Properties of Materials Flashcards
Stress is difficult to measure directly so the stress is calculated from the ratio of ___ per ___.
force per area
What are the 5 types of stress?
Tension Compression Shear Torsion Bending
___ - elongation forces are directed away from each other in the same straight line. molecules resist being pulled apart
Tension
___ - Shrinkage forces directed toward each other in the same straight line. Molecules resist being forced more closely together.
Compression
___ - Forces directed parallel to each other not along the same straight line. One portion resists sliding past the other.
Shear
___ - Twisting forces
Torsion
___ - Results from a bending moment
Bending
___ is a deformation caused by stress measured as a unit less value or as a %. (Deformation = deformation/length)
Strain
___ is the greatest stress sustained without deviation from the linear proportionality of the stress and strain
Proportional limit
___ is the greatest stress sustained without permanent deformation
Elastic limit
For ____ materials, the Proportional Limit and Elastic Limit represent the same stress within the structure.
linearly elastic
Elastic Deformation is ___ while plastic deformation is ___.
non-permanent permanent
___ is the stress at which the material begins to function in a plastic manner. Limited permanent strain has occurred.
Yield strength
Fun Fact about Yield Strength…
The exact point at which permanent deformation occurs is difficult to detect precisely so an arbitrary amount of deformation is chosen which can be measured accurately. Displayed as B on the graph.
Permanent deformation can be ___ or ___ in the oral cavity.
good or bad
What is an example of a constructive permanent deformation?
orthodontic wires must be bent to retain shape. Partial clasps must be readjusted
___ is the greatest stress an object can withstand.
It is represented by which letter on the graph?
Ultimate strength. Displayed as C on Strain/Stress graph
___ is the max stress that a material can withstand in tension.
Ultimate Tensile Strength (UTS)
___ is the max stress a material can withstand in compression
Ultimate Compression Strength (UCS)
___ is the stress at which a brittle material fractures.
Fracture Strength
A material does not always fracture at the point of greatest stress. It may elongate excessively reducing the cross-sectional area (called ____) causing a reduction in stress.
necking
___ is the deformation that results from the application or tensile force. It indicates the ___ of an alloy. Expressed as a %.
Elongation workability
___ is the measure of elasticity. Represents the stiffness of a material within the elastic region. The slope of the Stress/Strain curve in the elastic portion.
Elastic Modulus
___ is the resistance of a material to permanent deformation. Indicates the amount of energy needed to deform a material to the ___ Limit.
Resilience Proportional
___ is the resistance of a material to fracture.
Toughness
Toughness is the combination of ___, ___, and ___.
Yield Strength, Ultimate Strength and Strain
___ characterizes the behavior of materials with cracks or flaws.
Fracture mechanics
Defects generally ___ a material and may result in fractures at stresses well below the yield stress. This occurs more in ___ materials that have no ability to deform and redistribute stresses.
weaken brittle
Because tensile properties of ___ materials are hard to measure the ___ test is used.
brittle Diametral Compression
____ is useful for comparing materials that are brittle and generally weak in tension. These materials will have both elastic and plastic properties but the ___ response is small.
Compression strength plastic
___ is the stress at which a material fails under repeated loading This depends on the ___ of the load and the ___ of loadings.
Fatigue Strength magnitude, number
___ is the stress at which the material can be loaded an infinite number of times without failing.
Endurance Limit
Regarding viscoelasticity, Rate of ___ is important for many materials. Some properties of these are dependent on how fast they are stressed. Increasing the loading rate produces different S/S curves with ___ rates giving ___ values for E, PL, US
loading higher, higher
Materials with mechanical properties dependent on loading rate are termed ____.
Viscoelastic
___ is the resistance of a fluid to flow. It is often ___ and ___ dependent.
Viscosity time and temperature
___ is an increase in strain in material under constant stress.
Creep
___ is resistance to tearing forces. Depends on ___
Tear Strength rate of loading (Rapid loading = higher values)
Slope A is ___ than the slope of B.
An equal stress produces a ___ strain in B than A
greater
greater
What is represented by the yellow shaded area?
Resilience
Characteristics of Graph 1
Stiff
Ductile
Strong
Tough
Characteristics of Graph 2
Stiff
Brittle
Strong
Characteristics of Graph 3
Stiff
Ductile
Weak
Characteristics of Graph 4
Stiff
Brittle
Weak
Characteristics of Graph 5
Flexible
Ductile
Strong
Resilient
Characteristics of Graph 6
Flexible
Brittle
Strong
Resilient
Characteristics of Graph 7
Flexible
Ductile
Weak
Characteristics of Graph 8
Flexible
Brittle
Weak
What materials are those that will fracture below their yield stress due to a flaw.
Glass, diamonds, sheetrock, models with bubbles, nicking adjacent enamel/porcelain.
Between Yield Strength and Ultimate Strength, which is of more importance in dentistry and why?
Yield Strength may be of greater importance than Ultimate Strength in dentistry because it is an estimate of when a material will start to deform permanently.
For most dental alloys and ceramics subjected to tension, the ___ and ___ will be similar
Ultimate Strength and Fracture Strength
____ forces are responsible for the property of elasticity. The ___ the forces, the more stiff or rigid the material.
Interatomic/intermolecular
stronger
___ is compromised if a material has a defect
Fracture Toughness
