Biaxial fatigue loading of notched composites

Abstract

Thin walled, 2.54-cm (1-in.) diameter tubular specimens of T300/934 graphite/epoxy were fabricated and fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0/90)S and (+ or - 45)S; all tubes contained a 0.48-cm (3/16-in.) diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on the Hill plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good