1. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Summary of Material Science Chapter 1: Science of Materials Chapter 2: Properties of Materials Chapter 3: Material Testing Chapter 4: Alloys of Materials Chapter 5: Plain Carbon Steels Chapter 6: Heat Treatment Chapter 7: Cast Iron Chapter 8: Plastics/Polymers Chapter 9: Composite Materials Chapter 10: Ceramics Chapter 11: Semiconductors & Diodes Chapter 12: Biomaterials Chapter 13: Electrochemistry

2. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MATERIAL SELECTION What materials could be used for containers of Coca-Cola?

3. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MATERIAL SELECTION What materials could be used for containers of Coca-Cola? Buy Coca-Cola in aluminium cans, glass bottles, and plastic bottles. Container material must be: Rigid, so that the container does not stretch unduly Strong, withstand the weight of the Coca-Cola Resist chemical attack by the Coca-Cola Able to keep "fizz" in the bottle, (prevent gas escape) Low density so that the container is not too heavy Cheap to buy Easy and cheap to produce the required shape

4. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MATERIAL SELECTION A bridge! Requirements include: Strength  it will not break. Stiff  will not stretch unduly. Can be produced and joined in lengths long enough to span the gap to be bridged. The materials cost and the fabrication costs are not too high. Corrosion resistant or can be protected. Can be maintained at a reasonable cost over a period of years.

5. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MATERIAL SELECTION Material Selection depends on three main factors: 1.The requirements imposed by conditions under which the product is used, i.e. the service requirements. 2.The requirements imposed by the methods of manufacture of the product. (if a material has to be bent as part of it's processing, it must be ductile enough to be bent without breaking.) 3.Cost

6. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials PROPERTIES OF MATERIALS 1.Mechanical properties. These are displayed when force is applied to a material and include: Strength Stiffness Hardness Toughness Ductility

7. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials PROPERTIES OF MATERIALS 2.Electrical properties These are seen when the material is used in electrical circuits or components and include resistivity, conductivity, and resistance to electrical breakdown. 2.Magnetic properties These are relevant when the material is used as, for example, a magnet or part of an electrical component such as an inductor that relies on such properties. Properties such as ferromagnetism, paramagnetism or diamagnetism (magnetic permeability).

8. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials PROPERTIES OF MATERIALS 4.Thermal properties. These are displayed when there is a heat input to a material and include thermal expansion and heat capacity. 5.Physical properties. These are the properties, which are characteristic of a material and are determined by its nature, including density, colour, and surface texture. 6.Chemical properties. These are, for example, relevant in considerations of corrosion and solvent resistance.

9. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials TESTING OF MATERIALS HDPEStainless Steel

10. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MATERIALS SELECTION TESTING OF MATERIALS

11. Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MECHANICAL PROPERTIES The mechanical properties are about the behaviour of materials, when subject to forces. When a material is subject to external forces, then internal forces are set up in the material, which oppose the external forces. (a) Tensile F F Area A o (b) Compressive F F Area (c) Shear F F Area 3 Types

12. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MECHANICAL PROPERTIES Important consideration: Force per unit area. If one stretched a strip of material by a force F applied over its original cross-sectional area A o, then the force applied per unit area is F/A o. The term stress (  ) is used for the forced per unit area: Stress has the units of Pascal (Pa), with 1 Pa being a force on 1 Newton (N) per square metre (m), i.e. 1 Pa = 1 N/m 2

13. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MECHANICAL PROPERTIES *Note you must convert millimetres to metres (SI units)

14. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MECHANICAL PROPERTIES L0L0 LL

15. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials MECHANICAL PROPERTIES

16. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Strength The Strength of a material is the ability of it to resist the application of forces without breaking. The forces can be tensile, compressive or shear. The tensile strength is defined as the maximum tensile stress a material can withstand without breaking:

17. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Strength Often it is not the strength of a material that is important in determining the situations in which a material can be used but the value of the stress at which the material begins to yield (i.e. deforms). L0L0 LL Elastic Plastic

18. Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Strength (a)Force-extension graph, A = limit of proportionality, B = upper yield point, C = lower yield point, D = maximum force, E = breaking point. (b)Stress-strain graph D Break Extension Force Limit of proportionality Tensile strength Upper yield stress Lower yield stress

19. Limit of proportionality Tensile strength Upper yield stress Lower yield stress Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Strength The limit of proportionality is given at point A. Up to this point Hooke's law is obeyed and the material shows elastic behaviour, beyond it shows a mixture of plastic and elastic behaviour. The stress at which the material starts to behave in a non-elastic manner is called the elastic limit. Generally at almost the same stress the material begins to stretch without any further increase in force, and therefore is said to have yielded (or deformed). For some materials such as mild steel there are two yield points, termed the upper and lower yield points. A

20. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Strength While in some other materials, such as aluminium alloys, the yield stress is not so easily identified and the term proof stress is used as a measure of when yielding begins. This is the stress at which the material has departed from a straight-line force- extension relationship by some specified amount. The 0.1 % proof stress is defined as the stress at which results in a 0.1 % offset. Proof stress

21. Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Stiffness The stiffness of a material, is the ability of a material to resist bending. Thus a stiff material would be one that undergoes a small change in length when subject to such forces. For most materials a graph of stress-strain gives initially a straight-line plot. The straight-line part of a stress-strain graph is called the modulus of elasticity (Young's modulus). Typical values are about 200 GPa (G represents 10 9 ) for steels and 70 GPa for aluminium alloys. A stiff material has a high value of modulus of elasticity.

22. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Ductility/Brittleness A measure of ductility is obtained by determining the length of a test piece of material, then stretching it until it breaks and then, by putting the pieces together, and measuring the final length of the test piece. A brittle material will show little change in length from that of the original test piece, but a ductile material will indicate a significant increase in length. Stress Strain 0 (a) Brittle Stress Strain 0 (b) Ductile Breaks

23. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Finding Yield Point (a)Shows stress-strain graph for a sample of mild steel. The upper yield stress is about 280 MPa. (b) Shows part of the stress-strain graph for a sample of an aluminium alloy. The 0.1% proof stress is about 460 MPa, and the 0.2% proof stress is 520 MPa. (c) Shows a typical plastic where there is no real straight-line part of the stress- strain graph. To measure the stiffness/Yield of the material, a secant modulus is often used. Unusual Case Usual Case (a) (b)(c)

24. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Ductility/Brittleness The percentage elongation indicates the measure of ductility, i.e. % Elongation = [Final Length(L 1 ) minus Initial Length(L 0 )] divided by [Initial Length(L 0 )] x 100 A reasonably ductile material, such as mild steel, will have an elongation of about 20%, or more. A brittle material, such as a cast iron, wiII have an elongation of less than 1 %. ΔLΔL

25. Chapter 2: Properties of Materials Speed (Rate) of Test The stress-strain properties of plastics are much more dependent than metals on the rate at which the strain is applied.

26. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Stress Strain FILL IN MISSING INFORMATION! Yield Point & Young’s Modulus based on slope Ultimate Tensile Strength Breaking Point

27. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Toughness A tough material is one that absorbs energy and plastically deforms without fracturing A Tough material requires more energy to break it than a less tough one.

28. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Toughness The area under the stress strain curve is a measure of the energy required to deform the material or the toughness Toughness Elastic energy released at fracture

29. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Toughness Extension Load Work Done A length of material being stretched by an amount x 1 as a result of a constant force F 1, then the work done is: Work Done = Force x distance….we know this! => Work Done = Force x extension Work Done = F 1 X 1 Work Done = F 1 X 1 + F 2 X 2 + F 3 X 3 +…(∫Fdx) That is the area under the graph Derivation

30. However, material toughness is defined as the amount of energy per unit volume. Since Stress = Force/Area  Force = Stress × Area Strain = Extension/Length  Extension = Strain × Length  Work Done = (Stress x Area) x (Strain x Length) Since the product of the area and length is the volume of the material, then [Work Done] / Volume = Stress x Strain  Toughness = Stress x Strain Thus the work done in stretching a material of unit volume to a particular strain is the sum of the work involved in stretching the material to each of the strains up to this strain. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Toughness

31. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 2: Properties of Materials Toughness The area under the stress strain curve is a measure of the energy required to deform the material or the toughness Toughness Elastic energy released at fracture

32. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Alternative ability of a material to withstand shock loads. Impact tests  Charpy and Izod tests. Energy needed to break a sample is measured (expressed in Joules (J)). A brittle material will require less energy to break it than a ductile one. Chapter 2: Properties of Materials Toughness

33. Chapter 2: Properties of Materials Impact Test (Toughness ) Units: Joules Or Joules /mm 2

34. Chapter 2: Properties of Materials Impact Test (Toughness ) Car crash: http://www.youtube.com/watch?v=_xwYBBpHg1I http://www.youtube.com/watch?v=_xwYBBpHg1I

35. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Fracture toughness: the ability of a material to resist the propagation of a crack. The toughness is determined by loading a specimen, which contains a deliberately introduced crack of length 2c and recording the tensile stress , at which the crack propagates. Symbol, K c and its units MPa m 1/2 is given by: Chapter 2: Properties of Materials Fracture Toughness Stress to propagate crack (K 1C ) Stress to initiate crack

36. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Fracture toughness is an intrinsic material characteristic and should be independent of the testing method Take for example an isotropic 2-phase material: Same force but longer distance  higher energy  higher toughness Chapter 2: Properties of Materials Fracture Toughness Elongated grainsUniaxial grains

37. Chapter 2: Properties of Materials Fracture Toughness

38. Chapter 2: Properties of Materials HARDNESS

39. Brinell Test: Hardened Steel Ball Vickers: Diamond /Pyramid Shape Cone Rockwell Tests (A,B,C): Uses depth not Area, Cone/Ball

40. Chapter 2: Properties of Materials ELECTRICAL PROPERTIES R=Resistance A=Area L = Length Intrinsic/ specific

41. Chapter 2: Properties of Materials THERMAL PROPERTIES λ

42. Chapter 2: Properties of Materials PHYSICAL PROPERTIES Weight (Kg), Appearance, Density (Kg/m 3 ) An aircraft under-carriage is required not only to be strong but also to be also of low mass. Required as high a strength as possible with as low a density as possible. Specific Strength. Steels tend to have specific strengths of the order of 50 to 100 MPa / Mg m -3, magnesium alloys about 140 MPa / Mg m -3, and titanium alloys about 250 MPa / Mg m -3.

43. Chapter 2: Properties of Materials CHEMICAL PROPERTIES Attack on materials by the environment in which they are situated is often a major problem, e.g. the rusting of iron. Attack of materials, when exposed in various environments, e.g. in aerated (exposed to air) water, in salt water, to strong acids, to strong alkalis, to organic solvents, to ultraviolet radiation. Plastic materials may dissolve in some liquids or absorb sufficient amounts of the liquid to have their properties changed. When the absorption occurs the plastic becomes permeable (flow into every part) in the liquid. The permeability is of vital concern if the plastic is being considered as a container for liquids (e.g. Coca Cola in a plastic bottle).

44. Chapter 2: Properties of Materials RANGE OF MATERIALS