Glossary Terms

Measure of the relative change in the size or shape of a body. Linear strain is the change per unit length of a linear dimension. True strain (or natural strain) is the natural logarithm of the ratio of the length at the moment of observation to the original gage length.

Increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range.

Force per unit area, often thought of as force acting through a small area within a plane. It can be divided into components, normal and parallel to the plane, called normal stress and shear stress, respectively. True stress denotes the stress where force and area are measured at the same time.

Annealing designed to relieve internal stresses caused by machining, welding, casting, cold working, quenching or normalizing.

Method of evaluating elevated-temperature durability in which a tension-test specimen is stressed under constant load until it breaks. Data recorded commonly include initial stress, time to rupture, initial extension, creep extension and reduction of area at fracture.

Fatigue fracture feature, often observed in electron micrographs, that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front across that crystal during one stress cycle, and a line normal to the striations indicates the direction of local crack propagation.

Abrasive tools made from diamond or cubic boron nitride, the hardest materials known. See CBN, cubic boron nitride; diamond; PCD, polycrystalline diamond; single-crystal diamond.

Tough, difficult-to-machine alloys; includes Hastelloy, Inconel and Monel. Many are nickel-base metals.

Cooling below the temperature at which an equilibrium phase transformation can take place, without actually obtaining the transformation.

Heating above the temperature at which an equilibrium phase transformation should occur, without actually obtaining the transformation.

Ability of certain metals to undergo unusually large amounts of plastic deformation before local necking occurs.

Machining of a flat, angled or contoured surface by passing a workpiece beneath a grinding wheel in a plane parallel to the grinding wheel spindle. See grinding.