Numerical Modelling of Lightweight Deployable Structures

Researchers

Lee Wilson
Sergio Pellegrino

Description

Thin-film structures are an important component of many lightweight space systems, including deployable sunshields, inflatable structures and especially gossamer spacecraft that utilise solar sails.  One key feature all these applications share is the need to be packaged into a tight configuration for launch, and this introduces a large number of creases into the film.  These creases can greatly affect the film properties and how it behaves once in space.  Of particular interest are the loads required to package and deploy these systems, and their final shape once deployed.

Above: Wrapping and unwrapping simulation of a thin-film sheet around an eight sided hub.  The black lines represent creases that allow the film to fold.  However, during folding the thin-film must also bend and buckle, which requires finite element analysis software to capture.

Above: Wrapping and unwrapping simulation of a thin-film sheet around an eight sided hub.  The black lines represent creases that allow the film to fold.  However, during folding the thin-film must also bend and buckle, which requires finite element analysis software to capture.

Creased or origami-inspired structures are often modelled as rigid panels joined by hinges.  This allows kinematics to be studied, but breaks down as the material becomes more flexible.  Alternatively, other solar sail simulations have treated the film as an assembly of springs, rods and point masses.  To gain a detailed understanding of the underlying behavior, models need to incorperate film bending stiffness and all the contact inherent in elastic origami structures.  Here we are taking a more detailed approach, and model the thin-film with shell elements in finite element packages such as LS-Dyna and Abaqus.  The creases are treated as lines of zero-bending stiffness.  We then use forces and boundary conditions to fold elastic origami structures such as solar sail models.  With this approach we can capture the contact during folding and deployment, the structural equilibrium configurations during deployment, as well as predict the forces required to deploy and unfold the structure.