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BME 312 Exam 1 > Week 2: Mechanical Properties & Viscoelasticity > Flashcards

Week 2: Mechanical Properties & Viscoelasticity Flashcards

1
Q

For material property requirements, what is performance based on?

A

intended use and classifications (I-III)

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2
Q

What are the four concepts within safety of a medical device?

A
  • withstands wear
  • fatigue
  • maximum loads
  • structural integrity
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3
Q

What are the four concepts within efficacy for a medical device?

A
  • cellular proliferation
  • wound healing
  • drug delivery
  • structural stability of tissue
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4
Q

What are the four topics for composition of structure?

A
  • arrangement/alignment of tissue
  • crystallinity
  • molecular weight
  • thickness
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5
Q

What does increased molecular weight cause (6)?

A
  • impacts resistance
  • less mobility
  • absorb more energy
  • chemical resistance
  • thermal stability
  • greater viscosity
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6
Q

What is the equation for stress?

A

force over cross-sectional area

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7
Q

What are the two forces for stress?

A

tension and compression

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8
Q

What is the equation for tensile strain?

A

change in length over initial length

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9
Q

What is the equation for lateral strain?

A

change in diameter over initial diameter

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10
Q

What is the equation for poisson’s ratio?

A

negative lateral (transverse strain) over longitudinal (axis)

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11
Q

What is the equation for Hooke’s Law?

A

stress equals elastic modulus times strain

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12
Q

What are two properties of elastic deformation?

A

nonpermanent and reversible

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13
Q

What is the equation for simple tension?

A

Force times initial length all over elastic modulus times cross-sectional area

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14
Q

Materials with a large modulus of elasticity deform ____________

A

less

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15
Q

What is yield strength?

A

the strength at which noticeable plastic deformation has occured.

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16
Q

How do you find yield strength?

A

Using 0.2% offset

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17
Q

What is tensile strength (TS)?

A

the maximum stress on the stress-strain curves

18
Q

What is ductility?

A

the amount of plastic deformation at failure

19
Q

What is the equation for percent elongation (%EL)?

A

change in length divided by initial length multiplied by 100%

20
Q

What is resilience?

A

the ability of a material to absorb energy during elastic deformation

21
Q

What is toughness?

A

the amount of energy absorbed before fracture.

22
Q

Rank the toughness of metals, reinforced polymers, and ceramics

A

ceramics - tall and short curve
reinforced polymers - short but long curve
metals - tall and long curve

23
Q

What is the equation for true stress?

A

force over instantaneous cross-sectional area

24
Q

What is the equation for true strain?

A

natural log of instantaneous length over initial length

25
Q

What is hardness?

A

measure of resistance to surface plastic deformation (dent or scratch).

26
Q

What does a large value of hardness mean?

A

high resistance to deformation from compressive loads

27
Q

What is Rockwell Hardness?

A

combination of load magnitude and indenter size

28
Q

What is the importance of design/safety factors?

A

allowances must be made to protect against unanticipated failure.

29
Q

What is the equation for working stress?

A

yield strength divided by factor of safety (N)

30
Q

What is the expected value for factor of safety

A

between 1.2 to 4. the higher the number the greater the safety

31
Q

What does “visco” mean?

A

resistance demonstrated by a fluid when it is being sheared or stressed.

32
Q

What does “elastic” mean?

A

ability to return to original shape or form once shear or stress is removed.

33
Q

What are the parameters for a viscoelastic material?

A

can exhibit elastic behavior ONLY at low temperatures, and viscous behavior at high temperatures. Performs VISCOELASTIC at temperatures between those two regions.

34
Q

What are the three tests to measure viscoelasticity?

A
  1. creep
  2. stress-relaxation
  3. oscillatory stress
35
Q

What is creep?

A

when a sample is subjected to constant stress and deformation (strain) is measured as a function of time.

36
Q

What is stress-relaxation?

A

A material is deformed rapidly and the stress necessary to maintain deformation is measured as a function of time. (constant strain)

37
Q

What is oscillatory stress?

A

measured with rheometer which records a material’s response to oscillatory stress.
- rotating plate

38
Q

What is a dashpot?

A

a damper that resists motion via viscous friction (visco)

39
Q

What is a spring?

A

compresses to a certain length and returns to it’s original state (elastic).

40
Q

What is the purpose of the Maxwell model?

A

it can model tissue and predict the deformation.

BME 312 Exam 1 (4 decks)

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