Application of thermal wave imaging and phase shifting method for defect detection in Stainless steel

Shrestha, Ranjit,Park, Jeonghak,Kim, Wontae Elsevier 2016 Infrared physics & technology Vol.76 No.-

<P><B>Abstract</B></P> <P>This paper presents an experimental arrangement for detection of artificial subsurface defects in a stainless steel sample by means of thermal wave imaging with lock-in thermography and consequently, the impact of excitation frequency on defect detectability. The experimental analysis was performed at several excitation frequencies to observe the sample beginning from 0.18Hz all the way down to 0.01Hz. The phase contrast between the defective and sound regions illustrates the qualitative and quantitative investigation of defects. The two, three, four and five-step phase shifting methods are investigated to obtain the information on defects. A contrast to noise ratio analysis was applied to each phase shifting method allowing the choice of the most appropriate one. Phase contrast with four-step phase shifting at an optimum frequency of 0.01Hz provides excellent results. The inquiry with the effect of defect size and depth on phase contrast shows that phase contrast decreases with increase in defect depth and increases with the increase in defect size.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Infrared thermography deals with the acquisition and analysis of thermal data. </LI> <LI> Phase shifting method determines the phase map from a set of thermographic images. </LI> <LI> Contrast to noise ratio is used to distinguish the two regions of interest. </LI> <LI> Four-step phase shifting provides the excellent result at optimum frequency 0.01Hz. </LI> </UL> </P>

Detection of Subsurface Defects in Metal Materials Using Infrared Thermography

Shrestha Ranjit,Won Tae Kim 한국비파괴검사학회 2014 한국비파괴검사학회지 Vol.34 No.2

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.

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

Shrestha Ranjit,Wontae Kim 한국비파괴검사학회 2015 한국비파괴검사학회지 Vol.35 No.6

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.

열 적외선 영상의 데이타처리를 통한 정량적 결함 특성에 관한 연구

Shrestha Ranjit,정윤재,김원태 한국기계기술학회 2015 한국기계기술학회 학술대회논문집 Vol.2015 No.03

Numerous experiments have demonstrated that infrared thermographic methods are effective for detection of subsurface defects in the materials. The response of the material to the thermal stimulus is dependent on the existence of subsurface defects and their features. In order to obtain the information about defects, the material’s response to the thermal stimulus is studied. In this study, image processing was applied to infrared thermography images to detect defects in metals that were widely used in industrial fields. When analyzing experimental data from infrared thermographic testing, thermal images were often not appropriate. Thus, four point method was used for processing of every pixel of thermal images using MATLAB program for quantitative evaluation of defect detection and characterization which increased the infrared non-destructive testing capabilities since subtle defects signature became apparent..

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

Ranjit, Shrestha,Kim, Wontae The Korean Society for Nondestructive Testing 2015 한국비파괴검사학회지 Vol.35 No.6

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 Hz down to 0.032 Hz. 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.

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

Ranjit, Shrestha,Kim, Won Tae The Korean Society for Nondestructive Testing 2014 한국비파괴검사학회지 Vol.34 No.2

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 Behavior Variations in Coating Thickness Using Pulse Phase Thermography

Shrestha Ranjit,Yoonjae Chung,Wontae Kim 한국비파괴검사학회 2016 한국비파괴검사학회지 Vol.36 No.4

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.

Quantification of defects depth in glass fiber reinforced plastic plate by infrared lock-in thermography

Shrestha Ranjit,ManYongChoi,Wontae Kim 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.3

The increasing use of composite materials in various industries has evidenced the need for development of more effective nondestructive evaluation methodologies in order to reduce rejected parts and to optimize production cost. Infrared thermography is a noncontact, fast and reliable non-destructive evaluation technique that has received vast and growing attention for diagnostic and monitoring in the recent years. This paper describes the quantitative analysis of artificial defects in Glass fiber reinforced plastic plate by using Lockin infrared thermography. The experimental analysis was performed at several excitation frequencies to investigate the sample ranging from 2.946 Hz down to 0.019 Hz and the effects of each excitation frequency on defect detachability. The four point method was used in post processing of every pixel of thermal images using the MATLAB programming language. The relationship between the phase contrast with defects depth and area was examined. Finally, phase contrast method was used to calculate the defects depth considering the thermal diffusivity of the material being inspected and the excitation frequency for which the defect becomes visible. The obtained results demonstrated the effectiveness of Lock-in infrared thermography as a powerful measurement technique for the inspection of Glass fiber reinforced plastic structures.

Investigation on Topcoat Uniformity of Thermal Barrier Coating Using Pulsed Infrared Thermography

Shrestha Ranjit,Wontae Kim 한국비파괴검사학회 2018 한국비파괴검사학회지 Vol.38 No.2

In this study, the uniformity of the topcoat of a thermal barrier coating (TBC) was investigated using pulsed infrared thermography. Two plasma-sprayed TBC samples on different substrate materials, with non-uniform topcoats varying from 0.1 mm to 0.6 ㎜ were considered. A short high-energy light pulse was applied to the surface of the samples, and an infrared camera was used to record surface temperature evolution during the entire thermal transient period. The relationship between the measured temperatures and their spatial distributions in the non-uniform topcoat was studied, and it was observed that temperatures in the thinner topcoat region were lower than those in the thicker topcoat region. Furthermore, the recorded thermal image sequences were processed using Fourier transforms to obtain phase angle images, and the phase angle distribution was examined as a function of the non-uniform topcoat. It was found that phase angle decreased with topcoat thickness. Our results showed that variations in temperature and phase angle were significantly correlated with non-uniformity in our investigation of TBC topcoat uniformity.

Non-destructive testing and evaluation of materials using active thermography and enhancement of signal to noise ratio through data fusion

Shrestha, Ranjit,Kim, Wontae Elsevier 2018 Infrared physics & technology Vol.94 No.-

<P><B>Abstract</B></P> <P>Active thermography has emerged as an attractive and reliable technique for non-destructive testing and evaluation of a variety of materials, structures, and components due to its non-contact, whole-field, high speed and qualitative and quantitative inspection capabilities. However, the existence of non-uniform heating, low spatial resolution, and environmental noise cause some difficulties for defect detection and characterisation; demanding the necessity of various signal processing methods. Fourier transform has proved to be an effective method to extract amplitude and phase images from the recorded thermal sequences. Phase image has received extensive attention to the quantitative analysis, even though the amplitude image may contain useful information as well. Present work explores the possibility of enhancing the signal to noise ratio of inclusion defects in a GFRP composite sample through data fusion of amplitude and phase images as an innovative approach. Amplitude and phase images with several simulated inclusions of various shapes and sizes at different depth levels were considered. The well established and recognised pixel-level data fusion based on PCA and DWT techniques was performed and compared to detect and evaluate the inclusions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Data fusion was used to enhance SNR of inclusion defects in a GFRP composite sample. </LI> <LI> A fusion of amplitude and phase images was proposed as an innovative NDT&E approach. </LI> <LI> Pixel-level data fusion based on PCA and DWT techniques was performed. </LI> <LI> PCA based data fusion enhanced SNR and accuracy for detection of inclusions. </LI> </UL> </P>