Abstract
Material choice is crucial to engineering design as material properties greatly affect the
performance of a component. Material properties also dictate shape and size a component
should be in order to be effective.
In this report, the findings of a tensile test (conducted on aluminium, high carbon steel and low
carbon steel samples), torsion test (conducted on aluminium, cast iron and low carbon steel
samples) and Charpy impact test (conducted on aluminium, high carbon steel and low carbon
steel samples, each at a high and low temperature) are presented. The data from the tensile
test and torsion test was plotted on stress-strain and shear stress-shear strain graphs. From
the torsion test, Young’s modulus, proof stress, ultimate tensile strength and failure strain
could be calculated. From the torsion test: shear modulus and toughness. From the impact
test: the impact toughness.
These tests were done in order to choose a suitable material, and subsequently calculate the
dimensions, of a pin and rod for use in an aircraft. This report finds that the rod should be
construced of high carbon steel and should have a thickness of 10 mm and a diameter of 4.64
mm. The pin should be made of low carbon steel and ashould have a diameter of 2.62 cm.
1.
Introduction
Various tests can be conducted in order to calculate the material properties of various
materials. For example, tensile properties such as Young’s modulus, ultimate tensile strength
and proof stress can be calculated using the data obtained by conducting a tensile test.
Similarly, the shear modulus and toughness of a material can be calculated using the data
obtained by conducting a torsion test and the impact toughness can be calculated using an
impact test.
Material choice is crucial to ensure systems and components do not fail when in use and so
the properties of a selection of potential material choices must be known and understood when
designing anything. Material choice also affects the design of objects, as components that
must perform the same task will have to be be different shapes and sizes if they are
constructed from different materials.
The aim of this report is to calculate the required material properties of aluminium, high carbon
steel, low carbon steel and cast iron, in order to make an informed decision on which material
should be used in the composition of both a pin and rod for use in an aircraft. Once a material
has been selected in accordance with the design requirements and data produced from the
tests, the dimensions of both the rod and pin will be calculated.
Aircraft components experience huge loads and a large range of temperatures, that can vary
from -50 °C to 85 °C. The material(s) selected in this report should be able to cope with these
conditions, whilst avoiding any plastic deformation or material fracture.
2.
Methods
3. Tensile Test
The tensile test was conducted using a Universal Testing Machine, as shown in Figure 1. The
sample was loaded into the machine and then preloaded with a 5kN tensile force, using the
control panel, in order to remove the slack from the experimental set up, before the
displacement value was set to zero. The three samples were: aluminium, high carbon steel
and low carbon steel. Before the samples were loaded into the machine, their gauge length
was recorded using vernier callipers and their diameter was measured at 3 points along their
gauge lengths using a micrometer. The diameter measurements for each sample samples
were then averaged out. Once a sample was inserted into the grips of the machine, the
extensometer was attached (as shown in Figure 2) in order to accurately measure small strain
extensions in the sample during elastic deformation. However, once the material began to
yield, the extensometer had to be removed so as not to damage it. The UTM was connected
to a computer that recorded the time, force, displacement, tensile stress and tensile strain data
of the experiment as a .csv file. The .csv files for the tensile test of each experiment were then
used in a python script in order to calculate the Young’s Modulus, proof stress, ultimate tensile
strength and failure strain of each material. This was done by plotting a stress-strain curve
and identigying various key points on the curve that corresponded to ultimate tensile strength
and failure strain. Young’s modulus was calculated by finding the gradient of the elastic region
and proof stress was found by drawing a line parallel to the elastic region, offset by a strain of
0.2%.