FE Mechanical Glossary
Key terms and definitions for the Mechanical Engineering exam.
Enthalpy
A thermodynamic property equal to internal energy plus the product of pressure and volume. Changes in enthalpy represent heat transfer in constant-pressure processes.
Entropy
A thermodynamic property that measures the degree of molecular disorder in a system. In reversible processes, entropy change equals heat transfer divided by absolute temperature.
Carnot Cycle
An idealized thermodynamic cycle consisting of two isothermal and two adiabatic processes. Represents the maximum possible efficiency for a heat engine operating between two temperatures.
Reynolds Number
A dimensionless number that predicts whether fluid flow will be laminar or turbulent. Defined as the ratio of inertial forces to viscous forces in a fluid.
Stress
Force per unit area applied to a material. Normal stress acts perpendicular to a surface (tension or compression) and shear stress acts parallel to a surface.
Strain
A dimensionless measure of deformation, defined as the change in length divided by the original length for normal strain, or the angular distortion for shear strain.
Rankine Cycle
The ideal thermodynamic cycle for steam power plants, consisting of isentropic compression, constant-pressure heat addition, isentropic expansion, and constant-pressure heat rejection.
Nusselt Number
A dimensionless number representing the ratio of convective to conductive heat transfer across a boundary. Higher values indicate more effective convective heat transfer.
Fatigue
Progressive structural damage that occurs when a material is subjected to cyclic loading below its ultimate tensile strength. Characterized by S-N curves and endurance limits.
Viscosity
A measure of a fluid resistance to shear deformation. Dynamic viscosity has units of Pa-s, and kinematic viscosity equals dynamic viscosity divided by fluid density.
Conduction
Heat transfer through a solid or stationary fluid by molecular interaction without bulk fluid motion. Governed by Fourier law, which relates heat flux to the temperature gradient.
Convection
Heat transfer between a surface and a moving fluid. Can be forced (driven by external means like a pump) or natural (driven by buoyancy from temperature differences).
Thermal Conductivity
A material property that measures its ability to conduct heat. Appears in Fourier law and has units of W/(m-K). Metals have high values while insulators have low values.
Mohr Circle
A graphical representation of the state of stress at a point, showing normal and shear stresses on planes at all orientations. Used to find principal stresses and maximum shear stress.
Von Mises Criterion
A yield criterion for ductile materials that predicts yielding when the von Mises equivalent stress reaches the material yield strength. Accounts for combined multiaxial stress states.
Natural Frequency
The frequency at which a system vibrates when displaced from equilibrium and released without external forcing. Depends on the mass and stiffness of the system.
Damping Ratio
A dimensionless measure of how oscillations decay over time in a vibrating system. A ratio less than 1 is underdamped, equal to 1 is critically damped, and greater than 1 is overdamped.