Design of a Single Stress-Relaxation Test for Pressure Connections

Pressure connections, for example, solderless wrap, sprit beam type, etc., have a common design principle of maintaining a high pressure at the interface of the wire and the terminal. Because of the creep characteristics of all materials, such connections can lose their pressure sustaining ability with time and temperature. Considering the long expected life of a connection, usually 40 years, and the ever in· creasing operating temperatures, made necessary by miniaturization of telephone equipment, the loss of force in a connection may become exceedingiy large and may make the connection vulnerable to mechanical disturbances and attacks from the pollutants in the environment. A method of extrapolating force loss at the contact interface from short-term data to long-term expectation is discussed. Based on the concept of thermally activated processes, an accelerated stress-relaxation test is designed that would cause the expected service rife relaxation to occur in a shorter period. Finally, it is shown that, to simulate a given service condition for all alloys of a common base metal, it is possible to choose a metal system among them that will yield a severe test condition for all alloys in that group. For example, it is shown that the 118°C-33 day stress-relaxation test used for simulating service conditions of 57°C for 40 years of copper C102 (OF copper) would induce as much or more relaxation than would occur in 40 years at 57°C in any copper-based alloy used as a spring material.