MatSE 259 Exam 1 Review Session
1. Exam structure – 25 questions, 1 mark each
2. Do NOT forget to write your student I.D. on the
answer sheet
3. 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
Steel designation
AISI-SAE numbering system for steels
XX XX
Percent carbon (wt) x 100
Alloy content
For example, 5060 has ???
Aluminium alloy designation
Numbering system for Al alloys not the same as steels
Number
1xxx
2xxx
3xxx
4xxx
5xxx
6xxx
7xxx
8xxx
Major alloy addition
Cu
Mn
Si
Mg
Mg & Si
Zn
other
Numbering system also includes heat treatments – see
website
Changing Mechanical Properties
• C content in steel
• Alloying elements
• Heat treatment
- annealing, normalizing, tempering…
• Mechanical working
- cold rolling, hot rolling,
STRUCTURE
changes
Phase Diagrams
Differentiate between “phase” and “state”.
Phase: A phase is a homogenous part of a system that has
uniform physical and chemical characteristics.
Phase 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.
Mechanical properties
Tensile testing
•
Elastic deformation – Plastic deformation –
Yield
•
Hooke’s Law
Hardness testing
•
Penetration by indenter under load
•
Types – Rockwell, Brinell, Vickers, Knoop,
Mohs
•
Hardness-strength conversion
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
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…..
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.
Dislocations
•
Dislocations move along slip planes – ductility
•
It is possible to plastically deform a material
which contains dislocations
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)
Dislocation Interactions
•
With each other
- annihilate
- entangle
- form generators
•
With grain boundaries
- disappear
- pile-ups
Resolved Shear Stress
R=(F Cos )/(A Cos )=CosCos
The critical resolved shear stress is the least stress
required to cause slip.
T4
Temp
Time
Natural Aging
T4 (contd.)
Properties
Al 2024-O
Tensile Strength
Yield Strength
179 MPa
75.8 MPa
26000 psi
11000 psi
Al 2024-T4
Tensile Strength
Yield Strength
469 MPa
324 MPa
68000 psi
47000 psi
Charpy/Izod Bar
Close-packed unit cells