Lecture 2 - Mechanical Properties of Materials

Question 1

What do extensive properties depend on?

Answer 1

the amount of a material

Question 2

What are two examples of extensive properties?

Answer 2

mass and volume

Question 3

What do intensive properties not depend on?

Answer 3

the amount of a material

Question 4

What are two examples of strength

Answer 4

stress and strain

Question 5

What is stress?

Answer 5

force applied to deform a structure

Question 6

What is the formula for stress?

Answer 6

sigma = F/A

Question 7

What are the units for stress?

Answer 7

pascal (MPa) or PSI

Question 8

What are the 3 kinds of stresses?

Answer 8

compression, tension, shear

Question 9

How is compression created?

Answer 9

when force is applied inward on an object

Question 10

How is tension created?

Answer 10

when forces are pulled away from the object

Question 11

How is shearing created?

Answer 11

when a parallel force is applied to the area

Question 12

What does strain result in?

Answer 12

deformation of a material from a force

Question 13

What kind of direction of deformation can a strain have?

Answer 13

perpendicular or parallel

Question 14

What is strain?

Answer 14

change in the length of materal/resting length of material

Question 15

What is the formula for strain?

Answer 15

e = deltaL/L

Question 16

What is a stress-strain curve?

Answer 16

a graph relating stress to strain

Question 17

What are stress-strain curves useful for?

Answer 17

• examining how materials change with age
• examining how materials react to different forces
• examining how materials react to everyday stress

Question 18

What happens during the toe region?

Answer 18

initial un-crimping of fibers

Question 19

What are the 4 regions of stress-strain curves?

Answer 19

toe region, elastic region, plastic region, failure point

Question 20

What happens during the elastic region?

Answer 20

material returns to original length when load is removed

Question 21

What happens during the plastic region?

Answer 21

structure does not return to original length when load is removed

Question 22

What happens during failure point?

Answer 22

fracture or breaking point

Question 23

What is Young’s modulus also referred to?

Answer 23

modulus of elasticity (material’s stiffness)

Question 24

What is Young’s modulus?

Answer 24

the slope of the straight line (elastic region) of a stress-strain curve

Question 25

A material with a high Young's modulus undergoes....

Answer 25

less strain under a given load

Question 26

A material with a low Young's modulus undergoes...

Answer 26

more strain under a given load (stiffer)

Question 27

What kind of material is ductile?

Answer 27

it deforms plastically before failure

Question 28

What kind of material is brittle?

Answer 28

fails before plastic deformation

Question 29

What kind of relationship is brittle failure?

Answer 29

stress-strain

Question 30

What happens at ultimate tensile strength?

Answer 30

the material breaks

Question 31

What is ductile failure?

Answer 31

when material yields with continued increase in the applied load

Question 32

What does Poisson's Ratio state (2)?

Answer 32

1. when a material is stretched in one direction it tends to get thinner in the other two directions 2. when a material is compressed in one direction it tends to get thicker in the other two directions

Question 33

What is Poisson's Ratio?

Answer 33

the ratio between a material's transverse and longitudinal strain when it is stretched

Question 34

What does the negative sign do in Poisson's Ratio?

Answer 34

it keeps the Poisson's ratio positive for objects in which stretching longitudinally leads to a decrease in the lateral dimension

Question 35

Most materials have Poisson ratio between...

Answer 35

0 and 0.5

Question 36

What is material fracture?

Answer 36

when a material is compressed in one direction it tends to get thicker in the other two directions

Question 37

When does fatigue fracture happen?

Answer 37

when a material is loaded and unloaded repeatedly, and the maximum loads are below the ultimate tensile strength(UTS)*

Question 38

What is fatigue limit?

Answer 38

the stress below which the material will never fail in fatigue

Question 39

What are stress rates?

Answer 39

psi/second or MPa/second

Question 40

What are strain rates?

Answer 40

pure frequency, per second, inch/inch/second, mm/mm/second

Question 41

What is sensitive to strain rate?

Answer 41

soft tissues

Question 42

What is stress relaxation?

Answer 42

the reduction of stress within a material over time as the material is subject to constant deformation

Question 43

What is creep?

Answer 43

the continued deformation of material over time as the material is subjected to a constant load

Question 44

What do bones have a similar fashion to?

Answer 44

beams

Question 45

What is a neutral axis?

Answer 45

the location where a beam experiences zeros tress

Question 46

How are the stresses on each side of the neutral axis defined as?

Answer 46

compressive and tensile

Question 47

What is applied instead of a bending movement?

Answer 47

a torque or twisting force

Question 48

What does torsion generate?

Answer 48

shear stresses that are distributed over the entire structure

Question 49

What is buckling?

Answer 49

fracture mode of a structure

Question 50

Short and wide column =

Answer 50

compression under a load

Question 51

As a column gets taller and thinner,

Answer 51

it becomes less stable

Question 52

What happens to a perfectly centered force on a column?

Answer 52

it will continue to compress

Question 53

What will cause the column to bow out?

Answer 53

an off-centre force