tafila technical university

Faculty engineering

Experiment #3

Rubber test

Name: Salam Fayez Albaradie

Lecturer name: Dr.Tamer Alshaqarin

Date of submission: 23/3/2014

1. Introduction

Modulus of Rigidity or (Shear Modulus) which relates the components of the shearing Stress

and shearing strain is the coefficient of elasticity for a shearing force. It is defined as "the

ratio of shear stress to the displacement per unit sample length (shear strain)".

FIG (1): Shear stress and Shear strain

Rubber, there is two type of it. The nature rubber which formed naturally as a bark of a tree

and industrial rubber _which will be used in this report_ which used in wide Range as a

vibrations resistant in cars, engines, and other machines and it 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. Poisson’s ratio means that when a material

is stretched in one direction it tends to become thinner in other two directions.

2. Objective

Measure the shear deformation of the block.

To determine the variations of deflection with applied load.

To investigate the relationship between shear stress and shear strain.

Determination of Modulus of Rigidity.

Become familiar with Modulus of Rigidity, and its experiment.

3. Equipment

A rubber block 150 x 75 x 25 mm is bonded to two aluminum alloy plates. One of the Plates

is pined to wall. And there is a weight hanger (which have the load). And a dial gauge to

indicate the deformations in rubber block. See Fig (2) and there is some blocks used to apply

forces. See Fig (3)

4. Procedure

1. At first, adjust the dial gauge to zero reading. To avoid Zero error.

2. Put a weights, start from 5 N to 30 N, in 5 N increments.

3. After each 10 N write down the reading of the dial gauge (which represent the

Deformation of the rubber block), until the travel of the gauge is exceeded.

4. Record the reading in table (1).

5. Plot the results, and calculate the Modulus of Rigidity G.

5. Results

Table (1): Recorded Readings

force N elongation(mm) area m^2 shear (kpa) length (mm) tan(Strain

angle rad)

Strain angle

rad

4.9 0.11 0.00375 1.306666667 75 2.55852E-05 2.55852E-05

9.8 0.26 2.613333333 6.04738E-05 6.04741E-05

14.7 0.44 3.92 0.00010234 0.000102341

19.6 0.63 5.226666667 0.00014653 0.000146533

24.5 0.84 6.533333333 0.00019537 0.000195378

29.4 1.4 7.84 0.000325592 0.00032563

At first place the relationship between shear and strain angle, and calculate the Modulus of

Rigidity G.

These are the mathematical equations

FIG (4): Shear stress and Shear strain

Slope= the Modulus of Rigidity = 21.8 (mpa)

6. Comments and Recommendations

Errors founded and may be affected on results in the experiment due to many reasons listed

below:

1. Zero error: If the dial gauge’s reading isn’t zero at zero loads.

2. Human error: if the experimenter red the dial gauges and calculates incorrectly.

3. Environmental error: environment affects in rubber block properties, which

Mean that the reading of dial gauge which represent the deflection in rubber

Block depends on the temperature of the lab.

7. References

1. Books:

1. Beer, Ferdinand and other, Mechanics of Materials, 6th edition, Mc Graw Hill,2012.

2. Websites: 1. http://www.engineeringtoolbox.com/modulus-rigidity-d_946.html

2. http://eng.najah.edu/apparatus/2265

y = 21824x + 1.4602 R² = 0.93

0

1

2

3

4

5

6

7

8

9

0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E-04 2.50E-04 3.00E-04 3.50E-04

she

ar (

kpa)

(Strain angle rad)