Stress relaxation in beryllium copper contacts: 115°C testing and FEM prediction

Multilam contacts used in high-current plug-in connectors are made from age-hardened CuBe2 (C17200), combining high strength, spring properties and conductivity. The study combined long-term ageing tests with finite element modelling to relate stress relaxation to long-term connector performance.

Samples were compressed to a nominal gap between two bolted pressure plates and aged at 90°C and 115°C, using either an oven or current heating, while contact resistance and residual contact force were measured. At 115°C, force per lamella fell to 50% of initial after 10,100 hours in the oven and to 70% after 8,200 hours with current heating.

Contact resistance did not deteriorate with falling force and stayed close to initial values, indicating limited electrical impact as long as the contact area does not separate. SEM showed no significant change in precipitates or grain size after ageing, so the loss stems from recovery rather than microstructure change, allowing power-law creep parameters to predict behaviour up to 180°C.