Wednesday  |  Salon 7  |  02:30 PM–02:50 PM

#15675, The Development of a Novel Photoelastic and Mechanoluminescent Coating for Full-Field Strain Measurements

Reflection photoelastic strain analysis (RPSA) is a well-established experimental strain analysis technique that provides users with immediate qualitative and quantitative information. However, existing RPSA methods contain a number of issues, including complicated application methods, long timescales for data collection and limited to measuring only the principal strain difference.
This research introduces a new photoelastic coating, developed to improve upon the current RPSA procedures used in industry. The aim of this research was to develop a coating that could reduce the overall data collection time by focusing on coating application and curing methods whilst maintaining a sensitivity to strain comparable to existing photoelastic materials. The research was extended to design a novel dual-technique coating to make RPSA more insightful. By introducing a mechanoluminescent (ML) phosphor, a light distribution could be measured concurrently with RPSA. The ML data could potentially be used to define individual principal strain components when used alongside RPSA.
A standard operating procedure was developed for using a rationally designed UV curable formulation as a thin photoelastic coating alongside automated RPSA acquisition and processing equipment. The setup is able to measure principal strain differences to a resolution of 20 micro-strain whilst being able to calculate the thickness of the coating to correct for any thickness mismatches. The ML phosphor was also combined with the UV curable formulation without issue and used within the same setup.
By following the procedure, a thin (~50 µm) UV curable coating may be applied, cured and ready for RPSA measurements in under an hour. The calibration procedure for just the photoelastic coating is highly repeatable, possessing a calculated strain-optic coefficient of 0.08 ± 0.002 - a medium-high sensitivity photoelastic coating. The dualtechnique coating is able to generate a photoelastic response and a measurable ML light distribution.
The new photoelastic coating has a comparable performance to existing coatings but is much thinner, faster and easier to apply. By introducing a ML material there is the possibility to combine RPSA with ML in order to create a more insightful measurement technique. The outcomes of upcoming dual-technique coating investigations will be discussed at this conference.

William Fraser   University of Sheffield
Andrew Parnell   University of Sheffield
Rachel Tomlinson   University of Sheffield