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The static tensile strength of metals.
Introduction.
In this experiment, we are looking to determine the strength and ductility of three
metal samples, being Aluminium, Brass and Steel.
We hope to find which of the properties, % elongation or % reduction of area, will
produce the most suitable indication of the ductility in each of the materials.
These properties are found by clamping the dogbone shaped samples in a
testing machine and applying a vertical axial stretch load.
The load is increased at a constant rate until the sample yields and it is pulled
apart.
The initial length, original cross sectional area, the applied load, final cross
sectional area and the final length are measured and from these the graph of
load vs. extension can be produced.
From this graph, values for the Yield Load, Yield Stress & Tensile Strength can
be obtained.
We can use the data acquired to then predict the failure of these metals in
everyday situations, and which metals would be more relevant for different uses
in construction.
These finding are extremely important in construction as the incorrect use of a
metal for the structure of a building could have catastrophic consequences ie
collapse.
If we have figures of Yield Load Tensile Strength we can see at which loads the
metal will cope with before there is a permanent deformity and also the load at
which the metal will fail.
Barry Heffron
Student No. 10401006
Session B2
Group 8
1
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View Full Document Theory.
To determine the values required to fulfil our aims, there are a number of steps
and calculations that need to be followed and carried out.
As the load is applied to the specimen, at first it will remain in the elastic portion
of the graph of Stress vs. Strain i.e. Hooke’s Law. If we were looking for a value
of Young’s Modulus we could do so by using the slope of the graph for this area.
As long as the sample remains in this portion, when the load is released from it, it
will return to its original state.
If however, we apply a load that takes us out of the elastic region, we will enter
the area where the sample will behave in a plastic manner, where there will be a
permanent deformation.
The point where this passes from elastic to plastic is called the limit of
proportionality. As we pass this limit, the specimens suddenly go through a
period where there is and extension with little or no increase in the applied load.
This is known as the Yield Point and we can determine the Yield Stress from this
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This note was uploaded on 11/24/2011 for the course SUR BLD115 taught by Professor Chapman during the Fall '11 term at Uni. Ulster.
 Fall '11
 Chapman

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