Further comments on J-shaped stress-strain curves and the crack resistance of biological materials

The assertion by Kendall and Fuller (1987) that biological materials with J-shaped stress-strain curves are not necessarily more difficult to tear than Hookean solids, as suggested by Gordon (1978) is re-examined. While it is true that under certain conditions cracking is easier in materials with J-shaped stress-strain curves, the authors show that these conditions are not at all representative of biological materials. Gordon’s hypothesis remains true, therefore, that biological materials are difficult to break because of their lack of shear stiffness.