A randomly oriented, shorter-fibre-reinforced composite plate having a central through- thickness crack of length 2a is subjected to a uniaxial stress , as shown in figure 1. The composite has a fracture toughness Kic = 45 MPa-m1/2 and a critical crack size ac = 15mm. 2.1 2.2 Determine the critical stress that will cause crack growth. (5) Determine the strain energy released by the crack, if the composite plate material has an elastic modulus of 30 GPa and a plate thickness t = 2 cm. (5) 2a. 0 Figure 1