Study on surface configuration control of inflatable structures with SMA actuator

Abstract

Compared to traditional mechanical systems, inflatable structures have the advantage of a much lower cost, weight, and packaging volume as well as more favorable thermal gradient and damping characteristics. However, inflated membrane space structures are faced with many challenges, particularly the need to achieve and maintain precise shape. So the reliable maintenance of the surface precision during the mission life is one of the most important technologies for the demonstration of inflatable structures. In this research, the methodology for maintaining the surface configuration of the inflatable structure using shape memory alloy (SMA) thin film actuators is numerically demonstrated. For the understanding of the nonlinear characteristics of the inflated membrane structures, the numerical algorithm of wrinkling based on Miller-Hedgepeth membrane theory is developed using user material (UMAT) subroutine. Wrinkled area and deformed shape of the inflated membrane structure are investigated by using ABAQUS with UMAT subroutine of wrinkling algorithm. Experiments of inflated cylindrical beam made by Tedlar film are conducted to obtain the load deflection curves at different pressure levels. The wrinkled deformed shape and deflection of inflated cylindrical beam are investigated. To investigate the thermomechanical behaviors of SMAs as an actuator, the numerical algorithm of the 3-D SMA constitutive equations based on Lagoudas model is developed using user material (UMAT) subroutine. For the numerical results, the ABAQUS finite element program has been utilized with UMAT subroutine of the numerical algorithm of SMAs. For the application of thin film of SMA actuator, the general expression of 3-D SMA constitutive equations is modified as plane stress condition. New concept parameters related with thermodynamic energy equation are introduced to describe the specific behaviors of SMA thin film. Thermomechanical behaviors of Ni-Ti shape memory alloy (SMA) ribbon are ex...