Woven Carbon Fabric Research Articles

EXPLORING THE EFFECTS OF STITCHING PROCESS ON THE MECHANICAL PROPERTIES OF THREE- DIMENSIONAL (3D) STITCHED UNIDIRECTIONAL COMPOSITES

The stitching process has obvious effects on the out- of- plane mechanical properties of composites such as impact damage mechanism or impact energy absorption. However, the effects on the in- plane mechanical properties of composites have been under discussion and need to be clarified. In the previous studies, tensile, shear and bending behaviors of 3D stitched biaxial woven carbon composite were investigated. The unidirectional carbon woven fabrics constitute the significant part of raw materials in the composite industry. For this reason, the research study was expanded to examine the in- plane mechanics of 3D stitched unidirectional carbon woven composites. In this study, the unstitched and 3D stitched unidirectional woven carbon composites were manufactured and tested under the shear, tensile and bending loads. While the stitching process improved the tensile and shear modulus of composite, it could not create the significant difference in the bending behavior. The highest module and maximum stress values were obtained in the tensile test. The bending and shear test results follow them, respectively. Moreover, it was proven that the fabric architecture of stitched composite layer has the substantial effect on the tensile properties of 3D stitched composite.

Effects of Thermoforming Parameters on Woven Carbon Fiber Thermoplastic Composites.

The quality of woven carbon fiber fabric/polycarbonate thermoplastic composites after thermoforming and demolding was investigated using finite element simulation and the Taguchi orthogonal array. The simulation utilized a discrete approach with a micro-mechanical model to describe the deformation of woven carbon fabric, combined with a resin model. This simulation was validated with bias extension tests at five temperatures. The thermoforming process parameters considered were blank temperature, mold temperature, and blank holding pressure, with three levels for each factor. Optimal values for the fiber-enclosed angle, spring-back angle, mold shape fitness, and the strain of the U-shaped workpiece were desired. The results indicated that the comparison of the stress-displacement curve of bias extension tests verified the application of the discrete finite element method. Results from the Taguchi array indicated that blank holding pressure was the dominant parameter, with the optimal value being 1.18 kPa. Blank temperature was the second most significant factor, effective in the range of 160 °C to 230 °C, while mold temperature had a minor effect. Furthermore, the four quality values are dependent and have a similar trend. The best combination was identified as a blank holding press of 1.18 kPa, a blank temperature of 230 °C, and a mold temperature of 190 °C.

An experimental investigation of nano clay and functionalized nano graphene oxide effects on ablation of carbon/phenolic nanocomposites

This work aims to study thermal stability and ablative behaviors of Carbon/Phenolic composites containing nano clay, nano graphene oxide and hybrid additives. To this end a detailed explained and illustrated process is involved to synthesize factionalized graphene oxide based on Hummers method. The XRD test result shows a major shift in basal plane reflection to below 2θ = 20° in the provided spectrum, which indicates achievement in the functionalization process. Prepared nanoparticles suspensions are then mixed by resol resin with desire wt% to outcome nanocomposites. An in-depth analysis of SEM images with focus on the dispersion, morphology, and interaction of the nanofillers with the resin matrix reveals that nanoparticles are dispersed properly with no agglomeration. 200 gr/m2 carbon woven fabric is then impregnated with prepared nanocomposites employing an own made prepreg machine to use to construct standard flexural as well as oxy acetylene test specimens. Using bending test, thermogravimetric analysis and oxyacetylene torch test, effects of different percentages of considered nanoparticles on the mechanical properties, thermal stability and ablative of carbon/phenolic composites are assessed and the results are reported. According to the results, adding only 0.1 wt% of nano graphene oxide increases char yield around 5% and remain back surface temperature under 100°C during flame test. Moreover samples with 0.2 wt% of nano clay and hybrid (0.05 wt% nano graphene oxide and 0.1 wt% nano clay) additives provides best reaming amount of solid.

Impact of Air-Cathodes on Operational Stability of Single-Chamber Microbial Fuel Cell Biosensors for Wastewater Monitoring

The increasing global water pollution leads to the need for urgent development of rapid and accurate water quality monitoring methods. Microbial fuel cells (MFCs) have emerged as real-time biosensors for biochemical oxygen demand (BOD), but they grapple with several challenges, including issues related to reproducibility, operational stability, and cost-effectiveness. These challenges are substantially shaped by the selection of an appropriate air-breathing cathode. Previous studies indicated a critical influence of the cathode on both the enduring electrochemical performance of MFCs and the taxonomic diversity at the electroactive anode. However, the effect of different gas diffusion electrodes (GDE) on 3D-printed single-chamber MFCs for BOD biosensing application and its effect on the bioelectroactive anode was not investigated before. Our study focuses on comparing GDE cathode materials to enhance MFC performance for precise and rapid BOD analysis in wastewater. We examined for over 120 days two Pt-coated air-breathing cathodes with distinct carbonaceous gas diffusion layers (GDLs) and catalyst layers (CLs): cost-effective carbon paper (CP) with hand-coated CL and more expensive woven carbon cloth (CC) with CL pre-applied by the supplier. The results show significant differences in electrochemical characteristics and anodic biofilm composition between MFCs with CP and CC GDE cathodes. CP-MFCs exhibited lower sensitivity (16.6 C L mg−1 m−2) and a narrower dynamic range (25 to 600 mg L−1), attributed to biofouling-related degradation of the GDE. In contrast, CC-MFCs demonstrated superior performance with higher sensitivity (37.6 C L mg−1 m−2) and a broader dynamic range (25 to 800 mg L−1). In conclusion, our study underscores the pivotal role of cathode selection in 3D-printed MFC biosensors, influencing anodic biofilm enrichment time and overall BOD assessment performance. We recommend the use of cost-effective CP GDL with hand-coated CL for short-term MFC biosensor applications, while advocating for CC GDL supplied with CL as the preferred choice for long-term sensing implementations with enduring reliability.

Impact response of hybrid composites under varying environmental conditions: A comparative study

AbstractComposite materials are widely preferred in the aviation, automotive, construction and maritime industries due to their many superior properties. As a result of this widespread use, composite structures are inevitably subjected to various environmental conditions. Various environmental conditions may negatively affect the mechanical performance of the structure, and the structure may become unable to maintain its initial mechanical properties, especially in the face of critical loading, such as low‐velocity impacts. This research investigated the influence of various environmental conditions on the low‐velocity impact strength of composite materials. 12‐layer plate samples with epoxy matrix reinforced with woven glass fabric (GF), woven carbon fabric (CF), and hybrid fabric (HF), where the two fabrics are used together, were produced. Low‐velocity impact tests were conducted to these specimens at 20 and 40 J energy levels. Damages occurring in the material as a result of the low‐velocity impact test were interpreted using high‐resolution camera and optical microscope images. Force‐time and force‐ displacement curves were drawn and interpreted. It was concluded that as the impact energy values increased, the maximum force and displacement values also increased.Highlights The influence of various environmental conditions to which composite materials may be exposed on the dynamic response of the structure has been investigated. Various environmental conditions significantly affected the composite structure's impact behavior. While glass fabric (GF) composite samples were more affected by the seawater environment, carbon fabric (CF) composite samples were more affected by the HCl environment. Hybrid (HF) composite samples were affected by seawater and HCl in approximately equal amounts.

Comparative Study of the Mechanical Properties of a Novel Epoxy Composite Material Reinforced by Bidirectional Woven Carbon Fabric and Hybrid Kevlar/E-Glass

The objective of this work is to carry out a comparison of different materials in the form of a bidirectional carbon fabric and hybrid Kevlar and glass as reinforcements in an epoxy matrix with a loading rate of 30wt%. Two experimental tests have been carried out in order to determine the mechanical properties, such as tensile and Brinell hardness tests. In the case of tensile and Brinell hardness tests, the characterization was performed on two types of composite plates reinforced with Woven Carbon Fiber and Hybrid Woven Kevlar and E-Glass with Epoxy (WCF-HWKG/EPOXY) and Hybrid Woven Kevlar and E-Glass with Epoxy (HWKG/EPOXY). Consequently, it has been observed that the tensile and hardness properties of the hybrid composite material (HWKG/EPOXY) are respectively 36% and 46.43% lower compared to (WCF-HWKG/EPOXY). Based on these findings, the studied materials demonstrate potential applications across various fields, including aeronautics, aerospace, and high-performance automotive sectors.

Quasi‐static and high‐rate in‐plane shear tests on aramid and carbon fiber woven composites featuring a nanoparticle‐enriched high‐density polyethylene matrix

AbstractNanoparticles are known to enable the modification of the properties of the material they are integrated into. In the context of ballistic protection, previous works have demonstrated that graphene and Montmorillonite (MMT) particles included in high‐density polyethylene (HD‐PE) and used as a matrix enable an increase in the ballistic performance, of consolidated woven aramid fabrics. Furthermore, the ballistic performance has been reported to be influenced by the in‐plane shear properties of the impacted materials. In this context, quasi‐static and high‐rate in‐plane shear tests have been conducted on two types of reinforcements, aramid, and carbon woven fabrics, consolidated by a high‐density polyethylene matrix enriched by graphene, MMT and a mix of graphene and MMT nanoparticles. The conducted investigations provide for the first time in the literature the results of high‐rate in‐plane shear tests on aramid woven reinforcement consolidated with nanoparticle‐enriched and not enriched high‐density polyethylene composites. Despite the use of the same reinforcement and enriched matrix material as in previous works of literature, no significant differences in terms of in‐plane shear behavior have been observed for any of the different types of nanoparticles integrated into the matrix. Nevertheless, the obtained results demonstrate a clear strain rate sensitivity of the tested materials.Highlights Aramid and carbon fabrics were consolidated with nanoparticle‐enriched HD‐PE Quasi‐static and high‐rate in‐plane shear tests were conducted No influence of the nanoparticles could be identified A clear strain‐rate sensitivity could be identified for both composites

Unleashing the potential of CFRP laminate: enhancing mechanical characteristics with STF-Impregnated woven carbon fabric

The objective of this study is to evaluate the potential for enhancing the mechanical characteristics of carbon fiber reinforced polymer (CFRP) composites through the embedding of STF-impregnated woven carbon fabric within their structure, referred to as STFFC. The dynamic and static characteristics of the proposed STFFC were evaluated through a series of experimental tests including tensile, modal, dynamic mechanical analysis (DMA), low-velocity impact (LVI), and compression after impact (CAI) tests. The shear thickening fluid (STF), which was prepared by dispersing nano-silica particles in a solvent of polyethylene glycol (PEG), exhibited an abrupt increase in storage and loss modulus upon exceeding a critical shear strain. The result of the modal test revealed that the addition of STF-impregnated fabric into the CFRP composite led to greater damping ratios of 17.71–417.86%, despite the degradation of tensile strength by 10.81% and Young’s modulus by 12.49%. DMA results show that the STFFC has a larger tan δ except for between intersections of 118 °C, and 161 °C. For impact responses, the STFFC resulted in a lower contact force, with a reduction of 2.41–3.30%, and an increase in absorbed energy of 2.87–5.00%. Meanwhile, the CAI strength of the STFFC was degraded by 3.62 to 6.20%. Despite the reduction of tensile, impact, and CAI characteristics of the STFFC, it is noteworthy that the CFRP composites exhibited relatively minor degradation even with the application of STF. The results of the study suggest that embedding STF-impregnated woven carbon fabric can enhance the potential of CFRP composites, making them even more promising solutions for various applications.

Investigation of flexural performance of concrete beams with nonwoven/polymer composites versus steel-rebar reinforcement

The research investigates the unique characteristics and benefits of using nonwoven fabrics and polymer I cross-section composites in concrete beams. These materials show improved strength, flexibility, and corrosion resistance compared to conventional steel-reinforced beams, offering promising solutions for various construction applications. This study constructed an I-beam structure using a nonwoven polyester fabric/polyester composite cast in a concrete beam. Other designs included woven carbon fabric or Kevlar nonwoven fabric applied to the bottom flange of the I-beam for reinforcement. The flexural behavior of an I-beam polyester nonwoven/polyester composite with Kevlar or carbon-reinforced concrete beams was examined. The comparison between the different samples indicates that: flexural strength: the carbon sheet-reinforced sample exhibits the highest flexural strength, followed by the steel rebar and Kevlar-reinforced samples. The ductility: The steel rebar-reinforced sample shows the highest ductility, indicating better deformation capacity before failure. Carbon sheet reinforcement also provides substantial ductility. Bending stiffness: The highest bending stiffness is observed in the Kevlar-reinforced sample, suggesting a stiffer and less flexible beam. These observations highlight the trade-offs between stiffness, strength, and ductility in reinforced concrete beams. The reinforcement material choice depends on the application-specific requirements, such as the need for higher bending strength, better flexibility, or greater stiffness.

Manufacturing woven carbon fabrics with electrode function via high-pressure spray of active lithium-ion particles

In this paper, an innovative approach was presented to manufacture woven carbon fabric cathodes via high-pressure spray to coat LiFePO4 (LFP), acetylene black (AB) and polyvinylidene fluoride (PVDF) onto carbon fibers. The fabrics were desized to improve conductivity prior to coating. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were adopted to ensure that the selected process parameters could achieve complete removal of the polymer sizing and dispersion of the LFP particles on both the spray surface and inner architecture of the fabrics. The subsequent electrochemical characterization showed that the fabric cathodes could, on average, produce excellent specific capacities of over 110 mAh/g and areal capacities of over 3.0 mAh/cm2 with good rate performance. With 98% efficiency and 0.97 retention after 100 cycles, the cathodes also depicted superb long-cycle performance, meaning that the coating with electrochemical activity could adhere firmly to the fiber surface.

Multi-objective optimal design for carbon and basalt fibre-reinforced hybrid composites under flexural loading

This paper presents a study on the optimal design of hybrid composites reinforced by woven carbon and basalt fibre fabrics. The investigation focuses on evaluating the flexural properties of these hybrid composites through finite element analysis (FEA)-based simulations. To determine potential optimal stacking sequences, design rules are employed. For each stacking sequence, a regression model is developed to establish the correlation between the flexural strength and the fibre volume fractions. Using these regression models, solutions meeting the minimum required flexural strength are found for each stacking sequence. With the objectives of minimising both cost and weight, the optimal solutions are found from these solutions. It is shown that for most optimal solutions, basalt/epoxy and carbon/epoxy plies should be placed on the compressive and tensile sides, respectively. When the minimum required flexural strength is high (800 MPa or 900 MPa), sandwich type stacking sequences with carbon/epoxy plies on both the compressive and tensile sides can also be the optimal solutions. Key findings from this study include.1. Stacking sequences [C]8, [B2C6], [B2C2BC3], [B2C2]2, [B2C2B3C], [B2CB4C], and [B7C] are optimal solutions for all minimum flexural strengths.2. Stacking sequences [B3C]2 and [B]8 are optimal solutions when the minimum flexural strength is up to 800 MPa.3. Stacking sequence [BC7] can be one of the optimal solutions when the minimum flexural strength is 600 MPa or 700 MPa.4. Stacking sequence [C4B2C2] is one of the optimal solutions when the minimum flexural strength is 800 MPa or 900 MPa, and stacking sequence [C3B3C2] is one of the optimal solutions when the minimum flexural strength is 900 MPa.

Manufacturing carbon fabric composite structural batteries using spray with high-pressure and high-temperature and vacuum-bag assisted infusion techniques

This paper introduces a strategy for manufacturing composite structural batteries, integrating the dual roles of energy storage and load-bearing functionality. In the manufacturing process, both cathodes and anodes were produced by coating electrode materials on woven carbon fabrics via high-pressure and high-temperature spray method. A modified vacuum-bag assisted technique was employed to infuse electrolytes and assemble entire battery cells. Scanning electron microscopy was utilized to observe that the active electrode particles were effectively dispersed throughout the woven carbon fabrics. Electrochemical characterization demonstrated that the fabricated batteries could achieve a high energy density of 34.12 Wh/kg with benign rate performance and high Coulombic efficiency. Meanwhile, uniaxial tensile tests illustrated that the structural batteries had an ultimate tensile strength of 118.70 MPa and Young's modulus of 13.07 GPa along the yarn direction. Bias-extension experiments indicated that the shear modulus and yield strength were 2.87 GPa and 20.82 MPa, respectively. These results suggest that the multifunctional efficiency of the manufactured structural batteries was over 1, validating the effectiveness of the proposed manufacturing approach for composite structural batteries.

Thermal response of an induction-heated fabric reinforced thermoplastic composite with anisotropic electrical conductivity: An experimental study

In this study, the electrical conductivity of PolyEtherKetoneKetone reinforced with five harness satin weave carbon fabric was measured. Induction heating experiments using a hairpin shaped coil were conducted on the same material. The study points out that the thermal response depends on the direction in which the eddy currents are generated in the laminate. The thermal response showed a linear relation with the measured in-plane anisotropic electrical conductivity, pointing towards Ohmic heating mechanisms being dominant during induction heating of the used material. This relation enables the accurate and efficient simulation of the induction heating of woven fabric reinforced composites, using only the electrical conductivity measured in one of the fabric’s weave directions and in the fabric’s 45° off-axis direction.

Manufacturing woven carbon fabric electrodes with high areal capacity via high-pressure spray of active lithium-ion particles

Woven carbon fabrics have great potential to work as current collectors of electrodes in Lithium-ion batteries due to their high electric conductivity and complex 3D architecture with large inner areas. To realize this concept of multifunctional materials with both load bearing and electricity storage capabilities, an innovative approach was established to manufacture carbon fabric cathodes using high-pressure spray to coat LiFePO4 (LFP), acetylene black (AB) and polyvinylidene fluoride (PVDF) onto carbon fibers. Before coating, the fabrics were desized for optimal conductivity. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were adopted to ensure that the process parameters could achieve complete removal of the polymer sizing as well as well dispersion of the LFP particles on both spray surface and inner architecture of the fabrics. The following electrochemical characterization demonstrated that on average, the obtained fabric cathodes could achieve excellent specific capacity of over 110 mAh/g and areal capacity of above 2.7 mAh/cm2 with good rate performance. The cathodes also illustrated superb long-cycle performance, with 98% efficiency and 0.97 retention after 100 cycles, indicating that the coating with electrochemical activity could adhere securely to the fiber surface and that the established high-pressure spray approach was capable of producing the multifunctional woven carbon fabric cathodes with stable performance.

Spring-in behavior of woven carbon fiber/polycarbonate thermoplastic composites

The spring-in behavior of woven carbon fiber/polycarbonate thermoplastic composite is investigated by both the experiment and simulation ways. These thermoplastic composite plates are thermoformed into V-shaped structures, and the final bending angle is measured after demolding. In the finite element simulation to describe the thermoforming and spring-in behavior of the composite, the discrete approach is adopted to simulate the behavior of woven carbon fabric and combined with a resin model. The results from both the experiment and the simulation indicate the spring-in behavior of this thermoplastic composite. For [(±45)]6 blanks, the spring-in angle is around 2.60° for a 60-degree V-shape and around 1.72° for a 90-degree V-shape. For [(0/90)]6 blanks, the spring-in angle is around 2.38° and 1.19° for 60-degree and 90-degree V-shapes, respectively. The [(±45)]6 blank always has a slightly higher spring-in angle than the [(0/90)]6 blank, even though the difference is small. The finite element results show 6% to 12% differences with the experimental values if the spring-in angle is used, and the error is less than 0.6% when the bending angle is compared. By using the present finite element analysis, the results indicate that the stacking sequence could have an evident effect on the spring-in angle, and symmetric laminates have less spring-in effect as compared to their unsymmetric counterparts.

Fatigue and Wear Performance of Autoclave-Processed and Vacuum-Infused Carbon Fibre Reinforced Polymer Gears

This study focuses on investigating the fatigue and wear behaviour of carbon fibre reinforced polymer (CFRP) gears, which have shown promising potential as lightweight and high-performance alternatives to conventional gears. The gears were fabricated via an autoclave process using an 8-layer composite made of T300 plain weave carbon fabric and ET445 resin and were tested in pair with a 42CrMo4 steel pinion and under nominal tooth bending stress ranging from 60 to 150 MPa. In-situ temperature monitoring was performed, using an infrared camera, and wear rates were regularly assessed. The result of the wear test indicates adhesive wear and three-body abrasion wear mechanisms between the CFRP gears and the steel counterpart. A finite element analysis was performed to examine the in-mesh contact and root stress behaviour of both new and worn gears at various loads and a specified running time. The results point to a substantial divergence from ideal meshing and stress conditions as the wear level is increased. The fatigue results indicated that the CFRP gears exhibited superior performance compared to conventional plastic and composite short-fibrous polymer gears. The described composite gear material was additionally compared with two other composite configurations, including an autoclave-cured T700S plain weave prepreg with DT120 toughened resin and a vacuum-impregnated T300 spread plain weave carbon fabric with LG 900 UV resin. The study found that the use of the T700S-DT120 resulted in additional improvements.

Enhancing the mechanical performance of carbon fiber reinforced polymer using carbonized coconut shell particles

Inorganic fillers have been used to improve the out-of-plane mechanical properties of carbon fiber reinforced polymer (CFRP) composite laminates for decades. Nonetheless, its associated high cost and environmental unfriendliness is a concern. Biomaterials are currently being explored as fillers in polymeric materials due to their low cost, wide availability, and biodegradability. However, the use of coconut shell based biofillers together with carbon fibers in epoxy matrix has not been investigated. This research seeks to improve the out-of-plane mechanical properties of CFRP with low fiber volume fraction using carbonized coconut shell particles (CCSP). Five hybrid epoxy biocomposites with varying concentrations of CCSP were used to impregnate four plies of woven carbon fabric, making up a fiber volume fraction of 29%. The tensile, flexural, and impact behavior of the laminated biocomposites were investigated. The mechanical properties of the biocomposite laminates were enhanced compared to a reference CFRP without CCSP. This work provides a cheaper and greener alternative to inorganic CFRP hybrid composite for potential use in automotive and aerospace industries.

Mechanical Characterization of a Twill Weave Carbon Fabric for Macro-scale Forming Simulation

Mechanical Characterization of a Twill Weave Carbon Fabric for Macro-scale Forming Simulation

Vibro-acoustic characteristics of multifunctional carbon fiber reinforced panel

This paper deals with the assessment of vibro-acoustic properties of a multifunctional carbon fiber reinforced panel manufactured by bulk infusion, a modified resin film infusion process. The components of the epoxy resin were chosen to contrast the electrical insulating property and poor flame resistance of the epoxy resins impregnating carbon woven fabric. To confer electrical conductivity to the resin a percentage of 0.5 wt% of Multi-Wall Carbon Nanotubes (MWCNTs) was dispersed in the resin, whereas to increase flame resistance a percentage of 5 wt% of Glycidil Polyhedral Oligomeric Silsesquioxanes (GPOSS) was solubilized in the epoxy mixture. Furthermore, as hardener agents, a mixture of 4,4’-DiaminoDiphenyl Sulfone (DDS) (53.4 wt%) and Bis(3-Aminophenyl) Methyl Phosphine Oxide (BAMPO) (46.7 wt%) was used. The values of the electrical conductivity were found satisfactory enough, being 4.02 × 10−2 S/m for the multifunctional resin and 1.39 × 104 S/m for the in-plane conductivity of the panel, whereas the Limiting Oxygen Index (LOI) value of the multifunctional resin was found to increase from 27% to 36%. Considering these promising results, an experimental assessment of the vibro-acoustic properties of the manufactured multifunctional panel was also performed. The panel was tested mainly to evaluate its low-frequency vibration damping and sound insulation characteristics. The manufactured panel demonstrated an improved efficiency if compared to a baseline configuration, presenting almost the double modal damping and a gain of 10 dB on the global noise reduction.

Experimental investigation on low-velocity impact response of carbon/glass hybrid S-shaped foldcore sandwich structure

Hybrid composites offer an effective method of improving toughness and impact properties while reducing the cost of an advanced composite material. This paper aims at experimentally investigating the influences of impact energy, impact position and ply combination on the low-velocity impact responses of carbon/glass hybrid S-shaped foldcore sandwich structures. Carbon/glass hybrid S-shaped foldcore sandwich structures were manufactured using plain weave carbon fabrics and satin weave glass fabrics with epoxy resin. Low-velocity impact tests were carried out to study the impact behavior. The results show that the damage mode of the sandwich panel gradually changed from the local damage of the top face sheet and the foldcore to the complete penetration damage of the sandwich panel with the increase of the impact energy. And the node position has higher load carrying capacity, energy absorption capacity, and resistance to deformation compared with the base position. Although the initial load carrying capacity of carbon/glass hybrid sandwich panels is lower than that of the carbon fiber reinforced plastic (CFRP) sandwich panels, the addition of glass fabrics can improve energy absorption capacity and perforation threshold of CFRP sandwich panels.