Wojciech Gilewski

Smart Metamaterial Based on the Simplex Tensegrity Pattern

In the present paper, a novel cellular metamaterial that was based on a tensegrity pattern is presented. The material is constructed from supercells, each of which consists of eight 4-strut simplex modules. The proposed metamaterial exhibits some unusual properties, which are typical for smart structures. It is possible to control its mechanical characteristics by adjusting the level of self-stress or by changing the properties of structural members. A continuum model is used to identify the qualitative properties of the considered metamaterial, and to estimate how the applied self-stress and the characteristics of cables and struts affect the whole structure. The performed analyses proved that the proposed structure can be regarded as a smart metamaterial with orthotropic properties. One of its most important features are unique values of Poisson’s ratio, which can be either positive or negative, depending on the applied control parameters. Moreover, all of the mechanical characteristics of the proposed metamaterial are prone to structural control.

Self-stress control of real civil engineering tensegrity structures

The paper introduces the impact of the self-stress level on the behaviour of the tensegrity truss structures. Displacements for real civil engineering tensegrity structures are analysed. Full-scale tensegrity tower Warnow Tower which consists of six Simplex trusses is considered in this paper. Three models consisting of one, two and six modules are analysed. The analysis is performed by the second and third order theory. Mathematica software and Sofistik programme is applied to the analysis.

A simple method for the analysis of correctness of FEM formulations

In recent years finite element analysis of shell/plate/beam structures has been of considerable interest and practical importance, mainly due to the growth of shell design in areas such as aerospace, nuclear and off shore engineering. For moderately thick shell/plate/beam theories one or more strain fields must vanish in certain physical regimes (thin structures, inextensional bending, etc.). This ensures that the vanishing constraints are trully met in the finite element discretization. Failure to do so results in problems such as “shear locking”, “incompressible locking”, “parasitic shear”, “stress oscilations”, “zero energy modes”, etc. For derivation of a shell/plate/beam element, one may adopt either the displacement or a multi-field approach. When C-0 elements are used within the framework of the displacement model the formulation is too poor to describe vanishing constraits mentioned above. In order to remove the problem several remedies have been proposed (reduced/selective integration, mode decomposition, substitute strain fields, etc.). All modifications of the standard displacement model commit “variational crimes”. Mathematical analysis of the correctness of modified displacment models is difficult and sometimes not possible or not clear.