A study on a tightening method for optimizing bolt preload distribution in high-precision assembly of curvic couplings for aerospace applications

Non-uniform residual preload in bolt groups can reduce the assembly accuracy and interface-load uniformity of aerospace curvic-coupling structures. This study investigates residual-preload redistribution in a ten-bolt curvic-coupling assembly under different tightening strategies and initial preload levels. An equally sized shaft disk is used as a flat-interface reference structure to isolate the influence of contact-interface morphology from other geometric and material factors. Finite-element simulations are combined with an elastic-interaction framework to compare single-step, two-step, and three-step tightening paths. The results show that the periodic tooth-to-tooth interface of the curvic coupling changes local contact stiffness and load-transfer paths, thereby markedly amplifying bolt-to-bolt residual-preload differences compared with the shaft disk. Although the curvic-coupling structure does not change the basic role of tightening sequence in shaping the relative distribution pattern, it increases the sensitivity of residual preload to loading path and staged tightening. Among the investigated strategies, sequential tightening is not recommended, whereas the dual-axis crisscross strategy provides better preload uniformity. For high-precision assembly, the three-step dual-axis crisscross path of 40%-80%-100% provides the best overall uniformity under the present working conditions. The study clarifies why conclusions obtained from conventional flat-interface bolted joints cannot be directly transferred to curvic couplings and provides process-level guidance for tightening-path design in high-precision curvic-coupling assembly.