Post on 16-Mar-2018
Choice of materials
Engineering Materials and Processes
Reference Text Section
Higgins RA & Bolton, 2710. Materials for Engineers and Technicians, 5th ed, Butterworth Heinemann
Ch 27
Reference Text Section
Introduction (Higgins 27)
Engineering Materials and Processes
Bicycle development - frames
Ashby diagram:
Specific strength vs
Specific stiffness
27.2 Selection of materials (Higgins 27.2)
Engineering Materials and Processes
• The ability of the material to withstand service conditions.
• The method(s) by which it will be shaped.
• The overall cost, i.e. the cost of the material(s), with in some cases
the availability of the material, and the cost of the shaping
process(es).
27.3 Service requirements (Higgins 27.3)
Engineering Materials and Processes
Mechanical properties
Physical properties
Chemical properties
27.3.1 Tensile strength and specific strength
27.3.2 Stiffness, modulus of elasticity and specific modulus
27.3.3 Toughness and impact value
27.3.4 Fatigue resistance
27.3.5 Creep resistance
27.3.6 Refractoriness
27.3.7 Friction and wear resistance
27.3.8 Stability in the environment
27.3.9 Electrical conductivity
27.3.10 Relative costs of important engineering materials
27.4 Choice of shaping process (Higgins 27.4)
Engineering Materials and Processes
• Malleability
• Ductility
• Strength
• The effects of temperature on the above properties
• Castability
• Machinability
• Can it be heat treatment?
• How can it be joined?
27.4 Choice of shaping process (Higgins 27.4)
Engineering Materials and Processes
27.4.1 Processes
• Number of components required
• Equipment, tooling and labour costs, i.e. the capital costs to set up a
process and then the running costs
• Processing times
• Material costs and availability
• Component form, detail such as holes required, and dimensions
• Dimensional accuracy and surface finish required
27.4 Choice of shaping process (Higgins 27.4)
Engineering Materials and Processes
27.8.2 Changing conditions
Environmental Factors (Additional)
Engineering Materials and Processes
Disposal (bury it or burn it)
Reuse (collect it intact, clean it up and use it again)
Recycle (collect it as scrap and recover the material and use it somehow).
• Aluminium is very energy intensive to produce from ore, but as it is easy to
remelt, it is particularly cost effective to recycle.
• Although thermoplastics can be easily recycled once separated, the bulkiness of
scrap polymer products like drink bottles means that very large volumes have to be
collected, which is rarely economic.
• Even if they can be collected, mixed thermoplastics are difficult to separate and it
is probably more economic to burn the material to produce energy.
• In spite of their higher cost, composites are difficult to recycle because the fibre
and matrix cannot easily be separated, and ceramics cannot effectively be
recycled at all.
Recycling (Additional)
Engineering Materials and Processes
Ashby Diagram
Recycle Fraction - Cost
Energy cost (Additional)
Engineering Materials and Processes
Ashby Diagram
Energy content - Cost
Selection Summary(Additional)
Engineering Materials and Processes
Overview
Advanced Design and
Technology Third Edition,
Norman, Cubitt, Urry and
Whittaker. Longman 2000
p363
Engineering Materials and Processes
Wikipedia: Welding
Resources.
HI-RESOLUTION ASHBY CHARTS:
http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/hardcopy/colour/Photoshop300dpi/
DESIGN CASE STUDIES AND TUTORIALhttp://www-materials.eng.cam.ac.uk/mpsite/design.html
Glossary
Engineering Materials and Processes
Specific (density/stress etc)
Mechanical properties
Physical properties
Chemical properties
Service conditions
Duty cycle
Industrial design
Manufacturing energy content
Recycle fraction
Disposal
Re-use
Recycle
Product life-cycle
QUESTIONS: Joining of Materials
Higgins Ch27, Ashby, Norman
1. Define all glossary terms
2. On the specific stiffness - strength chart (Ashby Chart), the bubbles for the metals and alloys
tend to be elongated parallel to the strength axis. By considering the physical origins of
Young's modulus and strength in these materials, explain why this is so. (Norman 2000)
3. Explain why bike frames are made from steel, aluminium alloy, titanium alloy and carbon
fibre composites. Why are carbon fibre composites and titanium generally only found in
performance racing bikes. Discuss the practicality of making a bicycle frame out of a
polymer. (Norman 2000)
4. The dominant material in car bodies is steel, but there is now fierce competition from
aluminium and glass fibre composites. Use the energy content and recycle fraction selection
charts to compare how these materials compete with steel in a life cycle analysis of the car.
(Norman 2000)
5. Briefly the relative advantages and disadvantages of timber, metal and plastic window-
frames. Your answer should refer to one specific named material from each of the three
groups of materials: (i) manufacturing methods employed; (ii) durability and maintenance; (iii)
aesthetic factors. (Norman 2000)
Engineering Materials and Processes
QUESTIONS: Joining of MaterialsHiggins Ch27, Ashby, Norman
6. Research the manufacture of large wind turbine blades. List the required performance
needs, the potential materials and associated production processes. You may need to
research the size, design life, factors influencing wear, storm and other damage, risk factors.
(Norman 2000)
7. Old cars have metal door handles but today they are mostly plastic. Investigate the older
metal door handles and their finish and compare to the modern ones. List the reasons and
outline the pro’s and con’s of such a change. Describe design changes necessary when
switching from a metal to a plastic.
8. Designing and making a one-off product is very different to producing many thousands.
Using, as an example, a project you have made, discuss and sketch the changes which
would be needed to make it viable for mass production. Your answer should compare your
one-off product with a similar mass produced one in terms of: (i) choice of material, (ii)
shaping and forming, (iii) joining and assembly, (iv) applying finishes, and (v) evaluating and
testing. (b) Discuss the disadvantages of mass production of products. (Norman 2000)
9. Explain how a CO2-based penalty/incentive scheme (carbon-tax) would influence material
and process selection for a significant area of industry (e.g. transport, housing,
manufacturing etc). What are the pros and cons of this concept in terms of meeting an
environmental objective? Can you think of a better way to manage environmental resources?
Engineering Materials and Processes