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Ortho BMSc > Deformable body Mechanics Unit 1: Mechanical properties of materials and structures (class) > Flashcards

Deformable body Mechanics Unit 1: Mechanical properties of materials and structures (class) Flashcards

1
Q

What is a structure?

A

an arrangement of one or more materials in a way that is designed to sustain loads

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2
Q

What is a material?

A

a type of matter used to construct structures

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3
Q

Are mechanical properties independent of material or structure?

A

structure

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4
Q

Which symbol represents stress?

A

sigma σ

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5
Q

Which symbol represents strain?

A

epsilon ε

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6
Q

Which symbol represents the coefficient of velocity?

A

eta η

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7
Q

What is deformation?

A

change in shape or size of a structure or any part of it

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8
Q

How do we calculate stress?

A

force (N) / area (m2)

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9
Q

What units do we use for stress?

A

pascal = N/m2

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10
Q

How can stress tell us the strength of a material?

A

it is the same regardless of size or shape of material

a bar with twice the cross-sectional area will require twice to break it but the stress within them will be the same

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11
Q

What is strain and how do we calculate it?

A

a measure of deformation

change in length/ original length

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12
Q

What are axial loads?

A

a load applied a geometric axis of a structure producing pure tension or compression

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13
Q

What do stress-strain curves show?

A

how a material deforms as it is loaded

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14
Q

What is the proportional limit in a stress-strain curve?

A

the point at which the straight line finishes and stress stops being directly proportional to strain

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15
Q

What is the elastic limit in a stress-strain curve?

A

the greatest stress that may be applied to a material without causing any permanent deformation

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16
Q

describe a material that exhibits elastic behaviour

A

it instantly deforms under a load and returns immediately to its original size and shape eg rubber

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17
Q

describe a material that exhibits plastic behaviour

A

it deforms instantly under a load and retains this new shape/size when the load is removed eg putty

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18
Q

In structures which region of the stress-strain curve must the material remain within?

A

elastic region as a material that is plastic is of no use because it will deform greatly under a small increase in load

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19
Q

What happens beyond the yield point?

A

the material will undergo considerable elongation without an increase in stress ie. just maintaining the load will cause continual deformation

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20
Q

What type of behaviour is in the region following the yield point?

A

plastic

21
Q

What happens after the ultimate strength of the material is reached?

A

stretching occurs with a reduction in stress

results in a reduced cross-sectional area called necking

22
Q

What do we call

a) a material that can sustain only limited strain before breaking?
b) a material that deforms plastically before breaking?

A

a) brittle

b) ductile

23
Q

What is Hooke’s law?

A

up to the proportional limit, the strain is proportional to the applied stress

24
Q

What is Young’e modulus a measure of and how do you calculate it?

A

the stiffness of a material

stress/strain

25
Q

What symbol represents young’s modulus?

A

E

26
Q

What is rigidity?

A

the ability to resist axial deformation

27
Q

How do we calculate rigidity?

A

young’s modulus x cross-sectional area

28
Q

What are the units of rigidity?

A

N

29
Q

What is stiffness?

A

the force required to produce a unit deflection

30
Q

How do we calculate stiffness? give 2 ways

A

applied force / change in length

young’s modulus x cross sectional area / original length

31
Q

What is flexibility?

A

the deflection under a unit load

32
Q

How do we calculate flexibility and what units do we use?

A

1/stiffness

m/ N

33
Q

Is strength determined by Young’s modulus?

A

no

34
Q

Describe viscous behaviour

A

material does not deform instantly when a load is applied. The strain is prolonged. once the load is removed the material will not return to its original size and shape.

this means that no energy is stored in the material and all the energy is required to deform is dissipated as heat.

35
Q

Give 3 examples of materials that exhibit viscous behaviour

A

water
blood plasma
air

36
Q

What are stresses arising in viscous materials dependent on?

A

strain rate

37
Q

What is the coefficient of viscosity equal to?

A

η = stress/ strain rate

38
Q

How do we represent strain rate?

A

epsilon dot

39
Q

What is the strain rate?

A

change in strain / change in time

40
Q

what are the units for the coefficient of viscosity?

A

Nm-2.s / Pa.s

41
Q

Describe viscoelastic behaviour

A

viscous in that it responds to the rate of loading and elastic in that it returns to its original size and shape after the load is removed

42
Q

Give 2 examples of materials that show viscoelastic behaviour

A

articular cartilage

cortical bone

43
Q

What is creep?

A

developing strain over time when a constant load is applied

44
Q

Name some examples of creep

A

soft metals eg lead
wood
concrete (noticeable after years)

45
Q

What is stress relaxation?

A

in a material under constant strain the stress diminishes over time

46
Q

what is strain hardening?

A

material undergoes changes in its atomic and crystalline structure resulting in an increased resistance to further deformation

47
Q

Give the regions of the strain stress curve in order

A

elastic
plastic
strain hardening
necking

48
Q

what is young’s modulus equal to on the stress-strain curve?

A

gradient upto the proportional limit ie. the elastic region

49
Q

In a stress-strain curve what is the highest stress on the diagram?

A

ultimate stress

Ortho BMSc (14 decks)

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