Manufacture of long spars: Laminate design, experimental trials and non-destructive evaluation

Although an enabler of high-rate manufacture, automated forming of components from flat laminates can result in fibre wrinkling. For the first time, fibre length is demonstrated to be a key driver of wrinkling defects when forming a C-spar with a central recess, at industrial length scales. Three such spars, of equal in-plane stiffness, were manufactured using Single Diaphragm Forming. Two contained standard ply angles (0 degrees, 90 degrees or +/- 45 degrees) including 6 m long 0 degrees fibres but had different stacking sequences, one shown to be formable in short spar trials, the other un-formable. A third spar also had a formable sequence but contained non-standard ply angles (angles other than 0 degrees, 90 degrees or +/- 45 degrees) so that maximum fibre length was less than 0.6 m. Wrinkles occurred in both standard angle spars but did not occur in the non-standard angle case, demonstrating that use of formable, non-standard angle laminates can reduce scrappage of automatically formed aerospace parts, leading to significant time and cost savings in production.

Automated summary

For the first time, the length of the fiber is shown to be a key factor in wrinkling defects during automated forming of components. By using non-standard stacking sequences with shorter fiber lengths, it was demonstrated that wrinkling can be reduced, leading to significant time and cost savings in aerospace production.