Chapter 6 (Mechanical Properties)

Question 1

Stress equation

Answer 1

stress=F/A

Question 2

Strain equation

Answer 2

strain=delta L/L0

Question 3

which type of deformation is reversible

Answer 3

elastic

Question 4

which type of deformation is permanent

Answer 4

plastic

Question 5

Yung’s Modulus equation

Answer 5

stresss=(Yung’s)*Strain

Question 6

what does the elastic modulus(yungs) tell us about a material

Answer 6

how much it will stretch

Question 7

How to compare E between materials

Answer 7

compare the slopes of stress-strain curves

Question 8

what is Yield strength

Answer 8

the stress at which noticeable plastic deformation has occurred

Question 9

what is tensile strength

Answer 9

the MAXIMUM stress on the stress-strain curve

Question 10

what is ductility

Answer 10

measure of the amount of plastic deformation before a material breaks

Question 11

what is toughness

Answer 11

the energy required to break a unit volume of a material

Question 12

how would you approximate the toughness of a material

Answer 12

compare the areas under the curves (stress-strain)

Question 13

what is Resilience

Answer 13

the ability of a material to absorb energy during the ELASTIC deformation and give it back when unloaded

Question 14

Ur(Resilance)=

Answer 14

area under curve until yield strength

Question 15

what is hardness

Answer 15

a measure of the resistance to LOCALIZED plastic deformation

Question 16

what is the conventional unit we use for stress?

Answer 16

MPa

Question 17

what are the units of strain

Answer 17

strain is dimensionless

Question 18

what does E(yung’s modulus) tell us microscopically?

Answer 18

its is a measure of how well the atoms are bonded together

Question 19

is it possible to alter the stiffness of a metal?

Answer 19

impossible

Question 20

what is poisson’s ratio?

Answer 20

a ratio of how much strain occurs on a material in the X & Y directions when strained in the Z direction

Question 21

simple tension equation

Answer 21

sigma=FLo/EAo

Question 22

simple torsion equation

Answer 22

alpha=2MLo/(pi)(r^4)G, where G is the elastic shear modulus

Question 23

what is yielding

Answer 23

when deformation changes from elastic to plastic

Question 24

when does the tensile strength occur for metals

Answer 24

when noticeable necking starts

Question 25

when does the tensile strength occur for polymers

Answer 25

when the polymer backbone chains are aligned and about to break

Question 26

what is the tensile strength equation?

Answer 26

sigma(ts)=MAX FORCE/ORIGINAL AREA

Question 27

area of a cylinder

Answer 27

pi*((diameter/2)^2)

Question 28

how do you compare ductility(%EL)

Answer 28

compare the areas under the graph

Question 29

true or false, toughness is synonymous with ductility

Answer 29

true

Question 30

what is the qualitative harness scale

Answer 30

Moh’s scale

Question 31

list the different scales of quantitative hardness

Answer 31

1. Rockwell
2. Brinell
3. Vickers
4. Knoop