Polymers Strain-Stress Machine

Don't waste your time. Buy one.

Instron : Materials Testing Machines for Tensile, Fatigue, Impact ...

believe me that the cheaper Instron is very far away from my research budget.

Well then, it's pretty straight forward.

You need a base and a movable cross head that is driven by some mechanical means. Instron uses a screw drive.

Strain guages to measure stress/strian and precision instrumentation to record the results.

Mechanical Hand-Held Tension Meters, Yarn Tension Meter

Or,

Images of precision fish scales

Maybe you can find a materials test lab to do the work.

I forgot to inclure that I can make the structure, with mechanical screws powered by stepper motors, but the hard part to me is the circuit board to control the strain gauges and their connection to a computer softwre.

I would

1. 'strain gages for plastics'

2. 'interface strain gage to computer' or 'strain gage bridge circuit to computer'

Have a read of this. Strain in plastics can be difficult to measure because the material behaves, well, plastically. It can continue to extend with no increase in load.

This happens in metals and minerals also. It is called CREEP. Even materials that are normally considered totally elastic exhibit CREEP to some degree. If op can't afford an Instron or equivalent machine, consider having the work done at an outside lab, or use a different measuring technology such as photo-elastic.