Design of Machine Elements (DME) Key Vocabulary Flashcards

A comprehensive vocabulary review set covering essential definitions, concepts, and formulas for Design of Machine Elements (DME) Units 1 through 4.

Adaptive Design

A design approach in which an existing design is adapted without significant modifications, requiring no special design skills.

Development Design

A design process where an existing design is modified to obtain a better machine by applying scientific principles and technical knowledge.

New Design

The creation of an entirely new machine from scratch through the application of scientific laws, principles of mechanics, technical know-how, and creative thinking; also known as an invention.

Analytical Design

A design method carried out purely by mathematical formulas based on material strength and mechanics principles.

Empirical Design

A design method based on empirical relations derived from past experience and existing practice.

Working Stress

The actual stress induced in a machine element under its operational working conditions.

Design Stress

The maximum stress value permitted for a machine element during operation, set by the designer considering all potential modes of failure.

Factor of Safety

The ratio used to keep design stress well below yield stress (for ductile materials, $F.S = \frac{\text{Yield Stress}}{\text{Design Stress}}$) or ultimate stress (for brittle materials, $F.S = \frac{\text{Ultimate Stress}}{\text{Design Stress}}$) to prevent failure.

Kinematic Link

Each part of a machine that moves relative to another part and acts as a resistant body capable of transmitting forces with negligible deformation.

Rigid Link

A kinematic link that undergoes no deformation while transmitting motion, such as a crank or connecting rod.

Flexible Link

A kinematic link that deforms partly in a manner that does not affect motion transmission and transmits tensile forces only, such as belts, ropes, chains, and wires.

Fluid Link

A kinematic link formed by fluid in a receptacle that transmits motion through pressure or compression only, such as in hydraulic presses, jacks, and brakes.

Kinematic Pair

Two machine elements or links in contact with each other whose relative motion is completely or successfully constrained in a definite direction.

Sliding Pair

A kinematic pair connected such that one element can only slide relative to the other, such as a piston and cylinder or lathe tailstock on a lathe bed.

Turning Pair

A kinematic pair connected such that one element can only turn or revolve about a fixed axis of another link, such as a shaft with collars in a circular hole.

Rolling Pair

A kinematic pair connected such that one element rolls over another fixed link, such as ball and roller bearings.

Screw Pair

A kinematic pair connected such that one element turns about another by screw threads, such as a bolt with a nut or a lathe lead screw with a nut.

Spherical Pair

A kinematic pair connected such that one spherical element turns or swivels about another fixed element, such as a ball and socket joint.

Lower Pair

A kinematic pair having surface contact between elements during relative motion, such as sliding, turning, and screw pairs.

Higher Pair

A kinematic pair having line or point contact between elements during relative motion with motion partly turning and partly sliding, such as toothed gearing, belt drives, and cam and follower.

Self-Closed Pair

A kinematic pair mechanically connected together such that only the required relative motion occurs without requiring external force.

Force-Closed Pair

A kinematic pair kept in contact by the action of external forces (such as gravity or spring forces) rather than a mechanical link, such as a cam and follower.

Completely Constrained Motion

Relative motion between a pair that is limited to a definite direction irrespective of the direction of the force applied.

Incompletely Constrained Motion

Relative motion between a pair that can take place in more than one direction depending on the direction of the applied force, such as a circular shaft in a circular hole.

Successfully Constrained Motion

Relative motion between elements that is not constrained by itself but is restricted to a single direction by external means, such as a shaft in a foot-step bearing held down by an axial load.

Kinematic Chain

A combination of kinematic pairs joined such that each link forms a part of two pairs and relative motion between links is completely or successfully constrained.

Mechanism

A kinematic chain in which one of the links is fixed, used for transmitting or transforming motion.

Inversion of Mechanism

The method of obtaining different mechanisms by fixing, in turn, different links in a kinematic chain.

Grashof's Law

A condition for a four-bar mechanism stating that continuous relative motion requires the sum of the shortest and longest link lengths to be no greater than the sum of the remaining two link lengths.

Single Slider Crank Chain

A modified four-bar kinematic chain consisting of three turning pairs and one sliding pair, typically converting rotary motion into reciprocating motion or vice versa.

Double Slider Crank Chain

A kinematic chain consisting of two turning pairs and two sliding pairs, with inversions such as elliptical trammels, Scotch yoke mechanism, and Oldham's coupling.

Welded Joint

A permanent joint obtained by fusing the edges of two parts together, with or without pressure and filler material.

Lap Joint (Fillet Joint)

A welded joint obtained by overlapping two plates and welding their edges, producing a weld cross-section that is approximately triangular.

Butt Joint

A welded joint obtained by placing the main plates edge-to-edge in the same plane.

Throat Thickness

The perpendicular distance from the hypotenuse to the intersection of legs in a fillet weld, calculated as $t = s \times \text{sin}(45^\text{o}) = 0.707\text{s}$, where $s$ is the size or leg of the weld.

Transverse Fillet Weld Strength

The tensile strength of a transverse fillet weld joint, given by $P = 0.707\text{s} \times l \times \text{σ}_t$ for a single fillet and $P = 1.414\text{s} \times l \times \text{σ}_t$ for a double fillet weld.

Parallel Fillet Weld Strength

The shear strength of a parallel fillet weld joint, given by $P = 0.707\text{s} \times l \times \text{τ}$ for a single parallel fillet and $P = 1.414\text{s} \times l \times \text{τ}$ for a double parallel fillet weld.

Pitch (Rivet)

The distance from the centre of one rivet to the centre of the next rivet, measured parallel to the seam.

Back Pitch

The perpendicular distance between the centre lines of successive rows of rivets.

Diagonal Pitch

The distance between the centres of rivets in adjacent rows of a zig-zag riveted joint.

Margin (Rivet)

The distance between the centre of a rivet hole and the nearest edge of the plate.

Major Diameter

The diameter of an imaginary cylinder bounding the crest of an external thread or the root of an internal thread.

Minor Diameter

The diameter of an imaginary cylinder bounding the root of an external thread or the crest of an internal thread.

Pitch Diameter

The diameter of an imaginary cylinder whose surface passes through screw threads where thread width equals space width.

Lead (Screw Thread)

The distance a nut moves parallel to the screw axis during one complete turn, given by $L = n \times p$, where $n$ is the number of starts and $p$ is pitch.

Shaft

A rotating machine element of circular cross-section that transmits power and rotational motion (torque).

Axle

A stationary machine element used to support rotating machine elements, designed to take bending moment only and not used for torque transmission.

Spindle

A short rotating shaft designed mainly for rigidity that takes both torque and bending moment.

Power Transmitted by a Shaft

The work done per second by a shaft, calculated as $P = \frac{2\text{π} N T}{60}$\,Watts, where $N$ is shaft speed in rpm and $T$ is torque in N·m.

Sunk Key

A key fitted half into the key seat of a shaft and half into the keyway of a hub, transmitting torque via shear resistance.

Gib Head Key

A tapered sunk key provided with a projecting head at one end to facilitate easy removal.

Feather Key

A special parallel sunk key fastened to a shaft or hub that permits relative axial movement along the shaft while transmitting torque.

Woodruff Key

An adjustable sunk key in the form of a semi-circular disc of uniform thickness that aligns itself in a semi-circular keyway cut into a shaft.

Saddle Key

A tapered key that transmits power purely through friction, requiring a keyway only in the hub.

Splines

A series of keys formed integral with a shaft that fit into broached keyways of a mating hub, providing a positive drive with axial movement.

Radial Bearing

A bearing in which the primary load acts perpendicular to the axis of rotation of the shaft.

Thrust Bearing

A bearing in which the primary load acts along or parallel to the axis of rotation of the shaft.

Sliding Contact Bearing

A bearing where relative motion between contacting surfaces is sliding, separated by a lubricating oil film.

Rolling Contact Bearing

A bearing where relative motion between surfaces is rolling, achieved by interposing steel balls or rollers between fixed and moving elements.

Journal Bearing

A radial sliding contact bearing where the bearing pressure is normal to the axis of rotation and relative movement is sliding.

Cam

A rotating machine element that imparts reciprocating or oscillating motion to a contacting element called the follower.

Base Circle

The smallest circle that can be drawn tangent to the cam profile.

Trace Point

A reference point on the follower (such as the roller center or knife edge) used to generate the pitch curve.

Pitch Curve

The curve generated by the trace point as the follower moves relative to the cam.

Pressure Angle (Cam)

The angle between the direction of follower motion and a normal to the pitch curve.

Prime Circle

The smallest circle that can be drawn from the cam centre tangent to the pitch curve.

Lift or Stroke

The maximum linear displacement of the follower from its lowest position to its topmost position.

Dwell Period

The period during cam rotation in which the follower remains stationary at rest.

Governor

A device that automatically regulates the mean speed of an engine under varying load conditions by controlling the supply of working fluid.

Watt Governor

The simplest form of centrifugal governor, consisting of a conical pendulum with revolving balls connected by links to a sleeve of negligible mass.

Porter Governor

A dead-weight centrifugal governor formed by adding a central heavy weight load to the sleeve of a Watt governor.

Sensitiveness of Governor

The ratio of the difference between maximum and minimum equilibrium speeds to the mean equilibrium speed, given by $\frac{N_2 - N_1}{N}$.

Hunting

The continuous fluctuation of engine speed above and below the mean speed caused by an overly sensitive governor.

Flywheel

A mechanical reservoir that stores energy during periods of excess supply and releases it when demand exceeds supply, reducing speed fluctuations during each cycle.

Coefficient of Fluctuation of Energy

The ratio of maximum fluctuation of energy to the work done per cycle.

Coefficient of Fluctuation of Speed

The ratio of maximum fluctuation of speed to the mean speed during a cycle, given by $\frac{N_1 - N_2}{N}$.

Rigid Coupling

A coupling used to connect two perfectly aligned shafts that cannot tolerate any misalignment.

Flexible Coupling

A coupling designed to connect shafts while accommodating small amounts of angular or lateral misalignment.

Spur Gear

A cylindrical gear with straight teeth cut parallel to the axis of rotation, used to transmit motion between parallel shafts.

Bevel Gear

A gear with teeth cut on conical surfaces, used for transmitting power between intersecting shaft axes.

Helical Gear

A gear with teeth cut inclined to the axis of rotation, ensuring gradual engagement and smooth, quiet power transmission.

Worm Gear

A gear drive comprising a screw-like worm meshing with a worm wheel, used to connect non-intersecting perpendicular (skew) shafts.

Circular Pitch

The distance between corresponding points of adjacent gear teeth measured along the pitch circle, given by $p_c = \frac{\text{π} d}{T}$.

Module (Gear)

The ratio of pitch circle diameter in millimeters to the number of teeth on a gear, expressed as $m = \frac{d}{T}$.

Diametral Pitch

The number of gear teeth per unit length of pitch circle diameter, expressed as $P_d = \frac{T}{d} = \frac{1}{m}$.

Simple Gear Train

A gear train in which each shaft carries only a single gear.

Idle Gears

Intermediate gears in a simple gear train that change the direction of rotation and adjust center distance without affecting the velocity ratio.

Compound Gear Train

A gear train in which each intermediate gear shaft carries two gears rigidly keyed to it to achieve higher velocity ratios.

Reverted Gear Train

A special compound gear train in which the driver and follower gears are mounted on coaxial shafts and rotate in the same direction.

Epicyclic Gear Train

A gear train in which the axis of at least one gear moves relative to another fixed axis.

Open Belt Drive

A belt drive used for parallel shafts rotating in the same direction, where the driver pulls the belt on the lower tight side and delivers it to the upper slack side.

Crossed Belt Drive

A belt drive used for parallel shafts rotating in opposite directions, where the belt crosses itself between pulleys.

Slip of Belt

The relative motion between pulleys and a belt resulting from insufficient frictional grip, which reduces the driven shaft speed.

Creep of Belt

The slight relative slipping motion caused by elastic expansion and contraction of belt elements as tension changes between tight and slack sides.

Centrifugal Tension

The additional tension induced in a high-speed belt or rope due to centrifugal force, calculated as $T_c = m v^2$.