EMT3701 Major Test 1

UNIVERSITY OF SOUTH AFRICA
SCHOOL OF ENGINEERING
CONTINUOUS ASSESSMENT
MAJOR TEST NO: 1
2021
EMT3701
ENGINEERING MATERIALS TECHNOLOGY II
Examiner: M Msibi Moderator: Z Shaikh

External Moderator: Y Kareem Marks: 80
Weight of Assessment: 35%
INSTRUCTIONS TO ALL STUDENTS:
This paper consists of 5 pages including this front page and formula sheet
1. You may answer the questions in any order

2. Use three decimal places for your calculations
3. Use your own discretion where information is not given, unclear or when
discrepancies occur, add a note to substantiate your reasoning
4. Do not submit a read only file, it will not be marked
5. Encrypted or password files will not be marked
6. Your file must be a PDF
Welcome to the School of Engineering.
NB you may download your paper from the myExams site!
To proceed with the writing of the test, click on the link below:
https://myexams.unisa.ac.za/portal/login
QUESTION 1
1.1 In the engineering manufacturing industry, one of the most common impacts is material.
There is always an opportunity to improve the material which is currently being used to a
material with good mechanical properties. Composite material is one of the materials
identified with good mechanical properties.
1.1.1 Name five advantages of using composite materials. (5)

1.1.2 List three limitations of using composite materials. (3)
1.1.3 If a manufacturing company is working on a low budget, which other material can
be used with similar mechanical properties as composites. (2)
1.2 There are currently more than eight manufacturing processes, comparing each of them
according to the achievable fiber volume fraction,
1.2.1 Which manufacturing process has the highest fiber volume fraction and what is
the range of the volume fraction. (3)
1.2.2 What is this manufacturing process used for (3)
1.2.3 Using a labelled diagram, explain how it works (10)
[26]
QUESTION 2
2.1 Explain qualitatively why the sandwich structure the figure below has such a high flexural
stiffness to weight ratios. Explain the key parameters affecting the flexural stiffness to weight
ratio of a sandwich panel. (10)
High strength
Film adhesive composite laminate
bonds facings to facings
core
Low density
honeycomb core
Figure 1: Composite Sandwich Structure
2.2 Using the table below, estimate the components of the matrices and develop the stiffness
and compliance matrices for an orthotropic lamina of AS/3501 carbon/epoxy.
(15)
[25]
QUESTION 3
3.1 The concrete composite post in Figure 2 is 1.5 m long with a 0.3 x 0.3 m square cross
section. The post is reinforced by four vertical steel rods of the same length having a cross-
sectional area of As = 0.00135 m2 each, and is loaded by a single vertical load P = 600 kN
applied on the rigid cover plate as shown below. The modulus of elasticity for concrete is Ec
= 17 GPa, whereas the modulus of elasticity of steel is Es = 200 GPa. Determine the stresses
in the steel rods and concrete. (20)
Figure 2: Composite concrete post
[20]
QUESTION 4
Using a diagram, explain how you would determine 𝐺!" , 𝑣"! and 𝐸! for an orthotropic,
transversely isotropic material from a single tensile test. (9)
[9]
TOTAL 80
FORMULA SHEET
𝐸# = 𝐸$# 𝑣$ + 𝐸% 𝑣% 1
𝜎: = < 𝜎𝑑𝑉
𝑉
1 + 𝜉𝜂𝑣$
𝐸! = 𝐸% ' , 1
1 − 𝜂𝑣$ 𝜀̅ = < 𝜀𝑑𝑉
𝑉
1
𝑆&# = 1
𝐸# 𝛿̅ = < 𝛿𝑑𝑉
𝑉
𝜈&!
𝑆&! = −
𝐸&
𝑈! = 𝑈' + 𝑈&
1
𝑆'' = 1
𝐺!" 𝑈! = - 𝜎!( 𝜀!( 𝑑𝑉
2 !
𝐶&& 𝐶&! 𝐶&" 0 0 0 1

⎡𝐶 𝑈' = - 𝜎'( 𝜀'( 𝑑𝑉
𝐶!! 𝐶!" 0 0 0 ⎤ 2 )!
⎢ && ⎥
𝐶 𝐶!" 𝐶"" 0 0 0 ⎥
𝑆 = ⎢ &"
⎢ 0 0 0 𝐶'' 0 0 ⎥ 1
⎢ 0 0 0 0 𝐶(( 0 ⎥ 𝑈& = - 𝜎&( 𝜀&( 𝑑𝑉
2 )"
⎣ 0 0 0 0 0 𝐶)) ⎦
𝜎# (𝑡$ + 𝑡% ) = 𝜎&$ 𝑡$ 𝑐𝑜𝑠 % 𝛼$ + 𝜎&% 𝑡% 𝑐𝑜𝑠 % 𝛼%

𝐸$# 𝜎' (𝑡$ + 𝑡% ) = 𝜎&$ 𝑡$ 𝑠𝑖𝑛% 𝛼$ + 𝜎&% 𝑡% 𝑠𝑖𝑛% 𝛼%
7𝐸 8 − 1
𝜂= %
𝐸$#
7𝐸 8 + 𝜉
%
1
𝜌! =
∑#"$%%𝜔"'𝜌" (
𝜌!
𝑣& = 𝜔
𝜌& &
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UNISA 2020

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UNIVERSITY OF SOUTH AFRICA

MAJOR TEST NO: 1

ENGINEERING MATERIALS TECHNOLOGY II

Examiner: M Msibi Moderator: Z Shaikh

1. You may answer the questions in any order

Welcome to the School of Engineering.

NB you may download your paper from the myExams site!

1.1.1 Name five advantages of using composite materials. (5)

Figure 1: Composite Sandwich Structure

Figure 2: Composite concrete post

𝐶&& 𝐶&! 𝐶&" 0 0 0 1

𝜎# (𝑡$ + 𝑡% ) = 𝜎&$ 𝑡$ 𝑐𝑜𝑠 % 𝛼$ + 𝜎&% 𝑡% 𝑐𝑜𝑠 % 𝛼%

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