Systematic studies were conducted to investigate the effect of the introduc tion of a soft thermoset adhesive layer at appropriate interface to the interlaminar fracture and intralaminar fracture of the BMI matrix based composite laminates. Tests include DCB and ENF tests for measuring interlaminar fracture toughnesses, quasi static tension test on the crossply laminates and edge delamination test for measuring matrix crack initi ation, edge delamination onset, mixed-mode interlaminar fracture toughness and the ulti mate laminate strength. The improvements of the interlaminar fracture toughnesses of the GFRP and CFRP laminates are significant. An elastic foundation beam model is intro duced to analyze the interleaved DCB specimen. Results show stress concentration at the crack-tip of the interleaved DCB specimen is reduced. Besides the factor of the possible formed plastic zone in interleaf, the modified interlaminar bond strength of the adhesive/ composites interface may lead to higher interlaminar fracture toughness. The edge delamination strength and the mixed-mode interlaminar fracture toughness in interleaved laminate are raised significantly. However, the interleaf has no significant effect on the laminate strength because the interfacial interleaf only improves the interlaminar fracture feature while the final laminate fracture is controlled by the intralaminar properties of the lamina. On the matrix cracking in interleaved laminate, both the matrix crack growth rate and its final saturation crack density decrease in the interleaved multidirectional laminate. The matrix crack was found to initiate early in the interleaved crossply laminate. This*Author to whom correspondence should be addressed Journal of REINFORCED PLASTICS AND COMPOSITES, Vol. 13-June 1994 0731-6844/94/06 0509-32 $6.00/0 @ 1994 Technomic Publishing Co., Inc.result agrees with the analysis of the one-dimensional shear-lag model. But in the edge delamination specimen, matrix crack initiation is raised by the interleaf.
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