MatSE 259 Exam 1 Review SessionMatSE 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 Major alloy addition

1xxx -2xxx Cu3xxx Mn4xxx Si5xxx Mg6xxx Mg & Si7xxx Zn8xxx other

Number Major alloy addition

1xxx -2xxx Cu3xxx Mn4xxx Si5xxx Mg6xxx Mg & Si7xxx Zn8xxx 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

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.

Phase Diagrams

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

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.)

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…..

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.

Crystal Structures

• Dislocations move along slip planes – ductility

• It is possible to plastically deform a material which contains dislocations

Dislocations

• 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)

Dislocations (contd.)

• With each other

- annihilate

- entangle

- form generators

• With grain boundaries

- disappear

- pile-ups

Dislocation Interactions

Resolved Shear Stress

R=(F Cos )/(A Cos )=CosCos

The critical resolved shear stress is the least stress required to cause slip.

Temp

Time

Natural Aging

T4

Properties

Al 2024-OTensile Strength 179 MPa 26000 psiYield Strength 75.8 MPa 11000 psi

Al 2024-T4Tensile Strength 469 MPa 68000 psi Yield Strength 324 MPa 47000 psi

T4 (contd.)

Charpy/Izod Bar

Close-packed unit cells