Week 3

Question 1

What is the equation for stress?

Answer 1

Force/Area

Question 2

What is the equation for strain?

Answer 2

displacement (Lf-Li)/ initial length (L)

Question 3

What is the sign for tension?

Answer 3

+

Question 4

What is the sign for compression?

Answer 4

-

Question 5

Describe what happens during a tension or compression test.

Answer 5

tension test = machine moves up (pulls)
compression test = machine moves down (pushes)

Question 6

What happens when the load reaches a maximum point during a tension or compression test?

Answer 6

it starts to plateau

Question 7

After the load reaches its maximum point, what happens to the material?

Answer 7

nicks form

Question 8

What happens end of the compression or tension test?

Answer 8

• material breaks off
• you’ll have two pieces of metal and a graph called a force-displacement curve

Question 9

If you want to be able to compare materials what must you do to the force-displacement curve?

Answer 9

convert force –> stress and
displacement –> strain

Question 10

Temporary deformation of a material’s shape that is self-reversing after removing the load

Answer 10

elastic deformation

Question 11

E, ratio of stress to strain

Answer 11

Elastic modulus/modulus of elasticity/ Young’s modulus

Question 12

What denotes material stiffness and is determined by the slope of the elastic (linear) portion of the stress-strain curve?

Answer 12

elastic modulus

Question 13

Materials with high elastic modulus have (low/high) stiffness

Answer 13

high

Question 14

What is an example of a material with high elastic modulus?

Answer 14

ceramic materials

Question 15

Materials with low elastic modulus have (low/high) stiffness.

Answer 15

low

Question 16

What are two examples of a material with low elastic modulus?

Answer 16

polymers and resins

Question 17

is the stress when it ceases to be linear

Answer 17

proportional limit

Question 18

permanent deformation

Answer 18

plastic deformation

Question 19

the ability of a material to be drawn or plastically deformed without fracture

Answer 19

ductility/plastic deformation

Question 20

tendency crack or break

Answer 20

britterless

Question 21

What is yield strength?

Answer 21

σY, stress corresponding to the yield point at which the material begins to deform plastically. Is the stress at which there is a specified deviation from stress-to-strain proportionality, usually 0.1%, 0.2%, or 0.5% of the permanent strain. Always slightly higher than PL.

**where plastic and elastic curves meet and follow that point and draw a parallel line to the y-axis

Question 22

the maximum stress sustained before failure

Answer 22

ultimate tensile strength

Question 23

ability to absorb mechanical energy up to the point of failure

Answer 23

toughness

Question 24

Describe the stress-strain curve for a brittle material

Answer 24

ONLY ELASTIC DEFORMATION

E= elastic modulus
strain e = elastic deformation

(*): tensile strength and fracture strength are the same

no yield point because there is no plastic deformation

Question 25

Describe the stress-strain curve for ductile polymers

Answer 25

E = elastic modulus has a yield stress Is the maximum strength useful? No. because you have 300% deformation, so that point in polymer materials is not used. If you want to use something to determine if the material is useful, you must use the yield strength

Question 26

Compare mechanical properties (stress-strain curve) for ceramic, metal, hard tissue, and polymers.

Answer 26

ceramic = brittle = no plastic deformation polymer = low stiffness = low load = lots of plastic deformation *metals can move around the graph depending on what type of metal you're referring to hard tissue = bone, dentin, cementum

Question 27

Materials that undergo large amounts of plastic deformation are called

Answer 27

ductile

Question 28

What is the area of a circle

Answer 28

A = π r²

Question 29

The tensile strength of a material refers to: A) Yield point B) Fracture strength C) Elastic modulus D) Stress at the maximum point

Answer 29

D) Stress at the maximum point

Question 30

Upon removal of a deforming force, the ability of the body to regain its original shape and size is known as A) Plasticity B) Undeformation C) Elasticity D) Hook's Constant

Answer 30

C) Elasticity

Question 31

Upon the removal of a deforming force, the inability of the body to regain its original shape and size is known as A) Plasticity B) Undeformation C) Hook's Constant D) Elasticity

Answer 31

A) Plasticity