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KNPE 254 > Term Test 2: Tissue Mechanics > Flashcards

Term Test 2: Tissue Mechanics Flashcards

1
Q

External forces

A
  • Resisted by internal forces
  • Can cause deformation of the internal structures of
    the body
  • Cartilage, tendons, ligaments, bones and muscle
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2
Q

Amount of deformation produced

A

Is related to the stress caused by the forces and the material that is loaded

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3
Q

Mechanical stress

A

The internal force divided by the cross-sectional area of the surface on which the internal force acts

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4
Q

Three types of stresses

A
  1. Tensile
  2. Compressive
  3. Shear
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5
Q

Tensile stress

A
  • Axial stress (acts perpendicular to analysis plane)
  • Result of a force that pulls molecules apart
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6
Q

Axially loaded

A

The object tends to deform by stretching or elongating in the direction of the external loads

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7
Q

Compressive stress

A
  • Axial stress (acts perpendicular to analysis plane)
  • Result of a force that pushes molecules together
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8
Q

Shear stress

A
  • Transverse stress (acts parallel to the analysis plane)
  • Result of a force that pushes molecules past each
    other, acting parallel to this plane
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9
Q

Simple (uniaxial loads)

A

Only produce one type of stress, that is uniform across the whole plane

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10
Q

Bending

A

An object with greater depth (and more cross-sectional area) is able to withstand greater bending loads

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11
Q

Stresses during bending

A

Tensile and compressive stresses = lower during bending because they have a larger moment arm

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12
Q

Weight bearing

A

When the foot is weight-bearing, the load is distributed among several structures
- Bones of the feet bear compressive stress
- Plantar fascia and dorsal muscles bear tensile
stress

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13
Q

Torsion

A

An object with a greater diameter (greater cross-sectional area) is able to withstand greater torsional loads

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14
Q

Stresses during torsion

A

Shear stresses are lower because they have a larger moment arm

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15
Q

Uniaxial Tension

A
  • Muscles, tendons and ligaments behave like ropes
    or cables
  • Only carry one type of load; uniaxial tension
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16
Q

Combined Loads

A
  • Bones and cartilage can be loaded in many ways
  • Uniaxial tension, compression or shear loads
  • Produces uniform stress, bending and torsion loads,
    leading to more complex stress
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17
Q

Three types of strain

A
  1. Mechanical strain
  2. Linear strain
  3. Shear strain
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18
Q

Mechanical strain

A

Quantification of the deformation of a material

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19
Q

Linear strain

A
  • Change in length
  • Result of tensile or compressive stress
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20
Q

Shear strain

A
  • Change in the orientation of adjacent molecules
  • Result of molecules slipping past each other due to
    shear stress. Quantified as a change in angle
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21
Q

Stress-strain relationship behaviors

A
  • Elastic behaviour
  • Linear elastic behaviour
  • Plastic behaviour
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22
Q

Elastic behaviour

A
  • Stretches under a tensile load
  • Returns to its original shape when the load is
    removed (like a rubber band)
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23
Q

Linear elastic behaviour

A

As the stress increases, the strain increases by a proportional amount (the line on the graph is linear)

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24
Q

Plastic behaviour

A

When a permanent deformation of the object occurs under a load

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25
Q

Material strength

A
  • Maximum stress (or strain)
  • The material is able to withstand failure
  • Several qualifications of strength depend on which
    function one is interested in
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26
Q

Yield point

A

Point on the stress-strain curve where further stress will cause permanent deformation

27
Q

Yield strength

A

Stress at the elastic limit of a materials stress-strain curve

28
Q

Ultimate stress

A

Maximum stress the material is capable of withstanding

29
Q

Failure strength

A
  • Stress where failure actually occurs
  • Stress corresponds to the endpoint of the stress-
    strain curve
  • Failure means breakage or rupture
30
Q

Four types of materials

A
  1. Ductile materials
  2. Brittle materials
  3. Hard materials
  4. Soft materials
31
Q

Ductile materials

A

Have large failure strains

32
Q

Brittle materials

A

Have small failure strains

33
Q

Hard materials

A

Have large failure stresses

34
Q

Soft materials

A

Have small failure stresses

35
Q

Toughness

A
  • Ability to absorb energy
  • A material is tougher if more energy is required to
    break it
  • An estimation of the toughness of a material is given
    by the area under the stress-strain curve
36
Q

Elastic Modulus (Young’s Modulus)

A

The ratio of stress to strain is shown graphically as the slope of the stress-strain curve

37
Q

Viscoelastic materials

A
  • Material that exhibits both viscous and elastic
    characteristics
  • In the body this is bone, tendon, ligament, cartilage
    and muscle
38
Q

Four properties of viscoelastic materials

A
  1. Strain-rate dependency
  2. Stress-relaxation
  3. Creep
  4. Hysteresis
39
Q

Strain-rate dependency

A
  • The rate at which you deform/strain a tissue will
    affect the stress (internal load) it feels
  • A faster loading rate will create more stress than a
    slower loading rate
40
Q

Stress-relaxation

A
  • When tissue is stretched and maintained at a
    constant length (strain), the stress within the tissue
    will reduce over time
  • Eventually, the stress will reach an equilibrium
41
Q

Creep

A

If a constant load (stress) is applied to a tissue, it will slowly continue to deform and eventually reach an equilibrium length

42
Q

Hysteresis

A

The loading and unloading stress-strain curves of viscoelastic materials will differ. This is energy lost due to heat

43
Q

Mechanical Properties of Musculoskeletal system

A
  • Muscle tissue and connective tissue
  • (bone, cartilage, ligament and tendon)
44
Q

Muscle tissue vs Connetive tissue

A

Active elements vs Passive elements

45
Q

Connective tissue

A

Composed of living cells and extracellular components
- Collagen
- Elastin
- Ground substance
- Minerals
- Water

46
Q

Collagen

A
  • Fibrous protein is the most abundant substance
  • Muscles of collagen align together to form collagen
    fibrils that bind together to form fibres
47
Q

Collagen Features

A

Very stiff
- Brittle
- Failure strain of 8% to 10%
- High tensile strength (hard)
- Unable to resist compression because its long
fibres are not supported laterally

48
Q

Elastin

A
  • Fibrous
  • Pliant (soft)
  • Extensible
  • Ductile
  • Failure strain as high as 160%
49
Q

Isotropic materials

A

Have the same mechanical properties in every direction

50
Q

Anisotropic materials

A

Have different mechanical properties depending on the direction of the load

51
Q

Connective tissue: activity

A
  • Strength of CT increases with regular use
  • Due to an increase in the size of the tissue cross-
    section
  • Inactivity and immobilization result in decreased
    strength of tissues and shortening of ligaments and
    tendons
52
Q

Connective tissue: age

A

CT shows an increase in ultimate strength with age until the third decade of life, after which strength decreases. Bones become more brittle and less tough with increasing age. Tendons and ligaments become less stiff

53
Q

Connective tissue: bone

A
  • Bones are strongest in compression and
    weakest in shear
  • High tensile strength
  • High compressive strength
  • Strongest and stiffest material of the
    musculoskeletal system
54
Q

Two types of bone

A
  1. Cortical or compact
  2. Cancellous
55
Q

Cortical/ compact bone

A

Found in the dense and hard outer layers of bone

56
Q

Cancellous bone

A

Less dense, porous bone that is spongy in appearance and found deep to cortical bone near the ends of long bones

57
Q

Bone features

A

Bone is an anisotropic material. Strongest in compression, then tension and is weakest in shear

58
Q

Bone loading types

A
  • Unloaded
  • Tension
  • Compression
  • Bending
  • Shear
  • Torsion
  • Combined loading
59
Q

Connective tissue: cartilage

A

Is able to withstand compressive, tensile and shear loads

60
Q

Three types of cartilage

A
  1. Hyaline
  2. Fibrous
  3. Elastic
61
Q

Hyaline cartilage

A

Covers the ends of long bones at joints. Collagen fibres are arranged parallel to the articular surface. At the surface of joints, therefore need to handle large compressive loads

62
Q

Fibrous cartilage

A

Found within some joint cavities, in intervertebral discs, at the edges of joint cavities and at the insertions of tendons and ligaments into bone

63
Q

Elastic cartilage

A

Found in the external ear and in several other organs that are not part of the musculoskeletal system

KNPE 254 (3 decks)

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