| Ideal crack |
A simplified model of a crack used in elastic-stress analysis. In a stress-free body, the crack has two smooth surfaces that are coincident and join within the body along a smooth curve called the crack front; in two-dimensional representations, the crack front is called the crack tip. |
| Ideal critical diameter |
(DI). Under an ideal quench condition, the bar diameter that has 50% martensite at the center of the bar when the surface is cooled at an infinitely rapid rate (that is, when H = ∞, where H is the quench severity factor). |
| Ideal gas laws |
The law relating pressure, temperature and volume of an ideal (perfect) gas pV = mRT, where R is the gas constant. The law implies that at constant temperature T, the product of pressure p and volume V is constant (Boyle’s law), and at constant pressure, the volume is proportional to the temperature (Charles’ law). |
| Impact |
Sudden loading of a body or component, as in a vehicle collision or striking by a hammer. |
| Impact energy |
The amount of energy required to fracture a material, usually measured by means of an Izod test or Charpy test.The type of specimen and test conditions affect the values and therefore should be specified. |
| Impact energy (Unit J) |
1. The sum of the kinetic energies of all the bodies involved at the instant of collision of two or more moving bodies. 2. The energy required to fracture a specimen in a Charpy or Izod impact test. |
| Impact extrusion |
The extrusion of separate components of soft metals whose properties permit the action to be performed quickly. |
| Impact loads |
Especially severe shock loads such as those caused by instantaneous arrest of a falling mass, shock meeting of two parts (in a mechanical hammer, for example), or by explosive impact, in which there can be an exceptionally rapid build-up of stress. |
| Impact strength |
The resiliency or toughness of a solid as measured by impact energy. |
| Impact strength 1. (Unit Pa) |
The stress to cause failure (by yielding or fracture) under conditions of high strain rate. 2. (Unit J) A term sometimes used to describe the energy required to fracture a specimen in a Charpy or Izod impact test even though the unit is not that of strength. |
| Impact test |
A test for determining the energy absorbed in fracturing a test piece at high velocity, as distinct from static test. The test may be carried out in tension, bending, or torsion, and the test bar may be notched or unnotched. |
| Impact testing |
Determination of the mechanical properties of materials under high-rate conditions. Often determined from the behaviour of a testpiece when struck by a pendulum or a weight falling from a known height, or when sandwiched between two Hopkinson bars. |
| Impact wrench |
An air- or electric-powered wrench in which multiple blows from tiny hammers are used to produce output torque to tighten fasteners. |
| Impact wrench |
A pneumatically-or electrically-powered socket wrench used to tighten or loosen nuts through the application of torque in a rapid series of impulses. |
| Imperial system |
The units of measurement developed in the UK. Formerly known as the fps system, which is an abbreviation for the ‘foot-pound-second system of units. |
| Imperial system of units |
British imperial system of units) An obsolete system of units first defined in the British Weights and Measures Act of 1824. Its three base units were second (time), yard (length), and pound avoirdupois (mass). The imperial unit of capacity was the gallon. The many associated units introduced subsequently include cubic inch, cubic foot, cubic yard, pint, and quart for both liquid and dry measures of capacity (i.e. volume); ounce, hundredweight, short and long ton for avoirdupois mass; poundal for force; minute and hour for time; fahrenheit for temperature; and British thermal unit for energy. Closely related to the imperial system of units is the US customary system of units. Each imperial unit is now legally defined in terms of the metric (i.e. SI) equivalent. |
| Inch (in) |
A non-SI unit of length now defined as 25.4 mm. The conversion to SI is 1 in = 2.54 × 10−2 m. |
| Inch-pound force/inch2 |
A non-SI unit for the specific work of fracture (fracture toughness). The conversion to SI is 1 in.lbf/in2 = 1.751 268 × 102 J/m2. |
| Inclusions |
Small pieces of nonmetallic impurities trapped within the base metal of. |
| Indentation hardness |
The resistance of a material to indentation as determined by hardness testing. The indenter, which may be spherical or diamond shaped, is pressed into the surface of a metal under specified load for a given time. |
| Indentation hardness |
(Unit Pa or, non-SI, kgf/mm2) A measurement of hardness taken by means of an indenter, pressed into a material by a load, which makes a permanent impression. The hardness is given by the load divided by the projected (sometimes surface) area of the indentation. Plasticity theory shows that the hardness is about 2.5–3 times the uniaxial yield stress. |
| Induction hardening |
A surface-hardening process in which only the surface layer of a suitable ferrous workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched. |
| Induction heating |
Heating by combined electrical resistance and hysteresis losses induced by subjecting a metal to the varying magnetic field surrounding a coil carrying alternating current. |
| Induction tempering |
Tempering of steel using low-frequency electrical induction heating. |
| Infinite life diagram |
A simple plot experimentally derived fatigue-life data, showing the conditions required for infinite life. |
| Initial preload |
The tension created in a single bolt as it is tightened. Will usually be modified by subsequent assembly operations or by in-service loads and conditions. |
| Initial strain |
The strain in a specimen immediately upon achieving the given loading conditions in a creep test (before creep occurs). Sometimes referred to as instantaneous strain. |
| Initial stress |
The stress produced by strain in a specimen immediately on achieving the given constant-strain conditions in a stress-relaxation test before stress-relaxation occurs. Sometimes referred to as instantaneous stress. |
| Inspection gauge |
Any of various gauges used in manufacturing and quality control to check dimensions, finish, etc. |
| Intense quenching |
Quenching in which the quenching medium is cooling the part at a rate at least two and a half times faster than still water. |
| Intercritical annealing |
Any annealing treatment that involves heating to, and holding at, a temperature between the upper and lower critical temperatures to obtain partial austenitization, followed by either slow cooling or holding at a temperature below the lower critical temperature. |
| Intergranular cracking |
Cracking or fracturing that occurs between the grains or crystals in a polycrystalline aggregate. Also called intercrystalline cracking. |
| Intergranular fracture |
Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Also called intercrystalline fracture. |
| Intermediate annealing |
Annealing wrought metals at one or more stages during manufacture and before final treatment. |
| International Bureau of Weights and Measures |
(BIPM, Bureau International des Poids et Mesures) The intergovernmental organization which has the mandate to provide the basis for a single, coherent system of measurements, traceable to the International System of Units. |
| International Practical Temperature Scale (IPTS) |
A close approximation to the thermodynamic temperature scale based upon the triple points of hydrogen (13.8 K), neon (24.6 K), oxygen (54.4 K), argon (83.8 K), mercury (234.3 K), and water (273.2 K); the melting point of gallium (302.9 K); and the freezing points of indium (429.7 K), tin (505.1 K), zinc (692.7 K), aluminium (933.5 K), silver (1 234.9 K), gold (1 337.3 K), and copper (1 |
| International System of Units |
(SI system of units, Le Système international d’unités) The standard system of units now used almost universally in science and engineering except in the United States. The definitive reference on the SI is a booklet published by the International Bureau of Weights and Measures, often referred to as the BIPM SI Brochure. There are seven base units: metre (symbol m) for length; kilogram (kg) for mass; mole (mol) for amount of substance; second (s) for time; kelvin (K) for temperature; ampere (A) for electric current; and candela (cd) for luminous intensity. New SI unit definitions, based upon the values of the universal constants of nature (also termed the fundamental physical constants: the Avogadro constant, the Boltzmann constant, and the Planck constant), came into effect on 20 May 2019. Minor adjustments were also made to the values of these constants. In addition to the base units, there are 22 coherent derived units, including radian (rad) for plane angle, steradian (sr) for solid angle, hertz (Hz) for frequency, newton (N) for force, pascal (Pa) for pressure, joule (J) for energy, work, and amount of heat, and watt (W) for power and radiant flux. Recommended practice is to avoid combinations such as N/mm2, MN/m2 being preferred.(kg) for mass; mole (mol) for amount of substance; second (s) for time; kelvin (K) for temperature; ampere (A) for electric current; and candela (cd) for luminous intensity. New SI unit definitions, based upon the values of the universal constants of nature (also termed the fundamental physical constants: the Avogadro constant, the Boltzmann constant, and the Planck constant), came into effect on 20 May 2019. Minor adjustments were also made to the values of these constants. In addition to the base units, there are 22 coherent derived units, including radian (rad) for plane angle, steradian (sr) for solid angle, hertz (Hz) for frequency, newton (N) for force, pascal (Pa) for pressure, joule (J) for energy, work, and amount of heat, and watt (W) for power and radiant flux. Recommended practice is to avoid combinations such as N/mm2, MN/m2 being preferred. |
| Interrupted aging |
Aging at two or more temperatures, by steps, and cooling to room temperature after each step. |
| Interrupted quenching |
A quenching procedure in which the workpiece is removed from the first quench at a temperature substantially higher than that of the quenchant and is then subjected to a second quenching system having a different cooling rate than the first. |
| Ion carburizing |
A method of surface hardening in which carbon ions are diffused into a workpiece in a vacuum through the use of high-voltage electrical energy. Synonymous with plasma carburizing or glowdischarge carburizing. |
| Ion nitriding |
A method of surface hardening in which nitrogen ions are diffused into a workpiece in a vacuum through the use of high-voltage electrical energy. Synonymous with plasma nitriding or glowdischarge nitriding. |
| Isothermal annealing |
Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which austenite transforms to a relatively soft ferrite carbide aggregate. |
| Izod test |
A type of impact test in which a V-notched specimen, mounted vertically, is subjected to a sudden blow delivered by the weight at the end of a pendulum arm. The energy required to break off the free end is a measure of the impact strength or toughness of the material. |
