Evolution of interfacial contact during low pressure rotary friction welding: A finite element analysis

Abstract

Development of rotary friction welding (RFW) is of critical importance for extending the RFW technology to join large-scale structures, such as rods/pipes for generator rotors and nuclear power plants. In this paper, finite element (FE) analysis is employed to analyze the thermal-mechanical process during low-pressure rotary friction welding (RFW), and the dynamic evolution process of interface contact is illustrated. Low-pressure RFW process of D50Re steel rod with a diameter of 100 mm is investigated by using the fully coupled thermal-mechanical FE analysis. In the analysis process, the two work pieces are regarded as two contacting entities, and a new method based on equivalent thermal expansion (TE) coefficient is proposed in order to study the dynamic contact behavior during low-pressure RFW. Three simulation cases, which consider no TE, real TE coefficient and equivalent TE coefficient respectively, are performed. It is shown from the comparison between the simulation results and the experimental data that, the equivalent TE coefficient is viable approach in the FE analysis to improve the prediction on the axial shortening and the welding torque. It was demonstrated that significant incomplete interfacial contact occurs during the friction stage in low-pressure RFW. The formation and expansion of the contact zone is in a thermo-mechanical fully coupled manner. Since the temperature is not uniform across the friction interface, the contact area is first formed in the high temperature area, and the expansion of the contact area occurs subsequently. When the temperature at the interface is uniform, almost full contact would be achieved over the friction interface. The modeling and simulation method proposed in this paper is helpful for understanding the underlying physical phenomenon during RFW process. If experimental tests can be extended to determine the equivalent TE coefficient, the accuracy and the reliability of the proposed simulation method in this paper will be further improved.