• compositi
• Fabric
• modellazione
• Triaxial
• Woven

The objective of this study performed at E.S.A.-ESTEC was to create a faithfull finite element model of Triaxial Woven Fabric and to investigate the mechanical behavior of it.
Triaxial Woven Fabric (TWF) is composed of three set of yarns that interlace at 00 –60 +60 degrees. The ability of TWF to maintain structural integrity even with a very open
construction is unique among textile structures; a particular attraction of this material is that it is almost mechanically quasi-isotropic on a
macroscopic scale, and so it can be used to construct ultra-thin structural elements from a single ply. This feature makes it particularly attractive to designers of spacecraft antennas and the next generation of low cost deployable structures. However the strong influence of the geometrical parameters on the mechanical behavior and the difficulties one has to implement this material in analysis codes is a drawback.
The starting finite element model considered as starting point is a detailed one; it accounts for all the geometrical parameters of the yarn but it is made up of straight elements so it does not account for the real curved slopes that characterize the free parts of the yarn because of the cross regions of the fabric. Moreover the
material definition is linked to Coordinate Systems whose orientation is fixed, so the material properties cannot follow the shape of the yarn itself.
Starting from this, a new finite element model was created introducing improvements in the definition of the yarn geometry, the material
properties and the number of Solid elements used for meshing the surfaces of the yarn. It will be shown in detail how the model is built. Validation was performed by comparing the prediction of the homogenized E1 modulus
of the fabric using different models and test results available from literature.
A comparison between old and new results showed an unclear behavior which needed to be explained through additional tests. It was concluded
that solid element model could have to be even more refined to obtain accurate results. Since such a refinement was not possible in the scope of
this work, a new Shell element model was introduced instead. Simulation of mechanical test showed good agreement with models and test results found in literature. Finally an attempt was made to reduce the degrees of freedom
of a complex TWF model with the use of superelement theory. Mechanical tests were simulated using the superelement TWF models in order to verify this technique. The results will be shown in detail and suggestions for
future work will be made.