The Effects of Discontinuities on Compression Fatigue Properties of Advanced Composites PDF Download

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Languages : en
Pages : 346

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Book Description
This study is directed at assessing the static compression and R = 10 compression fatigue properties of graphite epoxy composites with ply drop-off discontinuities under severe operating environments including room temperature dry and wet, -65 F wet, and 218 F dry and wet. In 30-ply (+/-45)5/016/904c laminates, two 0 deg plies or four 45 deg plies are dropped off symmetrically in the middle of the specimen. Static strengths and moduli of elasticity are unaffected by these discontinuities, however, some proportional limit and Poisson's ratio values are changed significantly. At 1.25x106 cycles of constant frequency fatigue the maximum endurance limit stress level is degraded significantly in all cases by the two 0 deg ply dropoffs, but for the four 45 deg ply dropoffs it is unaffected or increased significantly. Surviving specimens exhibit residual strength that varies directly with the maximum applied cyclic compressive stress up to a threshold level. Detail data tables and plots are included. Scanning electron microscopy observations of the failed specimen fracture surfaces combined with micromechanics/point stress analysis and the analysis of ply dropoff effects are also included. (MM).