ABSTRACT

A Study on the Application of Modulating Laser
using ESPI and Shearography integration algorithm
system development

Kim, Seong Jong
Dept. of Mechanical Design
The Graduate School
Chonbuk National University


A stable energy supply is indispensable for human life, given the fact that energy demand has been sharply increasing because of rapid industrial expansion. Extensive piping facilities are used in heat power plants and nuclear power plants, which supply most of the energy worldwide. Hence, there is a need to develop a system for avoiding breakage of pipes in piping facilities and to perform precise inspections of power facilities for defects to ensure a stable and continuous energy supply. When piping facilities involve extensive use of pipes and pressure vessels, defects from corrosion will be a common occurrence in such facilities. Such defects may often remain unnoticed until some destruction has been occurred.
There are some method such as Ultrasonic wave, X-ray and eddy current which are recognized a reliability and used as conventional inspection methods to find a internal defect. However these methods are headed and almost in contact with the target that is to be checked but these methods have disadvantage such as unable to detect at once over a wide area. In contrast, inspection methods using the Electronic Speckle Pattern Interferometry (ESPI) and the shearography have advantages as a wide range of test coverage, fast inspection speed close to real time, a precise measurement of small deformation and non-contact/ non-destructive inspection.
Laser interferometry is widely used as a measuring system in many fields because of its high resolution and its ability to measure a broad area in real-time all at once. In conventional laser interferometry, for example Out-of-plane ESPI, In plane ESPI, Shearography, it uses PZT or other components as a phase shift instrumentation to extract 3-D deformation data, vibration mode and others. However, in most cases PZT has some disadvantages, which include nonlinear errors and limited time of use. In the present study, a new type of laser interferometry using a laser diode is proposed. Using Laser Diode Sinusoidal Phase Modulating (LD-SPM) interferometry, the phase modulation can be directly modulated by controlling the laser diode injection current thereby eliminating the need for PZT and its components. This makes the interferometry more compact. This paper reports on a new approach to the LD Modulating interferometry that involves four-frame phase shift method. This study proposes a four-frame phase mapping algorithm, which was developed to have a guaranteed application, to stabilize the system in the field and to be a user-friendly GUI. In this paper, the theory for LD wavelength modulation and sinusoidal phase modulation of LD modulating interferometry is shown. The existing algorithm is based on reliability for the specimens to be applied to the industrial field were defects measured. Experiments were carried out with aluminum liner and carbon steel pressure vessels, pressure vessel. These specimens are applied to the industry, and a more reliable research. In addition, To save on fuel in natural gas buses and carbon steel the internal defects of the pressure vessel was measured quantitatively then by using Finite Element Method(FEM). Comparison of algorithm of modulating laser improved newly with actual displacement compares transformation price through 3D. Comparison of interface(4-frame phase mapping, Unwrapping, 3D is then introduced. The measurement program reliability was ensure.