Parametric study of scarf joints in composite structures

Bonded scarf or stepped repairs are used in composite structures when high strength recovery is needed or when there is a requirement for a flush surface to satisfy aerodynamic or stealth requirements. Scarf repairs are complex to design and require the removal of significant parent structure, particularly for thick skins.

A parametric finite element (FE) model has been developed to allow a broad study into the effect of various parameters on the performance of a scarf joint. The stress distribution along the bondline has been investigated, and the sensitivity of peak stresses determined with respect to changes in scarf angle, adhesive thickness, ply thickness, laminate thickness, over-laminate thickness and lay-up sequence. Furthermore, the adhesive stresses resulting from joining matched and mismatched laminates was investigated. The benefit of load by-pass of a repair was also examined using a 3D model of a circular patch. The results of this investigation provide further insight into the stresses that develop in scarf repairs of composite structures under load. This insight may lead to improved design and analysis techniques of scarf joints in composite structures.