Cross ply laminates of (02,902)s configuration having AS4 graphite fibers in three epoxy resins of different toughness: 3501-6, Tactix® 556 and Tactix® 695, have been tested to determine their transverse cracking behavior and the associated mechanical response under longitudinal tensile loading. The test data are analyzed using Talreja's con tinuum damage model [1-3]. The material constants needed in the model to predict the in- plane stiffness changes are determined. The measured Poisson's ratio, which shows signifi cant change, is compared with the prediction of the model. The constants for the three materials are found to increase with the increase in their fracture toughness.

Transverse ply cracking of five toughened and untoughened graphite/epoxy and graphite/polycyanate laminates was studied using crossply laminates. Two different theoretical approaches, variational mechanics and resistance curves based on shearlag approximation, were used to analyze the data. Resistance of the laminates to transverse ply cracking was determined. Both theories show the same ranking of the laminates with respect to their resistance to microcracking. These results were compared with the critical strain energy release rate data obtained on the resins and the laminates.