Development of a hybrid model of the tensile behaviour of weft-knitted structures for medical compression stockings

Compression stockings are the most common treatment for lymphatic and venous diseases of the lower limbs. Their mechanical behaviour is governed by a specific weft-knitted design, in which an inlay yarn is inserted into each course of the loop structure, acting as reinforcement. Numerous studies have modelled the knitted fabric to predict its tensile behaviour. Specifically, numerical finite element models are increasingly used to evaluate the performance of compression garments. However, they do not represent the local fabric structure and often rely on homogenised approximations. This study proposes a hybrid model to predict the circumferential tensile response of compression stockings. The model incorporates the elastic properties of the loop structure and inlay yarn, as well as the local distribution of inlay yarn, which plays a key role in fabric circumferential stiffness. A unit cell was used to model the weft-knitted fabric at a mesoscopic level. 3D-shell elements and connectors were combined in the unit cell to model the mechanical behaviour of the loop structure and the inlay yarn, respectively. Mechanical and structural parameters were identified from experimental data. The model was applied to the two main zones of a medical compression stocking, ankle and calf. The results were validated through comparison with experimental tensile data, showing strong agreement. This approach is considered suitable for future finite element models aimed at simulating pressure distribution in medical compression fabrics.