Properties of materials

Question 1

Types of Stress Shear

Answer 1

forces directed parallel to each other not along the same straight line

Question 2

Types of Stress

Tension

Answer 2

elongation forces are directed away from each other in the same straight line, molecules resist being pulled apart

Question 3

Types of Stress Compression

Answer 3

shrinkage forces directed toward each other on the same straight line molecules resist being forced more closely together NOTE: different than Shear in that it IS on the same straight line as opposed to NPT

Question 4

Stress

Answer 4

Ration of force per area

Question 5

Types of Stress Torsion

Answer 5

Twisting forces

Question 6

Types of Stress Bending

Answer 6

results from a bending moment

Question 7

Types of Stress

Answer 7

Shear Tension Torsion Bending Compression

Question 8

Strain

Answer 8

Deformation caused by stress measured as a % of Deformation = deformation/length

Question 9

Proportional limit

Answer 9

The greatest stress sustained without deviation from the linear proportionality of the stress and strain.

Question 10

In Proportional limit below A is_______ and is called______

Answer 10

reversible strain occurs Elastic Region exception superelastic materials

Question 11

In proportional limit Above A is ___________and is called the ________

Answer 11

irreversible or permanent strain plastic region exception superelastic materials

Question 12

Elastic limit

Answer 12

The greatest stress sustained without permanent deformation Note: for lineraly elastic materials the PROPORTIONAL LIMIT AND ELASTIC LIMIT THE SAME STRESS WITHIN THE STRUCTURE. exception are the superelastic materials

Question 13

Elastic deformation

Answer 13

Non permanent

Question 14

Plastic deformation

Answer 14

permanent

Question 15

Yield strength

Answer 15

The stress at which the material begins to function in a plastic manner. Limited permanent strain has occurred .2%

Question 16

Yield strength is slightly______ than the proportional limit because it includes a slight amount of permanent deformation

Answer 16

Higher

Question 17

Permanent deformation can be good or bad in the oral cavity in what two ways

Answer 17

1. Destructively- fillings crowns bridges (causes improper occlusion and marginal breakdown) 2. Constructively- orthodontic wires

Question 18

Ultimate strength

Answer 18

Greatest stress occurs at C, the spot on the graph right before it begins to decrease the stress.

Question 19

Ultimate tensile strength or UTS is the

Answer 19

Max stress that a material can withstand in tension

Question 20

Ultimate compression strength UCS is the

Answer 20

Max stress a material can withstand in compression

Question 21

Fracture strength Sf

Answer 21

stress at which a brittle material fractures at D, the decreasing portion of the graph NOTE: a material does not always fracture at the point of greatest stress C.

Question 22

Why might a material not fracture at the point of greatest stress C.

Answer 22

It may elongate excessively reducing the correctional area (necking) causes a reduction in stress

Question 23

Dental alloys and ceramics subjected to tension have similar

Answer 23

Ultimate strength and Fracture strength (Sf)

Question 24

Elongation

Answer 24

deformation that results fro the application of tensile force. Will indicate the workability of the alloy. Expressed as a %

Question 25

What does 0-A and A-D represent in regards to elongation

Answer 25

1. below proportional limit- deformation not permanent 2.permanent deformation- plastic elongation

Question 26

Elastic Modules (Young's Modulus)

Answer 26

Elastic Modules (E)- the measure of elasticity represents the stiffness of a material within the elastic region. the slope of S/S in the elastic portion.

Question 27

Elastic Modules- what is responsible for the property of elasticity

Answer 27

interatomic/intermolecular forces are responsible for the property of elasticity. The stronger the forces the more stiff or rigid the material. NOT AS RIGID A SLOPE E=stress/strain

Question 28

Elastic modulus

Answer 28

the higher the value of E the more stiff or rigid the material is. example are Metals and Ceramics have a HIGH E Elastomers and polymers have a low E

Question 29

Resilience

Answer 29

resistance of a material to permanent deformation, area under the elastic portion.

Question 30

Toughness

Answer 30

resistance of a material to fracture, indicates the amount of energy needed to cause fracture. Area under both the plastic and elastic area

Question 31

Combination of yield strength-ultimate strength- strain. increasing any of these also increases

Answer 31

toughness

Question 32

Fracture toughness Fracture mechanics are characterized as

Answer 32

the behavior of materials with cracks or flaws defects generally weaken a material, occur in more bridle materials glass diamonds sheet rock enamal

Question 33

General properties of stress/strain curves

Answer 33

Question 34

Tensile properties of brittle materials Diametral compression test is used when

Answer 34

measureing brittle materials tensile properties examples include amalgam, cements ceramics plaster nad stone

Question 35

Compressive properties Brittle materials such as Amalgam, resin composites, cements, plaster, investments

Answer 35

will have both elasti and plastic properties but the plastic response is small

Question 36

Fatigue Strength

Answer 36

the stress at which a material fails under repeated loading depends on teh _Magnitude_ of the load and the _Number_ of loads

Question 37

Endurance Limit

Answer 37

A type of Fatigue Strength stress at which the material can be loaded an infinite number of times without failing

Question 38

Viscoelasticity Rate of loading

Answer 38

important for many materials (alginate elastomeric impression materials, waxes, amalgam, polymers. increases values for E, PL and US

Question 39

Viscoelasticity Materials with mechanical properties _dependent_ on loading rate are termed

Answer 39

Viscoelastic

Question 40

Materials with mechanical properties _independent_ of loading rate are termed

Answer 40

Elastic

Question 41

Viscosity

Answer 41

The resistance of fluid to flow time and temperature dependant

Question 42

Viscoelastic materials Stress Relaxation

Answer 42

Reduction in stress in a material subjected to constant strain ortho bands for example

Question 43

Viscoelastic material CREEP

Answer 43

Increase in strain in material under constant stress (amalgam)

Question 44

Tear Strength

Answer 44

Resistance to tearing forces, important for polymers in thin sections, impression materials in the sulcus, soft liners, depnds on rate of loading rapid loading = higher values.