Homework 6 on chapter 6
Reading assignments: Chapter 6 from textbook, notes and slides StudentName: MTSUID:

Honorpledge:I acknowledge that I have neitherreceived

nor given any unauthorized help/aid during this assignment.

Part 1 Key Engineering Terms: fill intheblanks -

1. Hotworking: permanent deformation ofmetalsand alloys above the recrystallizationtemperature.

2. Coldworking: permanent deformation ofmetalsand alloys above he recrystallizationtemperature.

3. Hardness and ductilityexhibit inverse relationship.

4. Ductility: The measure of degreeofplastic permanent deformation that has been sustained at fracture.

5. Elastic deformation: if a metal is deformed by aforce Return to its original dimensions after force isremoved.

6. Engineeringstress:average uniaxial force dividedby original cross-sectionalarea.

7. Engineering strain: change in length of the sample divided byunit Original length.

8. Shear stress:ratioof shear forcedivided by area on which itacts.

9. Modulus of elasticity: stress divided by strain inthe Elastic region of an engineering stress-straindiagram.

10. Yield strength:thestress at which material just begins to plasticallydeform.

11. Offset yield strength: value ofstressat 0.2%strain.

12. Resilience: it is the capacity of material to absorb energy whendeformed Elastically .

13. Toughness: Property that is indication of material's resistanceto Brittle fracture when a crack ispresent.

14. Ultimate tensile strength:the maximum stress into engineering stress strain curve before material fractures.

15. True stress: loaddivided by instantaneouscross-sectionarea.

16. Hardness: Measure of material's resistance tolocalized Plastic deformation.

17. Dislocation:a linedefect whereanarray of atoms are missing resulting in latticedistortion.

18. Slip: the process by which plastic deformation is producedby Dislocation motion.

19. Critical resolved shear stress: the minimum amount of shear stress required toinitiate slip.

20. Twin boundary: a special grain boundary across which the grainsshow Mirror latticesymmetry.

21. Recovery: the first stage in the annealing process that results in removalof Residual stresses and formationof Low energy dislocationconfigurations.

22. Grain boundary actsasa barriertodislocation movement.

23. Recrystallization: the second stage of annealing process in which new grains start to grow and dislocation density_ decreases significantly.

24. Solid solution strengthening: alloying materialswith Solute atoms that go intoSubstitutionalorinterstitial solidsolution.

25. Strain hardening: it is a phenomenon by which ductile material becomes harder and stronger asit is plastically/permanently deformed.

26. Superplasticity: the ability of some metals to deform plasticallyby 1000% to 2000% at high temperatures and low loadingrates.

Part 2:Learningconcepts/reflections/problems -

1. (a) Explain the three stages of annealing treatment in 2-3 sentenceseach.

(b) Explain any five properties that we can measure using a stress-strain curve under uniaxialtensileloading.

2. What are the 4 strengthening mechanisms of metals? Explain each mechanism in 4-5 sentences.

3. Consider a cylindrical specimen of some hypothetical metal alloy that has a diameterof 10.0 mm. A tensile force of 1500 N produces an elastic reduction in diameter of 6.7 × 10- 4 mm. Compute the elastic modulus of this alloy, given that Poisson's ratio is 0.35.

4. A 0.505-in.-diameter aluminum alloy test bar is subjected to a load of 25,000 lb. If the diameter of the bar is 0.490 in. at this load, determine

(a) the engineering stress andstrain and

(b) the true stressandstrain.

5. (a) A 10-mm-diameter Brinell hardness indenter produced an indentation 2.50 mm in diameter in a steel alloy when a load of 1000 kg was used. Compute the HB of this material.

(b) What will be the diameter of an indentation to yield a hardness of 300 HB when a 500-kg loadisused?

Part 3:Materialsdesign -

1. Why are nanocrystalline materials stronger? Explain answer based on dislocation activity.

2. What are the five important factors that affect the recrystallization process inmetals?

3. Consider casting a cube and a sphere on the same volume from same metal. Which one would solidifyfaster?Why?

4. Why is it difficult to improve both strength and ductility simultaneously?

Bonusquestions: -

1. Why are cast metal sheet ingots hot rolled first instead of being coldrolled?

2. Why does slip in metals usually take place on closed packed planes and in closedpacked directions?