Coated woven fabrics for innovative membrane structures: new linear and nonlinear constitutive approaches and in-situ verification
Jörg Uhlemann, Institute for Metal and Lightweight Structures, University of Duisburg-Essen, Essen, GermanyMehran Motevalli, Chair of Continuum Mechanics, Ruhr-University Bochum, Bochum, GermanyJörg Uhlemann, Institute for Metal and Lightweight Structures, University of Duisburg-Essen, Essen, GermanyNatalie Stranghöner, Institute for Metal and Lightweight Structures, University of Duisburg-Essen, Essen, GermanyDaniel Balzani, Chair of Continuum Mechanics, Ruhr-University Bochum, Bochum, Germany
Structural membranes made from coated woven fabrics carry loads only by tensile and low shear forces. This leads to lightweight and sustainable structures. Pairing with the great variety of possible architectural forms promises an excellent perspective for these composite materials in civil engineering applications like wide-span roofs and facades. Membranes could be used even more innovatively when combined with power generation devices. International research is currently undertaken in order to develop flexible photovoltaics (PV) devices to be attached to flexible structural membranes or to use fabrics and their big deformations themselves for power generation, using e. g. piezoelectric effects. In both cases, a precise prediction of strains under various loading situations is fundamental; in the first case, small strains which suit the specifications of the PV devices need to be ensured. In all other cases, the quantitative prediction of even large strains is the basis for the prediction of the possible amount of power that can be generated. The objective of the presented research is to develop new approaches to model the stress-strain behaviour of coated woven fabrics. Up to date, linear-elastic constitutive laws are used as a rough approximation of the actual nonlinear and inelastic material behaviour. Additionally, the stress-strain behaviour of fabrics depends highly on the stress ratio in the principal directions. An improved adjustment of test and evaluation procedures for an enhanced determination of elastic constants for day to day design purposes is the first objective of this research project. The second objective is the development of a new nonlinear elastic constitutive model. The latter is a big step towards the precise simulation of the measured stress-strain paths in all stress ratios and over the complete service stress range. Both approaches will be verified with a novel membrane component test stand which has been developed and will allow for in-situ verification.