口挙動 : 第II領域におけるき裂進展速度曲線の折れ曲りと荷重変動の影響

概要

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Fatigue crack growth tests were crried out on two aluminum alloys, ZK141-T7 and A7075-T6, under constant amplitude, repeated two-step and random loadings. Crack length and crack closure were measured by using the minicomputer-aided unloading elastic compliance method. The crack growth rate curve represented in terms of effective stress intensity range, ΔK_<eff>, exhibited a trilinear from in so-called Region II for both testing materials under constant amplitude loading. the relation between da/dn and ΔK_<eff> of ZK141-T7 under repeated two-step loading was found different from the constant amplitude results due to load interaction, whereas the relation of A7075-T6 was hardly affected by load variation. The crack opening stress intensity, K_<op>, under variable loading was found for both materials to be controlled by the maximum stress intensity range-pair, (Δ_<rp>K)_<max>, and its stress ratio, and further to coincide with the constant amlitude test results having the identical stress intensity range ΔK and stress ratio R. Fatigue crack growth under random under random loadings could be well predicted in terms of ΔK_<eff>, using the modified ralation between da/dn and ΔK_<eff> obtained from the repeated two-step loading tests accounting for crack growth characteristics depending on materials.
社団法人日本材料学会の論文
1985-10-15