Fatigue crack interaction and propagation in welded aluminum alloy propellant tanks for reusable launch vehicle

This paper investigates the interaction and propagation mechanisms of fatigue cracks in the welded joints of reusable launch vehicle propellant tanks, utilizing a combined FRANC3D/ABAQUS finite element simulation based on fracture mechanics. Three typical defect scenarios, that is, single crack, coplanar double cracks, and non-coplanar double cracks, were systematically modeled to evaluate the effects of loading parameters (stress ratio R ), crack geometry (inclination angle θ, size), and spatial arrangement. Results demonstrate that for a single crack, the stress ratio and inclination angle are the primary determinants of fatigue life. For coplanar cracks, both spacing and relative size critically influence propagation, with coalescence leading to severe life reduction; at a 1 mm spacing, the life of equal-sized double cracks is only 54% of a single crack’s. In non-coplanar configurations, reduced spacing induces a significant shielding effect on smaller cracks, and asymmetric propagation emerges upon loss of symmetry. The developed simulation framework provides a robust tool for damage tolerance assessment and establishes a fundamental theoretical basis for the structural optimization of welded aerospace structures .