Galicia PAU Technology and Engineering II flashcards

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

Hooke's law

Within the elastic range, stress is proportional to strain: σ = E·ε, where E is Young's modulus. The relationship holds up to the yield strength of the material.

Ductile-brittle transition

Temperature range in which a material changes from ductile to brittle fracture behaviour. Body-centred cubic steels show it clearly; Charpy impact tests reveal the transition temperature curve.

Martensite

Hard, brittle phase formed when austenite is quenched quickly and carbon is trapped in a distorted lattice. Tempering after quenching restores toughness at some cost in hardness.

Brinell hardness test

A hardened steel ball is pressed into the surface under a known load; the indentation diameter gives HB. Suited to coarse or heterogeneous materials such as grey cast iron.

Static equilibrium

A body at rest satisfies ΣF = 0 and ΣM = 0. Reactions are obtained from the free-body diagram: pin support gives two unknowns, roller one, fixed support three.

Bending stress formula

σ = M·y/I, maximum at the outer fibre y = c. For a rectangular section I = b·h³/12, so stress depends on the section's second moment of area.

Euler buckling load

Critical compressive load Pcr = π²·E·I/(k·L)². The effective-length factor k is 1 for pinned-pinned, 0.5 for fixed-fixed and 2 for a cantilever column.

Grashof condition

A four-bar linkage has at least one fully rotating link when shortest plus longest link is less than or equal to the sum of the other two link lengths.

Gear train ratio

For meshing gears the speed ratio equals the inverse tooth ratio: i = ωin/ωout = zout/zin. Torque increases by the same factor that speed decreases, minus losses.

Kirchhoff's laws

Current law: sum of currents at a node is zero. Voltage law: sum of voltages around a closed loop is zero. Together they solve any linear DC network.

Impedance in AC circuits

Z = R + j(XL − XC), with XL = 2πfL and XC = 1/(2πfC). Resonance occurs when XL = XC; impedance is then purely resistive and current is maximum.

Three-phase power

In a balanced system P = √3·VL·IL·cos φ, where cos φ is the power factor. Star connection relates line and phase voltage by VL = √3·Vphase.

Thyristor (SCR)

Four-layer semiconductor that conducts only after a gate pulse and turns off when anode current drops below the holding value. Used in controlled rectifiers and AC power control.

De Morgan's theorems

Boolean identities ¬(A·B) = ¬A + ¬B and ¬(A + B) = ¬A·¬B. They allow logic expressions to be converted between NAND, NOR and AND-OR forms.

NTC thermistor

Resistor whose resistance decreases as temperature rises, because more charge carriers are released. Used in temperature sensing and inrush current limiting circuits.

Closed-loop control

The controller compares the measured output with the setpoint and acts on the error e = r − y. Feedback reduces sensitivity to disturbances and reduces steady-state error.

PID controller

Control law u = Kp·e + Ki∫e dt + Kd·de/dt. Proportional action gives fast response, integral action removes offset, derivative action damps overshoot and improves stability.

PLC scan cycle

Repeating sequence: read all inputs, execute the user program, update all outputs. Scan time affects response speed; ladder logic contacts and coils are evaluated in order.

Servo motor

Motor with position or speed feedback, usually an encoder, driven in closed loop. It provides accurate positioning and high torque at low speed for robot joints and axes.

Robot repeatability

The spread of positions reached when the same command is repeated. It is usually smaller than accuracy, which is the difference between commanded and actual position.

Pascal's principle

Pressure applied to a confined fluid is transmitted undiminished in all directions. Force multiplication follows F2/F1 = A2/A1 in a hydraulic press.

Hydraulic power

Power transmitted by a fluid is P = p·Q, with pressure in pascals and flow in cubic metres per second. Pump efficiency reduces the power delivered to the actuator.

5/2 directional valve

Pneumatic valve with five ports and two positions, used to extend and retract a double-acting cylinder. In each position it connects one cylinder port to supply and the other to exhaust.

Meter-out speed control

Throttle valve placed on the exhaust line of a cylinder. It gives smooth, stiff control for overrunning loads because the oil or air resists the motion directly.

Cutting speed

Peripheral speed of the tool relative to the workpiece, vc = π·D·n. It depends on material and tool grade; excessive speed shortens tool life through heat and wear.

Micrometer reading

Precision instrument with typical resolution 0.01 mm, reading the barrel scale plus the thimble division. Used for external diameters and thicknesses of small precision parts.

Process capability Cp

Cp = (USL − LSL)/(6σ) compares tolerance width with process spread. Cpk also accounts for centring; values below 1.33 indicate the process is not capable.

Interference fit

Assembly where the shaft is larger than the hole, producing elastic contact pressure that transmits torque without keys. Fitted by press, shrink or expansion methods.

Carnot efficiency

Maximum possible efficiency of a heat engine between hot and cold reservoirs: η = 1 − Tc/Th, temperatures in kelvin. No real cycle can exceed this limit.

Wind power equation

Power available in the wind is P = ½·ρ·A·v³. Because it depends on the cube of wind speed, siting and hub height strongly affect the output of a turbine.

Heat pump COP

Coefficient of performance COP = Qh/W, typically 3-4 for domestic heat pumps. A value above 1 means more heat is delivered than electrical energy consumed.

Life-cycle analysis

Assessment of environmental impacts of a product from raw material extraction through manufacture, use and disposal. It supports carbon footprint and circular economy decisions.