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An accurate estimate of interlaminar stresses is crucial to understanding as well as predicting many delamination-related failures in composite materials. A new model for ply-level sublaminate analysis is presented and applied. The homogeneous plate theory developed earlier by the authors is further refined, and the equations are reduced appropriately for the classical finite-width free-edge laminate elasticity problem and a related delamination crack growth problem. It is applied to the laminate on a ply-by-ply basis. This theory incorporates all the essential physical effects and appears to be an adequate model for predicting the behavior of individual layers in equilibrium. On the basis of the number of equations and boundary conditions required for the implementation of layer equilibrium, this theory also appears to be the simplest of its kind presented so far. The stress induced in the free-edge region of a (0,90,90,0) laminate in uniform extension and the energy release rates for the delamination between the −30° and 90° plies of a (±30,±30,90,90)s laminate are computed using the new analysis. The results are in excellent agreement with the existing numerical solutions. The new ply behavioral model appears to be very promising; it yields stresses and displacements that are statically and kinematically compatible at interlaminar surfaces.
interlaminar stresses, interlaminar fracture, composite materials, strain energy release rate, sublaminate analysis
NRC Research Associate, NASA Lewis Research Center, Cleveland, OH
Professor, School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA