Materials Flashcards
State Hooke’s Law
Force is directly proportional to extension, up to the limit of proportionality
What is the stiffness constant, k, dependent on?
How stretched an object is
What is the limit of proportionality?
The point beyond which force is no longer proportional to extension
What is the elastic limit?
The force beyond which a material will be permanently stretched
What is the yield point?
The stress beyond which a material becomes plastic
Define elastic deformation
The object will return to its original shape when the deforming force is removed
Define plastic deformation
- The object will not return to its original shape when the deforming force has been removed
- Extension will be permanent
Define tensile force
A force which stretches an object
Define compressive force
A force which squashes an object
Define tensile stress
Force applied, divided by the cross-sectional area, in N/m² or Pascals
Define tensile strain
Extension, divided by the original length of the materail, no units
Define breaking stress
The maximum tensile force that can be applied to an object before it breaks
What is elastic strain energy?
The potential energy stored in a stretched material from work being done to stretch the material
What happens to the stored elastic strain energy in a spring when the tensile force is released
The stored elastic strain energy is transferred to kinetic energy and gravitational potential energy
- The spring then compresses and kinetic energy is transferred back to elastic strain energy
What is the conservation of energy equation for an oscillating spring?
Change in kinetic energy = change in potential energy
Describe how energy conservation is used in transport design
- Cars are designed with crumple zones that deform plastically in a crash
- This means some of the car’s kinetic energy is transferred into changing the shape instead of the inside, increasing safety
What is the Young Modulus?
The measure of how stiff an object is, up to the limit of proportionality
What does the gradient of a Stress-Strain graph represent?
The Young Modulus, E
What does the area under the graph of a Stress-Strain graph represent?
Strain energy per unit volume
What is a brittle material?
A material which doesn’t deform plastically, but snaps when the stress on it reaches a certain point
Define brittle fracture
When a stress applied to a brittle material causes small cracks on the material’s surface to get larger until the material breaks completely
What is on the axes for a graph showing loading and unloading of an elastic material?
- x axis = Extension
- y axis = Force
