Biaxial Fatigue Loading of Notched Composites

Thin-walled, 2.54-cm diameter tubular specimens of graphite/epoxy (Fiberite T300/1034) were fatigue cycled in combinations of axial, torsion al, and internal pressure loading. Two different four-ply layup configura tions were tested: [0/90] s and [±45] s ; each tube contained a 0.48-cm 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 a 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 experi mental data proved to be remarkably good.