Forschungspublikationen

As part of the IGF project 01IF22817N (Nonwoven Thermo-Fabric), ITM carried out the development of advanced woven architectures and weave constructions for integrally woven insulation structures characterized by high design flexibility and a maximized volume of entrapped air. Furthermore, ITM developed the required preparation and feeding unit for the processing and the insertion of nonwoven strips in weft direction into the weaving process.

Introduction

Insulation structures are widely used in the apparel sector, particularly in sportswear and outdoor products, and form the basis for numerous leisure activities. Owing to the high demands placed on comfort and thermal insulation performance, consumers are willing to pay premium prices for functional garments intended for activities such as hiking, skiing, and horseback riding. As a result, this market segment represents a significant contributor to the overall performance of the German apparel industry [1]. Beyond clothing applications, insulation structures also play an important role in technical sectors such as the automotive industry, where they are used in roof liners and cabin insulation systems.

The prevailing construction principle for bulky thermal insulation materials in apparel applications is based on quilted structures. Their production involves a complex, multi-stage process chain comprising the manufacture of insulation, outer shell, and lining materials, textile printing and finishing, quilting, and garment assembly [2]. However, these structures exhibit an inherent design-related disadvantage that prevents the full exploitation of the insulation potential of the individual components. The quilting seams required to ensure structural integrity create locally compressed regions which, according to the principles of heat transfer, act as thermal bridges and reduce the overall insulation performance. Depending on stitch density, the thermal transmittance coefficient can increase by up to 40 % [3]. This loss in insulation efficiency is typically compensated by increased material consumption.

Furthermore, quilting seams introduce visible interruptions across the fabric surface, substantially limiting design flexibility and product customization. Various approaches, such as spacer quilting, attempt to mitigate the compression of the insulation layer by reducing thread tension during the quilting process and bridging greater material thicknesses. However, these methods achieve only a limited reduction in thermal transmittance, typically in the range of 10–14 % [4]. In addition, aesthetic considerations remain largely unaddressed.

To enhance thermal insulation performance, increase design freedom, and reduce the complexity of conventional manufacturing processes, the present research project fundamentally re-evaluated both the structural design and production of insulation materials. By implementing an integral weaving process capable of incorporating all relevant material components and by developing a structural architecture and yarn arrangement that simultaneously ensure structural integrity and enable visually appealing, highly customizable designs, it was possible to significantly reduce thermal transmittance and substantially improve the performance of textile insulation structures.

Objectives

The objective of the project was the simulation-based design and development of chambered insulation structures in combination with an advanced weaving process that enables the inline integration of high-volume nonwoven strips with minimal permanent structural deformation while simultaneously incorporating a textile heating structure into the woven architecture. To achieve this objective, a thermodynamic design methodology was established, from which the arrangement of the yarn systems and the geometric configuration of the unit cells were derived. This approach enabled the identification and analysis of thermal conduction paths and facilitated the design of insulation chambers in such a way that the nonwoven strips remained largely uncompressed within the structure (Figure 1).

A systematic process chain for weave development was established, allowing the face layers to be patterned through Jacquard weaving while simultaneously ensuring the controlled guidance of the binding warp yarns required to connect the individual layers. In addition, binding solutions were developed to achieve both an aesthetically appealing integration of the binding warp yarns into the face layers and the concealed incorporation of the heating structure, masking it invisible from the fabric surface.

For the integration of nonwoven strips in weft direction, a modular preparation and feeding unit was developed. This system enables the processing of nonwoven material by cutting it into strips corresponding to the dimensions of the chamber geometry, modifying them to withstand the tensile loads occurring during weft insertion, and subsequently presenting them to the rapier system for insertion into the weaving shed.

The produced functional structures were validated qualitatively based on visual assessment criteria and through the identification of thermal bridges using infrared thermography. Quantitative evaluation was performed by determining the thermal transmittance coefficient using the Guarded Hot Plate method and comparing the results with those obtained from a conventional quilted reference structure. The developed insulation structures were manufactured on a Jacquard rapier weaving machine equipped with the modular preparation and feeding unit, thereby demonstrating the technical feasibility of the proposed process and structure concept.

Results

Process Chain for the Integral Manufacturing of Nonwoven Thermo-Fabrics

The integral production of chambered insulation structures is based on a novel approach that combines the previously separate process steps of fabric manufacturing, insulation integration (quilting), and functional integration (heating) into a single automated weaving process. The process chain developed at ITM enables the production of complex multilayer chambered structures with enhanced thermodynamic properties while simultaneously providing a high degree of design flexibility. The development process begins with the specification of material parameters, including yarn fineness and insulation characteristics, as well as target values for thermal transmittance and heating performance. Based on these requirements, a simulation-driven thermodynamic design is performed using a finite element heat conduction model implemented in MATLAB. This model allows the determination of the optimal geometric arrangement of the layers, such as offset chamber structures for minimizing thermal bridges, as well as the optimal positioning of integrated heating elements.

Structural and weave development are carried out digitally using the specialized textile design software EAT DesignScope Victor. The overall structure is divided into functional zones, including edge areas, patterned face layers, and binding warp zones. A key technological challenge is the synchronization of the weave combinations of the upper and lower layers with the trajectories of the binding warp yarns to ensure the formation of stable chambers for the integration of nonwoven strips. Through the use of complementary weave structures, both the binding points of the binding warp yarns and the integrated heating yarns can be visually concealed within the face layers.

A central element of the process chain is the automated inline preparation of the insulation material. The nonwoven material, supplied in roll form, is slit longitudinally, cut to length, and permanently bonded to a load-bearing auxiliary yarn by ultrasonic welding. This reinforcement is essential for safely withstanding the inertial forces acting during weft insertion on the rapier weaving machine and for preventing permanent deformation and necking of the nonwoven material. During the integral weaving process, all components, including the face layers, binding warp yarns, preassembled nonwoven strips, and heating yarns, are combined into a single structure. Precise control of weaving machine parameters, particularly shed closing timing and heald frame stroke, ensures the low-compression integration of the hig-bulk nonwoven strips into the fabric chambers.

Simulation-Based Thermodynamic Design of the Structures

The development of the insulation structure required a precise thermodynamic design of the multilayer offset chamber structures. The objective of the simulations was to determine heat transfer and heating performance while accounting for the complex interactions between the constituent materials. For this purpose, a two-dimensional steady-state finite element heat conduction model was implemented in MATLAB using the PDE Toolbox. The model was based on the steady-state heat conduction equation, with material-specific thermal conductivities assigned to the geometrically defined regions representing nonwoven insulation, face layers, and binding zones.

The primary objective of the simulation was to optimize the arrangement of layers and the positioning of the heating structure in order to minimize heat losses and maximize surface temperature homogeneity. Local heat fluxes were calculated using Fourier’s law, and the effective thermal transmittance coefficient was determined across the width of the representative unit cell. The fully parametric simulation environment enabled systematic variation of layer thicknesses, chamber widths, and the number and arrangement of insulation layers.

The numerical analyses revealed that heat transfer in conventional structures predominantly occurs through the binding regions, resulting in non-uniform temperature distributions. By implementing an offset arrangement of the insulation chambers, these direct heat conduction paths were effectively interrupted, thereby minimizing thermal bridges. Validation of the model was achieved through comparison of experimentally measured thermal resistances with calculated values. Iterative adjustment of structure- and process-related parameters, particularly those associated with layer contact and compression effects, resulted in a highly accurate model with a maximum deviation of only 2 %. A two-layer offset arrangement of the nonwoven strips was identified as the optimal solution and subsequently served as the basis for the weave design.

Structural and Weave Development for Multilayer Chambered Fabrics

The transfer of thermodynamic requirements into a manufacturable textile structure was achieved through the systematic organization of yarn systems and the development of a modular weave architecture. Using EAT DesignScope Victor, a color-coded design image was created and divided into functional zones that served as the basis for assigning the complex multilayer binding patterns.

A total of 5,172 warp yarns supplied from two separate warp beams were incorporated into the developed insulation structures. The fabric width was divided into four functional regions: edge zones for fabric stabilization and weft fixation, patterned regions for the upper and lower face layers, and binding warp regions responsible for layer connection and positioning (Figure 2). This modular organization enabled independent modification of design elements and binding warp trajectories without requiring regeneration of the complete Jacquard control file.

A key aspect of the weave development was the design of the binding warp paths, which ensure both structural integrity and chamber formation for nonwoven integration. The binding warp yarns were supplied separately from a creel and arranged in pairs at intervals of 4 cm, corresponding to the intended width of the nonwoven strips.

To minimize thermal bridging, a two-layer offset chamber arrangement was developed. This required a modified binding warp configuration in which the yarns are guided above, between, or below the insulation layers depending on their position within the structure. Through systematic optimization of the binding regions, surface irregularities and out-of-plane displacement of weft yarns were minimized (Figure 3).

To satisfy the high aesthetic requirements of sportswear and outdoor applications, strategies for concealing the functional components were implemented. Float-dominated weave structures, such as 4/1 satin, effectively masked the binding points of the binding warp yarns (Figure 4). Similarly, complementary weave constructions were employed for the integration of the heating structure. Conductive heating yarns were bound to the inner side of the body-facing layer, while opposite twill weaves enabled the heating yarns to be concealed beneath the surface weft yarns, rendering them invisible from the exterior.

The developed weave system was validated using four functional prototypes ranging from simple single-layer structures to highly complex multilayer fabrics with independently patterned face layers, offset insulation chambers, and integrated heating functionality.

Design and Development of the Nonwoven Integration Module

The objective of the engineering development was the realization of a modular system for the automated inline integration of nonwoven strips into chambered woven structures. A systematic design process based on VDI 2221/2222 was applied, including a detailed analysis of the available installation space around the rapier weaving machine and the geometry of the weaving shed.

The system was divided into functional modules corresponding to the process steps of feeding, cutting, joining, presentation and insertion. Circular blade cutting was identified as the preferred solution for cutting the nonwoven roll material into strips because, unlike scissors or ultrasonic cutting systems, it does not permanently compact the material edges and therefore preserves the insulation performance. Length cutting is performed using a specially designed guillotine cutter that facilitates insertion of the voluminous strips into the weaving shed.

A key technological innovation of the module is the reinforcement of the nonwoven material. To withstand the inertial forces occurring during weft insertion at machine speeds of up to 200 rpm, a load-bearing auxiliary yarn is permanently bonded to the nonwoven strip using ultrasonic welding. The resulting nonwoven-yarn composite is subsequently stored in a meander-shaped accumulator, enabling nearly resistance-free outlet during insertion and minimizing mechanical stress on the weld seam.

For precise transfer to the rapier system, the original weft presentation mechanism of the weaving machine was modified with specially designed guide elements. These ensure twist-free guidance of the nonwoven strip and reliable transfer to the rapier gripper.

Technological Implementation and Inline Production of Functional Prototypes

The developed technology was implemented on a Dornier PTS 4/J rapier weaving machine equipped with a Stäubli UNIVAL 100 Jacquard machine and the newly developed nonwoven preparation and integration module. A major focus of the technological trials was the synchronization of the individual process steps and the iterative optimization of weaving machine parameters to ensure stable production under industrially relevant conditions.

Precise adjustment of warp tensions and shed geometry was required to reliably process the voluminous nonwoven strips. Owing to their high take-up, the binding warp yarns were supplied directly from a creel at minimal tension. Experimental investigations demonstrated that excessive binding warp tension leads to local compression of the insulation material and consequently reduces thermal performance. Therefore, an optimal tension level was identified that ensured stable shed formation while minimizing compression.

Reliable insertion of the nonwoven-yarn composite further required adaptation of the shed closing sequence. While the edge regions employed an earlier shed closing to improve weft fixation, the shed closing of the binding warp yarns was deliberately delayed. This configuration prevented displacement of warp yarns by the bulky nonwoven strip during insertion and thereby preserved structural accuracy. Successful commissioning of the complete system demonstrated the feasibility of automated inline integration of high-performance insulation materials into integral woven chambered structures (Figure 5).

Thermodynamic validation

The final evaluation of the developed chambered structures involved a comprehensive characterization of their thermal and mechanical performance in comparison with conventional quilted structures. Thermal analyses were conducted using the Guarded Hot Plate method in accordance with DIN EN 12667 and supplemented by infrared thermography.

A primary objective was the reduction of thermal transmittance and the improvement of surface temperature homogeneity through the elimination of structural thermal bridges. The results demonstrated that the continuous, largely uncompressed insulation layer and the offset arrangement of the insulation chambers significantly enhanced thermal performance. While the conventional quilted reference structure exhibited a thermal conductivity of λ = 0.056 Wm−1K−1, the developed two-layer offset chamber structure achieved a value of λ = 0.037 Wm−1K−1, corresponding to an improvement of 33.9 %.

Infrared thermography further confirmed the superior temperature homogeneity of the developed structures. Whereas the quilted reference exhibited a surface temperature range of 12.6 K due to local compression at seam locations, the offset chambered nonwoven structure reduced this value to only 3.5 K.

In addition to thermal performance, the mechanical properties of the materials and structures were evaluated. Overall, the validation results demonstrate that the developed nonwoven thermo-fabrics outperform conventional quilted systems with respect to thermal efficiency, mechanical performance, and process stability.

Summary and Outlook

Within the framework of the research project, a novel weaving technology for the integral production of highly efficient chambered insulation structures with integrated heating functionality was developed. The primary objective was to overcome the technological limitations of conventional quilted insulation structures, particularly the occurrence of thermal bridges at seam locations and the high manufacturing effort associated with multi-stage production processes by the development of a process chain (Figure 6).

The core innovation of the developed technology is a modular retrofit system for the inline preparation and integration of nonwoven strips. This module enables high-performance insulation materials to be slit longitudinally, cut to length, and reinforced through a permanent bond with a load-bearing auxiliary yarn by means of ultrasonic welding. As a result, the nonwoven strips can be reliably processed as weft material on rapier weaving machines.

Based on simulation-driven thermodynamic design using a validated MATLAB finite element model, multilayer woven structures with offset chamber arrangements were developed. This specific structural configuration effectively minimizes thermally conductive pathways and substantially reduces the formation of structural thermal bridges. The technological implementation was realized on a Jacquard weaving machine. Through the use of complementary weave constructions, both the binding warp attachment points and the integrated heating structures could be visually concealed within the fabric architecture, resulting in an aesthetically homogeneous surface appearance.

Validation of functional prototypes and a vest demonstrator confirmed a significant improvement in thermal insulation performance compared with the current state of the art. The developed structures achieved a thermal conductivity of λ = 0.037 Wm−1K−1, compared to λ = 0.056 Wm−1K−1 for the conventional quilted reference structure, corresponding to an improvement of 33.9 %. Simultaneously, surface temperature homogeneity was substantially enhanced, with the temperature range decreasing from 12.6 K for the reference structure to less than 4 K.

Owing to its modular design and the process guidelines established within the project, the developed technology is readily scalable and suitable for industrial implementation, particularly by small and medium-sized enterprises operating in the sportswear, outdoor, and automotive sectors.

Acknowledgement

The IGF-Project 01IF22817N of the research association Forschungskuratorium Textil e.V., Wallstraße 58/59, 10179 Berlin, was funded by the German Federal Ministry for Economic Affairs and Energy via the German Aerospace Center (DLR) as part of the program for the promotion of Industrial Collective Research (IGF) based on a resolution of the German Bundestag.

The authors would like to thank the aforementioned institutions for providing the financial resources. The research report and further information are available from the institute of Textile Machinery and High Performance Material Technology at TU Dresden.

References

[1]      Mouwitz, P.; Larsson, J.; Peterson, J.: Beyond mass customisation : Mass individualisation.

[2]      Yu, W.; Wang, L.; Liu, H.; Rodrigue, D.; Du, Z.; Yu, W.; Wang, X.: Optimization of the quilting method and filling quality of cold-proof down clothing based on thermal insulation performance. Textile Research Journal 93(2023)21-22, S. 5007-5016

[3]      An, Y.-Y.; Tu, L.-X.; Shen, H.; Xu, G.-B.; Zhang, G.-R.; Zhu, H.-Q.; Wang, H.-C.: Numerical simulation and validation on heat transfer of four structures of sleeping bag. International Communications in Heat and Mass Transfer 129(2021), S. 105707 f.

[4]      Saeed, H.; Rödel, H.; Krzywinski, S.; Hes, L.: ‘Spacer stitching’, an innovative material feeding technology for improved thermal resistance. IOP Conf. Ser.: Mater. Sci. Eng. 254(2017)13, S. 132004 f.

 

Within the IGF project 01IF22946N (“Durchströmbare Rohrknoten”), the ITM conducted the complex structural and weave pattern development of a woven thick-walled T- and Y-shaped pipe joint for media transport based on the application of reversing warp yarns.

Introduction

Pipeline systems constitute essential functional components in numerous industrial applications, particularly in chemical plant engineering, mechanical and automotive engineering, as well as in energy and environmental technologies. In addition to straight pipe sections, branches in the form of T- and Y-shaped pipe joints represent safety-critical components whose structural integrity decisively determines the operational reliability of the overall system. Especially in pressure-loaded media lines, complex three-dimensional stress states arise in the transition zone between the main pipe and the branch, imposing stringent requirements on both material and structural design. While established manufacturing processes such as filament winding and centrifugal casting are available for straight fiber-reinforced composite (FRC) pipes, no integral and industrially scalable solutions currently exist for highly load-bearing, fiber-reinforced polymer (FRP) pipe joints for media transport. Fiber-reinforced polymers (FRP) offer significant potential for pipeline systems due to their low weight, high specific strength, and corrosion resistance.

Metallic pipe joints are typically manufactured by welding and are associated with high mass, susceptibility to corrosion, and mandatory inspections of weld seams. Although filament-wound composite solutions enable a higher pressure resistance, the fiber orientation in the branching region is not aligned with the principal load paths, resulting in structural overdimensioning and increased material consumption. Consequently, textile-based approaches with load-path-oriented structural design are particularly promising. In particular, the weaving technology developed at ITM enables the realization of structurally complex pipe joints through sophisticated weave architectures. However, the previously developed woven 3D node elements are, due to weave and technological constraints, internally separated and therefore unsuitable for media-conveying pipeline systems [1, 2]. This results in a fundamental conflict between integral textile manufacturing and the required flow capability of the components. Against this background, there was a substantial need for research aimed at developing a novel weaving technology incorporating a dedicated warp yarn reversal module, enabling for the first time the integral production of flow-through FRP pipe joints with load-path-optimized fiber architecture.

Objectives

The objective of the project was the development of a simulation-based process chain for the integral manufacturing of woven pipe joints for media transport up to the consolidated composite component for internally pressurized FRP pipeline systems. First, a structural-mechanical design was carried out based on macro- and mesoscopic finite element models. The aim was to determine the principal stress directions in the joint region and to derive a load-path-oriented fiber architecture, particularly within the branching zone. Based on the simulated, load-adapted fiber orientations, the complete and highly complex weave architectures of the three-dimensional pipe joints were developed.

A key technological innovation was the development and implementation of a modular add-on system for warp yarn reversal on Jacquard weaving machines. This system enables, for the first time, the controlled deflection of selected warp yarns at the fabric edge and thereby establishes the prerequisite for forming an open, flow-through branching region while simultaneously realizing a load-path-optimized reinforcement structure. Only through the implementation of the warp yarn reversal module, fiber trajectories can be aligned with the principal stress directions without structurally separating the internal cavity between the main pipe and the branch. Material overdimensioning in the branching region, that is typical of filament-wound pipe joints, was completely eliminated using this approach. Validation was carried out using three functional prototypes and a three-dimensional FRP demonstrator in the form of T- and Y-shaped pipe joints. The developed FRP pipe joints were successfully manufactured and demonstrated.

Results

Process chain for the manufacturing of woven FRP pipe joints

Integrally woven three-dimensional FRP pipe joints are based on tubular multilayer fabrics produced on a shuttle weaving machine equipped with at least four shuttles. A prerequisite for forming a tubular structure is a circumferential weft yarn insertion, i.e., a closed fabric edge, enabling a seamless pipe wall configuration. This structural feature can only be realized using shuttle weaving technology. The primary challenge in manufacturing pipe joints lies in combining a tubular structure with a branching geometry that features a continuous wall structure while maintaining an open internal cavity.

The pipe joint is initially produced in a two-dimensional state as a 2.5D woven structure. The transformation into the three-dimensional geometry is subsequently achieved by the targeted and automated removal of excess lengths of floating warp yarn within the fabric, causing the textile structure to deploy into the intended three-dimensional shape.

The complete manufacturing process (Figure 1) of an integrally woven pipe joint begins with the definition of the target geometry, including diameter, wall thickness, pipe lengths, and branching angle. Based on these parameters, a CAD model of the final geometry is created. The surfaces defined in the model are then flattened into the plane, taking into account the required layer architecture, in order to generate a colour-coded image from the developed surfaces.

Subsequently, an individual weave pattern is developed for each coloured area within this colour image. These partial weave patterns are combined into an overall weave pattern using weave design software (EAT DesignScope Victor). The corresponding machine control data are generated and transferred to the weaving machine. In the subsequent weaving process, the 2.5D preform is manufactured integrally according to the developed weave architecture. After completion of the weaving process, the textile preform is automatically shaped into the previously defined three-dimensional pipe joint geometry.

The final FRP component is produced by consolidating the preform using a resin transfer molding (RTM) process with a tool adapted to the outer diameter of the pipe joint. After demolding, the manufacturing process is completed by final trimming of the component.

Simulation-based design of pipe joints for media transport

The development of pipe joints for media transport requires a load-path-oriented design of the warp yarn systems. A boundary condition of the simulation was the arrangement of warp and weft yarn systems in such a way that no structural separation of the internal cavity between the main pipe and the branch occurs, thereby ensuring the flow capability of the pipe joint.

To this end, the stress distribution within the pipe joint geometry under internal pressure loading was first determined numerically. The highest stresses occur in the transition zone between the main pipe and the branch (Figure 2). This region therefore represents the governing design zone for the fiber architecture.

Based on the calculated stress distribution, a load-path-oriented architecture of the warp yarns was defined in order to fully exploit the tensile properties of the warp yarn material. This optimized warp yarn architecture forms the basis for the subsequent weave development of the pipe joints for media transport.

Development of Prototypes

The development of the weave architecture for an integrally woven pipe joint begins with a three-dimensional CAD model of the joint geometry. The simulated warp yarn systems and their trajectories are color-coded in Figure 3 (left).

Subsequently, the surfaces of the model are flattened into the plane and merged into a color-coded image. Each colored area represents a structurally induced modification within the woven architecture.

For each color-coded area, individual weave patterns are developed and subsequently combined into a unified weave pattern of an integrally woven pipe joint for media transport using the software EAT DesignScope Victor. This integration is achieved through the coordinated control of the shuttles, the fabric take-up system, and the assignment of heddles.

Development of a Warp Yarn Reversal Module

The developed weave patterns were transferred to the shuttle weaving machine “Mageba SL RTEC1200/1” and manufactured using four shuttles. In order to realize the load-path-oriented warp yarn trajectories, an additional module for processing reversing warp yarns is required. This module was designed as a CAD model, taking into account the available installation space in the take-up area of the weaving machine, and subsequently integrated into the machine. The module can be implemented cost-effectively and is adaptable and retrofittable to other weaving machines.

The functional principle for processing reversing warp yarns is based on joining two predefined warp yarns prior to the start of fabric production, thereby forming a loop. The connection point is displaced from the weaving zone toward the creel to make sure it does not become part of the woven pipe joint to be produced. This procedure is repeated until all warp yarns designated for reversal in the two fabric layers are present as loops.

To apply a warp yarn tension comparable to that of the continuously running warp yarns, the loops are integrated into the fabric take-up system by means of the module. The warp yarn tensions of both yarn types were recorded and analyzed using a warp tension measuring device. Both the controlled fixation of the warp yarn loops and their integration into the fabric take-up system represent central functions of the developed warp yarn reversal module.

Application of the module and manufacturing of the prototypes

After the formation of the warp yarn loops, the textile preform is manufactured. In the first section of the pipe joint, the loop-forming warp yarns initially remain fully floating. Following the production of the oval branching region, these warp yarns are integrated into the structure in a regular manner.

From the oval region onward, the use of four shuttles becomes necessary in order to realize the superimposed tubular fabric layers in the second section of the pipe joint. Within the oval region, one shuttle inserts a separate weft yarn that supports the formation of the oval fabric edge. The manufactured textile preform is shown in Figure 4.

For the reproducible production of this highly complex weave architecture, uniform weft insertion is essential. In particular, during the fabrication of the oval region, the weft yarns must reverse within the fabric structure rather than being inserted across the full fabric width, as is typical in conventional weft insertion. The precision of this process step significantly influences both the quality of the three-dimensional pipe joint geometry and the quality of matrix infiltration during consolidation. The textile preforms were successfully manufactured (Figure 4).

3D-shaping and consolidation of the woven prototypes

To transform the 2.5D preform into the three-dimensional structure, a dedicated 3D-shaping process developed specifically for pipe joints with flow capability is applied. A shape-defining internal core is inserted into the tubular structure, defining the target contour during the shaping process. The 3D-shaping is achieved by the targeted elimination of the excess warp yarn lengths introduced during the geometric flattening process. These excess lengths are withdrawn from the structure at the cut edge of the woven structure. A process-specific sequence to eliminate the floating warp yarns must be strictly followed in order to prevent material damage and to reproducibly achieve a precise warp yarn alignment after the shaping process. An automation concept for this shaping technology was developed.

Since the warp yarn loops in the first section of the fabric remain floating up to the edge of the oval region, the corresponding warp yarn excess lengths can be withdrawn. As a result, this warp yarn system is integrated into only one half of the woven structure within the pipe joint. After the preform has been shaped into its three-dimensional configuration, consolidation is carried out. An RTM tool specifically adapted to the contour of the flow-through pipe joint was designed and manufactured (Figure 5). The result after consolidation is a fully consolidated T-joint for media transport with high surface quality and reproducible geometric accuracy.

The material overdimensioning in the branching region typical of filament-wound FRP pipe junctions was completely eliminated through the integral, fabric-based manufacturing approach employing reversing warp yarns.

Summary and Outlook

FRP pipe joints can, for the first time, be manufactured both integrally woven and flow-capable by means of an add-on module for existing shuttle weaving machines. The textile preform is produced in a single-stage weaving process. Following a 3D-shaping procedure specifically developed for the novel yarn architectures, the 2.5D preform can be consolidated into a load-bearing lightweight FRP pipe branch using established RTM processes.

The weave patterns developed, along with the underlying design methodology, can be made available to SMEs for industrial implementation. The geometry of the pipe joint (diameter, wall thickness, pipe lengths, and branching angle) can be individually adapted with minimal modification effort. In addition to T-joints, Y-shaped pipe joints can also be manufactured using the newly developed methodology and weave system, enabling application-specific realization of different topologies.

The results achieved within this project form the foundation for a scalable and load-path-optimized manufacturing technology for FRP pipe joints for media transport.

 

Acknowledgement

 The IGF project 01IF22946N of the research association Forschungskuratorium Textil e.V., Wallstraße 58/59, 10179 Berlin, was funded by the German Federal Ministry for Economic Affairs and Energy via the German Aerospace Center (DLR) as part of the program for the promotion of Industrial Collective Research (IGF) based on a resolution of the German Bundestag.

The authors would like to thank the aforementioned institutions for providing the financial resources. The research report and further information are available from the Institute of Textile Machinery and High Performance Material Technology at TU Dresden.

 

References

 

 

[1]      Matthias Hübner; Monireh Fazeli; Thomas Gereke; Chokri Cherif: Geometrical design and forming analysis of three-dimensional woven node structures. Textile Research Journal 88(2018)2, S. 213-224

[2]      Schegner, P.; Fazeli, M.; Sennewald, C.; Hoffmann, G.; Cherif, C.: Technology Development for Direct Weaving of Complex 3D Nodal Structures. Applied Composite Materials 26(2019)1, S. 423-432