This research was carried out to investigate behaviour of a knitted orthopaedic knee support in simulated real conditions as well as to propose a new approach to compression evaluation to preclude the possibility of any error in designing of new orthopaedic supports with exact compression level. Fully finished supports with all additional non-textile elements were analysed in this research. The support is defined as a corrective or orthopaedic item intended to grip or support any movable part of the body in the correct position and allows movement of that body part. The ways how textile material deforms under applied stresses as well as relaxation processes over the time play an important role in its processing and end use. A strong linear dependence between elongation of the support and compression generated by the support was found in this research. However, investigation on stress relaxation over the time showed that stress decrease over 36,000 s coincides with ranges of one full compression class, and the highest change (approx. 50%) in tensile force occurs during the first 100–200 s of relaxation. Such a change of compression has significant influence on the predictive pressure value generated by the compression garment and undermines its functionality. The obtained results indicate that a new approach to compression evaluation methodology must be adopted for theoretical compression value computation. Consequently, evaluation of the compression according to the tensile force must be performed not earlier than after at least 120 s relaxation.
PurposeAir permeability has a valuable role in comfort parameters. It is known that air permeability of elastomeric yarns is firmly low. Despite that, usage of elastomeric inlay-yarns is the most common and the most effective way to generate compression for knitted textile. This study aims to investigate the influence of elastomeric inlay-yarn linear density, insertion density and elongation of the sample to the air permeability of compression knitted materials.Design/methodology/approachTwo different types of knitting patterns were investigated: rib 1 × 1 pattern with different elastomeric inlay-yarn linear density (four variants) and insertion density (without inlay yarn and with inlay-yarns inserted into every single, second or fourth course) and combined laid-in jacquard pattern. The air permeability test for these structures was performed without any deformation and at 10 and 20 per cent fixed transverse elongation.FindingsAccording to the investigation, insertion density of inlay-yarns has a huge impact on air permeability; however, air permeability of knitted material is not linearly proportional to the total amount of inlay-yarns. Also, it was found that air permeability increases by increasing elongation, regardless of knitting pattern and total amount of elastomeric inlay-yarn in the knitted structure. Alteration of the loop geometry at natural state and 20 per cent fixed elongation was established, and the increase of air permeability at fixed elongation may be dependent on changes of knitted material porosity.Originality/valueAccording to the obtained results, recommendations to perform air permeability measurement at least with minimal specific wear elongation are presented.
This work was focused on changes of the compression generated by knitted orthopedic supports during the stress relaxation in order to find in which period of the stress relaxation the most significant part of the compression is lost. The influence of knitted structure, elastomeric inlay-yarn insertion density and shape/orientation of the rigid element fixed on the fabric on the compression and its changes under the stress relaxation was also investigated in this study. 11 different knitted structures and constructions were used in this research. It was found that the higher density of elastomeric inlay-yarn insertion into the knitted structure is not only responsible for higher compression generation, but also makes compression degradation during the time slower. In addition, the higher pre-tension of the elastomeric inlay-yarn leads to the faster relaxation process. Moreover, the shape and orientation of the rigid element can significantly affect the compression generation, however behavior of all variants during the stress relaxation is very similar. Evaluation of the tensile force after at least 120-300 s of the stress relaxation has to be used in design algorithm of very different compression products and applied in estimation of the compression at different manufacturing stages of the product.
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