Materials Flashcards
What is Hooke’s Law?
the extension is directly proportional to the force applied - F =kx
-> below limit of proportionality
Materials that return to their original shape:
elastic
Materials that don’t return to their original shape:
plastic
what is tensile stress?
the measure of internal forces in a continuous material when a stretching force is applied
what is the equation for tensile stress?
F/A
F - force
A - cross-sectional area of wire
= πr2 or πd2/4
what is the equation for tensile strain?
x/L
x - extension
L - length
what is UTS?
ultimate tensile stress
- the maximum stress the material can withstand
what occurs before UTS?
extension is uniform along the wire
what occurs after UTS?
wire loses strength and narrows at weakest point (necking)
- the wire continues to extend until breaking point (fractures)
what is Y1?
Yield point 1 - where wire weakens
increased strain = reduction in stress (the material ‘gives’)
- large scale sliding
what is Y2?
small increase in stress -> large increase in strain
- material is ‘ductile’
what is plastic flow?
large dislocations ocurring in the material
what is the equation for elastic potential energy?
1/2 x Force x extension
what is the equation for elastic strain energy? graphically?
1/2 x stress x strain
- area under stress-strain graph
What are the 4 material properties?
- Stiffness
- Strength
- Brittle
- Ductile
define ‘Stiffness’
resistance to being stretched
-> on a stress-strain curve, a greater slope = greater stiffness
define ‘Strength’
maximum stress a material can bear
UTS: highest point on a stress-strain curve
define ‘Brittle’
material cracks or breaks without plastic deformation, doesn’t stretch beyond elastic limit
define ‘Ductile’
can be stretched, doesn’t return to original shape after stretching force is removed
How do you determine the Young Modulus of a material? Step 1
- A piece of wire held by a G-clamp is sent over a pulley with the smallest mass attached
- keeps the wire straight, while not extending it
How do you determine the Young Modulus of a material? Step 1, 2 and 3
- A piece of wire held by a G-clamp is sent over a pulley with the smallest mass attached
- keeps the wire straight, while not extending it - Measure length from clamp to pointer (original length)
- Use a micrometer to measure diameter of wire (in several places), then find cross-sectional area
How do you determine the Young Modulus of a material? Step 1, 2, 3, 4 and 5
- A piece of wire held by a G-clamp is sent over a pulley with the smallest mass attached
- keeps the wire straight, while not extending it - Measure length from clamp to pointer (original length)
- Use a micrometer to measure diameter of wire (in several places), then find cross-sectional area
- Add a mass to a loaded end of the wire
- Record extension by measuring how far pointer has moved
How do you determine the Young Modulus of a material? Step 1, 2, 3, 4, 5, 6 and 7
- A piece of wire held by a G-clamp is sent over a pulley with the smallest mass attached
- keeps the wire straight, while not extending it - Measure length from clamp to pointer (original length)
- Use a micrometer to measure diameter of wire (in several places), then find cross-sectional area
- Add a mass to a loaded end of the wire
- Record extension by measuring how far pointer has moved
- Repeat for several masses, but ensure elastic limit is not reached
- Remove masses one at a time, taking note of another reading of extensions
How do you determine the Young Modulus of a material? Step 1, 2, 3, 4, 5, 6, 7, 8 and 9
- A piece of wire held by a G-clamp is sent over a pulley with the smallest mass attached
- keeps the wire straight, while not extending it - Measure length from clamp to pointer (original length)
- Use a micrometer to measure diameter of wire (in several places), then find cross-sectional area
- Add a mass to a loaded end of the wire
- Record extension by measuring how far pointer has moved
- Repeat for several masses, but ensure elastic limit is not reached
- Remove masses one at a time, taking note of another reading of extensions
- Calculate stress and strain for each mass
- Plot a graph of stress against strain, the gradient is the Young Modulus
what equipment is needed to determine the Young Modulus of a material?
clamp, metre ruler, sticky tape pointer, pulley, wire, load
what is Young Modulus? equation?
the ratio of stress to strain for a material
equation: E = stress/strain
what is the equation for tension?
T = mg + ma
