Q1: What metallurgical tests diagnose hydrogen cracking?
A1: Scanning electron microscopy reveals "fish-eye" fractures at 5,000× magnification. Thermal desorption spectroscopy detects >2ppm trapped hydrogen. Vickers microhardness mapping identifies HAZ brittleness. The 2018 Genoa bridge failure showed 35ppm hydrogen at fracture origins.
Q2: How distinguish fatigue from overload fractures?
A2: Beach marks indicate cyclic failure; dimpled rupture suggests sudden overload. Striation counting determines crack growth rates (e.g., 10⁻⁹ m/cycle). Macro-etching exposes welding defects invisible to X-rays.
Q3: What digital tools trace counterfeit materials?
A3: Laser-Induced Breakdown Spectroscopy (LIBS) verifies alloy composition in 30s. Blockchain-tracked mill certificates prevent documentation fraud. 3D scanning compares as-built dimensions against specs within ±0.15mm.
Q4: Why do torsion failures create 45° fractures?
A4: Shear stresses peak at 45° to longitudinal axis. Web-flange junctions experience 4× strain concentration. High-speed cameras capture failure propagation at 1,200 m/s. Post-collapse twist >8°/m confirms torsion overload.
Q5: How assess fire-damaged angles?
A5: Pulsed eddy current testing measures residual thickness through scale. Metallographic replication preserves microstructure evidence. Charpy impact tests at -20°C verify ductility loss. ASTM E119 calculations determine residual load capacity.
