1. Industrial Engineering Department 2 – Properties of Materials
ÜYD
Properties of Material
ANADOLU U N I V E R S I T Y
Industrial Engineering Department
2 – Properties of Materials
Spring 2005
Saleh AMAITIK

2. Properties of Materials
Manufacturing Processes
Properties of Materials
Spring 2005

3. Properties of Materials
Manufacturing Processes
Properties of Materials
Mechanical Properties.
Mechanical properties are useful to estimate how parts will
behave when they are subjected to mechanical loads (stresses)
Properties include: Strength, ductility, hardness, elasticity, toughness, creep, fatigue …etc.
Physical Properties.
Physical properties define the behavior of materials in response to physical forces other than mechanical
Properties include: density, specific heat, melting point, thermal expansion, conductivity, magnetic properties.
The manufacturing engineer should appreciate the design viewpoint and the designer should be aware of the manufacturing viewpoint
Spring 2005

4. Mechanical Properties
Manufacturing Processes
Mechanical Properties
Stress - Strain Relationships.
Strength
Ductility
Elasticity
Fatigue.
Creep.
Toughness
Hardness
These mechanical properties are usually determined by subjecting prepared specimens to standard laboratory tests
Spring 2005

5. Stress – Strain Relationships
Manufacturing Processes
Stress – Strain Relationships
Three types of static stresses to which materials can be subjected:
Tensile Stress - tend to stretch the material
Compressive Stress - tend to squeeze it
Shear Stress - tend to cause adjacent portions of material to slide against each other
Spring 2005

6. Manufacturing Processes
Tensile Test
Most common test for studying stress‑strain relationship, especially metals
In the test, a force pulls the material, elongating it and reducing its diameter
Spring 2005

7. Manufacturing Processes
Tensile Test
ASTM (American Society for Testing and Materials) specifies preparation of test specimen
Spring 2005

8. Manufacturing Processes
Tensile Test Machine
Spring 2005

9. Typical tensile test progress
Manufacturing Processes
Tensile Test
Typical tensile test progress
beginning of test, no load;
uniform elongation and reduction of cross‑sectional area;
continued elongation, maximum load reached;
necking begins, load begins to decrease; and
fracture.
If pieces are put back together as in (6), final length can be measured
Spring 2005

10. Tensile Test Video Clip
Manufacturing Processes
Tensile Test Video Clip
Spring 2005

11. Tensile Test Video Clip
Manufacturing Processes
Tensile Test Video Clip
Spring 2005

12. Defined as force divided by original area:
Manufacturing Processes
Engineering Stress
Defined as force divided by original area:
where
e = engineering stress;
F = applied force; and
Ao = original area of test specimen.
Spring 2005

13. Defined at any point in the test as
Manufacturing Processes
Engineering Strain
Defined at any point in the test as
where
e = engineering strain;
L = length at any point during elongation (instantaneous length); and
Lo = original gage length.
Spring 2005

14. Engineering Stress – Strain Curve in Tensile Test
Manufacturing Processes
Engineering Stress – Strain Curve in Tensile Test
It shows the basic relationship between stress and strain
Spring 2005

15. The two regions indicate two distinct forms of behavior:
Manufacturing Processes
Engineering Stress – Strain Curve
Two Regions of Stress‑Strain Curve
The two regions indicate two distinct forms of behavior:
Elastic region – prior to yielding of the material
Plastic region – after yielding of the material
Spring 2005

16. Elastic Region in Stress – Strain Curve
Manufacturing Processes
Elastic Region in Stress – Strain Curve
Relationship between stress and strain is linear
Material returns to its original length when stress is removed
The material obeys Hooke's Law: e = E e
where
E = modulus of elasticity (Young's modulus )
Spring 2005

17. Manufacturing Processes
Young’s Modulus
Young's modulus measures the resistance of a material to elastic (recoverable) deformation under load.
Its value differs for different materials
A stiff material has a high Young's modulus and changes its shape only slightly under elastic loads (e.g. diamond). A stiff material requires high loads to elastically deform
A flexible material has a low Young's modulus and changes its shape considerably (e.g. rubbers).
The stiffness of a component means how much it deflects under a given load.
Spring 2005

18. Manufacturing Processes
Yield Strength in Stress – Strain Curve
As stress increases, a point in the linear relationship is finally reached when the material begins to yield.
Yield Strength Y can be identified by the change in slope at the upper end of the linear region
Y = a strength property
Other names for yield strength = yield point, yield stress, and elastic limit
Spring 2005

19. Yield point marks the beginning of plastic deformation.
Manufacturing Processes
Plastic Region in Stress – Strain Curve
Yield point marks the beginning of plastic deformation.
The stress-strain relationship is no longer guided by Hooke's Law .
As load is increased beyond Y, elongation proceeds at a much faster rate than before, causing the slope of the curve to change dramatically.
Spring 2005

20. Tensile Strength in Stress – Strain Curve
Manufacturing Processes
Tensile Strength in Stress – Strain Curve
As the load is further increased, the engineering stress reaches a maximum and then begins to decrease.
The maximum engineering stress is called the Tensile Strength - TS (or Ultimate tensile Strength – UTS) of the material.
TS =
Spring 2005

21. Ductility in Tensile Test
Manufacturing Processes
Ductility in Tensile Test
Ability of a material to plastically deform without fracture
There are two common measures of Ductility
% Elongation
lf = specimen length at fracture; and
lo = original specimen length
lf is measured as the distance between gage marks after two pieces of specimen are put back together
% Reduction of Area
lf = final (fracture) cross-sectional area of the specimen; and
lo = original cross-sectional area of the specimen
Brittleness is simply the lack of significant ductility
Spring 2005

22. Mechanical Properties of Various Materials
Manufacturing Processes
Mechanical Properties of Various Materials
Spring 2005

23. Manufacturing Processes
True Stress
True Stress is defined as the ratio of the applied load F to the actual (instantaneous) cross-sectional area A of the specimen.
where
 = true stress;
F = applied force; and
A = actual (instantaneous) area resisting the load
Spring 2005

24. True Strain (natural or logarithmic strain) is calculated as
Manufacturing Processes
True Stress
True Strain (natural or logarithmic strain) is calculated as
where
 = engineering strain;
L = length at any point during elongation (instantaneous length); and
Lo = original gage length.
Spring 2005

25. Manufacturing Processes
True Stress – Strain Curve
If previous engineering stress‑strain curve were plotted using true stress and strain values
Spring 2005

26. (1) compression force applied to test piece; and
Manufacturing Processes
Compression Test
Applies a load that squeezes the ends of a cylindrical specimen between two platens
(1) compression force applied to test piece; and
(2) resulting change in height
Spring 2005

27. Compression Test Machine
Manufacturing Processes
Compression Test Machine
Video
Spring 2005

28. Engineering Stress in Compression
Manufacturing Processes
Engineering Stress in Compression
As the specimen is compressed, its height is reduced and cross‑sectional area is increased
where
F = applied force
Ao = original area of the specimen
Spring 2005

29. Engineering Stress in Compression
Manufacturing Processes
Engineering Stress in Compression
As the specimen is compressed, its height is reduced and cross‑sectional area is increased
where
F = applied force
Ao = original area of the specimen
Spring 2005

30. Engineering Strain in Compression
Manufacturing Processes
Engineering Strain in Compression
Engineering strain is defined
where
h = height at any point during elongation (instantaneous); and
ho = original height of the specimen
Since height is reduced during compression, value of e is negative (the negative sign is usually ignored when expressing compression strain)
Spring 2005

31. Engineering Stress – Strain Curve in Compression Test
Manufacturing Processes
Engineering Stress – Strain Curve in Compression Test
Shape of plastic region is different from tensile test because cross‑section increases
Spring 2005

32. Shear Stress and Shear Strain
Manufacturing Processes
Shear Stress and Shear Strain
Application of stresses in opposite directions on either side of a thin element
Shear Stress
Shear Strain
Shear stress is defined as
Shear Strain is defined as
where
F = applied force; and
A = area over which deflection occurs.
Where
 = deflection element; and
b = distance over which deflection occurs
Spring 2005

33. Shear Stress – Strain Curve
Manufacturing Processes
Shear Stress – Strain Curve
Typical shear stress‑strain curve from a torsion test
Spring 2005

34. where E = elastic modulus
Manufacturing Processes
Shear Elastic Stress – Strain Relationship
In the elastic region, the relationship is defined as
where
G = shear modulus, or shear modulus of elasticity
For most materials, G  0.4E
where E = elastic modulus
Spring 2005

35. Shear Plastic Stress – Strain Relationship
Manufacturing Processes
Shear Plastic Stress – Strain Relationship
shear strength S = Shear stress at fracture
Shear strength can be estimated from tensile
strength: S  0.7(TS)
Since cross‑sectional area of test specimen in torsion test does not change as in tensile and compression, engineering stress‑strain curve for shear  true stress‑strain curve
Spring 2005

36. Manufacturing Processes
Hardness
The ability of a material to resist scratching, wear and indentation.
Good hardness generally means material is resistant to scratching and wear
Most tooling used in manufacturing must be hard for scratch and wear resistance
Commonly used for assessing material properties because they are quick and convenient.
Several methods have been developed to measure the hardness of materials.
Most well‑known hardness tests are Brinell and Rockwell
and Vickers.
Spring 2005

37. Manufacturing Processes
Hardness Tests
Spring 2005

38. Widely used for testing metals and nonmetals of low to medium hardness
Manufacturing Processes
Brinell Hardness Test
Widely used for testing metals and nonmetals of low to medium hardness
A hard ball is pressed into specimen surface with a load of 500, 1500, or 3000 kg
Spring 2005

39. Brinell Hardness Number (BHN) = Load divided into indentation area
Manufacturing Processes
Brinell Hardness Test
Brinell Hardness Number (BHN) = Load divided into indentation area
where
BHN = Brinell Hardness Number;
F = indentation load, kg;
Db = diameter of ball, mm; and
Di = diameter of indentation, mm
Spring 2005

40. Temperature Effect Manufacturing Processes
General effect of temperature on strength and ductility
Spring 2005

41. Energy consumed = work done = force x distance
Manufacturing Processes
Toughness
Toughness is an estimate of how much energy is consumed before the material fractures.
Energy consumed = work done = force x distance
which you can easily see, is related to the stress and strain. So:
Toughness = the strain energy = area under the stress-strain curve
To compute toughness, True stress and True strain are used, which measure the instantaneous stress.
The tensile test can provide a measure of this property.
Spring 2005

42. For most materials, creep rate increases with increase in temperature.
Manufacturing Processes
Creep
If a material is kept under a constant load over a long period of time, it undergoes permanent deformation. This phenomenon is seen in many metals and several non-metals.
For most materials, creep rate increases with increase in temperature.
The phenomenon does not have much direct implication in manufacturing, but has significant use in design of parts that, for example, carry a load permanently during their use.
Spring 2005

43. The behavior is different for different materials
Manufacturing Processes
Fatigue
Fatigue is the fracture/failure of a material that is subjected to repeating cyclical loading, or cyclic stresses.
There are two factors: the magnitude of the loading and the number
of cycles before the material fails.
The behavior is different for different materials
Spring 2005

44. Weldability: depends on particular welding (joining) technique.
Manufacturing Processes
Machinability, Formability and Weldability
Machinability: depends not only on worked material but on applied machining process (range of meanings).
Formability (malleability, workability): materials suitability for plastic deformation (depends on process conditions).
Weldability: depends on particular welding (joining) technique.
Spring 2005

45. Physical Properties Defined
Manufacturing Processes
Physical Properties Defined
Properties that define the behavior of materials in response to physical forces other than mechanical
Includes: volumetric, thermal, electrical, and electrochemical properties
Components in a product must do more than simply withstand mechanical stresses
They must conduct electricity (or prevent conduction), allow heat to transfer (or allow its escape), transmit light (or block transmission), and satisfy many other functions
Spring 2005

46. Manufacturing Processes
Physical Properties in Manufacturing
Important in manufacturing because they often influence process performance
Example:
In machining, thermal properties of the work material determine the cutting temperature, which affects how long tool can be used before failure
Spring 2005

47. Thermal Expansion Manufacturing Processes
Thermal expansion is the name for this effect of temperature on manufactured part.
Measured by coefficient of thermal expansion 
Coefficient of thermal expansion is defined as change in length per degree of temperature, such as mm/mm/C.
Change in length for a given temperature change is:
L2 ‑ L1 = L1 (T2 ‑ T1)
where
= coefficient of thermal expansion;
L1 and L2 are lengths corresponding respectively to temperatures T1 and T2
Spring 2005

48. Thermal expansion is used in shrink fit and expansion fit assemblies
Manufacturing Processes
Thermal Expansion in Manufacturing
Thermal expansion is used in shrink fit and expansion fit assemblies
Part is heated to increase size or cooled to decrease size to permit insertion into another part
When part returns to ambient temperature, a tightly‑fitted assembly is obtained
Thermal expansion can be a problem in heat treatment and welding due to thermal stresses that develop in material during these processes
Spring 2005

49. Manufacturing Processes
Melting Properties of Metals
Melting point Tm of a pure element = temperature at which it transforms from solid to liquid state
The reverse transformation occurs at the same temperature and is called the freezing point
Heat of fusion = heat energy required at Tm to accomplish transformation from solid to liquid
Spring 2005

50. Metal casting - the metal is melted and then poured into a mold cavity
Manufacturing Processes
Importance of Melting in Manufacturing
Metal casting - the metal is melted and then poured into a mold cavity
Metals with lower melting points are generally easier to cast
Plastic molding - melting characteristics of polymers are important in nearly all polymer shaping processes
Sintering of powdered metals - sintering does not melt the material, but temperatures must approach the melting point in order to achieve the required bonding of powders
Spring 2005

51. Manufacturing Processes
Specific Heat
The quantity of heat energy required to increase the temperature of a unit mass of material by one degree
To determine the energy to heat a certain weight of metal to a given elevated temperature:
H = C W (T2 ‑ T1)
Where
H = amount of heat energy;
C = specific heat of the material;
W = its weight; and
(T2 ‑ T1) = change in temperature
Spring 2005