Pres Res: Mechanical Properties of Dental Materials Flashcards
Type of deformation for elastic:
Recoverable
Type of deformation for plastic:
Permanent
The maximum stress that a material will withstand without permanent deformation:
Elastic limit
* looking at the material
The greatest stress that a material will sustain without a deviation from the linear proportionality of stress to strain:
- essentially same as elastic stress, but differs by definition.
- looking at the graph.
Proportional limit
The stress value at which a material exhibits a specified amount of strain:
Yield strength
* Usually 0.2% (percent offset) is used.
The maximum stress that a material can withstand before failure in tension:
Ultimate Tensile Strength
The stress at which a material fractures:
* not necessarily equal to ultimate strength.
Fracture Strength
The slope of a line on stress-strain graph indicates:
Stiffness within elastic range.
Steep slope= stiff
Gradual slope= flexible
Examples of brittle dental materials:
amalgam
composites
cements
ceramics
The ability of a material to be plastically deformed:
Ductility
Ex: gold
The resistance of a material to permanent deformation:
* area under elastic portion
Resiliency
The resistance of a material to fracture:
* area under entire curve
Toughness
The maximum stress that a material can withstand before failure in compression:
Ultimate compressive strength
The maximum stress that a material can withstand before failure in shear mode:
Shear strength
A measure of a material’s resistance to brittle fracture when a crack is present:
Fracture Toughness
Viscosity (slope) remains constant:
Ex: water, some dental cements and impression materials
Newtonian fluid
No flow until a certain shear stress is reached (yield point):
Ex: toothpaste
* Line starts higher up on y-axis
Plastic
Decreasing viscosity (slope) as shear rate increases:
- easier to mix with increase stirring speed.
Ex: silicone impression materials some endodontic cements
* line looks ductile, runs low.
Pseudoplastic
Viscosity (slope) increase with shear rate:
- Harder to mix with increased stirring (shear rate)
Ex: denture- base resins
* exponential line
Dilitant
Time- dependent decrease in viscosity (slope):
- Yield pt. (similar to plastic)
- Not reversible shear stress/strain rate curve (structure alteration).
Ex: tap new ketchup bottle, flows (yield point), next time usually don’t have to tap to get flow.
Thixotropic
