Optimization of the ultrasonic welding of PEEK-Carbon composites

The ultrasonic welding of PEEK-carbon composites was studied in order to better understand the process and determine the optimum welding conditions. The parameters varied were the applied pressure and the welding time. The optimum applied pressure at the hem-sample interface was found to be 3.8 MPa. The joint properties were evaluated through fracture tests in both Mode I (opening) and Mode II (shear). It was found that the optimum welding time depends very much on the physical configuration of the specimen being welded; this affects the efficiency of conversion of the ultrasound into thermal energy in the composite. However, for both types of specimen tested (Mode I and Mode II) the optimum joint strength was found to correspond to a specific value of total energy input, namely 6.8 J/mm(2). This gave critical strain energy release rates of G(Ic) = 3.2 kJ/m(2) and G(IIc) = 4.6 kJ/m(2). A variation of the energy by 10% in either direction resulted in a decrease in properties by about half. Hence the weld energy can be used as a reliable control parameter to produce joints with strengths equivalent to those of molded composite.