FALSTAFF flight load spectra History of engineering & technology Technology: general issues Titanium alloys XFEM analytical framework crack closure crack growth discontinuous displacements fatigue fatigue crack fatigue crack growth fatigue damage fatigue life prediction fracture analysis height digital image correlation helicopter flight load spectra high-temperature fatigue investment casting lattice structures metallic materials metallography nickel-based superalloy nonstationary random loadings optical profilometry plasticity power spectral density (PSD) random loading random loadings repair welding thermal shock