Composites

Question 1

Max E value

Answer 1

E = E1V1 + E2V2, Uniform strain

Question 2

Min E value

Answer 2

1/E = V1/E1 + V2/E2, Uniform Stress

Question 3

Cross - Ply malinate E values

Answer 3

Eo = xE(para) + (1-x)E(perp)
E90 = xEperp + (1-x)E(para)

Question 4

Strength of a UD ply

Answer 4

sigmapara = sigmaf x Vf + sigma’m x Vm

Question 5

Strength of a cross ply laminate

Answer 5

sigma(o) = xsigma*para
sigma(90) = (1-x)sigma*para

Question 6

Fatigue of composites

Answer 6

Cracks form in the plies that are transverse to the loading direction
These cracks multiply, eventually spreading to the perpendicular direction
This results in a multiplying of cracks and a small reduction in the youngs modulus
Eventually, large delaminations form parallel to the plies, so compressive strength is lost, and fails in a catastrophic brittle manner.