Answer Happy

Question 4 Chopped hemp fibre reinforced polyester with 55% volume fraction of fibres: hemp fiber radius is 7.2 x 102 mm • an average fiber length of 8.3 mm • fiber fracture strength of 2.8 GPa • matrix stress at the composite failure of 5.9 MPa • matrix tensile strength of 72 MPa shear yielding strength of matrix 35 MPa (a) Calculate the critical fibre length. (6 marks) (b) With the aid of graph for stress vs. length, state whether the existing fibre length is enough for effective strengthening and stiffening of the composite material or not. (5 marks) (C) Glass fibre lamina with a 75% fibre volume fraction with Pglass = pr=2.5 gcm', v=0.2, Vm = 0.3, Pepoxy = Pm= 1.35 gem?, E= 70 GPa and Em= 3.6 GPa. Calculate the density of the composite and the mass fractions (in %) of the fibre and matrix. (14 marks)