4. Glass fiber reinforced polymer composites have a very high toughness relative to their constituents. Take a glass fiber composite with 12m diameter fibers, a fiber volume fraction V = 60% and stiffness of the fiber and matrix of E = 75 GPa and Em = 3.2 GPa respectively. It is found through a fiber pushout test that the interfacial shear strength between the fiber and epoxy is t = 50 MPa. Plot the energy dissipated during fracture from fiber pullout (Gcp) as a function of pullout aspect ratio from s = 1 - 60. If the toughness of the composite was found to be G = 100 kJ/m, what do you expect the average pullout length to be? What is the fracture toughness (KI) of the composite? (20 points)