dental 3.2

Question 1

what is plasticity

Answer 1

when a material exceeds the elastic limit

Question 2

what is ductile

Answer 2

when the material experiences a large amount of plastic behaviour
metals tend to be ductile

Question 3

what is brittle

Answer 3

when the material undergoes little or no elastic behavior

ceramics tend to be brittle

Question 4

what is elongation

Answer 4

overall deformation as a result of tensile force application
change in length/ OG length * 100
increase elongation= material can be bent without danger of fracture
alloys with high elongation= precious alloys
high elongation means good ductility and malleability of metal alloys

Question 5

ductility

Answer 5

the ability of a material to be plastically strained in tension
enables the material to be drawn and shaped into a wire by means of tension
gold and silver are most malleable and ductile in metals

Question 6

malleability

Answer 6

enables material to be hammered and rolled into sheets without fracture

Question 7

burnishing

Answer 7

amount of force necessary to ease deformation

burnishing index is used to rank the ease of burnishing alloys

Question 8

poissons reaction

Answer 8

within the elastic range, the ratio of the lateral to the axial strain
rubber - 0.5
rigid material - 0.3

Question 9

what is resilience

Answer 9

the resistance of a material to permanent deformation

indicates the amount of energy needed to deform material to proportional limit

Question 10

toughness

Answer 10

amount of energy needed for a fracture

mMN /m3 or mMPa/m

Question 11

fracture toughness

Answer 11

the ability of a material containing a crack to resist a fracture
metal 25-60 mpa/m1-2
ceramics 0.75

Question 12

how to increase fracture toughness

Answer 12

presence of fillers in polymers

adhesion of 50% by weight of zirconia to ceramics