高力Al合金における微小切欠きの疲労き裂伝ぱおよび破断寿命への影響

概要

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The dependency of stress intensity factor range, ΔK, on crack growth rate, da/dN, at the early stage, which initiated from a small notch with notch length of 50 μm or 200 μm and the notch root radius of about 25 μm, was examined using a high strength aluminum alloy. The effect of notch length on crack propagation cycles was discussed by integration of da/dN - ΔK curves. The results are as follows. (1) The da/dN of a high strength aluminum alloy can be expressed by the power law as a function of ΔK. The da/dN-ΔK curves can be separated into three stages. (2) In the stage I (20<ΔK<8.7 kg/mm^<3/2>). the da/dN is discontinuous due to the formation of non-propagating cracks. (3) There is a well defined minimum apparent stress intensity factor for crack propagation from a notch. For R=0.1, this factor is constant regardless of the length of the notch. (4) The apparent crack length for non-propagating cracks for the smooth specimen is 32 μm under R =0.1. (5) When the length of a crack from the notch tips, a_P, is almost equal to or larger than the notch length, a_N, the number of cycles required for a crack to propagate to a_P, N_P, increases with a_N under constant ΔK_<a_p> and ρ, where ΔK_<a_p> is the apparent stress intensity factor range and ρ is the notch root radius.
社団法人日本材料学会の論文
1978-10-15