On the Theory of Surface Interactions

I use the term interaction as an abstraction that applies, for example, to force-interactions, torque-interactions, and heat-transfers.

If an interaction is a surface-interaction it can be characterized, under suitable conditions, by a contactor. In the case of force-interactions, torque-interactions, and heat-transfers, the contactor is the field of stress-tensors, couplestress-tensors, and heatflux-vectors, respectively.

The first to prove, making suitable assumptions, the existence of such a contactor was Cauchy in 1823, and there has been a large literature on this subject since then.