Influence of bias angle of stitching on tensile characteristics of lapped seam parachute canopy fabric – Part I: Mathematical modelling for determining test specimen size

This study embodies evaluation of ideal test specimen dimension for the study of tensile characteristics of lapped seam parachute canopy fabric. Due to anisotropic nature of textile fabrics, the mechanical property of unseamed and seamed fabric changes with the change in specimen test direction. Therefore, measurement of tensile property at different bias angle (an acute angle between warp and specimen length/test direction) becomes more important in parachute canopy where joining of its various parts is not only in principle direction but also at different bias angle. The present paper deals with the influence of bias angle of stitching on breaking strength and elongation of unseamed and lapped seam parachute canopy fabric using test specimen dimension based on previous practice. Present study reveals that there is need of re-specification of specimen dimension for evaluation of tensile properties of parachute fabric. With the changes in angle of bias, width and gauge length of test specimen, the number of different category of warp and weft yarns available between the specimen grip lines changes and can be calculated mathematically. This has important role in affecting the ultimate properties of parachute fabric. Based on the study, an optimized dimension of test specimen has been postulated for evaluation of tensile characteristics of parallel/opposite stitched specimen through which reliable test result can be obtained. The proposed dimension can be used for comparative analysis of breaking strength and elongation of unseamed and seamed fabric at different bias angle.