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?