Carbon Fiber Reinforced Plastic Components Research Articles

Monitoring techniques for carbon fibers reinforced plastics used as complex structures

Carbon fiber reinforced plastics (CFRP) have become an indispensable part of modern life. CFRP materials continue to be used in a large number of applications ranging from aerospace systems to automotive, industrial and consumer products. CFRP have evolved both in reinforcement and matrix. The epoxy resin was the most usually matrix for CFRP. The reliability of these materials is essential, especially when it comes to safety-relevant components. The service life of CFRP components is affected by aging processes or improper use. Nondestructive evaluation methods which can be applied for examination carbon/epoxy laminates, manufactured by autoclave processing method with different ply stacking sequences [0]8 and [(45/0)2]s are presented. The samples were realized from 4 plates of carbon-epoxy manufactured at the Faculty of Mechanical Engineering, University of Ljubljana, Slovenia. The paper present influence of thermal treatment and stacking sequence on damage delamination’s due to impact about mechanical properties. Ultrasound and electromagnetic nondestructive evaluation methods are used for good localization of damage and characterization composite materials and other techniques can provide complementary information once the damage location is known.

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.

Life cycle impact assessment of different manufacturing technologies for automotive CFRP components

A comparative life cycle assessment analysis among pressure bag molding and bag molding with autoclave for the manufacturing of car components in carbon fiber reinforced plastic (CFRP) was carried out. Four scenarios were analyzed: i) autoclave bag molding with aluminum mold, ii) autoclave bag molding with CFRP mold and plastic master, iii) autoclave bag molding with CFRP mold and medium density fiberboard master, and iv) pressure bag molding with aluminum mold. The collected data for life cycle inventory derives from an Italian manufacturer of CFRP car components, scientific references and Ecoinvent database. Cumulative energy demand, global warming potential, ReCiPe midpoint and endpoint methods were used as impact and damage categories for quantifying the environmental impacts of the different manufacturing processes investigated. The results showed that the pre-impregnated composite fibers with thermoset polymer matrix, used as input material for the four investigated scenarios, represents the main source of total environmental impact, due to the use of polyacrylonitrile as a precursor for carbon fibers. The comparison among the environmental assessments of the different scenarios demonstrated that the most impacting process is the autoclave bag molding with composite mold and polyurethane master, whilst the most sustainable process is the autoclave bag molding with aluminum mold.

Simulation of current distribution in a wind turbine blade using the FDTD method

Lightning can pose one of the major natural threats to wind turbines. In special, rotor blades are the most sensitive components to lightning due to their material, constructive nature and movement. Modern multimegawatt wind turbine blades use a combination of glass fiber and carbon fiber reinforced plastic components (CFRP). The last one is electrically conductive and needs to be considered as part of the lightning protection system. In this paper, we present the application of the FDTD method to investigate the lightning current distribution in a wind turbine blade equipped with a 25 m CFRP spar. We found, that for low spar-to-down conductor bonding electric contact resistances, peak currents are higher in the spar, but most of the energy is conducted by the down conductor. The high peak currents in the CFRP would produce intense resistive voltage drops at the connections with the risk of sparks if milliohm connection resistances cannot be achieved. The simulations show that voltages between isolated CFRP laminates of the spar should not pose a threat of sparking if the insulation properties of glass fiber can be ensured in the entire spar. Dangerous voltages between the down conductor and the CFRP spar can occur if the bonding connection at the tip is located far from the end of the spar.

Laser Wavelengths Suitable for Generating Ultrasonic Waves in Resin-Coated Carbon Fiber Composites

Abstract For the non-destructive inspection of carbon fiber-reinforced plastic (CFRP), lasers can be used to generate ultrasonic waves. It is important to optimize the wavelength of the laser to ensure the intense excitation of a usable propagating mode. Real CFRP components used in the construction of airplanes and automobiles are often coated with several types of resin to protect against weathering. These resin layers change the excitation of the ultrasonic waves. Thus, the optimum laser wavelength may be changed by the coating resin. In this paper, we investigated the excitation of ultrasonic waves in a resin-coated CFRP plate using different laser wavelengths. We conducted experiments to convert the laser wavelength using periodically poled LiNbO3 (PPLN) devices. By injecting mid-infrared laser to a coated sample, we observed excited ultrasonic waves using a laser Doppler vibrometer. We found that transparent resins significantly increase the amplitude of the first-arriving longitudinal wave. Furthermore, when the laser was strongly absorbed in the surface layer, the excitation of longitudinal waves was suppressed. These results were clarified by a one-dimensional model of the thermal generation of ultrasonic waves. We concluded that a laser passing through a resin layer is a viable candidate for the effective inspection of coated CFRP by laser ultrasonic waves.

Influence of surface treatment with infrared nanosecond laser on adhesion performance of adhesion-bonded carbon fiber/epoxy composite

The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm laser pulse can remove the polymer matrix from composite surface to expose the carbon fibers by expansion of the pyrolysis gas resulting from laser-induced polymer degradation. The influences of laser power density and scan strategy on matrix removal process have been studied. The bonding strength of laser processed, adhesion-bonded CFRP (carbon fiber reinforced plastic) increase with lower matrix residues on the fibers and a linear relation is found. The adhesion-bonding strength of CFRP surfaces, tested by lap-joint shear test, exceeds the strength measured for untreated and abrasion treated (SiC paper) samples. The main origin of fiber damage of the laser-treated surface is mechanical fracture rather than thermal damage as found by laser scanning confocal microscope and scanning electron microscope. The characteristic morphologies and failure modes of shear-tested surfaces are analyzed. The obvious improvement of adhesive strength is achieved by the laser-treated surfaces attributed to matrix removal and carbon fibers protruding. A 1 D model is established to describe temperature and internal gas pressure of the irradiated surface. The new laser treatment method needs less laser energy and low pulse numbers and prove the way to an efficient, low-cost surface treatment for preparation of high quality adhesion bonded CFRP components.

Sampling phased array technology for the detection of voids in carbon fiber-reinforced plastics

In the lightweight material industries, the current focus is on fiber-reinforced plastics, in particular on carbon fiber-reinforced plastics (CFRPs), since they offer higher relative specific tensile strength and stiffness as well as reduced weight compared to conventional metallic materials. Currently, the quality assurance of manufactured CFRP components represents a major challenge for CFRP manufacturers. Voids are generated during the infusion process of CFRPs, which in turn reduce the mechanical performance of CFRPs. This article presents the possibility to detect the distribution of voids across the surface of CFRPs by using a non-destructive testing method, the so-called sampling phased array ultrasound technology. Two types of CFRPs with six carbon layers in the same direction are fabricated by means of a vacuum-assisted resin infusion process. Voids in CFRPs are generated using a foaming agent during the impregnation process. The C-scan images produced through the sampling phased array technology are subsequently analyzed by the optical image analysis software in order to determine the amount of voids for each type of manufactured CFRP.

Preparation of carbon fibers coated with epoxy sizing agents containing degradable acetal linkages and synthesis of carbon fiber-reinforced plastics (CFRPs) for chemical recycling

New epoxy resins containing degradable acetal linkages were synthesized by the addition reaction of bisphenol-A (BA) and epoxy-functionalized vinyl ethers containing hydrophilic oxyethylene chains, 2-(vinyloxy)ethyl glycidyl ether (VEGE) and 2-[2-(vinyloxy)ethoxy]ethyl glycidyl ether (VEEGE). Carbon fibers were applied with the obtained degradable epoxy resin-based sizing agents (designated as BA-VEGE and BA-VEEGE) in ordinary (1.4 ~ 2.2 wt%) or excess (6.4 ~ 13.4 wt%) amounts. Interfacial adhesion between the carbon fibers applied with the degradable epoxy resin-based sizing agents and matrix resins (bisphenol-A-type epoxy resin) was evaluated by the microdroplet method. Carbon fibers with both degradable epoxy resins as a sizing agent showed improved adhesive properties compared with the desized carbon fibers. Using the degradable sizing agent-applied carbon fibers, carbon fiber-reinforced plastics (CFRPs) were prepared by laminating prepreg sheets and heating them under pressure. The tensile properties of the CFRPs with [0]50 lay-up did not depend on the structure of the sizing agents, but the tensile strength decreased as the amount of sizing agent used increased. On the other hand, the tensile properties of the CFRPs with [0/90]12S lay-up were not dependent on the structure or volume of sizing agents used. The impact toughness of the CFRPs was evaluated by the charpy impact test. When an ordinary volume of sizing agent was applied, the CFRPs with degradable epoxy resin-based sizing agents exhibited higher levels of impact strength than the commercial sizing agent-based CFRPs. However, applying an excessive volume of sizing agent to carbon fibers led to a decline in impact strength. The degradation reaction was conducted under acidic conditions by the treatment of HCl at room temperature or 70 °C. CFRPs with degradable epoxy resins as sizing agents in ordinary volumes were barely decomposed due to insufficient degradable regions in the CFRP components. However, the CFRPs applied with excess degradable sizing agents decomposed and carbon fibers were recovered. The new epoxy resins containing degradable acetal linkages were synthesized and used as sizing agents for carbon fibers. Using the degradable sizing agent-applied carbon fibers, the carbon fiber-reinforced plastics (CFRPs) were prepared via laminating prepreg sheets and heating them under pressure. The mechanical properties of the obtained CFRPs were comparable with those of the conventional CFRPs. With the treatment of acidic conditions, the CFRPs with the degradable sizing agents on carbon fiber surface were decomposed and the carbon fibers could be recovered.

Design, data analysis and measurement uncertainty evaluation of an eddy-current sensor array for in-process metrology of carbon fiber reinforced plastics

Composite lightweight components of carbon fiber reinforced plastics (CFRP) provide great potential for the automotive industry. Yet, due to their complexity, there is a high amount of quality defects in their production processes. Thus, this article deals with an approach for in-process metrology of CFRP components by means of an eddy-current sensor array. First, the development of the sensor design and its in-process integration is introduced. Second, a method for the quantitative evaluation of the measurement data as well as the measurement uncertainty is elaborated. Finally, a machine learning approach for the classification of crucial defects is shown.

Measurement Analysis for Increasing Resource Efficiency during Autoclave Processes for the Production of Fiber Composites

Fiber-reinforced plastics are known as outstanding lightweight composite material, which are used in various areas. Especially the demand for components made of carbon fiber reinforced plastics (CFRP) has steadily increased within the last years due to their high strength and stiffness combined with light weight. The manufacturing of CFRP components is a cost-intensive and time-consuming process due to frequently required and challenging manual operations for several working steps. In order to remain competitive and meet the small-batch production because of increasing desire for individuality and diversity, the manufacturing process of CFRP components needs further development. In order to face these challenges, this paper focuses on the resource efficiency of curing processes with the autoclave technology. The measurement analysis of the different energy consumers of the autoclave at changing the curing parameters (temperature, pressure, time) shows how the settings affect the resource efficiency of curing processes. Finally, the authors present their recommendation for action in order to increase resource efficiency.

Damage Monitoring of Composite Components under Vibration Fatigue using Scanning Laser Doppler Vibrometer

This research article proposes experimental methods for monitoring damage propagation of Carbon Fibre Reinforced Plastic (CFRP) components under vibration fatigue. High cycle fatigue (HCF) behaviour of composites is often not as dramatic as that of metal alloys, where any crack initiation might rapidly lead to failure. Instead, composites HCF behaviour is often a prolonged state of continuous degradation of the resin-to-fibre bonding. Furthermore, the interlaminar contact conditions at any opening delamination cause complex dynamic responses, which can be nonlinear and temperature dependent. Vibration fatigue is generally caused by large deformations which can be suitably measured by non-contact measurement systems. Hence, this paper explores the application of the scanning laser vibrometer to monitor damage propagation of CFRP components under vibration fatigue loading. The objective is to show how this measurement system can systematically implement a set of experimental methods aimed at monitoring the dynamic properties during the crack propagation caused by fatigue. The set of experimental techniques are autonomously executed by a custom-made control panel. A thermal camera is also part of the measurement chain and provides qualitative information about location of temperature hot spots and damage evolution.

Edge trimming of carbon fibre reinforced plastic

In recent years the use of Carbon Fibre Reinforced Plastic (CFRP) has transitioned towards mass manufacture applications, heightening the requirement to improve both the processing capability and production cost. Machining is a key process which CFRP components often undergo, in order to achieve final assembly requirements, however, it can introduce delamination, poor surface roughness and even result in component scrap. Furthermore, the rate of tool wear and subsequently cost of tooling can be high. This paper investigates the effect of cryogenic CNC machining using liquid nitrogen on tool wear and machined surface quality for edge trimming of CFRP using different cutting tool geometries. The results show that the cutting environment has a significant effect on CFRP surface roughness and delamination for both cutting tools beyond a short period of accelerated tool wear. The cryogenic environment improved the average surface roughness of samples by 28.1% independent of cutting tool geometry compared to dry machining. Improvement to delamination was only found in samples machined with the up-down compression cutting tool, which resulted in 49.9% reduction in delamination. The lack of improvement to delamination found with the multi-tooth cutting tool is likely due to increased prevalence of the chipping mode of tool wear in cryogenic cutting environment. In contrast, the abrasive wear zone of the up-down compression cutting tool exhibited higher sharpness than in dry machining and the geometry appears to be well suited for achieving improvements in surface quality and tool wear under cryogenic machining. This research indicated the high interaction between cutting tool geometry and machining environment.

Modeling for CFRP structures subjected to quasi-static crushing

Carbon fiber reinforced plastic (CFRP) composite materials demonstrate significant promise to further improve weight to performance in automotive engineering. Nevertheless, design of CFRP components for crashworthiness criteria remains rather challenging and typically requires laborious trial-and-error processes. This study aims to promote computational design of CFRP structures by establishing effective constitutive model that is implemented in the commercial finite element code Abaqus/Explicit. Two different numerical models (namely, the single layer shell model and the stacked shell model) were developed to simulate experimental crushing tests on the square CFRP tube. The effects of key parameters for these two FE models were analyzed, respectively. The comparisons of numerical results with experimental data indicated that the 9 layers stacked shell model is capable of reproducing experimental results with relatively higher accuracy. Based on the validated modeling approach, crushing behaviors of several CFRP thin-walled structures with different cross sectional geometries and thicknesses were further explored. The failure modes and key indicators in relation to the structural crashworthiness were investigated for identifying a best possible sectional configuration. It is found that the circular tube shows superior specific energy absorption capacity of all different tubal configurations with the same wall thickness, meaning that the tube with circular section is of good potential asa crashworthy CFRP structure.

Crash concepts for CFRP transport aircraft – comparison of the traditional bend frame concept versus the developments in a tension absorbers concept

ABSTRACTDue to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.

Surface grinding of CFRP composites with rotary ultrasonic machining: a mechanistic model on cutting force in the feed direction

For carbon fiber-reinforced plastic (CFRP) composite components, especially advanced CFRP components with complex three-dimensional features, surface grinding is often needed to generate final dimensions and functional surfaces. Surface damages are frequently induced during surface grinding, reducing the load-bearing capability and service life of the components. Therefore, it is desirable to perform surface grinding of CFRP in a high-quality and high-efficiency way. Rotary ultrasonic machining (RUM) surface grinding has been investigated to machine CFRP for improved surface quality. Cutting force is one of the most important output variables for evaluating RUM surface grinding. The modeling of cutting force is essential to effectively control the occurrence of surface damages during RUM surface grinding of CFRP. In the RUM surface grinding process, the workpiece material is primarily removed by abrasives on the tool peripheral surface, thus it is essential to investigate the feed-direction cutting force model. However, such models are not available in the literature. In this study, for the first time, a mechanistic feed-direction cutting force model in RUM surface grinding of CFRP is established based on the assumption that the material is removed by brittle fracture. The mechanistic model has one parameter, fracture volume factor of the workpiece material, which needs to be determined by an experiment. There is a good consistency between theoretically predicted trends and experimentally observed results on the relationships between feed-direction cutting force and input variables.

Method for Quantitative 3D Evaluation of Defects in CFRP Using Active Lock-in Thermography

To guarantee an economic application of carbon fibre reinforced plastics (CFRP) throughout the entire product life cycle, the long term operational reliability and reparability of the products must be assured. The typical repair process starts with the defect detection and the defect evaluation. Based on the size and position of the defects the mechanical properties are evaluated and the most efficient repair process is selected. Therefore, the accuracy of the defect detection is essential for an economic repair process.One approach to detect defects in CFRP is the active lock-in thermography, which is an imaging non-destructive testing method. The application of image processing algorithms on phase images enables automated defect detection in CFRP components. The determination of the depth position of defects is still a challenge since the phase images contain a superposition of different depth layers.This paper introduces a method to quantitatively evaluate the 3D defect geometry from a stack of thermography images captured with different excitation frequencies. The phase images of blind bore holes are analysed. Digital evaluation criteria, e.g. area, enveloping circle and position, are defined. Algorithms for image correction, feature extraction and image analysis are implemented for automated defect detection.The stack of thermography images captured with different excitation frequencies is used to estimate the defect's depth range. With the given thermal diffusivity and the excitation frequency the depth information is calculated. The results are visualized three-dimensionally. The method is validated by the comparison of the experimental results with calibrated coordinate measuring machine data.

Rotary Ultrasonic Surface Machining of CFRP Composites: A Comparison with Conventional Surface Grinding

Rotary ultrasonic machining (RUM), a hybrid nontraditional process technology combining ultrasonic machining and grinding, has been proven to be a promising method for hole making of CFRP. Due to its advanced capabilities, RUM has been further extendedly applied in surface machining: rotary ultrasonic surface machining (RUSM). Carbon fiber reinforced plastic (CFRP) composites have found extensive applications in areas such as aerospace, automotive, and sports due to their superior material properties. CFRP components are usually near net shaped after molding processes, however, additional surface machining is still required to generate the final dimensions and functional surfaces of the advanced CFRP components especially with three-dimensional features. However, the investigations on RUSM of CFRP are very limited and there are no reported studies on comparisons between RUSM and conventional surface grinding (CSG) of CFRP. In this paper, for the first time, a comparative study between these two processes of CFRP in the aspects of axial and infeed-directional cutting forces, torque, and surface roughness is conducted. In order to better understand the material removal differences between these two processes, the kinematic motions of the abrasive grains are also analyzed and compared.

Experimental Investigation of the Hole Accuracy, Delamination, and Cutting Force in Piercing of Carbon Fiber Reinforced Plastics

Legislative regulations limit allowable CO2 emissions from automotive vehicles. One possibility to reduce CO2 emissions is lightweight design using carbon fiber reinforced plastics (CFRP). However, high costs of CFRP components prevent them to be adapted for price sensitive and high volume applications in the automotive industry. CFRP components are manufactured near-net-shape. In order to fulfill geometric or functional requirements, they have to be trimmed or pierced in finish processing. In high volume production, shearing can be potentially implemented for a highly productive and cost e_cient piercing and trimming of CFRP components. Up to now, there exists little technological knowledge on the applicability of shearing for CFRP finish processing. In order to address this knowledge gap, an experimental investigation of CFRP piercing with round cutting line was performed in this work. The e_ects of the process parameters like cutting clearance, blank holder pressure and cutting edge radius on the dimensional and shape accuracy of the pierced holes as well as the cutting forces were experimentally investigated and possible explanations for the observed phenomena formulated.

Low-frequency modulation-assisted drilling of carbon-epoxy composite laminates

Carbon fiber-reinforced plastics (CFRPs) have a wide spectrum of industrial applications because of their outstanding multifunctional properties. However, the machining performance of CFRPs is poor which has restricted further expansion of their application range. The damage that is induced during machining is considered as a major hindrance for the applicability of CFRP components for structural applications. In order to mitigate this perplexing challenge, an emerging machining method namely, modulation-assisted machining has been adopted which has not been investigated earlier in context of drilling of CFRP laminates. The drilling performance of the CFRP laminates has been analyzed using both conventional and modulation-assisted drilling techniques. The influence of the feed, frequency of rotation, drill geometry, frequency of modulation, and modulation amplitude on the force and subsequently damage has been experimentally investigated. The results indicate that modulation-assisted drilling technique produces better quality holes than conventional drilling under identical conditions.

A novel method for curing carbon fiber reinforced plastics by high-pressure microwave

Traditional autoclave molding process is energy-consuming and time-consuming. To deal with this issue, a novel method for curing the high performance carbon fiber reinforced plastics (CFRP) by high-pressure microwave is presented. The high-pressure microwave curing equipment has been developed, which enables the microwave energy be imported into the autoclave under high pressure, and the temperature of the component could be real-time monitored and controlled. A series of tests have been carried out to study the curing effects of this equipment. The results show that, comparing with traditional autoclave curing, the high-pressure microwave curing save energy and time significantly. Furthermore, the properties of the CFRP irradiated by microwave under the high-pressure outweigh those cured by autoclave. Specifically, there are no obvious defects in the CFRP components cured by high-pressure microwave; the CFRP exhibits more ductile behavior which cured by high-pressure microwave. The mechanical properties of the specimens are enhanced. The failure of the CFRP mainly occur in the inner of the resin matrix, which indicate that the interfacial strength is stronger. In conclusion, it is promising to improve the interfacial properties and mechanical property of CFRP in an efficient and economical way by high-pressure microwave curing.