2PropertiesOfMaterials

Question 1

*What is the formula for stress? What is the unit of measurement?

Answer 1

S=Force/Area…1 Newton/m^2= 1 Pascal

Question 2

*What are the 5 types of stress?

Answer 2

1.Tension 2.Compression 3.Shear 4.Torsion 5.Bending

Question 3

*What type of stress occurs when elongation forces are directed away from each other in the same straight line and the molecules resist being pulled apart?


Answer 3

Tension

Question 4

*Which type of stress occurs when shrinkage forces are directed toward each other in the same straight line and molecules resist being forced more closely together.

Answer 4

Compression

Question 5

*Which type of stress occurs when forces are directed parallel to each other NOT along the same straight line and one portion resists sliding past the other.

Answer 5

Shear

Question 6

*Which type of stress occurs when there are twisting forces?

Answer 6

Torsion

Question 7

*Which type of stress results from a bending moment?

Answer 7

Bending..haha. lol.

Question 8

*What is Deformation caused by stress? How is it measured? What is the formula for deformation?

Answer 8

STRAIN…Measured unitless or as a %…Deformation=Deformation/Length

Question 9

*What is the stress at which the material begins to function in a PLASTIC manner? Limited permanent strain HAS occurred…What is the % of permanent strain?

Answer 9

Yield Strength…0.2% permanent strain

Question 10

*Is Permanent Deformation Constructive or DeStructive in the oral cavity?

Answer 10

It can be Destructive(crowns/partials) OR Constructive(ortho wires)!

Question 11

*Where can I find Ultimate Strength on the Strain/Stress curve?

Answer 11

Ultimate Stress=Highest point on curve

Question 12

*What is the max. stress that a material can withstand in tension?

Answer 12

Ultimate Tensile Strength

Question 13

*What is the max. stress a material can withstand in

compression?

Answer 13

Ultimate Compression Strength

Question 14

What’s another word for “permanent deformation”?

Answer 14

Failure

Question 15

*Why is Yield Strength of greater importance then Ultimate Strength in dentistry?

Answer 15

Yield strength is an estimate of when a material will start to FAIL!

Question 16

*What is the stress at which a brittle material fractures?

Answer 16

Fracture Strength

Question 17

What is the term for a material that elongates excessively causing a reduction in stress before permanent deformation?

Answer 17

“Necking”

Question 18

*For most dental alloys and ceramics subjected to tension, the ______ _______ and ________ _______ will be similar.

Answer 18

Ultimate Strength and Fracture Strength

Question 19

*__________ –deformation that results from the application of TENSILE FORCE. Indicates the workability of alloy. Expressed as a ___.

Answer 19

Elongation….%

Question 20

Elongation: a gold alloy with 20% elongation would be considered _______, while a material with 1% elongation would be ________.

Answer 20

20%=Ductile, 1%=brittle

Question 21

*What is the measure of elasticity and represents the stiffness of a material within the elastic region… Namely the slope of the S/S curve in the elastic portion. WHAT IS another name for it?

Answer 21

Elastic Modulus (E)..Youngs Modulus

Question 22

________/__________ forces are responsible for the property of elasticity. The stronger the forces,
the more stiff or rigid the material.

Answer 22

Interatomic/intermolecular

Question 23

What is the formula for elasticity?

Answer 23

E=Stress/Strain

Question 24

*The higher the value of the _______ _______, the more stiff or rigid the material.

Answer 24

Elastic Modulus

Question 25

*What is resistance of a material to permanent deformation AND indicates the amount of energy needed to deform a material to the proportional limit AND is the area UNDER the elastic portion? WHAT dental material is it useful to evaluate?

Answer 25

Resilience...Ortho Wires and Springs

Question 26

*What is the resistance of a material to fracture AND indicates the amount of energy needed to cause fracture AND is the area under the elastic AND plastic area?

Answer 26

Toughness

Question 27

*What three things can you increase to increase TOUGHNESS?

Answer 27

1.Yield Strength 2.Ultimate Strength 3.Strain (All increase the area under the stress/strain curve)

Question 28

*_______ generally weaken a material and may result in fractures at stresses WELL BELOW the yield stress. Occurs more in _______ materials that have no ability to deform and redistribute stresses.

Answer 28

Defects...Brittle

Question 29

*Because tensile properties of BRITTLE materials are hard to measure the _______ ________ ______ is used. It's a good test for brittle materials – amalgam, cements, ceramics, plaster, and stone.

Answer 29

Diametral Compression Test

Question 30

*What is unique about the plastic portion of the stress-strain curve for a Brittle material?

Answer 30

The plastic response is SMALL!

Question 31

What are the two important characteristics of Endo files?

Answer 31

Flexure and Torsion

Question 32

*______ _______ – the stress at which a material fails under repeated loading. Depends on the ________ of the load and the ______ of loadings.

Answer 32

Fatigue Strength...Magnitude.....Number

Question 33

*_______ _______ – stress at which the material can be loaded an infinit of times without failing.

Answer 33

Endurance Limit

Question 34

*What is the RATE of loading measured by? Think Impression materials! Hence: Materials with mechanical properties dependent on loading rate are termed ________.

Answer 34

ViscoElasticity....Viscoelastic

Question 35

*What is the Resistance of a fluid to flow? What is the unit?

Answer 35

Viscosity...Poise

Question 36

*What is the reduction in stress in a material subjected to constant strain (ortho bands)?

Answer 36

Stress Relaxation

Question 37

*What is the increase in strain in material under constant stress?

Answer 37

CREEP

Question 38

*What is resistance to tearing forces? Important for Polymers in thin sections and depends on the RATE of loading (rapid loading=higher values)

Answer 38

Tear Strength

Question 39

What is the loss of material resulting from removal and relocation of materials through the contact of two or more materials?

Answer 39

Wear

Question 40

How does the Linear Thermal Coefficient of Expansion of Composite compare to Human Teeth?

Answer 40

Composite= 2-6x human teeth (WANT THEM TO BE CLOSE!)