1. Shear in Rubber Apparatus
Exp. 3

2. Introduction
Rubber blocks in shear force are often used on engine and in equipment mounting to isolate vibrations. They do this by absorbing shock energy by deforming. This deformation leads to a decrease in cross-section as the block lengthens, an effect described by Poisson's Ratio.

3. Shear Modulus (Modulus of Rigidity)
The shear modulus is the elastic modulus we use for the deformation which takes place when a force is applied parallel to one face of the object while the opposite face is held fixed by another equal force.
The bigger the shear modulus the more rigid is the material since for the same change in horizontal distance (strain) you will need a bigger force (stress). This is why the shear modulus is sometimes called the modulus of rigidity.

4. Objective Measure the shear deformation of the block.
Determination of modulus of rigidity .

5. Equipment
A rubber block 150 x 75 x 25mm is bonded to two aluminum alloy plates.

6. Shear Modulus (Modulus of Rigidity)

7. Results 10 20 30 40 50 60 70 80 90 100 110 120 Load (N) Dial Gauge
(mm)
Deflection 10 20 30 40 50 60 70 80 90
100
110
120

8. Questions Plot the load against deflection
Draw the "best fit" straight lines through each set of points and determine the gradients. Then compute the modulus of rigidity (G).
Where the results are linear?
Would greater or lesser deflection improve linearity?