Load sharing ability of the liner in type III composite pressure vessels under internal pressure

In this work, the load sharing ability of metallic liners in type III composite overwrapped pressure vessel was investigated by means of accurate numerical models based on finite element method in order to realistically represent the hybrid metal-composite structure. The varying thickness of the composite layers throughout the dome, as well as their angles, were accounted for in the model. The study focused on the influence of material properties and liner-to-composite thickness ratio on the stress and strain distribution between liner and composite at the cylindrical, dome, and polar boss regions. Two novel concepts for the evaluation of the structural response of a composite overwrapped pressure vessel were introduced, namely: (i) the liner stress and strain fractions, and (ii) the correlation with liner-to-composite thickness ratio. The results show complex overall behavior close to the onset of plasticity of the liner, which is critically investigated. A decrease in liner stress fraction was found for higher internal pressure loads since the stress field is increasingly dominated by the composite overwrap. Also, the von Mises equivalent stress along the longitudinal profile of the structure showed a peak at the dome of the liner, whereas for the composite, the peak was at the shoulder region. This was justified considering that, at low pressure, the liner operates elastically in compression-tension mode and the composite in tension-tension mode.