有限要素法を用いた疲労き裂進展下限界に及ぼす過大荷重効果のモデル化

概要

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A model of overload effect for hardening elastic-plastic solids is proposed to evaluate the stress intensity factor for compressive residual stress Krs at fatigue crack-tip fields. The residual stress σrs introduced at the tip in SUS316 by overload Kov = 6, 15, 30 and 45 MPa·m1/2 can be estimated using Finite Element Method (FEM). The Krs values as a function of fatigue crack growth length Δa were calculated from the σrs according to Dugdale model. It was found that the calculated Krs decreased significantly with increasing Δa and reached to maximum value of |Krs|. Therefore, the maximum stress intensity factor Kmax will decrease apparently because of the action of Krs. As a result, effective stress intensity factor range given by ΔKeff = Kmax+Krs decreased with increasing Δa. Defining the fatigue crack cannot grow when ΔKeff = ΔKth, the apparent fatigue crack growth threshold ΔNKth can be estimated. Then, we can obtain the theoretical equation as ΔNKth=0.30Kov+4.10. The equation showed in good agreement with experimental results.