アルミニウム合金2017-T3および7057-T6における混合モード負荷による疲労き裂の発生および進展

概要

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Fatigue crack initiation and growth characteristics under mixed mode loading have been investigated on aluminum alloys 2017-T3 and 7075-T6, using a newly developed apparatus for mixed mode loading tests. In 2017-T3, the fatigue crack initiation and growth characteristics from a pre-crack under mixed mode loading were divided into three regions-shear mode growth, tensile mode growth and no growth-on the ΔK_I-AK_<II> Plane. The shear mode growth was observed in the region expressed approximately byΔK_<II> >3 Mpa√<m> andΔK_<II>/ΔK_I >1. 6. In 7075-T6, the condition of shear mode crack initiation was expressed by ΔK_<II>>8Mpa√<m> andΔK_<II>/ΔK_I >1.6, and continuous crack growth in shear mode was observed only in the case ofΔK_I /ΔK_<II>≒0. The threshold condition of fatigue crack growth in tensile mode was described by the maximum tensile stress criterion, which is given by Δσ_θmax√<2πγ>≒1.6Mpa√<m>, in both aluminum alloys. The direction of shear mode crack growth approached to the plane in whichΔK_I decreases andΔK_<II>increases towards the maxi-mum with crack growth. The da/dN-ΔK_<II>relation of the curved cracks growing in shear mode under mixed mode loading agreed well with the da/dN-AKn relation of a straight crack under pure mode II loading.
社団法人日本材料学会の論文
1987-06-15