BIAXIAL TENSILE TESTER FOR FABRICS

The overall goal of the program is the development of an instrument for determining the stress-strain response of coated fabrics used in the construction of air-supported tents. During Phase I of the program a survey of the scientific literature on biaxial tensile testers was carried out. The purpose of the survey was to examine the design features and operating techniques of previously constructed testers and to note design innovations and shortcommings. A theoretical analysis of the load-extension behavior of idealized plain-weave fabrics subjected to biaxial stresses is presented. Fabric strains resulting from both crimp interchange and yarn extension are considered. The analtyical expressions derived have been solved with the aid of a digital computer for both linearly elastic and elasto-plastic materials. Time effects, although not explicitly included, are discussed. Generalized plots of the results are given for the two extremes of initial fabric structure 1 equal crimp distribution in both sets of yarns 2 one set of yarns straight noncrimped. The predicted and measured response of two model fabrics are compared. Two typical coated fabrics representing approximately the extremes in fabric weight and strength currently of interest for air-supported tent applications were evaluated. The design of an improved biaxial tensile tester is outlined. The proposed design concept utilizes the results of the literature survey, model fabric study and coated fabric evaluation.