Zbigniew Mikołajczyk

This publication presents the results of research aimed at analyzing the dynamic stretching process of multifilament polyester and polyamide threads with medium linear densities. Building virtual design tools for the mechanical properties of textiles under dynamic impact conditions on their structures is a fundamental challenge for identifying textile technological processes and their behavior in real operating conditions. In the Autodesk^® Inventor^® software environment, a virtual analogue model was built based on appropriately connected modules of the Kelvin–Voigt rheological models, for which the input parameters of the selected rheological models were defined. The nonlinear static and dynamic elasticity coefficients were determined based on the obtained results of experimental tests carried out in static conditions on a testing machine at a speed of 33 × 10⁻⁶ m/s and in dynamic conditions on a constructed measuring device. The nonlinear viscosity coefficient was calculated based on data read from the force-time characteristics obtained by measuring forces during stress relaxation in the threads. To conduct this research, an original research stand was designed and built. A series of simulation calculations of the dynamic stretching process were performed for different values of linear densities, lengths of stretched thread sections, and stretching speeds. A comparative analysis of the characteristics obtained from experimental and modeling studies was performed. A very good agreement between the experimental and numerical simulation curves was obtained, which leads to the conclusion about the usefulness of the tools used in the work for the physical description of the thread stretching process.

This paper summarizes the possibility of employing knitted textile barriers as a shield against electromagnetic fields to protect the human body from their negative impact. Ten variants of knitted fabrics made of electrically conductive yarns, steel, and copper wire that differed in stitch pattern, structural parameters, and raw material, were designed, manufactured, and tested. The knitted fabrics produced differed in structural parameters, including course and wale density, surface density, thickness, thread length in the loop, wale and course take-up, volume cover factor, and surface porosity. These parameters were examined in accordance with the research methodology used in knitting. Barrier measurements were taken in the direction of the wales and in the direction of the courses for two frequencies of electromagnetic fields: 2–4 GHz and 4–7 GHz. It was observed that the shielding effectiveness of the manufactured materials depends on the structural parameters of the fabric, the stiches applied, and the type of yarn.

This article examines the anthropotechnical design of orthopedic footwear for patients with diabetic foot syndrome. A 3D spacer knitted fabric was used as a barrier between the researcher's foot and the ground. For the purpose of the research, 7–11 mm thick knitted fabrics with longitudinal elasticity from 45–90 kPa were designed and produced on a double-bar warp knitting machine. The FreeMed Professional mat was used to measure the pressures exerted by the foot on a “bare” walking surface and on the surface equipped with the spacer knitted fabric and compared, proving that in the latter case the unit pressure on the patient's foot decreased by 30%. The obtained measurements provide a good starting point for further research on the optimization of loads on human feet.

Material selection is an important stage in the design of footwear, which determines not only its appearance, but also the comfort of use. The paper presents the methodology for the design of sports textile footwear manufactured by innovative hybrid technology. The upper part of the footwear, designed in CAD and a graphics program, consisted of two elements. Both of them were characterized by a three-layer knitted and embroidered structure. The air permeability and thermal insulation parameters were determined for each layer and for the whole package. The conducted tests demonstrated that the openwork spacer knitted fabric, as a component of the package, increased the air circulation inside the footwear as well as improved the heat transfer outside.

The first part of the publication presents a substantively insightful literature study on the essence and effects of light waves on wound healing in living organisms, including the use of phototherapy in the treatment of the diabetic foot. A knitted textile dressing was designed and manufactured for phototherapy of patients with diabetes suffering from diabetic foot syndrome (DFS). The proposed solution is intended for the treatment of dermal tissues within the patient's foot affected because of diabetic disease at an early stage. Thus, the use of a knitted dressing with incorporated fiber optic structures and powered by a semiconductor laser emitting a 405 nm light wave from its entire surface would prevent further anomalies of the patient's tissues and help to avoid surgical intervention.

Data published by European and World Health Organizations show that since 1990 the number of births has been steadily decreasing, which poses the risk of lack of generational replacement. According to WHO report, every year, 2.6 millions of newborns in the world die in the first month of their life. One million of them in the first 24 h so they require special care and medical supervision, so for the first days or even months of their lives they remain in incubators. The purpose of the research was to develop the construction and build a prototype of a textile incubator, whose most important function is to keep the baby warm, with the possibility of cooling it during therapeutic hypothermia. The incubator model was built in three variants of material packages, and each of them consisted of five material layers. An innovative solution is using for the external thermal insulation layer a composite connecting a knitted fabric with aerogel. The total thermal conductivity resistance for the developed material packages of the incubator was measured using a thermally insulated sweating hot plate known as the ‘skin model’. The obtained values of thermal resistance coefficient R_ct are within 2.07–2.83 clo, and in case of the package with an additional insulation layer R_ct = 3.68 clo. It turned out that when the infant was placed in a textile incubator without a functional heating and cooling mat its heat balance for the adopted ambient temperatures from −5 to 24 °C was negative and ranged from −0.04 up to −50.50 W. In cases of positive heat balance, especially for all ambient temperatures, which took place for the second package where ΔQ = 0.10 ÷ 6.51 W, there is a risk of overheating the baby. The analysis of the heat balance components shows that convection and radiation have the greatest impact on the total heat loss, as on average they constitute 85.6% of the heat lost by a baby in a textile incubator.

On the medical device market there are several types of stationary and portable incubators that can be used in the care of infants. The prototype of a textile incubator made as part of this work consists of five material layers. The textile incubator is equipped with a functional heating and cooling mat, which is made on the basis of 3D channeled weft-knitted fabric. Its function is to generate heat and maintain it inside the textile incubator or to cool the baby's body while using therapeutic hypothermia. The mat is equipped with hoses transporting the heating or cooling medium. The mat, depending on variable input parameters, can emit heat in the range from 1.15 W to 86.88 W. In case of the cooling function, it can receive heat in the range from −4.32 to −27.96 W. This indicates a large adjustment range of the amount of heat supplied and received, which is a positive feature, and enables programming the heat balance to ensure comfort for the baby. The analysis of temperature measurements on the mat surface confirmed that maximum temperature differences do not exceed 1.6°C.

The assumptions of instrumental methodology for measuring dynamic loads of knitted barrier meshes were defined. A test stand was built, original in terms of both mechanical construction and electronic measuring system, connected to a computer data analysis system. Maximum values of dynamic forces in the mesh fastening strings were determined. The correctness of the strain gauges construction and measurement data transmission systems was confirmed. Tests of multidirectional resistance to dynamic loads in the mesh fastening strings were carried out. The experiment involved dropping a ball with a mass of 5 kg and a diameter of 10 cm, from a height of 1 m and 2 m onto the mesh surface. The potential impact energy equaled Ep1 = 49.05 J and Ep2 = 98.1 J. The tests showed that the highest force values were observed for meshes with square-shaped a-jour structure, and for mesh with diamond-shaped a-jour geometry the force values were lower. A symmetrical forces distribution was observed in all the strings. The highest forces were recorded in the middle strings and the lowest in the outer ones. The conducted tests confirmed the correctness of the adopted constructional solutions of test stand for identification of dynamic stress distribution in mesh fastening strings. The developed method is a useful verification tool for numerical analysis of mechanical properties of barrier meshes.

This article focuses on the analysis of mechanical properties of knitted barrier meshes and refers to general problems related to safety engineering. The conducted analysis of the effectiveness of absorbing impact energy by textile barriers, which positively affect the human body, clearly indicates the possibility of applying them in the field of road engineering as a new generation of road barriers. The characteristic features of the new generation of barriers are their openwork multiaxial structure based on various geometric shapes of the a-jour structure. Twenty models of barrier meshes with a-jour structure in the shape of tetragons (squares and diamonds), triangles, regular polygons (hexagons, octagons, and dodecagons), and circles were designed. Simulation research that aimed to optimize the structure of knitted openwork meshes to obtain minimum reduced stresses in strings, knots, and arms of the mesh was performed. The preferred solution is the four-axial eight-thread mesh with square-shaped a-jour structure with stress equal to Δб = 0.43 GPa/kg and the mesh with thickened diamond-shaped a-jour geometry with stress equal to Δб = 0.53 GPa/kg. Low stress values were also recorded for a four-axial six-thread mesh with square a-jour structure, for which Δб = 0.66 GPa/kg. The analyzed mesh models were implemented in the form of dozen designs of stitch constructions based on warp-knitting technology.

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informuj?ce swoich czytelnik?w o najnowszych osi?gni?ciach naukowych i nowoczesnych rozwi?zaniach technicznych w Polsce i na ?wiecie, popularyzuje problemy techniczne oraz poszerza wiedz? i kultur? techniczn?.