The opening behavior of lockstitch seams (seam type 1.01.01, SSa-1, stitch type 301 ) under cyclic loading conditions has been analyzed, using models of the slippage of yarns in the fabric and the deformation of the stitch itself. The extension properties of the sewing thread under constant cyclic loading conditions were included by using an empirical formula to predict the maximum strain in terms of the applied load and its number of repetitions. Similarly, an empirical formula was used to predict the amount of yarn slippage in woven fabric, in terms of the applied load and its number of repetitions. This formula was obtained from experiments in which the sewing threads in a lockstitch seam were replaced by pins. These results were combined to provide a method for predicting the deformation of a stitch under cyclic loading conditions. The amount of seam opening actually occurring was measured experimentally under different conditions and compared with the calculated values. Reasonable agreement was obtained, with the model explaining the influence of thread properties, stitch density, thread consumption, applied load, and the number of loading cycles. The model was therefore effective in predicting seam opening behavior under cyclic loading conditions. Seams are essential to the construction of clothes and other textile goods. In general they are subjected to large numbers of loading and unloading cycles during use. If sewing conditions have been unsuitable, repeated loading will give rise to seam defects such as the familiar slippage and grinning.When a seam (such as the superimposed seam type 1.01.01 ( SSa 1 ) used in this work) is stretched at right angles to its direction, seam opening normally occurs. If the opening is conspicuous, it is regarded as a sewing defect. In this study we have assumed that such an opening originates mainly in the slippage of fabric yams and the deformation of the stitches in the seam. The former is connected with seam slippage and has been reported to be influenced mainly by fabric characteristics such as weave, type of weaving yarn, coefficient of friction between yarns, fabric density, and so on [ 4,7,10,12 ] . The latter is thought to be affected by stitch density, thread characteristics such as thickness and extensibility, thread consumption, etc. Although in some studies [ 2,3,8,9] the shape of the stitch has been obtained geometrically, as far as the problem of seam opening is concerned, a dynamic approach is desirable. Ajiki [I] attempted such a dynamic approach recently.If seam opening is influenced by many factors, it is very important from the point of view of sewing technology to elucidate the relationship between sewing parameters and seam opening behavior under cyclic loading conditions. In this paper, we analyze seam opening behavior using a simple model, and we examine the usefulness of the model. '
Mechanisms of Seam OpeningWe have assumed, as mentioned above, that seam opening behavior can be explained largely in terms of the slippage of yarns in the woven fa...