8/9/2019 Lab6B Experiment Guide
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MAE 244 circular beam under combined stress Lab 6-B.
Experimental guidelines for Strain Gage Application:
A Circular Beam under Combined Loading
Objective1). Use "Wheatstone Bridge" circuits to measure the
resistance change of a strain gage due toan applied load.
2). Use strain rosettes for determining principal directions and
stresses in a combined torsionand bending of a circular shaft
clamped at one end.
3). Related data and/or modeling analyses.
Procedure1). Specimen dimensions and material properties will be
given and/or measured in the lab
session.
2). Properly connect strain gage lead wires to the strain
indicator. Be familiar with the stepsto operate the strain
indicator.
3). The Circular Shaft:
Record the location of each rosette and the directions of all
the individual gages,
Connect each gage to a separate channel of the switch and
balance unit,
Connect the Switch and Balance unit to the strain indicator,
With no load, balance each gage circuit,
Apply 400 lb and 800 lb loads to the specimen. Record the strain
readouts of each
applied load from the strain indicator.
Data Analysis and Report1). For each applied load, based on the
measured strains, determine the principal directions
and the principal strains and stresses at the location of the
rosette.
2). For each applied load, an illustration of the graphical
solution by using Mohrs circle ofstrain.
3). For each applied load, derive the stresses (x, y, xy) at the
location of the rosette
from the experimental measurement by approachB in Page 3. Also,
calculate the stresses
(x, y, xy) by the theoretical approach in Page 2. And then
compare the results.Discuss
the results of comparison.
(To be continued on next page)
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8/9/2019 Lab6B Experiment Guide
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MAE 244 circular beam under combined stress Lab 6-B.
Combined Beam LoadingFor the circular beam as shown in the
following figure, theoretical stress solution can be
obtained by considering the torque T, shear force Vand bending
momentMx.
From free-body diagram, we know,Torque T =My= PL
Shear force V=P
Bending Moment Mx= PY
Polar moment of inertia4
2
1rJ = , where ris the radius of circular beam
Moment of inertia for the circular beam4
4
1rI =
The stress state at the free surface is,
At the surface, we know, Q=0, so
Material: Steel
E = 29.0 106 psi (200 GPa)
G = 11.2 106 psi (77.5 GPa)
= 0.29
Strain Gage Information:
R = 3500.2%
Sg = 2.045 0.5%
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