Interface in mechanically fastened steel joint, studied by contact electrical resistance measurement

A steel-to-steel joint obtained by mechanical fastening at a compressive stress of 7% (or less) of the yield strength was found to exhibit irreversible changes in the contact electrical resistance upon repeated fastening (loading) and unfastening (unloading). These changes occurred even after many cycles of fastening and unfastening, although the changes were more severe during the initial few cycles. They were primarily due to plastic deformation at asperities.