Experimental characterization and damage identification of polymeric film constituting stratospheric super pressurized balloons

Abstract

Super-pressure balloons developed by the Centre National d'Etudes Spatiales (CNES) provide a cheap, non-polluting, and quickly operable platform for in-situ measurements at altitudes of up to about 25 km, and for remote sensing of the earth, the atmosphere, and space from regions inaccessible to other means of transport over similar observation periods. They are lifted by a helium-filled, approximately spherical, closed envelope made of a polyethylene terephthalate (PET)-based multi-layer polymeric film. It appears that during working flights, these balloons may sometimes explode prematurely. For this reason, the CNES is carrying out research programme and experiments in order to predict better stability of balloon flight and guarantee a life span corresponding to the technical requirements. In this article, experimental results are presented concerning the identification and characterization of film damage induced by simple and triple wrinkling. The present authors started from microscopic observations of damage involving wrinkles and from unidirectional tensile tests of the damaged film with simple and triple wrinkles. During tensile tests, in order to observe the zone affected by wrinkling, an optical technique was used (electronic speckle pattern interferometry) to measure local strain in the damaged area. The correlation between the strain level in the wrinkles observed during tensile testing and the evolution of damage parameters depending on strain gives the damage parameter in the case of simple and triple wrinkling.