Masahiro Kusaka

This paper describes an analysis method of the friction torque and weld interface temperature during the friction process for steel friction welding. The joining mechanism model of the friction welding for the wear and seizure stages was constructed from the actual joining phenomena that were obtained by the experiment. The non-steady two-dimensional heat transfer analysis for the friction process was carried out by calculation with FEM code ANSYS. The contact pressure, heat generation quantity, and friction torque during the wear stage were calculated using the coefficient of friction, which was considered as the constant value. The thermal stress was included in the contact pressure. On the other hand, those values during the seizure stage were calculated by introducing the coefficient of seizure, which depended on the seizure temperature. The relationship between the seizure temperature and the relative speed at the weld interface in the seizure stage was determined using the experimental results. In addition, the contact pressure and heat generation quantity, which depended on the relative speed of the weld interface, were solved by taking the friction pressure, the relative speed and the yield strength of the base material into the computational conditions. The calculated friction torque and weld interface temperatures of a low carbon steel joint were equal to the experimental results when friction pressures were 30 and 90 MPa, friction speed was 27.5 s^-1, and weld interface diameter was 12 mm. The calculation results of the initial peak torque and the elapsed time for initial peak torque were also equal to the experimental results under the same conditions. Furthermore, the calculation results of the initial peak torque and the elapsed time for initial peak torque at various friction pressures were equal to the experimental results.

The joining phenomena during the friction process of pure titanium (Ti) and pure copper (OFC) friction welding was investigated. When the joint was made at a friction pressure of 60MPa or lower, the OFC side was deformed from both weld faying surfaces contacting. Then, the joint generated the sparkle from the Ti side with increasing friction time. The peripheral portion of the Ti side was heavily deformed and intensely upset when it had the sparkle. On the other hand, the joint did not have the sparkle of the Ti side when it was made at a friction pressure of 75MPa or higher. The deformation of the OFC side was large and intensely upset. The fact that the joining phenomena had dissimilarity was due to the difference of the yield strength at the temperature in the friction process.

This paper describes the effect of the friction welding condition on the joining phenomena and tensile strength of friction welded joint between pure copper (OFC) and low carbon steel (LCS). When the joint was made at friction pressure of 30 MPa with friction speed of 27.5 s^-1, OFC transferred to the half radius region of the weld interface on the LCS side, and then transferred toward the entire weld interface. The temperatures at the centerline, half radius and periphery portions on the weld interface of the LCS side were almost the same after the initial peak. When the joint was made at a friction time of 2.4 s, i.e. the friction torque was close to the initial peak, that had obtained approximately 40% joint efficiency and fractured from the weld interface with a little OFC adhering to the weld interface on the LCS side. The joint efficiency increased with increasing forge pressure, and it reached approximately 80% at a forge pressure of 180 MPa. This joint fractured at the softened OFC region adjacent to the weld interface. On the other hand, OFC transferred to the peripheral region of the weld interface on the LCS side when the joint was made at friction pressure of 90 MPa with friction speed of 27.5 s^-1. However, OFC transfer was not obtained at the central region because the temperature at the periphery portion was higher than that of the other portions. The joint efficiency increased with increasing friction time, and it obtained approximately 74% at a friction time of 1.2 s. Moreover, all joints fractured between the OFC side and the weld interface, although the joints were made with higher forge pressure. To obtain higher joint efficiency and fracture in the OFC side, the joint should be made with low friction pressure and high forge pressure, and with the friction time at which the friction torque reaches the initial peak.

Solid particle erosion is affected by many factors such as the impact velocity, the impact angle, the particle size, mechanical properties of the particle and the target. The computer simulation is effective to clarify the erosion mechanism. However, the simulation of erosion is troublesome, because the local surface roughness continuously changes during the process. In this paper, the Extended Distinct Element Method (EDEM) was applied to simulate solid particle erosion. The EDEM is a kind of the mesh-less method and it seems to be effective to simulate a dynamic process like erosion by the EDEM By obtaining the numerical results, the effectiveness of the EDEM for solid particle erosion was examined. The influence of the impact angle of solid particles on erosion was also shown.

This paper describes the analysis method of friction torque and weld interface temperature during friction process by FEM. The joining model of the wear and seizure stages was constructed from the joining phenomena that were obtained by the experiment In actual analysis, the contact pressure into the weld interface, the quantity of heat generation, and the friction torque were calculated using the coefficient of friction, which was assumed as the constant value during the wear stage. The thennal stress was also included in the contact pressure. Those values were calculated by using the coefficient of seizure, which was depended by the seizure temperature during the seizure stage. The relationship between the seizure temperature and the relative speed of the weld interface in the seizure stage were detennined using the experimental results. Also, the contact pressure and the quantity of heat generation, which depended on the relative speed of the weld interface, were solved by using the conditions that were coupled with the friction pressure and the yield strength of the base material. The calculated friction torque and weld interface temperatures were in approximate agreement with the actual measured results when friction pressures were 30 and 90 MPa, a friction speed was 27.5 s^<-1>, and a weld interface diameter was 12 mm for low carbon steel joint.