Valencian Community PAU Technology & Engineering II flashcards

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

Allotropic transformation

Change of crystal structure of a solid element with temperature or pressure, as in pure iron: BCC ferrite below 912 °C, FCC austenite between 912 and 1394 °C, BCC delta above.

Yield strength

Stress at which a material begins to deform permanently. Measured at 0.2 % permanent strain (proof stress) when no sharp yield point exists, as in aluminium alloys.

Martensite

Supersaturated, very hard and brittle phase of carbon steel formed when austenite is quenched rapidly and carbon cannot diffuse out; relieved by tempering afterwards.

Brinell hardness

Hardness test pressing a 10 mm tungsten carbide ball with a known load into the surface and measuring the indentation diameter; result expressed as HBW.

Jominy test

Hardenability test quenching one end of a standard cylindrical bar with a water jet and measuring hardness along its length to determine the depth of hardening.

Gear velocity ratio

Ratio of angular velocities of two meshing gears, equal to the inverse ratio of their teeth numbers: i = ω1/ω2 = Z2/Z1. Used to calculate torque and speed.

Euler buckling load

Critical compressive load at which a slender pinned strut buckles: P_cr = π²·E·I/L². Depends on material stiffness, section inertia and length squared.

Bending moment maximum

For a simply supported beam with a central point load P over span L, the maximum bending moment is M = P·L/4 and occurs at midspan.

Mechanical advantage

Ratio between the load and the effort in a machine. For a lever it equals effort arm divided by load arm; ideal machines conserve work.

Triangulation

Use of triangular frames in trusses to make a structure rigid, because a triangle cannot change shape without changing the length of one of its sides.

Ohm's law

Voltage across a resistor equals current times resistance, V = I·R. Combined with P = V·I it allows calculation of power dissipated in any resistive element.

Parallel resistors

Resistors connected across the same two nodes. Equivalent resistance satisfies 1/R_eq = 1/R1 + 1/R2 + …; R_eq is always smaller than the smallest resistor.

Transformer ratio

Relation V1/V2 = N1/N2 = I2/I1 for an ideal transformer. Step-up transformers raise voltage and reduce current, lowering I²R losses in transmission lines.

Zener diode

Diode designed to operate in reverse breakdown at a stable voltage, used as a voltage regulator and reference in power supply circuits.

Operational amplifier gain

Inverting configuration gain is −R_f/R_in; non-inverting gain is 1 + R_f/R_in. Ideal op-amp has infinite gain and input impedance and zero output impedance.

De Morgan's laws

Boolean identities ¬(A·B) = ¬A + ¬B and ¬(A + B) = ¬A·¬B, used to transform NAND into NOR logic and simplify digital circuits.

Closed-loop control

Control system that measures the output with a sensor, compares it with the setpoint and corrects the error, compensating disturbances that open-loop systems cannot handle.

PID controller

Controller combining proportional, integral and derivative action: P reacts to present error, I removes steady-state offset, D damps oscillations by anticipating error change.

PLC scan cycle

Repeated sequence of a programmable logic controller: read all inputs, execute the user program, update all outputs, then repeat continuously at high speed.

GRAFCET

Graphical modelling method for sequential automation using steps, transitions and conditions; directly translatable into ladder logic for a programmable logic controller.

Hysteresis in on/off control

Dead band between switch-on and switch-off thresholds of a two-position controller, preventing rapid chattering of the actuator around the setpoint value.

Thermistor NTC

Temperature sensor made of semiconductor oxide whose resistance decreases as temperature rises; inexpensive and sensitive, used in thermostats and temperature compensation.

Carnot efficiency

Maximum theoretical efficiency of a heat engine between hot and cold reservoirs: η = 1 − T_cold/T_hot with absolute temperatures. No real engine reaches it.

Kilowatt-hour

Energy unit equal to 3.6·10⁶ joules, corresponding to one kilowatt of power used during one hour. Domestic electricity bills are expressed in kWh.

Wind power equation

Power captured by a wind turbine: P = ½·ρ·A·v³·C_p. Because power depends on the cube of wind speed, doubling speed multiplies available power by eight.

Heat pump COP

Coefficient of performance: useful heat delivered divided by electrical work consumed. Values of 3–4 mean each kWh of electricity yields several kWh of heat.

Acid rain

Precipitation acidified by sulphur dioxide and nitrogen oxides from fossil fuel combustion, forming sulphuric and nitric acids that damage soils, forests and buildings.

Project memory

Written document of an engineering project stating objectives, background, calculations, technical annexes and conclusions, justifying the chosen solution.

First-angle projection

ISO orthographic system where the object lies between observer and plane: top view is placed below the front view and the left view to the right.

Drawing scale

Ratio between a dimension on the drawing and the real dimension, such as 1:50. Dimensions written on the drawing always give the real measurement.

ISO fit system

System of tolerances where holes are designated H and shafts h; combinations give clearance, interference or transition fits according to the selected tolerance zones.

Isometric perspective

Axonometric projection with three axes at 120° and equal foreshortening, showing length, width and height in a single view without vanishing points.