what does plastic deformation mean
when the solid material begins to flow rather like a liquid. if the change in shape or size remains when stress is removed= permenant set.
what happens when a material reaches their elastic limit
they will either fail or undergo plastic shape change
what does the region of proportionaility mean
its the region where materials exhibit hookes law- increasing the force, increases the extension-proportionaly.
where can the elastic limit be found on a stress and strain graph
the point beyond hookes law region indicating the meterial can not return to its original shape
what is tensile and compressive
tensile means to stretch, compressive means to squash
stress equation= force/ cross sectional area
during stress equation how do you find out the cross sectional area
1.pie r squared
2. pie d squared/ 4
why are there no units for strain
dimentionless ratio
why do materials need to have their tensile properties tested
so that their behaviour under load can be predicted and used in the design process
what is the ultimate tensile stress
maximum amount of stress a material can withstand
what happens at yield point on a stress and strain graph
a
when the material begins to strecth without any extra force- deformation takes place and intermolecular forces are broken- molecules slide past each other
how is a metal lattice structure formed
positive ions form thr cristal lattice while delocalised electrons move freely throughout the lattice, gluing the whole lattice together.
what makes a material/ metal ductile
regular arrays of similar atoms makes it easy for the layers to slide across one anothe
what can happen to ductile materials and what does it make them ideal for
they can be stretched into a thin wire/ drawn into a new shape which they can take permanently. and makes them ideal for maufacturing- rods, wires or tubes.
what does malleabilty refer to in metals
they can be formed into thin sheets through compressive forces.
what does brittleness mean
the ability of a material to fracture under stress
what happens to brittle materials under stress
tiny cracks in the material will get bigger and bigger until it breaks
what happens to a material under creep
tiny crystals in a random oreintation will cause tiny gaps that will slowly grow over time.
when does creep become severe
in materials that are subjected to large temperature changes
what causes fatigue and what is the outcome
caused by repeated loading and unloading forces which causes structural damage that grows over time until sudden brittle failure
what is creep a version of
how does creep increase and what could it lead to
plastic deformation- increases with temperature- lead to failure if components no longer fit or they neck in.
two ways to define strength
youngs modules
ultimate tensile strength
explain how the energy of a spring varies as it oscillates
