Week 2 Mechanical and Physical Properties Flashcards
Stresses from thermal expansion can?
stresses from thermal expansion can rupture adhesive bonds; divide by 11.4 so we can compare to tooth; closer to 1 is good
thermal diffusivity
heat transfer when temperature fluctuates
thermal conductivity? What does high K value mean?
steady state heat transfer (equilibrium achieves); higher value for k equals higher heat transfer; *enamel and dentin have LOW k= good bc we won’t feel every change in temperature
color fatigue
eye decreases its response spectrum when continually stimulated; quickly glance between shade and tooth
metamerism
different light sources produce different shade matches; *use northern daylight or color corrected lights
shade guides
hand held color matching guides
Lab*color measurement system
L= white (top) and black (bottom) axis a= red (+) and green (-) axis b= yellow (+) and blue (-) axis
Munsell color measurement system
3D coordinate system has a point for color based on hue, chroma and value
Hue: color, wavelength
Chroma: degree of color saturation, more intense closer to circle’s edge
Value: lightness or darkness of a shade
Flow
*amorphous material under constant applied force
Ex: waxes, glasses, plastics
Creep
*solid
plastic deformation
-time and temp dependent
-static or dynamic stress
viscosity
How thick aa material is –ability of liquid to resist flow
rheology
flow of matter
2-body abrasion
1 surface slides against another, rough surfaces often wear faster, hardness indirectly involved
3-body abrasion
loose particles in a liquid or gas medium with wear rates proportional to: applied pressure, speed of particles, lubrication, and hardness of particles
hardness? Hardness tests?
resistance to scratching or indentation
Tests= BHN, Rockwell, Vickers, Knopp, Shore
fatigue
material failure at LOW stresses due to repeated loading. # of stress cycles is important, surface cracks appear, failure is abrupt, dynamic vs. static
impact strength
energy required to cause fracture with a sudden, single blow, not a strength at all but an ENERGY, very different results from regular impact
resilience
amount of energy absorbed before elastic limit is exceeded, area under elastic strain
toughness
total energy required to fracture a material (elastic + plastic energy = toughness), total area under curve
brittleness
failure occurs with little or no permanent deformation (no plastic strain, opposite of malleable)
malleability
related to amount of COMPRESSIVE plastic strain (high plastic strain, opposite of brittle)
ductility
amount of TENSILE plastic strain
strength
maximum stress achieved
permanent deformation
=plastic strain reached, occurs when SS curve is no longer linear (starts to curve), object no longer returns to original form
