Sean Carey

Tafe No. 366851615

Lab Report:

Schenck Tensile

Test

October 2012

Schenck . Tensile Testing

In this lab Experiment we are recording force and time during the destructive

testing of the specimen.

We are after the following:

UTS - Ultimate Tensile Strength,

YS - Yield Strength.

By interpreting the data with the assumption that E is known (Modulus of

Elasticity. or Young's Modulus), we can also determine:

Strain

Toughness

Resilience

% Elongation

Schenck Testing Apparatus

Schenck Laboratory Procedure

Before starting the lab, you must calculate the maximum load that can be

applied to the specimen, assuming a sensible UTS of the material. Note that in

practice, the UTS is nearly always higher than the published values. This is

because the published data is usually a 'guaranteed' value, or the lowest

value you would rarely, if ever, encounter. See Materials.htm for our list of

material data.

1. Take measurements of the specimen. Diameter, Length, etc. Ascertain

the material as best you can.

2. Load the specimen into the machine and set the strain rate

3. Run the test while recording force values.

Tensile / Axial Stress: = F /A

Tensile / Axial Strain: = x / L

Modulus of Elasticity: E = s / s

= Axial Stress (MPa)

A = Cross-sectional Area (mm2)

F = Force (N)

= Axial strain (no units)

L = Gauge length - originally (mm)

x = extension (mm)

E = Modulus of Elasticity (MPa)

Using the Formulas Below & graphing the results we can determine

• Ultimate Tensile Stress (UTS), MPa

• Yield Stress (YS), MPa

• Use Modulus of Elasticity (E), to determine Yield Strain

• Plot F/x and Stress/Strain graphs with calibrated axes

• Quantify resilience and toughness

In this Experiment we are using:

Diam 6 x 80mm long, Mild steel, 0.4%C, normalised at 900°C

The Data Sheet For this Steel is available at:

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=m4130r

Calculating Machine settings:

We must first estimate a value to pre-set the tester to:

Using Tensile Strength = Force / Cross sectional Area to determine this

Ultimate Tensile Strength = 670MPa (from data sheet)

C.S.A. = π(6/2)² = 28.278mm²

Therefore Max Force = Tensile Strength x C.S.A.

= 670 x 28.278 = 18946.26N

Machine Results:

From the Schneck Machine we get a series of force values which can be

plotted on a graph as follows.

We can then go on to plot Stress / Strain. However this is not a true

representation as the reduction in C.S.A and elongation of the test piece is

not uniform throughout the duration of the test.

0

5000

10000

15000

20000

25000

0 100 200 300 400 500 600

Forc

e A

pp

lied

(N

)

Time (t)

Schneck Results Force/ Unit Time

Yield Point:

From these results we can determine the yield point, the point at which the

test piece will no longer return to its original size as approx. 45 units on the x-

axis. Zooming into our graph or checking our machine results will give us an

accurate value.

Force Unit Time Stress

13612.72 40 481.3891718

13612.72 41 481.3891718

13593.1 42 480.6952401

13298.76 43 470.2862649

13593.1 44 480.6952401

13867.82 45 490.4102836

13946.31 46 493.1860103

Ultimate Tensile Strength (UTS):

From these results we can determine the Ultimate Tensile Strength, the

maximum force the test piece can take before it starts to crack and break

apart as approx. 410 units on the x-axis. Zooming into our graph or checking

our machine results will give us an accurate value.

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600

Strr

ess

(M

Pa)

Strain ( No Units)

Schneck Results Stress/Unit Time

Force Unit Time Stress

19793.97 403 699.9776505

19793.97 404 699.9776505

19793.97 405 699.9776505

19813.59 406 700.6715821

19793.97 407 699.9776505

19793.97 408 699.9776505

19793.97 409 699.9776505

The limitations of this experiment are that without an accurate means of

measuring an accurate value at the necking point, we are unable to get a

true Cross Sectional Area value throughout the experiment. This also applies

to the elongation of the test piece which also is not uniform throughout the

experiment.

Therefore we are unable to ascertain true values for Strain and Modulus of

Elasticity as these values are required. We are limited to “calculated

estimates”.

Resilience

Resilience is defined as the amount of force the material will take and still

return to its original shape. This is taken as a line from the yield point back

parallel to the original extension.

Toughness

Toughness is defined as the amount of force the material will take before it

breaks. This is taken entire graph area between initial loading and breakage.

Yield Point and Proof Stress:

1: True elastic limit

2: Proportionality limit

3: Elastic limit

4: Offset yield strength

The yield strength or yield point of a material is defined in engineering and

materials science as the stress at which a material begins to deform

plastically. Prior to the yield point the material will deform elastically and will

return to its original shape when the applied stress is removed. Once the yield

point is passed some fraction of the deformation will be permanent and non-

reversible.

Proof stress

When a yield point is not easily defined based on the shape of the stress-

strain curve an offset yield point is arbitrarily defined. The value for this is

commonly set at 0.1 or 0.2% of the strain. High strength steel and aluminium

alloys do not exhibit an obvious yield point, so this offset yield point is used on

these materials.