Test One: 3 Basic Materials Flashcards
Strength
The ability to resist breakage or permanent distortion. Polymers is low while ceramics and metals are high.
Modulus of elasticity
Whether the material is elastic or stiff. Polymers are low/flexible. Ceramics and metals are high.
Ductility
The ability to be drawn, stretched, or hammered without breaking. Metals have high while the other two are low
Thermal expansion
The tendency to expand when heated and contract when cooled. Polymers are high while ceramics and metals are low
3 primary bonds
Ionic, covalent, metallic
What type of primary bonds are in ceramics?
Covalent and ionic
What primary bonds are in polymers?
Covalent
2 types of secondary bonds
Hydrogen and van der waals
In which dental material are secondary bonds of major importance?
Polymers
Which properties are determined by strong primary bonds?
High modulus of elasticity (stiffness), low thermal expansion, and high strength
Which properties are determined by weaker secondary bonds?
Low modulus of elasticity (flexibility), low strength, high thermal expansion
What is the formula relating stress, strain, and modulus of elasticity?
Modulus of elasticity= stress/strain. Stress = force/area. Strain is the amount a material elongates designated as a fraction of the original length. Something with high modulus is stiffer and will only elongate a small amount.
What is the key concept that makes ceramics brittle (low ductility)?
Stress concentration. Actual strength of ceramics is much lower than theoretical because of surface tears. At the tear there is a high stress bond that breaks and propagates the stress to the next bond.
What is the key concept explaining the ductility of metals?
Dislocation. Metals can deform their crystal lattice structures in order to decrease the amount of stress/blunt the sharp tip at a surface flaw.
Rounded notch will produce greater stress than a sharp notch. T/F?
False.
What is the key concept that explains the low strength and low elastic modulus(flexibility) of polymers?
Strong bonds within polymer chains and weak bonds between the chains.
When bending a material where is the tension/compression?
The tensile stress is on the outer/convex surface. This is the opposite side as where the force is being applied. The concave surface/inner has compressive stress. Stress/breaking occurs in areas of concentrated tensile stress. (Inside surface of a ppm crown–opposite of where the force is being applied)
Stress raiser
Any irregularity in an object. The sharper the stress raiser, the higher the stress
Permanent/plastic deformation
Yielding without breaking
Fracture strength
Force required to break a material
Yield strength
Force required to bend or deform a material
