Joining metal/composite structures

The interference-fit bolted joining of hybrid metal/composite can greatly improve the fatigue life of such joints, according to Chinese researchers.

Joints represent potential weak points in the structure, and the design of the overall structure tends to follow from the design of the joint. Metal/composite joints are prevalent in current aircraft structure. Some of the reasons for lower joint efficiency in composites include: brittleness, which means little stress relief around the highest loaded holes; anisotropy, which leads to higher stress concentration factors; low transverse strength; susceptibility to delamination; and sensitivity to environmental conditions.

All of these factors, together with the complexity of composite failure modes, make the analysis and design of composite joints far more complex than that of metallic joints. Fatigue failure is the root cause that makes aircraft unserviceable, and 75-80% of fatigue failures occur in the joints of structures. Therefore, researching joints is very important for improving aircraft life.