La Rioja PAU Tech & Engineering II (UR) flashcards

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

Young's modulus

Slope of the linear elastic part of the stress-strain curve, E = σ/ε. It measures stiffness: a higher E means less deformation for the same applied stress.

Section modulus W

Geometric property W = I/c, where I is the second moment of area and c the distance from the neutral axis to the extreme fibre. Maximum bending stress is σ = M/W.

Euler buckling load

Critical axial load of a slender column: P_cr = π²·E·I/L_e², with L_e the effective length set by end conditions. Valid only when slenderness exceeds the limit value.

Thévenin equivalent circuit

Any linear two-terminal network can be replaced by a voltage source V_th in series with R_th. V_th is the open-circuit voltage and R_th the resistance seen with all sources killed.

Power factor correction

Adding a parallel capacitor bank to raise cos φ from cos φ₁ to cos φ₂, with Q_C = P·(tan φ₁ − tan φ₂). It cuts line current and losses while active power stays the same.

Betz limit

Maximum theoretical power coefficient of a wind rotor, C_p = 16/27 ≈ 0.593. No turbine can extract more than 59.3 % of the kinetic energy of the wind stream.

Carnot efficiency

Upper limit on the efficiency of any heat engine between two reservoirs: η = 1 − T_c/T_h, using absolute temperatures. Real cycles always fall below this value.

PID controller

Control law u = K_p·e + K_i·∫e dt + K_d·de/dt. Proportional action speeds response, integral action removes steady-state error, derivative action damps and reduces overshoot.

PLC scan cycle

Repeating sequence of reading inputs, executing the user program and updating outputs. Scan time is the total duration; a watchdog timer faults the CPU if it is exceeded.

First-angle projection

ISO projection system where each view is placed on the side opposite the observer: top view below the front view and left-side view to its right. Standard in Europe.

Hole basis fit

Fits system where the hole tolerance is fixed at H and the shaft letter sets the type: a–h clearance, j–n transition, p–zc interference. Preferred in ISO design practice.

Critical path method

Scheduling technique where the longest chain of dependent tasks defines the minimum project duration; any delay on the critical path delays the whole project.

Hall-Petch relation

Yield stress increases as grain size decreases: σ_y = σ₀ + k·d^(−1/2). Finer grains mean more grain boundary area obstructing dislocation motion.

Resilience and toughness

Resilience is the elastic energy per volume, σ_y²/(2E). Toughness is the total area under the stress-strain curve to fracture, high when strength and ductility are both high.

Grashof condition

For a four-bar linkage, if s + l ≤ p + q (shortest plus longest link versus the other two), at least one link can rotate fully; otherwise it is a double-rocker.

Grübler mobility formula

Degrees of freedom of a planar mechanism: M = 3·(n − 1) − 2·j₁ − j₂, with n links, j₁ lower pairs and j₂ higher pairs. M = 1 means a single input drives it.

Star versus delta connection

In star, line voltage is √3 times phase voltage and line current equals phase current. In delta, line current is √3 times phase current. Balanced power is √3·V_L·I_L·cos φ.

Buck and boost converters

Switched DC-DC converters. Buck steps voltage down, V_o = D·V_i. Boost steps it up, V_o = V_i/(1 − D), where D is the duty cycle between 0 and 1.

Rankine cycle

Standard steam power cycle with pump, boiler, turbine and condenser. Efficiency rises with higher steam pressure and temperature and with lower condenser pressure.

Energy payback time

Time a generating installation needs to produce the energy consumed in its manufacture and installation. Shorter payback means a better sustainability profile for the technology.

Routh-Hurwitz criterion

Algebraic stability test: build the Routh array from the closed-loop characteristic polynomial. The number of sign changes in the first column equals the number of right-half-plane poles.

Stepper motor step angle

Angular advance per full step, typically 1.8° giving 200 steps per revolution. Position is set by counting pulses, so no feedback sensor is needed for basic positioning.

ISO 129 dimensioning rules

Dimensions state true size regardless of drawing scale, the unit is declared once in the title block, dimension lines are not crossed, and each feature is dimensioned only once.

Ra surface roughness

Arithmetic mean roughness expressed in micrometres. Lower Ra means a smoother, more expensive surface, so it is specified only where the function requires it.

Bill of materials

Itemized list of every component in a product or project, giving reference, description, material, quantity and often unit price. It links design, purchasing and budgeting.

FMEA risk priority number

Failure mode and effects analysis scores severity, occurrence and detection from 1 to 10; their product is the RPN, used to rank failure modes for corrective action.

Ashby performance index

Combination of material properties to maximize for a given design objective, e.g. E/ρ for a light stiff tie-rod or E^(1/2)/ρ for a light stiff bending beam.

Maximum power transfer theorem

A load receives maximum power when R_L equals the source's Thévenin resistance R_th, giving P_max = V_th²/(4·R_th). Efficiency at that point is only 50 %.

Carnot and real plant efficiency

Carnot sets the theoretical ceiling between two temperatures. Real fossil steam plants reach roughly 35–45 % because of irreversibilities and large condenser heat rejection.

PID integral action

The K_i term accumulates past error and drives steady-state error to zero, but it adds overshoot and phase lag, so excessive integral gain can destabilize the loop.

Parametric CAD modelling

Geometry is defined by dimensions and constraints stored as parameters. Changing a parameter regenerates the model and all derived drawings automatically.

Project budget structure

Material and labour give direct cost; add indirect costs as a percentage, then industrial profit, then VAT. The result is the total contract price of the project.