Week 1 - Biomechanics Intro

Question 1

Mechanotransduction

Answer 1

body senses mechanical stimuli and coverts it into cellular responses

Question 2

Force/load

Answer 2

mechanical disturbance or load

Question 3

What are the types of loading

Answer 3

Internal or external

• tension
• compression
• shear
• friction

Question 4

Tension

Answer 4

• pulling force
• positive force
• elongates material in direction of force

Question 5

Compression

Answer 5

• pushing force
• negative
• contraction of material in direction of force

Question 6

Normal forces

Answer 6

Tension and compression
- act perpendicular to SA

Question 7

Shear force

Answer 7

• acts in direction parallel to SA

Question 8

Friction

Answer 8

• resists relative movement between components
  e.g. opposing articular surfaces

Question 9

What can force do

Answer 9

• change shape (deformation)
• change speed or direction of mvt

Question 10

What effects what force does

Answer 10

• type
• magnitude
• duration
• frequency

Question 11

Force v stress

Answer 11

stress is force per unit area (N/m2)

Question 12

What symbol is used to refer to normal stresses

Answer 12

Sigma σ = F/a

Question 13

Deformation

Answer 13

Change of object shape

Question 14

Strain

Answer 14

relative deformation of object
- ratio of change in length (%)

Question 15

What is Poissons ratio

Answer 15

deformation of a material perpendicular to direction of loading

Question 16

Load-deformation v stress-strain

Answer 16

Load-deformation = graph relevant to materials with same DIMENSIONS

Stress-strain = graph relevant to things of same MATERIAL no matter size

Question 17

Features of stress-strain

Answer 17

Shows typical behaviour for certain material
O - origin
P - proportional limit
E - elastic limit
Y - yield point
U - ultimate stress
R - rupture point

Question 18

Elastic modulus

Answer 18

gradient of the initial line (O-P)
Equal to E = stress/strain

Question 19

What happens to material if strain happens during elastic region

Answer 19

No permanent deformation

Question 20

What happens if strain happens past elastic region (plastic region)

Answer 20

Permanent deformation to tissue

Question 21

Ultimate stress (strength)

Answer 21

highest value of stress on tissue

Question 22

Ultimate strain

Answer 22

point of rupture of tissue (R)

Question 23

Isotropy

Answer 23

Same mechanical behaviour regardless of force direction

Question 24

Anisotropy

Answer 24

mechanical behaviour depends on direction of force

Question 25

Stiffness

Answer 25

resistance to deformation

Question 26

Compliance

Answer 26

easy to deform

Question 27

Elasticity

Answer 27

ability to return to orginal shape when load removed

Question 28

Elastic deformation

Answer 28

temporary change - returns to og

Question 29

plastic deformation

Answer 29

permanent change after stress

Question 30

strength

Answer 30

ability to withstand stress without failure

Question 31

resilience

Answer 31

ability to absorb energy without sustaining permanent deformation

Question 32

toughness

Answer 32

capacity of material to tolerate plastic deformation - deforms plastically and absorbs energy

Question 33

brittle

Answer 33

fail without plastic deformation prior

Question 34

ductile

Answer 34

undergoes plastic deformation before breaking

Question 35

hysteresis

Answer 35

unloading behaviour doesn't follow loading behaviour

Question 36

Viscoelastic response to load

Answer 36

- some strain stored as potential energy - hysteresis - depends on rate of loading ans unloading Greater stress with faster strain rate

Question 37

Creep test

Answer 37

1. apply load 2. maintain stress for period of time 3. suddenly remove load

Question 38

How do viscoelastic materials respond to creep test

Answer 38

- gradual increase in strain - gradual decrease in strain with removal of load - eventually full recovery

Question 39

Stress-relaxation test

Answer 39

- strain material - maintain constant strain for period of time

Question 40

Viscoelastic response to stress-relaxation test

Answer 40

- initial high stress > relaxes over time when fluid moves - VE solid > increase in stress will never reduce to 0 - VE fluid > will eventually reduce to 0