The contact surface as a function of load, elastic and plastic properties of the members

Abstract

For the fundamentals of the theory of elasticity, plasticity and hardness, insofar as they are needed for this book, we refer to Appendix I. A statement of principle is that the deformation which determines the load bearing area, A _b , usually is elastic up to pressure limits of the order of the hardness, which is defined as an average pressure in the ball indentation test under the condition that the specific depth² is > 0.02, and is called contact hardness in Appendix I. It would be incorrect to speak of a definite upper pressure limit for the elastic deformation, above which plastic yielding takes place, since, in reality, the decisive agent is a heterogeneous stress and not a hydrostatic pressure. Actually, the average pressure, at which plastic flow commences in a contact, depends on the initial shape of the contacting faces of the members. Therefore, general formulas for the dependence of the contact area on the load cannot be given. But instructive formulas can be deduced for representative cases, just as in § 4 resistance formulas for particular cases were formed, which provide the possibility for fairly general computations.