Manufacturing feasibility of a bend free ellipsoidal composite pressure vessel using automated fibre placement

Composite pressure vessels are attracting high research interest for their low weight and remarkable structural performance. Suppressing bending in pressure vessels offers increased pressure capacity by enabling the efficient membrane stress state. Variable angle tow (VAT) laminates have been shown theoretically to achieve this stress state in composite ellipsoids. This paper presents steps towards manufacturing such vessels using automated fibre placement (AFP). It was found that the bend free design is suited to tanks with diameters greater than ≈ 1400 mm when considering the VAT limitations of typical AFP equipment. When compared to a perfect ellipsoid, the addition of a polar boss reduced the portion of the tank satisfying the bend free criteria by 29.6 %, but also reduced deformation by 28.9 %. The layup considering overlaps was optimised, and manufacturing simulation and coupon manufacturing trials were used to verify thickness and steering radius predictions and visualise defect formation.