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NDT Testing Methods & Applications in Structural Materials Assessment

Explore Acoustic Emission Testing principles, applications, & results in NDT. Witness AE monitoring of steel & composite specimens during tensile tests with detailed analysis.

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NDT Testing Methods & Applications in Structural Materials Assessment

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  1. NSI conference Three Rivers Technical Conference August 3-4, 2010NDT Testing of built-up sections and Electronic ComponentsPresenter: Rushie Ghimire Supervised by : Dr. Gary Anderson Team: Nikunj Parmar 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 Project Director: Dr. Fereidoon Delfanian

  2. NSI conference Different methods of NDT testing • Acoustic Emission Testing (AE) • Microscopic evaluation • Radiography (RT) – Uses high energy photons (X-ray machine)

  3. NSI conference Acoustic Emission (AE) Overview • 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).

  4. NSI conference AE Principle • 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

  5. NSI conference AE HIT and Parameters • 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.

  6. NSI conference AE Applications • 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.

  7. NSI conference Built up section

  8. NSI conference Objective of the test • 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.

  9. NSI conference steel and composite samples Steel specimens Dimensions: 7 inches long, 1 inch wide, and 0.125 inch thick. Carbon composite specimens Dimensions: 7 inches long, 1 inch wide, and 0.06 inch thick.

  10. NSI conference Cont.. 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.

  11. NSI conference Cont.. 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.

  12. NSI conference AE Tensile test • 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)

  13. NSI conference AE Tensile test result of steel • 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.

  14. NSI conference Cont.. • 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.

  15. NSI conference 1/4/2020 • 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.

  16. NSI conference Microscopic Image before and after failure

  17. NSI conference Images and plots at failure loading

  18. NSI conference Steel Failure Specimen failure plane was at approximately at 45 degree angle from the horizontal.

  19. NSI conference Steel afilure The failure plane was at approximately at 15 degree angle from the horizontal.

  20. NSI conference AE test on carbon composite • 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.

  21. NSI conference Composite failure results • Higher amplitude, number of counts, and duration are observed near failure. • Higher amplitude is the sign of the fiber breakage and matrix cracking.

  22. NSI conference Outer layer crack Fibers in composite specimen run bidirectional in the outer layer and unidirectional in the inner layers.

  23. NSI conference Fiber Breakage and Pullout from Matrix

  24. NSI conference Matrix Debonding

  25. NSI conference AE results of E-glass • 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

  26. NSI conference AE results of Fiber glass • 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.

  27. NSI conference 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.

  28. NSI conference NSI conference X-ray of the steel specimens

  29. NSI 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

  30. NSI conference Industrial task

  31. NSI 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

  32. NSI conference Questions? Thank you!

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