Damage Monitoring of Ultrasonically Welded Aluminum/ CFRP-Joints by Electrical Resistance Measurements

Ultrasonic metal welding is well suited to realize aluminum alloy/carbon fiber reinforced polymer (CFRP) – joints. Beside monotonic properties the cyclic deformation behavior of ultrasonic welded aluminum/CFRP-joints was inves-tigated. Load increase as well as constant amplitude tests were performed with a servohydraulic testing system at a frequency of 5 Hz. The joints are realized by temperature induced softening and mechanical replacing the polymer out of the welding zone as a result of the ultrasonic shear oscillation. In contrast to conventional joining procedures this is the pre-condition, which allows a direct contact between the carbon fibers and the aluminum. By the fact that the carbon fibers are welded directly onto the aluminum it is possible to use the hybrid welds as their own fatigue damage sensors. Therefore additional to standard mechanical data, the change in the electrical resistance ΔR is moni-tored during the fatigue tests and used to describe the actual fatigue status in detail. The evaluation of the fatigue results shows that the change in ΔR is much more reliable than the change in the displacement amplitude measured by strain gauges mounted on the surface of the Al- and CFRP-sheets because of the direct response out of the joining zone itself. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11