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Biomaterials > Mechanical Properties > Flashcards

Mechanical Properties Flashcards

1
Q

application is determined by? general

A

property

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2
Q

instron is what? testing?

A

a type of mechanical testing machine– UNDER COMPRESSIVE FORCES
- trying to break it

if material can last high stress/ high load –> should be a good material

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3
Q

load is a what? - very general

A

a force

how much force you apply

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4
Q

unit of force

A

newton

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5
Q

how do we standardize the load?

A

load per unit material

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6
Q

how do we standardize the load?

A

load per unit material

  • units are pascal and it is what STRESS not what load it breaks at
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7
Q

stress is?

A

load divided by the certain area

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8
Q

if have higher stress what does that mean?

A

it is stronger

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9
Q

describe the load deformation curve

A

any material / solid material when squeeze there is a dimensional change

it is SIZE AND SHAPE DEPENDENT

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10
Q

test with failure load?

A

no

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11
Q

force is

A

newton

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12
Q

deformation change is measured how

A

in mm

- shows deformation or displacement change

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13
Q

stress definitino

A

INTENSITY of the internal force acting on a specific AREA passing through a point

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14
Q

stress equation

A

Force / Area

Force is measures in load (newton) and area is meters squared (m2)

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15
Q

units SI?

A

1N/m2 = 1 pascal

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16
Q

1 megapascal uquals how many pascals?

A

1,00,000

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17
Q

hookes law is?

A

a linear representation of load and deformation

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18
Q

describe normal stress? what type

A

the intensity of the force acting normal to A

- compressive, tensile

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19
Q

what is shear stress

A

the intensity force acting TANGENT TO A

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20
Q

strain definition

A

used to describe the deformation of a body by changes in LENGTH OF LINE SEGMENTS (and the changes in the angle between them)

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21
Q

units of strain

A

unitless - expressed as a percentage

22
Q

equation for strain

A

(length - L0) / L0

LO - original length

23
Q

how do units change in strain

A

newton – megapascal

24
Q

ideal elastic material

A

Isotropic

Strain (deformation) is proportional to the stress applied to it

When unloaded the deformation fully recovers immediately

25
Q

deformation also called

A

strain

26
Q

does zirconia follow elastic deformation?

A

yes

- dont really see the deformation - but if too high of a load it can fracture

27
Q

what does bisacrylic follow?

A

plastic deformation

28
Q

plastic deformation

A

it deviates from the linear curve

- so starts to taper off

29
Q

applying load should be maintained within what?

A

the elastic deformation load range to keep the proper shape

30
Q

three points that occur in the elastic region and order

A
  1. proportional limit
  2. elastic limit
  3. yield stress
31
Q

parts of the plastic behavior

A
  1. yielding
  2. strain hardening
  3. necking
32
Q

true fracture stress?

A

the load at fracture divided by cross-sectional area

33
Q

ultimate stress and true fracture stress are where on curve?

A

in plastic behvior

34
Q

ultimate stress

A

stress material can handle before being broken

35
Q

plastic deformation definition

A

when unloaded, the deformation cannot fully recover - so get permanent deformation

36
Q

definition of malleability

A

whereby a material can be plastic deformed and shapes WHEN COLD

37
Q

ductility

A

whereby a material can be plastic deformed by elongation without fracture

38
Q

brittleness definition

A

whereby a material will fracture without appreciable prior plastic deformation

39
Q

if a material fractures without plastic deformation what do we characterize it as?

A

brittle

40
Q

strain hardening

A

aka work hardening and is characteristic of ductile materials like metal

  • occurs through plastic deformation
  • after this period you see necking
41
Q

why is a conventional stress-strain diagram important?

A

it provides a means for obtaining data about a materials tensile or compressive strength WITHOUT regard for the materials physical size or shape

42
Q

points on diagram in stress / strain

- which in which section

A

ELASTIC Portion

  1. proportional limit
  2. elastic limit
  3. yield limit

PLASTIC

  1. ultimate stress
  2. fracture stress
43
Q

what determines a ductile material?

A

any material that can be subjected to LARGE STRAINS before it fractures is a ductile material

44
Q

four distinct behaviors of a ductile material as it is loaded

A
  1. elastic behavior
  2. yielding
  3. strain hardening
  4. necking
45
Q

if have low yield?

A

can fracture suddenly

46
Q

example of ductile

A

mild steel

47
Q

example of brittle

A

gray cast iron, ceramic

48
Q

brittle materials have?

A

very little or no yielding and so they can fracture suddenly

49
Q

modulus of elasticity is represented by what on the stress-strain curve?

A

THE SLOPE – it is the slope of the proportional stress-strain curve

50
Q

poisoon ratio? what value is ideal

A

ratio is transverse strain divided by the axial strain

  • if a test piece is loaded in tension or compression, then in directions perpendicular to the load axis
  • so compressive - shrinks but gets wider (expands if compressive)
  • tensile - elongates but gets skinny (contraction if tensile)

CORRESPONDING LATERAL STRAINS WILL APPEAR

A CONTRACTION IF THE LOAD IS TENSILE , AN EXPANSION IF IT IS COMPRESSIVE

0 to 0.5 (0.5 is ideal)

Biomaterials (16 decks)

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