Materials Flashcards
What does Hooke’s law state
Extension is directly proportional to force applied given that environmental conditions remained constant (shown through straight line from origin in force-extension graph)
F = K * change in length
What is limit of proportionality and the elastic limit
Limit of proportionality (on the graph comes before elastic limit) is the point after which Hookes law is no longer obeyed
Elastic limit - just after if you increase the force applied the material will deform plastically (permanently stretched)
What does the spring constant measure
The stiffness of a spring
define tensile stress and tensile strain
Tensile stress - force applied per unit cross sectional area
Tensile strain - extension over the original length
What is elastic strain energy?
The work done on a material to stretch or compress it
Calculated by finding the area under a force-extension diagram or
elastic strain energy = 0.5 * F * change in length
What is breaking stress
The value of stress at which the material will break apart
What are the two main behaviours of materials on a force-extension graph:
plastic - experience large amount of extension as load is increased, especially beyond elastic limit
Brittle - material will extend very little and therefore likely to fracture.
What does the loading and unloading area indicate and why are they parallel to eachother?
Area shows the work done required to permanently deform a material
They’re parallel to eachother as the material’s stiffness is constant
How are materials used in designing car features:
Work done to deform crumple zones plastically will decrease the cars kinetic energy and seat belts stretch in order to convert passengers kinetic energy to elastic strain energy
Difference of stress-strain graphs and force-extension graphs
Stress-strain graphs describe the behaviour of materials where the latter describes the behaviour of specific objects.
Stress-strain graphs show Ultimate Tensile Stress (UTS) which shows maximum stress a material can handle.
The graphs shape indicates if the material is ductile, brittle or plastic
What does Young’s Modulus indicate?
Describes the stiffness of material
Hooke’s law shows stress can be proportional to strain therefore young’s modulus is the constant
Can be found by finding the gradient of a straight line in a stress-strain graph
What is elastic limit
The point until which an object returns to their original shape
How many forces cause tensile strain
Two forces along the same plane but opposite in direction
