誘導面電流와 面積形자기센서配列을 利用한 常磁性體 金屬의 非破壞評價

Abstract

Large mechanical structures such as aircrafts and power generation plants are operated in corrosive environment under high temperature and high pressure. In such conditions, cracks can easily develop, initiate and propagate. These cracks lead to various types of fractures in the abovementioned large mechanical structures. And the fractures not only result in the loss of economy and even worse, of life but also environment pollution. Therefore, cracks need to be inspected with equipment having high detection capability before they can initiate fractures. In this paper, a non-destructive testing method of metallic structures by visualization of alternating magnetic field is proposed. Up to now, the alternating magnetic field has been visualized by using the yoke-type magnetizer and linearly integrated Hall sensors array. Also, the static magnetic field has been visualized by using the matrix-type Hall sensors array. However, the 2-dimensional alternating magnetic field has not been visualized in real time. To realize the visualization system of a 2-dimensional alternating magnetic field, that is, an AC-type magnetic camera, a sheet-type induced current, matrix-type Hall sensors array and signal processing circuits were developed. An alternating magnetic field is distorted by a crack on a metallic structure. Therefore, the AC-type magnetic camera can inspect cracks. The crack inspection ability of the developed AC-type magnetic camera was verified by non-destructive testing of austenitic stainless steel and aluminum alloy. Austenitic stainless steel is used in nuclear power generation plants. Austenitic stainless steel is a paramagnetic metal, but it can have a ferromagnetic structure in certain environments. This ferromagnetic characteristic has obstructed the inspection of cracks in the previous non-destructive testing. Also, aluminum alloys are used in aircrafts. The fatigue cracks and corrosion of an aging aircraft have to be inspected and evaluated quantitatively. The developed AC-type magnetic camera and crack inspection method of metallic structures can be used in the non-destructive testing of large mechanical structures. Furthermore, this inspection method, with its accurate prediction ability, can also be used for damage tolerance engineering. The lifetime evaluations of aged structures and machines, which have a high accident probability, can be carried out more accurately.