materials Flashcards
what is meant by breaking stress?
the maximum stress a material can withstand before fracturing
what are examples of materials with a high breaking stress?
nylon, metals
what are examples of materials with a low breaking stress?
glass, concrete
what is meant by a brittleness?
the material can break quickly when subject to tensile stress
what are some examples of brittle materials?
glass, ceramics
what are some examples of non-brittle materials?
rubber, metals
when does compressive force/stress occur?
when the applied force acts to squash a material
what is meant by a creep?
the continual extension over a long period of time caused by a constant load
what is a creep an example of?
plastic deformation
what is density a measure of?
the concentration of matter within it
what does density depend on?
the types of atoms from which the material is made and how they are combined
what are examples of materials with a high density?
lead, gold
what are examples of materials with a low density?
air, expanded polystyrene
what is destructive testing?
where the material is damaged or destroyed by the testing process
what are examples of destructive testing?
melting point, hardness
what is meant by a dislocation?
an imperfection in the crystal lattice of a metal due to missing atoms
how does a dislocation affect the crystal structure?
it deforms it as the atomic layers have to bend around the incomplete areas
how can isolated dislocations move through a stressed structure?
by a process of atoms breaking and then remaking bonds
what could happen if there was a large number of dislocations are created in a metal? (aka?)
they can become tangled which stops them moving and making the metal harder to deform (work hardening)
what is meant if an object is ductile?
it can be drawn out into long threads by a tensile stress
what is an example of a ductile material?
metals
what are some examples of non-ductile materials?
glass, ceramics
what happens during elastic deformation?
the bonds between atoms simply stretch, they dont break
a stress- strain graph for elastic deformation is usually what kind of graph? (what is this proportionality called?)
a straight line (hooke’s law)
what is an elastic limit?
the point beyond which elastic deformation ceases and plastic deformation begins
what is electrical conductivity a measure of?
how easily electricity can flow through a material
will a material with a high electrical conductivity be a good or poor conductor of electricity?
good
will a material with a low electrical conductivity be a good or poor conductor of electricity? (meaning what?)
poor (its a good electrical insulator)
what is the opposite of electrical conductivity?
electrical resistivity
what do materials contain to be good conductors?
charged particles (usually electrons) that are free to move to carry electricity
what are some examples of electrically conducting materials?
metals, graphite
what are some examples of electrically insulating materials?
plastics, ceramics
what is meant by endurance? (aka?)
the stress below which a material can withstand loading and unloading indefinitely without exhibiting fatigue (fatigue limit)
what is an example of a high endurance material?
steel
what is an example of a lowendurance material?
thermosetting plastics
when does fatigue occur?
when a malleable material goes through repeated loading/unloading cycles which causes damage to the structure and the material eventually fractures
what is a spring/force constant?
the ratio of the tensile force applied to a wire of spring to the extension produced
how can the spring/force constant be found?
the gradient of a force-extension graph up to its limit of proportionality
what is hardness a measure of?
how resistant an object is to plastic deformation
what are some examples of hard materials?
glass, ceramics
what are some examples of non-hard materials?
plastics, metals
what is hooke’s law?
the force applied to a wire/spring is directly proportional to the extension produced provided the limit of proportionality is not exceeded
what is meant by hysteresis?
when the loading and unloading curves don’t lie on top of each other
what is meant by the limit of proportionality?
the point below which the force applied to a wire/spring is directly proportional to the extension produced
