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A theoretical estimate of the strain can be obtained by drawing on topics from CEEn 203. The stress on thesurface of a beam in bending is given by

equation (5)

where M is the applied moment at the location of interest, y is the distance from the neutral axis (in this case,the half height of the beam cross section), I is the area moment of inertia of the cross section with respect to the neutral axis.Recall that for a rectangular cross section,

equation (6)

Recall also that stress and strain are related by Young’s modulus:

equation (7)

For aluminum, E = 10.4x10^6 psi.

5. Using equations (5) through (7), estimate the strain where the gages are bonded to the beam. How does thetheoretically obtained strain compare to the value determined from measurements? If they are different, what are some possiblereasons?

Part 4: experiments with half and full bridges

Repeat parts 2 and 3 for the half bridge and the full bridge configurations.

Part 5: measurement of an unknown load

Based upon the calibration determined in step 2, use your beam to determine the weight of an arbitrary object.You may use the quarter bridge, the half bridge, or full bridge configuration for this test. Measure the actual weight using aprecision scale. How does the weight determined with your beam compare to the object's true weight? How certain is yourmeasurement? What are some possible sources of uncertainty?

Part 6: sensitivity to extraneous loads and temperature variations

Strain gages are often used as transducers to measure force in a structure or mechanical device. A perfect sensoris sensitive only to changes in the variable of interest and is completely insensitive to changes in extraneous parameters. (Such asensor is impossible to create.) In practice, every effort should be made to minimize sensitivity to extraneous variables. In thecase of the cantilever-beam scale, the objective is to measure the weight of objects or alternatively, to measure forces in thevertical plane. As such, a good design will be much less sensitive to loads in other directions (axial, lateral, torsional, etc.).Also a good design will not be sensitive to strains induced by other means, such as thermal expansion.

Your TA will supervise in the following two demonstrations.

6.1 lateral sensitivity

Use the instrumented beam of square cross section provided by your TA.

1. Clamp the beam in a cantilever fashion so that it will measure vertically applied loads.

2. Using your hand, gently apply lateral and axial loads to the beam. Do your best to not apply vertical bendingloads to the beam.

3. Compare the sensitivity of the quarter bridge to that of either the half bridge or full bridge to theseextraneous loads. Which configuration seems to work the best overall? Explain why this is so. Which extraneous loads are"rejected" by which configurations? Explain why. (Note: The steps of this paragraph are more easily said than done. The point is thatthe quarter bridge is more sensitive to off-axis loads than either the half bridge or full bridge. If you have difficultydemonstrating this, don't stress out.)

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
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Sherica
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what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
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a perfect square v²+2v+_
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
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or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
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ramon Reply
Kristine 2*2*2=8
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Differences Between Laspeyres and Paasche Indices
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No. 7x -4y is simplified from 4x + (3y + 3x) -7y
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is it 3×y ?
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J, combine like terms 7x-4y
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what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Cied
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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what is system testing?
AMJAD
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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AMJAD
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AMJAD
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Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
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Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
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Prasenjit
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Damian
silver nanoparticles could handle the job?
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Azam
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Introduction to mechanical measurements. OpenStax CNX. Oct 18, 2006 Download for free at http://cnx.org/content/col10385/1.1
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