Fiber Reinforced Plastic Components Research Articles

Test Setup for Investigating the Impact Behavior of Biaxially Prestressed Composite Laminates

AbstractInstrumented impact testing and compression-after-impact testing are important to adequately qualify material behavior and safely design composite structures. However, the stresses to which fiber-reinforced plastic components are typically subjected in practice are not considered in the impact test methods recommended in guidelines or standards. In this paper, a test setup for investigating the impact behavior of composite specimens under plane uniaxial and biaxial preloading is presented. For this purpose, a special test setup consisting of a biaxial testing machine and a specially designed drop-weight tower was developed. The design decisions were derived from existing guidelines and standards with the aim of inducing barely visible impact damage in laminated carbon fiber-reinforced plastic specimens. Several measurement systems have been integrated into the setup to allow comprehensive observation of the impact event and specimen behavior. A feasibility test was performed with biaxially prestressed carbon fiber-reinforced plastic specimens in comparison with unstressed reference tests. The compressive-tensile prestressing resulted in lower maximum contact forces, higher maximum deflections, higher residual deflections and a different damage pattern, which was investigated by light microscopic analysis. Finally, the functionality of the experimental setup is discussed, and the results seem to indicate that the test setup and parameters were properly chosen to investigate the effect of prestresses on the impacts behavior of composite structures, in particular for barely visible subsequent damages.

Spherically curved woven fabrics: geometrical calculation methods and weave pattern development

The demand for woven spherical shapes, particularly in applications such as fiber-reinforced plastic (FRP), is increasing. However, the production of woven two-dimensional fabrics in three-dimensional (3D) shapes using conventional weaving machines faces technical limitations. As a result, draping and cutting processes are commonly employed to transform flat woven fabrics into 3D shapes, leading to challenges such as structural distortions, thread interruptions, layer overlaps, and high cutting losses. To address these issues, this research introduces a novel weaving technology that enables the creation of spherically curved woven fabrics utilizing conventional weaving machines. Using the developed technology it is possible to fabricate double curved fabrics without the cutting and usual draping processes that can be implemented to reinforce FRP components. The study presents mathematical models capable of calculating the required 3D surfaces for such fabrics. By adopting this technology, the need for draping and cutting processes can be eliminated, leading to improved quality and structural integrity of the final product.

Investigation of the Bonding Mechanism between Overlapping Textile Layers for FRP Repair Based on Dry Textile Patches.

Lots of damaged fiber-reinforced plastic (FRP) components are replaced by new components instead of repairing. Furthermore, only very labor-intensive repair methods are available on the market to fully restore the integrity of the structure. This requires a high level of experience or, alternatively, very cost-intensive technology, such as the use of computer tomography and robotics. The high costs and CO2 emissions caused by the manufacture of FRP components then bear no relation to their service life. The research project IGF-21985 BR "FRP-Repair" aims to solve the named challenges. Using semiconductor oxide catalysts, the matrix can be locally depolymerized by ultraviolet (UV) radiation, and thus removed from the damaged area of the FRP component. Subsequently, the damaged fibers in this area can be detached. By using customized textile repair patches and local thermoset reinfiltration, the repair area is restored. With this process, the fiber structure can be repaired locally with new fibers on the textile level. The repair is similar to the original production of a fiber composite in an infusion process. No additional adhesive material is used. As a result, repaired FRP structures with restored mechanics and a near-original surface can be realized. This article provides an insight into the actual steps of the development of the FRP component repair process using dry textile patches. The empirical investigation of overlapped rovings and UD material showed the expected results. Residual fracture forces of up to 86% could be achieved. The most interesting approach on the roving level was splicing the overlapping fibers. The free ends of the fibers of the patch and part are mechanically bonded. This bond at the textile level is further strengthened by infusion with matrix.

3D Reconstruction Method of Carbon Fiber Reinforced Plastics Components Based on Pre-calibration Measurement Pose

According to the surface reflection characteristics of carbon fiber reinforced plastics and the geometric characteristics of aircraft panel parts, a robot automatic measurement system based on line laser scanning is designed. The selection criteria of measurement pose and the pre-calibration method of measurement pose based on a laser tracker are given. A 3D reconstruction method of global stitching of large-scale parts based on pre-calibration measurement pose is proposed, Finally, the correctness and effectiveness of the proposed method are verified by measuring typical samples with a prototype system.

Quantifying hole quality through geometry accuracy and surface qualities in rotary ultrasonic machining of carbon fiber–reinforced plastic composites

Rotary ultrasonic machining has been approved as an effective and efficient hole making process for carbon fiber–reinforced plastic composites. Hole quality plays an important role in assembling carbon fiber–reinforced plastic components and can be affected by the carbon fiber reinforcement structures. In this study, experiments are conducted to assess hole quality in carbon fiber–reinforced plastic composites with three carbon fiber reinforcement structures under different combinations of machining variables. Hole quality is quantified through geometrical accuracy (perpendicularity, cylindricity, and hole diameter) and surface qualities (delamination and surface roughness). Results show that the highest level of interlacement among yarn of plain woven structure induce the highest level of compression to the workpiece and the largest amount of additional material removal, leading to the largest perpendicularity and hole diameter. The worst fabric integrity of unidirectional structure generates the largest amount of non-uniform material removal on the machined surface, resulting in the largest cylindricity. It is also found that compared with woven structures, unidirectional structure is more likely to induce push-out delamination due to its smaller critical energy release rate. The lowest constancy of the fabric in twill woven structure leads to the largest surface roughness.

Adaptive FRP Structures for Exterior Applications

Regarding modern, daylight-flooded buildings with large window façades, appropriate shading systems to improve the energy consumption of climate controlling systems are becoming more relevant. Building envelopes contribute largely to the temperature control and should be at best installed on the outside to prevent the interior from heating up. Preferably, those systems work with minimum maintenance and maximum robustness, covering as much of the window area as possible. Previous shading systems were mostly based on rigid-body mechanisms using error-prone joints. Components, whose movability is achieved by a local compliance of the material, offer a way to avoid the usage of mechanical joints. Within this paper, a new fiber-reinforced plastic (FRP) façade shading demonstrator called “Flexafold” is presented. Its opening and closing movement are controlled by pneumatic cushions which are integrated directly into the laminate set-up. The Flexafold shows thereby the possibility of producing self‑supporting, adaptive FRP components whose actuators are integrated into the component and thus protected in exterior applications. The functional principles and components of Flexafold, e.g. the locally compliant FRP material, the folding pattern and the integrated actuator system, are explained within this paper. Furthermore, a comparison to existing adaptive façade shading systems “flectofin ® ” and “Flectofold” is given. Copyright © VBRI Press

Ultrasonic assisted peripheral milling of fiber reinforced plastics in consideration of clamping and cutting edge geometry

In the field of machining fiber reinforced plastics (FRP) with defined cutting edges, there is still a high demand for research and development, especially, when various fiber types are embedded. Thus, when machining glass fiber reinforced plastics, the application of uncoated tools from tungsten carbide is often state of the art. This material is subject to excessive wear during machining FRP, which negatively affects the process performance and makes a regular tool change necessary. This is caused by a high abrasiveness of the fibers and by vibrations of the FRP components, which affects the cutting edge. One approach to reduce the process forces and therefore reduce tool wear is to superimpose the tool movement with a longitudinal high-frequency movement in ultrasonic range. Many studies showed that this technology is able to generate advantages in drilling and face milling processes. Primarily it reduces tool wear and improves machining quality. This study shows that positive effects also occur during peripheral milling of FRP, especially when using an unstable clamping. In this case, ultrasonic assistance can reduce the machining forces significantly. Additionally, it is shown that the shape and the state of wear of the cutting edge affects the impact of ultrasonic assistance in this application case.

Engineering of three-dimensional near-net-shape weave structures for high technical performance in carbon fibre–reinforced plastics

To tap the full potential of reinforcing fibres for lightweight construction of sustainable carbon fibre–reinforced plastic components, woven three-dimensional reinforcement structures open up innovative approaches by integrating functional features. In this work, a novel three-dimensional shuttle weaving technology was taken advantage of to study carbon reinforcement structures with uninterrupted load trajectories from three points of view. Mechanical principals, economic and environmental issues were focused to provide an overall picture. Near-net-shape reinforcement fabrics with load trajectory–compliant yarn paths and interconnected layers that are interwoven in thickness direction were objects of investigation. The effects of a closed fabric selvedge, only producible by shuttle weaving, were investigated too. The here presented novel technology enables complex woven reinforcement structures that otherwise would demand several fabric layers leading to limited properties and lower performance of the carbon fibre–reinforced plastics due to missing interconnections between the layers. The studies on exemplary rods revealed a close relationship between different three-dimensional weave structures and the carbon fibre–reinforced plastic’s mechanical properties. The three-dimensional structures were woven in a single-step process and subsequently infiltrated with epoxy resin in the Vacuum Assisted Process (VAP®) and mechanically tested. Rounding off, universal guidelines for the layout of three-dimensional fabrics for rods were derived therefrom. The economic and environmental aspects of the complete process line were compared to the conventional manufacturing procedures for carbon fibre–reinforced plastic by material flow cost accounting. Looking at sustainability, material flow cost accounting showed that lightweight three-dimensional components with integrated features can be produced cost-effectively with less environmental impact by the novel weaving technology. Its capability for high-quality serial production of three-dimensional reinforcement structures is evident, which was one major result of the work.

Mechanical Characterisation of Carbon Fibre-Reinforced Plastics with Defined Defects

A steadily increasing application of fibre-reinforced plastics in the field of lightweight construction has been observed in the course of the past two decades. Currently a major challenge in the growing high technology market is the quality assurance of manufactured fibre-reinforced plastic components. During different stages in the manufacturing process of fibre-reinforced plastics, defects of different types and sizes are enclosed in them, exerting a destructive influence on the performance of fibre-reinforced plastics in various practical applications in terms of strength, stiffness and brittleness. Thus the aim of this research project was to investigate the effect of defined local defects on the mechanical properties, such as tensile, flexural and impact properties, of fibre-reinforced plastics, in particular carbon fibre-reinforced plastics. Results show that these mechanical properties depend significantly on the type and size of defect.

Adaptive fiber-reinforced plastics based on open reed weaving functionalization

It is aimed at realizing adaptive, and thus mechanically adjustable fiber-reinforced plastic (FRP) components with complex 2D layouts so that complex 3D deformation of adaptive FRPs can be achieved. Therefore, the textile-technical integration of shape memory alloys into reinforcing fabrics is required. Hence, this paper presents the development of adaptive FRPs, where nickel-titanium-based shape memory alloy was structurally integrated into textile-reinforced semi-finished products by means of open reed weaving technology to generate adaptive FRP components. After manufacturing of the functionalized preform, it was infused by both a thermosetting resin system and a thermosetting system modified by means of plasticizer. Results of thermo-mechanical characterization revealed that the deformation of adaptive FRPs increased fourfold by adding the plasticizer to the reference thermosetting resin system.

Structure optimisation of metallic load introduction elements embedded in CFRP

The combination of construction parts made of fibre-reinforced plastics (FRP) and metal holds great lightweight design potential but places high demands on the necessary joining technologies. Metallic load introduction elements that are embedded in the manufacturing process of FRP components are a promising joining technology. In order to fully exploit the potential of this technology, approaches to increase the load bearing capacity of inserts, particularly under pull-out loads, have been missing. The aim is therefore to derive a method for the simulative structural optimisation of embedded inserts. The load bearing capacity increases under pull-out loads through smoothing of failure-critical stress peaks using the optimisation of the thickness distribution of the insert’s base plate. The increase of the load bearing capacity of the optimised insert geometry is confirmed through experimental validation.

Challenges and Opportunities of RFID Sensortags Integration by Fibre-Reinforced Plastic Components Production

In the past decade the use of Radio Frequency Identifcation (RFID) technology has become a substantial part in our daily live. Applications such as supply chain management, inventory tracking and access control has been influenced by this emerging technology. In the course of Industry 4.0, RFID technology is considered to enable smart production processes, where the work-in-progress can be monitored in real time. In addition RFID tags with sensing capabilities (RFID sensortags) can contribute to an in-process control during manufacturing processes. The integration of RFID sensortags in fibre-reinforced plastic (FRP) components during the production process offers many opportunities. Such as controlling the process of vacuum infusion with integrated pressure sensors. In addition to this, it would also be possible to control the internal curing temperature of the resin during the hardening process using temperature sensors. This paper shows the integration of RFID sensortags in FRP during textile preforming. Therefore, two FRP with integrated RFID sensortags were manufactured and as functional test the internal material temperature was measured. The FRP were made out of glass- as well as carbon-fibres. Furthermore a concept of an automated integration process of RFID sensortags during a FRP production will be described. The production processes of FRP are automated for the most parts. One of the challenges is to involve the integration process of the RFID sensortags during the production process of FRP. Another challenge is the handling of the RFID sensortags themselves which comes in the form of gripping, positioning and bonding of RFID sensortags on the textiles. Therefore the RFID sensortag design has to be optimized for the automated production process.

Smart and energy-efficient dust suction concept for milling of fibre-reinforced plastics

Fibre-reinforced plastic (FRP) are becoming increasingly important in aerospace and premium automotive applications. Usually, the manufacturing of FRP components requires dry machining which generates large quantities of dust. Because of their small size, the dust particles are extremely harmful to machine components and the operator’s physical health. To prevent long-term damage an effective suction system is required. Currently, extraction systems are subsequently integrated into conventional machine tools with no regard to energy efficiency. Hence, this paper introduces the development of an energy-efficient and intelligent dust suction concept for dry machining of FRP. Numerical flow simulations are used to investigate the effectiveness of a central suction as well as local suction at the cutting tool. In order to evaluate the newly developed concept, the amount of extracted particles along with the necessary volumetric flow rates are assessed. The simulation results demonstrate an improved dust particle extraction and an energy saving potential of up to 70%.

Joining Parameters and Handling System for Automated Subpreform Assembly

The production and processing of fiber-reinforced plastics (FRP) is constantly increasing in industry. A commonly used method is resin transfer molding (RTM). FRP components are produced for large series by now. Therefore, the aspect of processing efficiency is becoming more and more important. The semi-finished product can be better exploited, for example, if large preforms were composed of single subpreforms. These subpreforms are easier to drape and can be produced within an automated line. Consequently, the necessary assembly of the subpreforms needs to be automated as well. This way, the process can be made time and resource efficient. The article that follows now will focus more closely on a concept that deals with the handling and subsequent assembling of subpreforms. Furthermore, the variables that can be adjusted for the assembly process are examined and their influence on the resulting connection quality is shown.

Development of seamless woven node element structures for application in integral constructions

In order to advance consistent lightweight construction principles in automotive and mechanical engineering, support frame construction made from high-performance materials is becoming more commonplace. These consist of complexly structured nodular connection elements. The required connection elements have not yet been produced satisfactorily. The developed node element structures in this paper are produced on a shuttle weaving loom by flattening and weaving them as multi-surface woven fabrics. The development of the woven concept for the realization of node element structures is based on the fragmentation of the individual sub-elements. The goal of this research is development of a flexible technology for weaving fabrics and intended for the integral realization of woven nodular semi-finished products with complex geometries and connections, which are to be used to connect Fiber-reinforced Plastic components in support frame structures.

Blanking of Unidirectional Carbon Fibre Reinforced Plastics

Fibre reinforced plastics (FRP) are being increasingly used for advanced applications where an appropriate mechanical performance should be achieved at minimum weight. A substantial increase of the FRP usage is expected across various industries e.g. in automotive sector in the nearest future. This leads to the mass manufacturing of FRP components. Reduction of manufacturing costs of FRP components is regarded as the main enabler for the usage of this material in mass production. Although FRP components are manufactured near-net-shape, they often have to be pierced or trimmed in one of the last manufacturing steps. With rising production numbers blanking is a potentially more cost efficient technology for trimming and piercing of FRP components compared to the conventionally performed abrasive water jet cutting or machining. The mechanisms of FRP separation in blanking have not yet been researched. In particular, the influence of the fibre orientation relative to the cutting line on the cutting force is not known. In the scope of this work an experimental study of blanking of a unidirectional carbon fibre reinforced plastic with a thermoset resin at different fibre orientations to the cutting line was performed. It was shown that the cutting force decreases from the perpendicular to the parallel fibre orientation to the cutting line. A possible mechanical explanation of this dependency was formulated.

Interpreting process data of wet pressing process. Part 1: Theoretical approach

The wet pressing process represents a new production method for carbon fibre-reinforced plastics components. Due to the low cycle times, it is suitable for use in the automotive industry. Therefore, a sufficient degree of industrialisation needs to be achieved, which is characterised by a stable process. The knowledge about relevant process parameters, their interactions, and influence on the part quality builds the basis of an economic process. This is a major challenge, since in the early stage of process development the available amount of recorded process data is small and the data sets are not complete. As the implementation of time-, material-, and cost-intensive experiments represents no acceptable alternative, a theoretical approach is chosen. This article describes a theoretical procedure to define the critical factors of the wet pressing process with significantly less resource input.

Integration Methods of Sensors in FRP Components

Structural health monitoring is an important research topic in the field of fiber reinforced plastics (FRP). An effective way to detect defects or overloads in these FRP has still not been found. One way to monitor the actual state of FRP components is via integrated sensors. Integrating current standard sensors negatively affects the flux of force. Therefore investigations about integration methods of sensors in FRP components have been made. The integration of an optical fiber sensor into FRP profiles via a pultrusion process was investigated. It could be shown that the pultrusion process is suitable method for the integration of fiber optic sensors for strain measurements. Another investigated sensor principle was the integration of piezoelectric polyvinylidene fluoride (PVDF) fibers via a vacuum assisted process. The PVDF fibers were integrated into 3-point bending specimen and the piezoelectric effect was tested with and without polarization. The investigation showed that it is possible to measure the piezoelectric effect of PVDF fibers integrated into a 3-point bending test specimen. It could also be shown that carbon fibers can be used as textile electrodes for the measurement of the generated charge on the PVDF surface.

Integrative Manufacturing of Textile-Based Sensors for Spatially Resolved Structural Health Monitoring Tasks of Large-Scaled Composite Components

For the continuous and non-destructive structural health monitoring (SHM) of fiber reinforced plastics (FRP), a one-step integration of one-or two-dimensional strain sensors based on piezo-resistive carbon filament yarns (CFY) into textile reinforced structures of subsequent FRP components has been realized during textile-technological manufacturing processes. The two-dimensional alignment of the sensor layouts is realized by a special process-integrated warp yarn path manipulation (WPM). With suchlike manufactured semi-finished reinforcement structures, a functional model of a small wind turbine blade in glass-fiber thermoset composite design has been build up. Using the CFYs’ piezo-resistive effect, mechanical strains can be measured and visualized due to a correlative change of the carbon filaments resistance. Performing quasi-static load tests on the blade and additional test specimens, comprehensible results of the electro-mechanical behavior and spatially resolving capacity of different sensor integration lengths have been achieved. The performed tests demonstrate, that global and even local mechanical stresses within complex FRP components can be measured spatially resolved using the approach of textile technologically integrated textile sensors.

Production of 3D Parts from Wood Chips in a Closed Mold Process

The application-oriented distribution of wood chips is a major obstacle in the production of 3D molded composite parts made of plastics and wood. Similar to fibers in conventional fiber-reinforced plastic components long chips can be used for force transmission. Short chips and wood powder can be distributed homogeneously between longer chips to increase the wood volume percentage and to allow post-processing-free edge areas. The applied process parameters during the incorporation of the matrix material determine the filling of the cavity and the impregnation of the chips. Different formaldehyde-free resin and adhesive systems, as well as thermoplastic powders are used as matrix material. By controlling the subsequent pressing process of the oriented and impregnated chips the density and wall thickness of the molded part can be influenced. In this work different production process variants and a concept for a modular 3D experimental mold are investigated. The flowability and bulk density of the wood chip fractions are characterized and the compression pressure required in the production process is determined. Initial tests with a panel mold are carried out and the bending strength of the manufactured specimen is examined.