PRC Mechanical Engineer flashcards

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

Lewis form factor

A gear-tooth geometry factor Y used in the Lewis bending equation stress = Wt/(b*p*Y), accounting for tooth shape and the point where load is applied.

Wahl factor

A stress-correction factor for helical springs, Kw = (4C-1)/(4C-4) + 0.615/C, where C is the spring index D/d; it accounts for direct shear and coil curvature.

Bearing L10 rating life

The life in revolutions at which 90 percent of a group of identical bearings survive, computed as L10 = (C/P)^p times 10^6, with p equal to 3 for ball bearings.

Soderberg fatigue criterion

A conservative design line relating alternating and mean stress: sa/Se + sm/Sy = 1/n, where Se is the endurance limit and Sy the yield strength.

Flat belt tension ratio

The ratio of tight-side to slack-side tension in a flat belt drive, T1/T2 = e^(mu*theta), where mu is the friction coefficient and theta the arc of contact in radians.

Uniform wear clutch torque

Torque capacity assuming uniform wear: T = mu*W*n*(ro + ri)/2, where n is the number of friction surfaces and W the total axial clamping force.

Key shear stress

For a rectangular key transmitting torque T on a shaft of diameter d, shear stress is tau = 2T/(d*w*L), where w is key width and L key length.

AISI 1045 steel

A plain carbon steel containing approximately 0.45 percent carbon, commonly used for shafts, gears and axles requiring moderate strength and hardenability.

Taylor tool life equation

V*T^n = C, where V is cutting speed, T tool life in minutes, n an exponent set by the tool material, and C a constant for the work-tool pair.

E6011 welding electrode

A shielded metal arc electrode depositing at least 60 ksi tensile strength, usable in all positions, with a high-cellulose coating for deep penetration on AC or DC.

Normalizing heat treatment

A process that heats steel above its critical temperature and cools it in still air, refining grain structure and relieving internal stresses.

Blanking sheet-metal operation

A shearing process in which the punched-out slug is the desired product, as distinguished from piercing, where the surrounding hole is the product.

Brinell hardness number

HB = 2P/[pi*D*(D - sqrt(D^2 - d^2))], where P is the test load in kgf, D the ball diameter, and d the measured indentation diameter in mm.

Ductile iron

Cast iron in which graphite appears as nodules instead of flakes, produced by magnesium or cerium treatment, giving higher strength and ductility than gray iron.

Rankine cycle efficiency

For a simple steam cycle, efficiency equals [(h1 - h2) - (h4 - h3)]/(h1 - h4), using turbine inlet, turbine exhaust, and pump enthalpies.

Boiler horsepower

A boiler capacity unit equal to evaporating 34.5 pounds of water per hour at 212 F, equivalent to 33,475 Btu per hour or about 9.81 kW.

Cooling tower approach

The difference between the cold water temperature leaving the tower and the entering air wet-bulb temperature; it shows how closely the tower reaches the wet bulb.

Ideal intercooler pressure

For a two-stage compressor with perfect intercooling, work is minimum when the intermediate pressure is the geometric mean of suction and discharge: P2 = sqrt(P1*P3).

Fan affinity laws

For geometrically similar fans at constant air density, volumetric flow varies with speed, static pressure with speed squared, and power with speed cubed.

Diesel cycle efficiency

Efficiency = 1 - [1/r^(k-1)]*[(rho^k - 1)/(k(rho - 1))], where r is the compression ratio, rho the cut-off ratio, and k the specific heat ratio.

Simpson's one-third rule

A numerical integration rule: integral of f dx is about (h/3)[f0 + 4(f1+f3+...) + 2(f2+f4+...) + fn], requiring an even number of intervals of width h.

Binomial probability

P(X = k) = C(n,k)*p^k*(1-p)^(n-k), giving the probability of exactly k successes in n independent trials each having success probability p.

Poisson probability

P(X = k) = e^(-lambda)*lambda^k/k!, giving the probability of k occurrences in a fixed interval when events are independent with mean rate lambda.

L'Hopital's rule

For an indeterminate limit of the form 0/0 or infinity/infinity, the limit of f/g equals the limit of f'/g', provided that latter limit exists.

Cramer's rule

A determinant method for solving linear systems: each unknown equals the determinant formed by replacing its column with the constant vector, divided by the coefficient determinant.

Geometric series sum

The sum of the first n terms of a geometric progression with first term a and common ratio r is a(1 - r^n)/(1 - r) for r not equal to 1.

Effective annual interest rate

i_eff = (1 + i/m)^m - 1, where i is the nominal annual rate and m the number of compounding periods per year; continuous compounding gives e^i - 1.

Capital recovery factor

A = P*[i(1+i)^n]/[(1+i)^n - 1], which converts a present amount P into an equivalent uniform end-of-period payment A over n periods at rate i.

Sinking fund factor

A = F*i/[(1+i)^n - 1], giving the uniform end-of-period deposit required to accumulate a future amount F in n periods at interest rate i.

Double declining balance

An accelerated depreciation method charging a constant rate equal to twice the straight-line rate, applied each year to the remaining undepreciated book value.

Perpetuity present worth

The present value of a uniform payment A received forever equals A/i, valid for a constant positive interest rate i.

Hooke's law

Within the elastic limit, stress is directly proportional to strain, sigma = E*epsilon, where E is the modulus of elasticity of the material.