3. For an ideal rubber,
(1) derive the rubber elasticity equations of stress versus extension ratio for a biaxial stress, i.e., find σx(λx,λy) and σy(λx,λy).
(2) If elastic modulus E (in uniaxial deformation) is 10.0 MPa, what are the stresses, σx and σy, required to deform the rubber to λx=2, λy=1/2?