2017-T3 Al合金および SUS 304 鋼における疲労き裂成長に及ぼす負の応力比の影響

概要

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Fatigue crack growth behaviors such as the crack growth rate and closure in the range of intermediate crack growth rate were studied using 2017-T3 Al alloy and SUS304 steel under various Combinations of the negative stress ratio, R and the maximum stress relative to the yield strength, σ_<max>/σ_y. The main results obtained are as follows ; (1) The fatigue crack growth rate, da/dN increased with a decrease of R and an increase of σ_<max> /σ_y for both 2017-T3 Al alloy and SUS 304 steel. In this case, it becomes clear quantitatively that the compression stress in the load cycle relative to the yield strength, S_c/σ_y is a very important factor which dominates the crack opening level and consequently da/dN in the both materials. The results are the same as those for S45C and SUS 329J1 which we reported previously. (2) Martensitic transformation taking place as the fatigue crack propagates complicates the effect of R on da/dN for SUS 304 steel, that is, the crack opening stress intensity factor relative to the maximum stress intensity factor, K_<op>/K_<max> increased and consequently da/dN decelerated with K_<max> particularly under the condition that σ_<max>/σ_y is small. These results are very different from those of other materials and it becomes clear that these fatigue crack growth behaviors correspond to the state of the formation of martensite at the vicinity of fatigue crack surfaces.
社団法人日本材料学会の論文
1991-05-15