Mechanical Properties Used to Characterize Dental Materials Flashcards

1
Q

force

A

an interaction that, when unopposed, changes the motion of the object
pushing and pulling

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2
Q

mechanical properties

A

used to determine how a material changes or what it can withstand with an applied force
direct consequence of the bonding and structure that develops from the bonding

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3
Q

stress

A

internal force is equal in intensity and opposite in direction the applied external force
inverse relationship of stress with area

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4
Q

types of stress

A

compression
tension
shear
bending
torsion

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5
Q

strain

A

the change in length per unit length of a body when subjected to stress, dimensionless

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6
Q

tensions vs compression

A

tension: causes an elongation of the body
compression: causes shrinkage/shortening of the material

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7
Q

elastic strain and response Hooke’s Law

A

recoverable change in shape, recovery of energy imparted to the material

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8
Q

linear elastic response

A

nominal stress is same as nominal strain

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9
Q

stress-strain curves

A

plotting a stress and resultant strain against each other
slope of line is called Young’s Modulus (E), or Elastic Modulus, strictly a materials property

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10
Q

elastic modulus of dental materials

A

a materials property
directly related to the inter-atomic or intermolecular bonds
gives the relative stiffness of a material
the stronger the basic attraction force, the greater the values of Elastic Modulus and stiffer the material

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11
Q

proportional limit: elastic vs plastic

A

the greatest stress a material can sustain without a deviation from the linear proportionality of stress to strain

irreversible-plastic
reversible-elastic

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12
Q

below the proportional limit

A

no permanent deformation occurs
when stress removed, the structure returns to original dimensions
reversible: the elastic region

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13
Q

above the proportional limit

A

results in a permanent or irreversible strain on the specimen
irreversible: the plastic region

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14
Q

plasticity at the atomic level

A

plastic or permanent strain: strain induced is not recoverable
-for metals, a permanent shifting of planes of atoms
-for polymers, chain sliding as secondary bonds are broken
-upon unloading, any elastic strain is recoverable

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15
Q

elastic limit

A

the stress at which a plastic strain starts

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16
Q

yield strength

A

the stress at which a material exhibits a specified amount of plastic deformation

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17
Q

ultimate strength

A

maximum stress that a material can withstand before failure, specific to type of stress

18
Q

fracture strength

A

the point at which the material fractures irreparably, not necessarily the highest load

19
Q

ductility

A

ability of a material to be plastically deformed; indicated by plastic strain
drawn into a wire under tensile force

20
Q

malleability

A

ability of a material to be hammered into thin sheets without fracturing, compressive force

21
Q

metals tend to be _____, ceramics tend to be ______

A

ductile, brittle

22
Q

brittleness

A

relative inability of a material to sustain plastic deformation before fracture of the material occurs
ceramics, composites and amalgams
sustain little (to no) plastic strain before they fracture
fractures at or near its proportional limit

23
Q

resilience

A

capacity to absorb energy when elastically deformed up to the proportional limit

24
Q

toughness

A

amount of energy that can be absorbed up to fracture

25
bending tests
measures a flexural strength 3 point bend test: complex stress state, compressive to tensile, neutral axis, shear
26
hardness testing
measuring the resistance to permanent deformation by surface indentation or scratching
27
critical hardness features
indenter material: steel, tungsten carbide, diamond indenter size and shape: sphere, cone, pyramid, needle force applied: 1-3000 kg indentation shape and measurement
28
viscoelasticity
mechanical response of a material is loading or strain rate dependent elastic solid and viscous fluid small to negligible dependence for metals and ceramics
29
flaws and mechanical properties
most if not all materials will contain flaws such as cracks and pores typically arising during processing allows for stresses to become concentrated around these defects
30
fracture toughness (Critical Stress Intensity)
measure of the resistance of a material to catastrophic propagation of flaws under and applied stress
31
stress relaxation
a reduction in stress over time when holding at a fixed strain rubber bands
32
fatigue strength
when stress is repeated, the strength may be reduced and ultimately cause failure; a progressive fracture under repeated loading is called fatigue
33
fatigue
progressive fracture under repeated (cyclic) loading
34
rotating beam fatigue test
alternating maximum tension and compression at the surface where the diameter is a minimum
35
fatigue properties
endurance limit: stress level below which the material can be cycled to infinity without failure fatigue strength: maximum stress level a material can withstand without fracture for a specified number of cycles
36
wear
loss of material through the contact of two or more surfaces undesirable, but when controlled it is beneficial
37
wear results from
inhomogeneity, crystal orientation, phases and inclusions present, microscopic contact, interaction between sliding surfaces, lubrication
38
adhesive wear
formation/disruption of microjunctions
39
corrosive wear
2nd, related to chemical activity
40
fatigue wear
surface weakened by cyclic loading
41
abrasive wear
soft and hard surface in contact