5 - Practical Design of Joints and Attachments

Summary

BACKGROUND

Need for Joints

Joints become necessary in a structure for three main reasons. These relate to production/processing restrictions, the need to gain access within the structure during its working life, and repair of the original structure.

Typical production/processing restrictions arise because of the need for:

1. i. Large and complex structures which cannot be formed in one process thereby needing several components to be joined to produce the completed structure. Considerations that limit process size include exotherm, resin working time, cloth size and “drapability”, and mould accessibility and release limitations.

2. ii. Splitting the load path (and hence the fibre path) around the structure. This typically involves the addition of stiffeners and bulkheads. Generally these out-of-plane elements cannot be formed at the same time as the rest of the structure and so need to be joined to it.

Considering access and repair considerations, if components within the structure require regular servicing then the structural elements that obstruct access need to be joined to the remaining structure in such a way as to allow them to be removed with reasonable ease. If the hidden components require only very occasional treatment (such as removal after a major breakdown) then the structure can be cut out as necessary and treated as a repair. Here the jointing method can be considered to be permanent.