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Biomaterials Exam 1 > Mechanical Properties > Flashcards

Mechanical Properties Flashcards

1
Q

what are the 2 objectives of measuring mechanical properties of a material

A
  1. to obtain fundamental properties - strength, elasticity, etc.
  2. to attempt to determine properties under conditions attempting to simulate service conditions of the material - impact, fatigue, abrasion, etc.
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2
Q

How do you test for hardness

A

press an indenter of known shape into surface with a known force for a known time

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3
Q

hardness

A

a surface property

the ability of a material to resist indentation/scratching

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4
Q

stress relaxation

A

when a material is deformed under a constant level of strain, it may show a drop in stress with time

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5
Q

define wear

A

result of abrasion

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6
Q

Name the classifications of bulk properties

A

fundamental properties

applied properties

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7
Q

proportional limit

A

highest value of stress where stress is proportional to strain
marks the end of the stress-strain graph following Hooke’s law
lesser than or equal to the elastic limit, depending on the material

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8
Q

define mechanical properties

A

the behavior of materials under applied forces

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9
Q

elongation

A

maximum deformation (strain) before a material breaks

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10
Q

why is strain dimensionless

A

because it is a change in length per unit length

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11
Q

plastic strain

A

permanent

if you remove the force, there is a permanent change in size and shape

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12
Q

name the fundamental types of stress

A

tension
compression
shear

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13
Q

define fundamental properties

A

classification of bulk properties

Obtained from test steadily increasing load (stress-strain)

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14
Q

which law of physics does the first portion of the stress-strain graph follow?

A

Hooke’s law

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15
Q

tension

A

a fundamental type of stress where the force is perpendicular to the resisting area
opposite of compression

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16
Q

the slope of the first (linear) part of the stress-strain graph is _____ and called ______

A

constant

Young’s modulus/modulus of elasticity

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17
Q

what is the only ‘pure’ elastic fundamental property?

A

Young’s modulus/modulus of elasticity

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18
Q

ultimate tensile strength

A

stress at which the material breaks

last point in the stress-strain curve

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19
Q

bulk properties

A

a classification of mechanical properties
consideration of the whole mass of material
strength, elasticity, etc.

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20
Q

elastic limit

A

stress at which a material changes from elastic to plastic strain

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21
Q

Hooke’s Law

A 
law of elasticity
for relatively small deformations of an object, the displacement/size of deformation is directly proportional to the deforming force/load
The linear (first) portion of the stress-strain graph follows this law
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22
Q

name the 2 consequences of viscoelasticity

A

creep

stress relaxation

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23
Q

how is strain considered in restorations and prostheses?

A

restorations/prosthesis are subjected to stress

plastic deformation in service must be avoided by choosing the right material and design

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24
Q

the design of prostheses depends on ___

A

mechanical properties

partial denture - clasps must be flexible, connectors must be rigid

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25
Q

Young’s moldulus

A

aka modulus of elasticity
slope of linear portion of stress-strain graph
stress/strain
constant
measure of rigidity/stiffness of material

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26
Q

ductility is measured by

A

% of elongation

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27
Q

viscoelasticity is ______ - viscous part is released/shown when constant stress/strain is applied for a certain period of time

A

time dependant

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28
Q

wear

A

result of abrasion

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29
Q

ductility

A

in TENSION
the ability of a material to be drawn into the form of a wire
measured by percentage of elongation

30
Q

the ultimate tensile strength and maximum strength correspond to…

A

the plastic region of the material

31
Q

a high percentage of elongation indicates a ______ material, and a low percentage of elongation indicates a _____ material

A

high - ductile

low - brittle

32
Q

define strain

A

a number that describes the relative deformation or change in shape and size of materials under applied forces (stresses)

33
Q

stress concentration

A

stress increases/concentrates at notches/grooves/cracks/surface irregularities
Importance of smooth surfaces

34
Q

stresses equal to or above the elastic limit…

A

will yield plastic (permanent) strain/deformation

35
Q

What are the x and y axis of the graph showing fatigue strength

A

x - log N (N = # cycles to failure)

Y - stress

36
Q

name the 2 (first) classifications of mechanical properties

A

bulk properties

surface properties

37
Q

In the fatigue strength graph, what does N represent?

A

the number of repetitions of low stresses applied to the material

38
Q

abrasion

A

loss of anatomic form from surface of restoration (or tooth)
surface property
difficult to measure relevantly and with reproducibility
UMN - artificial mouth
results in WEAR

39
Q

define applied properties

A

classification of bulk properties
impact - single sudden force
fatigue - repeated low loads
viscoelasticity - time dependant properties

40
Q

Modulus of resilience

A

amount of energy a material can absorb until it deforms permanently
area below linear portion of stress-strain line (up until the elastic limit)

41
Q

a ______ Young’s modulus indicates that the material is ____

A

higher modulus

more rigid

42
Q

define stress

A

the force per unit area within materials that arises from externally applied forces (solids)

43
Q

what is the major problem when testing mechanical properties of materials?

A

lab testing (in vitro) cannot adequately predict in vivo behavior

44
Q

name the combined types of stress

A

torsion

flexture/bending

45
Q

yeild point

A

when plastic strain becomes very pronounced
Higher than elastic limit
pretty much the same as the elastic limit

46
Q

strength/maximum strength

A

max stress the material undergoes during the stress-strain test
highest point on the stress-strain graph

47
Q

_____ are very sensitive to surface roughness because of stress concentrations at the top and bottom of topographical irregularities

A

ceramics and glasses

48
Q

Generally, materials that are more rigid are less _____

A

flexible

49
Q

name the types of strain

A

elastic

plastic

50
Q

flexibility

A

refers to when a material breaks

generally, materials that are more rigid are less flexible

51
Q

discuss strain as it pertains to alginate impressions

A

when inserted, the strain on the alginate is plastic - permanent deformation
upon setting, the alginate undergoes elastic strain as it is pulled out of the patient’s mouth

52
Q

viscoelasticity

A

combination of viscous (plastic) and elastic behavior

TIME DEPENDENT - properties depend on rate of testing

53
Q

fatigue limit

A

lowest stress value on the fatigue strengh graph
under this value of stress, the material will never break
aka endurance limit

54
Q

the first part of a stress-strain graph is _____, representing ____

A

linear

elastic strains/deformation

55
Q

how is impact strength tested

A

notched specimen hit with a swinging pendulum (knife edge mounted in a weighted hammer)
Energy to fracture material reduces amplitude of swing of pendulum

56
Q

shear

A

a fundamental type of stress where the force is parallel to the resisting area

57
Q

surface properties

A

a classification of mechanical properties

hardness, wear, etc.

58
Q

toughness

A

the amount of energy a material can absorb until it fractures
area of all space below stress-strain graph

59
Q

define hardness

A

resistance to indentation

60
Q

in a stress-strain graph, stress is on the ____ axis

A

stress is the Y axis

61
Q

strength is a value of…

A

stress

62
Q

fatigue strength

A

process of degradation by repeated low forces

63
Q

elastic strain

A

recoverable

if you remove the force, the material reverts to its original size and shape

64
Q

areas under the stress-strain graph has units of…

A

energy

J/m^3

65
Q

malleability

A

in COMPRESSION

the abiligy of a material to be hammered into a sheet

66
Q

creep

A

consequence of viscoelasticity
slow deformation with time of a material under a constant level of stress
amalgam, braces make of plastic

67
Q

ductility and malleability relate to…

A

plastic strain

68
Q

toughness is the opposite of…

A

brittleness

69
Q

compression

A

a fundamental type of stress where the force is perpendicular to the resisting area
opposite of tension

70
Q

impact strength

A

a measure of energy

sudden single force

Biomaterials Exam 1 (7 decks)

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