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

Abstract

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.

Investigation of the Effects of Different Bias Angles of Stitching on Seam Performance of Wool Suits

“…The anisotropic nature of textile fabric affects the mechanical properties of fabric stitched at different angles [2]. In garment manufacturing, seams that connect fabric layers in different directions are used [3].…”

“…. Although huge amount of work has been done related to seam strength characteristics [2,8,9,10], research on the strength of the seams applied at different angles is very limited [6,7] and work related to the impact of seam bias angles with different stitch densities in the trouser and jacket stitches of wool suits is very limited. This study is more focused on the performance of seams at the crotch area and the arm hole of trousers and jackets of wool.…”

Influence of bias angle of stitching on tensile characteristics of lapped seam parachute canopy fabric – Part II: Study on optimized test specimen dimension

“…As discussed in Part I of this paper that the seam angle directly related with fabric bias angle (an acute angle made between the direction of specimen length and its warp). Therefore measurement of tensile property at different bias angle becomes more important in parachute where the seam angle changes with the change of number of gores and type of constructions [15]. In this respect a study was accomplished for unseamed and seamed specimen at different bias angle using specimen dimension selected by Coplan and Bloch [16].…”

“…Therefore by considering the above mentioned limitations of specimen dimension as suggested by Coplan and Bloch [16], an optimized specimen dimension without any slit was postulated (as mentioned in Part 1 of this paper [15]). Present paper mainly analyses the influence of bias angle of stitching (keeping two fabric components in parallel as mentioned in Part 1 of this paper [15]) on tensile strength and elongation of unseamed and lapped seam parachute canopy fabric using postulated specimen dimension. The findings from the study are expected to be realistic and important in designing and development of parachute fabric.…”

“…On the other hand for the testing of lapped seam, samples are first prepared by cutting a fabric of dimension 219 mm length (including 75 gauge length, extra length of 44 mm for folded part of lap formation and 100 mm length for both top and bottom jaw's grip) and 80 mm width at different bias angle. This fabric sample is then cut at the middle across the length and then joined in parallel [15] by using LSC2 lapped seam with four stitches per cm. The distance between the two stitch lines are kept at 10 mm which is normally used in the joining of panels and gores of parachute canopy.…”