Mechanical Properties I and II Flashcards
- Describe the importance of the mechanical properties of dental biomaterials
to properly select materials and design devices and appliances in dentistry
- List the objectives in measuring mechanical properties of materials
- Know the fundamental properties (strength, elasticity, etc.)
- Determine how those properties hold up in conditions the material will be used (impact, fatigue, abrasion…)
State the 1st Classifications of mechanical properties:
o Bulk Properties
o Surface Properties
State the 2nd Classification of mechanical properties:
sub-classifications of bulk properties
fundamental properties
applied properties
1st Classification of Mechanical Properties DEFINE Bulk:
consider whole mass of material
(strength, elasticity)
1st Classification of Mechanical Properties DEFINE Surface:
hardness (indentation) and wear (abrasion)
2nd Classification of Mechanical Properties
How to obtain Fundamental Properties:
Fundamental: obtained from test applying steadily increasing load (stress-strain)
2nd Classification of Mechanical Properties DEFINE applied properties, 3 examples
Applied properties: specific conditions in service, such single sudden force (impact), repeated low loads (fatigue), time dependent properties (viscoelasticity).
Define Stress
force per unit area from externally applied forces, units: Pa/MPa.
Units for Stress
Pa/MPa
State the 3 Fundamental Types of Stress
Tension, Compression, Sheer
Define Tension (a fundamental type of stress)
force perpendicular to resisting area
Define Compression (a fundamental type of stress)
force perpendicular to resisting area, sense of load opposite to that of tension
Define Shear (a fundamental type of stress)
force parallel to resisting area
State the 2 combined types of stress: combination of fundamental stresses
Torsion and Flexure/Bending
Do stress concentrations increase or decrease on notches, grooves, cracks, surface regularities?
The stress concentrations increase - that is why we avoid sharp corners in teeth cavity preparations.
Ceramics and glasses (smooth surfaces) are sensitive to surface roughness because of _____ _______ at the top and bottom of topographical irregularities
stress concentrations
Define Strain
describes relative deformation or change in shape and size with respect to initial length (dimensionless)
State the 2 Types of Strain
Elastic and Plastic
Elastic is ____, Plastic is ______.
Elastic is recoverable, Plastic is permanent
Recording an impression - _____ on insertion (____ deformation). ______ on displacement from tissue (______ deformation)
Plastic on insertion (permanent deformation). Elastic on displacement from tissue (recoverable deformation
Define Elastic Limit
Stress at which material changes from elastic to plastic strain. Stresses equal or higher than the elastic limit produce permanent/plastic deformation in the material.