TENSION-TORSION BEHAVIOR OF GLASS EPOXY FLEXBEAM LAMINATES

Quasi-static tension-torsion and tension-torsion fatigue tests were co nducted on several candidate S2/F584 glass-epoxy flex-beam layups to e stablish their torsional strength and fatigue behavior in the presence of an axial load, determine typical damage mechanisms, and provide a database for developing predictive analytical methods. Tension-torsion specimens contained 0 degrees longitudinal plies and 15, 30, or 45 de grees angle plies in seven different stacking sequences. The angle pli es were +/- 45 woven cloth in one layup and prepreg tape in the other layups. In the tape laminates, fatigue failures began with matrix crac ks forming on the edge that initiated delaminations in the interfaces between the angle plies and 0 degrees plies. In the cloth laminates, a series of small ''stair step'' delaminations formed between the +/-45 cloth layers and initiated delaminations in the neighboring 0/45 inte rfaces. Tests indicated that the three layups with only 0 degrees and +/-45 degrees plies had the highest torsional strength in the presence of a constant axial load. Of the three strongest layups, the one in w hich the +/- 45 degrees plies were made of woven cloth fabric instead of prepreg tape was the strongest and had the longest fatigue life.