22MnB5 hot-stamped boron steel achieves ~1,500 MPa UTS after forming and in-die quenching. It is the standard B-pillar material in nearly every modern car due to its combination of ultra-high strength, formability at temperature, and cost-effectiveness at automotive volumes.

FCC metals have 12 easily activated slip systems, providing excellent ductility and formability. Unlike BCC metals, they have no ductile-to-brittle transition temperature (DBTT), maintaining toughness even at cryogenic temperatures.

2024-T3 is the classic fuselage skin alloy specifically because of its superior fatigue resistance and damage tolerance (KIC ~37 MPa√m vs ~29 for 7075-T6). While 7075-T6 is stronger, 2024-T3 allows cracks to grow slowly enough to be detected during inspection before catastrophic failure.

HP turbine blades operate in gas temperatures of 1,500°C+, which exceeds the ~1,300°C melting point of nickel superalloys. They survive through a combination of single-crystal metallurgy (no grain boundaries for creep), internal serpentine cooling passages, and thermal barrier coatings (TBC) that provide a ~150°C temperature drop.

Young's modulus is determined by atomic bonding forces and crystal structure — it's an intrinsic material property. All steel grades (mild steel through tool steel) have E ≈ 200 GPa regardless of heat treatment. Yield strength, hardness, and elongation can all be modified by processing and heat treatment.

FKM (Viton) is the standard seal material for fuel and aggressive fluid environments, with chemical resistance to gasoline, diesel, biodiesel, and transmission fluid at temperatures up to ~200°C. EPDM is excellent for weather sealing but swells in fuels. Silicone handles temperature but not fuels. NR has poor fuel resistance.

For a stiff beam at minimum weight, CFRP dominates with an index of ~5.4–7.6, and wood (spruce) scores ~7.7 due to its very low density. Aluminum (~3.1), titanium (~2.4), and steel (~1.8) are all similar and significantly lower. This is the beam-bending index E^(1/2)/ρ, which differs from the simple specific stiffness E/ρ.

Fatigue is responsible for an estimated 80–90% of all structural failures. Components fail under repeated cyclic loading at stresses well below the static yield strength. This is why fatigue testing (S-N curves, strain-life analysis) and fatigue-resistant design are critical in automotive, aerospace, and virtually all mechanical engineering.

A wing skin's primary loads are spanwise bending (carried by 0° plies along the span) and torsion from aerodynamic loads (carried by ±45° plies). The 10% 90° plies provide minimum transverse load capability and prevent splitting. A quasi-isotropic layup would use 25% in each direction, which is less efficient than this tailored design.

Eddy current testing is the standard for detecting fatigue cracks around fastener holes in aluminum. It can detect subsurface cracks without removing fasteners, is fast, portable, and works on non-ferromagnetic materials. Magnetic particle inspection doesn't work on aluminum (non-ferromagnetic). Radiography is poor at detecting tight planar cracks. Liquid penetrant only finds surface-breaking cracks and requires fastener removal.