Question

Part 1 Project description: You will need to select a material for “Frame of a Sport Car" using the criteria explained in chapter 7 The project is a short formal report and should include the following: . Cover page (the grading tool above and must be e-signed) • Table of content, figures and tables • Introduction (1 paragraph) • Theory about the part and its application (1 paragraph) The four steps of selecting material: (max 3 pages) Step 1- Translation: • Function - Objective - Constraint • Free variables . Step 2 - Screening (at least use one type of Ashby's chart) Step 3 - Ranking Step 4 - Select and verification (simply explain how you make sure your selection is correct or what type of testing you need to apply to verify your selection) . Consideration of the following factors: (max 2 pages) - Availability o Safety and risks o Environmental impacts . Conclusion (1 paragraph) References o Cost The project should not be more than 6 pages excluding the cover page, table of content and references. You must submit this part in a separate MS word or PDF file, using the same cover page as above, SIGNED and DATED. Part 2 Question 2.1: Explain the difference between ductile and brittle fractures. (2 marks)

Answer 1

2.1

Fracture can be defined as a separation of a body into pieces due to

stress, at temperatures below the melting point. The types of fracture

are ductile and brittle fractures.

1. Ductile fracture: It is a type of fracture that is characterized by

extensive deformation of plastic or necking. This type of fracture
$\textup{usually occurs prior to the actual fracture.}$

• 
  Extensive plastic deformation ahead of crack
  
• 
  Crack is stable, that is it resists further extension unless applied stress
  
  is increased
  
• 
  In ductile fracture, there is absorption of massive amounts of energy
  
  and slow propagation before the fracture occurs.
  

2. Brittle fracture: It is the sudden or very rapid cracking of

equipment under stress where the material exhibited little or no evidence

of ductility or plastic degradation before the fracture occurs.

• 
  Relatively little plastic deformation.
  
• 
  Crack is unstable, that is it propagates rapidly without increase in
  $\textup{applied stress.}$
• $\textup{Brittle fracture is often caused by low temperatures.}$

+ + + + + SHAPE OF ORIGINAL SPECIMEN BRITTLE FRACTURE DUCTILE FRACTURE

2.2

$\textup{Failure is mainly caused due to the defects in designing, process, or quality}$
which are the underlying cause of a failure. There are many different
$\textup{causes of failure such as:}$

• $\textup{Excessive deflection,}$
• $\textup{Buckling,}$
• 
  Creep,
  
• $\textup{Thermal shock,}$
• $\textup{Wear,}$
• $\textup{Corrosion.}$

2.3

$\textbf{Residual stresses} \textup{can be defined as stress fields that exist in the}$$\textup{absence of any external loads and are the result of any mechanical}$$\textup{process which can cause deformation. Generally residual stresses arise}$$\textup{whenever a component is stressed beyond its elastic limit and plastic}$$\textup{deformation occurs.}$

• $\textup{A residual tensile stress is sufficient enough to cause stress corrosion cracking.}$

2.4

$\textbf{A)} \textup{ Both Charpy and Izod impact testing are popular methods for}$$\textup{determining impact strength, or toughness of a material. These tests}$$\textup{measure the total amount of energy that a material is capable of absorbing.}$

B) The impact testing method is used to determine the appearance of

propagating fractures in plain carbon steels over the temperature range
$\textup{where the fracture mode changes from brittle to ductile.}$

2.5

Creep is a high temperature progressive deformation at constant stress.
$\textup{And a creep test involves a tensile specimen under a constant load}$$\textup{maintained at a constant temperature.}$

• $\textup{The test specimen design should be based on a standard tensile specimen.}$

2.6

$\textbf{Non-destructive testing (NDT)} \textup{is a testing and analysis technique}$
used by industry to evaluate the properties of a material, component,

structure or a system for characteristic differences and discontinuities
$\textup{without causing damage to the original part. NDT is also known as}$
non-destructive examination (NDE).

• 
  NDT does not directly measures mechanical properties but they are
  $\textup{used to locate defects or flaws in the component.}$