Engineer General Machinery flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Parallel-axis theorem

Moment of inertia about any axis equals the centroidal moment of inertia plus the area times the square of the distance between axes: I = Ī + Ad².

Coefficient of restitution

Ratio of relative separation speed to relative approach speed of two colliding bodies; e = 1 is perfectly elastic and e = 0 is perfectly plastic.

Truss determinacy rule

A plane truss is statically determinate when members plus reaction components equal twice the number of joints: m + r = 2j.

Goodman fatigue criterion

Failure line relating alternating and mean stress: σₐ/Se + σₘ/Sut = 1/n. Conservative for ductile steels and widely used for shaft design.

Marin endurance limit factors

Se = kₐk_bk_ck_dk_ek_f times the rotary-beam endurance limit; surface, size, load, temperature, reliability, and miscellaneous factors each reduce the ideal value.

Bearing L10 life

Rating life in millions of revolutions at which 90 percent of a bearing group survives: L10 = (C/P)^p, with p = 3 for ball and 10/3 for roller bearings.

Bolt stiffness ratio

Fraction of external tensile load carried by the bolt in a preloaded joint: C = k_b/(k_b + k_m); bolt load equals preload plus C times the external load.

Von Mises stress

Distortion-energy equivalent stress σ′ = √(σx² − σxσy + σy² + 3τxy²); compare with yield strength to predict yielding of ductile metals.

Plane stress principal angles

Principal planes occur at tan(2θp) = 2τxy/(σx − σy); maximum shear planes are 45 degrees from principal planes and carry (σ1 − σ2)/2.

Hall-Petch relation

Yield strength increases as grain size decreases: σy = σ₀ + k/√d. Grain refinement strengthens metal while generally retaining ductility.

Fracture toughness KIC

Critical stress intensity factor for plane-strain crack growth; a material property that sets the allowable flaw size for a given stress level.

Carnot efficiency

Maximum efficiency of any heat engine between two reservoirs: η = 1 − TL/TH, using absolute temperatures. No real cycle can exceed it.

Reynolds number

Inertial to viscous force ratio Re = ρVD/μ. Circular pipe flow is laminar below about 2300 and turbulent above about 4000.

Darcy-Weisbach equation

Head loss in pipe flow hf = f(L/D)(V²/2g). In laminar flow the friction factor f equals 64/Re and is independent of roughness.

Biot number

Ratio of internal conduction resistance to external convection resistance, Bi = hL/k. Values below 0.1 justify lumped-capacitance transient analysis.

Pump affinity laws

For a fixed impeller diameter: flow varies with speed, head with speed squared, power with speed cubed. Diameter trimming follows the same exponents.

NPSH margin

Available net positive suction head must exceed the required value to avoid cavitation; available NPSH falls as suction lift or suction-line loss increases.

Multistage compression ratio

Equal pressure ratio per stage, r = (Pfinal/Pinitial)^(1/n), minimizes total work; intercooling back to inlet temperature is assumed between stages.

Specific speed classification

Ns = N√Q/H^(3/4) ranks impeller shape: low values indicate radial centrifugal impellers, high values indicate mixed-flow and axial impellers.

Taylor tool life equation

Empirical relation VT^n = C between cutting speed V and tool life T; exponent n is about 0.1 to 0.2 for high-speed steel and higher for carbide.

Fillet weld throat

Effective throat of a 45-degree fillet weld equals 0.707 times the leg size; weld strength is computed from throat area times allowable stress.

Carbon equivalent

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 estimates weldability; values above about 0.4 require preheat to avoid hydrogen cracking.

Chvorinov's rule

Solidification time t = B(V/A)², where V/A is volume-to-surface area. Risers must have a larger modulus than the casting they feed.

Presence-sensing safety distance

Minimum distance D = K·T + C, where K is approach speed near 1.6 m/s, T total stopping time, and C a device-specific constant.

ASME Section IX scope

Covers qualification of welding procedures (WPS with supporting PQR) and welders or operators (WPQ); it does not set design stresses.

Penetrameter IQI

Radiographic image quality indicator of wires or holes; its visible image demonstrates achieved sensitivity, with smaller visible features indicating better sensitivity.

Earned value indices

CPI = EV/AC and SPI = EV/PV. A CPI below 1 means cost overrun; an SPI below 1 means the project is behind schedule.

Critical path float

Activities on the critical path have zero total float; delaying them delays project completion, so crashing targets them at least incremental cost.

Capital recovery factor

Converts present worth to an equivalent uniform annual amount: A = P·i(1+i)^n/[(1+i)^n − 1]. Used to compare alternatives on annual cost.

Engineering ethics paramountcy

Engineers must hold public safety, health, and welfare paramount, practice only within competence, and disclose conflicts of interest to affected parties.

Stress concentration factor Kt

Ratio of peak local stress to nominal stress at a geometric discontinuity; applied directly to brittle materials and modified by notch sensitivity for fatigue.

Reciprocating compressor clearance

Volumetric efficiency falls with clearance volume C: ηv = 1 + C − C(P2/P1)^(1/n). High pressure ratio sharply reduces delivered flow.