Experimental Study On The Peeling Properties Of T-Type Brazing Joints

Plate-fin structure heat exchangers are the key equipment of the whole high temperature systems, such as aerospace, nuclear power, petroleum, chemical industry and so on. They are mainly manufactured by using vacuum brazing. Due to the structural discontinuity and mismatch in mechanical properties under the high temperature and pressure, the surface and volume defects such as cracks and voids will be greatly affected by the complicated load and temperature fluctuations. Those defects will expand to the critical size and then lead to the joints fracture. Thus the joint becomes the most dangerous location of the equipment. It demonstrates that the weld cracking is the main cause of failure of plate-fin structure heat exchanger in engineering practice.That will causes gas and liquid leakage, even explosion. Therefore, the study of high temperature mechanical properties of brazing joint for the plate-fin structure heat exchanger is significant. Due to the lack of reliable test standard, the weld failure mechanism of the plate-fin structure is not clear.According to the issue mentioned above, a high temperature mechanical property testing method for brazing joints is developed in the present paper. Then the peeling properties of T-type brazing joints are tested by using the proposed method. The crack propagation process of brazing joint is simulated by FEM and the EEM results are compared with the experimental results. The main research works are as follows:1) According to the actual structure and the force status of plate-fin heat exchangers, T-type brazing tensile sample is designed. Then high temperature short-time peel tests have been carried out. The load displacement curves for 316L brazing joint specimen at high temperature were obtained.2) The effect of loading rate, test temperature and structural parameters on the test results were analyzed. The reasonable test condition for T-type brazing joints was summarized Combining with study of microstructure, the failure mechanism of the plate-fin structure was discussed.3) The crack propagation process of T-type brazing joints was simulated by using 3D cohesive model. It shows that the simulation results agree with the testing results. It indicates that the cohesive model can be used to well predict the T-type brazing joint crack propagation.