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Quasi-static tension-torsion and tension-torsion fatigue tests were conducted on several candidate S2/F584 glass-epoxy flex-beam layups to establish 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° longitudinal plies and 15, 30, or 45° angle plies in seven different stacking sequences. The angle plies were ±45 woven cloth in one layup and prepreg tape in the other layups. In the tape laminates, fatigue failures began with matrix cracks forming on the edge that initiated delaminations in the interfaces between the angle plies and 0° 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 interfaces. Tests indicated that the three layups with only 0° and ±45° plies had the highest torsional strength in the presence of a constant axial load. Of the three strongest layups, the one in which the ±45° plies were made of woven cloth fabric instead of prepreg tape was the strongest and had the longest fatigue life.
McDonnell Douglas Helicopter System, Mesa, AZ
NASA Langley Research Center, Hampton, VA
Stock #: CTR10241J