Numerical simulation of ultrasonic welding for CFRP using energy director

For ultrasonic welding of carbon fiber-reinforced plastics (CFRPs), a sharp shaped resin called the energy director (ED), is usually inserted between them. In this study, finite element analyses for ultrasonic welding of CFRPs were performed using a two-dimensional model. The effects of the shape of the ED on the temperature increase, deformation history, and dissipated energy behaviors are discussed. Flat and triangular ED shapes are considered. From the results, it is easier for a triangular ED to increase the temperature than for a flat ED, and hence, the consumed energy and time are less for a triangular ED than for a flat ED. However, in the triangular ED, the temperature is distributed significantly, that is, there is a very high temperature at some point and a very low temperature at other points. Thus, unexpected chemical reactions, such as oxidation, may occur. This study concludes that a triangular ED is not always better than a flat ED. In any case, it was found that an abrupt temperature increase was caused by a synergistic effect. That is, the increase in temperature causes the viscoelastic and frictional dissipated energy to be remarkable, and the increase in the dissipated energy increases the temperature.