4 Find the local stresses at the top of the 60° ply in a [90/-30/60] graphite/epoxy laminate subjected to a bending moment of My = 60 N-m/m. Each lamina thickness is 0.125 mm. What is the percentage of the bending moment load taken by each of the three plies? The properties of graphite/epoxy are given in Table 2.1. TABLE 2.1 Typical Mechanical Properties of a Unidirectional Lamina (SI System of Units) Glass/ Boron/ Property Symbol Units epoxy epoxy Graphite/ epoxy Fiber volume fraction V 0.45 0.50 0.70 Longitudinal elastic modulus E₁ GPa 38.6 204 181 Transverse elastic modulus E₁₂ GPa 8.27 18.50 10.30 Major Poisson's ratio V12 0.26 0.23 0.28 Shear modulus G₁₂ GPa 4.14 5.59 7.17 Ultimate longitudinal tensile (σ) MPa 1062 1260 1500 strength Ultimate longitudinal (σi) MPa 610 2500 1500 compressive strength Ultimate transverse tensile (σ) MPa 31 61 strength Ultimate transverse (σ9) MPa 118 202 compressive strength Ultimate in-plane shear (112) MPa 72 ཙ ི 40 246 67 68 strength Longitudinal coefficient of thermal expansion α μm/m/°C 98 8.6 6.1 0.02 Transverse coefficient of μm/m/°C 22.1 30.3 22.5 thermal expansion Longitudinal coefficient of B₁ m/m/kg/kg 0.00 0.00 0.00 moisture expansion Transverse coefficient of B₂ m/m/kg/kg 0.60 0.60 0.60 moisture expansion Source: Tsai, S.W. and Hahn, H.T., Introduction to Composite Materials, CRC Press, Boca Raton, FL, Table 1.7, p. 19; Table 7.1, p. 292; Table 8.3, p. 344. Reprinted with permission. 14