Biomaterials Flashcards
Fretting corrosion
contact sites subjected to micromotion under load
galvanic corrosion
two different metals create an electrochemical potential - screws and plate, impurities in metal
crevice corrosion
differences in oxygen tension due to geometry or defects in manufacturing
pitting corrosion
localized symmetric corrosion form pits
polymer degradation corrosion
exposure to harsh environments- ex oxidation of uhmwpe
loads
compression/tension - perpendicular to surface
shear - parallel to surface
torsion - rotational force
stress
force(F)/cross-sectional area (A)=stress(E)
E=F/A
unit N/m2 or Pascals (Pa)
strain
deformation of material due to force
strain (sigma)=change in length (delta L)/ original length (L)
sigma=delta L/L
modulus of elasticity
elasticity (E)=stress/strain=slope of curve
high modulus => stiff
yield stress
stress at which the object has permanent deformation
transition between elastic and plastic deformation
ultimate stress
stress after which the object will continue to deform despite decreasing stress loads that that ultimately leads to failure
brittle vs ductile
brittle - small strains during plastic deformation before failure
ductile - large strains during plastic deformation prior to failure
toughness
area under curve represents total energy absorbed by material prior to failure
fatigue failure steps
crack
propagation
catastrophic failure
viscoelastic materials
stress-strain curve that are time/rate dependent due to internal friction
hysteresis is the area between load and unload portions of stress-strain curve
creep is increased displacement of material over time due to force
