My assumption is that the question relates to a paint added to a test sample for use as a distance reference in a non contact extensiometer. Paints separate from the support when the paint is less elastic than the test sample and/or the bond between the paint and test piece is weak. Try a different paint or, if possible, a very small area of a thin paint spot to minimize the adhesion challenge of paint.
Check on whether you can use Dynamic Mechanical Analyzer (DMA) which utilizes thermal analysis for the same.
may be you can use spray. If you have a optical system small spray drops are better to follow the displacement or the deformation.
Dear Yuxiang,
I have tried to implement in my laboratory the utilization of non-contact laser extensimeter to measure with high precision the strain during the tensile testing. The polymeric materials have been very different and in many cases, they were similar problems such in your case.
For polymer materials where you have a limited number of specimens (usually minimum 5) the situation is more dramatically if you are losing the data (strain vs. tensile strength) due to the incorrect information given by extensimeter. Could be also big errors in the calculus of Young’s modulus…
In this context, we have preferred to use the D 638 - 02a (Standard Test Method for Tensile Properties of Plastics) which allows to calculate the strain (nominal strain, nominal strain at break) using as initial parameter the distance between the grips of the tensile testing machine.
Nominal Strain -Nominal strain is the change in grip separation relative to the original grip separation expressed as percent.
Nominal strain at break- Calculate the nominal strain at break by reading the extension (change in grip separation) at the point of rupture.
Hoping that this information will be useful to you, I will not exclude the other suggestions given by our RG colleagues which can help even more…
Good luck in your R&D works and best regards,
Marius
We are using often such technique, first make the test when the paint is really fresh and it's sometimes easier to just follow two small points make from paint by using digital image correlation
Regards
Dear Yuxiang, dear RG colleagues,
I know well the R&D works realized by the team of Professor Franck Lauro, so I will recommend to follow this expertise. The digital image correlation is also very helpfully if you have the additional equipment.
However, if the number of tests/specimens is very big (e.g. from current pilot-scale or industrial production), and function of your practical possibilities, it is remaining for you choice to select the most adapted method…
Good luck in your R&D works and best regards,
Marius
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