Refined biaxial test procedures for the determination of design elastic constants of structural fabrics

Jörg Uhlemann, Duisburg-Essen, Institut für Metall- und Leichtbau, Essen, Germany
Natalie Stranghöner, Duisburg-Essen, Institut für Metall- und Leichtbau, Essen, Germany
Klaus Saxe, Duisburg-Essen, Essener Labor für Leichte Flächentragwerke, Essen, Germany

In today’s structural design practise for textile structures, still one of the most challenging aspects is the determination of material stiffness parameters. The only constitutive law used in practice describes orthotropic linear-elastic stress-strain relations in the two principal directions. The elastic constants are “tensile modulus” and “Poisson’s ratio”. In contrast, the actual stiffness behaviour of architectural textiles is nonlinear and nonelastic. Moreover, the potential high orthotropy of textiles is often not sufficiently covered by the test and evaluation methods available.

This poster presents principles for refined biaxial test procedures that fit the requirements of structural fabrics. As a result, sets of elastic constants for design purposes are determined which ensure a very good correlation between measured and calculated strain on a specific stress level for all common PVC-coated polyester fabrics and PTFE-coated glass fibre fabrics. The application of the principles to anticlastic and synclastic or plane structures is presented. Furthermore, the refined method enables to model the very high transverse strains which are observed especially for glass-PTFE fabrics. Overall, the capability of the refined test and evaluation procedures is also striking evidence that the linear elastic constitutive law can actually be very useful in approximating the stress-strain behaviour of all common architectural fabrics.

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