Fundamentals 1 Flashcards
What are the three PRIMARY atomic bonds?
Ionic
Covalent
Metallic
Ionic bonds are a type of _______ bond which create ________.
Primary atomic, ceramics
Covalent bonds are a type of _______ bond which create ________.
Primary atomic, polymers
Metallic bonds are a type of _______ bond which create ________.
Primary atomic, metals
What are the four properties of materials?
- Chemical
- Physical
- Mechanical
- Dimensional
What is the difference between mechanical and physical properties of dental materials?
Mechanical properties have more to do with how much the material can WITHSTAND. Think strength, toughness, stiffness, elasticity, plasticity, brittleness.
Physical properties are more in regards to the actual activity of the material. Think density conductivity sound transmission absorption
Chemical properties include
Composition
Acidity or Alkalinity
Weathering
Corrosion
What are mechanical properties?
Change of material dimensions due to external forces such as mastication.
Force is _______________ an object.
What is weight?
pushing or pulling and object
Weight is the force of GRAVITY on an object
What is the formula for force?
F= Mass x Acceleration due to gravity.
What is the units for mass? What about for weight?
Mass: Kg
Weight: N because we are considering the force of gravity
Weight and Force both have Newton units. True or false?
What is the American version ?
True
lbs
Our mass is _______ on the Earth and Moon.
Our weight is ________ on Earth and Moon.
Same
Different due to force of gravity differences on Earth and Moon
______ and ________ are both units for force/weight.
Newtons and Pounds
Kg is a unit of weight. True or false?
FALSE
Kg is a measure of MASS
Which teeth can apply and take a lot of force?
Molars
Which teeth are not very conducive to lots of mastication?
Incisors!
What is stress?
Stress is ratio of Force/Area. This describes the DISTRIBUTION of force
Stress= F/A
What is the unit of stress?
Pascal
Since Stress = F / A this is the same as N/m^2
A pascal is a unit of _________. It is represented as _________.
Stress
N/m^2 or Pounds per square inch
The smaller the surface area the ___________ the stress compared to applying the same load/force on an object with larger surface area
Larger
For example, when comparing a flat boot to a stiletto, which shoe is experiencing more stress?
Stiletto because less surface area
100kg Man
Size 12 shoe
200cm^2 contact with ground
Stress: 0.05 MPa
50kg Woman
1.25 cm tall square heels
Contact area: 1.56cm^2
Stress: 32 MPa
Which one has higher load?
Which one has higher stress?
Load is higher on Man - Look at Weight
Stress is higher on Woman - Can also use F/A
A megapascal is ________ Pa
A gigapascal is ______ Pa
Mega- 10^6 Pa
Giga- 10^9 Pa
If given the mass of an individual in kgs, how do we find Force?
x 9.81 for Gravity!
Elongation involves which forces?
Axial and tension
Compression involves which forces?
Axial, compression
Shear involves which forces?
Shear (opposite diretions)
Torsion involves which forces?
Twisting movement
Bending involves which forces?
Bending (flexion)
What is the difference between tension and compression?
Tension is pulling
Compression is pushing
What is strain?
Strain = Change in length/ Original Length
What is the unit of strain?
NONE!
Reported as a percent
What is stiffness?
Ability of a material to resist deformation
How much force can the material support until it begins to deform.
What is strength?
Ability of a material to resist failure
How much force can the material support until it fails?
What is elasticity and plasticity?
Elasticity- Reversible Deformation once stress is removed
Plasticity- Permanent Deformation once stress is removed
Plasticity is basically the stage when elasticity is not possible. There is a certain amount of load that can be applied to a material before it looses elasticity and becomes irreversibly deformed.
What is toughness?
Ability of material to absorb energy WITHOUT failure
Aka Strength + ductility together
Ex. Tennis ball or golf ball
What is ductility and brittleness?
Brittle materials DO NOT HAVE plastic deformation
Ductile materials have high permanent deformation before they can break
AKA, things that shatter quickly are brittle and do not go through shape changes before breaking.
What is hardness?
Hardness is the ability of the material to resist scratching by another material.
Ex. Diamond is VERY hard because it can scratch other things but not often scratched itself.
What is creep?
How do all mechanical properties change with TIME?
Describe the difference between stiffness, strength, toughness, ductility, and hardness.
Stiffness is the ability of a material to resist deformation
Strength is the ability of a material to resist failure
Toughness is the ability of a material to absorb energy without failure.
Ductility is the ability of a material to undergo severe plastic deformation before failure.
Hardness is the ability of a material to resist, scratching by another material
What is fatigue?
How the material responds under cyclic loading.
AKA mastication
Two materials can both exhibit plasticity. What feature could be different between these materials that can help us decided if one can undergo more permanent deformation than another?
Ductility
How do we measure mechanical properties?
Stress-Strain Curve (Force Displacement Diagram)
We apply a TENSILE force (pull the material). The machine will measure
- Force being applied (N or lbs)
- Displacement of sample as force is applied
until the sample breaks
Why can we not just use force to gather data regarding mechanical properties of a material?
Force is just the measure of the applied weight.
HOWEVER, we need to consider the size of the material aka, Surface Area
Using _______ and _______of a material in an experiment; we can develop a ____________ curve.
force and displacement
Stress- Strain Curve
Stress: F/A^2
Strain: Change in displacement/ Original Length
What are the two regions of the Stress-Strain curve and what do they describe?
- A linear region - Elastic Deformation region
- A dip with growing into curve - Plastic Deformation Region
What point on the SSC signifies the ideal point for material design?
Elastic Deformation region / Linear part
What is stiffness and where is it found on the SSC?
Stiffness is the ability of a material to resist deformation.
It is the SLOPE of the liner/elastic deformation portion of the SSC
Modulus = Stress/ Strain
What is the proportional limit of SSC?
The tip of the elastic deformation section of SSC.
The y-axis number will tell us the max amount of stress the object can withstand to be able to reform once the stress is removed.
What is the yield stress?
The first part of the non-linear portion that occurs on the SSC after the Elastic Deformation region.
This is when the material is changing shape and enter the Plastic deformation section.
What is the maximum point of stress of an SCC?
Where is failure indicated?
When the SSC begins curving down in the Plastic Deformation region
The lowest point of the plastic deformation region at the end of the graph.
A material with a higher slope in the elastic portion of the SSC is __________.
STIFFER
More stress needs to be placed to cause a displacement
Rise/Run!
AKA steeper
How can strength be read on an SSC?
Look at the Yield Stress. Remember strength is the ability of a material to withstand force without failure.
The yield stress will tell you at what amount of force plastic deformation could start at.
Compounds with a higher yeild stress are STRONGER.
Brittle materials will only have a __________ on an SSC because ____________
Linear portion on the SSC because they only have elastic deformation
DUCTILE materials will have the elastic and plastic portion
How do you read stiffness and strength on an SSC?
Stiffness: Compare SLOPE of linear portion. High slope, more stiff
Strength: Compare Yield Stress. High stress, stronger
All molecules that are stiff are strong. True or False
FALSE
Sometimes, materials that are stiff may be weak due to a lower yield stress but in the elastic deformation region, can take a LOT of stress with little change to shape.
What two key properties can be calculated from an SSC?
How can they be calculated?
- Resilience
Ability of material to absorb energy in the ELASTIC region or energy needed to cross over to plastic deformation.
Measure area under curve of ELASTIC region
- Toughness
Energy required to completley fracture the material
Measure area under ENTIRE curve
________ have LOW resilience.
Glass
Glass is ______ which means on an SSC_______.
Brittle, does NOT have plastic deformation portion.
Tension has _____ stress and _____ deformation.
Compression has _____ stress and _____ deformation.
Bending has _____ stress and _____ deformation.
Positive, Positive
Negative, Negative
Positive stress, Positive DEFLECTION
Bending is tricky! The middle portion of the sample will experience compression while the outer portions will experience tension.
Deflection is where the middle of the sample bends down. We measure how much bending is happening.
We measure deformation in compression, tension and bending. True or false.
FALSE
Bending measures DEFLECTION
What is the elastic modulus?
Stress/Strain of SSC in elastic region
SLOPE
Dentin has a _______ elastic modulus than enamel.
Dentin has a _________-
lower
This means it is less stiff (more flexible)
The proportional limit is still in the elastic region. True or False
True
The yield strength is located ______ the proportional limit.
AFTER
Material with the highest stiffness
Ceramic
Material with highest strength
Ceramic
Material with the highest toughness
Metal
Highest yield strength
Metal
Highest ductility
Polymer
Highest resilience
Metal
On an SSC how do we asses the following?
Stiffness
Strength
Ductility
Toughness
Resilience
Yield Strength
Stiffness - Slope of elastic linear portion
Strength- Yield Strength point or highest Y-axis
Ductility - Furthest point on x-axis
Toughness - Area under WHOLE curve
Resilience- Area under elastic portion
Yield Strength- Where plastic deformation starts AFTER PL
Yield strength only exists for compounds with _________.
Plastic deformation as well
Why is the furthest point on the x-axis used to determine ductility?
This material has the largest displacement before it fractures meaning it can withstand lots of plastic deformation before fracturing.
