Stress-ratio effect on mode II propagation of interlaminar fatigue cracks in graphite/epoxy composites
- Nagoya Univ. (Japan). Dept. of Mechanical Engineering
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/{number_sign}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 = {minus}1.0, {minus}0.5, and 0.2. For each stress ratio, the crack propagation rate was given by a power function of the stress intensity range, {Delta}K{sub 11}, in the region of rates above 10{sup {minus}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, {Delta}K{sub 11th} = 1.8 MPa{radical}m. The crack propagation rate is determined by {Delta}K{sub 11} near the threshold, while by the maximum stress identity factor, K{sub 11max}, 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 micromechanism of Mode II fatigue crack propagation was discussed on the basis of the microscopic observations of fracture surfaces and near-crack-tip regions.
- OSTI ID:
- 566498
- Report Number(s):
- CONF-950569-; TRN: IM9805%%162
- Resource Relation:
- Conference: 6. ASTM symposium on composites: fatigue and fracture, Denver, CO (United States), 16-18 May 1995; Other Information: PBD: 1997; Related Information: Is Part Of Composite materials: Fatigue and fracture (sixth volume); Armanios, E.A. [ed.]; PB: 579 p.; ASTM special technical publication 1285
- Country of Publication:
- United States
- Language:
- English
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