Hi I have a polymer profile that has produced by extrusion process, I want to measure the residual stress along the transverse direction as far as I know XRD is not a good method for measuring residual stress of polymers and hole drilling is an expensive method for this purpose. can anybody offer me a method that is easily available and not an expensive method for this purpose?
I have attached the profile picture I want to measure the residual stress along the blue line.
Material is UPVC.
Thanks
Dear Mr. Dokhany
May I suggest two possible techniques:
Birefringence: I think it is the best method, easy to do and inexpensive. It needs only a pair of polarizer filters, easily obtained from internet. The disadvantage is it needs a transparent sample (you can prepare and extrudate your formulation without pigment) and is a bit difficult to interpret! But is the best I know.
Method: See the interference colours shown by the sample when observed between crossed polars. Judge the optical path difference, OPD, using the Michel Levy Chart and from the thickness calculate the birefringence. If the sample has a constant thickness then changes in the colour in different areas/points will indicate different levels of frozen internal stresses in the extrudate. With a bit of experience and training just by looking the sample through a pair of crossed polars will provide a lot of information. Mind that the calculated birefringence is a summation of internal stress and polymer chain orientation!
DMTA: dynamic-mechanical thermal analysis. Follow and compare the shape change of the storage elastic modulus E’ and tandelta intensity curves obtained during the first and second heating just below its Tg, which I foresee to be around 70 degrees C (you say it is an unplasticized PVC). Both variables (E’ and tandelta) curves will be displaced away from the curves shown by an unstressed UPVC sample (which is partially obtained after the first heating). The first heating will reduce the internal stress, showing the displacement of the curve after the heat treatment. The more displaced away the curve is the higher the frozen internal stress level in the sample.
Method: Slabs of 5mm width, 30mm long, use three-point bending, frequency 1Hz, heating rate 3 degree/min, Tamb < T < Tg + 30 degrees C, cut across the blue line.
Hope I have helped….. give a feed-back
Sincerely
Sebastian
Thanks Mr.Canevarolo for your accurate answer I will research about these methods and choose one of them to do.
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