Fatigue fracture initiation in notched graphite--epoxy specimens
An experimental program on fatigue of doubly notched (0/-60/+60)/sub s/ graphite-epoxy specimens was performed which had two major objectives: (1) To adapt a photomicrographic technique, previously developed for detecting fatigue crack initiation in metals, for use with composite materials; (2) to demonstrate the use of the technique in an exploratory fatigue program. Examination of enlarged images of photomicrographs, automatically exposed at periodic interval during the tests, revealed that fatigue cracks developed early in the test. It was also evident that the test material had many manufacturing irregularities such as non-uniform ply-thicknesses and fiber distribution, incomplete ply bonding, and random voids. Two fatigue specimens sustained 10 Kc of high level cyclic loading and had a residual strength of approximately the static value; a third specimen fractured on cycle 1 at 75% of the static strength. The inconsistent fatigue behavior may be due to the observed random distribution of manufacturing irregularities.
- Research Organization:
- Army Materials and Mechanics Research Center, Watertown, MA
- OSTI ID:
- 7212189
- Journal Information:
- J. Compos. Mater.; (United States), Journal Name: J. Compos. Mater.; (United States) Vol. 11; ISSN JCOMB
- Country of Publication:
- United States
- Language:
- English
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