C

C-scan - a data presentation method applied to pulse echo and transmission techniques. It yields a two-dimensional plan view of the object. No indication of depth is given unless special gating procedures are used.
Calibration - The process whereby the magnitude of the output of a measuring instrument is related to the magnitude of the input force driving the instrument (i.e. Adjusting a weight scale to zero when there is nothing on it).
Calibration Reflector - A reflector with a known dimensioned surface established to provide an accurately reproducible reference measurement.

Capacitance - The property of an electrical circuit that opposing a change in voltage. Capacitance enables devices or circuits to hold an electrical change.

Capacitive Reactance - The opposition to alternating current due to the capacitance of a capacitor, cable, or circuit.

Capillary Action - The phenomenon of a liquid such as water spontaneously creeping up thin tubes and fibers, this is caused by adhesive and cohesive forces and surface tension.

Capillary Pressure - The difference in pressure across the interface between two immiscible fluids.

Carbon Dating -A method of using the half-life of Carbon-14 to find the approximate age of an object that is up to 35,000 years old.

Carbonitriding - An evelated-temperature process (similar to carburizing) by which a ferrous metal absorbs both carbon and nitrogen into the surface when exposed to an atmosphere high in carbon and nitrogen. The carbon and nitrogen atoms diffuse into the metal to form a high-carbon and high-nitrogen zone near the surface.

Carburizing - An elevated temperature process by which a ferrous metal absorbs carbon into the surface when exposed to a high-carbon environment. Carbon atoms diffuse into the metal to create a high-carbon zone near the surface.

Case (Materials) - In a ferrous metal, the outer portion that has been made harder than the interior, or core.

Case Depth - The depth of the case, or hardened surface region, of a metal.

Cathode - A negatively charged electrode, as of an electrolytic cell, a storage battery, or an electron tube. The electrode at which reduction (and practically no corrosion) occurs. It is the opposite of anode.

Cathode Ray Tube - A vacuum tube containing a screen on which ultrasonic scans or oscilloscope traces may be displayed.

Characteristic Frequency Ratio - It allows the test coil operating point to be specified in terms of a single quantity rather than four independent variables.

Chemical Element - Any material that is composed of only one type of atom. It is also called a basic element or just an element.

Chemical Formula - A formula used to describe the types of atoms and their numbers in an element or compound.

Circuit - A closed path followed or capable of being followed by an electric current.

Circuit Diagrams - A type of diagram that is a pictorial way of showing circuits.

Circular Magnetism - The circular magnetic field around and inside a solid magnetic conductor when an electric current is passed through it.

Circumferential - Around the circumference, or periphery, of circular or cylindrical object. Also called tangential or hoop when referring to stresses.

Circumferential Coil - See encircling and internal probes.

Cladding - The outer layer, which provides corrosion protection or other desirable property, to a composite metal. The metal layers can be bonded together by rolling, welding, casting, heavy chemical deposition, or heavy electroplating.

Cleavage Fracture - A splitting fracture of a metal (usually polycrystalline) across the grains (or crystals).

Cloud Chamber (Penetrant) - (1) A station in a penetrant inspection processing line where the developer is applied by creating a cloud of developer that envelops the test component. (2) A device for detecting and measuring radioactivity and radiation. The cloud chamber was invented by Charles Wilson in 1911 and it makes it possible to visually see and photograph the path of ionizing radiation.

Coefficients - A constant chemical or physical property constant for a system with specific conditions (i.e. Coefficient of Friction).

Coefficient of Thermal Expansion - The linear expansion or contraction per unit length per degree temperatures between specified lower and upper temperatures.

Coercive Force - The reverse magnetizing force necessary to remove residual magnetism and demagnetize the part.

Cohesive Strength - The force that holds together the atoms in metal crystals. Analogous to tensile strength, but on a submicroscopic scale.

Coil - More than one loop of a conductor wound in a spiral. Also called a solenoid.

Coil Shot - A short "shot" of magnetizing current passed through a solenoid or coil for the purpose of producing a longitudinal magnetic field in a test component.

Cobalt 60 - A radioisotope of the element cobalt.

Cold Shut - (1) A discontinuity that appears on the surface of cast metal as a result of two streams of liquid metal meeting but failing to unite. (2) A lap on the surface of a forging or billet that was closed without fusion during deformation. Same as forging lap.

Cold Work - Permanent deformation caused by application of an external force to a metal below its recrystallization temperature.

Collimating Nozzle - A transducer assembly attachment designed to reduce the ultrasonic beam spread.

Collimation - The process by which a beam of energy or particles is aligned to form a parallel beam.

Collimator - A device for limiting the effects of beam spread.

Color-Contrast Penetrant - A penetrant incorporating a color dye or sufficient intensity to give good color contrast in indications against the background of the surface being tested, when viewed under white light.

Columnar Structure - A coarse structure of parallel columns of grains, having the long axis perpendicular to the surface.

Comparative Test Block - A metal block specially cracked and having two separate, but adjacent areas for the application of different penetrants so that a direct comparison can be obtain.

Compensator - An electrical matching network to compensate for electrical impedance differences.

Complex Electrical Impedance - In a typical AC circuit, resistance R and reactance X combine in vector fashion to form a complex impedance. Reactance is conventionally multiplied by the positive square root of -1 (j), to express Z as a complex number of the form R + jX.

Composite - A product that is produced by combining several different material products to arrive at desired set of properties. Fiber glass, carbon graphite epoxy, and carbon fiber are examples of composite material.

Compound - Any material that is composed of more than one type of atom.

Compression - The act of forcing or pressing together.

Compressional Wave - A wave in which the particle motion in the material is parallel to the wave propagation direction. Also called a longitudinal wave.

Compressive Strength - In compression testing, the ratio of maximum load to the original cross-sectional area. Fracture may or may not occur, depending on the applied forces and the properties of the material.

Compton Scattering - A process through which radiation is absorbed by the material it penetrates.

Computed Tomography - A radiographic technique in which the planar density data is stretched out in a third dimension and combined similar data taken at various angles to generate cross sectional images of the test component.

Concentration Cell - A cell involving an electrolyte and two identical electrodes, with the electrical potential resulting from differences in the chemistry of the environments adjacent to the two electrodes.

Conductivity - A measure of the ability of a material to conduct electrical current.

Conductors - Materials that have free electrons and allow electrical current to flow easily.

Consequent Poles - Magnetic poles that exist where the specimen has been successively magnetized in different sections to create more than two poles; e.g., two north poles with one south pole between them.

Constriction - Squeezing in the lines of force; i.e., a narrowing of section in a magnetized material.

Constructive Interference - The strengthening of waves that occurs when two waves interact and in phase portions of each wave combine to create a wave with a higher intensity.

Contact Method - The testing method in which the transducer face makes direct contact with the test object through a thin film of couplant.

Contact Transducers - An ultrasonic transducer that is designed to be used in direct contact with the surface of the test article.

Contaminant - Any foreign substance that interferes with a process or measurement.

Continuous Method - A magnetic particle inspection method in which the indicating particles are on the part while the magnetizing current is being applied.

Continuous Wave - A wave that continues without interruption.

Continuum - The name used for the combination of all colors an object, such as the Sun, emits, and also for the broad variation from color to color in how much light is emitted.

Contracted Sweep - A misnomer that refers to extending the duration of the sweep to permit viewing discontinuities or back reflections from deeper in the test object. The sweep appears to be compressed.

Contrast (radiographic) - The measure of difference in the film or detector density (darkness) from one area to another, resulting from various X-ray intensities interacting with the detector.

Contrast Ratio - The relative difference in the film or detector density (darkness) between the image background and a feature of interest.

Contrast Sensitivity - Being able to differentiate between an object and its background

Control Echo - An ultrasonic reference signal from a constant reflector, such as the back reflection from a smooth, regular surface. Loss of the control echo indicates that the UT system is not functioning properly due to a problem such as coupling loss.

Controlled Area - A defined area in which the occupational exposure of personnel to radiation or to radioactive material is under the supervision of the individual in charge.

Cooling Stresses - Residual stresses resulting from nonuniform distribution of temperature during cooling.

Corner Effect - The strong reflection obtained when an ultrasonic beam is directed toward the intersection of two or three mutually perpendicular surfaces.

Corrosion - Deterioration of a metal by chemical or electrochemical reaction with its environment.

Corrosion Embrittlement - The severe loss of ductility of a metal, resulting from corrosive attack, usually intergranular and often not visually apparent.

Corrosion Fatigue - Cracking that initiates and propagates due to the application of repeated or fluctuating stresses, and the initiation and propagation occurs more rapidly due to the presence of a corrosive environment.

Coulomb(ku`-lum) - A charge that moves past a given point in one second. A coulomb is the charge carried by 6.25 x 10^18 electrons.

Couplant - A substance (usually liquid) used between the transducer and the test surface to permit or improve transmission of ultrasonic energy into the test object.

Coupling - (1) The physical connect of an ultrasonic transducer to the test component. (2) The interaction of the coil's magnetic field with the test sample, which results in the generation of eddy currents in the sample and, in turn, a change in probe impedance.

Coupon - A piece of metal from which a test specimen is to be prepared. Often an extra piece that is cut from a casting or forging.

Crack - A long narrow discontinuity

Crack Growth Rate - The change in crack length per number of fatigue cycles.

Crack Tip Diffraction - A process using a beam transducer to determine the length and height of a crack

Creep - Time-dependent strain occurring under stress, or the change of shape that occurs gradually under a steady load.

Creep Strength - (1) The constant nominal stress that will cause a specified quantity of creep in a given time at constant temperature; (2) the constant nominal stress that will cause a specified creep rate at constant temperature.

Crevice Corrosion - Localized corrosion resulting from the formation of a concentration cell in a crevice between two surfaces.

Critical Angle - The first angel of the incident sound wave that generates a refracted wave that travels along the incident surface. The first angle that results in a surface following longitudinal wave is known as the 1st critical angle and the first angle that results in surface following shear wave is known as the 2nd critical angle.

Critical Flaw Size - Size of a crack or flaw that may cause catastrophic failure.

Cross Talk - The unwanted signal leakage (acoustical or electrical) across and intended barrier, such as leakage between the transmitting and receiving elements of a dual transducer. Also called cross noise and cross coupling.

CRT - See cathode ray tube.

Crystal - A three-dimensional array or atoms having a certain regularity in its arrangement. A crystal is composed of many cells or lattices, in which the atoms are arranged. In the field of metallurgy, a crystal is often called a grain.

Cumulative Dose (radiation) - The total dose (see threshold dose) resulting from repeated exposure to radiation of the same region or of the whole body.

Cup Fracture (cup-and-cone-fracture) - Fracture, frequently seen in tensile test pieces of a ductile material , in which the surface of failure on one portion shows a central flat area of failure in tension, with an exterior extended rim of failure in shear.

Curie - The basic unit of measure for describing the activity (radioactivity) of a quantity of radioactive material. The amount of radioactive material giving off 37 billion disintegrations per second. In the United States, the picocurie (1 pCi = 0.037 d.p.s.) is the unit used for many measurements of radioactive contamination.

Current (I) - The flow of electrons. Measured in amperes.

Current Density - Current divided by the electrode area (current per unit area of the electrode)

Curvature corrections - The method to account for degradation of signal amplitude when using a flat ultrasonic transducer to inspect an object with a curved surface.

Cutoff Frequency - The upper or lower frequency beyond which no appreciable energy is transmitted.

Cycle (Hertz) - One complete set of recurrent values of a periodic quantity comprises a cycle.

Cyclic Load - Repetitive loading of a material that sometimes leads to fatigue fracture.

Cyclotron - A device that is capable of accelerating charged particles (protons) in a circular path to energies that exceed 10 MeV. E.O. Lawrence developed the Cyclotron in the early 1930’s.