Week 2: Atomic Bonding & Material Failure

Question 1

Chemical structure _________ performance.

Answer 1

influences

Question 2

Atomic structure dictates what 4 properties?

Answer 2

1. chemical
2. electrical
3. thermal
4. optical

Question 3

Why is electronegativity important?

Answer 3

because the difference in electronegativity can help predict the bond formed between the two atoms.

Question 4

What are the ranges for electronegativity?

Answer 4

0 - 0.4 covalent
0.4 - 2 polar covalent
2 - 3.3 ionic

Question 5

What are the two primary atomic bonds?

Answer 5

ionic and covalent

Question 6

What bonds do the three biomaterials form?

Answer 6

metals - metallic
polymers - covalent, vanderwaal’s, and hydrogen
ceramics - ionic

Question 7

Net force equals

Answer 7

addition between attractive and repulsive forces

Question 8

The integral from r to infinity of attractive/repulsive force equals

Answer 8

attractive/repulsive energy

Question 9

The larger bond energy the

Answer 9

higher melting temperature

Question 10

What depends on the interatomic bonding forces?

Answer 10

elastic modulus (E)

Question 11

Ceramics form what bonds and what 4 characteristics do they have?

Answer 11

ionic and covalent
1. high bond energy
2. high melting temperature
3. large elastic modulus
4. small coefficient of thermal expansion

Question 12

Metals form what bonds and what 4 characteristics do they have?

Answer 12

metallic
1. bond energy varies
2. moderate melting temperature
3. moderate elastic modulus
4. moderate coefficient of thermal expansion

Question 13

Polymers form what bonds and what 4 characteristics do they have?

Answer 13

covalent + secondary
1. weak bond energy
2. low melting temperature
3. small elastic modulus
4. large coefficient of thermal expansion

Question 14

What is most responsible for polymers’ physical properties?

Answer 14

secondary bonding

Question 15

What causes material fracture and failure?

Answer 15

1. improper material selection
2. processing
3. degradation
4. raw materials

Question 16

What is included in “improper material selection” ?

Answer 16

1. long term stress/strain
2. extractables/leachable
3. chemical compatibility
4. stressors

Question 17

What is included in “processing” ?

Answer 17

1. induced micro-structure
2. high stress
3. improper mold design

Question 18

What is included in “degradation” ?

Answer 18

1. free radicals
2. hydrolysis
3. oxidation
4. sterilization

Question 19

What is included in “raw materials” ?

Answer 19

1. formulation incompatibility
2. resin heat/shear history
3. unexpected changes

Question 20

What is a ductile fracture?

Answer 20

material undergoes plastic deformation before breaking

Question 21

What is a brittle fracture?

Answer 21

occurs when there is little plastic deformation

Question 22

What are the two impact testing names?

Answer 22

Charpy and Izrod

Question 23

What do the Charpy & Izrod testing assess?

Answer 23

fracture properties of materials

Question 24

What does the Charpy & Izrod testing measure?

Answer 24

the impact energy or notch toughness

Question 25

What is a fast fracture?

Answer 25

when a crack rapidly propagates across material

Question 26

What is a fatigue fracture?

Answer 26

caused by repeated cyclic application of sub-yield stresses

Question 27

What is the inequality at which a crack will occur?

Answer 27

incremental work done by external loads > increase in elastic energy of material

Question 28

What is the equation for the critical intensity factor?

Answer 28

Kc = sqrt(E*Gc) E = elastic modulus Gc = toughness

Question 29

What is another name for the critical intensity factor?

Answer 29

fracture toughness

Question 30

What does the stress intensity factor equal?

Answer 30

K = stress * sqrt(pi * a) a = length of crack

Question 31

What does the value of Kc depend on?

Answer 31

1. orientation of bone 2. relative density (from age) 3. water content of bone

Question 32

What is an example of a ductile/brittle transition?

Answer 32

osteon-pull out

Question 33

What is the critical condition for crack propagation?

Answer 33

K > Kc

Question 34

What are two ways to improve failure?

Answer 34

1. reducing stress 2. surface treatments