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Abstract
Crystal cracking is one of the major defects when large copper structures are joined by gas tungsten arc welding (GTA welding). In order to research the mechanism of crystal cracking, the criterion for crystal cracking formation has been optimized based on Prokhorov's theory, which shows that the interior deformation rate (Δϵ) is the main factor that leads to crystal cracking. A finite element model of thick copper plates in GTA welding based on the rigid constraint experiments has been established, and the Δϵ variation of the welds is obtained. The physical model of the tendency of crystal cracking has been established, and then the mechanism of crystal cracking has been discussed systematically by comparing the variations between Δϵ obtained from numerical simulations and the weld ductility (Pmin) obtained from hot-tension experiments within the brittle temperature range (BTR). Results show that during GTA welding, the values of Δϵ and Pmin are varied, respectively, with the temperature descending, and the tendency of crystal cracking and expansion velocity can be controlled by the value of (Δϵ − Pmin). Then experiments with the preheated temperatures of 300°C and 500°C, verified the validity of the optimized criterion of cracking.