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Elastic modulus for Perspex

Hi I've completed an experiment on a sample of perspex to calculate E.
The experiment went as so...
Measured 'strain' on sample with Demac gauge at zero load, added a load, recorded immediate 'strain', then took readings every 20s for five mins.
When calculating E should I use the immediate 'strain' value, or an average, as it gradually increased for about two mins?
(I know strain=(reading at load-reading at zero load)xgauge factor)
The value of E for perspex is around 2.5 x 109Pa (depending on the type)
What have you obtained?
You seem to have stretched the sample beyond its elastic limit so any measurement of E is somewhat meaningless.
E is normally measured within the limits of stress-strain proportionality for the material.
What was the stated aim of the experiment? It it was to measure E then you have not really addressed this.
What you have done looks more like having the aim of investigating the behaviour of the material during plastic deformation.

Maybe you could tell us more about the precise aim of the experiment.
What level is this study at and on what course?
(edited 12 years ago)
Original post by FiverH
Hi I've completed an experiment on a sample of perspex to calculate E.
The experiment went as so...
Measured 'strain' on sample with Demac gauge at zero load, added a load, recorded immediate 'strain', then took readings every 20s for five mins.
When calculating E should I use the immediate 'strain' value, or an average, as it gradually increased for about two mins?
(I know strain=(reading at load-reading at zero load)xgauge factor)



Hi mate,

I am doing the same experiment and was wondering how you did it and what objectives to had and if you met them?

I am finding it quite difficult to understand the point. Also my value of E was 3.5 x 1011 Pa which is out by a factor 100!

any idea why
This is an old post from 2012 and is now closed.

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