Design, fabrication, and testing of a multiple-actuation shape memory alloy pipe coupler

Shape memory alloy pipe couplers use the shape memory effect to apply a contact pressure onto the surface of the pipes to be coupled. In the current research, a shape memory alloy pipe coupler is designed, fabricated, and tested. An in-house developed NiTi alloy is used for the coupler. The coupler is initially designed using finite element as well as analytical modeling to accommodate the required actuation temperature and contact pressure properties. The coupling pressure is then measured using strain gages mounted on the internal surface of an elastic steel ring. The thermal actuation response of the coupler is measured under both stressed and stress-free conditions. In addition, the state of anisotropy is investigated in the coupler by characterizing samples in the longitudinal and transverse directions. The NiTi coupler demonstrates a multiple-actuation response and a high contact pressure. The results show no change in transformation temperatures with respect to two perpendicular transverse and longitudinal directions. However, the material can undergo higher transformation strains in the longitudinal direction.