Elastic Properties Of Soft Biomaterials

Question 1

Stiffness

Answer 1

Measures the resistance of a material to elastic deformation

Question 2

Toughness

Answer 2

The total amount of energy that a material can absorb before fracture
- area under stress-strain curve

Question 3

Hardness

Answer 3

The ability of a material to resist penetration
- correlated with tensile strength since indicates resistance to plastic deformation

Question 4

Elastic strain energy definition

Answer 4

• Energy per unit volume associated with stretching a material
• given by area under curve

Question 5

Properties of J shaped curve

Answer 5

• lower part of curve gives large extension for low stress - accumulated strain energy remains low
• upper part of curve is steep - material gets much stiffer as failure point approaches - large extensions require large stresses
  Example: skin

Question 6

Elastic
Plastic
VIscoelastic

Answer 6

Elastic: When load is removed there is no permanent deformation
Plastic: When load is removed there is permanent deformation
VIscoelastic: When load is removed, material returns to original shape with time

Question 7

Describe elastic energy and cracks for brittle solids

Answer 7

• local energy density needed to break bonds at crack tip
• strain energy released from area

Question 8

Mechanisms by which biomaterials resist fracture (increase toughness)

Answer 8

• viscous effects within material prevent strain energy reaching crack tip
• fracture area convoluted and large so more energy needed to crack
• stress at crack tip defocused if tip is semi-circle not point
• material can be pre-stressed in opposite sense of load
• structures can be so small that required elastic energy cannot be stored