Strain_gage_lab

# Strain_gage_lab - Name: Date of lab: _ _ Section number: M...

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Name: ______________________________________________ Date of lab: ______________________ Section number: M E 345._______ Lab 8 Precalculations – Individual Portion Strain Gage Lab: Measurement of Strain Precalculations Score (for instructor or TA use only): _____ / 20 1. What are the color bands on a 120 Ω resistor? 2. Look up and report the value of Young’s modulus for aluminum . Be sure to give the reference and the units . Write it down somewhere before you turn in these Precalculations, because you will need it to complete the lab. 3. In the cantilever beam setup sketched in the Introduction, determine which strain gage (top or bottom) would have positive strain (tension), and which would have negative strain (compression). 4. If a positive output voltage is desired when weight is added to the cantilevered beam, which strain gage (top or bottom) should be used in place of resistor R 3 in the quarter bridge Wheatstone bridge circuit? Explain. 5. Why might it be advantageous to have two strain gages (top and bottom) rather than just one? 6. Develop equations for the theoretical axial stress and axial strain on the cantilevered beam as functions of applied force (weight) F , moment arm L , beam width b , beam thickness h , and modulus of elasticity, E . Note : The equation you derive here for theoretical strain will be used to compare to the strain measured experimentally, so write it down before you turn in these Precalculations.

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Cover Page for Lab 8 Lab Report – Group Portion Strain Gage Lab: Measurement of Strain Name 1: ___________________________________________________ Section M E 345._______ Name 2: ___________________________________________________ Section M E 345._______ Name 3: ___________________________________________________ Section M E 345._______ [Name 4: ___________________________________________________ Section M E 345._______ ] Date when the lab was performed: ______________________ Group Lab Report Score (For instructor or TA use only) : Lab experiment and results, plots, tables, etc. _____ / 50 Discussion _____ / 20 Neatness & grammar _____ / 10 TOTAL ______ / 80 Comments (For instructor or TA use only) : NOTE: The instructor or TA reserves the right to deduct points for any of the following: Arriving late to lab or leaving before your lab group is finished. Not participating in the work of your lab group (freeloading). Causing distractions, arguing, or not paying attention during lab. Other (at the discretion of the instructor or TA).
Strain Gage Lab: Measurement of Strain Author: John M. Cimbala, Penn State University Latest revision: 15 April 2008 Introduction and Background ( Note : To save paper, you do not need to print this section for your lab report.) Axial stress is defined as force per unit area. Axial strain is the fractional change in length (change in length divided by length) of a material. Although it is difficult to directly measure stress, it is fairly straightforward to measure strain. Fortunately, stress is linearly proportional to strain for non-deforming loads on beams; thus, stress can be measured indirectly by measuring strain. Strain is traditionally measured with resistive-type strain gages . Strain gages work on a simple principle when a wire is stretched, its resistance increases . The effect is more pronounced if the wire is long; the longer the wire, the greater the increase in resistance. An effectively longer wire

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## This note was uploaded on 07/23/2008 for the course ME 345 taught by Professor Staff during the Spring '08 term at Penn State.

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Strain_gage_lab - Name: Date of lab: _ _ Section number: M...

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