Franck Cevaer

Conceptual Design and Analysis of a Deployable Structure with Flexible Joints

The conceptual design of a self-deployable structure with flexible joints is presented in this paper. Joints store elastic energy in the folded, prestressed position and allow deployment until they are stopped by tendons. A study on a wire rope joint is first presented to determine its mechanical behavior with experimental, theoretical, and numerical approaches. An analysis is then performed on a bidimensional structure to propose the specific modeling of introducing prestress to the joints. The method is applied to a spatial system in an analysis that uses static equilibrium and kinematic deployment simulations. The results show good concordance among the different approaches.

Study and construction of a pentagon-based tensegrity ring

ABSTRACT Tensegrity rings are composed of strut circuits and based on straight prism geometry. Recently, authors developed a general study for this kind of structure and discovered their ability of folding. In this paper, we present our recent studies on the pentagon-based tensegrity ring from a mechanical, kinematical and experimental point of view. In term of theoretical study, numerical simulations are carried out. We analyse the influence of the self-stress level and element stiffness (cables and struts) on the global system. In matter of experimentation, we present design of our first human-scaled prototype which provides a remarkable lightness. Finally, we describe the folding of this system with a comparison between experiments and numerical simulations.

Stratégies de mise en précontrainte dans les systèmes de tenségrité et contrôle

ABSTRACT Tensegrity systems are innovative structures, whose stiffness is the result of internal effects occurring at the assembling stage. The chosen method for establishing the initial self-stress depends on design choices and also on the structure scale. The self-stress target is conditioned by the project conditions, and specifically by static and dynamic loads which will be applied on the structure. For the present case, choices that have been made for tensegrity systems design imply a tension control in active elements, with a dynamic procedure. Then a very good knowledge of constitutive laws for the components is essential. At the beginning of the process, a first self-stress state is established by a geometrical control of active element shortening. Then, a self-stress implementation method, based on an identified state, is submitted. Then, once a unitary influence basis has been chosen, the convergence toward the target state is realised by active element shortening. By this mean, final state is close to the target one.

An Event-Driven Algorithm in Dynamics of Multi-contact Systems

This study is in keeping with the general pattern of dynamical simulation of a set of rigid three dimensional bodies submitted to unilateral contact constraints with dry friction. An event-driven algorithm, developed so as to be applied to the folding/unfolding of tensegrity systems, is presented in this paper. Computational results related to the folding process of a tensegrity structure are exposed and commented; these results point out the ability of the numerical model to handle dynamics of multi-contact systems.

Composite profiles and membranes tensegrity panels

ABSTRACT The development of the “non standard” architecture, mainly based on curved surfaces using rigid frames combined with cladding panels, emphasizes on new needs. A lightweight innovative solution has been developed to provide adaptable flat or curved cladding panels fixed on the supporting structure, with thermal insulation and possible prefabrication. The panels are realized with an association of tensile membranes and a woven structure of prestressed composite profiles. They are designed on the principle of tensegrity and provide both properties of flexibility and rigidity. Mechanical studies have been performed to determine the relationships between the panel shape and its initial stresses (“form control” and “force control” strategies) and a FEM analysis allows identifying the behavior in association with experimental testing on a prototype system. In parallel, thermal studies have been initiated to evaluate the performance of this double membrane panel.

Bases d'un modèle numérique de pliage/dépliage de systèmes de tenségrité

ABSTRACT A numerical model is essential for the study of tensegrity systems folding, since complex behaviours like non-interpenetration of solids and unilateral rigidity of cables must be taken into account. A numerical model is presented, it is based on a dynamical formulation and uses an Event driven like method to treat unilateral contact between rigid bodies; this method consists in identifying time intervals over which the status of the various contacts remain unchanged.