Dental materials 1

rpopple's version from 2016-08-24 02:01

Section 1

Question Answer
key feature of ceramics brittle
key feature of polymersit EXPANDS AND FLEXIBLE 10x as much as metals or ceramics when heated the same amount , WEAK AND ABSORBS WATER
acronym to memorize the table for main properties of each categoryMSDT- modulus of elasticity, Strengh, Durability, Thermal Expansion. Then Ceramics, Metal, Polypers... except for durability, the polymp
a high modulus of elasticity means whatthat it is not very flexible... very stiff.
what is youngs modulussame as modulus of elasticity
what symbol is Y or Emodulus of elasticity
what is strengthability of a material to resist breakage or permanent deformity
fracture strength vs yield strengthyeild strength is the force required to bend or permanently deform something
the ability to form into a duct or tube aka be drawn, stretched or hammeredductibilty
why is ductility importantthey can yield to a force by bending or stretching
what are the primary bonds of ceramics, metals and polymers ceramics- covalent or ionic. metals- metallic bond. poylmers - covalent bonds
are secondary or weak bonds of major or minor importance to the 3 groupsceramics and metals- no. but for polymers- yes very important and include hydrogen and van der waal forces.
The type of bonds that are important contribute to with caterogies in the main table MS...modulus of elasticity, strength and thermal expansion. bc secondary bonds play an important role with polymers, they will be weak in strength, low in M of E and high Thermal
definition of tensionforce that stretches something
equation for finding stressforce by area - fucking A
Greek symbol for stresssigma
The modulus of elasticity relates to tension how?the greater the m.of Elasticity is, the more stiff it is and less it will stretch
definition of strainthe amount a material will stretch
lowercase Greek letter for strainepsilon
how to calculate strainfraction of the original length-- amount stretched / original.
calculate Modulus of elasticitystress / strain or stress to strain.

Section 2

Question Answer
how do you determine the theoretical strength the strength is 10 percent of the modulus of elasticity. it is the same as the inter-atomic PRIMARY bonds
MgO ( ceramic) follows the theoretical strength to about .01% Why is this so low?Irregularilities are the reasons why. Scratches in materials act as stress raisers. so the theoretical strength is reached a lot faster under low stress.
what is plastic deformation?when a material starts to yield without breaking aka bending
do polymers aka polyethylene have a standard moduli of elasticity?no, each is highly variable
Stress raisersthe irregularity.
as the radius of the tip of the notch becomes smaller... the stress concentration...becomes greater.
what happens during bending of particles on the outside and inside?outside, the bonds are stretched aka have tension aka tensile stress while the bonds on the lower are under compression
what are the two types of stresstensile stress- stress out and compressive stress.
Why are metals ductal and are not brittle ?when a stress raiser or scratch is present, the metal at the point is able to deform and create a more rounded edge, which reduces the stress.
Why can metals be ductal and ceramic be so brittleWith metal, the atoms are able to slide one by one and creates an extra space called lattice or dislocation
what is dislocation responsible forductile behavior of metal
what are two types of ceramicsamorphous and crystalline ceramic material.
do the glassy ceramics contain crystalline?no they do not. so they cannot have dislocations
do crystalline ceramics do dislocation?They technically can do dislocation but their atoms are charged, so they would have to move a great deal

Section 3

Question Answer
Is the stress needed to break the polymer the same for the stress coming perpendicular and parallel aka is the modulus of elasticity the same?No, the stress for parallel needed to break it is extremely high but perpendular it is very low. WITHIN the chains, there are strong bonds between atoms and weak bonds between the chains.
how are bulk polymers different then when the chains are aligned perfectlythe bulk polymers chains are more randomly tangled and there are less secondary bonds.
are the tangled polymer more flexible than the straight chain polymer?yes
what contributes to the low strength of polymersthe weak secondary bonds between chains and the strong bonds within the chains.
increasing the force does what to the stress?increases the stress
increasing the area does what to the stress?decreases the stress
what does stress concentration do?causes materials to be less strong