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Dental materials > Properties of materials > Flashcards

Properties of materials Flashcards

1
Q

Types of Stress Shear

A

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

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2
Q

Types of Stress

Tension

A

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

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3
Q

Types of Stress Compression

A

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

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4
Q

Stress

A

Ration of force per area

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5
Q

Types of Stress Torsion

A

Twisting forces

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6
Q

Types of Stress Bending

A

results from a bending moment

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7
Q

Types of Stress

A

Shear Tension Torsion Bending Compression

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8
Q

Strain

A

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

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9
Q

Proportional limit

A

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

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10
Q

In Proportional limit below A is_______ and is called______

A

reversible strain occurs Elastic Region exception superelastic materials

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11
Q

In proportional limit Above A is ___________and is called the ________

A

irreversible or permanent strain plastic region exception superelastic materials

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12
Q

Elastic limit

A

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

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13
Q

Elastic deformation

A

Non permanent

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14
Q

Plastic deformation

A

permanent

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15
Q

Yield strength

A

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

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16
Q

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

A

Higher

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17
Q

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

A
  1. Destructively- fillings crowns bridges (causes improper occlusion and marginal breakdown) 2. Constructively- orthodontic wires
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18
Q

Ultimate strength

A

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

19
Q

Ultimate tensile strength or UTS is the

A

Max stress that a material can withstand in tension

20
Q

Ultimate compression strength UCS is the

A

Max stress a material can withstand in compression

21
Q

Fracture strength Sf

A

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.

22
Q

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

A

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

23
Q

Dental alloys and ceramics subjected to tension have similar

A

Ultimate strength and Fracture strength (Sf)

24
Q

Elongation

A

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

25
Q

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

A
  1. below proportional limit- deformation not permanent 2.permanent deformation- plastic elongation
26
Q

Elastic Modules (Young’s Modulus)

A

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.

27
Q

Elastic Modules- what is responsible for the property of elasticity

A

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

28
Q

Elastic modulus

A

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

29
Q

Resilience

A

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

30
Q

Toughness

A

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

31
Q

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

A

toughness

32
Q

Fracture toughness Fracture mechanics are characterized as

A

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

33
Q

General properties of stress/strain curves

A
34
Q

Tensile properties of brittle materials

Diametral compression test is used when

A

measureing brittle materials tensile properties

examples include amalgam, cements ceramics plaster nad stone

35
Q

Compressive properties

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

A

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

36
Q

Fatigue Strength

A

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

37
Q

Endurance Limit

A

A type of Fatigue Strength

stress at which the material can be loaded an infinite number of times without failing

38
Q

Viscoelasticity

Rate of loading

A

important for many materials (alginate elastomeric impression materials, waxes, amalgam, polymers.

increases values for E, PL and US

39
Q

Viscoelasticity

Materials with mechanical properties dependent on loading rate are termed

A

Viscoelastic

40
Q

Materials with mechanical properties independent of loading rate are termed

A

Elastic

41
Q

Viscosity

A

The resistance of fluid to flow

time and temperature dependant

42
Q

Viscoelastic materials Stress Relaxation

A

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

43
Q

Viscoelastic material CREEP

A

Increase in strain in material under constant stress (amalgam)

44
Q

Tear Strength

A

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.

Dental materials (2 decks)

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