機械工学の英語

"thermal efficiency"

The ratio of useful work output to heat input in a thermodynamic cycle, expressed as a percentage

"The engineers improved the engine's thermal efficiency from 34% to 41% by redesigning the combustion chamber."

"enthalpy"

The total heat content of a system, equal to internal energy plus the product of pressure and volume

"The technician calculated the enthalpy change across the heat exchanger to determine the required flow rate."

"isentropic process"

A thermodynamic process that is both adiabatic and reversible, with no change in entropy

"For an ideal turbine, engineers model the expansion as an isentropic process to establish maximum theoretical performance."

"heat transfer coefficient"

A measure of the convective heat exchange between a surface and a fluid, expressed in W/(m²·K)

"A higher heat transfer coefficient allowed the cooling fins to be made shorter without sacrificing thermal performance."

"specific heat capacity"

The amount of energy required to raise the temperature of one kilogram of a substance by one kelvin

"Water's high specific heat capacity makes it the preferred coolant in most industrial heat exchangers."

"Carnot cycle"

The theoretical maximum efficiency cycle for a heat engine operating between two fixed temperature reservoirs

"The professor used the Carnot cycle to illustrate why no real engine can convert all input heat into work."

"adiabatic compression"

A compression process in which no heat is exchanged with the surroundings, causing the gas temperature to rise

"During adiabatic compression in the cylinder, the air-fuel mixture temperature increased sharply before ignition."

"latent heat"

The energy absorbed or released by a substance during a phase change at constant temperature and pressure

"Engineers accounted for the latent heat of vaporisation when sizing the boiler for the steam power plant."

"yield strength"

The stress at which a material begins to deform plastically and will not fully recover its original shape

"The design team chose a steel alloy with a yield strength of 550 MPa to ensure the bracket would not permanently bend."

"fatigue failure"

The progressive cracking and fracture of a material caused by repeated cyclic loading below its ultimate strength

"Metallurgical analysis confirmed that fatigue failure, not overload, caused the connecting rod to fracture after 12 million cycles."

"stress concentration factor"

A dimensionless multiplier that quantifies how much a geometric discontinuity amplifies local stress

"The sharp notch at the fillet produced a stress concentration factor of 2.8, triggering premature cracking."

"modulus of elasticity"

The ratio of tensile stress to tensile strain within the elastic region of a material, also called Young's modulus

"Aluminium has a modulus of elasticity of about 69 GPa, roughly one third that of steel."

"fracture toughness"

A material property that describes its resistance to crack propagation under an applied stress

"The pressure vessel specification required a minimum fracture toughness of 50 MPa√m to prevent brittle failure at low temperatures."

"creep"

The slow, time-dependent plastic deformation of a material under sustained stress, especially at elevated temperatures

"Turbine blade material selection prioritised creep resistance because blades operate continuously at over 900 °C."

"Poisson's ratio"

The ratio of lateral strain to axial strain when a material is stretched, characterising its compressibility

"The rubber seal had a Poisson's ratio close to 0.5, meaning it was nearly incompressible under axial load."

"ultimate tensile strength"

The maximum stress a material can withstand before necking and fracture under a uniaxial tensile load

"The bolt material specified an ultimate tensile strength of 800 MPa, providing an adequate safety factor for the joint."

"tolerance stack-up"

The cumulative effect of individual dimensional tolerances in an assembly, which can cause fit or function problems

"The tolerance stack-up analysis revealed that worst-case conditions would prevent the gearbox cover from seating properly."

"surface finish"

The texture and roughness of a machined surface, measured in Ra (average roughness) or similar parameters

"The bearing seat required a surface finish of Ra 0.8 µm to prevent fretting under dynamic loading."

"chip formation"

The process by which material is sheared away from a workpiece during cutting, affecting tool life and surface quality

"Optimising cutting speed and feed rate improved chip formation and reduced built-up edge on the carbide insert."

"die casting"

A manufacturing process in which molten metal is injected under high pressure into a reusable metal mould

"The housing was produced by die casting in aluminium alloy, achieving wall thicknesses as thin as 1.5 mm."

"work hardening"

The increase in hardness and strength of a metal caused by plastic deformation during cold-working operations

"Work hardening during cold rolling increased the tensile strength of the stainless steel strip by 30%."

"geometric dimensioning and tolerancing"

A standardised system (GD&T) using symbols to define the allowable variation in form, orientation, and location of features

"The engineer applied geometric dimensioning and tolerancing to specify the flatness and perpendicularity of the mating flange."

"heat treatment"

A controlled heating and cooling process applied to a metal to alter its mechanical properties such as hardness and toughness

"After rough machining, the shaft underwent heat treatment to achieve a surface hardness of 58–62 HRC."

"electrical discharge machining"

A non-contact machining process that erodes material using controlled electrical sparks between the tool and workpiece

"Electrical discharge machining was used to cut the hardened tool steel die to within ±0.005 mm accuracy."

"Reynolds number"

A dimensionless number that predicts whether fluid flow will be laminar or turbulent, based on velocity, density, and viscosity

"At a Reynolds number of 4,200, the flow in the pipe transitioned from laminar to turbulent, increasing pressure drop significantly."

"cavitation"

The formation and violent collapse of vapour bubbles in a liquid when local pressure drops below vapour pressure

"Cavitation damage on the pump impeller was caused by operating the system well below its design inlet pressure."

"Bernoulli equation"

A relation stating that for steady, inviscid flow, the sum of pressure, kinetic, and potential energy per unit volume is constant along a streamline

"The Bernoulli equation was applied to calculate the velocity of fuel at the carburettor venturi throat."

"hydraulic diameter"

An equivalent diameter used to characterise non-circular cross-sections in fluid flow calculations

"The engineer used the hydraulic diameter of the rectangular duct to determine the appropriate friction factor."

"viscosity"

A measure of a fluid's resistance to shear deformation or flow, important in lubrication and pipe flow calculations

"The lubricant's viscosity dropped sharply at high temperatures, requiring an oil with a higher viscosity index."

"head loss"

The reduction in total fluid energy due to friction, fittings, or valves as fluid flows through a pipe system

"The system curve plotted head loss against flow rate to identify the operating point with the centrifugal pump."

"continuity equation"

A conservation of mass equation stating that the mass flow rate entering a control volume equals that leaving it

"Applying the continuity equation showed that the fluid velocity doubled when the pipe diameter was reduced by half."

"boundary layer"

The thin region of fluid immediately adjacent to a surface where velocity gradients and viscous effects are significant

"The aerodynamicist tripped the boundary layer intentionally to delay flow separation over the wing model."

"gear ratio"

The ratio of the number of teeth on the driven gear to the number of teeth on the driving gear, determining speed and torque change

"A gear ratio of 4:1 reduced the motor output speed from 1,400 rpm to 350 rpm while quadrupling the output torque."

"preload"

A deliberately applied internal force in a bearing or fastener to eliminate play and improve stiffness and fatigue life

"The machine tool spindle bearings were set to a precise preload to minimise deflection during heavy cutting."

"interference fit"

An assembly in which the shaft diameter is larger than the bore, creating a compressive joint that transmits torque without fasteners

"The gear hub was press-fitted onto the shaft using an interference fit of 0.03 mm to transmit high torque reliably."

"backlash"

The small gap between mating gear teeth that allows for thermal expansion and manufacturing tolerances but can cause positioning error

"Excessive backlash in the steering rack caused the driver to feel looseness when reversing the direction of turn."

"dynamic loading"

Forces that vary with time due to vibration, impact, or acceleration, as opposed to static loads

"The gearbox housing was redesigned to withstand dynamic loading from road shocks that caused cracking in the previous version."

"safety factor"

The ratio of a component's failure load to its design load, providing a margin against unexpected overloads or material variations

"A safety factor of 2.5 was selected for the lifting hook to account for impact loads and material variability."

"keyway"

A slot cut into a shaft and hub to receive a key, preventing relative rotation while transmitting torque

"The technician fitted a parallel key into the keyway on the motor shaft to lock the coupling in position."

"torsional stiffness"

The resistance of a shaft or coupling to angular twist per unit applied torque

"Insufficient torsional stiffness in the driveshaft led to resonance at operating speed, causing vibration in the cabin."

"natural frequency"

The frequency at which a system oscillates freely after an initial disturbance, without any sustained external force

"The natural frequency of the pump foundation was 12 Hz, safely above the 8.5 Hz operating speed to avoid resonance."

"resonance"

The condition in which a driving frequency coincides with a system's natural frequency, causing large-amplitude vibration

"Resonance caused the pipe support to fracture after only 200 hours of operation at the new pump speed."

"damping ratio"

A dimensionless measure of how quickly a vibrating system loses energy and returns to rest after a disturbance

"Adding viscoelastic pads increased the damping ratio from 0.02 to 0.08, greatly reducing the settling time of the instrument frame."

"modal analysis"

A technique to determine the natural frequencies, damping, and mode shapes of a structure through experimental or numerical methods

"Finite element modal analysis identified three mode shapes below 500 Hz that could be excited by the compressor harmonics."

"critical speed"

The rotational speed at which a shaft's operating frequency equals its natural frequency, causing potentially destructive vibration

"The turbine rotor was designed to pass quickly through critical speed during start-up to minimise transient vibration amplitude."

"imbalance"

An uneven distribution of mass around the rotational axis of a rotor, causing centrifugal forces that excite vibration

"Field balancing eliminated the imbalance in the fan rotor and reduced bearing vibration from 8.2 mm/s to 1.1 mm/s."

"frequency response function"

A relationship describing the output amplitude and phase of a structure at each frequency relative to a unit input force

"The measured frequency response function showed a sharp peak at 147 Hz corresponding to the first bending mode of the beam."

"harmonic excitation"

A sinusoidal force applied to a structure at a single frequency, the simplest and most common type of dynamic loading

"Harmonic excitation from the rotating unbalance was modelled to predict bearing reaction forces at different operating speeds."