전자처리 스페클 패턴 간섭법을 이용한 용접 및 하중 조건에 따른 구조용 강재의 용접부 잔류응력 측정

Abstract

Welding plays a pivotal role in various industry fields, such as shipbuilding, nuclear power plant, airplane, automobile and architecture industry because welding has many strong points like waterproof and airtightness. However, welding structures can be able to destroy unexpectedly due to the fact that quality of the material, residual stress, deformation, welding defects have an aptitude to happen easily in welding structures because welding is a kind of joint method by increasing heat. Especially, a main reason for leading to defects or destruction of structure can be residual stress. The occurrence of welding residual stress caused by heat stress is influenced by external restriction of the parent metal, welding heat input, size and thickness of the parent metal during welding. The residual stress occurs for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. The size and state of distribution of welding residual stress before external load in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, Electronic Speckle Pattern Interferometry (ESPI), one of the optical non-destructive techniques, is applied to measure the residual stress of a welded specimen. When a welded specimen of structure steel is loaded by the tensile loading, the entire behavior caused by the residual stress is observed and obtained by ESPI. From the results, the deformation of a specimen generated by the tensile loading is used to calculate the strain distribution on the entire measuring plane of a specimen. During this process, the strains of the base metal and the weld zone can be obtained. These strains are converted into the elastic modulus of each part. Finally, using these values of strain and the elastic modulus, the residual stress can be calculated.