Abstract
A series of strain-controlled multiaxial low cycle fatigue (LCF) tests under proportional and non-proportional loading conditions have been conducted on notched specimens. Cylindrical bars of Al 6061 aluminum alloy and AISI 316L stainless steel with four values of stress concentration factors referred to the net section Kt,n were employed. The experimental results evidenced a reduction of fatigue life due to non-proportional loading. Furthermore, the crack initiation site has been detected to be moved from the notch tip in the case of steel for high values of notch radius under non-proportional loading. Stress concentration factor evaluated in the elastic field Kt,n has been included in the Itoh-Sakane parameter to evaluate the fatigue life, returning a general underestimation of fatigue life especially for high values of Kt,n. Material notch sensitivity and crack initiation position have been taken into account to further modify the model, improving the original results and showing a better assessment.
Highlights
M any industrial applications require notched components to undergo non-proportional multiaxial low cycle fatigue
Remarkable contributions for the evaluation of low cycle fatigue life were given by Brown-Miller [4], Fatemi-Socie [5] and Smith-Watson-Topper [6] whose models are based on critical plane, a surface which experiences the highest level of damaging over the cycle
The failure life corresponds to the cycle where the stress amplitude becomes the 3/4 of the maximum stress in a cycle to avoid the complete propagation of the crack and rupture of the specimen
Summary
M any industrial applications require notched components to undergo non-proportional multiaxial low cycle fatigue. In terms of evaluation of fatigue life under multiaxial loading, a wide variety of methodologies have been developed. Stress based models [1,2,3] evaluate fatigue life through an equivalent stress parameter obtained from the stress components of the loading cycle. Strain based models are instead typically associated with low cycle fatigue where significant plasticity may occur. Remarkable contributions for the evaluation of low cycle fatigue life were given by Brown-Miller [4], Fatemi-Socie [5] and Smith-Watson-Topper [6] whose models are based on critical plane, a surface which experiences the highest level of damaging over the cycle. Energy based models [7] are applicable to low cycle fatigue loading cases
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