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The fracture behavior of quasi-brittle material exhibits commonly brittle behavior with some ductility in the fracture processing zone. Therefore, a matrix of experimental works is performed to investigate the failure behaviors based on a parameter known as brittleness number, which is a measure of brittle behaviors. Glass fiber-reinforced epoxy laminates of three stacking sequences, cross-ply [0/90]2s and two quasi-isotropic [0/45/90]2s and [0/45/90/-45]s, are manufactured using hand lay-up technique. A matrix of different specimen geometric scaling with open hole of the same material is used. The fracture energy GIC and nominal strength of these composite laminates are measured experimentally using compact tension test, center crack specimen, and tension test, respectively. The results showed that the increase of homogeneity of composite laminates, which is introduced by inserting a certain angle ply for the laminate structure, enhanced the material ductility as the brittle number increased. The larger size of specimen leads to the increase of brittleness for the same stacking sequences due to the increase of stress concentration factor.

The prediction of nominal strength is very important in the design and evaluation of materials especially polymer matrix composites. Various cohesive laws forms are successfully used in predicting the nominal strength of laminated composite structures. For composite structures, fracture toughness is dominated parameter when using cohesive laws to predict their nominal strength. In spite of complex reported models, this study propose an easy simple model to predict the fracture toughness of multidirectional composite laminates using the fracture toughness of the 08 ply ones. This model is mainly based on the geometry of fiber orientation and linear elastic fracture mechanics and uses the fracture toughness of the 08 ply obtained from compact tension test specimens. A good prediction is obtained by comparing the model results with experimental data which are obtained from center-cracked specimens manufactured using different lay-ups orientations and materials.

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A bilinear cohesive law analyzes the in-plane nominal strength of Quasi-brittle material containing a single hole in which damage around the open hole is represented by a line crack loaded on its faces. This analysis of quasi-brittle structures has been done by taking into account the geometry and length of fracture processing zone and the shape of the cohesive law. The nominal strength based on size effect is analyzed for similarly shape specimen geometry. Simple design tables for the bilinear cohesive law have been developed respect to the specimen types offering a very useful for engineering designers.