SHEAR STIFFNESS OF A SOLID-SOLID MULTICONTACT INTERFACE

The macroscopic multicontact interface between two rough nominally fla t surfaces is a common object whose physics is only partly understood. This paper is aimed at giving experimental evidence for the linear el astic response of a multicontact interface to a moderate shear force, i.e. below the threshold for incipient sliding. Non-intuitive properti es of the interfacial shear stiffness are exhibited, in the spirit of macroscopic friction laws, which should be of practical interest when evaluating the performances of a built-up system. These are explained qualitively within the random surface framework prevailing in multicon tact mechanics, and a numerical treatment of the three-dimensional pro file of a real rough surface is proposed, which enables a direct quant itative simulation of the elastic stiffness. This is found to be compa tible with experimental data on a polymer glass and an aluminium alloy . The sensitivity of interfacial stiffness measurements is discussed, and illustrated by the experimental evidence of the plastic deformatio n of aluminium alloy asperities under light nominal pressure. This emp hasizes the need for an elastoplastic description of asperity deformat ion within a multicontact interface.