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

A polymer-polymer joint obtained by mechanical fastening at a compressive stress of 5% (or less) of the 1% offset yield strength of the polymer (nylon-6) was found to exhibit irreversible decrease in the contact electrical resistance upon repeated fastening (loading) and unfastening (unloading). The decrease occurred after up to 10 cycles of fastening and unfastening, although the decrease diminished with cycling. It is primarily due to local plastic deformation of the matrix. Moreover, the stress required for the resistance to reach its minimum in a cycle decreased with cycling, owing to softening of the matrix.