1. Prepared by Dr Diane Aston, IOM3

2. What is Materials Science and Engineering?
MODULE ONE
What is Materials Science and Engineering?
Prepared by Dr Diane Aston, IOM3

3. What is Materials Science and Engineering?
The aim of this module is to introduce you to the subject of materials science and engineering and give you an appreciation of why it is important to understand the processing, structure and properties of materials.
Prepared by Dr Diane Aston, IOM3

4. Understanding structure and properties
SESSION 2
Understanding structure and properties
Prepared by Dr Diane Aston, IOM3

5. Aims and objectives
This sessions aims to introduce techniques for characterising the structure and properties of materials and explore why this is important.
At the end of this session you should be able to:
Describe how the structure of materials can be characterised using different techniques;
Define key properties of materials such as tensile strength, yield strength, toughness, stiffness, hardness and explain why these are important to engineers;
Explain simple tests to measure the properties of materials.
Prepared by Dr Diane Aston, IOM3

6. What does it look like?
We need to be able to look at materials on a range of different scales in order to quantify aspects of their structure.
Prepared by Dr Diane Aston, IOM3

7. Characterising structure
Characterise structure in many ways:
Measure grain size
Measure particles in terms of their size and distribution
Measure degree of crystallinity
Measure relative amounts of different constituents
To do this we have to be able to observe the material on many levels.
Prepared by Dr Diane Aston, IOM3

8. Macrostructure This is the scale that we live at.
Can look at the material with the naked eye or use a magnifying glass or stereomicroscope.
Typical magnification is x2 to x10 and observing at a scale of a few millimetres.
Prepared by Dr Diane Aston, IOM3

9. Microstructure – using light
Optical microscopy, using either transmitted light or reflected light can be used to look at structure on a micrometre scale.
Typical magnification of up to a few hundred times.
240m
240m
Prepared by Dr Diane Aston, IOM3

10. Microstructure – using electrons
Scanning electron microscopy used to look at magnifications of up to a few thousand times.
Useful for looking at surfaces as get more appreciation of topography.
Sample needs to conduct electricity so may need to coat in gold or carbon.
Prepared by Dr Diane Aston, IOM3

11. Looking even smaller...
Transmission electron microscopy can be used to observe materials on the nanoscale. In this case electrons pass through the sample to produce the image.
Useful for characterising defects and particles in materials.
Use thin films or carbon replicas.
Prepared by Dr Diane Aston, IOM3

12. Looking smaller still...
Scanning tunnelling microscope is used for imaging surfaces at the atomic level and can achieve a resolution around 0.01 to 0.1 nanometres.
Atomic force microscopy newer and even more powerful.
Prepared by Dr Diane Aston, IOM3

13. Analysing structure and composition
X-ray diffraction can be used to determine crystal structure in metals.
Various spectroscopy techniques can be used to analyse chemical composition.
Prepared by Dr Diane Aston, IOM3

14. How does it behave?
We need to be able to define and quantify a range of different properties to help us to decide which material is best for a particular application.
Prepared by Dr Diane Aston, IOM3

15. Characterising properties
Physical and chemical properties:
Melting and boiling point, density, corrosion resistance, toxicity.
Structural or mechanical properties:
Strength, toughness, hardness, stiffness (Young’s Modulus), ductility, malleability, fatigue and creep resistance.
Functional properties:
Magnetic properties, thermal properties, electrical properties, optical properties, ‘Smart’ behaviour
Prepared by Dr Diane Aston, IOM3

16. Structural properties
Structural or mechanical properties are important to engineers as they tell us about how materials behave under different loading conditions.
We need to know how a material will behave under static and dynamic loading conditions during its service life and a number of tests are available.
By knowing the properties and understanding the mechanical behaviour of materials we can select the best one for the application.
By linking these properties to the structure of materials we can design them to suit our needs.
Prepared by Dr Diane Aston, IOM3

17. Quantifying strength The Tensile Test:
Uses standard test specimen which has a section with a constant cross section – gauge length.
Test piece is clamped into the machine and a load applied steadily until the specimen fails.
Prepared by Dr Diane Aston, IOM3

18. Tensile test results CERAMIC METAL POLYMER Ultimate tensile strength
Yield point
METAL
Stress
POLYMER
Stiffness
Strain
Prepared by Dr Diane Aston, IOM3

19. Quantifying toughness
The Charpy Impact Test:
Uses standard test specimen with a notch on one side.
Sample is placed in machine and hit with a swinging hammer.
Measure energy required to break the sample at different temperatures.
Prepared by Dr Diane Aston, IOM3

20. Impact test results
Materials experience a change in behaviour from ductile to brittle at a particular temperature (DBTT)
Behaviour varies with crystal structure.
Other factors also affect toughness.
Energy
Temperature
FCC
BCC
HCP
Prepared by Dr Diane Aston, IOM3

21. Quantifying hardness The Vickers Hardness Test:
A small pyramid-shaped diamond is pressed into the surface of a polished sample under a given load.
Measure indent to get hardness number.
Prepared by Dr Diane Aston, IOM3

22. Session 2 Summary
In order to understand materials fully we need to describe their structure and properties quantitatively.
A variety of techniques are available to characterise the structure of a materials on many different scales.
Material properties can be grouped in to physical and chemical, mechanical and functional behaviour and each of these is controlled by aspects of the structure.
A variety of test can be carried out to characterise mechanical properties and these are very important for engineers when selecting materials.
Prepared by Dr Diane Aston, IOM3

23. Prepared by Dr Diane Aston, IOM3

24. SUGGESTED ACTIVITIES
Following are a list of suggested practical activities, ideas for discussions and links to websites that you could use to support each session. This is by no means a comprehensive list and we encourage you to come up with other ideas and share these with us for future years.
Prepared by Dr Diane Aston, IOM3

25. Session 2 activities Electron microscopes Structures around you
Mechanical testing experiments
Prepared by Dr Diane Aston, IOM3

26. Electron microscopes
As an individual or small group research exercise investigate how one type of electron microscope works and what it is most useful for imaging:
Scanning electron microscope
Transmission electron microscope
Scanning tunnelling microscope
Atomic force microscope
Get each team to report their findings back to the group.
Prepared by Dr Diane Aston, IOM3

27. Structures around you
It is difficult to visualise the microstructures of the materials we take for granted.
Use a magnifying glass or microscope to investigate the macro and microstructure of common materials such as galvanised steel (crystals are usually visible on the surface), plywood, chipboard, wool, broken pottery, carbon fibre composite etc..
A number of microstructure image libraries are freely available on-line. Students could investigate the microstructure of a range of different materials and collect micrographs to demonstrate particular structures.
Prepared by Dr Diane Aston, IOM3

28. Mechanical testing experiments
Encourage students to do some research to define the following terms and describe why these properties are important to engineers:
Yield strength
Ultimate tensile strength
Stiffness (Young’s modulus)
Hardness
Toughness
Ductility
Malleability
A number of demonstrations to investigate mechanical properties are available on-line. In addition, many simple experiments are describes in the Teachers Pack on Experiments in Materials Science.
Prepared by Dr Diane Aston, IOM3

29. Prepared by Dr Diane Aston, IOM3