Unit 4 - Materials Flashcards
Define density
The mass per unit volume of a material
What two factors affect density?
The concentration of atoms and the intrinsic mass of these atoms
How do you work out the density of a material that is made up of two or more other materials?
- Total Mass/Total Volume
- Use the density and percentage volumes of the individual materials to calculate the overall density of the final material
Define extension
The amount of stretch a spring experiences when a tensile stretching force is applied to it
T/F: Extension is directly proportional to the tensile stretching force applied
True, up to a limit
What is Hooke’s Law?
Hooke’s law expresses the idea that the extension is directly proportional to the tensile stretching force applied to it. This is where the equation: F = k x e comes from.
What will happen to the extension of a spring if the spring constant decreases?
The extension will increase
What happens to the displacement when two springs are added in parallel?
The displacement will be half that of one spring with the same force applied
What happens to the displacement when two springs are added in series?
The displacement will be double that of a single spring with the same force applied
What does the gradient of a force-extension graph show?
The spring constant
What is the area under a force-extension graph equal to?
The work done when stretching the spring: Work Done = 1/2Force x Extension
What is stress?
Stress is equal to the force per unit area within a material
What is strain?
The extension per unit length of a material
What does the gradient of a stress-strain graph equal?
The Young’s Modulus of the material
How do we use stress and strain?
We can use stress and strain to compensate for the effect that thickness and length have on the property of a material
What is the area under a stress-strain graph equal to?
The energy per unit volume of a material: 1/2 x Stress x Strain
What are the 5 important points on a stress-strain graph?
- P - limit of proportionality
- E - elastic limit
- Y - yield points
- UTS - ultimate tensile stress
- BP - breaking point
What does a metals stress-strain graph look like?
Linear up to the limit of proportionality when the gradient decreases and it curves
How does rubber react to a tensile stretch force being applied to it?
Stretches easily at first and then stiffens and becomes harder to stretch
How does polythene react to a tensile stretch force being applied to it?
Difficult to stretch at first before yielding and becoming easier to stretch and then stiffening again
What does it mean if a material behaves elastically?
It will return to its original shape after being deformed
What does it mean if a material behaves plastically?
It will not return to its original shape after being deformed
Can materials behave elastically and plastically?
Yes, materials often behave elastically up to the elastic limit, if we load a material beyond that it will not return to its original shape
T/F: Changing the length of the wire or the width of the wire does not affect the extension
False, changing either of these factors will cause the extension to change
What is the opposite of a tensile force?
A compressive force
T/F: The Young’s Modulus of a material does not have a unit, it is dimensionless
True
What is the ultimate tensile stress?
The maximum stress a material can withstand before deforming rapidly to the breaking point
