M

Macroshrinkage - A casting defect, detectable at magnifications not exceeding ten diameters, consisting of voids in the form of stringers shorter than shrinkage cracks. This defect results from contraction during solidification where there is not an adequate opportunity to supply filler material to compensate for the shrinkage. It is usually associated with abrupt changes in section size.
Macrostructure - The structure of metals as revealed by examination of the etched surface of a polished specimen at a magnification not exceeding ten diameters.
Magnet - Any piece of iron, steel or magnetite that has the property of attracting iron or steel.
Magnetic Behavior - When two materials attract or repel each other.
Magnetic Discontinuity - This refers to a break in the magnetic uniformity of the part-a sudden change in permeability. A magnetic discontinuity may not be related to any actual physical break in the metal, but it may produce a magnetic particle indication.
Magnetic Domain - A region in which the magnetic fields of atoms are grouped together and aligned.
Magnetic Field - The space in which a magnetic force is exerted. This space exists within and around a magnetized material and a conductor carrying electrical current.
Magnetic Field Strength - The measured intensity of a magnetic field at a specific point. Usually expressed in amperes/meter or oersteds.
Magnetizing Force - See Magnetic field strength.
Magnetic Flux - A measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. The total number or lines of force existing in a magnetic circuit.
Magnetic Flux Density (B) - The normal magnetic flux per unit area. Usual expressed in Tesla or Gauss.
Magnetic Lines of Force - Imaginary lines in the magnetic field indicating how strong the magnetic force is (the closer together the lines, the stronger the force).
Magnetic Loop - If a conductor carrying an electric current is bent in a loop, the magnetic lines of force enter on one side of space within the loop is found to contain a magnetic field which has very definite directional properties. Polarity is created within the coil with one end being a north pole and the opposite end a south pole. The space enclosed by the loops is longitudinally magnetized.
Magnetic Materials - Materials are affected by magnetism in two general ways. Some of them are attracted by a magnet, while others exert a repellent force. The first is called "paramagnetic" and the later "diamagnetic." In Magnetic particle inspection we are not ordinarily concerned with either of the two classes, but with what may be termed a subdivision of the first class called "ferromagnetic materials."
Magnetic Moment - The ratio between the maximum torque exerted on a magnet, current-carrying coil or moving charge situated in a magnetic field and the strength of that field.
Magnetic Particle Inspection - A method of detecting cracks or defects by establishing a magnetic field in the object and using iron filings to see if the field lines are constant.
Magnetic Particle Testing - (see Magnetic Particle Inspection)
Magnetic Permeability - The ratio of the magnetic flux density, B, in a substance to the external field strength.
Magnetic Poles - Any place that a magnetic line of force exits or enters the magnet is called a pole.
Magnetic Testing (MT) - A nondestructive testing method used for defect detection.
Magnetically Hard Alloy - A ferromagnetic alloy capable of being magnetized permanently because of its ability to retain induced magnetization and magnetic poles after removal of externally applied fields; an alloy with high coercive force. The name is based on the face that the quality of the early permanent magnets was related to their hardness.
Magnetically Soft Alloy - A ferromagnetic alloy that becomes magnetized readily upon application of a field and that returns to practically a nonmagnetic condition when the field is removed; an alloy with the properties of high magnetic permeability, low coercive force and low magnetic hysteresis loss.
Magnetism - The force of attraction or repulsion in a material.
Magnetization - The property and the extent of being magnetized. Quantitatively, the magnetic moment per unit volume of a substance.
Magnetizing Force - The total force tending to set up a magnetic flux in a magnetic circuit. It is usually designated by the letter "H" and the unit is the "Oersted."
Magnetograph - A picture of a magnetic field made by the use of iron powder under conditions that allow it to arrange itself into the pattern of the field.
Magnetostrictive - Deformation of a ferromagnetic material (such as iron and steel) subjected to a magnetic field.
Main Bang - See initial pulse.
Malleability - The characteristic of metals which permits plastic deformation in compression without rupture.
Manipulator - In immersion testing, a device for angular orientation of the transducer.
Marie and Pierre Curies - Discovered two radioactive elements in pitchblende (polonium and radium). They were later awarded the Nobel Prize.
Markers - A series of indications on the horizontal trace of the cathode ray tube to show increments of time or distance.
Martensite - The very hard structure in certain irons and steels that is usually formed by quenching (rapid cooling) from an elevated temperature. Martensite may or may not be tempered to reduce hardness and increase ductility and toughness.
Mass Numbers - The number of protons and neutrons in a atoms.
Material Noise - Random signals caused by the material structure of the test object. A component of background noise.
Matrix - The principal phase of a metal in which another constituent is embedded. For example, in gray cast iron, the metal is the matrix in which that graphite flakes are embedded.
Matter - Anything that has mass and occupies space.
Maximum Permissible Dose (MPD) - That dose of ionizing radiation which competent authorities have established as the maximum that can be absorbed without undue risk to human health.
Mean Free Path - Average distance a particle travels between collisions.
Mean Life - The average time during which an atom or other system exists in a particular form.
Measuring Attenuation - Measuring the ultrasonic absorption and the scattering of a material.
Mechanical Properties – The properties of a material that reveal its elastic and inelastic (plastic) behavior when force is applied, thereby indicating its suitability for mechanical (load-bearing) application, fatigue limit, hardness, modulus of elasticity, tensile strength, and yield strength.
Megacycle (megahertz) - One million Hertz per second.
Metabolic Processes - The chemical and physical processes continuously going on in living organisms and cells.
Metal - An opaque, lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light. Most elemental metals are malleable and ductile and are, in general, heavier than the other elemental substances.
Metallographic - Pertaining to examination of a metallic surface with the aid of a microscope. The surface is usually polished to make it flat, and may be etched with various chemicals to reveal the microstructure.
Metallography - the science dealing with the constitution and structure of metals and alloys as revealed by the unaided eye or by such tools as low powered magnification, optical microscope, electron microscope and x-ray diffraction.
Metallurgy - The science and technology of metals.
Metal Smear - When defects that are normally open to the surface are partially or completely be covered over.
Mev - One million electron volts.
Micro - A prefix that divides a basic unit by one million.
Microfissure - A crack of microscopic proportions.
Micrograph - A graphic reproduction of the surface of a prepared specimen, usually etched, at a magnification greater than ten diameter. If produced by photographic means it is called a photomicrograph ( not a microphotograph).
Microhardness - The hardness of microscopic areas or of the individual microconstituents in a metal, as measured by such means as Tukon. Knoop or scratch methods.
Microscopic Stresses - Residual stresses which vary from tension to compression in a distance (presumably approximating the grain size) which is small compared to the gage length in ordinary strain measurements. Hence not detectable by dissection methods; they can sometimes be measured by x-ray shift.
Microsegregation - Segregation with a grain, crystal or small particle. Also called coring.
Microshrinkage - A casting defect, not detectable at magnifications lower than ten diameters, consisting of interdendritic voids. This defect results from contraction during solidification where there is not an adequate opportunity to supply filler material to compensate for shrinkage. Alloys with a wide range in solidification temperature are particularly susceptible.
Microstructure - The structure of polished and etched metals as revealed by a microscope at a magnification greater than 25-50 times.
Milli - A prefix that divides a basic unit by one thousand.
Milliampere - Unit of electric current equal to one thousandth of an ampere.
Milliroentgen - One thousandth of roentgen.
Miniature Angle Beam Block - A specific type of reference standard used primarily for the angle beam method, but also for straight beam and surface wave tests.
Misruns - Appears as prominent darkened areas of variable dimensions with a definite smooth outline.
Mode - The manner in which an acoustic wave is propagated, as characterized by the particle motion in the wave (shear, Lamb, surface or longitudinal).
Mode Conversion - The change of ultrasonic wave propagation mode upon reflection and/or refraction at an interface.
Mode of Vibration - Type of wave motion. Three common modes used in ultrasonic testing are longitudinal, transverse and surface wave.

Modification - The treatment of a aluminum silicon alloys in the molten state with a small percentage of an alkaline metal or salt, such as sodium fluoride, to change the size and shape of the silicon particles in the solid metal.

Modulation Analysis - An instrumentation method, which separates desirable from undesirable frequency signals from the modulating envelope of the carrier frequency signal. - Test sample must move at constant speed.

Modulus of Elasticity - A measure of the stiffness of a metal in the elastic range. The degree to which a metal will deflect when a given load of imposed on a given shape. Also called Young’s modulus.

Mold - A form or cavity into which molten metal is poured to produce a desired shape. Molds may be made of sand, plaster or metal and frequently require the use of cores and inserts for special applications.

Molecule - A Combination of two or more atoms held together by chemical bonds.

Momentum - The linear momentum (p) of a body is the product of its mass (m) and its velocity (v), i.e. p=mv.

Monitoring - Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination present in an occupied region.

Multi-Frequency Techniques - These kind of techniques simply involve collecting data at several different frequencies and then comparing the data or mixing the data in some way.

Multiaxial Stresses - Any stress state in which two or three principal stresses are not zero.

Multidirectional Magnetization - Two or more separate fields, having different directions can be imposed upon a part sequentially in rapid succession. When this is done magnetic particle indications are formed when discontinuities are located favorably with respect to the directions of each of the fields, and will persist as long as the rapid alternations of field direction continue. This, in effect, does constitute two or more fields in different directions at the same time, and enables the detection of discontinuities oriented in all directions in one operation.

Multiple Back Reflections - Repetitive echoes from the far boundary of the test object.

Mutual Inductance - When one circuit induces current flow in a second nearby circuit.