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Biomechanics 2241 > LECTURE #20 + 21 - mechanics of biological materials > Flashcards

LECTURE #20 + 21 - mechanics of biological materials Flashcards

1
Q

external (mechanical) loads (forces) deform internal structures in a addition to producing movement … in what parts of the body ?

A
  • ligament
  • tendon
  • cartilage
  • bone
  • muscle
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2
Q

what are the two types of mechanical load types ?

A

uniaxial and combined

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3
Q

what are some examples of uniaxial mechanical load types ?

A

compression, tension and shear

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4
Q

what are some examples of combines mechanical load types ?

A

bending and torsion

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5
Q

FILL IN THE BLANK

mechanical loads create mechanical _____

A

stress

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6
Q

what is stress ?

A

force (internal) per unit area over which the force acts

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7
Q

what are the units of stress ?

A

N/m^2 or pascal

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8
Q

what are the three principal types of mechanical stress ?

A

tension, compression and shear

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9
Q

what is tension ?

A

pulling or stretching force directly axially through a body

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10
Q

what is compression ?

A

pressing or squeezing force directly axially through a body

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11
Q

what is shear ?

A

force directed parallel to a surface (causes a sliding of surfaces in opposite directions)

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12
Q

what are combined loads ?

A

more common during function activities (multi axial)

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13
Q

what are some causes of combined loads ?

A
  • multiple stresses at analysis plane
  • different magnitudes of stress at analysis plane
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14
Q

what are the two types of combines loads ?

A

bending and torsion

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15
Q

what is torsion ?

A

fancy word for twisting

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16
Q

what is bending ?

A

loads applied to structure causing it to bend about a neutral axis

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17
Q

what is three point bending ?

A
  • compression and tension developed on opposite sides of axis
  • shear developed along axis
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18
Q

what is cantilever bending ?

A

is the bending or flexing of bones when subjected to off-center forces, similar to how a diving board bends under weight

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19
Q

what’s torsion ?

A

load producing twisting of a body around its longitudinal axis

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20
Q

where does shear stress occur in torsion ?

A

parallel to axis (greatest magnitude)

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21
Q

where does compression and tension occur in torsion ?

A

occur diagonal to axis

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22
Q

if you have an increase in distance from axis, what does that mean for magnitude ?

A

increase in magnitude

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23
Q

what is strain ?

A

defamation of material with external forces

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24
Q

TRUE OR FALSE

excessive deformation (strain) causes injury ?

A

TRUE

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25
Q

whats happening to our tendons during strain ?

A

there stretched and lengthen more than it should / can

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26
Q

whats the difference between stress and strain ?

A
  • mechanical stresses causes strain
  • strain is the actual response
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27
Q

what is linear strain due to ?

A

compressive or tensile loads

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28
Q

what is a load - deformation curve ?

A

is a graph that shows how a material deforms under the influence of an applied load. It typically illustrates the relationship between the amount of force applied (load) and the resulting deformation or displacement of the material

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29
Q

what are some factors of strength (resistance to deformation/failure) in regards to load - deformation curve :

A
  • yield strength
  • ultimate strength
  • failure strength
  • total deformation before failure point
  • energy stored before failure point
30
Q

what is a limitation for the load - deformation curve ?

A

can’t compare materials of different size and shape

31
Q

what is a fix for the load - deformation curve ?

A

stress - strain curve

32
Q

what are some functions of bone biomechanics ?

A
  • protect vital organs
  • support soft tissue
  • produce RBC’s
    reservoir for minerals
  • provide attachment site for skeletal muscle
  • act as a system of machines to receive muscle torques and make moment possible
33
Q

what are some factors influencing mechanical properties of bone biomechanics ?

A
  • structure
  • geometry
  • mode of loading
  • rate of loading
  • frequency of loading
  • muscle activity
  • age
34
Q

what are the 4 major structural components of bone

A
  • collagen
  • mineral
  • ground substance
  • water
35
Q

define collagen’s structure in bone :

A
  • 25-30% dry weight
  • tensile strength
  • provides some flexibility : however, relatively little
36
Q

define mineral’s structure in bone :

A
  • 60-70% dry weight
  • calcium and phosphate
  • compressive strength
37
Q

define ground substance’s structure in bone :

A
  • 5% dry weight
  • gel like substance surrounding collagen fibers
  • compressive strength
38
Q

define water’s structure in bone :

A
  • 20-25%
39
Q

define the geometry of bone biomechanics :

A
  • cross sectional area is proportional to ultimate failure point
  • increased area = increased ultimate strength
  • distribution of bone tissue around its neutral axis
40
Q

what does “polar moment of inertia” mean ?

A

ability to resist twisting (torsion)

41
Q

what does it mean for polar moment of inertia if mass distribution away from neutral axis ?

A

increased polar moment of inertia

42
Q

what does it mean for polar moment of inertia if mass distributed close to neutral axis ?

A

decreased polar moment of inertia

43
Q

mode of loading : what does anisotropic mean ?

A

stiffness & strebt depend upon mode of loading

44
Q

when is the failure point highest during ?

A

compression (193 MPa)

45
Q

when is the failure point second highest during ?

A

tension (133 MPa)

46
Q

when is the failure point lowest during ?

A

shear (68 MPa)

47
Q

what is the order of strangest to weakest in regards to load of loading for bone biomechanics ?

A

compression > tension > shear (aka shear break more common then a bone breaking due to compression)

48
Q

what is bending ?

A

loads applied to structure causing it to vend about a neutral axis

49
Q

where do compression and tension develop on a bone ?

A

on opposite sides of axis

50
Q

where does shear develop on a bone ?

A

developed along the axis

51
Q

what are the two major types of bending we talk about ?

A

three point bending and cantilever bending

52
Q

what are the factors influencing mechanical properties of bone biomechanics ?

A
  • structure
  • geometry
  • mode of loading
  • rate of loading
  • frequency of loading
  • muscle activity
  • age
53
Q

what does viscoelastic mean ?

A

stiffness and strength depend upon see of applied load

54
Q

when do we see a high loading rate ?

A
  • increased stiffness
  • increased ultimate failure point
  • increased energy storage prior to failure
55
Q

TRUE OR FALSE

loading rate influences fracture patters and sift tissue damage

A

TRUE

56
Q

if we see decrease loading rate what does that mean ?

A

cracking (no fragments), little or no soft tissue damage

57
Q

if we see increased loading rate what does that mean ?

A

comminuted (fragments displaced), extensive soft tissue damage

58
Q

what term is used to describe the following : materials may behave in both elastic and viscous manners with different rates of loading

A

viscoelasticity

59
Q

for rate-sensitive loading, higher loading rate = increased or decreased stiffness ?

A

increased stiffness

60
Q

for rate-sensitive loading, lower loading rate = increased or decreased stiffness ?

A

decreased stiffness

61
Q

what is bone fatigue ?

A

wearing of bone during repeated landing

62
Q

what are some factors that may lead to bone fatigue ?

A
  • magnitude of load
  • number of load applications
  • number of load applications in a given time
63
Q

for fatigue fractures (stress factors), high load = how many repetitions ?

A

high load = few repetitions

64
Q

for fatigue fractures (stress factors), low load = how many repetitions ?

A

many repetitions

65
Q

TRUE OR FALSE

muscles may produce tensile or compressive stresses on bone

A

TRUE

66
Q

TRUE OR FALSE

we see progressive decrease in bone density and strength with age

A

TRUE

67
Q

what factors do we see in bones as we age ?

A
  • decrease bone density
  • decrease bone mass
  • decrease bone size
  • decrease stiffness
  • decreased strength
68
Q

what does bone remodelling mean ?

A

altering size, shape and structure based on the imposed mechanical demands

69
Q

what is wolff’s law ?

A

bone tissue is gained or lost depending upon the level of stress sustained

70
Q

if we see an increase in mechanical stress, do we see an increase or decrease in bone tissue production ?

A

increase in bone tissue production

71
Q

if we see a decrease in mechanical stress, do we see an increase or decrease in bone tissue production ?

A

dec erase in bone tissue production

Biomechanics 2241 (21 decks)

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