MAE 3181 Materials and Structures Lab
1. (10p) Write down the expression providing the variation of shear stress on the cross section of a circular cylinder subject to torsion.
r=cross-sectional radius of cylinder at any point, varies from zero to R
J=polar moment of inertia
2. (10p) Why is the torsion of bars with noncircular cross section more difficult to analyze?
In plane warping changes the shape of the cross-section and out of plane warping making the cross-section not planar anymore.
3. (10p) Why are automotive springs sold in pairs?
Springs on the same axle need to have the same stiffness. Spring stiffness decimates over time so if only one was replaced the vehicle would not drive in a balanced manner. This can make one wheel lose contact with the ground and the vehicle lose control.
4. (10p) Briefly describe the experiment that you have witnessed in the video recording: what was tested, how, what was observed and what data was acquired.
The objective of this experiment is to perform torsion test which will be used to compare experimental strain with analytical strain. This test should prove the helical spring is a torsion device. There are 2 rosettes with 3 strain gages in each placed on a coil of the spring. Using a universal testing machine, a load is applied to the spring quasi-statically up to 1200 lbf. The gages are connected to a data acquisition software along with a sensor from a load cell. The strain in each gage and the load being applied are displayed in LabVIEW along with a plot showing the load applied at each crosshead displacement. Once 1200 lbf is reached, the crosshead is returned to its original position and the spring’s deformation can be seen.