The Study On The Crack Propagation Of Stainless Steel Brazed Joints By Using Cohesive Zone Model

With the development of modernized society, the contradiction between human’s demands and energy shortage becomes more critical. Therefore, energy conservation becomes the main target of modern industry. In order to improve efficiency of heat exchange, plate-fin recuperator with large heat transfer area and high efficiency is often used to pre-heat helium in high temperature gas-cooled reactor (HTGR) systems. For a recuperator, brazed seam of plate-fin structure is the most likely to crack under high temperature and high pressure. Therefore, it is necessary to study the crack propagation laws of the brazed seams of plate-fin structure. However, the existing researches are limited to brazing process optimization and the study on crack propagation law has not been reported in the open literatures.In view of the above problems, the crack propagation characteristics are investigated by using the cohesive zone model in this study. The main contents and conclusions are as follows:1) Uniaxial tension test, T-type cracking test and3-point bending test of brazed joints are preformed. The fracture mechanism of the joint fracture samples is analyzed. Then the critical cohesive energy of316L/BNi-2brazed joints is obtained experimentally.2) A cohesive zone model is developed for T-type brazing joint and the crack propagation process of T-type brazed joints is numerically simulated. Based on the numerical results, the crack propagation law of brazed joints is explained. Then a method to enhance joints’ anti-cracking ability is proposed in this paper.3) The crack propagation of the3-bending test specimen is analyzed by using the above cohesive zone model with the same parameters. It is verified that the critical cohesive energy and damage initial stress are independent of the structural parameters and loading mode.4) The L-M damage constitutive equation based cohesive zone model is extended to analysis creep crack propagation of T-type brazed joints. The subroutine is coded and inserted into the ABAQUS program. Then the crack propagation of the T-type brazing joint is numerically simulated and the crack initiation and propagation laws are analyzed accordingly.