Tissue Mechanics

Question 1

Mechanical stress

Answer 1

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

Question 2

Tensile stress

Answer 2

-axial stress that occurs at the analysis plane as a result of a force or load that tends to pull apart the molecules bonding the object together at that plane

Question 3

Compressive stress

Answer 3

-the axial stress that results when a load tends to push or squash the molecules of a material more tightly together at the analysis plane

Question 4

Shear stress

Answer 4

-a transverse stress that acts parallel to the analysis plane as a result of forces acting parallel to this plane

Question 5

Bending

Answer 5

-an example of a more complex load in which there are multiple stresses that occur across the analysis plane

Question 6

What is the pro of an object with greater depth/diameter

Answer 6

-if 2 objects have the same cross sectional area but one of them has a greater depth, the object with the greater depth can withstand greater bending loads because they have a greater moment arm (from the center)

Question 7

Torsion

Answer 7

-rotational stress
-object with a greater diameter can withstand greater torsional loads because the counteracting shear stresses are lower because they have a larger moment arm

Question 8

Combined loads

Answer 8

-bones and cartilage often encounter a combination of loading configurations, as opposed to a single load such as a rope or cable

Question 9

Mechanical strain

Answer 9

-quantification of the deformation of a material

Question 10

Linear strain

Answer 10

-change in length (as a result of tensile or compressive stress)

Question 11

Shear strain

Answer 11

-change in orientation of adjacent molecules (as a result of these molecules slipping past each other due to shear stress)

Question 12

Elastic modulus

Answer 12

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

Question 13

Elastic behaviour

Answer 13

-stretches under a tensile load, but returns to original shape when load is removed

Question 14

Linear elastic behaviour

Answer 14

-as stress increases, the strain increases by proportional amount

Question 15

Plastic behaviour

Answer 15

-permanent deformation of the object occurs under a load

Question 16

Material strength

Answer 16

-has to do with maximum stress the material is able to withstand before failure
-there are several qualifications of strength

Question 17

Yield point

Answer 17

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

Question 18

Yield strength

Answer 18

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

Question 19

Ultimate strength

Answer 19

-maximum stress the material is capable of withstanding

Question 20

Failure strength

Answer 20

-stress where failure actually occurs
-stress corresponding to the endpoint of the stress-strain curve
-failure in this sense means breakage or rupture

Question 21

Ductile materials

Answer 21

-have large failure strains

Question 22

Brittle materials

Answer 22

-have small failure strains

Question 23

Hard materials

Answer 23

-have large failure stresses

Question 24

Soft materials

Answer 24

-have small failure stresses

Question 25

Toughness

Answer 25

-ability to absorb energy -a material is tougher if more energy is required to break it -estimation of the toughness of a material is given by the area under the curve

Question 26

Viscoelastic materials

Answer 26

-any material that exhibits both viscous and elastic characteristics

Question 27

Viscoelastic properties

Answer 27

-strain-rate dependency -stress-relaxation -creep -hysteresis

Question 28

Strain-rate dependency

Answer 28

-the rate at which you deform/strain a tissue will affect the stress it feels -faster loading rate will create more stress than a slower loading rate

Question 29

Stress-relaxation

Answer 29

-when a tissue is stretched and maintained at a constant length, the stress within the tissue will reduce over time -eventually the stress will reach an equilibrium

Question 30

Creep

Answer 30

-if a constant load is applied to a tissue, it will slowly continue to deform and eventually reach an equilibrium length

Question 31

Hysteresis

Answer 31

-the loading and unloading stress-strain curves of viscoelastic materials will differ -this is energy lost due to heat

Question 32

Active elements of musculoskeletal system

Answer 32

-muscle tissues

Question 33

Passive elements of musculoskeletal system

Answer 33

-connective tissues

Question 34

Connective tissue

Answer 34

-composed of living cells and collagen, elastin, ground substance, minerals, and water

Question 35

Isotropic materials

Answer 35

-have the same mechanical properties in every direction

Question 36

Anisotropic materials

Answer 36

-have different mechanical properties depending on the direction of the load

Question 37

2 primary factors affecting mechanical properties of tissues

Answer 37

-activity -age

Question 38

What type of stress are bones strongest and weakest in

Answer 38

-strongest in compression -weakest in shear

Question 39

Types of cartilage

Answer 39

-hyaline cartilage -fibrous cartilage -elastic cartilage

Question 40

Tendons and ligaments

Answer 40

-ligaments have more elastin than tendons