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I major in microelectronics. I just want to apply a fixed and adjustable force to my flexible sample.

  • 'Fixed' means that the force could be hold for given time without change.
  • 'Adjustable' means that the force would be changed after my setting or its value could be changed with time and rule.

It would be better if the force was horizontal.

My sample can endure the force with value about 10 N. And I hope the force could be adjustable between 0 and 10 N.

I think a stepper motor with load cell may be the solution but I don't know how to realize it exactly. The only thing I can think of is to hang different balance weight to one side of my sample. I know some kind of universal testing machines could also get this done but they are too expensive.

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With a spring and a (accurate) actuator you can create one.

One end of the spring is the force applicator the other end is moved by the actuator so the spring compresses a certain amount.

Then by Hooke's law you can control the force that the spring applies to your test piece.

This works best if the test piece doesn't deform.

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  • $\begingroup$ Thanks. You inspired me. I can make a jig like this. But any ideas with automation with spring stuff? Because I want to test my sample with some fixed force repeatly. $\endgroup$ – Nova Koan Jul 5 '15 at 15:00
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You may want to look at a related question: Applying an adjustable force to a small area

From the answers to this question, a small piston powered by air pressure may work. It has the ability to adjust the pressure as needed and will also be useful for keeping the same pressure even if your sample deflects under the load.

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  • $\begingroup$ Thanks, but I can't find any useful links about cylinder driven by compressed air and it seems to be a little dangerous. $\endgroup$ – Nova Koan Jul 5 '15 at 14:32
  • $\begingroup$ @NovaKoan I think that you are over estimating the amount of air pressure required. The nice thing about air pressure is that it is easily adjustable. As for finding products. This is a DIY pnuematic cylinder $\endgroup$ – hazzey Jul 5 '15 at 18:24
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    $\begingroup$ Compressed air is not any more dangerous than any other energy source, like any energy source, you have to be smart and safe about it. A I/P transducer connected to a small air cylinder would be ideal for doing what you want and enable control. $\endgroup$ – DLS3141 Jul 10 '15 at 16:53
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The poor man's solution would be to simply stack weights onto your sample.

While that seems low tech, you need surprisingly little different weights, which you can usually buy in sets, to get a massive range of forces.

The applied force is guaranteed to be independent of deflection, and this solution is also rather cheap compared to building specialized rigs.

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  • $\begingroup$ Yeah, I'd like to do so. Any ideas with automation with weights? Because I want to test my sample with some fixed force repeatly. $\endgroup$ – Nova Koan Jul 5 '15 at 14:36
  • $\begingroup$ The problem with that is that material fatigue (especially in polymers) is also dependent on how fast the onset of your force is. A simple solution would be to just attach your weights to a reciprocating mechanism (e.g., a rope attached to a pulley), but if you want precise control of the force, you will need to invest in an sensor/actuator mechanism, although that should be perfectly possible as well. $\endgroup$ – Sanchises Jul 5 '15 at 18:58

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