Test 2. Chapter 8

Question 1

Ductile fracture occurs with _______deformation

Answer 1

plastic

one large piece, has large deformation

Question 2

brittle fracture has _______ deformation

Answer 2

it has little or no plastic deformation, catastrophic

many pieces and has small deformation

Question 3

ductile fracture is usually _______

Answer 3

desirable

Question 4

intergranular mean?

Answer 4

between grains

Question 5

transgranular means?

Answer 5

within grains

Question 6

crack propagates if above ___________

Answer 6

critical stress

Question 7

________, most stressed cracks grow first

Answer 7

largest

Question 8

why does an increase loading rate increase stress and tensile strength but degrease EL

Answer 8

an increased rate gives less times for dislocations to move past obstacles

Question 9

fatigue name some key points

Answer 9

can cause part failure, even though shear stress max < shear stress c

it causes 90% of mechanical engineering failures

Question 10

how can you improve fatigue life?

Answer 10

1. impose a compressive surface stress (to surppress surface cracks from growing)
2. remove stress concentrators

Question 11

creep

Answer 11

sample deformation at a constant stress vs time

Question 12

_________ :slope (creep rate) decreases with time

___________: steady state i.e., constant slope

_______________: slope (creep rate) increases with time, i.e. acceleration rate

Answer 12

primary creep

secondary creep

tertiary creep

Question 13

creep becomes more important at ___________ temperatures

Answer 13

elevated

Question 14

strain rate increase for higher _______, _________-

Answer 14

temperature and strain rate

Question 15

engineering materials dont reach __________–

Answer 15

theoretical strength

Question 16

____________produce ____________ that cause premature failure

Answer 16

flaws

stress concentrations

Question 17

_________ produce large stress concentrations and premature failure

Answer 17

sharp corners

Question 18

failure type depends on ______and ________-

Answer 18

temperature and stress

Question 19

for noncyclic, failure stress decreases with :

Answer 19

increased maxium flaw size

decrease T

increase rate of loading

Question 20

for cyclic shear stress

Answer 20

cycle to fail decreases as shear stress increases

Question 21

for higher temperature

Answer 21

time to fail decreases as shear stress or temperature increases