Fatigue Considerations in the Development and Implementation of Mechanical Joining Processes for Commercial Airplane Structures

The durability of commercial airplane structures is strongly influenced by build quality and the extent to which assembly processes can be controlled such that the fatigue quality is consistent with that assumed in the design throughout the production life of airplane programs. New developments in assembly technology and the continual quest for manufacturing cost reductions, as well as rising production rate pressures are translating into new, often non-traditional parts and build processes being applied to commercial airplane products. This technological evolution can only take place by exercising close coordination between the structural and manufacturing engineering functions in planning, evaluating, and bringing these parts and processes safely into production. Described in this paper are some of the new processes being used at Boeing Commercial Airplanes to produce metallic and hybrid (composite + metal) assemblies for large commercial transports, viewed from a broad structural engineering perspective. The discussion focuses on two specific mechanical joining technology thrusts: (1) One-up assembly (OUA) and process automation, and (2) assembly using pre-drilled holes at the part fabrication (detail) level. A number of case studies are outlined and considerations such as process selection, control, and qualification, and fatigue characterization are highlighted. This includes a discussion of the trade-offs in fatigue capability between traditional and new methods, including some quality issues that can arise with the new approaches.