16 C HAPTER Nondestructive Testing Glossary Richard D. Lopez, Iowa State University, Ames, Iowa From Nondestructive Testing Handbook, Third Edition: Volume 10, Overview © 2012. Reprinted with permission of The American Society for Nondestructive Testing Inc. Terms absolute pressure: Pressure above Introduction absolute zero value or pressure above that of space empty of all molecules. Equal to sum of local atmospheric Purpose pressure and gage pressure. absolute temperature: Thermodynamic Standards writing bodies take great pains temperature measured from absolute to ensure that their standards are zero temperature, expressed in definitive in wording and technical kelvin (K). accuracy. People working to written absorbed dose: In radiographic testing, contracts or procedures should consult amount of energy imparted to matter definitions referenced in standards when by an ionizing event per unit mass of appropriate. For example, persons who irradiated material at the place of work in accordance with standards interest. Absorbed dose is expressed in published by ASTM International are gray (Gy) or rad. See also dose rate; encouraged to refer to definitions in the dosimeter.14 ASTM standards.1 absorptance; absorptivity: Proportion (as The definitions in this Nondestructive a fraction of 1) of the radiant energy Testing Handbook volume should not be impinging on a material’s surface that referenced for tests performed according is absorbed into the material. For a to standards or specifications or in blackbody, this is unity (1.0). fulfillment of contracts. This glossary is Technically, absorptivity is the internal provided for instructional purposes. No absorptance per unit path length. In other use is intended. thermography, the two terms have sometimes been used interchangeably. On References absorption: In nondestructive testing, Definitions from other volumes of the reduction of the intensity of any form Nondestructive Testing Handbook are not of radiated energy as a result of energy referenced. This volume’s antecedent in conversion (absorption) in a medium, the second edition was the Nondestructive such as the conversion of sound Testing Handbook: Volume 10, energy into heat. Compare attenuation. Nondestructive Testing Overview (1996).2 absorption coefficient, linear (µL): However, most of the definitions in this Fractional decrease in transmitted glossary are from the various, superseding intensity per unit of absorber –1 15 method volumes.3-11 thickness. Expressed in units of cm . Measurement units and their symbols acceptable quality level (AQL): are covered in the introduction to this Maximum percent defective (or the volume. maximum percentage of units with For physical quantities and properties rejectable discontinuities) that, for the in materials science, the reader is served purposes of sampling tests, can be by reference books such as the CRC considered satisfactory as a process Handbook of Chemistry and Physics12 and average. Compare lot tolerance percent Leonard Mordfin’s Handbook of Reference defective. Data for Nondestructive Testing.13 acceptance criterion: Benchmark against which test results are to be compared for purposes of establishing the functional acceptability of a part or A system being examined. acceptance level; acceptance limit: absolute measurement: (1) Measurement (1) Test signal value used to establish made with an absolute coil. (2) the group to which a material under Measurement of a property without evaluation belongs (2) Measured value reference to another measurement of or values above or below which test that property. Compare comparative objects are acceptable. Compare measurement; relative measurement. rejection level. From Nondestructive Testing Handbook, Third Edition: Volume 10, Overview © 2012. Reprinted with permission of The American Society for Nondestructive Testing Inc. 516 Nondestructive Testing Overview acceptance standard: (1) Specimen, melting, phase transformations or similar to the product to be tested, thermal stresses. containing natural or artificial acoustic impedance (z): Frequency discontinuities that are well defined dependent property of a medium and similar in size or extent to the through which acoustic waves maximum acceptable in the product. propagate in units of kg·s–1·m–2. In its (2) Document defining acceptable simplified form, acoustic impedance is discontinuity size limits. See also the product of longitudinal ultrasonic reference standard; standard. wave velocity (m·s–1) and material –3 accommodation: Of the eye, adjustment density (kgm·m ). The relative of the lens’ focusing power by transmission and reflection at an changing the thickness and curvature interface are governed in part by the of the lens through its movement by acoustic impedances of the materials tiny muscles. on each side of the interface. accumulation test technique: In leak acoustic impedance, characteristic: In testing, detecting the total amount of ultrasonic testing, acoustic impedance leakage by enclosing the component typical or characteristic of a particular under test within a hood, bag, box, material. shroud or container. For pressure acoustic impedance, specific: In testing, any gas leaking from the ultrasonic testing, acoustic impedance component accumulates in the space in a particular test object or a defined (volume) between the component and volume of a specified material. the enclosure. For vacuum testing, any acoustic microscopy: In ultrasonic gas leaking into the component testing, general term referring to the accumulates in the leak detector use of high resolution, high frequency sampling the evacuated component. ultrasonic techniques to produce Accumulation of tracer gas in a images of features beneath the surface measured time period provides a of a test object. measure of the leakage rate. activation: In radiographic testing, accuracy: Degree of conformity of process by which neutrons bombard measurement to a standard or true stable atoms and make them value. radioactive. ACGIH: American Conference of activity: In radiographic testing, degree of Governmental Industrial Hygienists. radioactivity of a particular isotope. acoustic emission: (1) Transient elastic Activity is expressed as the number of waves resulting from local internal atoms disintegrating per unit of time. microdisplacements in a material. Measured in becquerels. acoustic emission activity: Number of AE: Acoustic emission testing. bursts (or events, if the appropriate acuity: See neural acuity, vision acuity. conditions are fulfilled) detected adhesive wear: See wear, adhesive. during a test or part of a test. agency: Organization selected by an acoustic emission count: Number of authority to perform nondestructive times the signal amplitude exceeds the testing, as required by a specification preset reference threshold. Sometimes or purchase order. called ringdown counts. agglomeration: Clustering where smaller acoustic emission event: Microstructural particles collide and adhere as groups. displacement that produces elastic aging: (1) The effect of long term waves in a material under load or environmental exposure on materials stress. or components. (2) Heat treatment acoustic emission hit: Acoustic emission method that alters material properties signal received on one channel. and microstructure because of the acoustic emission rate: Number of times duration of time at ambient (natural the acoustic emission signal amplitude aging) or elevated (artificial aging) has exceeded the threshold in a temperature. Aging is commonly specified unit of time. applied to alloys after hot working, acoustic emission signal: Electrical signal quenching from an elevated obtained through the detection of temperature or cold working. See also acoustic emission. precipitation hardening. acoustic emission testing (AE): Passive air flow: In leak testing, flow of air from nondestructive testing method that the probe inlet to the sensitive element monitors a component or assembly for of the halogen leak detector that transient elastic waves and converts carries the tracer gas from the leak to these ultrasonic waves into electrical the sensing diode. signals. Acoustic waves may be algorithm: Prescribed set of well defined produced by the formation or rules or processes for the solution of a movement of microstructural mathematical problem in a finite dislocations during crack propagation, number of steps.16 From Nondestructive Testing Handbook, Third Edition: Volume 10, Overview © 2012. Reprinted with permission of The American Society for Nondestructive Testing Inc. Nondestructive Testing Glossary 517 alkali ion diode: Sensor type for halogen analog-to-digital converter: Circuit gases. In this device, positive ions whose input is information in analog (cations) of an alkali metal are form and whose output is essentially produced on the heated surfaces the same information in digital (usually platinum) of the diode. One form.16 electrode is at a negative potential and angle beam: In ultrasonic testing, attracts cations that are released when ultrasound beam traveling at an acute a halogen gas passes between the angle into a medium. The angle of sensor electrodes. Provides an output incidence or angle of refraction is current to operate the indicator on the measured from the normal to the halogen leak detector. entry surface.15 alpha iron: See ferrite. angle beam test technique: In ultrasonic alpha particle: Positively charged helium testing, inspection technique in which ion emitted by certain radioactive transmission