Abstract
While the suitability of leather for outerwear has been the subject of several New Zealand-based studies, investigations into the influence of seams on the tensile behaviour of leather have been limited. Seams are an important structural component in garment production, and although other means of joining exist, stitched seams remain fundamental to the process of garment construction. Demands on a seam will differ according to its placement and/or application, although garments (in use) are typically subjected to low repeated stresses. These stresses include a combination of tensile, bending and shear forces, with failure occurring often in the seam area rather than other areas of a garment (Laing and Webster, 1998). Failure of seams through loss of tensile strength may be unacceptable in terms of aesthetics, and/or may render a garment no longer fit for purpose. Research on the seaming of textiles has been extensively investigated, but not so for leather. As tensile behaviour of seams is important to the overall integrity of a garment, the objective of this study was to investigate the effect of seaming on the tensile behaviour of leather, using New Zealand cervine leather.
The measurement of the stress response of a seam to the application of a known strain (10 mm extension) was investigated over 20 cycles, representing the early stages of ageing. Measurement of stress was carried out by examining multi-axial loading on selected non-seamed, primitive single layer seam (ISO 5.01.01), and cut and stitched double layer seams (ISO 2.01.01) formed in cervine garment leather, representing progressive complexity in seam construction. Test parameters examined included resistance to extension during cyclic loading, loss in strength over the testing period, and work (energy) required to multi-axially extend the leather to a specified extension limit. Factors included specimen direction, seam type, and number of cycles. Stitch ISO 301 (International Organization for Standardization, 1991a), widely used in garment manufacture and typically in the joining of leather, was used for this study. The factorial experimental design enabled several variables (i.e. seam type, cycles, and direction) to be examined simultaneously to determine the main effects on tensile behaviour, as well as the effects of interactions between the factors.
Under the specified test conditions, the addition of a seam did not influence tensile behaviour; both single layer seam ISO 5.01.01 and the more complex double layer cut and stitched seam ISO 2.01.01 did not affect tensile behaviour of the leather specimens differently from the non-seamed specimens under multi-axial loading. Furthermore, there was no evidence to suggest the strength of a seam increased with an increasing number of substrate (leather) layers in the seam. Seamed specimens were observed to be less variable than non-seamed specimens, supporting findings from earlier studies, and suggesting the seam may provide some stability to the leather. Cyclic loading had the most effect on tensile behaviour, indicating this form of ‘ageing’ has the largest influence on tensile behaviour of non-seamed and seamed leather. The most change in tensile behaviour was evident during the first five cycles, and a proportionally large change occurred between the first and the second cycle. Irreversible changes were evident during initial extension to both non-seamed and seamed structures, and reduced energy required to extend the specimen during the second and subsequent cycles. Direction (0°, 90°) was not an important factor in determining force at 10 mm extension over the 20 cycles tested, with similar mean values recorded between the two directions.
The primary objective of this work was to study the effect of seaming on the tensile behaviour when subjected to multi-axial forces. The results demonstrated that seaming had little effect on the tensile behaviour of cervine garment leather, irrespective of seam structure and specimen direction, and that cycling (mechanical ageing under laboratory conditions) had the most influence on tensile behaviour.