Exam 1 review Flashcards
stress refers to?
intensity of the internal force acting on a specific plane (area) passing through a point
units usually pascal
1N/m2 = 1 pascal
MPa - mega (1,000,000)
GPa- giga (1,000,000,000)
Changes in load-displacement curve to the stress strain curve
units switch to pascal (not newton)
because load is newton
ideal poisson ration
0-.5
direction is seen perpendicular to the load
Diametral tensile strength?
use compressive force but it is an indirect test of the tensile strength of a material
the break is under tensile force even though compressive
seen through the middle of the object
three point bending tests what? aka
why important
FLEXURAL
- biaxial flexural strenght
need to know that the three point bending is testing flexural strength and is is standardized and important test for dental materials
materials must meet a certain flexural strength
flexural strnegth is?
(or bend strength) is the stress at fracture
fracture usually always starts where?
at the tensile part
flexural strength requirements
800 MPa in the posterior over 4 units with monolithic
griffith’s theory
with a brittle material *
the ACTUAL tensile strength of materials is less than the theoretical values we see
the catestrophic growht of the crack ca be understood in simple terms – the amount of energy stored elastically - exceeds teg required for creation of new surfaces
the larger the crrack - the smaller amount of energy to break it
larger specimen - more change of a bigger flaw
materials appear how much stronger in compression than tension?
8x stronger in compression
brittle materials withstand which strnegth better?
compressive strength
resiliance vs toughness
resiliance - under elastic zone and looks at ability to absorb energy before deforation
- without any deformation (why it stays in elastic zone)
toughness - area under both elastic and plastic and looks at HOW MUCH energy a material can withstand / absorb before it fails
hardness test?
three examples
looks into indentations
- looking at the SIZE OF THE INDENTATIONS
1. rockwell
2. vikers
3. knoop
units for fracture toughness?
what does this look like?
MPa x METERS SQUARE ROOT m^(1/2)
also Kc1 – higher of this then better at resisting
critical stress intensity factor
looking at ability to resist crack propagation
test used to test crack propagation
SENB
- single edge notch beam
- indentation cracking
- can use notch with 3-pt bending (flexural test)
strain energy
energy stored in a material due to its deformation
if mesaured up to the proportional limit –> resiliance
if measured up to the ,point of fracture –> toughness
strength is?
the stress at the point of failure / rupture
depending on testing it can be flexural, compressive, shear bond strength, etc
main 7 points of information you can get from a stress- strain curve
see notes
thermal expansion of enamel and dentin
- 4
8. 3
thermal expansion of wax?
HIGH – 240-400 or higher
thermal expansion of zirconia and emax CAD?
10.3 and 10.5
thermal expansion of dental cement and composite
cement - 10-12
composite 20-50
usually a polymer or wax has what type of thermal expansion?
HIGH
vs enamel and ceramics have lower
T/F the viscosity of a fluid is highly temperature dependent
TRUE
