the role of lock-in thermography in non-destructive testing of steel structures

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.

2015.10.22~23 2015 Annual Fall Conference of KSNT

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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



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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…


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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