ISSN: 0884-6804
Page Count: 3

Preliminary Design of Cracked-Lap Shear Specimen Thickness for Determination of Interlaminar Fracture Toughness
Mangalgiri, PD
NRC research associate and senior research engineer, NASA Langer Research Center, NA

Johnson, WS
NRC research associate and senior research engineer, NASA Langer Research Center, NA

Abstract

This paper outlines a technique for preliminary sizing of the adherends for cracked-lap-shear specimen to assure delamination instead of adherend failure. The cracked-lap-shear specimen is a popular specimen used for determination of mixed mode interlaminar fracture toughness of composites. Thin adherends, on the order of three plies thick, have been used successfully in the past for determination of fracture toughness of rather brittle matrix systems. However, the tougher matrices now being considered for composite applications require thicker adherends in order to get composite delamination rather than adherend failure. The optimum thickness is obtained on the basis that the critical value of the strain energy release rate is reached at the delamination front before the ultimate strength is reached in the adherend. By proper design the specimen would delaminate and not use excessive material or load. A simple analysis for the optimum adherend thickness and experimental verification are included.

Keywords:
polymers, fracture toughness, aerospace industry, thickness

Paper ID: CTR10323J
DOI: 10.1520/CTR10323J
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