2PropertiesOfMaterials Flashcards
*What is the formula for stress? What is the unit of measurement?
S=Force/Area…1 Newton/m^2= 1 Pascal
*What are the 5 types of stress?
1.Tension 2.Compression 3.Shear 4.Torsion 5.Bending
*What type of stress occurs when elongation forces are directed away from each other in the same straight line and the molecules resist being pulled apart?

Tension
*Which type of stress occurs when shrinkage forces are directed toward each other in the same straight line and molecules resist being forced more closely together.
Compression
*Which type of stress occurs when forces are directed parallel to each other NOT along the same straight line and one portion resists sliding past the other.
Shear
*Which type of stress occurs when there are twisting forces?
Torsion
*Which type of stress results from a bending moment?
Bending..haha. lol.
*What is Deformation caused by stress? How is it measured? What is the formula for deformation?
STRAIN…Measured unitless or as a %…Deformation=Deformation/Length
*What is the stress at which the material begins to function in a PLASTIC manner? Limited permanent strain HAS occurred…What is the % of permanent strain?
Yield Strength…0.2% permanent strain
*Is Permanent Deformation Constructive or DeStructive in the oral cavity?
It can be Destructive(crowns/partials) OR Constructive(ortho wires)!
*Where can I find Ultimate Strength on the Strain/Stress curve?
Ultimate Stress=Highest point on curve
*What is the max. stress that a material can withstand in tension?
Ultimate Tensile Strength
*What is the max. stress a material can withstand in
compression?
Ultimate Compression Strength
What’s another word for “permanent deformation”?
Failure
*Why is Yield Strength of greater importance then Ultimate Strength in dentistry?
Yield strength is an estimate of when a material will start to FAIL!
*What is the stress at which a brittle material fractures?
Fracture Strength
What is the term for a material that elongates excessively causing a reduction in stress before permanent deformation?
“Necking”
*For most dental alloys and ceramics subjected to tension, the ______ _______ and ________ _______ will be similar.
Ultimate Strength and Fracture Strength
*__________ –deformation that results from the application of TENSILE FORCE. Indicates the workability of alloy. Expressed as a ___.
Elongation….%
Elongation: a gold alloy with 20% elongation would be considered _______, while a material with 1% elongation would be ________.
20%=Ductile, 1%=brittle
*What is the measure of elasticity and represents the stiffness of a material within the elastic region… Namely the slope of the S/S curve in the elastic portion. WHAT IS another name for it?
Elastic Modulus (E)..Youngs Modulus
________/__________ forces are responsible for the property of elasticity. The stronger the forces,
the more stiff or rigid the material.
Interatomic/intermolecular
What is the formula for elasticity?
E=Stress/Strain
*The higher the value of the _______ _______, the more stiff or rigid the material.
Elastic Modulus
*What is resistance of a material to permanent deformation AND indicates the amount of energy needed to deform a material to the proportional limit AND is the area UNDER the elastic portion? WHAT dental material is it useful to evaluate?
Resilience…Ortho Wires and Springs
*What is the resistance of a material to fracture AND indicates the amount of energy needed to cause fracture AND is the area under the elastic AND plastic area?
Toughness
*What three things can you increase to increase TOUGHNESS?
1.Yield Strength 2.Ultimate Strength 3.Strain (All increase the area under the stress/strain curve)
*_______ generally weaken a material and may result in fractures at stresses WELL BELOW the yield stress. Occurs more in _______ materials that have no ability to deform and redistribute stresses.
Defects…Brittle
*Because tensile properties of BRITTLE materials are hard to measure the _______ ________ ______ is used. It’s a good test for brittle materials – amalgam, cements, ceramics, plaster, and stone.
Diametral Compression Test
*What is unique about the plastic portion of the stress-strain curve for a Brittle material?
The plastic response is SMALL!
What are the two important characteristics of Endo files?
Flexure and Torsion
*______ _______ – the stress at which a material fails under repeated loading. Depends on the ________ of the load and the ______ of loadings.
Fatigue Strength…Magnitude…..Number
*_______ _______ – stress at which the material can be loaded an infinit of times without failing.
Endurance Limit
*What is the RATE of loading measured by? Think Impression materials! Hence: Materials with mechanical properties dependent on loading rate are termed ________.
ViscoElasticity….Viscoelastic
*What is the Resistance of a fluid to flow? What is the unit?
Viscosity…Poise
*What is the reduction in stress in a material subjected to constant strain (ortho bands)?
Stress Relaxation
*What is the increase in strain in material under constant stress?
CREEP
*What is resistance to tearing forces? Important for Polymers in thin sections and depends on the RATE of loading (rapid loading=higher values)
Tear Strength
What is the loss of material resulting from removal and relocation of materials through the contact of two or
more materials?
Wear
How does the Linear Thermal Coefficient of Expansion of Composite compare to Human Teeth?
Composite= 2-6x human teeth (WANT THEM TO BE CLOSE!)
