Thermoplastic composites from curvilinear 3D multi-layer spacer fabrics

Purpose The utilization of three-dimensional (3D) printing in composite materials reduces constraints and opens new possibilities for the development of protective textiles compared to conventional manufacturing processes. Previous studies have predominantly focused on investigating critical parameters that influence the adhesion quality of 3D printed layers on textile substrates, along with the structural characteristics of two-dimensional (2D) textile substrates. However, 3D fabrics with superior properties have not been extensively explored. This study aims to develop innovative 3 days printing auxetic structure–spacer fabric composites with enhanced protection and comfort. Design/methodology/approach Using an entry-level Fused Deposition Modeling (FDM) printer, polymer materials were directly deposited onto 3D spacer fabrics. A series of printing trials determined the optimal process parameters, after which composites with various tilting angles were fabricated. Their deformation behavior and energy absorption characteristics were then evaluated through systematic compression tests. Findings It is found that Thermoplastic Polyurethane (TPU) is more suitable for composite with spacer fabrics compared to Polylactic Acid (PLA). Optimal printing conditions were identified as a speed of 30–40 mm/s, a preheating temperature of approximately 209 °C and an extrusion temperature between 215 and 220 °C. Additionally, an appropriate Z-axis distance effectively combines the 3D printed components with the fabric while maintaining the comfort of the spacer fabric. Composites with a 45°tilting angle demonstrated the best compressive and energy absorption performance under 80 and 50% strain conditions. Practical implications The composites we fabricated with a single-layer thickness below 9 mm, especially the 45° tilting angle structure is only about 7 mm, meeting dimensional requirements for protective equipment (e.g. helmet liners and protective pads). Additionally, the uniform microporous array on the composites surface enhancing breathability without compromising surface smoothness, and contributing to improve comfort in wearable protective applications. The good performance in compressive strength and energy absorption capacity underscoring its potential in applications requiring efficient energy absorption at low strain, such as protective padding and sportswear components. Social implications The increasing demand for personal safety protection has driven the development of high-performance textile composites. Personal protective equipment must not only provide excellent protective functionality but also ensure comfort and portability. Composites with multifunctional gradually replace traditional textiles by balancing protection, flexibility and wearer comfort. Moreover, flexibility of 3D printing can meet the needs of different markets for customization of high-performance personal protective equipment. Originality/value These findings demonstrate the potential of composite materials in applications requiring high energy absorption at low strain conditions and also reflect the promise of integrating FDM 3D printing technology with spacer fabrics for the design and manufacturing of advanced auxetic materials for personal protective equipment.

Due to the thickness of the spacer fabric, it is usually assembled in a multi-layered manner as a cushion material. However, few studies have been conducted on the compression properties of the multi-layered spacer fabrics. Firstly, this paper analyzes the factors affecting the compression properties of multi-layered spacer fabrics, and explains the influencing mechanisms. Results show that the fixing condition between the sample and the indenter, the fixing condition between layers, the overlaying direction and the compression speed have little effect on the compression property. However, when overlaying spacer fabrics with different moduli, a better compression property can be obtained by placing the fabric with a higher modulus on top. Secondly, this paper focuses on the relationship between the layers and the compression property of the spacer fabrics. It shows that the relation between the compression work and the number of layers is linear, with a high correlation coefficient. The relationship between the modulus and the number of layers is in the form of a cubic function with a good correlation coefficient. Finally, the Kelvin model is modeled and is found to be suitable for characterizing the stage II compressive properties of multi-layered spacer fabrics. The above quantitative analysis provides theoretical support for the design of cushion materials with different moduli and support performance in different regions, and has practical guiding significance.

Reusable launch vehicles are designed for multiple missions and it undergoes severe aerodynamic loading conditions during its operation. Nosecap is one such hot structure in a reusable vehicle, which is a doubly curved conical structure whose cross-section varies with respect to height. Carbon-Carbon composite is mainly used in these hot environments. Generally the 3D composite structures for the hot structures are made from 3D textile preforms. The Nosecap experiences high temperature variations during the re-entry phase of the flight. Heat transfer analysis and thermo-structural analysis of the Nosecap are essential for estimating the design margins. The output of heat transfer analysis, which is the temperature distribution with respect to time, will be added to the corresponding pressure loads for carrying out thermo-structural analysis. Analytical methodology has been arrived at based on Representative Unit Cells for evaluating the 3D composites properties from the basic unidirectional material properties. In the present study thermo-mechanical properties of 3D Carbon-Carbon composite has been determined and selection of the best suitable textile preform has been addressed based on heat transfer and thermo-structural analysis of Nosecap using the finite element software NASTRAN. A total thermo-structural design procedure has been presented with the support of suitable numerical investigations.

It is demonstrated that spacer fabrics made of polyester can be coated with Al-doped ZnO (AZO) as thermoelectric (TE) material and conductive silver as contact material to enable smart textiles. An atomic layer deposition process was used for the AZO coating and the conductive silver paste was manually applied. A TE generator and cooling based on the Seebeck and Peltier effect can be observed if a temperature difference or direct current is applied, respectively. Both effects were proven to exist and evaluated. The Seebeck coefficient was determined of up to 50 µV · K−1 and a TE power of about 0.2 µW was generated. Without additional active heat dissipation or cooling, a temperature difference between both spacer fabric surfaces of up to 12 K was achieved. By changing the polarity of the electrical contacts it can significantly be shown that the cold-warm side is changed, as expected for a Peltier element. We observed experimentally the Peltier effect using a single element as well as electrically interconnected sample pairs, the latter could be important for the cooling application. Additionally, the heat transport through the spacer fabrics was tested and showed that there is no heat equalization between the surfaces via air and filaments at temperatures up to 50 °C. The Peltier effect as a fundamental TE effect, that enables site-specific and on-demand cooling applications, has not yet been comprehensively investigated using spacer fabrics and AZO as TE material. These investigations predict that AZO on spacer fabrics hold the special potential to enable flexible and textile solid-state cooling applications.

The effect of thermal properties on the three-dimensional knitted spacer fabrics made from functional fibers (i.e. Outlast®, Coolmax®) with different fiber compositions was studied. The spacer fabrics were specifically designed for mattress ticking applications. Samples were manufactured with two fabric tightness and knit designs, and four Outlast® fiber compositions. Thermal conductivity, thermal resistance, thermal absorptivity, thermal diffusivity, and relative water vapor permeability were considered as thermal comfort properties. Alambeta and Permetest devices were used for the measurement of thermal properties. Fabric design was the leading criteria on the thermal resistance and water vapor permeability, while fiber compositions became more important on the thermal absorptivity. The contribution of Outlast® fiber on the thermoregulatory efficiency of spacer fabrics was analyzed using a differential scanning colorimeter. The thermoregulatory effect of Outlast® fiber was slightly observed in the 33% Outlast® fiber composition. Water vapor permeability of open-skin samples was higher than the closed-skin samples, which was due to the holed/meshed structure of the open-skin structure for the same fiber content and fabric construction. Statistical analysis was also performed and confirmed the contribution of each factor, including their interactions. In particular, the interaction became more significant than the main factors for thermal diffusion behavior of samples.

This paper describes Part II of a study of hip protective pads made from spacer fabric treated with shear thickening fluid (STF). Hip fractures are a substantial contributor to morbidity and mortality in the elderly, and incidence is rising worldwide. Hip protective pads reduce fractures, but wearing adherence is poor. Pads made from breathable and comfortable fabrics can increase adherence and prevent more hip fractures. In this research, warp-knitted spacer fabrics were treated with STF using one of two methods. Treatment I involved STF and room temperature vulcanizing (RTV) silicone, while treatment II consisted of STF and a mixture of isopropyl alcohol and tetraisopropyl titanate. In Part I, STF-treated knitted spacer fabric was shown to have significantly greater force attenuation capacity than untreated fabric and comparable to force attenuation capacity of closed cell foam. In Part II, the effects on performance relevant to the thermal comfort of the wearer of each treatment method, the amount of STF used, and layering were assessed using a sweating guarded hot plate, and comparisons made between treated fabrics and with closed cell foam. Treatments I and II produced pads with significantly different permeability index and mass compared to closed cell foam. Treatment II produced pads with high force attenuation capacity, suitable permeability indexes, and low mass – preferred characteristics in hip protective pads. The study concluded that knitted spacer fabrics treated with STF, isopropyl alcohol, and tetraisopropyl titanate are potentially useful materials for hip protective pads.

Modern science and technology constantly require new and novel materials with special properties. Over the past decade, Nanocomposites materials have received significant attention as active materials in components ranging from sensors to biomaterials, electronics devices to structural parts. These novel composites have applications in many areas, such as energy, insulation, manufacturing, and the modern building industry. However, not all applications have the same requirements in terms of acoustic insulation, so it is useful to adapt the kind of core materials and their product specifications, such as particle size and porosity, to the different applications. Furthermore, in some applications, cheaper core materials, like precipitated silica, would be a reasonable alternative to replace the time-consuming series of measurements. Because of many bad conditions that affect acoustic insulation properties in modern buildings. And to summarize recent applications of nanotechnology as they relate to textile fibers, yarns, and fabrics for improving acoustic insulation in modern buildings and civilian communities, this paper discusses the ability to apply 3D woven spacer fabric (3DWSF) composite materials reinforced with epoxy, rigid polyurethane foam, and silica nanoporous particles, which were prepared by the sol-gel technique. Four samples had been prepared, all of these samples were textile composite materials, and reinforced with two types of nano silica 99.8% SiO2; mesoporous Ns particles with porosity up to 83%, true density 0.08 g/cm³, and particle size between 100 and 2000 nm and pore size 70–150 nm, which had been prepared by Sol-gel technique, and nonporous Aerosil®200 particles with surface area 200–225 m2/g, true density 0.25 g/cm³, and particle size between 2 and 20 nm. We used rigid polyurethane foam as core material, and epoxy resin for laminating the fabric. 3D spacer E-glass fabrics, and chopped E-glass microfibers had been used. The weight percentage of silica nano particles which were used in this research was 5% by weight, which was better for economic reasons, and enough, to enhance the acoustic absorption coefficient up to [Formula: see text] = 99.79%. The best sound absorption could be achieved by using mesoporous silica nanoparticles, and soundproofing of an insulator using this porous structure is better than using a nonporous one. We found in this research that the thickness 45 mm and semi-porosity structure of the 3DWSF composite insulator material were enough to make a difference, with reference to the thermal and acoustic insulation guide of buildings.

Warp-knitted spacer fabrics are featured by a 3d integral structure consisting of two warp-knitted fabric layers, which are kept on distance by vertical threads. This structure enables the realization of several functions like mechanical cushioning, permeability for air and moisture, and thermal insulation. Due to these functions, spacer fabrics can be used as moisture and thermal-regulating functional components in various sewing products, whereby compression stability is essential for the functionalities mentioned above. These can also be influenced locally by stitching. A numerical tool is preferred to compute the mechanical properties in an accurate way, taking into account the varying sewing parameters. This study's objective is to extend the macroscopic material law for spacer fabrics through numerical analysis of experimental data. For this purpose, 3d samples stitched at varying intervals were tested by a compression test. A regression analysis was applied to predict the compressive stress for each structure. The research steps included representing and approximating the coefficients and potencies for the experimental curves as explicit functions of the distance between the stitch lines. An effective contact model for spacer fabrics with stitches was developed, which is to be expressed in the form of seam distance in terms of the effective compression of the spacer fabrics. Thus, in the future, it will be much easier to predict the effective properties for selected semi-analytical applications with such materials.

Energy Absorption and Performance Relevant to Thermal Wear Comfort Evaluation of Existing Impact Protective Pad and Materials Intended for Impact Protective Pad

Importance of Architectural Asymmetry for Improved Triboelectric Nanogenerators with 3D Spacer Fabrics

Acoustic textiles are the most widely used acoustic materials to control room acoustic parameters in current practice. Based on porous acoustic absorption, they are able to achieve high absorption at middle and high frequencies. This behaviour is a limitation for spaces that host speech comprehension or activities that require concentration. For this reason, acoustic sector companies tend to explore the advancements in other sectors (e.g. technical apparel, transportation, etc.) to find solutions that can satisfy this requirement. This is the case of 3D spacer fabrics (3D SFs) which, thanks to the two horizontal layers and the internal connecting vertical pile, have complex and customisable structures adaptable according to the acoustic performance (absorption, reflection, diffraction). Originally developed to provide sound insulation in transportation vehicles, these materials’ acoustic performance has been explored, but a comprehensive and updated research review is lacking. In response, this paper presents a systematic review aiming to understand the correlation between the physical characteristics of these materials and their acoustic performance. The review is based on the literature of the last 10 years of reviewed and published papers. Absorption coefficients are gathered, sorted and compared with the most extensively used acoustic materials. This contribution shows that the main performance analysed is absorption and this depends on thickness, porosity, and flow resistivity of the horizontal layers. The complex pile structure of 3D SF enables absorption coefficients that are comparable with the most common acoustic materials. The analysed references are based on literature absorption coefficients measured in an impedance tube. Future research should explore the possibilities of 3D SF application at an architectural scale by analysing the absorption coefficients in a reverberant chamber or by analysing reflection and diffraction behaviours.

Textile structural composites are widely used in various industrial sections, such as civil and defense (Dow and Dexter, 1997; Kamiya et al., 2000) as they have some better specific properties compared to the basic materials such as metal and ceramics (Ko & Chou 1989; Chou, 1992). Research conducted on textile structural composites indicated that they can be considered as alternative materials since they are delamination-free and damage tolerant (Cox et al, 1993; Ko & Chou 1989). From a textile processing viewpoint they are readily available, cheap, and not labour intensive (Dow and Dexter, 1997). The textile preform fabrication is done by weaving, braiding, knitting, stitching, and by using nonwoven techniques, and they can be chosen generally based on the end-use requirements. Originally three dimensional (3D) preforms can be classified according to fiber interlacement types. Simple 3D preform consists of two dimensional (2D) fabrics and is stitched depending on stack sequence. More sophisticated 3D preforms are fabricated by specially designed automated loom and manufactured to near-net shape to reduce scrap (Brandt et. al., 2001; Mohamed, 1990). However, it is mentioned that their low in-plane properties are partly due to through-the-thickness fiber reinforcement (Bilisik and Mohamed, 1994; Dow and Dexter, 1997; Kamiya et al., 2000). Multiaxis knitted preform, which has four fiber sets as ±bias, warp(0 ) and weft(90 ) and stitching fibers enhances in-plane properties (Dexter and Hasko, 1996). It was explained that multiaxis knitted preform suffers from limitation in fiber architecture, through-thickness reinforcement due to the thermoplastic stitching thread and three dimensional shaping during molding (Ko & Chou 1989). Multiaxis 3D woven preform is developed in the specially developed multiaxis 3D weaving and it’s in-plane properties are improved by orienting the fiber in the preform (Mohamed and Bilisik, 1995; Uchida et al, 2000). The aim of this chapter is to review the 3D fabrics, production methods and techniques. Properties of 3D woven composites are also provided with possible specific end-uses.

Laminates for the automotive industry are composite materials that consist of at least two layers, at least one of which has textile properties. Automotive laminates are most commonly found in vehicle interiors, including door panels, dashboards, headliners, and seats. As part of the research, the influence of three-dimensional warp knitted spacer fabrics on the functionality of laminates was investigated. The experimental part was designed in such a way that the laminates were divided into two groups. The first group comprised laminates consisting of PU foam and two layers of warp knitted fabric (Locknit), while the second group comprised laminates consisting of polyurethane foam and three-dimensional warp knitted spacer fabric. The polyurethane foam in both groups was open cell. All laminates investigated in this work were produced by flame lamination. In the experimental part, the influence of the three-dimensional warp knitted spacer fabric on the typical mechanical properties and the permeability properties of laminates for car seats was analyzed. The results show that laminates with a thickness of more than 7 mm and a proportion of the 3D warp knitted spacer fabric of 50% achieve the highest permeability, delamination force, and tensile and compressive strength.

A series of cotton knitted fabrics was produced and finished according to three different recipes in order to compare the changes of their heat resistances. The heat resistance was measured using the sweating guarded hotplate. Measurements were carried out on one layer of produced knitted fabrics, as well as on two layers of fabrics. The results indicated significant influence of all carried finishing treatments to the decrease of heat resistance of knitted fabrics. It was shown that the high influence of finishing treatment to the total heat transfer trough fabric remains if the fabric is worn with additional knitted fabric layer. The presented results and performed statistical analysis indicated significant effect of finishing treatments to the changes of fabric parameters and furthermore to the changes of heat resistance what directly affects the total thermophysiological comfort of knitwear.

The main goal of this research was to determine the influence of the inner layer thickness and tightness, which depends on the length of the float determined by the float step and number of floats in the pattern repeat, on the thermal insulation and air permeability of the multilayered weft-knitted fabric. For this reason, weft-knitted spacer fabrics were produced by using woolen yarns for the outer layers and polyester filament yarn for the inner layer, with the number of floats in the inner layer varying between two and 20. Results from this research showed that the consequent increase in thickness and tightness of the spacer fabric’s inner layer has unequal effect on the thermal insulation and air permeability. Therefore, similar thermal insulation can be achieved by having significantly higher air permeability. This is especially evident over a long period of time.