4&5. Plastic properties and Tensile testing

Question 1

What is the progression of states on the stress-strain curve?

Answer 1

1. elastic to yield point
plastic from now on
2. work hardening
3. ultimate tensile strength
4. necking
5. fracture point

Question 2

define Plastic deformation

Answer 2

permanent (irreversible) deformation

Question 3

define Yield strength σy

Answer 3

Stress beyond which plastic deformation begins to accumulate (permanent and irreversible component)

Question 4

what is another name for yield strength

Answer 4

elastic limit

Question 5

define work hardening

Answer 5

the increase in stress required to continue deformation beyond the elastic limit

Question 6

define Ultimate tensile strength σUTS

Answer 6

The maximum stress on an ENGINEERING stress-strain curve

Question 7

what is the difference between hetergenous and homogenous yielding?

Answer 7

hetero –> abrupt transition between elastic and plastic deformation. jumps in stress strain curve
homo –> smooth stress strain curve`

Question 8

where is the true stress (sigma T) equation accurate until?

Answer 8

necking

Question 9

what is K in the true stress eq?

Answer 9

the strength coefficient

Question 10

what is n in the true stress eq?

Answer 10

the work hardening exponent

Question 11

when does necking start?

Answer 11

ultimate tensile strength σUTS

Question 12

define ductility

Answer 12

the amount of deformation a material will tolerate before failure

Question 13

what are the two methods for expressing ductility?

Answer 13

% elongation and % reduction in area

Question 14

formula for % elongation

Answer 14

(Lf-Lo)/Lo *100%

Question 15

formula for % reduction in area

Answer 15

(Ao-Af)/Ao * 100%

Question 16

define toughness

Answer 16

energy absorbed by a material before fracture

Question 17

what is the approximate formula for toughness?

Answer 17

toughness = (σY +σUTS)/2 *epsilonf

Question 18

for engineering strain and stress the ____ length and area are used

Answer 18

original

Question 19

for true strain and stress the ____ length and area are used

Answer 19

instantaneous

Question 20

true stress is ___ than engineering stress

Answer 20

greater

Question 21

true strain is ___ than engineering strain

Answer 21

less

Question 22

the yield stress is how much…

and the work stress is how much…

Answer 22

your material can take

you are going to put your material through (safety factor for safety!)

Question 23

define hardness

Answer 23

a material’s resistance to localized plastic deformation

Question 24

can hardness be determined from a tensile test?

Answer 24

no