Bending instabilities of soft biological tissues

Rubber components and soft biological tissues are often subjected to large bending deformations while "in service". The circumferential line elements on the inner face of a bent block can contract up to a certain critical stretch ratio λ_cr (say) before bifurcation occurs and axial creases appear. For several models used to describe rubber, it is found that λ_cr = 0.56, allowing for a 44% contraction. For models used to describe arteries it is found, somewhat surprisingly, that the strain-stiffening effect promotes instability. For example, the models used for the artery of a seventy-year old human predict that λ_cr = 0.73, allowing only for a 27% contraction. Tensile experiments conducted on pig skin indicate that bending instabilities should occur even earlier there.