Fracture analysis of packaging steel with thermal stress and residual stress

Fracture analysis of packaging steel with thermal stress and residual stress
　　 Generally speaking, thermal stress and residual stress (collectively called secondary stress) exist in a heated pressure vessel. Because Rice's j integral is no longer independent of the integration path when there is a secondary stress, and the magnitude and analysis of the welding residual stress is quite difficult, the secondary stress is a self-balancing force, and elastic-plastic fracture when there is a secondary stress Analysis also appears to be quite difficult.
　　 In recent years, the fracture analysis technology that considers the existence of secondary stress has been greatly developed, and the failure assessment chart method has been extended to the situation where there is a secondary stress load at the same time. For example, the engineering method of considering secondary stress adopted in the new R6. It is to introduce the influence of secondary stress in the expression of the reference stress method of A, and from the perspective of engineering use, even if there is a secondary stress, the failure assessment curve when there is no secondary stress is still used, and no further development is required. A set of failure assessment curves, and an engineering method of compensation with plasticity correction factor ρ is introduced. According to the deduced results and after appropriate simplification, the ratio of the secondary stress intensity factor to the mechanical load stress intensity factor and the mechanical load are close The degree of plastic yield load L determines the graph of ρ.
　　 At present, all engineering specifications that use failure assessment chart technology as fracture assessment, such as the new PD6493, the new IIW document, and the Swedish specification, all adopt the new R6 method to consider the secondary stress method, and abandon the 1970s The secondary stress treatment method used in the second stress is a certain percentage (such as 60%) of the secondary stress as the equivalent stress, and then treated as the primary stress.