Measurement and calculation of the decreasing joint force in high current aluminum joints

This work deals with the results of theoretical and experimental studies on the decrease of joint force by creep of the conductor material. The development of joint force in high current aluminum joints of electric power application is measured in long-term experiments. The experiments are carried out at different joint temperatures and for different joint geometries with and without disc spring washers or retightening. Moreover, the joint resistance is measured throughout the experiments. Based on the fundamentals of solid state physics the decrease of joint force is calculated by means of finite elements. For this purpose, the creep behaviour of the aluminum alloys used for the joints is studied in additional load and temperature change tests in a fatigue test system. Within the range of the uncertainty of the measured creep parameters a good fit between the results of calculation and the measured development of joint force is achieved. Therefore, the calculation of the development of joint force provides the advantageous ability to evaluate the long-term performance of the joint force up to the aspired life time of electrical apparatus in power application of 30 or 40 years.