SYMPOSIA PAPER Published: 01 January 1997

Stress-Ratio Effect on Mode II Propagation of Interlaminar Fatigue Cracks in Graphite/Epoxy Composites


The effect of the stress ratio on the propagation behavior of Mode II interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates, Toray T800H/#3631. End-notched flexure (ENF) specimens were used for fatigue tests under the stress ratios of R = 0.2, 0.5, and 0.6; and end-loaded split (ELS) specimens were used for tests under R = -1.0, -0.5, and 0.2. For each stress ratio, the crack propagation rate was given by a power function of the stress intensity range, ΔKII, in the region of rates above 10-9 m/cycle. Below this region, there exists the threshold for fatigue crack propagation. The threshold condition is given by a constant value of the stress intensity range, ΔKIIth = 1.8 MPa√m. The crack propagation rate is determined by ΔKII near the threshold, while by the maximum stress intensity factor, KIImax at high rates. A fracture mechanics equation is proposed for predicting the propagation rate of Mode II fatigue cracks under various stress ratios. The effect of the stress ratio on the micromechanisms of Mode II fatigue crack propagation was discussed on the basis of the microscopic observations of fracture surfaces and near-crack-tip regions.

Author Information

Tanaka, K
Nagoya University, Nagoya, Japan
Tanaka, H
Nagoya University, Nagoya, Japan
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Developed by Committee: D30
Pages: 126–142
DOI: 10.1520/STP19925S
ISBN-EB: 978-0-8031-5353-0
ISBN-13: 978-0-8031-2411-0