Experiment 4

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EXPERIMENT 4: STRAIN MEASUREMENTS USING STRAIN ROSETTES IN ALUMINUM BEAMS
Discussion and Conclusion
In this experiment, the rotational and transverse strain measurement for the aluminum beam were measured from the Strain Smart program and recorded. The pressure has been registered using the strain rosette indicator of the Smart Program. The program is the most convenient for use since it integrates the traditional Wheatstone bridge with the SGI measurements to give a more accurate value for the transverse and rotational strains. When we plot, the values of the recorded strains against the force applied as a load. It is revealed that the variation between the two is linear, but with a negative gradient straight lined graph. The Poisson’s ratio is manipulated from the comparison between the rotational and the oblique strains, with the constant stress beam. The negative gradient of the plotted graphs is equal to the Poisson’s ratio v which has also been calculated theoretically from the analysis above. For this experiment, the Poisson’s ratio turns out to be of value 0.26 for aluminum. The theoretical value for the Poisson’s ratio of aluminum is 0.33. Here, we note that the experiment is in fair agreement with the theory.
The Young’s modulus elasticity (E) is another important indicator in this experiment. E is a constant which can be calculated by applying the Mohr’s Cycle analysis. For the experiment, we plot a graph of rotational stress against the rotational strain.

The figure is likely to be a straight line with a positive gradient indicating that the variation is linear. The slope of the line is Young’s modulus, and for this case, it was calculated and found to be 10.3E6 (see the analysis), for aluminum. The other values that were calculated included: Shear Modulus of Elasticity (G), Applied Load (P), Bending Moment (M), and the Moment of Inertia (I). The summary of all these results is tabled as shown in the analysis sheet.
In conclusion, strain Rosettes was used to measure the rotational and transverse strains for an aluminum beam under constant stress. The values of the Youngs modulus and other constants were found to be very close to the expected theoretical values. The little variations could be as a result of the arrangements of the beams. The strain measurements were done using the Smart program that helped in minimizing the differences.