The tendency for free-edge delamination in laminates and its minimization

The laminate free-edge effect may have a detrimental impact on the effective strength of composite laminates. The reason for this is the occurrence of high interlaminar stresses in the immediate vicinity of free edges which are not taken into acccount by the classical theory of thin laminates. The present paper is devoted to a systematic reduction of the free-edge delamination tendency by structural optimization methods where different approaches are used for the assessment of the delamination tendency. In addition to considering the effective delamination moments as a result of the classical laminate theory, the free-edge stresses are calculated by the finite-element method and by a closed-form analytical approach. Furthermore an energy release criterion is used.