Question

Consider a unidirectional Kevlar/Epoxy lamina. The stiffness in the fiber direction must be at least 70 GPa, and the stiffness perpendicular to the fibers must be at least 10 GPa. The modulus of the Kevlar fibers is 124 GPa, and Poisson ratio is 0.35. The modulus of the Epoxy is 3.5 GPa and Poisson ratio is 0.33. You may use the 4 design equations from Lesson 6, Slide 17. a) Write 2 simple equations that define the 2 requirements you must meet. For example, for a made-up property x, you may say x=5, or x< 1. (2 points)

Answer 1

The mentioned equations are not given the question, hence the problem is completely solved.

Ef = 12uapa V = 0.35 Em-3,5 GPA Vm = 0.33 E = TOGPA E = 10opa By rule of mixtures: E, = Ef uft Emvm. ve volume Vm= 1- Vf fraction. 3,5 70 = 12u ut l-Uf) and um O 124 23.5 From ① and ② For condition : vt = 0.5518 (minimum) Uf = 0.6688 (minimum) © hence, U = 0.6688 (it satisfies both condition)