Materials Selection Assessment 2022

Materials Selection 1
MATERIALS SELECTION
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Materials Selection 2
Materials Selection
1. Aim, scope and significance
The main aim of this assessment task is to investigate mechanical properties of materials so as to select
materials that meet specific design criteria of the proposed component for the playground equipment –
the ladder. The task comprises of using experimental data to analyze mechanical properties of the
material, identify the unknown material, determine a range of suitable materials that can be used to
manufacture the component, and select the best material based on various design criteria and
requirements. This task ascertains the importance of examining mechanical properties of materials so as
to select the best materials that has the capacity to perform the intended function effectively and
efficiently.
2. Part 1: Mechanical properties
Stress= Force
Cross sectional area
Cross sectional area, A = πr2 = π x (4mm)2 = 50.2655mm2
Strain= Extension
Original length CITATION Shand3 \l 1033 (Sharma, (n.d.))
A. Stress-strain graph
The stress-strain graph from the experimental data given is as presented in Figure 1 below
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-50
0
50
100
150
200
250
300
Stress-strain graph
Strain
Stress, N/mm²
Figure 1: Stress-strain graph
The graph has elastic or linear region, yielding region and plastic region (Peshin, 2016).
B. Key design parameters
i) Young’s Modulus of Elasticity (E)
This is obtained as the gradient or slope of the elastic region (straight line) of the stress-strain graph. It is
determined as follows:

Materials Selection 3
E= ∆ y
∆ x
(0.00000438, 0.8709231) (0.002778, 247.1529973)
E=247.1529973−0.8709231
0.002778−0.00000438 =246.2820742
0.00277362 =88,794.45 N /mm ²
ii) Yield stress
The yield stress is read directly from the stress-strain graph
σy = 268.6335 N/mm2
iii) Ultimate stress
The ultimate stress is read directly from the stress-strain graph
σu = 268.1570 N/mm2
iv) Fracture stress
The fracture stress is read directly from the stress-strain graph
σf = 169.1808 N/mm2
v) Ductility
Ductility is the same as percent elongation, which is calculated as follows (Engineers Edge, 2019):
Ductility= Lf −Lg
Lg x 100 %
Where Lf = final length of the material and Lg = original length or gauge length of the material
Lf – Lg = maximum extension/elongation of the material
In this case, Lf – Lg = 9.25151 mm
Lg = 25.1 mm
Therefore
Ductility= 9.25151 mm
25.1mm x 100 %=36.86 %
vi) Modulus of toughness
Modulus of toughness is determined as the area under the stress-strain graph from the origin to the
fracture or rupture point. The area under curve in this scenario is calculated by dividing the region under
stress-strain curve into different regular shapes and calculating the area of individual shapes. The region
is divided into a rectangle and trapezium and their areas calculated as follows
Area of rectangle = length x width
= 0.25 x 268 N/mm2 = 67 N/mm2
Area of trapezium = ½ h (a + b)
= ½ x 0.12 x (256.2063 + 169.5743)
= ½ x 0.12 x 425.7806