(Received 18 May 2000; accepted 31 October 2000)
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In the present paper, the effect of a skew insert in a double-cantilever beam specimen in evaluating Mode I delamination fracture energy (GIc) of unidirectional laminated composites is investigated numerically. A delamination growth analysis incorporating the finite element method is utilized to calculate variation of load-displacement-delamination length for a prescribed GIc as delamination propagates along the specimen. In order to evaluate the values of GIc as a function of delamination length, the calculated data were treated as experimental data and processed using two ASTM standard test data reduction methods. These are the modified beam theory and the compliance calibration methods.
It is found that the skew front moves progressively to form a thumb-nail curved front during a few millimeters of growth. Part of this growth occurs within the specimen, not visible from the specimen edges where the delamination lengths were recorded during a test. It also is found that the difference between delamination lengths measured at each side of the specimen can have a significant effect on the calculated GIc. To eliminate this error in an actual test, it is suggested that the larger delamination length be used for data processing.
Assistant professor of aerospace structures, Air University of Shahid Sattari, Tehran,
Associate professor of mechanical engineering, Tehran University, Tehran,
Stock #: JTE12246J