G-clamp
Weighted hook
Vichy Strain Bridge
The metal bar, complete with the weighted hook is clamped to the table, and then the strain gauge is connected to the strain bridge and zeroed. So as not to get any false readings.
Weights are added in 1kg increments and readings are taken off the strain bridge. This tells us how much strain the bar is under as we load it up.
Results are as follows
Weight loaded Strain
As you can see the results go up uniform ally.
Theory
The following equations are used to calculate the final stress on the bar.
Length of the bar 0.25M
Width of the bar 0.04M
Depth of the bar 0.006M
Force = weight * gravity 1kg * 9.81 = 9.81
2kg * 9.81 =19.62
3kg * 9.81 =29.43
4kg * 9.81 =39.24
5kg * 9.81 =49.05
Mass = P * L 9.81 * 0.25 =2.45
19.62 * 0.25 =4.90
29.43 * 0.25 =7.35
39.24 * 0.25 =9.80 49.05 * 0.25 =12.26
I =bd 0.04*0.006/12
- =7.2 * 10-10
E for steel is =200 * 10 9
12.26 * 0.003/7.2 * 10-10
= 51.19 N/m2
Strain
51.19/200 * 10.9
=255 * 10-6
As you can see the actual result of 253 * 10-6 is very close to the theoretical figure of 255 * 10-6, so the actual test was correct.
