Question

The strain-energy function for an ideal rubber is
U=C1(λ12+λ22+λ32-3).
Where, λ1, λ2, λ3, are the principle extension ratios. If a piece of such a rubber is initially 1 m long and 1 m wide, find the stress required to give a extended 2m length and 2m width by applying for an equal two-dimensional stretching (biaxial stretching). C1 is 4X10^5 Pa.

Answer 1