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Materials Evaluation and Testing Laboratory (METLab)Mechanical Engineering Department, Box 2219 SCEH 214 South Dakota State University, Brookings, SD 57007-0294

Phone: (605) 688-4300, Fax: (605) 688-5878, http://www.sd-metlab.org

Three Rivers Technical Conference August 3-4, 2010

NDT Testing of built-up sections and Electronic Components

Presenter: Rushie Ghimire

Supervised by : Dr. Gary AndersonTeam: Nikunj Parmar

Project Director: Dr. Fereidoon Delfanian

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Acoustic Emission Testing (AE) Microscopic evaluationRadiography (RT) – Uses high energy photons (X-

ray machine)

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Different methods of NDT testing

AE is the transient elastic energy which is generated from the material due to fracture, deformation, dislocation or discontinuity in the material itself

AE technology is used to examine the defect, flaw and formation of cracks in structural materials (Health monitoring of structures).

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Acoustic Emission (AE) Overview

Sounds made by a material, structure, or machine in use or under load are heard and analyzed to determine its "state of health”

One or more sensors are attached to the object and the sounds are analyzed using computer based instruments

Noises may arise from:– crack growth – material changes (such as

corrosion)– friction

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AE Principle

• Peak amplitude - The maximum of AE signal. dB=20log10(Vmax/1µvolt)-preamlifier gain

• Energy – Integral of the rectified voltage signal over the duration of the AE hit.

• Duration – The time from the first threshold crossing to the end of the last threshold crossing.

• Counts – The number of AE signal exceeds threshold.• Rise time - The time from the first threshold crossing to the maximum

amplitude. • Count rate - Number of counts per time unit.

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AE HIT and Parameters

• During Production: welding, heat treatment, tempering, firing of ceramics.

• Quality Control: Testing of pressure vessels and pipes, proof testing of components.

• In-service Inspection: Pressure vessels and pipes, bridges, buildings, machines, ropes,dams.

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AE Applications

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Built up section04/22/23 7NSI conference

• Develop an AE method to properly quantifying AE signals that are measured on the outer steel liner or outer composite liner that are generated by the inner steel liner.

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Objective of the test

steel and composite samples04/22/23 9NSI conference

Steel specimensDimensions: 7 inches long, 1 inch wide, and 0.125 inch thick.

Carbon composite specimensDimensions: 7 inches long, 1 inch wide, and 0.06 inch thick.

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Dimensions of steel: 9 inches long, 1 inch wide, and 0.125 inch thick.Dimensions of composite: 7 inches long, 1 inch wide, and 0.06 inch thick.

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Dimensions of inner layer steel: 9 inches long, 1 inch wide, and 0.125 inch thick.Dimensions of outer layer steel: 7 inches long, 1 inch wide, and 0.125 inch thick.Dimensions of composite: 7 inches long, 1 inch wide, and 0.06 inch thick.

AE Tensile test 04/22/23 12NSI conference

Monitor the damage during the tensile test of the steel and composite specimens at different loadings.

After each load, a picture was taken of the microscopic image of the specimen and evaluated for structural damage.

The universal test machine was used to load the specimens.

Steel specimen:• Loaded to 25 kN • 28.68 kN (failure)

AE Tensile test result of steel

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0 20000 40000 60000 80000 100000 120000 140000

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25

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300Steel-04 Samples

Stre

ss (M

Pa)

Strain (µ)

Stress4

0 200 400 600 800 1000 1200 1400 1600

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125

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300 Steel-04 Samples

Stre

ss (M

Pa)

Cumulative Count

Stress4

• Yield stress is 175 MPa and Failure stress is 284 MPa• Yield stress from the plots of cumulative count is 168 MPa and

failure stress is 280 MPa• Increase in cumulative count after yield shows the formation and

growth of defects leading to failure.

Cont..

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The displacement plot on the right shows non-linearity around 210 seconds. Around 210 sec a large number of emissions are recorded with both higher and lower amplitude at the time of maximum load.

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The amplitude tends to start out small and increases in amplitude as the crack size increases.During crack growth there is a non-periodic cycling of event amplitude from 45-100 dB, suggesting the intermittent weakening at the crack front.

Microscopic Image before and after failure

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Images and plots at failure loading04/22/23 17NSI conference

Steel Failure04/22/23 18

Specimen failure plane was at approximately at 45 degree angle from the horizontal.

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Steel afilure04/22/23 19NSI conference

The failure plane was at approximately at 15 degree angle from the horizontal.

AE test on carbon composite04/22/23 20

•Load to 30.45kN•Load to 49.42kN (failure)

Specimen failed right across the grip which may be due the teeth of the grip penetrating the outer layer of the composite.

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Composite failure results

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Higher amplitude, number of counts, and duration are observed near failure.Higher amplitude is the sign of the fiber breakage and matrix cracking.

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Outer layer crack

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Fibers in composite specimen run bidirectional in the outer layer and unidirectional in the inner layers.

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Fiber Breakage and Pullout from Matrix

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Matrix Debonding

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AE results of E-glass 04/22/23 25

0 3000 6000 9000 12000 15000 18000 21000 24000

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135E-Glass Composite

Stre

ss (M

Pa)

Axial Strain (µ)

Stress

• Stress-strain plots of E-Glass showing maximum stresses at 117 Mpa

• The stress vs. cumulative count plot has a linear relationship from zero to yield stress, from where the plot begins to diverge from a straight line.

• Yield stress of E-Glass sample on cumulative count plot is at 90Mpa.

• Cumulative counts for E-glass increases rapidly after yield stress with little increase in stress

• Brittle failure

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0 10000 20000 30000 40000 50000

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135 EG Sample

Stre

ss (M

Pa)

Cumulative Count

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AE results of Fiber glass04/22/23 26

0 1x104 2x104 3x104 4x104 5x104 6x104

15

30

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120 FG Sample

Stre

ss (M

Pa)

Cumulative Count

Stress

Maximum stress of fiber glass sample: 125 MPa yield stress of Fiber glass sample is 55 Mpa on cumulative count plot. Cumulative counts for Fiber glass also increases rapidly after yield stress with little

increase in stress.

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0 4000 8000 12000 16000 20000

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140 Fiber Glass Composite

Stre

ss (M

Pa)

Axial Strain (µ)

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Use of X-ray in AE testing

• Microscopic picture can only show defects on the outer layer.

• The inner surface micro-crack can be seen using X-ray images.

• Several papers have discussed the use of CT-scan or x-ray to see the inner surface cracks and relate then to the AE hit pattern

• The use of CT-can or X-ray has been done rarely.

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X-ray of the steel specimens 04/22/23 28NSI conferenceNSI conference

AE can be problematic due to: Effect of mounting condition

• couplant (silicone gel or petroleum jelly)• mounting pressure• Thickness of the hot glue

Noise from the loading machine Degradation of the sensitivity of the system

• wiring faults• deterioration of electronics

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Industrial task04/22/23 30NSI conference

Conclusion

• AE technique is an excellent tool to determine when a micro cracks initiated in the specimens.

• The continuous high AE amplitude represents the failure of the material or that the material is at risk.

• AE can find yield in steel and composite.• AE can find failure of steel and composite

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Questions?

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Thank you!