MatSE 259 Exam 1 Review Session

1
MatSE 259 Exam 1 Review Session

• Exam structure 25 questions, 1 mark each
• Do NOT forget to write your student I.D. on the
  answer sheet
• Exams are sent to UTS for machine grading
  please mark your answers clearly. No credit will
  be given if the machine cannot decipher your score

2
Steel designation
AISI-SAE numbering system for steels XX XX
Percent carbon (wt) x 100 Alloy content
For example, 5060 has ???
3
Aluminium alloy designation
Numbering system for Al alloys not the same as
steels
Numbering system also includes heat treatments
see website
4
Changing Mechanical Properties

• C content in steel
• Alloying elements
• Heat treatment
• - annealing, normalizing, tempering
• Mechanical working
• - cold rolling, hot rolling,

STRUCTURE changes
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Phase Diagrams
Differentiate between phase and state. Phase
A phase is a homogenous part of a system that has
uniform physical and chemical characteristics. Pha
se diagram is a plot showing the relationship
between temperature, composition and the
quantities of phases in a system. On a phase
diagram, you should be able to understand simple
heat treatments, like the T6 studied in
class. For example, Al 2024-T4.
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Mechanical properties

• Tensile testing
• Elastic deformation Plastic deformation Yield
• Hookes Law
• Hardness testing
• Penetration by indenter under load
• Types Rockwell, Brinell, Vickers, Knoop, Mohs
• Hardness-strength conversion

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Mechanical properties (contd.)

• Impact Toughness testing
• Charpy and Izod
• Ductile-to-brittle transition
• Creep testing
• Primary, secondary, tertiary
• Steady-state creep rate
• Fatigue testing
• S-N curves
• Fatigue limit, fatigue strength, fatigue life

8
Mechanical properties (contd.)

• Fracture Toughness testing
• Pre-cracked specimen
• Large Kc ? ductile fracture, small Kc ? brittle
  fracture
• Fractures
• Investigation of the fracture surface for the
  origin of crack Chevron markings, striations,
  beachmarks
• Be able to recognize ductile fractures/ brittle
  fractures/ intergranular fractures/ transgranular
  fractures/ fatigue fractures..

9
Crystal Structures

• Most common crystal structures for metals are
• Cubic close-packed
• Hexagonal close-packed
• Close-packed unit cells
• A2 (Body centered cubic)
• close-packed most densely packed
• Slip planes are the most densely packed planes in
  these structures.

10
Dislocations

• Dislocations move along slip planes ductility
• It is possible to plastically deform a material
  which contains dislocations

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Dislocations (contd.)

• The ability of a metal to deform depends on the
  ability of the dislocation to move
• Restricting dislocation motion will strengthen
  the material. Methods
• - solid solution hardening
• - grain size reduction
• - strain hardening (work hardening)
• - precipitation hardening (age hardening
  or aging)

12
Dislocation Interactions

• With each other
• - annihilate
• - entangle
• - form generators
• With grain boundaries
• - disappear
• - pile-ups

13
Resolved Shear Stress
?R(F Cos ?)/(A Cos ?)??Cos??Cos? The critical
resolved shear stress is the least stress
required to cause slip.
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T4
Natural Aging
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T4 (contd.)

• Properties
• Al 2024-O
• Tensile Strength 179 MPa 26000 psi
• Yield Strength 75.8 MPa 11000 psi
• Al 2024-T4
• Tensile Strength 469 MPa 68000 psi
• Yield Strength 324 MPa 47000 psi

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Charpy/Izod Bar
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Close-packed unit cells