| Machine |
A mechanism that transmits power in the performance of a useful task. More than one machine in one place, either connected or performing separate functions, is termed machinery. |
| Machine screw |
A relatively small screw, usually less than 20 mm in diameter, with the thread running along the whole length up to the head, intended to be screwed into threaded holes. If inserted through plain holes in assembled parts and held together by a nut, an undesirable contact surface of threads bearing against the surface of a hole results. |
| Machine screw |
A countersunk, slotted screw with machined threads such as are found on bolts. |
| Machine tool |
A powered machine, such as a borer, grinder, lathe, milling machine or planer, used for cutting and shaping metal, plastics, composites, etc. (machining). A machining centre is a CNC machine tool working about several axes, having a stock of tools and automatic tool changing ability, which is capable of diverse machining operations under automated control. |
| Macrodeviation |
Errors from–irregular surface departures from the design profile, often caused by lack of accuracy or stiffness of the machine system. |
| Magnetic materials |
Materials in which the magnetic moment of adjacent atoms can adopt either parallel or antiparallel alignment. Ferromagnetism occurs when the magnetic moments adopt parallel alignment. When adjacent magnetic moments cancel due to antiparallel alignment, the material exhibits antiferromagnetism and has no overall magnetic moment. Examples of the latter include ferrous oxide and manganese oxide. The phenomenon of ferrimagnetism occurs when adjacent magnetic moments adopt antiparallel alignment but have unequal magnitude. The region of ferromagnetic or ferrimagnetic material in which the magnetic moments are aligned is known as a magnetic domain and adjacent regions are separated by domain walls. Diamagnetic and paramagnetic materials exhibit weak forms of magnetism that results from independent (uncoupled) alignment of magnetic atomic dipoles induced by an applied magnetic field. Ferromagnetic and ferrimagnetic materials can acquire high degrees of magnetization in relatively weak magnetic fields. They have different hysteresis characteristics and are classified as either hard magnets or soft magnets. Hard magnets retain large magnetization in the absence of an applied magnetic field and are used as permanent magnets. Conventional materials include magnet steels alloyed with tungsten or cobalt. Rare-earth magnets made from alloys of rare-earth elements produce significantly stronger magnetic fields. The most common of these are samarium-cobalt and neodymiumiron-boron permanent magnets. Their strength allows them to be small and used in numerous applications, including cordless tools, disk drives, headphones, toys, and motors for automotive components such as wipers, fans, washers, and windows. Soft magnets may be magnetized and demagnetized relatively easily. When subjected to an alternating magnetic field the energy loss due to hysteresis is small. Common materials include iron-silicon alloys (known as electrical steels), nickel-iron alloys (permalloy), soft ferrites, and amorphous nanocrystalline alloys, the last of which can be produced in the form of tape by meltspinning. Soft magnets are used to enhance the magnetic flux produced by an electric current. |
| Magnetic test |
Method used to test heat extraction rates of various quenchants. The test works by utilizing the change in magnetic properties of metals at their Curie point–the temperature above which metals lose their magnetism. |
| Major diameter |
On a straight thread, the diameter of the imaginary cylinder that just touches the crest of an external thread or the root of an internal thread. |
| Malleable cast iron |
A cast iron made by prolonged annealing of white cast iron in which decarburization or graphitization, or both, take place to eliminate some or all of the cementite. The graphite is in the form of temper carbon. If decarburization is the predominant reaction, the product will exhibit a light fracture surface, hence, “whiteheart malleable;” otherwise, the fracture surface will be dark, hence, “blackheart malleable.” Ferritic malleable has a predominantly ferritic matrix; pearlitic malleable may contain pearlitic, spheroidite or tempered martensite depending on heat treatment and desired hardness. |
| Manometer |
An instrument used in the measurement of a pressure difference in a fluid (manometry). |
| Maraging steels |
Very high-strength iron alloys named after ‘martensitic’ and ‘aging’. They contain nickel, chromium, cobalt, and molybdenum, and form martensite on air cooling with a strength of about 1 GPa. When reheated to about 500°C and aged for some hours, a room-temperature strength of some 2.4 GPa is reached. |
| Martempering |
(1) A hardening procedure in which an austenitized ferrous workpiece is quenched into an appropriate medium whose temperature is maintained substantially at the Ms of the workpiece, held in the medium until its temperature is uniform throughout–but not long enough to permit bainite to form–and then cooled in air. The treatment is frequently followed by tempering. (2) When the process is applied to carburized material, the controlling Ms temperature is that of the case. This variation of the process is frequently called marquenching. |
| Martensitic stainless steels |
Martensitic stainless steels are hardenable magnetic stainless steels that contain 9–18% chromium, 0.06–1.25% carbon, and typically up to about 2.5% in total of manganese, silicon, nickel, and molybdenum. They can be heat-treated such that martensite is the prime microconstituent, and are usually available in the annealed or quenched-and-tempered condition. They have excellent strength and high hardness, and good corrosion resistance. Uses include cutlery, surgical instruments, rifle barrels, steam turbine tubing and blading, jetengine components, hand tools, machine parts, fasteners, valves, springs, bearings, pump shafts, nozzles, mining equipment, and wear-resistant parts. |
| Mass flow meter |
An instrument, such as a Coriolis flow meter, which measures the mass flow rate of a fluid flowing through a pipe or other duct, rather than its volume flow rate. |
| Mass flow rate (ṁ) (Unit kg/s) |
The mass of a material, usually a fluid or powder, that flows across a surface or through a pipe or other duct per unit time. The corresponding mass flux (ṁ″), with unit kg/s.m2, is the mass flow across a real surface or through a duct, divided by the surface or cross-sectional area A, i.e. ṁ″ = ṁ/A or ṁ″ = ρV where ρ is the material density and V is its velocity normal to the surface. |
| Material velocity |
The velocity of sound in a body (e.g., a bolt). A term used in the ultrasonic measurement of bolt stress or strain. |
| Materials science |
The study of the properties, behaviour, and application of solid substances such as metals, ceramics, glasses, polymers, composites, biomaterials, and semiconductors, at all scales from the atomic to the macroscopic. The topic has its origins in metallurgy. |
| Materials selection |
The process of selecting the most suitable material for a particular application. In the case of solid materials, it involves assessment of candidate materials in terms of their physical properties (density, elastic moduli, fracture toughness, yield strength, hardness, fatigue resistance, coefficient of thermal expansion, thermal conductivity, resistance to thermal shock, creep resistance, corrosion resistance, radiation resistance, etc), and such factors as the function of the final product, its shape, method of manufacture, required tolerances, number to be made, ease of inspection and quality control, cost, and design methodology employed. |
| Maximum allowable operating pressure (Unit Pa) |
The highest pressure at which any pressure system may be operated, usually 10 to 20% below the maximum allowable working pressure. |
| Maximum allowable working pressure (Unit Pa) |
The pressure on which the design of a pressure system is based and the highest pressure at which relief valves should be set. The lowest-rated component in the system typically has a design safety factor of 4. |
| Maximum continuous load |
(maximum continuous rating) (Unit kg/s) The maximum rate of steam output that a boiler can supply for a specified period, usually 24 hours. |
| Maximum load (Pmax) |
(1) The load having the highest algebraic value in the load cycle. Tensile loads are considered positive and compressive loads negative. (2)Used to determine the strength of a structural member; the load that can be borne before failure is apparent. |
| Maximum material condition |
(maximum metal condition) The situation where the volume of a manufactured component corresponds to the upper limit for all toleranced external dimensions, and to the lower limit for all internal dimensions. |
| Maximum stress (Smax) |
The stress having the highest algebraic value in the stress cycle, tensile stress being considered positive and compressive stress negative. The nominal stress is used most commonly. |
| Maximum stress-intensity factor (Kmax) |
The maximum value of the stress-intensity factorin a fatigue cycle. |
| Maximum-and-minimum thermometer |
(minimum-maximum thermometer, Six’s thermometer) A liquid-in-glass instrument designed to register the maximum and minimum temperatures experienced over a given time period. |
| Mean diameter (Unit m) |
The average of the inside and outside diameters for a helical spring or hollow circular cylinder or sphere |
| Mean stress (Unit Pa) |
The average of the maximum and minimum stresses for a material subjected to a stress cycle, as in a fatigue test. |
| Mean value |
The average value of a number of data points. Computed by dividing the sum of all data by the number of data points. |
| Mechanical alloying |
Production of alloys from powders by consolidation, e.g. hotpressing or extrusion, followed by hot and/or cold working and final annealing. Materials such as dispersion-strengthened alloys, high-temperature aluminium alloys, and amorphous alloys can be made in this way. |
| Mechanical efficiency (η) |
1. In general for a machine, the ratio of output work to input work. 2. For a compressor, the ratio of indicated power to shaft power; for a reciprocating engine or an expander, the ratio of shaft power to indicated power. |
| Mechanical energy (Unit J) |
The sum of kinetic energy and potential energy for an object or a mechanical system, including the energy stored in springs, etc. |
| mechanical engineering |
That branch of engineering concerned with energy conversion, stress analysis, vibration, dynamics, and kinematics, especially applied to design (machine design, mechanical-engineering design). |
| Mechanical metallurgy |
The science and technology dealing with the behavior of metals when subjected to applied forces. |
| Mechanical properties of solid materials |
The strength and stiffness properties of solid materials such as fracture toughness, the moduli of elasticity, percent elongation, |
| Mechanical units |
The units of physical quantities, the dimensions of which includemass, length, and time. |
| Mechanical vibration |
The motion of a particle or body which oscillates about a position of equilibrium. |
| Mechatronics |
The integration of mechanical engineering, electrical engineering, electronic engineering, and software engineering. |
| Median fatigue life |
The middle value when all of the observed fatigue life values of the individual specimens in a group tested under identical conditions are arranged in order of magnitude. When an even number of specimens are tested, the average of the two middlemost values is used. Use of the sample median rather than the arithmetic mean (that is, the average) is usually preferred. |
| Median fatigue strength at N cycles |
An estimate of the stress level at which 50% of the population would survive N cycles. The estimate is derived from a particular point of the fatigue life distribution, because there is no test procedure by which a frequency distribution of fatigue strengths at Ncycles can be directly observed. |
| Melting point (Unit K or °C) |
The temperature at which a solid material undergoes the phase change to a liquid at a specified pressure, usually 1 atm. Pure metals and eutectics have single-valued melting points, while alloys with other compositions melt over a range of temperature such that there is a well-defined start and end to the melting process, but there are states in between where solid and liquid are both present. |
| Metallurgy |
The study of the atomic, crystallographic, microstructural, mechanical, and physical properties of metallic elements and alloys and their applications. |
| Metre (m) |
The base unit of length in the SI system. It is equal to the distance travelled by light in vacuum in 1/299 792 458 seconds. |
| Metric ton (tonne, t) |
An SI-accepted, but non-SI, unit of mass defined as 1 t = 103 kg. |
| Meyer hardness (Unit Pa) |
A material hardness similar to the Brinell hardness but based upon the projected area of the impression rather than the surface area. |
| Microhardness |
The hardness of a material as determined by forcing an indenter such as a Vickers or Knoop indenter into the surface of a material under very light load; usually, the indentations are so small that they must be measured with a microscope. Capable of determining hardnesses of different microconstituents within a structure, or of measuring steep hardness gradients such as those encountered in case hardening. |
| Microindentation hardness test |
Hardness test using a calibrated machine to force a diamond indenter of specific geometry, under a test load of 1 to 1000 gramforce, into the surface of the test material and to measure the diagonal or diagonals of the indentation optically. |
| Micrometer |
(micrometer gauge) A mechanical-contact device for the accurate measurement of the length, width, diameter, etc. of an object, the depth of a hole, the height of a step, etc. The usual arrangement is a spindle that is moved by rotation of a thimble, the distance then being read off a vernier scale. |
| Microscopic stresses |
Residual stresses that vary from tension to compression in a distance (presumably approximating the grain size) that is small compared with the gage length in ordinary strain measurements. They are not detectable by dissection methods, but can sometimes be measured from line shift or line broadening in an x-ray diffraction pattern. |
| Microstrain |
The strain over a gage length comparable to interatomic distances. These are the strains being averaged by the macrostrain measurement. Microstrain is not measurable by currently existing techniques. Variance of the microstrain distribution can, however, be measured by x-ray diffraction. |
| Millimetre of mercury |
A non-SI unit of pressure equal to the pressure exerted by a vertical column of mercury 1 mm high. Approximately equal to 133.3 Pa or 1 torr. |
| Millimetre of water |
A non-SI unit of pressure equal to the pressure exerted by a vertical column of water 1 mm high. Approximately equal to 9.81 Pa. |
| Milling |
Milling is a machining process in which metal is removed by a rotating multiple-tooth cutter; each tooth removes a small amount of metal with each revolution of the spindle. Because both workpiece and cutter can be moved in more than one direction at the same time, surfaces having almost any orientation can be machined. |
| Milling |
A machining process, typically for metals and plastics, in which a multi-tooth rotary cutter removes material to produce flat or profiled surfaces, slots, grooves, etc. |
| Minimum load (Pmin) |
In fatigue, the least algebraic value of applied load in a cycle. |
| Minimum material condition |
(minimum metal condition) The situation where the volume of a manufactured component corresponds to the lower limit of all toleranced external dimensions and to the upper limit for all internal dimensions. |
| Minimum stress (Smin) |
In fatigue, the stress having the lowest algebraic value in the cycle, tensile stress being considered positive and compressive stress negative. |
| Minimum stress-intensity factor (Kmin) |
In fatigue, the minimum value of the stress-intensity factor in a cycle. This value corresponds to the minimum loadwhen the load ratio is 0 and is taken to be 0 when the load ratio is ≤0. |
| Minor diameter |
On a straight thread, the diameter of the imaginary cylinder which just touches the root of an external thread or the crest of an internal thread. |
| Minute (min) |
A non-SI unit of time. The conversion to SI is 1 min = 60 s. |
| Mode of failure |
The various ways in which a material can fail when subjected to loading, surface damage, chemical attack, heating, cooling, or radiation, in either isolation or combination. The failure modes include fracture, fatigue, creep, corrosion, erosion, and embrittlement. |
| Modulus of elasticity (E) |
The measure of rigidity or stiffness of a metal; the ratio of stress, below the proportional limit, to the corresponding strain. In terms of the stress-strain diagram, the modulus of elasticity is the slope of the stress-strain curve in the range of linear proportionality of stress to strain. |
| Modulus of resilience |
The amount of energy stored in a material when loaded to its elastic limit. It is determined by measuring the area under the stress-strain curve up to the elastic limit. |
| Modulus of rupture |
Nominal stress at fracture in a bend test or torsion test. In bending, modulus of rupture is the bending moment at fracture divided by the section modulus. In torsion, modulus of rupture is the torque at fracture divided by the polar section modulus. |
| Mohr–Coulomb fracture criterion |
A fracture criterion, primarily for brittle materials, according to which failure occurs when the stress at a point in a material falls outside the envelope created by the Mohr’s circles for uniaxial tensile strength and uniaxial compressive strength. |
| Mohr–Coulomb yield criterion |
A pressure-dependent yield criterion, according to which yielding occurs when the stress at a point in a material falls on the envelope created by the Mohr’s stress circles at yielding for various tests such as tension, shear, and compression that have different components of hydrostatic stress. |
| Mohs hardness test |
A scratch hardness test for determining comparative hardness using 10 standard minerals—from talc (the softest) to diamond (the hardest). |
| Mohs scale |
A scale of scratch hardness originally developed for minerals. |
| Mole (mol) |
The base unit of the amount of substance in the SI system. It was previously defined as the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon-12. From 20 May 2019 it has been defined as the amount of substance containing exactly 6.022 140 76 × 1023 elementary entities. |
| Mole number (N) |
The number of moles in a given mass m of a substance, equal to m divided by the molar mass of the substance. |
| Monotron hardness test |
An obsolete method of determining indentation hardnessby measuring the load required to force a spherical penetrator into a metal to a specified depth. |
| Morse taper |
A self holding, standard taper largely used on drilling tools, drilling machine spindles, and some lathes. |
| Multiple threaded screw |
A screw with two or more threads cut around the periphery of the workpiece to provide an increased lead with a specified pitch. |
