스페클간섭법을 이용한 맞대기용접부의 잔류응력측정

Abstract

The state that exists in the bulk of some materials without application of an external load or other stress sources such as thermal gradients, is known as residual stress. They may be produced by fabrication operations such as casting, rolling, welding, heat treating or forging, or may occur during the life of a structural or mechanical component. The magnitude and distribution of residual stresses are very important to be known since the mechanical behavior of different materials will be affected when they are present. The hole drilling method is one of the most widespread techniques for measuring residual stresses. This technique involves monitoring the strains generated by the relieved stresses when a small hole is drilled into a stressed material. These strains are usually measured by means of strain gage rosettes. However, they have some practical and economical drawbacks. For instance, the hole must be drilled in the centre of the rosette since misalignments can cause significant errors. The difficulty can be overcome using optical techniques. Among them, electronic speckle pattern interferometry (ESPI) is a technique which is very attractive in optical metrology not only for its non-contacting nature but also for its relative speed of inspection procedure, mainly due to the use of video detection and digital image processing. The application of digital techniques in ESPI allows the automation of the data analysis process, which is usually based on the extraction of the optical phase distribution encoded by the generated correlation fringes. From these data, in-plane displacement fields can be measured over the whole surface of any rough object without making contact with it. The objective of this study is to measure residual stress of butt welding using in-plane displacement sensitive ESPI. In experiment, the butt-welded stainless steel specimen are extended by tensile testing machine and The strain distribution at right-angle to welding line is measured by y-axis displacement sensitive ESPI and the strain profile indicates base metal and welding zone. Also, Young’s modulus of base metal and welding zone are respectively determined by tensile testing. The residual stress distribution of butt-welded specimen can be estimated from the strain profile of ESPI and two Young’s modules. The presented method offers improved speed of evaluation due to elimination of the surface preparation time of hole-drilling technique.