Determination of the Frequency- and Temperature-Dependent Stiffness and Damping Properties of Thermoplastics for the Prediction of the Vibration and Heating Behaviour During Ultrasonic Welding

The precise and realistic simulation of the vibration and heating behaviour of thermoplastics in the ultrasonic welding process has so far been associated with great challenges. In particular, the determination of the required frequency- and temperature-dependent mechanical stiffness and damping properties in the high-frequency vibration range is only insufficiently possible according to the current state of the art, which prevents an early and valid numerical prediction of the weldability in the development process of new joining components. In order to provide more precise input data (storage and loss modulus) for describing the material behaviour of thermoplastics in the ultrasonic welding process in the future, a novel measurement concept was implemented that is based on the adaptation of simulation results to real structure-borne sound measurements. The test rig concept was successfully commissioned and calibrated at room temperature and the calculation routine for material data determination was implemented. On the basis of the generated material data, an increase in the prediction quality of the vibration behaviour in a frequency range of 1 Hz to 22.5 kHz of rectangular specimens at room temperature could already be achieved compared to the state of the art using dynamic mechanical analysis and a time–temperature shift approach. Measurements at different ambient temperatures up to 60 °C were also carried out. Although the prediction quality of the vibration behaviour was slightly improved at 60 °C, there is still a need for optimisation with regard to the test specimen geometry and the further development of the evaluation routine in order to increase the analysable temperature range on the one hand and the quality of the generated material data on the other.