Abstract
In cyclic multiaxial stress/strain condition under nonproportional loading in which principal direction of stress/strain are changed in a cycle, it becomes difficult to analyze stress/strain ranges because of complexity of multiaxial stress/strain states depending on time in cycles. In order to evaluate stress/strain simply and suitably under non-proportional loading, Itoh and Sakane have proposed a method called as IS-method and a strain parameter for life evaluation under non-proportional loading ??NP. In the method, 6-components of stress/strain are converted to an equivalent stress/strain indicating the amplitude and the direction of principal stress/strain as a function of time as well as an intensity of loading nonproportionality fNP. Based on IS-method, the authors also have developed a tool which enables to analyze multiaxial stress/strain condition with the nonproportionality of loading history and evaluate failure life under nonproportional multiaxial loading. The tool indicates the analyzed results on monitor and users can understand visually not only variation of the stress/strain conditions but also non-proportionality during the cycle, which helps the design of material strength.
Highlights
Structural components and materials such as aircrafts and nuclear equipment undergo complex non-proportional multiaxial loadings where directions of stress and strain are changed into various directions under multiaxial stress and strain states
In cyclic multiaxial stress/strain condition under nonproportional loading in which principal direction of stress/strain are changed in a cycle, it becomes difficult to analyze stress/strain ranges because of complexity of multiaxial stress/strain states depending on time in cycles
Equivalent strains and stresses based on von Mises and Tresca are considered as the most common theory. They lead to significant overestimation of fatigue lives under non-proportional loadings, a few other classical models such as critical plane approaches that correlate stress or strain with multiaxial fatigue lives have been proposed in recent years
Summary
Structural components and materials such as aircrafts and nuclear equipment undergo complex non-proportional multiaxial loadings where directions of stress and strain are changed into various directions under multiaxial stress and strain states. Based on IS-method, the authors have developed a tool which enables to analyze multiaxial stress/strain condition with the nonproportionality of loading history and evaluate failure life under nonproportional multiaxial loading. Multiaxial fatigue; Life evaluation; Non-proportional loading; Analysis tool; Cycle counting; Additional hardening.
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