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Summary
Fatigue damage development in notched (0/¿̐ư45/0)s, (45/0/¿̐ư45/0)s, (90/¿̐ư45/0)s, and (45/90/¿̐ư45/0)s graphite/epoxy laminates was investigated. Both tension and compression fatigue behaviors were studied. Most of the tests were conducted at load levels equal to two thirds of the ultimate tensile strength of the notched specimens. After fatigue loading, specimens were examined for damage type and location using light microscopy, scanning electron microscopy, ultrasonic C-scans, and X-radiography. Delamination and ply cracking were found to be the dominant types of fatigue damage. In general, ply cracks did not propagate into adjacent plies of differing fiber orientation. To help understand the varied fatigue observations, the interlaminar stress distribution was calculated with finite element analysis for the regions around the hole and along the straight free edge. Comparison of observed delamination locations with the calculated stresses indicated that both interlaminar shear and peel stresses must be considered when predicting delamination. The effects of the fatigue cycling on residual strength and stiffness were measured for some specimens of each laminate type. Fatigue loading generally caused only small stiffness losses. In all cases, residual strengths were greater than or equal to the virgin strengths.
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Reproduction Note
Electronic reproduction. W. Conshohocken, Pa. : ASTM International, 1981. Mode of access: World Wide Web. System requirements: Web browser. Access may be restricted to users at subscribing institutions.
