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
compliance
inverse slope of force-elongation curve (related to flexibility but based on shape)
flexibility
inverse of elastic modulus (1/E)
Hooke’s Law explains
linear proportionality between elastic stress and strain, E is slope of SS curve; Modulus of Elasticity
yield strength
the stress value where an offset line intersects the SS curve (0.1% or 0.2%)
proportional limit
the stress point at which the stress strain curve deviates from linearity and begins the area of plastic strain
elastic limit
stress that just exceeds the elastic strain limit
plastic strain
atoms are permanently displaced when stress is applied. Do NOT recover to original state
elastic strain
atoms return to original positions when stress is removed, it IS recovered
Poisson’s ratio
relates strain change in all 3 dimensions when a stress is applied along one axis, *remember forces are vectors so you have both magnitude and direction
stress definition and explain equation
RESISTANCE of a material TO APPLIED FORCE
*stress=load/area
larger area=lower stress; larger load=more stress
define strain? another term for strain?
is change in shape when force applied. also deforamtion (dimensionless)
tensile
pulled on strain (think fishing line)
compressive
pushing on object, atoms pushed together
shear
atoms/objects sliding past each other
torsional
twisting motion, atoms twist against something causing friction
diametral tension
compression test for brittle material
modulus of elasticity/Young’s modulus
represents stiffness, proportionally constant between stress and strain (or the slope) of the linear portion of S-S curve
stress-strain diagram
shows how stress and strain are related for a given material
flexure is what type of bend?
3/4 point bend, generating multiple types of stress with 1 or 2 applied forces
yield point
elastic limit has been reached and is going into plastic strain, deformation is occurring
percent elongation tests what?
test to measure ductility
ultimate strength
maximum stress a material can withstand
What is color?
psychological response to eletromagnetic radiation affected by light, object and individual
What is color hue?
the color itself determined by dominant wavelength
what is color value?
lightness or darkness of a shade
Chroma
degree of color saturation, more intense closer to circle’s edge
heat capacity
of heat units needed to change (1 mol of) a materail 1 degree
specific heat
ofheat units needed to change (1 gram of) a material 1 degree
