A Study Of The Mechanism And Evolution On The Welded Joint's Damage Of The Low-alloy Steel

Based on the essential characteristic of macroscopical mechanical heterogeneity in the welded joint, the welded joint of the low-alloy steel was absracted as a mechanical heterogeneity model and the experimental studies on the welded joint抯 damage were performed from three ways: the microcosmic organize?s evolution~ the macroscopical mechanical characteristic and computer simulate. At first, the dynamic microprocesses of microstructural damage and fracture in the welded joint model were observed directly by the Scanning Electron Microscopy(SEM) equipped with tensile platform. Research had revealed that the damage of the model happened generally after the neck contract and converged mainly in the soft area of the model. The main forms of the damage were cleavage in the brittle phase and on the grain boundary. Secondly, with the ways of Continuous Damage Mechanics (CDM), the low cycle fatigue damage behave of the welded joint model was investigated. A new continuum damage variable based on the material stress range was defined and a new continuum damage model of isotropic LCF was established. They were applied to study the low- cycle fatigue damage of welded joint. The LCF experimental results showed that with the increase of the width of the weld line in the overmatched welded joints the cycle numbers in LCF experiment decreased and the damage抯 development in the welded joint was faster. Thirdly, with the modified Gurson model of the MARC finite element method(FEM) soft, the damage behave of the welded joint was simulated. It was found that in the undermatched welded joint, the damage mainly happened in the soft weld line and with the decrease of the weld line抯 width, the damage抯 development was faster. As for the overmatched welded joint, the results showed that the damage mainly happened in the soft base metal and with the increase of the weld line抯 width, the damage抯 development was faster. While the width of the weld line was narrower than three millimeters, the high strength weld line could improve the anti-damage capability of the overmatched welded joint.