Warp-knitted Spacer Fabrics Research Articles

Viscoelastic behavior of warp-knitted spacer fabrics in iterative compression and decompression

In this study the viscoelastic behavior of warp-knitted spacer fabrics was investigated for compressional deformation. The fabric specimens were tested via loading and unloading time intervals under predetermined conditions. Following the upside tests, specimens were relaxed for 24 h to examine the recovery prior to completing the downside tests. The data obtained from the compression and decompression cycles were examined for stress relaxation and creep through stress–time plots. From the results it was observed that, despite the non-homogeneous structure of the spacer fabric, the specimens demonstrated exponentially changing behavior within the given time intervals. Since the response of fabrics to compression and decompression cycles can be expressed as a function of time, a mathematical approach was expressed in accordance with the time-dependent behavior of the fabrics regarding the monofilaments as bent beams. The responses of the fabrics to the experimental set up conditions were evaluated to determine the potential usage performances of the fabrics. Fabric thickness, number of monofilament yarns in the structure, and thickness of the monofilaments had the major effects on the performance of the fabrics. Future research could consider modeling studies to predict usage performance, and tailoring the fabrics before production.

Low-velocity impact behavior of foam-based sandwich composite reinforced with warp-knitted spacer fabric; numerical and experimental study

The aim of this research is to investigate experimentally and numerically the low-velocity impact behavior of foam-based composites reinforced with warp-knitted spacer fabric (WKSF). To prepare different foam-based composites, the structural parameters of WKSFs including cell size, position, and Z-fiber height were considered. A drop weight impact test with an initial energy of 5J was carried out to examine the low-velocity impact behavior of composites, followed by experimental analyses of Mises, shear, and normal stress on various composite components. Thereafter, the impact behavior of the composites was simulated using ABAQUS/CAE software. The comparison between experimental and numerical results showed a maximum error of 9.79% in predicting the acceleration of impactor. In addition, the results revealed significant stress disparities among samples. Stress analysis showed complex patterns across samples, emphasizing structural parameter influence on stress tolerance and load-bearing capabilities. Notably, Z-fibers displayed substantial stress tolerance, while the matrix predominantly undergoes shear stress. Consequently, the ideal structure for low-velocity impact applications includes small cell size, high thickness, and non-facing hexagonal cells.

Thermoelectric generator modules based on warp knitted glass fiber-metal hybrid composites

Thermoelectric generators (TEG) offer the potential to convert waste heat into electricity and thus contribute to reduce CO2 emissions. The conversion of electrical energy is based on the Seebeck effect of two electrically conductive materials without any mechanical conversion and therefore without wear. The application of conventional TEG modules is limited due to cost-intensive materials and production technology of TEG, and a limited structure design for the integration of Thermoelectric Elements (TE). To address this research challenge, this work presents the development of thermoelectric composite modules based on glass fiber reinforced warp knitted spacer fabrics. In a double needle bed warp knitting machine, glass fibers in warp, weft and pile direction are integrated. The contacting of TE in the form of wires with 45 TE cm−2 were implemented. A TEG module with 20.25 cm2 in size showed a maximum output power of 2.7 μW at a temperature difference of 60 K. The Seebeck factor of S = 142 μV K−1 was determined using this composite TEG with 10 TE strands and nearly 400 thermocouples. A thermoelectric model was developed for the calculation and the modules were characterized. For the first time, thermoelectric composite modules with sufficient structural-mechanical properties in terms of compressive and bending stiffness were realized based on spacer warp knitted fabrics, which can be used for the operation of sensors or small devices.

Enhanced broadband sound absorption of multi-layer composite material based on three-dimensional warp-knitted spacer fabric

Compared with other sound-absorbing materials, spacer fabric with a “sandwich” structure has many advantages, such as light weight, an environmentally friendly production process, recyclability, versatility, low production cost and high efficiency, and strong designability of the organizational structure. However, as a porous sound-absorbing material, the effective sound-absorbing frequency band of the spacer fabric is concentrated at high frequencies, so the sound-absorbing performance needs to be improved. This paper establishes a Johnson–Champoux–Allard theoretical model by using a genetic algorithm to characterize the sound absorption performance of the three-dimensional (3D) warp-knitted spacer fabric. The theoretical model is validated through finite element analysis and experimental methods. Based on this model, two composite materials are designed to improve the sound absorption performance: (1) multi-layer spacer fabric composite material and (2) multi-layer spacer fabric-aluminum foil composite material. Numerical simulation and experimental results show that the sound absorption performance is significantly improved by widening the effective frequency band and increasing the sound absorption coefficient. The contribution of this paper is twofold. Firstly, the theoretical acoustic model of 3D warp-knitted spacer fabric is established. Secondly, the superior sound absorption performance is achieved by proposing multi-layer and multi-material composite material. The spacer fabric-based composite material has broad application prospects in the field of noise reduction and sound insulation. The paper provides a theoretical basis and more strategies for the acoustic and multifunctional design of spacer fabric in the future.

Low-velocity impact behavior of warp-knitted spacer fabric reinforced with spiderweb shaped stitch

Warp-knitted spacer fabrics are a widely considerable material owing to its unique sandwich structure and superior performance, employed across diverse fields such as military, transportation, construction, and personal protection. However, they are inevitably subjected to impacts in practical applications. This work investigated the influence of surface layer structure on the impact resistance property of fabrics by drop weight tests. The damage tolerance of warp-knitted spacer fabrics was also studied through repeated impact experiments. To further improve the impact resistance property of the fabric, a simple sewing method was proposed in this work. Inspired by the spiderweb structure, a spiderweb shape was sewn on the fabric. The results demonstrated that hexagonal mesh as the impact surface provided better impact resistance for the fabric. As the number of impacts increases, the deformation of the fabric gradually intensifies, and the fabric is completely damaged during the fourth impact. The stitch can enhance its impact resistance, and the shape of the stitch had a significant influence on the impact resistance performance.

Compression behavior of warp-knitted spacer fabric based on simplified finite element method

Compression behavior of warp-knitted spacer fabric based on simplified finite element method

A Lotus Seedpods-Inspired Interfacial Solar Steam Generator with Outstanding Salt Tolerance and Mechanical Properties for Efficient and Stable Seawater Desalination.

Interfacial solar steam generators (ISSGs) can capture solar energy and concentrate the heat at the gas-liquid interface, resulting in efficient water evaporation. However, traditional ISSGs have limitations in long-term seawater desalination processes, such as limited light absorption area, slow water transport speed, severe surface salt accumulation, and weak mechanical performance. Inspired by lotus seedpods, a novel ISSG (rGO-SA-PSF) is developed by treating a 3D warp-knitted spacer fabric with plasma (PSF)and combining it with sodium alginate (SA) and reduces graphene oxide (rGO). The rGO-SA-PSF utilizes a core-suction effect to achieve rapid water pumping and employs aerogel to encapsulate the plasma-treated spacer yarns to create the lotus seedpod-inspired hydrophilic stems, innovatively constructing multiple directional water transport channels. Simultaneously, the large holes of rGO-SA-PSF on the upper layer form lotus seedpod-inspired head concave holes, enabling efficient light capture. Under 1kWm-2 illumination, rGO-SA-PSF exhibits a rapid evaporation rate of 1.85kgm-2 h-1 , with an efficiency of 96.4%. Additionally, it shows superior salt tolerance (with no salt accumulation during continuous evaporation for 10 h in 10% brine) and self-desalination performance during long-term seawater desalination processes. This biomimetic ISSG offers a promising solution for efficient and stable seawater desalination and wastewater purification.

Two‐step foaming process for fabrication of flexible polyurethane foam composites with spring‐like air‐layer structure

AbstractDue to its exceptional mechanical properties, polyurethane (PU) foam has found wide application in various fields. Microcellular foaming not only reduces weight but also enhances the cushioning properties of PU. However, current foaming methods have limitations in improving performance. Therefore, this study aimed to construct spring‐like sandwich‐structured flexible PU foam composites (SFFCs). These composites were prepared using a two‐step foaming method, utilizing a precise amount of polyol and isocyanate as raw materials, at room temperature (28–35°C). In the preparation process, warp‐knitted spacer fabrics (WKSFs) with spring‐like structures were encapsulated in the middle layer, while the top and bottom layers consisted of PUF (flexible PU foam with different ring radius differences) formed through the foaming process of polyol and isocyanate. The study focused on investigating the influence of the ring radius difference (r = 1, 1.5, 2) and the two‐layer layout (staggered, diagonal, overlapping) of the WKSFs on the compression and cushioning properties. The experimental results revealed a significant improvement in the mechanical properties of the PU with the incorporation of WKSFs. Particularly noteworthy was the excellent cushioning performance exhibited by the two‐layer WKSFs sample, RPUS‐1, in the dynamic impact test. RPUS‐1 absorbed 94.3% of the energy and reduced the impact value to 3921 N, which is 848 N (17.7%) lower than that of PU foam. Furthermore, even after 20 cycles of compression testing, the SFFCs retained excellent compressive properties, with the compressive stress only decreasing from 0.34 to 0.19 MPa. In conclusion, this study expands the application of PU in cushioning, demonstrating their potential in providing improved cushioning properties.

The mathematical study of compression behaviours of silicone rubber composites reinforced by warp-knitted spacer fabrics

To synthetically investigate the compressive mechanism of warp knitted spacer fabric reinforced silicone rubber matrix composite (SRWSF) under 20% deformation, a compression meso-mechanics theoretical model was established in this paper. The silicone rubber was processed as isotropic material according to the nonlinear constitutive equation, the spacer yarn was assumed as a continuous uniform element. The compression meso-mechanics theoretical model consists of the mechanical model of silicone rubber and the compression model of warp knitted spacer fabric (WSF), based on the Euler-Bernoulli beam theory and the Spence Invariant constitutive model theory. To verify the feasibility of the compression meso-mechanics theoretical model of SRWSF, the compression test of SRWSF was carried out. The simulated compression stress-strain curve was compared with the results of the experiment. The result shows that the compression theoretical model has a high agreement with the experimental result under 20% strain, as compared with the Polynomial fitting curve. This phenomenon indicates that the compression theoretical model established in this study can reasonably simulate the actual compression behaviours within 20% deformation for SRWSF. Moreover, the theoretical model can help understand the compression mechanism of SRWSF and optimise the designing of silicone- rubber-matrix composite reinforced by WSF for cushioning applications.

The pressure reduction property of silicone rubber reinforced by warp-knitted spacer fabric

The pressure reduction property of silicone rubber reinforced by warp-knitted spacer fabric

Investigation on Transmission Property of Warp-Knitted Spacer Fabric in Primary Resonance Using Nonlinear System Model

Investigation on Transmission Property of Warp-Knitted Spacer Fabric in Primary Resonance Using Nonlinear System Model

Warp-knitted spacer fabric flexible composites with high stability and low-velocity impact resistance infused by flock-reinforced shear thickening gel

Flexible protective materials with suitable properties are necessary for personal low-velocity impact (LVI) protection. Flock-reinforced shear thickening gel (FRSTG) can absorb energy through its state transition, thereby showing great potential in applications for LVI protection. However, the unstable state of FRSTG with a slight flow behavior challenges its LVI-resistant evaluation and in-depth development in use. Herein, three-dimensional (3D) warp-knitted spacer fabric (WKSF) composites were obtained by infusing FRSTG in high proportions (≥75%). FRSTG was observed to be stably and randomly distributed in the spacer layer of the WKSF, and the desirable flexibility of the composites was confirmed. The LVI protection effect of FRSTG was better than that of shear thickening gel at the same composite ratio, and the composite with an 83% FRSTG proportion absorbed more than 80% of the impact energy. Besides, FRSTG dominated the composites, showing enhanced responsiveness to the impact with increased velocity. Accordingly, this study constructed stable and LVI-resistant 3D flexible composites with FRSTG as the main functional component, which provided new ideas for the development of wearable protective equipment.

Mechanical properties of shear thickening fluid filled warp-knitted spacer fabrics

This paper reports the compressive behavior and low-velocity impact behavior of warp-knitted spacer fabrics (WKSFs) filled with shear thickening fluid (STF) when subjected to quasi-static compression and low-velocity impact loadings, respectively. In the steady rheological test, the STF experiences a shear thickening transition at a critical shear rate. Besides, the critical shear rate decreases with the increase of silica mass fraction. The compression curves of WKSFs filled with STF composites were consistent with those of WKSFs, including initial, elastic and compaction stage. As the compression speed increases, the overall compression load values of WKSF and WKSFs filled with STF composite increase. Moreover, the compression load of composite increases with the increase of silica mass fraction. Compared with WKSFs, WKSFs filled with STF composite composites need more work to deform under the same strain. The impact result reveals that STF-filled WKSF would absorb more energy and keep the peak load at a lower level than WKSF under the same impact loadings. In a certain range, the energy absorption of composites becomes more excellent with the increasing silica mass fraction. However, over a certain range, the energy absorption of the composite decreases with the increase of the mass fraction of silica. It was concluded that the STF-filled WKSF composite could be expected as a damping or energy-absorptive material for human body protection.

Preparation and Properties of Flexible Cushioning Composites Based on Silicone Rubber and Warp—Knitted Spacer Fabric

This paper aims to develop a new type of flexible cushioning composite material that can be applied to cushioning protective appliances. Room temperature vulcanized silicone rubber (RTV silicone rubber) was filled into five groups of warp knitted spacer fabrics with different structural parameters, and flexible cushioning composites with filling rates of 30%, 50% and 70% were prepared. At the same time, there was a group of warp knitted spacer fabrics without silicone rubber as control. Then the infrared spectrum of silicone rubber was analyzed to test the compression and impact properties of flexible cushioning composite. It is found that the increase of filling rate enhances the compressive and impact properties of flexible cushioning composites. The flexible cushioning composite material can show better compression performance at a larger compression ratio. The structural parameters affecting the impact properties of flexible cushioning composites are arranged in descending order as fabric thickness, spacer tilt angle, spacer density, mesh number. The established mathematical model can provide a theoretical basis for the performance study of such composite materials. The compressive properties and impact properties of flexible buffer composites are not correlated.

Optimization of Mass-spring Model Parameters by ICA for Assessing Compressional Behavior of Warp-knitted Spacer Fabrics Reinforced Polyurethane Cast Elastomer Composites

Optimization of Mass-spring Model Parameters by ICA for Assessing Compressional Behavior of Warp-knitted Spacer Fabrics Reinforced Polyurethane Cast Elastomer Composites

The effect of HydroSpacer implant placement on the wear of opposing and adjacent cartilage.

A HydroSpacer implant, that is,a swelling hydrogel confined by a spacer fabric, was developed to repair focal cartilage defects and to prevent progression into osteoarthritis. The present study evaluated the effect of implant placement height in an osteochondral (OC) plug on wear of the opposing and adjacent cartilage. Three-dimensional warp-knitted spacer fabrics, polycaprolactone with poly(4-hydroxybutyrate) pile yarns, were filled with a hyaluronic acid methacrylate and chondroitin sulfate methacrylate hydrogel. After polymerization of the hydrogel, these HydroSpacers were implanted in OC defects (ø 6 mm) created in bovine OC plugs (ø 10 mm) and allowed to swell to equilibrium. A custom-made pin-on-plate wear apparatus was used to apply simultaneous compression and sliding against bovine cartilage. Cartilage damage, visualized with Indian ink, was only seen for the group in which the HydroSpacer was placed flush with the surrounding cartilage. A significant increase on average surface roughness of the sliding path compared to the adjacent cartilage confirmed surface damage for this group. When the implants were recessed (with and without extra hydrogel layer on top of the implant), this damage was not observed, but the cartilage surrounding the implants was compressed (without damage) indicating substantial load sharing with the implant. Furthermore, it was shown that all defects treated with a HydroSpacer implant resulted in shear forces comparable to intact cartilage.Clinical significance: The present study suggests that placing a HydroSpacer implant recessed into the surrounding cartilage would decrease wear of the opposing cartilage. Altogether, this study supports the development of textile-constraining hydrogels for cartilage replacement.

Energy-Absorbing and Eco-Friendly Perspectives for Cork and WKSF Based Composites under Drop-Weight Impact Machine

Lightweight structures with high energy absorption capacity are in high demand for energy absorption applications in a variety of engineering fields, such as aerospace, automotive, and marine engineering. Anti-impact composites are made of energy-absorbing materials that are incorporated into structures to protect the occupant or sensitive components against strikes or falls. This study deals with an experimental investigation of multi-layer composites consisting of cork and warp-knitted spacer fabrics (WKSF) for anti-impact applications. Composites were designed and created with a laser cutting machine in eight different configurations. To measure the energy absorption of the manufactured composite samples, a low-velocity drop-tower machine was designed, and the maximum reaction force due to the strike of the impactor on the specimens was measured by a dynamometer located under the samples. Moreover, energy absorption and specific energy absorption capacities were calculated for each specimen. In the final part of this study, the Life Cycle Assessment (LCA) of the designed composites was calculated to understand the eco-friendly properties of the composites.

Mechanical and structural characterisation of a 3D warp-knitted spacer fabric subjected to compression

3D warp-knitted spacer fabrics show a growing importance, especially in cushioning or impact damping applications. The use of 3D fabrics saturated with fluids improves their impact damping capabilities and, in this case, evaluating the variation of material’s permeability with compression level is of great importance. In the past few years, our efforts were focused on evaluating this variation with the use of complex experimental devices, an approach that has proven to be very useful and thoroughly, but also time and resource consuming. Through this new initiative we aim to make a step further in our attempt to model the behaviour of dry or imbibed 3D warp-knitted spacer fabrics by considering their complex internal structure. A 3D model was built, based on a CT scan of a commercially available 3D fabric, which allowed us to simulate using the finite element method the structure’s response to different compression levels and conditions.

Study of the flexural properties of polyurethane-foam-core composites reinforced with warp-knitted spacer fabric

In this paper, novel ternary composites consisting of polyurethane-foam-core, warp-knitted spacer fabrics and polyurethane resin were involved. The composites obtain unique three-dimensional structures, high strength and a variety of surface structures. The aim of this study was to investigate the flexural properties of the composites. First, the warp-knitted spacer fabrics with different structural parameters were laminated with polyurethane foam to produce the foam-core materials. Meanwhile, two types of microspheres were incorporated into the polyurethane foam. Then the prepared foam-core materials were combined with polyurethane resin to fabricate the polyurethane composites. A flexural test was conducted to investigate the effects of the surface structure of spacer fabrics, microspheres types and contents on the flexural properties of the polyurethane composites. The findings show that the composites had excellent flexural properties and the flexural performance can be significantly improved by varying the surface structure of the fabric and the type of microspheres to meet specific end-user requirements

Finite Element Analysis of Compression Behaviors of Silicone Rubber Composites Reinforced by Warp-Knitted Spacer Fabrics

In this study, the compression behaviors of silicone rubber composites reinforced by warp-knitted spacer fabrics under 20% deformation were investigated by experiment and a finite element analysis method. Based on the compression test, including the compression tests of composites and the warp-knitted spacer fabrics, the compression behaviors of composites were investigated. This revealed that the composites exhibited excellent elastic recovery abilities. Furthermore, the finite element analysis model of composites was established based on the parameters of the geometry and performance of the composites. The simulated results by the finite element analysis model were compared with the experimental ones to verify the accuracy of the model. It is obvious that the compressive finite element analysis model had good agreement with the experimental results, indicating that the compression performance of composites can be effectively simulated by the finite element analysis method. It is a useful tool for understanding the compression mechanism of composites and optimizing the composites’ parameters for cushioning applications.