Stretch controlled shading capabilities of special elastomeric silicone films

Abstract

A hitherto unexploited effect: the reversible stretch-induced change of translucency and transparency of certain silicone materials is experimentally investigated with regard to an application in a new type of shading system for biaxial bent, free-form building envelopes. In a first step the silicone raw materials showing the effect are processed into membrane shape and the stretch-dependent optical characteristics of the silicone film samples are examined. Shading effects are measured during cyclic and long term uniaxial tension tests. For multiaxial loading conditions, as appearing in planar biaxial tension tests with cross shaped specimens and bulge tests with inflated circular specimens, optical inhomogeneity effects due to locally varying elongations are documented. Further results concerning a variable transparency depending on the distance of the observer and an object behind the membrane are discussed. A conceptual application of the materials into translucent facades for shading purposes is presented. The closed cavity concept of planar stretched films located between window screens and the implementation of silicone films as inflatable shading structures are discussed. Furthermore, the advantages of silicone films in these kinds of cladding types are pointed out, as typical problems i.e. fogging and high-temperature stability pose no major issue.