Measurement of Thermoplastic Dynamic Modulus using an Ultrasonic Welding System

This paper reports the preliminary results of a newly developed method for measuring dynamic modulus of thermoplastic materials at a given ultrasonic frequency. In the method, a material specimen is squeezed at the tip of the horn of a conventional ultrasonic welding machine. The mechanical impedance of the material specimen under loading is then deduced by processing the input electrical impedance of the ultrasonic welding machine. The mechanical properties of tested material can then be derived from the mechanical impedance. Analyzing the obtained output impedance will then provide the mechanical impedance of the tested material at the tip of the horn. Experimental results for both PP (Polypropylene) and PC (Polycarbonate) will be presented in the paper. Since the ultrasonic welding machine operates at a single frequency, the resulted dynamic modulus varies as a function of temperature.