Fatigue Strength Prediction under Multiaxial Stress

Abstract

A multiaxial fatigue failure criterion for composite materials is presented in this paper along with an assessment of the capability it offers for design under multiaxial constant or variable amplitude stresses. The applicability of this criterion, based on the well known quadratic failure tensor polynomial criterion for static loading, is validated through comparisons with uniaxial and multiaxial fatigue experimental data. Static and fatigue tests were carried out during this study on glass/polyester specimens cut off-axis from a multidirectional laminate at different angles. The agreement between experimental values and theoretical predictions is good. The proposed criterion is also compared to existing fatigue criteria and an overall assessment of their performance is given. Some theoretical design considerations for the case of irregular stress spectra, introducing the concept of multiaxial Miner coefficient, are finally presented.