Sizing tool for complex joints
Joint sizing for aerospace structures focuses predominantly on the static and dynamic mechanical loads, with the relevant safety factors, across the joint in question. The sizing tools used in these mechanical cases define fastener size pitch, edge distances, hole geometry and many other aspects based on an accumulation of standardised test data and are collated within design guides (CMH-17-3, for example), Finite Element packages and standards documents. Beyond the mechanical loading, other requirements on the joint performance including EMC and grounding requirements are layered on top. Satisfying these additional criteria often involves a substantial body of testing to establish the effectiveness of the additional electromagnetic compatibility (EMC) or grounding treatments, in addition to those required to demonstrate no detriment to the mechanical performance. The sizing of these additions to manage EMC aspects are generally taken from a much smaller body of evidence and is often based on the experience of experts in the field, which is then validated in application-specific tests. Currently there is not a specific sizing tool identified that could be used to size the EMC and lightning strike protection (LSP) requirements of a joint of any kind.
In D-JOINTS, the consortium will discuss with the Topic Manager the technologies currently being employed in reference joints and provide design improvements for the innovative joints that will be developed within the D-JOINTS project. A potential new innovative joint solution could include a combined use of Aluminium tufts with Aluminium sprayed surface. Such configuration could result in robust electrical pathways between the metal side of the joint and the composites side of the joint. A similar configuration with copper tufts and embedded copper mesh can also be implemented in the innovative joints, especially in the cases of grounding diverter strip and the CFRP joining straps.