アルミニウム合金におけるモード II 疲労き裂進展機構とその材料依存性

概要

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The behavior of mode II fatigue crack growth and its mechanism have been investigated on 2017-T3, 7075-T6, 7075-T651 aluminum alloys and 7N01-T4 aluminum alloy and 7N01-T4 aluminum alloyweldments by using a four -point-shear-loading method. In the aluminum alloys tested, the da/dN-ΔK_<II> relation and ΔK_<II>-threshold for mode II fatigue crack growth were found to be very material-sensitive, while da/dN-ΔK_<Ieff> relation for mode I growth was rather material-insensitive as is well known. Observation of the deformation around a growing crack tip has been made on the repricas taken at the successive stage-minimum load, maximum load , minimum load-in one load cycle. Two types of mechanisms of mode II fatigue crack growth have been proposed on the observed results, In 2017-T3 and 7N01-T4 base metal, HAZ and weld metal, a mode II fatigue crack grows due to the alternating shear slip mechanism at the crack tip, and in 7075-T6 shear -induced- decohesion taked place in addition to the alternating shear slip. The cyclic crack tip shear displacement Δ(CTSD)_p on theboundary of the cyclic plastic region measured on the repricas agreed well with Δ(CTSD) calculated from BCS theory in all the materials tested. It has been confirmed that the fractographical features observed support the proposed mechanism of mode II fatigue crack growth.
社団法人日本材料学会の論文
1985-10-15