Ductile materials (e
Materials - OCR A-Level Physics
- DuctileA material that can be drawn into wires and undergoes large plastic deformation before fracture. materials (e.g. copper, mild steel): undergo significant plastic deformationPermanent deformation in which the material does not return to its original shape when the deforming force is removed. before fracture. Long plastic region on the stressThe force applied per unit cross-sectional area of a material. Measured in pascals (Pa).-strainThe fractional change in length of a material under stress. It is dimensionless (no units). graph after the yield point
- BrittleA material that fractures with little or no plastic deformation, snapping suddenly. materials (e.g. glass, cast iron, ceramic): fracture with little or no plastic deformationPermanent deformation in which the material does not return to its original shape when the deforming force is removed.. They snap suddenly near the limit of proportionality
- PolymericA material made of long-chain molecules; shows very large elastic strain and a non-linear stress–strain curve. materials (e.g. rubber, polythene): show non-linear stressThe force applied per unit cross-sectional area of a material. Measured in pascals (Pa).-strainThe fractional change in length of a material under stress. It is dimensionless (no units). behaviour. Rubber shows hysteresisThe phenomenon where the loading and unloading curves of a material do not coincide; the area between them represents energy dissipated as heat. -- the unloading curve is below the loading curve, and the enclosed area represents energyThe capacity to do work. Measured in joules (J). dissipated as heat
- StrongA material with a high ultimate tensile stress — it can withstand large stresses before breaking. = high UTS (withstands high stressThe force applied per unit cross-sectional area of a material. Measured in pascals (Pa).). StiffA material with a high Young modulus — it resists deformation and has a steep stress–strain gradient. = high Young modulusThe ratio of stress to strainThe fractional change in length of a material under stress. It is dimensionless (no units). for a material in the elastic region. A measure of stiffness. Measured in pascals (Pa). (small strain for given stress). ToughA material that absorbs a lot of energy before fracturing — large area under the stress–strain curve. = large area under the stress-strain curve (absorbs lots of energyThe capacity to do work. Measured in joules (J). before fracture). These are three different properties
Common Mistake
MEDIUM
Students often: Don't confuse the terms 'strong', 'stiff' and 'tough', using them interchangeably.
Instead: $Strong = high UTS. Stiff = high Young modulusThe ratio of stress to strain for a material in the elastic region. A measure of stiffness. Measured in pascals (Pa).. Tough = large area under stress-strain curve. A material can be strong$ but not tough (e.g. cast iron: high UTS but brittle, small area under curve).
Instead: $Strong = high UTS. Stiff = high Young modulusThe ratio of stress to strain for a material in the elastic region. A measure of stiffness. Measured in pascals (Pa).. Tough = large area under stress-strain curve. A material can be strong$ but not tough (e.g. cast iron: high UTS but brittle, small area under curve).