Abstract

Upstone and Ward have shown that, in the region of strains below 2%, shoe upper leathers frequently have a low elastic modulus, which is much smaller than that for greater extensions. This is likely to be advantageous, because it permits a shoe to take up the shape of the foot without undue pressure, and yet resist deformations large enough to cause unsightliness and loss of shape. Experiments show that the shape of the stress/strain curve is frequently (and perhaps always) due to stresses in different layers of an unstrained leather, the grain layer being usually in tension when the leather is flat, and the corium and flesh in compression. Any leather strip which does not have this characteristic can be given it by suitable heat ‘setting’, such that an unstressed flat strip of the leather is left with its grain permanently in tension. Whether the ‘steps’ of the stress/strain curves are sufficiently large to be of practical importance is not clear. It is possible that heat setting during shoe making relaxes any differential stresses otherwise present, and that the steps consequently disappear in the made up shoe.