ME345_Lecture_27 - ( a ) To do : Will V o be positive or...

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M E 345 Spring 2008 Professor John M. Cimbala Lecture 27 03/24/2008 Today, we will : Review the pdf module: Stress, Strain, and Strain Gages Do some example problems – strain gages and Wheatstone bridges Discuss an additional item not in the pdf notes: Transverse strain Example Given : We are measuring the strain on the surface of a car chassis beam. The beam’s modulus of elasticity is E = 193 GPa. We use one strain gage on the bottom of the beam, as shown; the strain gage factor is S = 2.02. We construct a quarter bridge Wheatstone bridge circuit, with the strain gage on resistor 2, as sketched below. All resistors, including the strain gage itself (when unloaded) are 120 Ω . The supply voltage is 5.00 V DC, and the bridge is initially balanced when there is no load.
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Unformatted text preview: ( a ) To do : Will V o be positive or negative when a downward load is added? Solution : V s = supply voltage R 1 R 2 R 4 R 3 V o + − + − Strain gage F Strain gage ( b ) To do : For a loading in which V o = -1.25 mV, calculate the strain ε a in units of microstrain. Solution : ( c ) To do : Calculate the axial stress in the beam under this load. Solution : ( d ) To do : Suppose we want more sensitivity, so we glue another strain gage on top of the beam. Which resistor should we use for this second active strain gage? Solution : ( e ) To do : For the setup of Part (d) with the same strain as in Part (b), calculate output voltage V o . Solution : F Original strain gage New strain gage...
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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 Pennsylvania State University, University Park.

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ME345_Lecture_27 - ( a ) To do : Will V o be positive or...

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