Characterising mechanics of deployable coilable tape-springs

Abstract

Deployable structures play a vital role in a variety of applications such as aerospace structures, rapid development civil engineering projects, medical devices, reconfigurable robotics and many other engineering applications. Deployable thinwalled booms make use of elastic strain energy during storage and are capable of selfdeploying

to their fully deployed configuration which is an ideal candidate to overcome the bottleneck of limited launch vehicle capacity faced in space applications. In this research, an attempt has been made to characterise the mechanics of tape spring booms which are the simplest form among the coilable booms. Numerical and analytical frameworks are established to investigate the large deformation analysis of deployable coilable tape springs during the flattening process, which is the initial process of coiling. Geometrically non-linear finite element models implemented in Abaqus/Standard are used to characterize the flattening mechanics of isotropic tape springs under compressive deformation. The effects of geometric and material properties on flattening behaviour are investigated through a numerical parametric study. A simple analytical model is developed to predict the stresses and forces during compression flattening, and a good correlation has been found with the numerical study. The tension stabilized coiling behaviour of longer tape booms is then investigated through analytical and numerical studies. A useful analytical model is developed to determine the required minimum tension force to prevent instabilities such as blossoming instability and buckling instability. The influence of varying coiling radius due to the thickness of multiple turns is taken into account in the developed analytical framework. Also, the required minimum torque and power for tension stabilized coiling of tape spring are developed considering energy conservation where the effect of friction is also considered. Coiling of isotropic tape spring booms is simulated in commercially available finite element software Abaqus/Explicit. A good correlation has been found between the numerical and analytical results in terms of the required torque for coiling of longer tape-spring. Furthermore, a novel approach to predict the minimum required tension force to prevent the instabilities is proposed. A numerical parametric study is conducted utilizing this technique in order to study the effect of the coiling ratio on the required tension force. In terms of the bending and tension-dominated regimes, the numerical findings exhibit good qualitative agreement with the established analytical model. Furthermore, a linear trend is observed in the numerical results for the loss of uniqueness region, which is helpful for the development of analytical models.