6.1 - 6.4 Flashcards
what is the elastic limit
the maximum extent an object may be stretched without permanent deformation of its shape.
what is elastic deformation
a reversible change in the shape of an object due to tensile or compressive force. removal of the force will return the object to its original shape
what is plastic deformation
an irreversible change in the shape of an object due to tensile or compressive force. removal of the force causes a permanent change in shape.
what is Hooke’s law
the force applied is directly proportional to the extension of a spring before the elastic limit is exceeded
how can the spring constant be found from a force-extension graph
the gradient of the linear region
what is a hysteresis loop
a loop-shaped plot on a force-extension graph formed when loading and unloading a material produce different deformations
what does a hysteresis loop represent
the area inside the loop is the wasted energy
define tensile stress
the force per unit cross-sectional area. measured in pascals
define tensile strain
the extension per unit length. this quantity has no units. it can be written as a percentage
define ductile
easily drawn into wire
what is the limit of proportionality
beyond this limit, the stress is no longer directly proportional to the strain.
define Young Modulus
the ratio of tensile stress to tensile strain when they are directly proportional to each other. measured in pascals.
define ‘ultimate tensile strength’
the maximum extent an object can be stretched before a fracture occurs
whats the force-extension graph look like for a brittle material
a straight line through the origin with a large gradient
whats the force-extension graph look like for a polymeric material
hysteresis loop. no linear region as it doesn’t obey Hooke’s law. no plastic deformation (starts/ends at 0,0)
