1. Materials Chapter 2 Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

2. Chapter Outline Material Strength and Stiffness
Statistical Significance of Material Properties
Strength and Cold Work
Hardness
Impact Properties
Temperature Effects
Numbering Systems
Hot-Working Processes
Cold-Working Processes
Alloy Steels
Corrosion-Resistant Steels
Casting Materials
Nonferrous Metals
Plastics
Composite Materials
Materials Selection
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

3. Standard Tensile Test
Used to obtain material characteristics and strengths
Loaded in tension with slowly increasing P
Load and deflection are recorded
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

4. Stress-Strain Diagram
Linear relation until proportional limit, pl
No permanent deformation until elastic limit, el
Yield strength, Sy
Ultimate strength, Su
Ductile material
Brittle material
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

5. Elastic Relationship of Stress and Strain
E = modulus of elasticity
E is relatively constant for a given type of material (steel, copper)
Table A-5: typical values
Usually independent of heat treatment, carbon content, or alloying
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

6. True Stress-Strain Diagram
Engineering stress-strain diagram.
True stress-strain diagram
Engineering stress-strain
True Stress-strain
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

7. For ductile materials, Suc ≈ Sut For brittle materials, Suc > Sut
Compression Strength
For ductile materials, Suc ≈ Sut
For brittle materials, Suc > Sut
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

8. Torsional Strengths
Torsional strengths are found by twisting solid circular bars.
Max shear stress is related to angle of twist by
q = angle of twist (radians)
r = radius of bar
l0 = gauge length
G = shear modulus or modulus of rigidity.
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

9. Torsional Strengths Max shear stress is related to applied torque
J = polar second moment of area of cross section
Torsional yield strength, Ssy = max shear stress at the point where torque-twist diagram becomes significantly non-linear
Modulus of rupture, Ssu = max point on torque-twist diagram
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

10. Resilience
Resilience – Capacity of a material to absorb energy within its elastic range
Modulus of resilience, uR
Energy absorbed per unit volume without permanent deformation
Equals to area under stress-strain curve up to elastic limit
Elastic limit often approximated by yield point
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

11. Resilience Area under curve to yield point gives approximation
If elastic region is linear,
For two materials with the same yield strength, the less stiff material (lower E) has greater resilience
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

12. Toughness
Toughness – capacity of a material to absorb energy without fracture
Modulus of toughness, uT
Energy absorbed per unit volume without fracture
Equals area under stress-strain curve up to fracture point
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

13. Toughness Area under curve up to fracture point
Approximated by using average of yield & ultimate strengths and strain at fracture
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

14. Statistical Significance of Material Properties
Strength values are obtained from testing many nominally identical specimens
Strength, a material property, is distributional and thus statistical in nature
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

15. Example for Statistical Material Property
Histographic report for max stress of tensile tests on 1020 steel
Probability density: # of occurrences divided by total sample number
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

16. Example for Statistical Material Property
Probability density function (See Ex. 20-4)
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

17. Statistical Quantity
Statistical quantity described by mean, standard deviation, and distribution type
From 1020 steel example:
Mean stress = kpsi
Standard deviation = kpsi
Distribution is normal
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

18. Strengths from Tables
Property tables often only report a single value for a strength term
Important to check if it is mean, minimum, or some percentile
Common to use 99% min strength, indicating 99% of samples exceed the reported value
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

19. Cold Work
Cold work: Process of plastic straining below recrystallization temperature in the plastic region of stress-strain diagram
Loading to point i beyond yield point, then unloading, causes permanent plastic deformation, ϵp
Reloading to point i behaves elastically all the way to i, with additional elastic strain ϵe
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

20. Cold Work Yield point is effectively increased to point i
Material is said to have been cold worked, or strain hardened
Material is less ductile (more brittle) since the plastic zone between yield strength & ultimate strength is reduced
Repeated strain hardening can lead to brittle failure
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

21. Reduction in Area R is a measure of ductility
Ductility represents the ability of a material to absorb overloads and to be cold-worked
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

22. Cold-work Factor
Cold-work factor W: A measure of the quantity of cold work
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

23. Equations for Cold-worked Strengths
Dr. Mohammad Suliman Abuhaiba, PE

24. Example 2-1
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25. Example 2-1 (Continued)
Dr. Mohammad Suliman Abuhaiba, PE

26. Hardness
Hardness –resistance of a material to penetration by a pointed tool
Most common hardness-measuring systems
Rockwell
Brinell
Vickers
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

27. Strength and Hardness For steels For cast iron Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

28. Example 2-2
Dr. Mohammad Suliman Abuhaiba, PE

29. Impact Properties
Charpy notched-bar test used to determine brittleness and impact strength
Specimen struck by pendulum
Energy absorbed, called impact value, is computed from height of swing after fracture
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

30. Effect of Temperature on Impact
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

31. Effect of Strain Rate on Impact
Average strain rate for stress-strain diagram is in/(in·s)
Increasing strain rate increases strengths
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

32. Temperature Effects on Strengths
Strength vs. temperature for carbon & alloy steels
As temperature increases above RT:
Sut increase slightly, then decreases significantly
Sy decreases continuously
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

33. Creep
Creep: continuous deformation under load for long periods of time at elevated temperatures
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

34. Creep
Three stages
1st stage: elastic & plastic deformation; decreasing creep rate due to strain hardening
2nd stage: constant min creep rate caused by annealing effect
3rd stage: considerable reduction in area; increased true stress; higher creep rate leading to fracture
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

35. Material Numbering Systems
Common numbering systems
Society of Automotive Engineers (SAE)
American Iron and Steel Institute (AISI)
Unified Numbering System (UNS)
American Society for Testing and Materials (ASTM) for cast irons
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

36. UNS Numbering System Established by SAE in 1975
Letter prefix followed by 5 digit number
Letter prefix designates material class
G – carbon and alloy steel
A – Aluminum alloy
C – Copper-based alloy
S – Stainless or corrosion-resistant steel
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

37. UNS for Steels, G
First two numbers indicate composition, excluding carbon content
Second pair of numbers indicates carbon content in hundredths of a percent by weight
Fifth number is used for special situations
Example: G52986 is chromium alloy with 0.98% carbon
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

38. Alloy Steels Chromium Nickel Manganese Silicon Molybdenum Vanadium
Tungsten
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

39. Corrosion-Resistant Steels
Stainless steels
Iron-base alloys with at least 12 % chromium
Resists many corrosive conditions
Four types of stainless steels
Ferritic chromium
Austenitic chromium-nickel
Martensitic
Precipitation-hardenable
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

40. Casting Materials Gray Cast Iron Ductile and Nodular Cast Iron
White Cast Iron
Malleable Cast Iron
Alloy Cast Iron
Cast Steel
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

41. Nonferrous Metals Aluminum Magnesium Titanium Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

42. Nonferrous Metals Copper-based alloys Brass with 5 to 15 % zinc
Gilding brass, commercial bronze, red brass
Brass with 20 to 36 % zinc
Low brass, cartridge brass, yellow brass
Low-leaded brass, high-leaded brass (engraver’s brass), free-cutting brass
Admiralty metal
Aluminum brass
Brass with 36 to 40 % zinc
Muntz metal, naval brass
Bronze
Silcon bronze, phosphor bronze, aluminum bronze, beryllium bronze
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

43. Plastics
Thermoplastic – any plastic that flows or is moldable when heat is applied
Thermoset – a plastic for which the polymerization process is finished in a hot molding press where the plastic is liquefied under pressure
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

44. Table 2-2: Thermoplastic Properties
Dr. Mohammad Suliman Abuhaiba, PE

45. Table 2-3: Thermoset Properties
Dr. Mohammad Suliman Abuhaiba, PE

46. Composite Materials
Formed from two or more dissimilar materials, each of which contributes to the final properties
Materials remain distinct from each other at the macroscopic level
Usually amorphous & non-isotropic
Often consists of laminates of filler to provide stiffness and strength and a matrix to hold the material together
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

47. Composite Materials Common filler types: Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

48. Table 2-4: Material Families and Classes
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

49. Table 2-4: Material Families and Classes
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

50. Table 2-4: Material Families and Classes
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

51. Table 2-4: Material Families and Classes
Friday, April 14, 2017
Dr. Mohammad Suliman Abuhaiba, PE

52. Young’s Modulus for Various Materials
Dr. Mohammad Suliman Abuhaiba, PE