Material Properties: Elasticity, Deformation, and Fracture

Key Concepts in Material Properties

This document addresses several fundamental concepts related to the mechanical behavior of materials, including elasticity, deformation, and fracture mechanisms.

Elasticity and Deformation

• 3. Higher creep modulus, higher viscoelasticity: b) False.
• 4. Higher temperature (T), higher modulus of flow: a) True.
• 5. Higher tension, lower modulus of flow: b) False.
• 10. Modulus of elasticity of a material: e) Depends on the type of material. (It does *not* depend on the applied force or the material's area.)
• 11. A more elastic material deforms more than another under the same force and has a lower yield strength: a) True.
• 12. Plastic deformation is permanent, and stress occurs for a well-defined value: a) True.
• 14. The greater the modulus of elasticity: a) Increased rigidity, d) Less elasticity.
• 16. In a high-yield material: b) The movement of dislocations is difficult, d) Plastic deformation occurs with difficulty.
• 20. As a general rule, materials with a small elasticity modulus will have greater tenacity: b) False.

Tensile Testing and Material Strength

• 9. In a tensile test: a) Specimen elongates, c) Area decreases, e) Elongation depends on strength, g) Change in length (Δl) depends on elongation and area.
• 18. A material subjected to tension equal to its tensile strength: d) Begins to fracture.
• 19. Before the voltage achieves tensile strength: a) The cross-sectional area of the specimen decreases uniformly.
• 17. The movement of dislocations: b) Is a plastic deformation, d) Occurs after the yield point, e) Irreversibly alters the material.

Fracture Mechanics

• 6. Brittle materials, compared to ductile ones, absorb more energy in an impact: b) Not necessarily (NSRF), d) Whether the material is ductile or brittle does not solely determine the energy absorbed.
• 21. In a material with brittle fracture: f) There is no plastic deformation. (Options b and d are not always true; a small modulus of elasticity and tensile strength are not defining characteristics of *all* brittle materials, though they can be common.)
• 22. The greater the energy absorbed in an impact: a) The greater the ductility of the material, c) The material is more likely to be an FCC system.
• 23. Brittle fracture is favored by fluid movement and more dislocations: a) False. Brittle fracture is favored by *restricted* dislocation movement.
• 24. Ductile fracture is more common at high temperatures, where dislocation movement is more difficult: b) False. Ductile fracture is more common at high temperatures because dislocation movement is *easier*.
• 25. Above the ductile-brittle transition temperature, the material behaves in a ductile manner: a) True.
• 26. The fatigue of a material: c) Occurs for voltages below the yield strength, e) Is not (typically) associated with large-scale plastic deformation.

Material Selection (Crystal Structure)

• 7. Which of these metals would you use in applications with very large variations in temperature and where good toughness is required? c) FCC.
• 8. Which of these metals would you use in applications where variations of temperature are very large, and tenacity is not important? b) BCC.