Question

In: Mechanical Engineering

True or False 1. Ceramics often fracture below their theoretical strength due to cracks which concentrate...

True or False

1. Ceramics often fracture below their theoretical strength due to cracks which concentrate the applied stress.

2. The interstitial diffusion coefficient for a small atom diffusing in a metal is usually larger than its diffusion coefficient via a vacancy mechanism.

3. BCC, HCP, FCC are all Bravais lattices belonging to the cubic crystal system.

4. The larger the number of slip systems available to a metal, the easier it is to deform.

5. HCP has an "abab" stacking sequence, FCC has an "abcabc" stacking sequence.

6. Dislocations move most easily in a crystal along the highest density planes along the lowest density direction.

7. There are 14 Bravais lattices, each of which belongs to one of the 7 crystal systems.

8. Elastic deformation results from the breaking and reforming of bonds.

9. Thermal expansion in crystalline materials is the result of an asymmetry in the repulsive and attractive force curves between pairs of atoms.

10.Graphite and diamond are two different phases of carbon.

Expert Solution

1. True as cracks concentration decreases ceramic strength.

2. False converse is true interstitial diffusion coefficient for a small atom diffusing in a metal is usually smaller than its diffusion coefficient via a vacancy mechanism.

3. False as HCP structure is not Cubic crystal system as it is hexagonal in nature.

4. True as large number of slip system easier it is deform but deformation also depends upon several other factors also.

5. True stacking sequence of FCC is ABCABC and for HCP is ABAB.

6. True as strength require to move from high density plane to low density plane decreases.

7. True and seven crystal systems are Cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic, triclinic.

8. True because motion of dislocations involves breaking and reforming bonds which results in plastic deformation.

9. False thermal expansion is result of Temperature is related to average molecular kinetic energy of a substance. When a substance is heated, the kinetic energy of its molecules increases.

10.True there are 3 common phases of carbon graphite, diamond, and C60.

samet mamat answered 2 years ago

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