materials Flashcards
what is Hooke’s law
force and extension are directly proportional
is Hooke’s law always true
no. it doesn’t apply after the limit of proportionality has been passed. (when a force-extension graph is no longer linear)
what makes an object ‘elastic’
if it returns to its original shape after being stretched/compressed
what is the elastic limit
the maximum force a spring can sustain and still return to its original shape
what is the study of stress and strain
the study of how forces affect and objects shape
what’s the name of a force that stretches and a force that squashes an object
stretches- tensile force
squashes- compressive force
what is elastic strain energy and how is it calculated
it’s the energy that’s used to stretch and object. its found from the area under a force-extension graph
what is braking stress
its the stress required to break a material
what is ultimate tensile stress
its the maximum tensile stress an object can withstand
difference between rigid and flexible plastics
rigid plastics will fracture with very little stress but flexible plastics have a large extension before fracture
what is a brittle material
a material which won’t have any plastic deformation
what is meant by an object behaving plastically (or inelastically)
it undergoes permanent deformation under stress. this happens after the elastic limit
what is meant by a fracture
when an object completely breaks
what is young modulus
the ratio of the stress and strain of a material to give its stiffness. it doesn’t change for any sample of the material no matter the size
how can youngs modulus be found
from the gradient of the linear part of a stress-strain graph
