Flashcards in materials Deck (22):
what is density?
defined as "the mass per unit of volume of a material", density can be used to distinguish between two similar materials.
what is the elastic region?
the elastic region is where a material will return to their original shape and dimension's when applied stress is removed.
what is the plastic region?
the plastic region is entered after the material no longer acts elastically, this occurs when the applied stress is so great that the material is unable to return to its original dimensions and remains permanently deformed.
what is a perfectly plastic material?
A perfectly plastic material is a material ,like plasticine, and it remains in the exact shape it was forced into.
what is a material called with no plastic region?
A material with no plastic region, like glass or nylon, is very brittle and will snap.
what is stress measured in?
stress is measured in N/m2
what is ultimate tensile stress?
UTS is the maximum value of stress that a material can withstand and occurs at the breaking point.
what do brittle materials do at the breaking point?
brittle materials fracture, this is because it cracks and this crack spreads rapidly through the material.
what do ductile materials do at the breaking point?
at the breaking point a ductile material will waist/neck before a fracture occurs. when it does fracture it breaks into two jigsaw like pieces.
what is strain?
strain is the measurement of the affect the stress has had on a material.
brittle material features:
-no elastic region
-its elastic limit and breaking point is at the same point
-only has an elastic region
what is young's modulus?
young's modulus takes into account the dimensions and its material property from Hooke's law.
energy stored in stretched wire:
when a wire is extended a force does work in causing it to extend. the work done on the wire is stored as potential energy and it is this energy that allows it to spring back.
in the elastic region:
Force is proportional to extension.
energy stored in a stretched wire on a graph:
is the area under the graph.
what happens when a material is stretched beyond its elastic limit?
slip will occur between atomic layers. this movement between the layers causes the material to heat up internally. Since the energy stored is less than the work done the molecules will never be able to return to their original shape.
if the deformation is elastic, then the material returns to its original shape when the forces on it are removed.
if the deformation is plastic, then the material does not return to its original shape when the forces are removed.
what is bending?
bending is a combination of tensile and compressive strain.
what is fatigue in a metal?
if a metal is put under stress over and over a fatigue fracture may occur before the ultimate tensile stress is reached.
what is creep?
this is the deformation which happens in some materials if stress is maintained.