MPPSC SES Mechanical key terms

A second-order tensor that fully specifies the state of stress at a point, giving the traction vector on any plane through that point via its normal direction.

The normal stress acting on a plane where shear stress vanishes; found as eigenvalues of the stress tensor and used to predict yielding or fracture.

An equivalent scalar stress combining the deviatoric stress components, used to predict yielding of ductile metals according to the distortion-energy criterion.

The critical axial compressive load at which an ideal slender column becomes unstable, proportional to flexural rigidity and inversely proportional to the square of effective length.

The ratio of a column's effective length to its least radius of gyration; it decides whether buckling or direct compression governs the column's strength.

A geometric property of a cross-section expressing resistance to bending about a chosen axis, computed as the integral of area times squared distance from that axis.

The ratio of a section's second moment of area to the distance from the neutral axis to the extreme fibre; it converts bending moment directly into maximum bending stress.

The ratio of peak local stress near a geometric discontinuity, such as a hole or fillet, to the nominal stress in the same cross-section.

The stress level a material can endure for a stated number of load cycles before failure; below the endurance limit, steels may survive indefinitely.

A plot of alternating stress amplitude against the number of cycles to failure, used to characterise fatigue behaviour and locate the endurance limit.

An assembly where the shaft diameter slightly exceeds the hub bore, creating radial pressure and friction that transmit torque without keys.

The number of independent inputs needed to define the configuration of a mechanism, obtained from Gruebler's or Kutzbach's criterion using links and joints.

A planar mechanism of four rigid links connected by four turning pairs, whose output motion depends on link lengths and Grashof condition.

The acceleration component of magnitude twice angular velocity times sliding velocity, arising when a point slides along a rotating link.

The frequency at which a system oscillates freely after disturbance, determined by its mass and stiffness distribution.

The condition where excitation frequency approaches a system's natural frequency, producing large amplitude response limited only by damping.

A dimensionless measure of how quickly oscillations decay, comparing actual damping to the critical value that prevents oscillation entirely.

A dimensionless ratio of inertial to viscous forces in a flow, used to classify flow as laminar or turbulent and to scale model experiments.

A dimensionless ratio of inertial to gravitational forces, important in open-channel flow and in hydraulic model scaling with free surfaces.

The thin region adjacent to a solid surface where velocity rises from zero at the wall to the free-stream value, dominating skin friction and separation.

A dimensionless or dimensional index relating pump speed, discharge and head at best efficiency, used to select impeller type and shape.

Net positive suction head: the margin of absolute pressure above vapour pressure at the pump inlet, preventing vapour cavities that cause cavitation damage.

Formation and violent collapse of vapour bubbles in low-pressure liquid regions, producing noise, erosion and loss of pump or turbine performance.

The ideal thermodynamic cycle for steam power plants, comprising isentropic pumping, constant-pressure heat addition, isentropic expansion and constant-pressure condensation.

The ideal gas-turbine cycle of isentropic compression, constant-pressure heat addition, isentropic expansion and constant-pressure heat rejection.

A thermodynamic property equal to internal energy plus the product of pressure and volume, conveniently expressing heat transfer in steady-flow constant-pressure processes.

The maximum useful work obtainable from a system as it reversibly reaches equilibrium with its environment; destroyed by irreversibilities such as friction and finite-temperature heat transfer.

The effective driving temperature difference for a heat exchanger, computed from inlet and outlet stream temperatures and used in the overall heat-transfer equation.

A combined conductance relating total heat flux to bulk temperature difference, incorporating conduction through walls and convection on both sides.

A dimensionless ratio of convective to conductive heat transfer across a fluid layer, correlating convection coefficients with Reynolds and Prandtl numbers.

The ratio of internal conduction resistance to external convective resistance in a solid, indicating whether lumped-capacitance analysis is acceptable.

An empirical relation stating cutting speed times tool life raised to an exponent equals a constant, used to select speeds for economic machining.

A force diagram for orthogonal metal cutting relating cutting force, thrust force, shear angle and friction angle at the tool-chip interface.

The fractional change in electrical resistance of a strain gauge per unit strain, quantifying its sensitivity in experimental stress analysis.

A network scheduling technique identifying the longest duration path through project activities, which determines minimum project completion time and float of other activities.

A systematic examination of method and time to improve productivity, comprising method study and work measurement.

A hardenability test where a standard bar is quenched at one end and hardness measured along its length, revealing how deeply martensite forms.

A post-quenching heat treatment at sub-critical temperature that reduces brittleness and relieves internal stress while adjusting hardness and toughness.

Heating steel above its critical temperature to form austenite, the necessary first step before quenching or normalising to develop desired microstructure.