[AS] Materials Flashcards
What is Hooke’s Law?
F = kL
What is the point at which Hooke’s Law stops working?
The limit of proportionality, P
After what point is the material permanently stretched?
The Elastic Limit, E
After the load is released, what happens to an elastically deformed material?
The material returns to its originally shape
The atoms return to their equilibrium position
After the load is released, what happens to an plastically deformed material?
The material is permanently stretched
The atoms don’t return to their original position
If a deformation is elastic, what happens to the work done?
It is stored as elastic strain energy
What is the question for tensile stress?
(Force) divided by (cross-sectional area)
What is the equation for tensile strain?
(Change in length) divided by (original length)
What is a stress big enough to break a material called?
Breaking stress
What is the ultimate tensile strength (UTS)?
The maximum stress that the material can withstand.
What is the area under a force-extension graph?
Elastic strain energy
How do you calculate energy stored in a stretched material?
E = ½Fdx E = ½kdx^2
What is the units for the Young Modulus?
Nm^-2
How do you calculate the Young Modulus?
Stress over strain
What is the Young Modulus a measurement of?
Stiffness
What does a high Young Modulus indicate?
High stiffness
What is the gradient of a stress-strain graph?
Young Modulus
What is the area under a stress-strain graph?
Energy per unit volume
What is the equation for energy per unit volume?
½ x stress x strain
What are the units for energy per unit volume?
Jm^-3
Define brittle
Material breaks suddenly without deforming plastically
Define ductile
Material can be drawn into wires without losing strength
Define strong
Material can withstand high stress (a lot of force) without deforming or breaking
Define hard
Material is very resistant to cutting, indentation and abrasion
Define stiff
Material has a high resistance to bending and stretching
Define tough
Material can absorb a lot of energy before breaking
What is the area between the loading and unloading curves for a stress-strain graph of rubber?
Amount of energy converted to heat per unit volume
How do you calculate elastic strain energy from a graph?
the area under a force-extension graph
How do you calculate energy per unit volume from a graph?
the area under a stress-strain graph
How do you calculate Young Modulus from a graph?
the gradient of a stress-strain graph
What is the structure of a metal?
Metal ions in a “sea” of free electrons
forming metallic bonds
What structural terms describe metals?
Tough; Ductile
What structural term describes ceramics?
Brittle; Stiff
