Madrid PAU Tech & 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

In the elastic range, stress is proportional to strain: σ = E·ε, where E is Young's modulus. It fails above the proportional limit, where plastic deformation begins.

Ductile vs brittle

Ductile materials (low-carbon steel) deform plastically and warn before fracture; brittle ones (cast iron, glass) fracture suddenly with almost no plastic strain, so design must limit tensile stress.

Specific stiffness

Young's modulus divided by density (E/ρ). It measures how well a material resists elastic deflection for a given mass, which is decisive in lightweight structures such as aircraft and bicycles.

Thermoplastic vs thermoset

Thermoplastics soften reversibly when heated and can be remoulded; thermosets cross-link permanently and cannot be remelted. This governs recyclability and joining methods.

Galvanic corrosion

Two dissimilar metals in contact in the presence of an electrolyte form a galvanic cell; the more anodic metal corrodes. Prevention: avoid dissimilar couples, insulate joints, or use sacrificial zinc.

Composite material

A matrix reinforced by fibres or particles. The constituents keep their identities, and the result has high specific strength and stiffness, often anisotropic, as in glass-fibre reinforced polyester.

Static equilibrium equations

For a planar rigid body: ΣFx = 0, ΣFy = 0, and ΣM = 0 about any point. These three equations yield at most three unknown support reactions.

Support reaction types

A roller gives one reaction perpendicular to the surface; a pin gives two (horizontal and vertical); a fixed support gives two forces plus a moment. Excess unknowns make a structure indeterminate.

Method of joints

Truss analysis in which each pin joint is treated as a particle in equilibrium. Members carry only axial force; identifying zero-force members simplifies the calculation considerably.

Bending stress formula

σ = M·y/I, maximum at the extreme fibre. Using the section modulus W = I/c gives σmax = M/W, so a deeper section resists bending far better than a wider one.

Second moment of area

A geometric property of a cross-section about an axis, I = b·h³/12 for a rectangle about its centroid. It measures resistance to bending and appears in deflection and buckling formulas.

Euler buckling load

Critical load for a slender pinned-end column: Pcr = π²EI/L². It falls with the square of length, so long slender members fail by buckling before reaching the yield stress.

Factor of safety

The ratio of failure stress to working stress, n = σf/σw. It must exceed 1 and is chosen according to load uncertainty, material variability, and consequences of failure.

Gear train ratio

The ratio of input to output speed equals the ratio of driven to driving teeth: i = Zdriven/Zdriver. Stage ratios multiply; idler gears reverse direction without changing speed.

Belt drive velocity ratio

Without slip, belt speed is equal on both pulleys, so ω₁r₁ = ω₂r₂. Crossed belts reverse the driven pulley's rotation; open belts keep the same direction.

Mechanical power and torque

Rotary power P = T·ω with angular velocity in rad/s; linear power P = F·v. Efficiency is output power divided by input power and is always below one.

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 links.

Worm gear characteristics

A worm drive gives a large speed reduction in one stage, with ratio equal to wheel teeth divided by worm starts. At small lead angles it is self-locking.

Kirchhoff's laws

The sum of currents entering a node is zero, and the sum of voltage changes around a closed loop is zero. Together with Ohm's law they solve any DC network.

Thevenin equivalent circuit

Any linear two-terminal network can be replaced by a voltage source Vth in series with a resistance Rth. Vth is the open-circuit voltage; Rth is measured with sources deactivated.

Faraday and Lenz laws

An induced emf equals the negative rate of change of magnetic flux, ε = −dΦ/dt. The minus sign means the induced current opposes the change that produced it.

Transformer voltage ratio

For an ideal transformer, Vs/Vp = Ns/Np = Ip/Is. Power is conserved ideally, but copper and iron losses make real efficiency lower than 100 %.

Diode rectification

A diode conducts when forward-biased above about 0.7 V in silicon. A half-wave rectifier passes one half-cycle; a bridge rectifier passes both, doubling ripple frequency.

Universal logic gates

NAND and NOR alone can implement any Boolean function. For example, a NAND with both inputs tied together acts as a NOT gate.

Open vs closed loop

Open-loop control acts without measuring the output; closed-loop control measures it and corrects the error between setpoint and actual value, improving accuracy and disturbance rejection.

PID control action

Proportional action responds to present error, integral action removes steady-state offset, and derivative action damps overshoot. Gains are tuned to balance speed and stability.

PLC scan cycle

The controller reads all inputs, executes the stored program, and updates all outputs, then repeats. This cyclic execution makes behaviour deterministic and repeatable.

Stepper motor step angle

The angular advance per pulse equals 360° divided by steps per revolution. Position is controlled by counting pulses, so simple open-loop positioning is possible.

Robot degrees of freedom

The number of independent joints. Six degrees of freedom allow an end effector to reach a position and any orientation within the workspace.

First-angle projection

A multiview system in which the object lies between observer and plane, so the left-side view is placed on the right of the front view. Standard in ISO and DIN drawings.

Drawing scale

The ratio of drawing length to real length, such as 1:10 for reduction or 2:1 for enlargement. Dimensions always state true size, never measured from the drawing.

Weighted decision matrix

A design-evaluation tool in which criteria carry weights summing to one and each option is scored on the same scale; weighted scores are summed to rank alternatives objectively.