Shrestha Ranjit

Detection of Subsurface Defects in Metal Materials Using Infrared Thermography; Image Processing and Finite Element Modeling

Infrared thermography is an emerging approach to non-contact, non-intrusive, and non-destructive inspection of various solid materials such as metals, composites, and semiconductors for industrial and research interests. In this study, data processing was applied to infrared thermography measurements to detect defects in metals that were widely used in industrial fields. When analyzing experimental data from infrared thermographic testing, raw images were often not appropriate. Thus, various data analysis methods were used at the pre-processing and processing levels in data processing programs for quantitative analysis of defect detection and characterization; these increased the infrared non-destructive testing capabilities since subtle defects signature became apparent. A 3D finite element simulation was performed to verify and analyze the data obtained from both the experiment and the image processing techniques.

Thermal Imaging for Detection of SM45C Subsurface Defects Using Active Infrared Thermography Techniques

Abstract Active thermography techniques have the capability of inspecting a broad range simultaneously. Byevaluating the phase difference between the defected area and the healthy area, the technique indicates thequalitative location and size of the defect. Previously, the development of the defect detection method used avariety of materials and the test specimen was done. In this study, the proposed technique of lock-in is verifiedwith artificial specimens that have different size and depth of subsurface defects. Finally, the defect detectioncapability was evaluated using comparisons of the phase image and the amplitude image according to the size anddepth of defects. Keywords: Lock-in, Infrared Thermography, Defects Detection, Data Processing, Thermal Imaging[Received: May 12, 2015, Revised: June 16, 2015, Accepted: June 17, 2015] * , **공주대학교대학원기계공학과 공주대학교 공과대학 기계자동차공학부, Corresponding Author: Div. of Mechanical and Automotive Engineering,Kongju National University, Cheonan, Chungnam, 331-717, Korea (E-mail: kwt@kongju.ac.kr)

Thermal Behavior Variations in Coating Thickness Using Pulse Phase Thermography

This paper presents a study on the use of pulsed phase thermography in the measurement of thermal barrier coating thickness with a numerical simulation. A multilayer heat transfer model was ussed to analyze the surface temperature response acquired from one-sided pulsed thermal imaging. The test sample comprised four layers: the metal substrate, bond coat, thermally grown oxide and the top coat. The finite element software, ANSYS, was used to model and predict the temperature distribution in the test sample under an imposed heat flux on the exterior of the TBC. The phase image was computed with the use of the software MATLAB and Thermofit Pro using a Fourier transform. The relationship between the coating thickness and the corresponding phase angle was then established with the coating thickness being expressed as a function of the phase angle. The method is successfully applied to measure the coating thickness that varied from 0.25 mm to 1.5 mm.

Detection and Quantification of Defects in Composite Material by Using Thermal Wave Method

This paper explored the results of experimental investigation on carbon fiber reinforced polymer (CFRP) composite sample with thermal wave technique. The thermal wave technique combines the advantages of both conventional thermal wave measurement and thermography using a commercial Infrared camera. The sample comprises the artificial inclusions of foreign material to simulate defects of different shape and size at different depths. Lock-in thermography is employed for the detection of defects. The temperature field of the front surface of sample was observed and analysed at several excitation frequencies ranging from 0.562 ㎐ down to 0.032 ㎐. Four-point methodology was applied to extract the amplitude and phase of thermal wave’s harmonic component. The phase images are analyzed to find qualitative and quantitative information about the defects.

Thermal Analysis of Silicon Carbide Coating on a Nickel based Superalloy Substrate and Thickness Measurement of Top Layers by Lock-in Infrared Thermography

In this paper, we investigate the capacity of the lock-in infrared thermography technique for the evaluation of non-uniform top layers of a silicon carbide coating with a nickel based superalloy sample. The method utilized a multilayer heat transfer model to analyze the surface temperature response. The modelling of the sample was done in ANSYS. The sample consists of three layers, namely, the metal substrate, bond coat and top coat. A sinusoidal heating at different excitation frequencies was imposed upon the top layer of the sample according to the experimental procedures. The thermal response of the excited surface was recorded, and the phase angle image was computed by Fourier transform using the image processing software, MATLAB and Thermofit Pro. The correlation between the coating thickness and phase angle was established for each excitation frequency. The most appropriate excitation frequency was found to be 0.05 Hz. The method demonstrated potential in the evaluation of coating thickness and it was successfully applied to measure the non-uniform top layers ranging from 0.05 mm to 1 mm with an accuracy of 0.000002 mm to 0.045 mm.