materials Flashcards
does a higher young modulus mean a higher or lower stiffness
stiffness increases
define stress
force per unit area of cross section
define elasticity of a material
a material that returns to its original size and shape when the load deforming it has been removed
elastic limit / limit of proportionality
the maximum load which a body can experience and still regain its original size and shape once the load has been removed
hookes law
extension of an elastic object will be directly proportional to the force applied to it up to the object’s limit of proportionality.
what is the young modulus?
the ratio of stress to strain for a material
yield point
the yield point is the point reached where there is a marked increase in extension when stress is increased beyond the elastic limit.
this is because the internal structre of the material has been changed and the material is said to be showuing plastic behaviour.
few materials exhiit a yiled point (eg. mild steel does.)
what happens up to the limit of proportionality?
up to this point stress is proportional to strain and the gradient is the young’s modulus
what is strength?
relates to the maximum force which can be applied to a material without it breaking
what is breaking stress/ ultimite tensile strength (UTS)
maximum stress which can be applied to a material
what is stiffness?
relates to the resistance which a material offers to having its size and/or shape changed
what is a ductile material?
a material that can be permenantely streched
hardness
resistance to scratching
fatigue
a cause of fracture which occurs when a material is subjected to a large number of cycles of varying stress even of these stresses lie below the maximum that a material can withstand
what is creep?
used to describe the gradual increase in strain which occurs when a material is subjected to stress for a long period of time
