Influence of Sewing Thread Properties on Seam Strength and Yielding Behavior in Woven Fabrics

The mechanical performance of sewn seams is commonly evaluated using parameters such as seam strength and seam efficiency, which primarily describe the behavior of the seam at ultimate failure. However, these parameters provide only limited information about the initiation of structural deterioration that precedes rupture. An operational definition of the Seam Yielding Point (SYP) is proposed as an experimentally identifiable indicator of the onset of seam degradation during tensile loading. Nine woven fabric variants differing in structural characteristics were sewn using four polyester sewing threads with different linear densities. Seam tensile tests were performed according to the relevant international standard, while force–elongation curves were continuously recorded. The SYP was identified as the first local decrease in force observed on the force–elongation curve. Photographic documentation was used only for qualitative interpretation of the deformation process. The experimental results showed that the proposed SYP could be consistently identified in all tested specimens prior to ultimate seam failure. The corresponding yielding force and elongation depended on both the sewing thread properties and the fabric structure. In addition to conventional seam strength measurements, the proposed approach provides valuable information regarding the initiation of irreversible structural changes within the seam. Overall, the proposed operational definition of the SYP represents a useful complementary parameter for evaluating seam mechanical behavior and contributes to a more comprehensive assessment of seam performance.