Abstract
In this paper, a multiaxial fatigue life prediction model is proposed under general multiaxial random loadings. First, a brief review for existing multiaxial fatigue models is given and special focus is on the LiuMahadevan critical plane concept, which can be applied to both brittle and ductile materials. Next, new model development based on the Liu-Mahadevan critical plane concept for random loading is presented. The key concept is to use two-steps to identify the critical plane: identify the maximum damage plane due to normal stress and calculate the critical plane orientation with respect to the maximum damage plane due to normal stress. Multiaxial rain-flow cycle counting method with mean stress correction is used to estimate the damage on the critical plane. Equivalent stress transformation is proposed to convert the multiaxial random load spectrum to an equivalent constant amplitude spectrum. The equivalent stress is used for fatigue life prediction. Following this, experimental design and testing is performed for Al 7075-T6 under various different random uniaxial and multiaxial spectrums. The developed model is validated with both literature and in-house testing data. Very good agreement is observed for the investigated material. Finally, conclusion and future work is given based on the proposed study.
Highlights
Multiaxial fatigue models can be classified into four major categories: stress-based [1,2,3], strain-based [4,5], energy-based [6,7], and fracture mechanics-based approaches [8]
Other models assume that the maximum normal stress range plane as the critical plane which is mostly suitable for brittle failure [11,12,13]
One successful approach is to let the critical plane change its orientation for different failure modes, i.e., along the maximum normal stress range plane for brittle materials and along the maximum shear stress range plane for ductile materials
Summary
Multiaxial fatigue models can be classified into four major categories: stress-based [1,2,3], strain-based [4,5], energy-based [6,7], and fracture mechanics-based approaches [8]. The basic concept of the critical plane approach is to use the stress/strain components on a plane to calculate the fatigue damage of material under general multiaxial cyclic loadings. Other models assume that the maximum normal stress range plane as the critical plane which is mostly suitable for brittle failure [11,12,13]. The energy-based model can be applied to a wide range of materials (both brittle and ductile) under both proportional and non-proportional loadings without the need of calibration parameters. Based on the above discussion, the authors attempt to develop a multiaxial fatigue model for random loading by integrating the Liu-Mahadevan critical plane approach along with Rainflow counting and Miner’s damage rule, from which an equivalent stress on critical plane can be calculated and used to determine fatigue life with the proposed model
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