Chapter 9 - Mechanics of Biological Materials

Question 1

Define mechanical stress

Answer 1

Aka pressure, refers to the distribution of a force over the body that it acts on

Question 2

Define strain

Answer 2

External forces that act on the body affect the internal structures of the body are called stress. The effect stress has on the tissues is called strain.

Question 3

Define tension (tensile strain and tensile stress)

Answer 3

Tension is one of two longitudinal stresses. Tension (or tensile stress is a force that tends to pull apart the molecules bonding the object together. When object undergoes tension, it tends to stretch or elongate. Acts perpendicular to the surface.
Tensile strain is the result of loads that tend to pull molecules apart as the object lengthens.

Question 4

Define compression (compressive strain and compressive stress)

Answer 4

Compression is the second of two longitudinal stresses. Compression (or compressive stress) is a force that tends to push the molecules bonding the object together. When an object undergoes compression, it tends to deform. Acts perpendicular to the surface.
Compressive strain is the result of loads that push molecules together as the object shortens

Question 5

Define shear (shear strain and shear stress)

Answer 5

Shear stress acts parallel to the surface(s) (sliding stress) (blisters)
Shear strain is the result of loads that tend to slide molecules past each other as the shape of the object becomes distorted.

Question 6

Define torsion (torsional stress)

Answer 6

Torsion loads occur when there is a torque about the long axis (standing and turning without moving your feet).
Spiral fracture

Question 7

Describe the general stress–strain relationship for an elastic material

Answer 7

For an elastic material, an object stretches under tension and deforms but then returns to its original shape

Question 8

Describe the general stress–strain relationship for a plastic material

Answer 8

For a plastic material, an object stretches, and the load exceeds a certain limit there will be some permanent deformation

Question 9

Define the various descriptors of material strength: yield strength, ultimate strength, and failure strength

Answer 9

Yield strength: stress at the elastic limit
Ultimate strength: maximum stress the material is capable of withstanding
Failure strength: where failure actually occurs

Question 10

The more ductile a material is, the ____ its failure strain

Answer 10

higher

Question 11

Bones carry almost all the _____ forces in the body

Answer 11

compressive

Question 12

Bones are capable of resisting large ____ and ____ loads

Answer 12

shear, tensile

Question 13

What determines the strength and stiffness of bone?

Answer 13

Porosity

Question 14

Rate of loading and bones

Answer 14

Stronger and stiffer when load applied quickly, weaker and less stiff when load applied slowly

Question 15

Tendons and ligaments consist primarily of what?

Answer 15

Water and collagen

Question 16

Collagen fibers in tendons and ligaments are arranged how?

Answer 16

In parallel bundles

Question 17

Collagen fibers appearance

Answer 17

Slightly wavy of crimped

Question 18

Total strain that tendons and ligaments can withstand

Answer 18

8-15%

Question 19

Muscle tissue is capable of _____ _____ to produce its own _____

Answer 19

actively contracting, tension

Question 20

Stiffness of passive muscle is high or low?

Answer 20

Low

Question 21

Stretching a muscle past the point where the contractile filaments no longer overlap is resisted by?

Answer 21

The connective tissue component of muscle

Question 22

Failure strain for muscles (muscle tissue only)

Answer 22

50%

Question 23

Failure strain for muscles (muscle and connective tissue)

Answer 23

58-65%