SEDL / STP / STP1156-EB / STP24749S

Effects of Stress Ratio on Edge Delamination Characteristics in Laminated Composites

Scrivner, GC
Graduate student, Material Science and Engineering, University of Texas at Arlington, Arlington, TX

Chan, WS
Associate professor, Center for Composite MaterialsUniversity of Texas at Arlington, Arlington, TX

Pages: 14    Published: Jan 1993

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Abstract

The effects of stress ratio on delamination onset behavior under cyclic loading was investigated in AS4/3502 [+/-25²/90]^s graphite/epoxy laminates. For the purpose of this study, delamination onset was defined as a delamination 5% of the laminate width. The resulting data showed definite changes in delamination behavior between stress ratios (R ratio) of 0.1 and 0.5.

For maximum amplitude stresses below about 80% of the static delamination stress, delamination onset occurred later at R = 0.5 than for R = 0.1. Also for the corresponding G^max, delamination growth rates at delamination onset were slower for R = 0.5 than for R = 0.1. This was reflected in changes of power law exponent from 10.2 for R = 0.1 to 31.6 for R = 0.5 and the constant from 1.10 × 10^-2 for R = 0.1 to 254 for R = 0.5.

Fractographic analysis suggested that the failure mode, which appeared to be predominantly Mode I, remained unchanged; however, the density of shallow hackles was greater for R = 0.1 than for R = 0.5. This presumably was due to a more rapid coalescence of microcracks which was consistent with the larger crack opening displacements for R = 0.1.