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

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

Multistable Slit Caps

Multistable shells are structures that have more than one stable state of self-stress. We demonstrate for the first time that an initially stress-free, hemispherical cap with isotropic behaviour can gain at least three additional stable shapes and, hence, states of self-stress, if it is sliced partially along a given axi-symmetrical meridian. The usual initial and inverted configurations are only slightly affected by slicing. The other configurations are elicited by extra deformations about the inverted shape, which now performs a pre-stressing role. The experimental results are confirmed by finite-element simulations, and it is shown that initially rotationally symmetric structures can gain three stable configurations. Motivated by this, a simplified analytical approach using Foppl-von Karman plate theory is undertaken to analyse the bistable properties of shallow spherical segments. It is shown that the boundary conditions have a dominating influence on the occurrence of multistability

The flexural mechanics of creased thin strips

Many structures in Nature and Engineering are dominated by the influence of folds. A very narrow fold is a crease, which may be treated with infinitesimal width for a relatively simple geometry; commensurately, it operates as a singular hinge line with torsional elastic properties. However, real creases have a finite width and thus continuous structural properties. We therefore consider the influence of the crease geometry on the large-displacement flexural behaviour of a thin creased strip. First, we model the crease as a shallow cylindrical segment connected to initially flat side panels. We develop a theoretical model of their coupled flexural behaviour and, by adjusting the relative panel size, we capture responses from a nearly singular crease up to a full tape-spring. Precise experiments show good agreement compared to predictions

On the shape of bistable creased strips

We investigate the bistable behaviour of folded thin strips bent along their central crease. Making use of a simple Gauss mapping, we describe the kinematics of a hinge and facet model, which forms a discrete version of the bistable creased strip. The Gauss mapping technique is then generalised for an arbitrary number of hinge lines, which become the generators of a developable surface as the number becomes large. Predictions made for both the discrete model and the creased strip match experimental results well. This study will contribute to the understanding of shell damage mechanisms; bistable creased strips may also be used in novel multistable systems