A simple relationship with a rational basis has been found to connect stress with strain for a series of homogeneous compression curves published by Cook and Larke. At large deformations each of the curves becomes asymptotic to a definite stress, and the difference between this final stress and the threshold stress at which plastic deformation begins to become appreciable may therefore be regarded as the total stress capacity of the material. Similarly, the difference between any particular applied stress and that which is finally attained is the stress capacity remaining available after the application of the stress in question. Defining the plastic modulus, comparable with the elastic modulus, as the rate of change of stress with respect to true (logarithmic) strain, it is shown that the plastic modulus at any instant is proportional to the available stress capacity.

The same relationship appears to hold for tension as well as for compression as long as the deformation remains homogeneous. For example, it seems to be true up to the incidence of necking in the tensile test, and even beyond it in special circumstances which are described.

While this relationship cannot be regarded as established, it is tentatively put forward and discussed with illustrative examples in the hope of stimulating further research.