Introduction
Objective
Using the tensiomenter estimate the
following properties of the given material on graph:
- Elasticity
- Plasticity
- yield stress
- fracture point
Apparatus
- Tensiometer
- Table
- Graph paper
- Test materials (i.e. Brass and Carbon steel).
Safety
Procedures
Tensiometer is an isolated instrument
so we do not have to take much safety precautions however using gloves and eye
protection may be essential as the material that we may use drop some particle
around. Further the specimen will fly off when it breaks, so the people around
must be paying attention.
Test
Procedure
Setup the tensiomenter on the table;
place a graph paper at the drum of the tensiometer, before fastening the
specimen in position we need to reset the gauge to zero (this will be on no
load condition), after placing the specimen in position as we put the material
in stress condition by turning the cam, as the more stress is applied it began
to elongate gradually and finally fails.
While the tensile force is applied we
keep marking the reference points which will help determining us the different
properties of the material on graph.
Before the material reaches its
fracture point and fails it goes through two stages
i)
Elastic range
ii)
Plastic range
Elastic range is the position wherein the material may show some abnormal behaviour
but it can retrieve to its original stage.
Plastic range is the position in which material show the abnormal behaviour but its
too late for it to be able to retrieve to its original position.
We repeated the same procedure for
two different specimen materials, i,e, brass and carbon steel.
Observation
As the material is elongated (due to
the stress applied) the area is reduced. The reduction in area leads the
material to its breakdown, apart from few of material was worn down and could
be seen under the tensiomenter.
The elongation and reduction in area
is noted in both the material. These properties are due to the yield stress
that any material has. Brass having lower yield stress breaks with lower stress
applied but have more elongation elastic or plastic range (material tend to be
less stiff). Carbon steel having higher yield stress has less elongation (both
elastic and plastic) but breaks with higher stress applied (material tend to be
more stiff).
Result
Brass showed more elongation and Carbon
steel showed lesser elongation before it broke. The following schematics are
obtained from the graph:
Brass has longer elastic and plastic
ranges and lower yield stress and ultimate tensile strength comparable to the
carbon steel i.e. carbon steel has short elongation ranges and higher yield
stress and ultimate tensile strength.
Conclusion
The higher the yield stress of
material, the lesser will be area reduction and hence more force required to
deform the material before it reaches its fracture point.
