In this paper, effects of ply orientation of adjacent plies with (ϕ//θ) interfaces on mode II critical strain energy release rate (fracture toughness) of multidirectional (MD) laminate has been studied. Ply orientation of adjacent plies is one of the most important parameters affects the mode II critical strain energy release rate () in the initiation of the delamination. To study this parameter, End Notch Flexure (ENF) specimen has been used for measuring of laminated composites. Eventually, the purpose is to predict of of MD composite specimen, without direct experimental tests and finite element modeling using the results of unidirectional (UD) ply. First, of unidirectional composites will be studied and by the results obtained, the behavior of multidirectional laminated composites is predicted. In this context, a comprehensive method was proposed that combines prediction methods, and analytical modeling. The obtainedof multidirectional laminated composites with (ϕ//θ) interfaces can be used for design purposes. Results obtained using this method has been compared with the results of numerical and theoretical methods. This prediction method reduces the calculation costs of FE and analytical models, and also the costs of experiments significantly. تفاصيل المقالة