Analysis and improvement of the methodology of estimation of strength of threaded joints of shoe upper parts

Relevance. The quality of footwear largely depends on a comprehensive set of properties, among which the strength of footwear is a significant indicator. The footwear strength is primarily determined by the strength of its joints (adhesive, thread-adhesive, welded, etc.). Structural analysis of studies on operational defects of footwear reveals that 15–20 % of returned shoes exhibit defects in threaded joints. The largest percentage of defects falls on such positions as “tearing of the workpiece material along the stitching”, “upper edge tearing”, “stitch detachment from part edges”, “stitching breakage”. This is due to various factors arising from manufacturing processes, operational stresses and material properties. Current methods for evaluating quality of threaded joints fail to account for dynamic wear factors or replicate real-world operation conditions. The standard method of strength tests of seams under single-cycle stretching does cannot reliably predict the operational durability of shoe upper joints. Therefore, the problem of improving the strength and reliability of the joints of footwear remains relevant, since the rupture of joints is one of the main defects of footwear. Thus, there is a need to study the strength of threaded joints and materials used in the manufacture of seams, in order to identify the shortcomings of the methodology for assessing the strength of threaded joints in shoe upper parts and to propose improvements. The purpose of the work: To investigate the strength of thread joints and materials used in the manufacture of seams, identify the shortcomings of the methodology for assessing the strength of thread joints in shoe upper parts, and propose recommendations for its improvement. Methods of research: Standard test methods focused on the physical-mechanical and strength properties of materials for shoe upper and threaded joints. Results of the work: Recommendations to eliminate the shortcomings of the standardized method used to assess the strength of threaded joints of shoe upper parts.