Autofrettage analysis of a fibre-reinforced composite tube structure incorporated with a SMA

By adopting an advanced material design concept that combines a composite with a shape memory alloy (SMA), a structure was developed that not only has the characteristics of the composite, such as high specific strength and an adjustable design, but also the shape memory effect of the SMA. This design method replaces the traditional autofrettage method of pre-stressing and improves the concentration of stress and the structural deficiency of a cylindrical pressure vessel. This research investigated the improvement obtained by adopting this advanced material concept in the design of a tube structure with a thick wall, comparing the application of the SMA laminations in various configurations with specific activation temperatures. A layer-wise linear 3-D elastic analysis model was adopted to explore the displacement and stress conditions of the composite tube combined with the SMA. In the analysis process, the material’s behaviours, such as the change in stiffness after the activation of the SMA and the activated recovery stress, were integrated into the mechanical model of the laminated tube. By further re-computing the overall stress–strain relationship, the reaction of the tube produced by activating the alloy with heat could be analysed. This analysis showed that 20–30% of the shear stress, τxθ, and 7.9% of the hoop stress could be reduced. As for the reduction in the radial and axial stresses, the improvement was relatively insignificant. With regard to the overall efficiency, the advanced material’s structural design concept prevented the delamination condition in the laminates, achieved the objective of autofrettage, and enhanced the load-bearing effectiveness of the tube structure.