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Paint Coating Characterisation for Thermoelastic Stress Analysis

This research explores the use of paint coatings in thermoelastic stress analysis, assessing the characteristics of different paint types and thicknesses. Theoretical and experimental approaches are compared to determine suitable coating parameters.

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Paint Coating Characterisation for Thermoelastic Stress Analysis

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  1. Paint Coating Characterisation for Thermoelastic Stress Analysis Andrew Robinson, Janice Dulieu-Barton, Simon Quinn, Richard Burguete

  2. Contents • Introduction to Thermoelastic Stress Analysis (TSA) • Basics and Setup • Surface Coatings for TSA • Characteristics • Paint Type • Paint Thickness • Theoretical vs. Experimental • Conclusions

  3. Thermoelastic stress analysis Bakis C.E. and Reifsnider K.L. (1991) The adiabatic thermoelastic effect in laminated fiber composites. Journal of Composite Materials , 25, pp 809-830. Wong A.K. (1991) A non-adiabatic thermoelastic theory for composite laminates. Journal of Physics and Chemistry of Solids,52(3), pp 483-494. Wang, W.J., Dulieu-Barton, J.M. and Li, Q. “Assessment of non-adiabatic behaviour in thermoelastic stress analysis of small scale components”, Experimental Mechanics, in press. DOI: 10.1007/s11340-009-9249-2.

  4. Motivation • Conventional thermoelastic stress analysis (TSA) is a well established non-contact, full-field stress analysis technique. • Residual stress measuring second order nonlinear effects: Temperature variations much smaller than those resolved during normal TSA. • Recent development in infra-red camera technology has lead to renewed interest into residual stress analysis using TSA. • Signal attenuation from paint coating is more significant. • This research is relevant to all practitioners of TSA where a surface coating is applied. 4

  5. ..what does this mean? Metallics: Surface Coatings for TSA Why do we use a paint coating? • Usually for metallic materials • To enhance and standardise emissivity • Avoid reflected radiation What do we normally do? • The standard used for previous TSA tests • “two passes of RS matt black paint”

  6. “two passes of RS matt black paint” ..is RS still applicable? ..what does ‘two passes’ mean? Coating Characteristics • Paint type • Paint Thickness – Operator Dependent • Loading Frequency effects How do we approach this? By comparing analytical and experimental thermoelastic constants RESULTS… 6

  7. Paint Type - Results Aluminium strip specimens: Calculated thermoelastic constant: 9.54 x 10-12 Pa-1 Good results for RS Matt Black and Plasti-kote Matt Super Black (Two passes applied for each paint) Further testing revealed RS Matt Black was better Paint thickness?

  8. Paint Thickness How was it applied? Successive passes of aerosol spray, from 1 – 6 passes. Very Operator Dependent • How was it quantified? • Confocal laser microscopy Typical thickness measurement data • Steel strip specimens • Calculated thermoelastic constant - 3.02 x 10-12 Pa-1 8

  9. Paint Thickness - Results 3.02 x 10-12 Pa-1 9

  10. Paint Thickness - Results • What is 2 or 3 passes? • 2 passes ranged from 12 to 23µm • 3 passes ranged from 17 to 29µm • Analysis suggests suitable paint thickness of between 15 to 25µm • Frequency range 7.5 to 15Hz 3.02 x 10-12 Pa-1 What next? 10

  11. Experimental vs Theory Theoretical coating response modelled as a complex wave problem: Theory (1993) Welch and Zichel What does this mean in reality? 11

  12. Theory How does theory compare to experimental results? Updated parameters – Our theory 12

  13. Theory Ideal TSA test conditions: Low thickness, Low frequency Theory predicts a decrease in response with increasing thickness or frequency In reality we have a trade off: Low frequency gives non-adiabatic conditions Low thickness and the surface is too reflective Experimental work suggests the variation is minimal if either frequency or thickness is sufficiently small. Experimental vs

  14. Surface Coatings - Conclusions • For thermoelastic stress analysis of metallic materials, RS matt black paint is a suitable coating. • A cyclic loading frequency of between 7.5 and 15Hz should be employed for future testing. • Acceptable paint thickness for thermoelastic measurements range from between 2 to 3 passes. This coating should correlate to a thickness of between 15 and 25µm. Paint coating characteristics are an important consideration for TSA

  15. Thank you…

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