Effect of Shape Memory Alloys on the Pressure Capacity of Polymer Composite Pipes

This study presents a novel approach for enhancing the pressure capacity of carbon/epoxy composite pipes by embedding pre-strained NiTi shape memory alloy (SMA) wires within the laminate structure. A three-dimensional finite element model was developed to simulate the thermo-mechanical behaviour of filament-wound composite pipes with a [±55⁰] layup, incorporating SMA helical reinforcements as active secondary actuators. The influence of SMA coil diameter (55–70 mm) and coil pitch (5–20 mm) on the hoop and radial stress responses was systematically evaluated. The SMA behaviour was implemented via a user-defined UMAT subroutine, enabling accurate modelling of phase transformation and recovery effects. The results demonstrate that an optimal configuration with a coil diameter of 70 mm and a pitch of 5 mm resulted in a 20% increase in internal pressure capacity compared to pipes without SMA reinforcement. This enhancement is attributed to the active compressive forces generated by SMA recovery, which effectively counterbalance residual tensile stresses induced during curing and internal loading. The proposed model showed good agreement with experimental trends reported in the literature, confirming its applicability for pressure vessel design optimization using smart materials.