Flashcards in 3. Mechanical Properties Deck (38)

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1

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Mechanical Properties of Dental Materials

Properties defined by the laws of ____.

The response of a material to an

____ force. A sub-set of ____ properties.

###
mechanics

applied

physical

2

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Forces on Dental Materials

Three types of forces or loads may be applied to a solid material.

____

____

____

###
tensile

compressive

shear

3

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Stress and Strain

We can define force intensity because if

we have the same force on two materials of different sizes, we need to be able to describe the effects of the force on the two different sizes of material. We use what I'm calling a force intensity, which is referred to as ____. Stress is ____ divided by the ____ of the object, so if we are putting a tensile force on this material, we are pulling it apart, there will be an increase in ____. We can describe this increase in ____ divided by the ____, that is the fractional change in length of the material, which is referred to as ____

###
stress

force

area

length

length

original length

strain

4

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Stress

The internal force within a material which ____ an externally applied force or load.

stress = ____ (lb/inch^2), (psi), ____, ____)

Tensile

Compressive

Shear

###
resists

F/A

N/m^2

Mpa

5

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Strain

Change in ____ of a material which results from an externally applied force.

e = ____ (inch/inch, mm/mm)

###
dimensions

(L1 - L0)/L0

6

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Modulus of Elasticity

(1) Two springs, difference in the stiffness (same force applied to both)

Dividing stress by strain > ____ (measure of stiffness of material)

Continue pulling on spring: becomes permanently ____, where you exceed its elastic limit; plot the stress vs strain

###
young's modulus

elongated

7

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S/S curve for stainless steel

(2) Initially, force is ____ to elongation (straight line) up to proportional limit; once you exceed this point it begins to deform ____ > continue elongation until the spring breaks (____)

Use it to describe mechanical properties of materials > the slope of the initial portion: measure of the ____ of the spring; next property of importance is the ____ > want to deform 0.2% of starting length > and can use comparatively between two materials

###
proportional

permanently

ultimate tensile strength

stiffness/rigidity

yield strength (YS)

8

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Stress/Strain Curves

(3) Degree to which a material deforms permanently is a measure of its ____, so when we measure we are looking at the full range of the material

### ductility

9

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Stress/strain Curves

Elastic Strain

Strain which ____ completely when the applied force is removed

Permanent (Plastic) Strain

Strain which remains ____ after the applied force is removed

###
disappears

permanently

10

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Elastic Limit

Stress corresponding to the first measurable ____.

- Yield Strength

Stress corresponding to a designated amount of permanent strain - ____ - ____

Units: Psi, Mpa

Units for YS are the units for ____

###
permanent deformation

0.1%

0.2%

stress

11

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Proportional Limit (PL)

The value of stress at which the stress/strain diagram deviates from the initial ____ relation

The useful ____ of a dental material

###
linear

strength

12

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Elastic Limit vs. Proportional limit vs. Yield Strength

All of these are essentially ____

### equal

13

##
Modulus of Elasticity

____ of the initial linear portion of the stress/strain diagram

____ of a material

Modulus of elasticity = ____

###
slope

rigidity

stress (MPa) / Strain

14

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Ultimate Strength

The stress corresponding to the ____ value of applied load or stress a material can withstand without rupturing

Units: psi, MPa

Some materials fracture at the maximum stress, so the UTS is the ____; some materials you exceed the UTS, so you will have a ____ fracture strength from the UTS

###
maximum

fracture strength

different

15

##
Failure of Dental Restorations

A permanent deformation of a dental appliance under occlusal loading represents a functional failure - by changes in ____ and ____

###
occlusal relationship

fit

16

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Ductility/Elongation

The ability of a material to undergo

permanent ____ deformation without ____.

Clasp adjustment, ____ and crowns, preparation of ____ appliances

The material shown on graph has some ductility to it; a good example of ductility is ____ to improve the marginal fit on the tooth

###
tensile

fracture

burnishing of inlays

orthodontic

burnishing inlays

17

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Malleability

The ability of a material to undergo permanent ____ deformation without fracturing.

Brittleness:

Material behavior characterized by fracture with little or no prior ____

Opposite of the two is brittleness (i.e. ceramic plates, drinking glasses > not able to deform permanently when a stress is placed upon them) (i.e. all dental ____ materials, porcelain)

###
compressive

permanent deformation

ceramic

18

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Modulus of Resilience

Resilience:

Amount of ____ energy stored in a material during ____ deformation

Indicates ____ of material

Area under ____ portion of SS

curve

R=(1/2) P^2/E

###
recoverable

elastic

springiness

linear

19

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Resilience and Toughness

Resilience is the ____ portion of the stress-strain curve; ____ of material is the energy that is stored throughout the curve before it fractures

###
linear

toughness

20

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Toughness

Total energy absorbed

by a unit volume of material prior to ____ of the material specimen.

Tough materials have high ____, ultimate strength and ____ at rupture

Ceramic plate on one hand, and a metallic plate on the other; if you drop both, the ceramic plate will crack and the metal plate will recoil > metallic plate only deformed up to the elastic limit, ceramic plate has little ____ so it cracks

###
fracture

proportional limit

strain

resilience/toughness

21

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S/S Curves for Materials with Different Properties

Materials with high slope of linear portion > ____; the non-linear part, has a significant amount of plastic deformation (top left, ____, the one next is brittle); strong material has a high ____ and high ____; tough because of the ____ located under the curve

###
stiff

ductile

YS

UTS

large area

22

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S/S curve for stainless steel

Curve is different; look at S/S Curves for Enamel/Dentin; enamel has higher ____ and it is stronger because the ____ is higher, however it is not as ____ as dentin (dentin is also more ____)

###
stiffness

UTS

tough

ductile

23

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Other Mechanical Properties

Transverse strength, bend test:

The maximum ____ which a material can support before failure when loaded as a beam supported at ____ ends.

###
stress

two

24

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Three Point Bend Test

Stress at where it breaks is the ____ strength (same as flexural); modulus of rupture: determining the ____ using the bend test

###
transverse strength

modulus of elasticity

25

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Diametral Tensile Strength

Tensile properties of ____ materials are obtained by loading a ____ of the sample:

epsilon = 2P/piDT (psi, MPa)

###
brittle

disk

26

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Diametral Tensile Strength

Stresses are ____ to the force and it breaks right down the ____; calculate tensile strength using this test (used for ____ and ____)

###
perpendicular

middle

amalgam

composites

27

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Hardness

Resistance of a material to ____ or to being ____ by another material

###
permanent indentation

scratched

28

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Hardness Measurements

Brinell

Rockwell

____

____

____

###
Vickers

Knoop

Barcol

29

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Hardness Measurements

Bronell uses a hardened ____ and loaded, and the projected area of indention (load/projected area of indentation); rockwell has a ____, similar principle; vickers, knoop and barcol are more useful for ____ measurements; vickers and knoop are ____ indentations

###
round-tip

steel-tip

dental

diamond-tipped

30