Damage Monitoring of Ultrasonically Welded Aluminum / CFRP-Joints during Cyclic Loading via Electrical Resistance Measurements

摘要

Aluminum alloys and carbon fiber reinforced polymers (CFRP) are two important materials for lightweight design and the combination of these dissimilar materials becomes increasingly important. Recent investigations have shown that ultrasonic metal welding is a well suited process to realize aluminum/CFRP-joints.The ultrasonic shear oscillation parallel to the welding zone with a simultaneous welding force perpendicular to the aluminum/CFRP-sheets melts the polymer matrix and squeezes the polymer matrix out of the welding zone. This allows a direct contact between the carbon fibers and the aluminum. Beside mono-tonic properties the cyclic deformation behavior of these ultrasonically welded aluminum/CFRP-joints is essential. Therefore in addition to monotonic shear load tests, fatigue experiments with constant force amplitudes and load-increase-tests were performed on a servo hydraulic test system with a frequency of 5 Hz. The electrical conductivity between carbon fibers and the metal sheet was used to determine changes in the electrical resistance AR during cyclic loading.The investigations have proved that in comparison to the measurement of the displacement amplitude, the change of AR is much more reliable because of the direct response of the deformation process in the joint.