The Influence of Long Term Thermal and Mechanical Loads on the Young's Modulus of Cu-Alloys - Determination of Stress Relaxation in Electrical Connectors

Copper alloy metal strips are widely used to manufacture electrical connectors. These connectors experience stress relaxation during operation. The reduced contact force may lead to contact failure. For the given design of connectors, the contact force is proportional to the Young's modulus which depends on interatomic bonds, alloying elements and the microstructure of metal grains. According to the literature, it is assumed that Young's modulus does not change significantly during long-term mechanical stress and aging at temperatures below the recrystallization temperature of copper alloys. Based on this assumption, the relaxation of connectors from lifetime tests and from long-term used field vehicles can be determined by the comparison of spring deflection of connectors before and after long-term tests or long-term use. The focus of this paper is to answer the question, whether this assumption is accurate. For this purpose, the influence of long-term thermal and mechanical loads on the Young's modulus of various copper alloys is investigated. The temperature in test approximately matches the maximum design temperature of automotive connectors and the mechanical stress is comparable to that in a typical connector.