Midterm study

Question 1

Major classifications of materials

Answer 1

1) metals- found on periodic table
2) ceramics- compound of metal and nonmental
3) plastics(polymers)- organic compounds based on C and H
4) semiconductors- electrical properties b/w metal and ceramics
5) composites- consists of more than one material type

Question 2

why are compositors made of fibers?

Answer 2

• fibers are stronger than bulk materials
• flaws are smaller
• even if there is a flaw, the whole composite still remains intact

Question 3

4 components involved in design, production, and utilization

Answer 3

1) processing- structure of material
2) structure- arrangement of internal components

3) properties- trait or response to stimulus
mechanical, electrical, thermal, magnetic, optical, deteriorative

4) performance- function of property

Question 4

Primary bonding

Answer 4

1) ionic- electron transfer (ceramics)
nondirectional

2) covalent- electron sharing (polymers)
directional

3) metallic- electron cloud (metals)
nondirectional

Question 5

secondary bonding

Answer 5

1) van der waals
2) dipoles
3) hydrogen bonding

Question 6

atomic models and differences

Answer 6

1) wave mechanical
cannot pinpoint exact location of the electrons

2) bohr model
electrons orbit in specific orbit
electrons jump by emitting or absorbing energy in a fixed quanta

Question 7

Common Crystal structures

Answer 7

1) face centered cubic (FCC)
#atoms/unitcell = 4
CN = 12

2) body centered cubic (BCC)
#atoms/unitcell = 2
CN = 8

3) hexagonal close packed (HCP)
#atoms/unitcell = 6
CN = 12

Question 8

crystallographic

• directions
• family of directions
• planes
• family of planes

Answer 8

• directions [ ]
• family of directions < >
• planes ( )
• family of planes { }

Question 9

how to calculate crystallographic directions and planes

Answer 9

1) place vector rail at unitcell origin (corner)
2) determine projection or intercept on each axis
3) reduce to smallest integer value
4) enclose accordingly

Question 10

what is the driving force for recrystallization?

Answer 10

The difference in internal energy between the strained and unstrained material

Question 11

what is the driving force for grain growth?

Answer 11

The reduction in grain boundary energy as the total grain boundary area decreases

Question 12

when does slip occur?

Answer 12

slip will occur in plane if

τR(max) >= τcrss

Question 13

τcrss (critical resolved shear stress)

Answer 13

minimum shear stress required to initiate slip

Question 14

how is τcrss related to yield strength

Answer 14

σy = τcrss/ cosφcosλ

Question 15

τR (resolved shear stress)

Answer 15

τR = σ cos φ cross λ

σ = applied stress
φ = between load direction and normal to slip plane
λ = between slip direction and load direction
φ + λ =/= 90