Research Of Burst Pressure Of Copper Brazed Joint Considering Temperature History

In the practical production of equipment such as air conditioner, torch soldering is usually used to weld copper tube. After welding, the property of welded joint will change obviously after the welding joint experiences welding thermal cycle, which leads to change both in mechanics and material properties. The mechanical factors for the property of welding joint are welding defects, discontinuity of joint shape, welding residual stress and welding distortion. The main factors in material nature are the effect of welding thermal process and structural change after post weld heat treatment: that is the structure of welding seam and heat affected zone is obviously different with that of base metal.In this article, the change in material properties is researched, that is the heat affected zone of welding joint will become the most feeble part of welding structure as the structure is softened, and the strength is reduced dramatically, much lower than the strength of base metal.First of all, a simple tube model is established by FEA software MSC.Marc to obtain a reasonable temperature field. Temperature history and material properties changes according to temperature are both took into consideration during the simulation. Both of the stress and strain fields of the tubes in different radius are calculated. Calculated burst pressure and theoretical burst pressure are compared to confirm the modified burst pressure formula for tube. The result is that the calculated burst pressure is 1.28 times of theoretical burst pressure.And then the conditions of different models under the pressure load considering temperature history are researched. The results showed that calculated burst pressure accords with test result. The influences of both symmetry property of temperature history and mesh subdivision are researched. The result said symmetry property of temperature history has no radical effect on the calculation of bursting pressure, and mesh subdivision could zoom out the boundary effect in structure. In the condition that mesh is divided into 9 lays , the maximum stress concentration factor is up to 1.57, in the place where practical burst was occurred.Finally, the tendency of crack extend of the model 3 is evaluated by implementing criterions as J2. It indicates that high tendency of the place where practical burst was occurred after the welding process.