Strain-controlled Biaxial Tests of Coated-Fabric Membranes

A better understanding of the mechanical behaviour of coated fabrics used for architectural membranes can lead to significant improvements in the design of tensile surface structures. The plane biaxial test on a cruciform specimen is considered to be the most appropriate test to characterise the complex non-linear behaviour of such membrane material. The biaxial tests described in the literature are usually carried out under prescribed stress histories at various, constant stress ratios. The present contribution describes some strain-controlled biaxial tests carried out at Politecnico di Milano, in which the strains in the central square of the specimen are prescribed. Such tests can be particularly meaningful in relation to installation and re-tensioning processes. Since they imply a variable stress ratio, the results obtained by these non-traditional tests complement the ones of stress-controlled experiments. It appears that these two types of biaxial tests can be exploited jointly in order to select and calibrate constitutive models for coated fabrics; these are needed for the overall modelling of tensile structures, with the aim of simulating both the response under external loadings and the installation process.