the role of lock-in thermography in non-destructive testing of steel structures
TRANSCRIPT
The Role of Lock-in Thermography in The Role of Lock-in Thermography in Non-destructive Testing of Steel StructuresNon-destructive Testing of Steel Structures
Shrestha Ranjit and Wontae KimShrestha Ranjit and Wontae Kim*Thermal Design & Infrared LabThermal Design & Infrared Lab
Division of Mechanical & Automotive EngineeringDivision of Mechanical & Automotive EngineeringKongju National University, KoreaKongju National University, Korea
E-mail: [email protected]: [email protected]
Outline of the Presentation:
• Motivation of the Research
• Principle of Operation
• Experimental Setup
• Data Acquisition and Analysis
• Analysis Results
• Conclusion / Discussion2015.10.22~23 2015 Annual Fall Conference of
KSNT2
Motivation for the Research:
Development of fast, non-contact and reliable method for non-destructive revealing of hidden non-homogeneities (defects) inside 3D objects. •For this purpose Lock-in Infrared Thermography is a very effective tools with superior resolution.
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Schematic setup of Lock-in Thermography
Principle of Operation:
• Sample receives the periodic load and thermal wave is generated.
• The presence of defects inside the object will exhibit a phase delay at the corresponding area.
• Defect detection is thus related to phase detection.
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LIT Configuration Principle of Phase detection
Experimental Setup:
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Detail of Specimen:
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Specimen PropertiesDensity (ρ) 7900 kg/m3
Thermal Conductivity (k) 16.2 W/m/KSp. Heat capacity (Cp) 477 J/kg.KThermal Diffusivity 4.29E-6 m2/s
Geometry of the specimen with artificial defects
Data Acquisition and Analysis:
Four Step Phase Shifting Method:
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Principle of computation of thermal image, amplitude and phase image
Data Acquisition and Analysis:
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Cont…
Analysis Results:
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Analysis Results:
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
Phas
e (R
adia
n)
Excitation Frequency (Hz)
Defect Phase Sound Phase Phase Contrast
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Phase Contrast vs. excitation frequencies
• Defect A1 with Diameter 16 and depth 8 mm was considered for the analysis.
• Maximum – ve phase angle: Optimum Frequency
• Zero Phase angle: Blind Frequency
• Maximum +ve Phase angle: Optimum frequency
• The blind frequency should be avoided and the optimum frequencies should be selected.
Excitation Frequency:Cont…
Data Acquisition and Analysis:
5 6 7 8
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
Pha
se (R
adia
n)
Defect Depth (mm)
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Phase contrast vs. defect depth for defect size 16 mm
Defect Depth:
• Defects B1, D1, C1 & A1 with Depth 5, 6, 7 & 8 mm respectively with fixed Diameter 16 mm were considered for the analysis.
• The phase contrast increases with the increasing defect ’s depth for the fixed defect size.
Cont…
Analysis Results
8 10 12 14 16
0.30
0.35
0.40
0.45
0.50
0.55
Pha
se (R
adia
n)
Defect Diameter (mm)
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Phase contrast vs. defect size for defect depth 8 mm
Defect Size:
• Defects A3, A4 & A1 with Diameter 8, 12, & 16 mm respectively with fixed Depth 8 mm were considered for the analysis.
• The phase contrast increases with the increasing defect ’s diameter for the fixed defect depth.
Cont…
Analysis Results:
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3D presentation of phase image at frequency 0.01 Hz
Cont…
Conclusion:
• Infrared thermography is a reliable non-destructive method for the defect size and depth and the detachability improves as the defect radius to defect depth ratio approximates unity.
• An excitation frequency of 0.01 Hz was determined to provide the strongest phase contrast response for defects in 10 mm STS 304 plate investigated.
• The study also found that both the defect diameter and defect depth had appreciable effects on the observed phase contrast
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Thank You
Thermal Design & Infrared Lab
Kongju National University
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