Fracture Simulation of Electrofusion Joining.

Abstract: This Master thesis investigates mechanical failures of electrofusion joints. This type of joints are used for weld high density polyethylene pipe systems where tting and pipe will be welded together by the heat caused by the resistance of the copper cables to electric current. There have been some failures where a brittle crack has grown through the fusion zone. Polyethylene as a material has a ductile character but brittle behavior occurs due to an unsuccessful welding by a poor fusion interface. In this study, we have chosen to investigate the plausible load cases that can cause the failure and studied the e ect of the geometry of the tting on the fracture toughness of the welded structure. We used the nite element method numerical analysis. We have approached unsuccessful welding (brittle) with a linear model and non-linear (CZM) model and successful welding (ductile) with a non-linear XFEM model. The material parameters needed for these models are gathered by series of experiments. The results shows that the inside pressure is the critical load case. The linear model and CZM model are consistent in terms of predicted responses to the geometrical parameters for the unsuccessful welding. Decreasing the inner cold zone length, increasing the fusion length and the thickness of the tting will improve the fracture toughness of the welded structure.