Materials Science Glossary - R

random copolymer. A polymer in which two different repeat units are randomly distributed along the molecular chain.

recovery. The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.

recrystallization. The formation of a new set of strain-free grains within a previously cold-worked material; normally an annealing heat treatment is necessary.

recrystallization temperature. For a particular alloy, the minimum temperature at which complete recrystallization will occur within approximately one hour.

rectifying junction. A semiconductor p–n junction that is conductive for a current flow in one direction and highly resistive for the opposite direction.

reduction. The addition of one or more electrons to an atom, ion, or molecule.

reflection. Deflection of a light beam at the interface between two media.

refraction. Bending of a light beam upon passing from one medium into another; the velocity of light differs in the two media.

refractory. A metal or ceramic that may be exposed to extremely high temperatures without deteriorating rapidly or without melting.

reinforced concrete. Concrete that is reinforced (or strengthened in tension) by the incorporation of steel rods, wires, or mesh.

relative magnetic permeability (_r).

The ratio of the magnetic permeability

of some medium to that of a

vacuum.

relaxation frequency. The reciprocal of the minimum reorientation time for an electric dipole within an alternating electric field.

relaxation modulus [Er(t)]. For viscoelastic polymers, the time-dependent modulus of elasticity. It is determined from stress relaxation measurements as the ratio of stress (taken at some time after the load application—normally 10 s) to strain.

remanence (remanent induction,Br). For a ferromagnetic or ferromagnetic material, the magnitude of residual flux density that remains when a magnetic field is removed.

repeat unit. The most fundamental structural unit found in a polymer chain. A polymer molecule is composed of a large number of repeat units that are linked together and successively repeated.

residual stress. A stress that persists in a material that is free of external forces or temperature gradients.

resilience. The capacity of a material to absorb energy when it is elastically deformed.

resistivity (). The reciprocal of electrical conductivity, and a measure of a material’s resistance to the passage of electric current.

resolved shear stress. An applied tensile or compressive stress resolved into a shear component along a specific plane and direction within that plane.

reverse bias. The insulating bias for a p–n junction rectifier; electrons flow into the p side of the junction.

rolling. A metal-forming operation that reduces the thickness of sheet stock; also, elongated shapes may be fashioned using grooved circular rolls.

rule of mixtures. The properties of a multiphase alloy or composite material are a weighted average (usually on the basis of volume) of the properties of the individual constituents.

rupture. Failure that is accompanied by significant plastic deformation; often associated with creep failure.