An isotropic pressure-dependent yield criterion for polymers, of the form f = A(σ 1 + σ 2 + σ 3) + B[(σ 2 - σ 3)2 + (σ 3 - σ 1)2 + (σ 1 - σ 2)2]1/2 = 1, has been proposed.
A. Evaluate A and B in terms of T and C. Here T is the yield strength in tension and C is the absolute magnitude of the compressive strength. Consider a 1-direction tension test in which σ 1 = T, σ 2 = σ 3 = 0 at yielding and a 1-direction compression test in which σ 3 = C, σ 2 = σ 3 = 0 at yielding.
B. Use the ?ow rule dεij = dλ(∂f/∂σ ij) to evaluate the relative volume change on yielding. Express dδ/dε1 as a function of T/C. Here dδ = dv/v = dε1 + dε2 + dε3 is the volume strain.