Abstract
Background: Despite the emergence of sophisticated technologies in clothing production system, sewing remains common in garment assembling. Seam tensile behaviour is one performance-related topic which has attracted interest for many years, typically involving uni-axial test methods. A more realistic approach in studying seam tensile behaviour was attempted in the present study, and is believed to better represent the in-use condition of a seam. The main aim of this thesis was to investigate the behaviour of stitch type ISO 401 on different seam types in selected workwear fabric using a multi-axial test methods.
Experimental approach: Experiments focused on the effect of different seam types on aspects of tensile behaviour of seamed woven and knitted fabrics. Factors included fabric types, seam direction and seam types.
There were three parts to the study:
Part 1 aimed to determine the effect of stitching a single piece of fabric (termed the primitive seams) on seam tensile behaviour of heavy drill (HD), lighter drill (LD) and single jersey (SJ). Seam types ISO 5.01.01 (one-row of stitching), ISO 5.01.02 (two-row of stitching), and the non-seamed of the original fabric, were studied. The stitching was made on three different seam directions; warp, weft and 45° bias. Analyses included the force-at-break (N), defined as seam strength, and work-to- failure (J) defined as work. Stitch failures prior to fabric failure in the single jersey fabric at relatively low forces needed separate investigation.
Part 2 focused on the cut-and-stitched seams, which involves 'cut-lapped' and 'cut-fold-lapped' seams. Five seam types were investigated; ISO 2.01.02, ISO 2.02.01, ISO 2.04.02, ISO 1.01.01 and seam code S5 (no ISO designation). The fabric and seam direction remained as in part 1. Seam behaviour prior to total seam failure (defined in force (N) at selected time points during the multi-axial load application were analysed (force-at-4s, force-at-6s, force-at-8s). The work-at-4s, work-at- 6s, and work-at-8s, was also analysed. The first-stitch-failure of single jersey was analysed separately.
The objective of part 3 was to investigate the behaviour of seams when subjected to multi-axial cyclic forces at low load (heavy drill was excluded). Three types of selected primitive and 'cut-and-stitched' seams from parts 1 and 2 were used (seam types ISO 2.10.02, and ISO 2.02.01). All specimens were subjected to 5000 continuous loading cycles during which the seams were extended to 8% at the same speed (150mm/min). The first part of the analyses was focused on the seam strength (N) behaviour at different level across 5000 cycles (1, 50, 100, 500 cycles, and at every following 1000th cycle). Pronounced changes in behaviour were noticed at the early stage of the loading cycles. Therefore, an analysis was made to determine the initial behaviour of seam during the first 600 cycles. The seam strength (N) and the percent loss in strength (%) during the first 600 cycles were determined. In order to further investigate the behaviour of the seams at the very early stage of the cyclic loading (which is the stage when the seam was first impacted by multi-axial force), analyses were narrowed to three initial cyclic phases; first cycle, first 20 cycles, and first 50 cycles. The percent loss in strength (%) during the initial stages was determined.
Conclusions: Introducing a seam (stitch type ISO 401) to a fabric has marked effect on the tensile strength of a fabric. Using a multi-axial test method, a simple proposition that the strength of a seam increases with the increasing number of fabric layers in the seam structure was not evident with the cut-and stitched seams selected in this work.
Cyclic testing (extension at 8%) suggested that the behaviour of seam types at low load differed. However, the percent loss in strength across cycles between all seam tested (including non-seamed) were similar. Seam type greatly affected strength at first-stitch-failure, evidenced by significant differences in force-at-first-stitch-failure in single jersey fabric. There was a trend for the increased number of fabric layers in a seam component to be associated with greater strength at first-stitch- failure. The dominant effects of type of fabric in relation to differences in seam tensile behaviour were evident in the investigation of force-at-break and work-at-break, force-prior-to-failure (at 4s, 6s, and 8s), and force-at-8% extension.
In all three parts of the study, the ball burst test apparatus attached to the Instron 4464 tensile tester was used. The application of forces from multi directions by means of the spherical ball simulates the multi-axial forces on an actual seam during use. Furthermore, the surface contact between the spherical ball and the specimen created a compression effect to the tested material, which is a more realistic measurement procedure (in comparison with the non-surface contact of the seamed part with the test apparatus in uni-axial test). The use of factorial experimental designs, a series of preliminary studies prior to the test set up of the actual investigations, and a systematic development of seam construction planned in this study have contributed to improved understanding of seam tensile behaviour.
Recommendations have been included.