properties of materials

Question 1

mechanical properties use

Answer 1

used to indicate how a material or component will respond to use

Question 2

what are many materials supplied as

Answer 2

2 compounds mixed together

Question 3

what do you need to consider in material

Answer 3

unmixed compounds
during mixing
set materials

Question 4

mechanical properties

Answer 4

stress and strain
fatigue
hardness
abrasion resistance

Question 5

stress and strain catagories

Answer 5

elastic limit
plastic flow
fracture strenght
yeild stress
ultimate tensile strength
ductility 
resilence
fracure toughness
youngs modulus

Question 6

loading types

Answer 6

compression
tension
shear

Question 7

what is stress

Answer 7

cross sectional area that is action on a material

Question 8

equation for stress

Answer 8

F/As (Force/original cross area)
units
Mpa = newtons per square meter

Question 9

strain

Answer 9

fractional change in the dimensions cause by the force

no units as it is a ration of lengths

Question 10

strain equation

Answer 10

(L1-L0)/L0
L0 original length
L1-L0 change in length

Question 11

youngs modulus

Answer 11

how bendy something is

Question 12

what happens as you increase stress

Answer 12

you increase strain

Question 13

elastic area

Answer 13

can go back to its original shape even when stressed

Question 14

plastic flow

Answer 14

material will break once this is reached

Question 15

toughness

Answer 15

amount of energy a material can absorb to the point of fracture

Question 16

resilience

Answer 16

amount of energy a material can absorb without undergoing any plastic deformation

Question 17

ductility

Answer 17

amount of plastic strain at fracure

Question 18

brittle material

Answer 18

no plastic region

Question 19

brittle plastuc

Answer 19

will frature at lower strengths

still no plastic region

Question 20

elasomer

Answer 20

huge plastic region

will deform a lot, but not break until after plastic reion

Question 21

fatigue properties

Answer 21

given as fatigue life or fatigue limit or fatigue strength

Question 22

fatigue life

Answer 22

number of cycles to failure

Question 23

fatigue limit or strength

Answer 23

cyclic stress required to cause failure for a set number of cycles

Question 24

what can accumulation of stress casue

Answer 24

crack propagation leading to failure

Question 25

hardness

Answer 25

ability to withstand surface indentation by a compressive force

Question 26

what can hardness be measure by

Answer 26

indentation techniques or scratch test

Question 27

what does a scratch test measure

Answer 27

indicates material resistance to wear

Question 28

what is hardness directly proportional to

Answer 28

size of the indentation and therefore is given a number large for soft materials - small for harder materials

Question 29

chemical and physical properties

Answer 29

``` elasticity viscosity viscoelascity durability and degredation thermal properties adhesion colour and aesthetics biological properties ```

Question 30

thermal properties

Answer 30

thermal conductivity thermal diffusivity thermal expansion exothermic reactions

Question 31

elasticity viscosity viscoelascity indications

Answer 31

working times | setting times

Question 32

durability and degredation

Answer 32

solubility corrosion erosion

Question 33

elastic materials

Answer 33

strain when stretched | instantaneously return to original state once stress removed

Question 34

viscous material

Answer 34

resists flow and strain linearly with time when stress is applied

Question 35

viscoelastic material

Answer 35

have elements of both elastic and viscous materials | - exhibit time dependant strain

Question 36

solubility

Answer 36

extend to which a material dissolves in a fluid

Question 37

erosion - general and in dentistry

Answer 37

materia is removed and transported away therefor both chemical and mechanical components in dentistry - used to describe destruction of enamel and dentine by acid attack, which can be compounded by mechanical forces such as brushing

Question 38

durability

Answer 38

ability to withstand an environment

Question 39

corosion

Answer 39

``` deterioration of a material electrochemical processes (can be considered destructive oxidation) ```

Question 40

the 3 types of degradation can lead to

Answer 40

leaching of constituents into oral envrionment | - these leaked constituents must be safe locally and systemically

Question 41

thermal conductivity

Answer 41

Rate of heat flow per unit of temperature gradient under steady state conditions - property of metal to conduct heat

Question 42

when does conductor occur

Answer 42

when there is a temperature gradient | the temp gradient is directional i.e. from hotter to colder

Question 43

thermal diffusivity equation

Answer 43

Thermal conductivity /(p CP) p= density CP= heat capacity

Question 44

what happens when transient heat is applied to teeth/dental material

Answer 44

a proportion will be expended rating the temperature of the tooth/material the remainder will be conducted to the pulp - materials with low thermal diffusivities are generally preferred

Question 45

what is thermal expansion. due to

Answer 45

increased amplitude of atomic/molecular vibrations due to the absorption of heat energy

Question 46

importance of thermal expansion

Answer 46

need to ensure restoration material won't expand otherwise tooth under stress may fracture

Question 47

thermal expansion in solids

Answer 47

often stated as linear coefficient of thermal expansion which is fractional length change per degree of temperature change - metals expand the most due to the sea of e- that can move about

Question 48

exothermic reaction

Answer 48

heat is generated transferred to the surrounding tooth tissue need to be careful with the pulp