Experimental analysis of interfacial pressures in crimped joint assemblies

Utilization of crimped joints is common in plastic parts and assemblies and, if improperly employed, can lead to fracture, loosening, stress cracking, etc., long before reaching design performance time. In order to examine the reliability of such assemblies, experimental methods based on mechanics of interference have been developed, analyzed and applied to the measurement of interfacial pressures in axial-symmetric assemblies of crimped fits consisting of plastic (or metal) insert, plastic tube and metal crimping ring. In the methods, strain gages were applied to the external ring followed by ring slicing or tube boring, and successfully characterized the circumferential stresses and normal stresses acting between the components. The details of the development of recovery strain during uncrimping were identified in each method (ring slicing and tube boring) and they are used to provide better understanding of the interfacial pressure measurement. Various correlations have been made with regard to degree of crimping, effect of relaxation and method of measurement. The technique can be applied to any type of crimped and interference fit system and is particularly useful for determining the interfacial pressures for assemblies already in use.