Draping Process Research Articles

Properties of Solar Wind Current Sheets in the Martian Space Environment

Transient current sheets (CSs) are common magnetic structures in the solar wind that can significantly disturb the planetary space environment and cause space weather phenomena. This study focuses on their properties in the Martian space environment and investigates their transformations caused by the Martian bow shock. Based on 14 months of data from the Mars Atmosphere and Volatile Evolution mission during similar solar activity, 786 CSs with directional changes greater than 90° and magnetic field depression were automatically identified, including 256 events in the upstream solar wind and 530 events in the Martian magnetosheath. After crossing the bow shock, the duration and thickness of the CSs decrease, while their current density and occurrence rate significantly increase. In the Martian magnetosheath, CSs located on the dayside exhibit stronger current density, a relatively lower occurrence rate, and a smaller Bx/BT than CSs located on the nightside. From the dayside to the nightside, the predominant magnetic field component of CSs changes to Bx due to the draping process. Moreover, a clear dawn–dusk asymmetry in CS properties emerges from the foreshock to the downstream region of the Martian bow shock. Our results reveal the properties and evolution of solar wind CSs in the Martian space environment.

Investigating the factors influencing the bridging of dry non-crimp fabric on a concave L-shaped mold in an automated draping process

Dry technical textiles tend to bridge when draping in concave areas or complex geometries such as internal corners. The extent of bridging is based on the spring-back of the textile. In this study, the value for the spring-back for dry technical textiles is defined and a method to quantify the spring-back value is proposed. An automated continuous draping process is presented based on manual lay-up and draping process of dry non-crimp fabrics (NCF) which is used in the production of rotor blade shells for wind turbine blades. This process provides the basis for the study of spring-back behaviors. Within this process, a triaxial NCF sample is manually laid-up on an L-shaped mold and then automatically draped onto the edge using a draping tool. A laser scanner records the draping result and bridging of the NCF sample. Test series show the influence of the process parameters such as drape speed and drape force on the spring-back behavior. For the draping process under consideration, quadratic dependencies of these factors on the spring-back could be determined.

Membrane behavior of uni- and bidirectional non-crimp fabrics in off-axis-tension tests

The production of high-performance composite parts with non-crimp fabrics (NCFs) requires a profound understanding of the material’s behavior during draping to prevent forming defects such as wrinkling and gapping. Simulation methods can be used to model the complex material behavior of NCFs and predict their deformation during the draping process. However, NCFs do not intrinsically deform under pure shear like most woven fabrics, but often under superimposed shear, transverse tension and in-plane roving compaction. Therefore, non-standard characterization methods have to be applied besides typical picture frame tests or bias-extension tests. Off-axis-tension tests (OATs) utilize a simple setup to characterize a fabric’s membrane behavior under different ratios of superimposed shear, transverse tension and in-plane compaction. OATs at three different bias angles (30^circ , 45^circ and 60^circ ) are conducted to investigate a unidirectional and a bidirectional NCF. A method is presented to measure the fiber curvatures in addition to the occurring strains. The investigations reveal a relatively symmetrical, shear-dominated behavior with limited roving slippage for the Biax-NCF. The behavior of the UD-NCF strongly depends on the stitching load during tests and is characterized by an asymmetric shear behavior as well as significant roving slippage. The off-axis-tension test results can be used as the basis for the development and validation of new simulation methods to model the complex membrane behavior of NCFs.

Analysis of the performance of a new concept for automatic draping of wide reinforcement fabrics with pre-shear: A virtual prototyping study

The layup process of large composite structures made from dry reinforcement fabrics is considered. One such structure is a wind turbine blade, for which the current draping process is mostly manual. Automating the draping process will, therefore, lower the costs. Based on a literature review, a new concept is synthesized and analyzed using an advanced finite element model with rigid multi-body kinematics and a dedicated material model for the fabric. The material model is calibrated using experimental coupon tests, i.e. the bias-extension test (shear) and Peirce's cantilever test (out-of-plane bending). The concept is analyzed numerically by means of a simple parameter study and draping test cases on a flat mold as well as a general double-curved mold. The simulation results show that the concept is feasible for the draping operation and is thus qualified for the subsequent physical prototyping.

A textile architecture-based discrete modeling approach to simulating fabric draping processes

Fabric draping, which is referred to as the process of forming of textile reinforcements over a 3D mold, is a critical stage in composites manufacturing since it determines the fiber orientation that affects subsequent infusion and curing processes and the resulting structural performance. The goal of this study is to predict the fabric deformation during the draping process and develop in-depth understanding of fabric deformation through an architecture-based discrete Finite Element Analysis (FEA). A new, efficient discrete fabric modeling approach is proposed by representing textile architecture using virtual fiber tows modeled as Timoshenko beams and connected by the springs and dashpots at the intersections of the interlaced tows. Both picture frame and cantilever beam bending tests were carried out to characterize input model parameters. The predictive capability of the proposed modeling approach is demonstrated by predicting the deformation and shear angles of a fabric subject to hemisphere draping. Key deformation modes, including bending and shearing, are successfully captured using the proposed model. The development of the virtual fiber tow model provides an efficient method to illustrate individual tow deformation during draping while achieving computational efficiency in large-scale fabric draping simulations. Discrete fabric architecture and the inter-tow interactions are considered in the proposed model, promoting a deep understanding of fiber tow deformation modes and their contribution to the overall fabric deformation responses.

Machine vision system for digital twin modeling of composite structures

Although the structural design of composite structures has already been carried out on a virtual level, composite mechanical properties remain sensitive to fiber orientation and therefore to the quality and reliability of the production process. Considering both manual single-unit manufacturing and advanced mass-unit fabrication, requirements on the production quality may differ, but certainty on the achieved result is crucial. A digital twin model, deterministically derived from produced parts, can be transferred into a virtual simulation environment to check for potential deviations of fiber alignment, resulting from variations in source material or composite production. Transferring that deterministic information into a virtual simulation environment allows for an estimation of the part’s structural potential despite any possible deviations by carrying out numerical simulation predictions on that model. This step of quality assessment can help reduce scrap parts by relying on simulation data that may demonstrate the feasibility of parts despite the containment of deviations with an otherwise uncertain impact. Therefore, further steps toward digitalization of the composite production process chain, especially on the characterization of the production quality, are aspired. In this contribution, a vision system based on a Microsoft Azure Kinect RGB-D camera is introduced which is used to digitalize the composite preform configuration from machine vision data by evaluating the achieved local fiber orientation as result of the complex preform draping process by digital image processing. A digital workflow is introduced that enables to feed the captured real-world data back into a digital environment where numerical simulations with the “as-built” fiber orientation can be carried out. The obtained results are used for assessing production quality and composite performance in the presence of possible deviations. The system, which consists of a camera array of consumer grade, can acquire real-world data and then transfer the data into a virtual environment.

Integrated design for the forming process and structural performance of variable-thickness laminates

The manufacturing process of composite laminated parts has a significant influence on the final performance, especially since the draping process can change the predefined fiber orientation at local sites. With the maturing of draping-process simulation technology, an integrated structure–process–performance design has become possible. This article reports a computational framework for the integrated design of the draping process and structural performance of variable-thickness (VT) laminates. The framework is a two-loop optimization workflow. Specifically, a genetic draping optimization method features the inner optimization loop to find the optimal draping strategy and obtain the resulting fiber orientations and manufacturing layout. Structural performance optimization outlines the outer optimization loop, where a parametric method for the physical configuration of VT laminates is proposed to evaluate the structural performance considering the draping strategy. The entire framework is demonstrated by an automotive B-pillar reinforcement. The benefits of incorporating the draping design versus no draping design are illustrated by comparing the corresponding design results. The comparison results show that the integrated design not only contributes to pretreating manufacturing defects but also allows the use of reoriented fiber directions caused by draping to improve the mechanical properties and engage the load bearing. It thus achieves a further weight reduction of 18.63%. This framework facilitates resource-friendly process design, comprehensive performance evaluation, and structurally efficient laminate design.

Continuous mapping of large surfaces with a quality inspection robot

This paper addresses the problem of mapping large surfaces with a moving sensor. In particular, it proposes image registration and mapping algorithms that enable to use in continuous motion sensors that need multiple shots to perform a measurement. These methods exploit the knowledge of the shape of the part to inspect in a both efficient and accurate fashion, thus allowing to obtain a measurement quality comparable to that of static measurements, while guaranteeing fast sensor motion and thus short scanning times. This work describes the application of these methods for the mapping of carbon fibre parts with an inspection robot equipped with a sensor estimating 3D carbon fibre orientation from multiple 2D images captured with different illumination. Experiments on carbon fibre preforms of complex 3D shape demonstrates that this system accurately reconstructs in real-time the 3D fibre orientations of the outer layer of carbon fibre parts. Accuracy assessments report small errors within the tolerances allowed by the automotive industry on flat and generic 3D surfaces. The inspection robot system presented in this paper has been demonstrated both as an in-line quality inspection robot for production of carbon fibre preforms and as a measurement device for improving the draping process in the prototyping of carbon fibre parts.

A Helpful Assistant for Disinfection in Hand Surgery Procedures: The LocArm Holder.

Although there is no consensus regarding the best skin disinfection technique, whatever antiseptic solution is used, the "prep and drape" portion of most upper extremity procedures requires the presence of at least one operative room assistant or scrub nurse to elevate and hold the hand and forearm. Nonetheless, especially in a busy hand surgery practice and during fast procedures, an operative room assistant or scrub nurse are frequently not available leading to a reduced time efficiency between procedures. This article describes an innovative easy-to-use and hands-free device that helps the surgeon during disinfection of the skin and the setup of the surgical field by keeping elevated the upper limb with respect for tissues. The development of the surgical arm holder starts from three easily available and washable thermoplastic splint sheets 40 × 60cm with 2.5cm thickness. The final device measures 40 × 25 × 15cm and is placed underneath the proximal third of the humerus in order to keep the upper limb suspended at about 10-15cm from the operating table. A retrospective analysis of the "surgical malpractice claims" and institutional non-conformities registered in the period 2011-2020 was conducted in our Hospital looking for bone or soft tissue complications related to the use of the device. Three thousand one hundred eighty-seven surgical procedures were performed between 2011 and 2020 using this device. The retrospective analysis of all "surgical malpractice claims" showed no skin lesions, no neurological complications (such as neuroapraxia), no need for secondary bone procedures or interference with the draping process. Our device proved to be a low-cost, easy to use and alternative solution helping surgeons during the disinfection phase, improving hospital pre-operative flow and reducing the need for other staff members to be engaged in holding the upper limb in the operating room.

3D topology optimization of sandwich structures with anisotropic shells

The development of a density-based 3D minimum compliance topology optimization approach for sandwich structures with anisotropic shells is presented. A constant thickness shell is enforced at the interface of a base structure through a two-step filtering approach. Homogenous effective properties of a cellular material are assigned to the base structure while the shell is treated as a constant stiffness laminate with anisotropic properties. Local shell normal vectors are obtained from the density gradient introduced in the second filtering step and local material orientations in the shell’s tangent plane are approximated based on the fabrication process of the structure. Simple approximating strategies using the Gauss map are presented for a fabric draping process and the fused filament fabrication additive manufacturing process. The effect of material anisotropy on the optimal topology is studied on the Messerschmitt Bölkow Blohm beam benchmark problem. An application to composite structures is then presented where a square, simply supported laminate is reinforced on one face by a topology optimized sandwich structure. Though manufacturability cannot be ensured in the current implementation, careful consideration of the optimization parameters allow to constrain the problem towards manufacturable solutions using additively manufactured cores.

Development of a Shape Replicating Draping Unit for Continuous Layup of Unidirectional Non-Crimp Fabrics on Complex Surface Geometries

The manufacturing of large-scale structural components is still dominated by manual labor in many sectors of the modern composite industry. Efforts are being made to establish an automated layup technology for complex structural elements. Processing dry non-crimp fiber fabrics (NCF) offers great cost opportunities and high deposition rates, compared to prepreg-based technologies like automated fiber placement (AFP). Here, the fabric architecture is considered during the draping of the plane textile on curved surfaces. In this paper, the development of a draping unit for balancing fabric tension and consolidating continuously across the layup width is presented. We introduce a geometrical process model to achieve a fabric-friendly draping of the used unidirectional NCF. The shape of the resulting draping front depends on the surface geometry, the shearing of the previously laid-up textile, and the positioning of the material feed. To consolidate the fabric at the altering draping front in an automated layup process, the shape of the continuous consolidation element can be controlled by the elongation of serial soft actuators, manipulated by parallel robot kinematics. The shape replication ability of the draping unit is promising for the implementation of a continuous, fabric-friendly draping process for complex surface geometries.

Production of hybrid tubular metal-fibre preforms: development of a digital twin for the draping process

Hybrid shafts or rods with a metallic end fitting and a load transmitting area made of fibre reinforced plastics possess a great potential in terms of lightweight design, e.g. in automotive industry or aviation. One essential and quality-defining process step in the manufacturing of such parts is the draping of dry braided fibre fabrics onto the shape of the metallic end fitting. To explore the immature draping process and to derive the draping tool geometry a digital twin based on finite element simulation has been developed and validated by first experiments.

The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites.

Unidirectional non-crimp fabrics (UD-NCF) are often used to exploit the lightweight potential of continuous fiber reinforced plastics (CoFRP). During the draping process, the UD-NCF fabric can undergo large deformations that alter the local fiber orientation, the local fiber volume content (FVC) and create local fiber waviness. Especially the FVC is affected and has a large impact on the mechanical properties. This impact, resulting from different deformation modes during draping, is in general not considered in composite design processes. To analyze the impact of different draping effects on the mechanical properties and the failure behavior of UD-NCF composites, experimental results of reference laminates are compared to the results of laminates with specifically induced draping effects, such as non-constant FVC and fiber waviness. Furthermore, an analytical model to predict the failure strengths of UD laminates with in-plane waviness is introduced. The resulting stiffness and strength values for different FVC or amplitude to wavelength configurations are presented and discussed. In addition, failure envelopes based on the PUCK failure criterion for each draping effect are derived, which show a clear specific impact on the mechanical properties. The findings suggest that each draping effect leads to a “new fabric” type. Additionally, analytical models are introduced and the experimental results are compared to the predictions. Results indicate that the models provide reliable predictions for each draping effect. Recommendations regarding necessary tests to consider each draping effect are presented. As a further prospect the resulting stiffness and strength values for each draping effect can be used for a more accurate prediction of the structural performance of CoFRP parts.

Material Modeling in Forming Simulation of Three-Dimensional Fiber-Metal-Laminates – A Parametric Study

Forming of fiber-metal-laminates (FML) into complex geometries is challenging, due to the low fracture toughness of the fibers. Several researchers have addressed this topic in recent years. A new manufacturing process has been introduced in our previous work that successfully combines deep drawing with thermoplastic resin transfer molding (T-RTM) in a single process step. During molding, the fabric is infiltrated with a reactive monomeric matrix, which polymerizes to a thermoplastic after the forming process is completed. In our previous work, a numerical modeling approach was presented for this fully integrated process, investigating a hybrid laminate with 1 mm thick metal sheets of DC04 as top layers and three inner glass fiber layers. Although initial results were promising, there were still some pending issues regarding the modeling of material behavior. The current study aims to address several of these open issues and to provide a general modelling framework for future enhancements. For this purpose, the existing modelling approach is extended and used for parameter analysis. Regarding the influence of different material characteristics on the forming result, shear, bending and compression properties of the fabric are modified systematically. It is shown, that the compression behavior and particularly the tension-compression anisotropy of the fabric is of high importance for modelling the combined forming of fabric and metal. The bending and shear properties of the fabric are negligible small compared to the metal stiffness which dominates the draping process. Finally, it is demonstrated that modelling the fabric layers using continuum shells provides a promising approach for future research, as it enables a suitable way to account for transversal compaction during molding.

Wrinkle and boundary detection of fiber products in robotic composites manufacturing

PurposeThe paper aims to focus on a vision-based approach to advance the automated process of the manufacturing of an Airbus A350’s pressure bulkhead. The setup enables automated deformation and draping of a fiber textile on a form-variable end-effector.Design/methodology/approachThe proposed method uses the information of infrared (IR) and color-based images in Red, Green and Blue (RGB) representative format, as well as depth measurements to identify the wrinkles and boundary edge of semi-finished dry fiber products on the double-curved surface of a flexible modular gripper used for laying the fabric. The technique implements a simple and practical image processing solution using a sequence of pixel-wise binary masks on an industrial scale setup; it bridges the gap between laboratory experiments and real-world execution, thereby demonstrating practical and applied research.FindingsThe efficacy of the technique is demonstrated via experiments in the presented work. The two objectives as follows boundary edge detection and wrinkle detection are accomplished in real time in an industrial setup.Originality/valueDuring the draping process, tensions developed in the fibers of the textile cause wrinkles on the surface, which are highly detrimental to the production process, material quality and strength. The proposed method automates the identification and detection of the wrinkles and the textile on the gripper surface. The proposed work aids in alleviating the problems caused by these wrinkles and helps in quality control in the production process.

Experimental Characterization of the Fiber Angles of Multiple Curved Laminate Segments Using Prepreg-Based Carbon Fiber Reinforced Polymers as a Structure for a Non-Engaging Bellows Coupling

This paper deals with the experimental characterization of the fiber angles of multiple curved laminate segments using prepreg-based carbon fiber reinforced polymers as a structure for a non-engaging bellows coupling. The main task of this generic shaft coupling is the torsionally stiff torque transmission and the compensation of axial displacement as well as the angular misalignment of metallic shafts. The multiple curved structure can be manually draped by several cut segments using epoxy-based fabric prepreg. Moreover, the intended initial fiber orientation of the laminate is ±45° with respect to the rotation axis of the structure. For the experimental determination of the local fiber angles various CFRP cut segments were defined as CFRP specimens with varying number of layers and constant width. All investigations were based on cured CFRP specimens. The measurements were performed with a robot-assisted optical surface sensor and an optical digital microscope. The influence of the manual draping process according to the z-method could be quantitatively determined by the fiber angle measurements.

Development of a Modular Draping Test Bench for Analysis of Infiltrated Woven Fabrics in Wet Compression Molding

The wet compression molding (WCM) process enables short cycle times for production of fiber-reinforced plastics due to simultaneous infiltration, viscous draping and consolidation in one process step. This requires a comprehensive knowledge of occurring mutual dependencies in particular for the development of process simulation methods and for process optimization. In this context, it is necessary to develop suitable test benches to enable an evaluation of the outlined viscous draping behavior. In order to evaluate and suitably design the draping process, grippers are mounted on a surrounding frame, which enables targeted restraining of the local material draw-in during forming. In supporting the development of the new test bench, first experimental and simulation results are compared, which thereby enables a first validation of the simulation approaches. Results show a good agreement between experimental and numerical results in terms of shear deformation and final gripper displacement under dry and viscous conditions. Results recommend that future development for investigations of viscous draping effects should focus an enabling measurement of gripper displacement during the forming process. Beyond that, the modular test bench design enables experimental and virtual draping optimization and deduction of blank holder concepts for WCM tools.

Influence of tension–shear coupling on draping of plain weave fabrics

Although tension–shear coupling of weave fabrics in large deformation has been observed in experiments, most constitutive models for weave fabrics often ignore this coupling effect for simplicity. In this paper, a nonlinear anisotropic hyperelastic constitutive model is proposed to consider this tension–shear coupling effect. Draping experiments of a plain weave fabric over a tetrahedron mold are carried out to validate the proposed coupling constitutive model. Subsequently, the influences of tension–shear coupling on draping processes are investigated. Numerical simulation results indicate that the tension–shear coupling effect significantly changes fiber reorientation during draping process, which makes shear deformation tend to be uniform and reduces the local shear deformation concentration and should not be neglected in woven fabric stamping with salient double curvatures.

Automated Planning and Optimization of a Draping Processes Within the CATIA Environment Using a Python Software Tool

This thesis deals with the challenge of the virtual generation and optimization of complex production processes within the Computer Aided Design (CAD) environment CATIA V5. A flexible robot end-effector –(Modular Gripper) is used for automated draping process which serves as an example application. Previous experiments have shown that manually selecting all process parameters that are needed to adapt the grippers geometry is a very time consuming and inaccurate method. For this reason, a tool was developed that is able to determine or optimize the end-effector specific process parameters offline. Since all existing models are available in the CATIA environment, the goal was to perform this optimization process within the same environment. The software tool is based on a hierarchical architecture where all calculations and logic optimization processes are processed in the programming language Python. All commands in the CATIA environment are performed with the help of small, modularized CATScript programs that are able to interact with main Python algorithms. This work is intended to lead to a virtual optimization process that can be universally applied to complex manufacturing processes. Since it is based on a Python framework that is able to interact directly with the CATIA environment, it is flexible enough so that it can be adapted to further processes.

Development of a membrane-shaped MR-based composite draping tool

Nowadays, the manufacturing process of composite parts is still dominated by a high level of cost-intensive manual tasks which impedes the use of these materials in composite processing SMEs as well as in high-end automotive and aerospace industries. The draping of fibre sheets is often still carried out manually because of the difficult handling properties, the high variety and complexity of the materials and the product contours. Even the current manipulation tools, for composite draping or preforming in moulds, often lack controllability and flexibility to cope with a high mix of features in the composite product. In automation, these problems are often answered by cost-increasing multi-robotic systems, using multiple degrees of freedom in combination with a large range of feature-specific tools. The need for rather simple, cost-effective manipulation tools triggered the development of a membrane-shaped magnetorheological (MR) based composite draping tool. First, a fluid-filled bag will cover the mould entirely and will perform the initial forming of the composite material whilst both preventing the creation of wrinkles and securing the readily draped areas during further processing. Subsequently, by applying local pressure on the fibre sheet through magnetic activation, draping in narrow or corner-like features will be enhanced. Furthermore, slippage of fibrous material between the membrane and the mould surface can be mastered during forming, facilitating the control of fibre orientation and shear angles. First experimental tests indicate that this technique shows large potential to enable full automation of the entire draping process by the flexible use of a single robot arm and multitool whilst being product and feature independent.