Materials and Material Properties flashcards

$\rho =\frac{m}{V}$: density = mass / volume, in g/cm³ or kg/m³ (1 g/cm³ = 1,000 kg/m³). Example: 1,580 g / 200 cm³ = 7.9 g/cm³, typical of steel.

Stress $\sigma =\frac{F}{A}$ (force N / area mm², 1 N/mm² = 1 MPa). Strain $\epsilon =\frac{\Delta L}{L_0}$ (change in length / original length), a unitless ratio.

$E=\frac{\sigma }{\epsilon }$ in the elastic range. It measures stiffness (stress per unit strain), not breaking strength. Steel is about 200 GPa, aluminum about 70 GPa.

No. Hardness resists scratching and denting; toughness absorbs impact energy without cracking. A file or glass is hard but shatters; rubber is soft but tough. Scratch/wear means hardness, shock/blows means toughness.

Ductile: permanently stretched under tension, e.g. drawn into wire. Malleable: permanently flattened under compression, e.g. hammered or rolled into sheet or foil.

Fatigue: cracking from loads repeated many times, even below yield (bending a paper clip back and forth). Creep: slow ongoing deformation under a steady load over time (a plastic shelf sagging).

Hardening: heat then quench fast, making steel hard but brittle. Tempering: reheat to a lower temperature, trading some hardness for toughness. Annealing: heat and cool slowly to soften it.

When two different metals are electrically connected in an electrolyte such as salt water. The more active metal (zinc, aluminum) corrodes faster; the more noble one (copper, stainless) is protected.