Carbon Fibre Reinforced Plastics Parts Research Articles

Multiscale modeling for viscoelasticity of woven CFRP considering preforming and curing effects via finite element and long-short term memory analysis

The constitutional model is crucial to model the complex response of woven carbon fiber reinforced plastics (CFRPs) during curing. This study developed a multiscale modeling method to describe the viscoelastic behavior of preformed woven CFRP parts during curing. The essence of the viscoelastic modeling lies in the stiffness matrix, which was predicted via the long-short term memory (LSTM) model. A library of viscoelastic stiffness components for the LSTM model was created through finite element method (FEM) on mesoscopic representation volume elements (RVEs). Specifically, FEM models for RVEs with different configurations were established first, and then utilized for virtual relaxation tests to build the stiffness component library for the woven CFRP. Afterwards, the LSTM model was embedded into the material model for FEM at the part-level. Finally, prediction accuracy of the multiscale modeling method for viscoelasticity of the woven CFRP samples were validated by experiments with the average error of 6.62%.

Ultrasonic full guided wavefield for damage detection in curved CFRP parts

Guided waves can propagate from flat plates to curved structures and carry structural health information. In this paper, an ultrasonic guided wave inspection method is proposed for detecting damages in curved parts made of carbon fibre reinforced plastics (CFRPs), such as hat-stringer-stiffened panel. By collecting full wavefield information, we obtain the standing wave information formed by the interaction between guided waves and damage. The interaction mechanism between guided waves and damage is simulated through finite element simulation, and the wavefield curvature imaging algorithm is used to generate a damage image in the curved area. Furthermore, a specimen with delamination damages is fabricated, and full wavefield information is collected through a scanning laser Doppler vibrometer (SLDV). We then use the proposed imaging algorithm to detect delamination damages of different sizes. The experimental results were consistent with the simulation results, confirming the effectiveness of the proposed method. Notably, the technology combines the advantages of guided waves and SLDV, which can obtain full wavefield information without contact, including damage-related characteristics. This work provides a convenient and comprehensive method for collecting wavefield information on complex curved CFRP parts for structural health monitoring, which would significantly improve quality control for CFRP components in various fields.

Investigation of Drilling Holes in CFRP for Aircraft Using cBN Electroplated Ball End Mill Using Helical Interpolation Motion

Investigation of Drilling Holes in CFRP for Aircraft Using cBN Electroplated Ball End Mill Using Helical Interpolation Motion

Influence of carbon fiber non-crimp fabrics stitching parameters on the out-of-plane permeability in liquid composite molding process

The widespread use of carbon-fiber-reinforced plastics (CFRP) has attracted many industries such as defense, and aerospace as well as in sailboats, automotive, and rotor-blades, where high strength-to-weight ratios are required. For the aerospace and defense customer today, the importance is no longer just on minimum weight and therefore performance, but primarily on cost of ownership. Textile-manufactured composites, particularly of non-crimp fabric (NCF) type offer significant cost savings in terms of reduced labor time and higher deposition rates over the unidirectional prepreg tape which is the most traditional method. Vacuum vacuum-assisted infusion method is the most used production technic in CFRP parts which also offers high fiber ratios. The most important goal is the impregnation of carbon fiber package in a through-the-thickness direction to get good quality parts in infusion. The behavior of the impregnability depends mainly on the out-of-plane permeability of the fabric. The fiber type, orientation of the fibers, and the stitching parameters, mainly influence the permeability of the fabric. In this study, the influence of textile parameters on the out-of-plane permeability of UD (unidirectional) carbon fiber NCF was investigated. The stitching yarn parameters (stitch pattern, stitch tension, and stitch length) were varied to see the influence on the out-of-plane permeability. The out-of-plane permeability was measured using a tailored visual flow front monitoring method by measuring resin flow distance on the X and Y axes of the fabric during infusion. The results show that the out-of-plane permeability of the UD (0°) carbon fiber NCF is significantly affected by the stitch pattern, stitch tension, and stitch length.

Additive manufacturing-inspired approach to re-manufacture fiber reinforced plastic with programmable orientation of recycled carbon fiber

The carbon fiber recycled from end-of-life Carbon Fiber Reinforced Plastic (CFRP) offers a low-cost and environmentally friendly option to produce CFRP parts. However, the reclaimed carbon fibers (rCFs) are usually in a discontinuous and disordered form, which limits the performance of fiber-filled composite. An additive manufacturing-inspired approach is proposed to re-manufacture CFRP, in which the rCFs were dispersed and orderly deposited to form a slice of pre-defined rCF sheet with programmable fiber orientation, then the rCF sheets were stuck layer by layer to fabricate aligned rCF reinforced plastic (rCFRP). Experiments show that preferential alignment degree, flexible strength and electric conductivity of designedly aligned rCFRP were 0.96, 393.53 MPa and 7.23 × 10−1 S/cm, respectively, which are significantly higher than the unoriented rCFRP (0.28, 217.59 MPa and 1.07 × 10−2 S/cm). This approach paves the way for additively fabricating rCFRP parts with customized performance by arranging rCFs orientation.

Ultrasonic fatigue analysis of 3D-printed carbon fiber reinforced plastic

The development of 3D printing technologies using composite materials has revolutionized additive manufacturing. Using these technologies, various products can be fabricated with strengths beyond the limits of the strength of the polymer used. However, although parts manufactured using carbon fiber reinforced plastic (CFRP) 3D printing have excellent characteristics, research on their durability is lacking, making their application difficult in the real industry. In this study, an ultrasonic fatigue test was conducted on a CFRP material manufactured by 3D printing to evaluate fatigue performance. Because of the characteristics of CFRP, the strength varies depending on the orientation angle of the carbon fiber, and the durability also varies. Therefore, an experiment on three types of specimens mixed in the bi-direction and uni-direction of 0° and 90° was conducted. For the ultrasonic fatigue test, a specimen design with a special shape is required according to the resonance frequency and dynamic modulus of the material. To this end, a specimen was designed based on measurements of the physical properties of the material according to the angle of the fiber, which were verified by Finite element method (FEM) modal analysis, and the fatigue life was estimated through an actual experiment. The fatigue failure life was simulated by FEM fatigue analysis considering the measured fatigue test results and the derived anisotropic properties simultaneously. Additionally, based on the advantages of CFRP 3D printing, which adjusts the fiber pattern, we fabricated a specimen with a concentric pattern to derive the fatigue life and calculate the actual life improvement. Based on the results of this study, the specific rigidity of the CFRP parts can be optimized by adjusting the fiber pattern. Additionally, the results of this study can aid in the analysis of the fatigue characteristics of 3D-printed CFRP materials.

Automatically controlled laser-based welding process for repair of CFRP parts

Due to a high strength-to-weight ratio, carbon fiber-reinforced plastics (CFRPs) have become a standard in the lightweight industry, which results in the development of new machining and repairing methods. Specifically, CFRP with a thermoplastic matrix material is more attractive for many applications as a thermosetting matrix material. Thermoplastic matrix materials enable new joining processes due to their thermoformability and weldability. Currently, the repair process is mainly executed manually. In order to reduce repair costs, an automated, reliable, and fast process is needed. For the new laser-based repair process, first a scarf joint is prepared in a CFRP laminate consisting of a thermoplastic polyphenylene sulfide matrix material. To refill the scarf, a patch with the same matrix material and fiber setup as the original laminate is cut into shape and welded into the scarf area. In order to obtain a reliable and stable welding process resulting in high weld seam qualities, an automated controlled welding process is being used, which controls the laser power via the surface temperature, which is detected by a pyrometer. For the development of the welding process, the influence of the welding time and the surface temperature on the resulting weld seam quality were evaluated. For the analysis of the joining quality, overlap samples were welded and tested in order to determine the weld seam strength. In addition, cross sections were prepared and analyzed with a microscope. Finally, the measured results were correlated in order to determine a parameter set generating a high-quality weld seam.

Improvement of Mechanical Properties and Forming Efficiency during Hot Gas Forming of CFRP Curved Surface Components.

Carbon fiber reinforced plastics (CFRP) are widely used in aerospace and new energy vehicles due to their high specific strength and flexible design ability. At present, the traditional forming process of CFRP curved surface components has problems of low mechanical properties and long processing time. In this paper, a new method of hot gas forming was proposed to obtain CFRP components. By applying high temperature and high-pressure gas on one side of CFRP, the material was forced to deform and solidify at the same time. A special device for hot gas forming was designed and developed. The curing behavior and mechanical properties of original CFRP plates were studied. The main defects and the corresponding control methods of hot gas forming parts were analyzed by forming spherical parts, and the feasibility of the hot gas forming process was verified. Taking the battery cover plate of a new energy vehicle as the research object, the influence of forming temperature, gas pressure, pressurization rate and other process parameters on the mechanical properties of complex CFRP components were analyzed. The mechanism of both strength and efficiency improvement was analyzed. The results showed that with the increasing of gas pressure, the tensile strength and forming efficiency of the CFRP curved components were improved obviously. Under reasonable forming parameters, the tensile strength of the obtained parts was increased by 37%, and the forming efficiency was increased by 58%. The fiber bundles were distributed more evenly and compactly under the hot gas forming. This showed that the use of hot gas forming had good potential in the preparation of high-performance CFRP parts, which was helpful to improve the processing efficiency and forming quality of CFRP curved parts in the aerospace and new energy automotive fields.

Variable thickness design for composite materials using curvilinear fiber paths

Carbon fiber reinforced plastic (CFRP) laminates are often used in a quasi-isotropic manner, such as in cross-ply lamination; thus, the mechanical properties of the CFRP cannot be fully exploited. In this study, we proposed a carbon fiber design method, which uses fiber orientation and thickness as the lamination parameters, where the fiber orientation is determined using the principal stress direction and the fiber thickness is determined by iterative calculations of the maximum stress theory using the bisection method. The method also accounts for manufacturability by considering fiber bundles and modifies the fiber orientation and thickness accordingly. As a result of implementing this method, the weight of wing plate model was reduced by approximately 5% with a failure index of approximately 0.7 compared with that using the constant thickness linear lamination model. Thus, the weight can be reduced while maintaining the strength, which may be useful for further weight reduction of conventional CFRP parts.

Continuous manufacturing of CFRP sheets by rolling for rapid fabrication of long CFRP products

The application of CFRP (carbon fiber reinforced plastic) parts in the automotive industry is limited by their labor-intensive and time-consuming manufacturing processes. Moreover, the strong demand for long products, such as components with a length of 25 m used in high-speed railroad vehicles, requires the manufacturing of long CFRP sheets, which are extremely difficult to produce using the conventional autoclave process. To achieve the rapid production of long CFRP products, a method of continuously manufacturing CFRP sheets by rolling is proposed in this study, and the effects of the preheating and curing times as well as the gap between rollers on the properties of the produced CFRP sheets such as void fraction, thickness, strength and formability are investigated. The CFRP sheets produced by the newly proposed rolling process have comparable performance characteristics such as void fraction, strength, formability, energy absorption and load tolerance to those of the CFRP sheets fabricated by the autoclave process. Owing to its much higher manufacturing efficiency, the rolling process is expected to replace the conventional time-consuming autoclave process for the fabrication of long CFRP sheets for a wider range of engineering applications.

Blank geometry design for carbon fiber reinforced plastic (CFRP) preforming using finite element analysis (FEA)

Carbon fiber reinforced plastics (CFRPs) have attracted growing attention from transportation industry because of their superior performance over metal counterparts. The thermoforming process has been invented for mass-production of CFRP parts. This thermoforming process involves multiple steps and numerous parameters, and one of the most important process parameters is the initial blank geometry. To optimize blank geometry in thermoforming and minimize trimming work for the final part, an innovative approach integrating automatic mesh adjustment and FEA modeling method for preforming is developed as foundation of design and reported in this paper. Preliminary trial-and-error optimization algorithm demonstrates that this newly-developed approach can accurately design blank geometry under various typical process conditions.

Self-resistive electrical heating for rapid repairing of carbon fiber reinforced composite parts

Carbon fiber reinforced plastics have been widely applied in aircraft structures, which require more rapidly repairing process when carbon fiber reinforced plastics structures are damaged. A novel method of self-resistive electrical heating to rapidly repair carbon fiber reinforced plastics parts was investigated, which utilizes the electrical current passing through the carbon fiber to generate heat and directly cure the whole carbon fiber reinforced plastics patches. A portable self-resistive electrical repairer with automatic temperature control unit was developed. Repair experiments of self-resistive electrical and the electrical blanket heating were conducted, in which the heating temperature distribution field was observed by the thermal infrared imager. The degree of cure of different samples was characterized, and the cross-section morphology and void content of different samples were assessed. Flexural and inter-laminar shear tests were carried out. The experiment results showed that the flexural and interlaminar shear strength recovery ratio of self-resistive electrical repaired samples attained to 85.48% and 65.89%, which was the same or even slightly higher level as the blanket repairing process, but only cost 62% repairing period and 58% repairing energy of the later one. Finally, from the experimental results, the heat transfer behavior of different processes was analyzed.

Hybrid Structure Design of Lightweight Robotic Arms Based on Carbon Fiber Reinforced Plastic and Aluminum Alloy

Some light materials, such as hollow sphere composite (HSC), carbon fiber reinforced plastic (CFRP), and aluminum alloy (AA), are currently used in the design of lightweight robotic arms. However, the high cost limit the use of HSC, the CFRP has a relatively low cost but poor processing property, and the AA has good processing property but relatively high density. To make up respective shortcomings, this study focuses on the design issues of lightweight robotic arms by using two kinds of materials. Based on the CFRP and AA, a hybrid structure design approach is proposed to minimize the total mass of the lightweight robotic arms with CFRP/AA hybrid structure. To accomplish the objective, structural dimensions and layer parameters in hybrid structures are parameterized as design variables subject to the strength, stiffness, and dynamic constraints. Moreover, the bonding strength of the interaction surfaces between CFRP and AA parts is also considered on the basis of the cohesive zone model (CZM). In optimization design, the ABAQUS and elitist non-dominated sorting genetic algorithm (NSGA-II) in modeFRONTIER utilizing the Python script are respectively employed for the structural analyses and iteration calculation. Finally, a design example and an experimental prototype are provided to validate the proposed method and compare with the previous AA prototype in mass with a reduction of 24.32%.

Shell 要素を用いたCFRP 部品のモデル化

Shell 要素を用いたCFRP 部品のモデル化

Numerical and experimental investigation of manufacturing and performance of metal inserts embedded in CFRP

Due to their outstanding specific mechanical properties, carbon fibre reinforced plastics (CFRP) exhibit a high application potential for lightweight structures. With respect to multi-material design and to avoid drilling of structural CFRP parts to join them to other components, embedded metal elements, so called inserts, can be used. The inserts consist of a shaft and a baseplate which is embedded between the fibre layers. So far, only punctiform inserts have been subject to research. One feasible geometry are linear inserts which have not been studied yet. In this work, the performance of two different types of linear inserts will be investigated. The shapes are based on a punctiform insert which is made out of a threaded shaft welded onto a baseplate whose performance under different types of loading has been investigated before. The first type of linear inserts has the same cross-section as the reference punctiform insert but is of a linear form. The second type is a quasi-linear insert which consists of a baseplate with the same dimensions as the first linear inserts and three threaded shafts welded onto it. All samples are manufactured by resin transfer moulding (RTM). Depending on the geometry of the insert and the preforming concept it is potentially possible to maintain the fibre continuity. For the inserts with a continuous shaft and in the proximity of the insert, it is necessary to cut fibres of the top layers which are aligned perpendicular to the shaft. For the quasi-linear insert, it is possible to maintain the fibre continuity as the fibres are guided around the circular shafts. Additional to mechanical tests that are carried out, mould-filling and curing simulations are performed for different inserts to analyse the influence of the process parameters onto the part quality. In the main series of tests, the specimens are characterized regarding their failure behaviour and load bearing capacity under quasi-static loads. The results of the experiments show that, compared to the punctiform reference insert, the linear load introduction elements exhibit higher load bearing capacity. However, the linear load introduction elements are inferior regarding specific load bearing capacity and furthermore increase process complexity during preforming and production.

Damage detection of cracks in carbon fibre reinforced composites by pulsed eddy-current testing

Non-destructive evaluation techniques that are based on electromagnetic methods are commonly used for inspection of metallic and carbon fibre reinforced plastics parts. Some of these inspection methods are based on eddycurrents which are generated by the electromagnetic induction phenomenon occurring under variable magnetic induction field. In eddy-currents testing, the depth of penetration into the material is controlled by the conductivity of the tested material and also the work frequency. Transient eddy-currents, also called pulsed eddy-currents, is an emerging non destructive technique that employs a pulsed excitation to induce a transient electromagnetic response from defects lying deep within a conducting structure. Such defects are difficult to inspect by conventional techniques, such as harmonic eddy-currents or ultrasonics. A large number of recent scientific publications have dealt with the theoretical understanding of the pulsed eddy-currents phenomenon and have also undertaken the design feature of appropriate probes. Finite element solution of the governing equations has been used to simulate the output signals as function of the input electrical excitation signal. Considering a B-scan strategy, simulation of a pulsed eddy-currents based probe is performed in this work with the objective to assess detectability of small defects through monitoring impedance changes of a detection probe.

Prediction of mechanical properties of porous CFRP specimens by ANNs and X-ray CT data

Carbon fiber reinforced plastics (CFRPs) have evolved into the primary material for several lightweight structures. However, despite their extensive use and the quality amelioration, CFRPs remain susceptible to a variety of manufacturing defects, the most common of which are the pores. Predictive tools capable of correlating the mechanical properties of CFRP parts with the characteristics of defects as derived from non-destructive testing (NDT) techniques or even further with the manufacturing parameters could serve as an effective tool for the quality control of CFRP structural parts. In the present paper, the characteristics of pores as evaluated by X-ray Computed Tomography (CT) have been correlated with the matrixdominated mechanical properties of unidirectional porous CFRP specimens using Artificial Neural Networks (ANN). Thirty (30) porosity scenarios have been created and given as input to the numerical model. That multi-scale numerical model, which had been validated experimentally, has been used for training the ANN model. The predictions of the ANN agree very well with results from mechanical tests. Moving one step forward, a second ANN has been developed to correlate the autoclave pressure directly with the mechanical properties of the CFRP specimens. The validity of the latter ANN depends on the accuracy of the relation between the autoclave pressure and the characteristics of the pores. The present work represents a step towards the development of effective quality control tools for composite materials.

A numerical methodology for simulating the mechanical behavior of CFRP laminates containing pores using X-ray computed tomography data

Abstract Pores are the most common defect in carbon fiber reinforced plastics (CFRPs). Numerical predictive tools capable of taking into account the porosity characteristics, as detected by efficient non-destructive testing techniques, could be potentially contribute to the quality control process applied by the industry in manufacturing of CFRP parts. In the present paper, a numerical methodology is developed for simulating the mechanical behavior of porous CFRP unidirectional (UD) laminates by exploiting data extracted from X-ray computed tomography scans. The analysis of detected pores is performed using the VG Studio MAX software. The software parameters are validated by optical microscopy measurements. The progressive damage modeling method is applied in three simulation levels. In the first level, the behavior of the epoxy resin, in the presence of small pores, is simulated by means of a representative unit cell (RUC). In the second level, the behavior of the epoxy resin, in the presence of small and large pores, is simulated by means of a RUC comprising the epoxy resin, in which the behavior simulated from the first level simulation is assigned, and a single pore (MObject) in which all large pores are clustered. The elastic properties and strengths of the porous UD ply, needed in the simulation of the specimen (third level), are computed using analytical micromechanics relations. The proposed methodology was used to simulate the transverse tensile behavior and predict the properties of three different UD CFRP laminates containing pores of different content. The numerical results show a small decrease of transverse stiffness and a significant decrease of transverse tensile strength with increasing the pore content. The methodology was validated through comparison with tension tests.

Investigation of an automated dry fiber preforming process for an aircraft fuselage demonstrator using collaborating robots

High-performance carbon fiber-reinforced plastics (CFRP) see a continuous growth of their share in structural weight. In particular, in Aerospace, this includes the production of large components, where the key issue of significant high costs remains persistent. The Center for Lightweight Production Technologies in Augsburg as a part of the German Aerospace Center (DLR) addresses this problem with solutions for process automation to increase repeatability, process robustness, and cost-efficiency. This paper presents an approach for automated preforming of large CFRP parts by means of collaborative robots. Investigations include process development for robotic handling of large-carbon fiber cut- pieces and validation on a full-scale demonstrator. The experimental verification is focused on a demonstrator geometry that represents a fuselage section of a typical short- to mid-range aircraft. The work is completed by a discussion about the challenges, solution approaches, and observations. The presented semi-automated preforming process with collaborating robots is an important intermediate step on the way to a fully automated production process for large Aerospace parts made of CFRP.

Spinning of Staple Hybrid Yarn from Carbon Fiber Wastes for Lightweight Constructions

The reuse of CF-wastes (rCF) is desirable due to the energy-intensive manufacturing, high price and the disposal problem of carbon fibers. It is a challenging process to spin yarn from rCFs in a short staple spinning production line which ensures a much higher strength later in the manufacturing of CFRP (carbon fiber reinforced plastics) parts than that of the parts from rCF-nonwovens or, from short-fiber reinforced injection molded parts. This spinning technology consists of several subsequent processes such as carding, drafting and spinning on a flyer frame. It is possible to produce hybrid yarn up to 2000 tex, which fineness is similar like a roving. The machines used to produce yarn for this purpose were specially modified and adapted, so that the brittle CF can be processed smoothly. Carded and draw frame slivers with different fiber lengths and mixing ratios were produced and later the high-quality hybrid yarn has been spun with different yarn twists.