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  • Lateral force transducer design for indenter materials testing apparatus

    Discussion in 'The main mechanical design forum' started by biggoron, Jun 29, 2015.

    1. biggoron

      biggoron New Member

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      Hello,

      I am designing a simple solution to expand a commercial indenter apparatus (example: http://www.phase2plus.com/vickershardnesstesters/900-390.htm) to have the capacity for scratch testing procedures according to ASTM G171. To do this I need to add the capability for constant velocity lateral traveling for the stage which I plan to do with a simple stepper motor and drive belt attached to the x-axis micrometer. I also would likely to have the capability to measure lateral forces on the indenter stylus or stage due to this motion in order to measure a friction coefficient for the tested specimen.

      So far my only design idea for a lateral force transducer is an LVDT in series with a spring. However I don't think this is the best solution possible and I wouldn't know how to mount the LVDT to the stage/stylus properly to measure the lateral force accurately. Any suggestions or criticisms would be appreciated.
       
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    3. JPfalt

      JPfalt Member

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      Strain gage

      Place a tie bar between the driver and the stage an place a strain gage on the tie bar. Basically same idea as lvdt and spring, but cheaper, more compact, easier to calibrate and less likely to need maintenance.
       
    4. biggoron

      biggoron New Member

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      Thank you for the response JPfalt. Strain gauges on a cylindrical rod should have been the first idea that came to me coming from a mechanical engineering background.

      I haven't had good success finding commercial tie bar products online so I will likely machine a cylindrical rod for this application.

      Say I am machining a cylindrical aluminum rod as a tie bar. I am going to bore a hole (3-4 mm length) through the axis of the cylinder to allow it to mount axially onto the probe of a micrometer actuator using two radial set screws. Is there a standard for how far to place the strain gauge from such a borehole so as not to affect the uniformity of the stress intensities? This would effect the length of the tie bar I machine.
       

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