Joint resistance depending on joint force of high current aluminum joints

Abstract

This work deals with the results of theoretical and experimental studies on the relationship between the joint resistance of high current aluminum joints and their decreasing joint force by creep of the conductor material. The joint resistance of aluminum busbar joints with machined and with randomly rough joint surfaces is measured depending on joint force. In the case of joints with machined joint surfaces the plastic deformation on the joint surface after releasing the joints is ascertained by optical microscopy. It is assumed that the plastically deformed portion of the joint surface equals the area of a-spots. Thus the number and the mean radius of the a-spots and the distance between them are determined. Holm's and Greenwood's formulas for multi-spot-contacts are used to calculate the joint resistance. In the case of joints with randomly rough joint surfaces the surface profile is measured by means of a laser profilometer. The rough surfaces are described by model-surfaces with spherical summits. The elastic and plastic deformation of load-bearing summits is calculated by means of the finite element method (FEM). The number and the load-bearing area of the summits under an increasing and afterwards decreasing normal force (tightening and releasing) is determined. Furthermore it is assumed, that the load bearing area equals the area of a-spots. Holm's formulas for multi-spot contacts and Greenwood's theory of the mechanical contact of randomly rough surfaces are used to calculate the joint resistance depending on an increasing and afterwards decreasing joint force. The results of calculation are compared to those of the measurements.