(a) Define what a composite material is and list any TWO advantages (in terms of properties) of polymer composites over metals such as steel and aluminum. (4 marks) (b) The development of polymer composite materials has led to significant improvements in properties such as strength, stiffness and toughness. Explain how a fiber reinforced polymer (e.g., CFRP or GFRP) results in higher strength and stiffness compared to the polymer matrix and higher fracture toughness compared to both the polymer matrix and fiber reinforcement phases. (5 marks) (c) A unidirectional fiber reinforced polymer composite is made from materials having the following properties: Ef=100GPa, Gf=300MPa, Em = 5GPa, om = 30MPa. (i) Under isostress condition, the elastic modulus of the composite perpendicular to the fiber axis is 7GPa. Determine the volume fraction of the fibers in the composite. (3 marks) (ii) Under isostrain condition, the composite is designed to elastically resist a tensile stress (oc) of 70MPa along the fiber axis. The corresponding strain is 0.003. What should be the fiber volume fraction? (6 marks) (d) The average density of a carbon-fiber-epoxy composite is 1.615g/cm. The density of the epoxy resin is 1.21g/cm and that of the carbon fibers is 1.74g/cm. The tensile modulus of elasticity of the carbon fiber and epoxy matrix is 189GPa and 3.7GPa respectively. (i) What is the volume percentage of carbon fibers in the composite? (4 marks) (ii) Calculate the tensile modulus of elasticity of the composite if it is stressed under isostrain condition. (3 marks)