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. Number Major alloy addition 1xxx - 2xxx Cu 3xxx Mn 4xxx Si 5xxx Mg 6xxx Mg & Si 7xxx Zn 8xxx other 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

5. 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.

6. 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

7. 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

11. 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.

14. Temp Time T4 Natural Aging

15. 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

16. Charpy/Izod Bar

17. Close-packed unit cells