SEDL / STP / STP937-EB / STP24381S

Frequency and Load Ratio Effects on Critical Strain Energy Release Rate G^c Thresholds of Graphite/Epoxy Composites

Adams, DF
Professor of mechanical engineering and staff engineer, University of Wyoming, LaramieWY,

Zimmerman, RS
Professor of mechanical engineering and staff engineer, University of Wyoming, LaramieWY,

Odom, EM
Composites engineer, General Electric Corp., Albuquerque, NM

Pages: 18    Published: Jan 1987

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Abstract

Graphite/epoxy composite laminates of T300/BP907 and AS6/HST-7 in layup orientations of [±35/0/90]^s and [±30²/90/¯9¯0]^s were axial tension fatigue tested. Tests were conducted at 5 and 10 Hz, and at loading ratios of R = 0.1 and R = 0.5. Edge delamination as a function of number of fatigue cycles was monitored by monitoring stiffness reduction during fatigue testing. Delamination was confirmed and documented using dye-enhanced X-ray and optical photography. Critical strain energy release rates were then calculated. The composites delaminated readily, with loading ratio having a significant influence. Frequency effects were negligible.