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Stress and Strain

By Cindy Harper,2014-06-24 00:33
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Stress and Strain Stress and Strain

    Stress and Strain

    Danial J. Neebel, Joseph R. Blandino, and David J. Lawrence,

    College of Integrated Science and Technology

    James Madison University

    Instructor’s Portion

    Summary

    This lab illustrates the use of a strain gage. The gage is bonded near the

    clamped end of a cantilever beam. Weights are applied to the free end of

    the beam. The strain gage measures the axial elongation of the beam. The

    students plot a force vs. strain curve using LabVIEW. They then analyze

    the data and plot a stress vs. strain curve. From this curve, the students

    determine the modulus of elasticity of the beam. The students must

    determine the material used to fabricate the beam.

    Uses

    This exercise applies to mechanical engineering, physics, or a general

    instrumentation course.

    Equipment List

    ? Computer running Windows, Macintosh, Linux, Sun, or HP-UX

    (visit http://www.ni.com/labview/lv_sysreq.htm for

    requirements specific to your operating system)

    ? SCXI Bundle from National Instruments (part number 777448-37)

     LabVIEW Full Development System

     PCI-6024E Data Acquisition Board

     SCXI 1000 chassis

     SCXI 1349 cable

     SCXI 1180 feedthrough panel (not used in this experiment)

    ? SCXI Module from National Instruments

     SCXI 1121 4 Channel Isolation Amplifier

    (part number 776572-21)

    ? SCXI Terminal Block from National Instruments

     SCXI 1321 For use with the SCXI 1121

    (part number 777687-21)

    ? Strain Gage

    ? Cantilever beam

    ? Metal plate

    ? Clamp

    ? Mass hanger and variety of masses

    ? Balance for accurately measuring the masses

    ? Websites

     Omega www.omega.com

     National Instruments www.ni.com

    Setup

    Computer-based measurement systems are used in a wide variety of applications. In laboratories, in field services and on manufacturing plant

    floors, these systems act as general-purpose measurement tools well-suited for measuring voltage signals. However, many real-world sensors and transducers require signal conditioning before a computer-based measurement system can effectively and accurately acquire the signal. The front-end signal conditioning system can include functions such as signal amplification, attenuation, filtering, electrical isolation, simultaneous sampling, and multiplexing. In addition, many transducers require excitation currents or voltages, bridge completion, linearization, or high amplification for proper and accurate operation. Therefore, most computer-based measurement systems include some form of signal conditioning in addition to plug-in data acquisition (DAQ) devices. For more information on signal conditioning for computer-based data

    acquisition systems you can find National Instruments Application Note 48 online at www.ni.com.

    The LabVIEW VI is the Strain VI. Students input the beam dimensions

    and the applied load. The students must be careful to use consistent units. The bridge circuit is balanced using the offset potentiometer on the VI

    Stress and Strain 2

    front panel. Using the offset potentiometer is preferable to having the students adjust the offset on the SCXI-1321 terminal block.