FEM Simulation And Experimental Research On Thermal Stress Filed Of Brazed Diamond Joint

Thermal stress is an important factor affecting the performance of brazed diamond tool. Overlarge thermal stress will lead to microscopic cracks initiation in the brazed joint, which will cause diamond grit abnormally fall off from matrix during grinding, and it will also result in abrasive underutilized as well as the decline of grinding productivity and machining quality. In order to solve this problem, some simulation analysis have been done on the brazed diamond joints’ thermal stress field by the FEM(Finite element method).The influence mechanism of brazing temperature and cooling rate on the thermal stress filed in the brazed joint have also been studied by FEM. Laser Micro-Raman Spectrometer has been employed to measure brazed diamond joint’s residual stress to do experimental verification of FEM model,Firstly, the state-of-the-art and achievements of brazed diamond technique have been discussed. Research progress of brazed diamond joint’s thermal stress has also been studied. Besides,it gives a brief introduction to the Abaqus software, and put forward this project’s goal, meaning and research contents.Secondly,many instruments(e.g Netzsch DIL 402 C,Netzsch LFA 457,Instron33 69) have been separately employed to measure thermal conductivity, specific heat, thermal expansion coefficient, elastic modulus and yield strength in order to prepare thermo-physical properties of Cu-Sn-Ti braze for FEM simulation.FEM theory about heat transfer and elastic plastic material behavior have been analyzed. Elastic-plastic material behavior mainly includes the yield criterion, flow rule, the hardening rule as well as the elastoplastic constitutive relations. Based on elastic-plastic FEM theory, the FEM model of brazed diamond joint has been established after model drawing, meshing, boundary conditions loading etc, and the geometric model has similar micro-interface characters as the real one.The instantaneous and residual thermal stress field in the brazed joint during the cooling process has been accessed after solving and calculating the established FEM model. The analysis results indicate that thermal properties mismatch is the main factor influencing thermal stresses. there is obvious stress concentration phenomena at the corners of the diamond grit; The plastic deformation can release thermal stress in some extent; In residual thermal field, Ti C layers at the side of diamond grit mainly endure tensile stresses, while the other parts mainly endure compressive stresses.The experiment of the residual stress measurement in the brazed diamond grains by Micro-Raman has been finished to verify the correctness of established FEM model. The corresponding experimental results indicate that the measured residual stresses are basically in accordance with the simulation results. Thermal stress measurement equipment, brazed diamond grains sample preparation equipment and experimental procedures have been introduced.Finally, the effect of brazing temperature and cooling rates to brazed diamond joint’s thermal stress field and Cu-Sn-Ti’s plastic strain have been studied with verified FEM model. It shows that brazing temperature and cooling rates have great influences on diamond grits’ stress and plastic strain of Cu-Sn-Ti, but have small impa cts on the Cu-Sn-Ti’s thermal stress field.