Eversion of bistable shells under magnetic actuation: A model of nonlinear shapes

We model in closed form a proven bistable shell made from a magnetic rubber composite material. In particular, we incorporate a non-axisymmetrical displacement field, and we capture the nonlinear coupling between the actuated shape and the magnetic flux distribution around the shell. We are able to verify the bistable nature of the shell and we explore its eversion during magnetic actuation. We show that axisymmetrical eversion is natural for a perfect shell but that non-axisymmetrical eversion rapidly emerges under very small initial imperfections, as observed in experiments and in a computational analysis. We confirm the non-uniform shapes of shell and we study the stability of eversion by considering how the landscape of total potential and magnetic energies of the system changes during actuation

On the folding and deployment of tape springs: a large displacements and large rotations rod model with highly flexible thin-walled cross-section

International audienceIn the framework of deployable structures, we focus on the modeling of tape springs, i.e. rod-like elastic bodies with thin-walled cross-section which develop localized folds due to a flattening of the cross-section. A rod model with highly deformable cross-section and few kinematics parameters is derived from a complete shell model, for large displacements, large rotations and dynamics. The simplicity of the model is achieved by introducing an elastica kinematics to describe the changes in the cross-section shape. This model is able to handle the formation of localized folds which can move along the rod line, merge or split, allowing to simulate complex scenarios of folding and deployment

In-situ neutron diffraction study of micromechanical shear failure in an aerospace composite

Glass fibre reinforced polypropylene (GF/PP) composite is a well-established material system for fabricating bistable composite tape-spring (CTS) structure. It is light-weight and multifunctional, and has attracted growing interest in shape-adaptive and energy harvesting systems in defence, civil and especially aerospace engineering. The factors governing its bistability have been well-understood; whist there is limited research concerning the micromechanics and microstructural failure. In this research, we investigate the failure mechanisms of the GF/PP composite. This is achieved by performing in-situ neutron diffraction on composite specimens using the ENGIN-X neutron diffractometer at Rutherford Appleton Laboratory. Shear failures are characterised at both macroscopic and microscopic scales. Elastic and viscoelastic strain evolutions at different levels reveal the micromechanical shear failure. The failure mechanisms are then proposed, which will benefit optimisation of structural design and structural integrity of the CTS in aerospace applications

Time-efficient geometrically non-linear finite element simulations of thin shell deployable structures

Isogeometric analysis of thin shells can provide higher continuity and exact geometric description. It is shown in the existing literature that isogeometric analysis converges with fewer degrees of freedom than C⁰-continuous finite elements that use Langrange polynomial shape functions, but the speed of the solutions has not been previously assessed. In this research, the geometrically nonlinear bending of a thin shell deployable structure, a tape spring is studied, using both NURBS-based and C⁰-continuous finite elements. The complex deformation of a tape spring makes it a perfect case study to compare the computational efficiency of the mentioned techniques. The simulations are carried out in the commercial software ABAQUS and LS-DYNA, and it is found that isogeometric analysis is at least three times slower than the C⁰-continuous finite element methods

In-situ multiscale shear failure of a bistable composite tape-spring

A bistable composite tape-spring (CTS) is stable in both the extended and coiled configurations, with fibres oriented at ±45°. It is light weight and multifunctional, and has attracted growing interest in shape-adaptive and energy harvesting systems in defence-, civil- and, especially aerospace engineering. The factors governing its bistability have been well-understood, but there is limited research concerning the mechanics of structural failure: here, we investigate the shear failure mechanisms in particular. We perform in-situ neutron diffraction on composite specimens using the ENGIN-X neutron diffractometer at Rutherford Appleton Laboratory (STFC, UK), and shear failure is characterised at both macroscopic and microscopic scales. Elastic and viscoelastic strain evolutions at different strain levels reveal the fundamentals of micromechanical shear failure, and their temperature dependency. Multiscale shear failure mechanisms are then proposed, which will benefit the optimisation of structural design to maintain structural integrity of CTS in aerospace applications.ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Science and Technology Facilities Council (STFC), Grant no. RB1910213 Innovate UK, ‘‘Large Landing Gear of the Future: Bistable Composite Technologies’’, Grant no. 113077 EPSRC, "NRFIS", Grant no. EP/P013848/

Micromechanical modeling of deployment and shape recovery of thin-walled viscoelastic composite space structures

The first part of the paper presents an experimental study of the deployment and shape recovery of composite tape-springs after stowage at an elevated temperature. It is found that tape-springs deploy quickly and with a slight overshoot, but complete recovery takes place asymptotically over time. Stowage has the effect of slowing down both the shortterm deployment and long-term shape recovery. The second part of the paper presents a micromechanical finite element homogenization scheme to determine the effective viscoelastic properties of woven composite laminas. This solution scheme is employed in numerical simulations of deployment and shape recovery of composite tape-springs. The proposed micromechanical model predicts both the short-term deployment and long-term shape recovery response with close agreement to the experimental measurements

Micromechanical modeling of deployment and shape recovery of thin-walled viscoelastic composite space structures

The first part of the paper presents an experimental study of the deployment and shape recovery of composite tape-springs after stowage at an elevated temperature. It is found that tape-springs deploy quickly and with a slight overshoot, but complete recovery takes place asymptotically over time. Stowage has the effect of slowing down both the shortterm deployment and long-term shape recovery. The second part of the paper presents a micromechanical finite element homogenization scheme to determine the effective viscoelastic properties of woven composite laminas. This solution scheme is employed in numerical simulations of deployment and shape recovery of composite tape-springs. The proposed micromechanical model predicts both the short-term deployment and long-term shape recovery response with close agreement to the experimental measurements