Biomechanics

Question 1

Crevice Corrosion

Answer 1

• occurs in fatigue cracks due to differences in oxygen tension
• 316L stainless steel most prone to crevice corrosion

Question 2

Fretting Corrosion

Answer 2

• description
  
  • a mode of destruction at the contact site from the relative micromotion of two materials or two components
• clinical significance
  
  • common at the head-neck junction in hip arthroplasty
  • most common cause of mid-stem failure in modular revision type stems
    
    • arthroplasty involving modular implants are at risk for fretting corrosion and failure between the components of the final implant
    • increased risk with the increased number of interfaces between the various components

Question 3

Galvanic Corrosion

Answer 3

• dissimilar metals leads to electrochemical destruction
• mixing metals 316L stainless steel and cobalt chromium (Co-Cr) has highest risk of galvanic corrosion
• can be reduced by using similar metal

Question 4

Toughness

Answer 4

• definition
  
  • amount of energy per volume a material can absorb before failure (fracture)
• calculation
  
  • area under the stress/strain curve
• units
  
  • joules per meter cubed, J/m3

Question 5

Creep

Answer 5

increased load deformation with time under constant load

Question 6

Load Relaxation

Answer 6

decrease in applied stress under conditions of constant strain

Question 7

When analysing complex geometric form and material property distributions, the structure of interest may be divided up into numerous connected subregions or elements within which approximate functions are used to represent the unknown quantity. What is the name for this technique?

Answer 7

Finitie analysis

Question 8

Some relative values og Youngs Modulus

Answer 8

1. Ceramic (Al2O3)
2. Alloy (Co-Cr-Mo)
3. Stainless steel
4. Titanium
5. Cortical bone
6. Matrix polymers
7. PMMA
8. Polyethylene
9. Cancellous bone
10. Tendon / ligament
11. Cartilage

Question 9

Viscoelastic Material

Answer 9

• a material that exhibits a stress-strain relationship that is dependent on duration of applied load and the rate by which the load is applied (strain rate)
• a function of the internal friction of a material
• examples
  
  • ligaments
  • bone

Question 10

Fatigue Failure

Answer 10

• failure at a point below the ultimate tensile strength secondary to repetitive loading
• depends on magnitude of stress and number of cycles

Question 11

Endurance Limit

Answer 11

Endurance limit

• defined as the maximal stress under which an object is immune to fatigue failure regardless of the number of cycles