Macro-Modelling of Rib-Knitted Tubular Parts

The aim of the research was to improve the process of knitted products design. The use of modern software helps us predict the physical and mechanical behaviour of materials, using their three-dimensional models. A macro-model of rib-knitted tubular parts was developed in the study. This model allows its implementation into algorithms, describing the peculiarities of the stretching process. Recent findings in the field of 3D modelling and simulation of knitwear behaviour aim at working with models of different scales of structural hierarchy. The use of macro-models provides the opportunity to simplify the geometry and significantly reduce the time required for simulation. Rib stitch structures are among the most popular weft-knitted ones. When using threads of usual stretchability (with breaking elongation that does not exceed 10–12%), the stretchability of some rib stitch structures in the course-wise direction can reach up to 350% and even more. When stretched in the course direction, rib-knitted stitches undergo a number of stages. The stretching process includes: decreasing the width-wise curling; mutual shifting of knit and purl stitches; reducing the curvature of the loop feet and loop heads; pulling the yarn from the loop legs to the loop feet; stretching of the yarn. The assumption was made that such parts of knitted garments as cuffs and borders on sweaters, cuffs on socks, where rib stitch patterns are used, can be described as thin-walled elastic shells. A part of a human body surface, covered with a rib-knitted garment part, can be approximated by a truncated cone. The mid-surface of the shell can be represented as a ruled surface created upon a set of Bezier curves, located along the circumference of the upper and lower bases of the truncated cone. The mathematical description, elaborated in the course of the research, was used for the computer program LastikTube, which was developed to create 3D macro-models of ribbed tubular garments.