Material properties

—> often materials will experience plastic deformation and therefore do not obey Hooke’s Law.

Plastic deformation: the material can bend, be compressed. In a state that it can’t go back to its original shape.

—> the graph shows the stress and strain relationships for materials of different types.
—> the lines represent the materials finish when the materials break.

—> Brittle - can withstand a high stress without straining very much.

—> Strong but not ductile - it can withstand a high stress by won’t strain very much.

—> Ductile - when you apply stress, it will at first follow Hooke’s Law, past a certain point it will withstand any stress.

—> Plastic - will strain under very little stress.

—> a brittle material experiences very little elastic deformation before breaking.

—> the material experiences no plastic deformation.

—> this is because the molecules can’t experience any plastic flow meaning that they don’t move over one another.

—> brittleness is defined as the tendency of a material to fracture under stress.

—> a ductile material allows molecules to ‘slip’ across one another and find new rest positions which keep the structure intact.

—> these are raw materials that can easily be stretched into a wire like copper and aluminium.

—> ductility is defined as the ability of a material to form new shapes by means of tensile stress.

—> many materials that are ductile are also considered to be malleable.

—> malleability refers to the ability of material to be shaped by compressive forces

E.g. rolling, hammering, stamping

—> however, not all malleable materials are ductile.

—> the structure of solid metals is made up of tiny crystals (microcrystalline).

—> due to the regular arrays of identical atoms it makes it easy for these atoms to slip over each other to new stable, rest positions.

—> these materials are known as ductile.

—> most metals show some ductility.

—> the maximum stress experienced by these materials prior to breaking is known as maximum tensile stress.

—> the majority of non-metallic solids are brittle.

—> the exception to this are plastics.

—> brittle materials have a small elastic region but tend to be very stiff.

—> these materials don’t experience any plastic deformation meaning that if stress is applied beyond the elastic limit, brittle failure occurs.

—> if a material can be shaped to not many different shapes from compressive forces it is known as malleable.

—> objects made form rubber behave differently when loaded and unloaded.

—> a stress vs strain graph for rubber shown an hysteresis curve where the area of this loop represents the energy stored by the material in the form of potential.