1. Exp.3: Extension of Wires
ENG. IBRAHIM KUHAIL
ENG. AHMED AL AFEEFY
Exp.3: Extension of Wires
2/19/2019

2. Objective
To verify that the modulus of elasticity is independent of wire size, and that it depends on the material from which the wire is made.
Exp.3: Extension of Wires
2/19/2019

3. Introduction
Hooke's Law stating that the deformation of a body is proportional to the magnitude of the deforming force, provided that the body's elastic limit is not exceeded.
If the elastic limit is not reached, the body will return to its original size once the force is removed.
Virtually any solid object will deform in some way when a force is applied to it, such as if it is squeezed or stretched.
Exp.3: Extension of Wires
2/19/2019

4. Introduction cont.
A simple physical system where we can observe this behavior is a wire acted on by a stretching force. If a force, F, acts on a wire of original length, L, the wire should stretch and its length should be greater by a change in length ΔL. If the wire behaved elastically according to Hooke's Law, we would expect that ΔL would be proportional to F:
F α ΔL
F= K ΔL
 ΔL = F/K
Exp.3: Extension of Wires
2/19/2019

5. Modulus of Elasticity σ = F/A , ε = ΔL / L σ α ε σ = E ε
F/A = E ΔL / L
E = F. L / ΔL. A
Exp.3: Extension of Wires
2/19/2019

6. Procedure Effect of cross sectional area.(same material)
Three test specimens of 16, 18 and 20 swg hard drawn brass wire are provided
Effect of material.(same cross sectional area)
For one size of wire, 18 swg, ( Steel ,brass) select test specimens in the other three materials
Exp.3: Extension of Wires
2/19/2019

7. Loading schedule for the wires
Material
Size
(swg)
Max. Load
(N)
Increments
Brass 20
100 10
16,18
200
Steel 18
Copper
Aluminum 80
Exp.3: Extension of Wires
2/19/2019

8. Results P (N) Steel 20 (0.88mm) Al 18 (1.23mm) Steel 18swg (1.23mm) 10
Reading (mm)
ΔL (mm) 10 20 30 40 50 60 70 80 90
100
Exp.3: Extension of Wires
2/19/2019

9. Results &Discussion Plot the load against extension for Part 1
Draw the "best fit" straight lines through each set of points and determine the gradients.
Then enter the experimental data in the formula for the modulus of elasticity. E = stress/strain = P/A•L/ΔL = L/A × gradient
Compare the three values of E.
On a second graph of load against extension plot the results of Part2, and add the comparable results for the same size wire from Part1. Obtain the gradients for each set of points and hence calculate the modulus of elasticity.
Exp.3: Extension of Wires
2/19/2019

10. Questions
What is the effect of cross sectional area on modulus of elasticity?(keep the material constant)
What is the effect of material on modulus of elasticity? ?(keep the size of wire constant)
Describe the effect of lack of straightness of the wire at "zero" load.
To what extent did the results conform to Hooke's law?
Exp.3: Extension of Wires
2/19/2019