4.2 Materials Flashcards
Define density.
Mass per unit volume
What is Hooke’s law?
Extension is directly proportional to force applied
Define tensile strain.
The ratio of an object’s extension to its original length.
Define tensile stress.
Force applied per unit cross sectional area
What is the equation for Elastic Potential Energy
aka Elastic strain energy
What is the area of a force-extension graph?
Energy stored
or
Elastic Potential Energy
Define breaking stress.
Maximum stress an object can withstand before failure.
Define brittle.
A material that will not plastically deform by allowing cracks to propagate through it.
Having little elasticity.
Define tough.
A material that can absorb energy before breaking and is resistant to the propagation of cracks.
Ability to deform plastically/permanently.
Define ductile.
A material can be drawn into wires without losing strength. Or just have their shape
changed/deformed without losing strength.
Define malleable.
A material that may lose strength when its shape is deformed.
Define hard.
A material that is very resistant to cutting, indentation, stretching, and abrasion.
Cutting tools have to be harder than the material they are cutting.
Define stiff.
A material that is resistant to bending and stretching/resistant to deformation under the action of an applied force.
Measured by Youngs modulus. Higher Youngs modulus, the stiffer it is.
Define strength.
A material that is resistant to breaking under the strain of an applied force/the stress required to break a material.
Define fracture stress.
Is the level of stress at which a material will fracture.
Define elastic limit.
aka yield strength or yield stress
Is the level of stress at which a material will deform permanently.
Define elastic deformation.
A material will return to its original shape once the forces acting on it have been
removed.
Define plastic deformation.
A material’s ability to be permanently stretched or deformed.
When force is removed, atoms don’t return to their original positions.
Define brittle fracture.
Cracks are
allowed to propagate through the material.
What does elastic deformation look like on a force-extension graph?
What does plastic deformation look like on a force-extension graph?
What does the enclosed area of a plastic deformation graph represent?
Work done to permanently deform the material.
Which graph is for a brittle material?
D
Which graph is for a ductile material?
B
What is the area of a force extension graph?
Elastic strain energy
aka Elastic Potential Energy
Provided material obeys Hooke’s law
How is energy conserved in elastic deformation?
Work done is stored as elastic strain energy.
How is energy conserved in plastic deformation?
Work is done to separate atoms. Energy is not stored as strain energy.
Mostly dissapated as heat
State the energy transfers when a mass on a sping is pulled down and released.
The work done in pulling the spring down (stretching it) is stored as elastic strain energy, when the spring is released this is converted to kinetic energy which is converted to gravitational potential energy as the spring rises.
What is a stress-strain curve and its features?
Which curves are brittle, ductile, and plastic?
- Blue is brittle
- Purple is ductile
- Green is plastic
How is the dissipation of energy in plastic deformation used to design safer vehicles?
Crumple zones deform plastically in a crash using the car’s kinetic energy so less is transferred to the passengers.
Define Young’s Modulus.
Gradient of a stress-strain graph.
