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As hydrogen plays increasingly vital role in the future energy network, storage, one of the essential processes, has attained much attraction. It is necessary to develop efficient methods to assist in designing, manufacturing and evaluating hydrogen storage vessels for different application scenarios and standards. In this work, the theoretical calculation of fatigue life for cryo-compressed hydrogen (CcH 2) storage vessel have been detailed studied. Firstly, the temperature and pressure variation on the vessel liner were calculated under the refueling and discharging cycle. Subsequently, the stress cycling of the fragile winding layer was transformed by elastic-plastic mechanics method. Furthermore, the S–N curve method and residual strength/stiffness theory were used to calculate the fatigue of the winding layer and optimize the fatigue life, respectively. Finally, the rationality of the calculated fatigue life was verified by the comparison with existing research. The results shows that the fatigue life of CcH 2 storage vessel under cryogenic temperature will be smaller than under normal temperature. The optimized calculation of fatigue causes a certain change in the actual fatigue life, which can reach 1% compared to not correcting the fatigue life. The main failure form is transverse fracture of composite materials caused by compression. • Studying the vessel state of the refueling and discharging cycle process. • Studying the stress changes of the winding layer throughout the cycle. • Combing S–N curve, residual strength/stiffness theory to calculate the fatigue. [ABSTRACT FROM AUTHOR]

A chemical oxidation method for decomposing thermosetting epoxy resin at 40 °C is presented. This approach is notably more energy-efficient than previous methods. The recovered carbon fiber exhibits mechanical properties similar to virgin carbon fiber and improved surface properties. [Display omitted] • Chemical recycling proposes to decompose epoxy resin at a low temperature of 40 °C. • It is an outstanding energy-efficient method of chemical recycling methods for CFRP. • Recovered CF has similar mechanics to virgin CF and has improved surface properties. Here we report a novel chemical recycling of carbon fiber-reinforced plastic (CFRP) using meta -chloroperoxybenzoic acid (m CPBA) as the representative oxidizing agent. The optimal decomposition conditions for the epoxy (EP) resin in CFRP were investigated by varying m CPBA concentration and reaction time. The CFRP decomposed completely within 6 h using a 1.5 M m CPBA solution at 40 °C. Tensile strength of recovered CF (r-CF) measured 4.4 GPa, 93.6% of virgin CF (v-CF), and electrical conductivity reached 590 S/cm, 95% of v-CF. Furthermore, the interfacial shear strength (IFSS) of the recovered carbon fibers (r-CF) using EP resin and polyamide 6 (PA6) was analyzed. For EP resin, the IFSS of r-CF was 88 MPa, a 26 % increase compared to v-CF. In the case of PA6 resin, IFSS values were 80 MPa for r-CF, a 17% improvement over v-CF. The study highlights superior mechanical properties and favorable IFSS of r-CF, positioning them as promising for composite regeneration. Remarkably, this method operated at relatively low temperatures compared to existing technologies, with energy consumption recorded at 35 MJ/kg, establishing it as the most energy-efficient recycling method available. [ABSTRACT FROM AUTHOR]

• Based on the principle of superposition, the proposed method provides the displacements as the measured displacements. • The strain distributions are obtained from measured displacements without errors due to numerical differentiation. • The strains near the fiber-matrix interface are evaluated compensating for the insufficient resolution of microscope images. A DIC-FEM hybrid method is proposed to capture micro-scale deformation behavior near the fiber-matrix interface by combining displacement distributions measured using digital image correlation (DIC) with finite element method (FEM) analysis. Images of CFRP cross section with fine random pattern before and after deformation are taken with a laser microscope. The in-plane displacement components near the interface of fiber and matrix are obtained using digital image correlation and they are used as the input of the hybrid method. Not only the displacement distributions but the strain fields are determined using the proposed hybrid method, based on the superposition principle, so that the same distributions are obtained as those obtained by the measurement. The proposed DIC-FEM hybrid provides the strains near the interface between fiber and matrix, compensating for the insufficient resolution of microscope images. [ABSTRACT FROM AUTHOR]

• A bio-inspired CFRP tube was designed by mimicking the ceiba pentandra. • Quasi-static and dynamic axial crushing responses were studied. • Mesoscale failure mechanisms were explored by the scanning electron microscope. • Bio-inspired tube exhibited superior quasi-static and dynamic SEA than square tube. The multi-corner design approach can effectively enhance the energy absorption capacity of thin-walled metallic tubes under axial quasi-static and dynamic loading conditions. However, its efficacy in augmenting the crashworthiness performance of carbon fiber reinforced plastic (CFRP) tubes remains inconclusive, particularly due to the different failure mechanisms and pronounced strain rate effects inherent to CFRP materials compared to their metallic counterparts. Therefore, a type of bio-inspired multi-corner CFRP tube structure was designed by mimicking the non-convex cross-sectional shape of the root of ceiba pentandra tree, and its axial crushing responses were studied experimentally and numerically. Quasi-static compression and dynamic impact tests were conducted to compare the energy absorption capabilities of square and bio-inspired tubes with the same mass. The results showed that the specific energy absorption (S E A) of the square CFRP tube increased after adopting the bio-inspired design; however, different percentages of increase in S E A values were found under quasi-static and dynamic crush conditions, 13.5 % and 4 %, respectively. With the aid of finite element analysis and electron scanning technologies, the energy absorption mechanisms of bio-inspired tubes were further studied. It was found that the increase in S E A values was attributable to the increased number of axial splitting and secondary squeezing effects between internal fronds in the crushed tubes. Moreover, most of the fibers at the corner in a tube failed in tensile fracture mode during quasi-static testing, whereas they failed in both tensile and shearing fracture mode in dynamic testing, thereby leading to a reduction of energy absorption. Finally, two novel multi-corner tubes based on bio-inspired design and corner fractal design methods were proposed and they showed higher SEA values than initial one under dynamic impact. [ABSTRACT FROM AUTHOR]

Al/FeCoNiCrMo high-entropy alloy (HEA) coatings were prepared on the surface of carbon fiber reinforced plastic using plasma spraying technology. The microstructure of the HEA coatings was characterized under different spraying currents, and the hardness, interfacial bonding, corrosion resistance and friction and wear properties of the coatings were tested. The results showed that with the increase of the current, the unfused particles in the coatings decreased, and the coating porosity and thickness also decreased gradually; the hardness, corrosion resistance and friction and wear resistance properties increased with the increase of the current, in which the maximum hardness was 740.3 HV 0.1 , and the minimum self-corrosion current was 1.21 × 10−5 A·cm−2, and the minimum volumetric wear rate was 7.66 × 10−5 mm3·N−1·m−1. • Preparation of FeCoNiCrMo coatings with special properties on CFRP surfaces using plasma spraying technology. • Preparation of Al transition coating on CFRP to improve the interfacial properties between the coating and substrate. • FeCoNiCrMo coatings prepared with different spraying currents were studied. [ABSTRACT FROM AUTHOR]

In order to meet the hydrogen storage requirements of fuel cell vehicles, and improve the storage density of hydrogen, a cryo-compressed hydrogen storage method was proposed. The performance of cryo-compressed hydrogen storage vessel was analyzed in this paper. Based on the classical laminate theory and heat transfer solution, the stress and displacement of carbon fiber were precisely calculated to guarantee the cryo-compressed vessel severing in the cryogenic condition. Subsequently, the Tsai-Wu failure criterion was used to judge the failure of carbon fiber reinforced plastics layers. The stacking sequence, winding angle, comparison of the vessel's performance at room temperature and low temperature were conducted. The numerical results showed that the properties of storage vessel decreased at cryogenic condition, and the thickness of carbon fiber at cryogenic temperature at least increased by 47.06% than that at the room temperature. Mainly influence of low temperature on the cryo-compressed vessel were concentrated on the hoop stress of helical winding and the axial stress of hoop winding. For the vessel design, it is achievable to increase these two parts by using higher strength resin materials. • A method to design CcH 2 storage vessel was developed for vehicle applications. • Distributions of stress, strain and deformation of CcH 2 vessel were calculated. • Normal compressed vessel failed under cryogenic situation unless thickening. • Influence of low temperature can also be reduced by higher strength resin materials. [ABSTRACT FROM AUTHOR]

• Ex-ante analysis of recycling and recovery infrastructures for GFRP/CFRP waste. • Impacts of potential political regulations. • Impacts of potential markets for secondary materials. • Optimal choice of recycling and recovery options for GFRP/CFRP waste. Establishing recycling and recovery infrastructures for innovative materials like high-performance composites is very challenging. For such materials, recycling and recovery infrastructures are not yet established, research on end-of-life treatment technologies is still in the development state, and secondary markets for recycled materials are still missing. Against this background, we provide an ex-ante analysis on the design of future cost-minimal recycling and recovery infrastructures for glass (GFRP) and carbon (CFRP) fiber reinforced plastic waste from rotor blades of wind power plants based on a mathematical optimization model. We present insights into future capacities and technologies for the recycling and recovery infrastructures within the EU-28. We systematically analyze the impacts of political regulations and of secondary markets on the design of these infrastructures. While future recycling of CFRP mainly depends on the development of secondary markets independent of political regulations, GFRP is mainly combusted in incineration plants or co-processed in cement clinker plants. Hence, political decision makers should focus on providing measures that support the development of secondary markets for recycled carbon fibers and provide incentives for co-processing of GFRP to overcome capacity limitations. [ABSTRACT FROM AUTHOR]

• CFRP was recycled by using oxidative hydroxyl radicals generated in aqueous solution of NaOCl. • Chemical recycling efficiency was greatly improved through the use with surfactant. • There were few defects on the surface of the recovered carbon fiber, and it showed excellent quality. • It will improve the sustainability of CFRP through eco-friendly recycling method using water. The properties of infusibility and insolubility in organic solvent of cured epoxy resin makes it difficult to recycle carbon fiber reinforced plastics (CFRP). We have reported the recycling of CFRPs using the oxidizing power of hydroxyl radicals generated from NaOCl solution. In our study, we used benzyltrimethylammonium bromide (BTAB) and sodium dodecyl sulfate (SDS) for the interfacial separation between the epoxy resin and carbon fibers (CF). The surfactant system maximized recycling efficiency in both pretreatment and the main reaction of the CFRP recycling process. In the second step, the reaction time to successfully reclaim the CFs was much shorter, only one hour, compared with the two-hour reaction time for the non-SDS process previously reported by us. Scanning electron microscope images and Raman analyses showed that the surface of the reclaimed CF (r-CFs) was clean and smooth without any defects, and there was no significant structural change compared to virgin CF (v-CFs). The tensile strength of r-CF was 3.42 GPa which is 96.9% of the v-CF. Thus, the CFRP recycling process using SDS not only results in r-CF with good mechanical and physical properties, but also increases recycling efficiency by reducing the time. [ABSTRACT FROM AUTHOR]

• Glass and carbon fiber reinforced plastic waste masses within the European Union. • Material specific weight functions in dependence on rotor blade length. • Realistic projection of masses by normally distributed lifetimes of rotor baldes. • Simulation study to account for uncertainties within the estimation. The European Union is aiming at a circular economy and increased resource efficiency, which requires a waste management at the end-of-life of products. This is especially challenging for new and innovative products for which no recycling infrastructure exists so far. Wind power plants are such a product, for which large amounts of waste are expected within the next years as more and more plants reach their end-of-life. Especially the end-of-life rotor blades of wind power plants pose challenges with regard to waste management, since treatment options for the installed glass and carbon fiber reinforced plastics are still in a development stage. Moreover, material specific characteristics and technical aspects require separate treatment of these materials. To plan efficient treatment infrastructure, detailed knowledge on future waste streams is required. Against this background, this paper aims at estimating the mass of glass and carbon fiber reinforced plastic waste from rotor blades. To do so, we derive material specific weight functions and material specific shares to calculate the amount of installed glass and carbon fiber reinforced plastics in rotor blades. We apply normally distributed life times to project the calculated installed masses into the future and account for uncertainties within a simulation study. The estimation model is applied to a dataset of wind power plants within the European Union. Based on the considered dataset, we estimate that 570 [Mt] of fiber reinforced plastic waste will occur between 2020 and 2030 in the European Union of which 18 [Mt] are carbon fiber reinforced plastic waste. [ABSTRACT FROM AUTHOR]

• An ultrasonic imaging method is proposed to identify delamination accurately in CFRP laminates. • An anisotropic acoustic model is constructed to extrapolate forward and backward wavefields. • A solution to far-field radiation patterns based on the group velocity distribution of qP-wave is proposed. • Structural noise and artifacts caused by the anisotropy and multilayered structure properties can be degraded. In ultrasonic reflection method, the precision of defect detection in thick carbon fiber reinforced plastics (CFRP) is compromised by acoustic energy attenuation. An energy-compensation reverse time migration (ECRTM) method is proposed to identify multiple defects accurately. Forward and backward wavefields are formed using the finite element method within an anisotropic acoustic model based on the Christoffel equation and Bond transformation. To enhance the imaging quality of CFRP laminates, a novel cross-correlation imaging condition is introduced to compensate for energy dissipation caused by geometric diffusion and variations of the far-field radiation intensity at the emitter with the propagation direction. Employing ultrasonic detection technology with a multi-element array, numerical and experimental research on defect imaging was conducted, considering delamination with various sizes and positions in a multidirectional CFRP laminate. In comparison to other ultrasonic imaging methods, the near-surface artifacts in RTM images are mitigated by the far-field radiation directivity factor, while the deep information is enhanced by the geometric diffusion compensation factor in the ECRTM images. As a result, the precise position of delamination in CFRP laminates is achievable, demonstrating superior imaging capabilities, especially for deep delamination. [ABSTRACT FROM AUTHOR]

In this study, X-ray computed tomography (X-ray CT) was used to investigate internal defects generated on machine milled carbon fiber reinforced plastics (CFRP). Internal defects such as cracks, fractures, and deformation of the carbon fibers, which are invisible from the surface, were observed using the X-ray CT method. Defects were generated based on the machining method and direction of the fibers. A large number of defects were generated when using the conventional cut method along 45°, 90°, and the climb cut method along 90°. Few internal defects were observed when using the climb cut method along 45°; however, the machined surface was very rough. The mechanism for these phenomena was investigated by studying surface observations and cutting force, in addition to X-ray CT imaging. These results indicate that X-ray CT is a powerful tool for visualizing internal defects in CFRP, which differ significantly based on the direction of the fiber and machining method used. • Internal defects generated on machined CFRP was observed by X-ray CT method. • The species of internal defect differed by the fiber direction and machining method. • The mechanism for defect generation was studied by surface shape and cutting force. [ABSTRACT FROM AUTHOR]

Due to its inherent material properties, the implementation of niobium carbide (NbC) as hard phase in cutting materials represents a promising alternative to machining. Recent investigations show equivalent tool life in metal cutting compared with cemented carbides based on tungsten carbide (WC). Besides metal cutting, the machining of high-performance composite materials poses an increasing importance due to its growing demand in the automotive and aeronautical sector. NbC and its wear resistance against abrasion can be suitable for this specific application. Additionally, the low density of NbC indicates an advantageous dynamic behaviour. Thus, this study focuses on the milling of carbon fiber reinforced plastics (CFRP). Complex tool geometries are implemented in a peripheral milling strategy. The machining trials are conducted with uncoated NbC-based cutting materials in CFRP with varying cutting speeds v c. The utilized NbC compositions (NbC-10TiC)-6Ni7.5VC and (NbC-15TiC 7 N 3)-5Ni7.5WC2.5Mo 2 C embedded in a Nickel (Ni) matrix were applied and compared towards their performance with an industrial available cemented carbide (WC-Co). As tool life criteria, a tool diameter reduction of Δd = 0.1 mm and a cutting path of l c = 10.000 mm were defined. Apart from tool life performance, the workpiece quality was assessed. An inferior performance was identified with (NbC-10TiC)-6Ni7.5VC in terms of tool life compared to WC-Co, which can be attributed to microstructure issues. Yet, (NbC-15TiC 7 N 3)-5Ni7.5WC2.5Mo 2 C shows a competitive performance in machining with an achieved cutting path l c identical to WC-Co. It can be stated, that NbC-Ni systems can accomplish an equivalent performance in comparison to WC-Co when machining CFRP. [ABSTRACT FROM AUTHOR]

Abstract Accurate determination of ultrasonic travel time from a start point to an end point with known positions is fundamental to the application of total focusing method (TFM) to ultrasonic array imaging. However, this is particularly challenging for CFRP laminates whose wave propagation is complex due to material anisotropy and refractive ply interfaces. In this paper, a ray tracing method using Dijkstra's path-finding algorithm is presented and used to calculate time delays of TFM. This modified TFM, termed ray tracing TFM, was demonstrated by post-processing full matrix capture (FMC) data from a 5.79-mm-thick multidirectional CFRP laminate containing three 1.5 mm diameter side-drilled holes (SDHs) at 3 mm depth. It shows that the ray tracing TFM enables the FMC signals to be accurately delayed and coherently summed to synthesize a focus at every image point. Consequently, peak amplitudes of the SDHs were increased by up to 49.74 dB and 2.69 dB with respect to those from paintbrush acquisition and the isotropic TFM with a constant velocity, respectively. Ray tracing results have also confirmed that use of a coupling layer is a simple way to minimize the anisotropic effect of CFRP and to reduce the structural noise from reflections at ply interfaces. [ABSTRACT FROM AUTHOR]

Abstract The assessment of structural damage is of great significance for ensuring the service safety of carbon fiber reinforced plastics (CFRP) structures. In this paper, the damage degree prediction method of CFRP structure based on fiber Bragg grating and epsilon-support vector regression was studied. The structural dynamic response signals were detected by fiber Bragg grating sensors. Then, the Fourier transform was used to extract the dynamic characteristics of the structure as the damage feature, and the damage feature dimensionality was reduced by using the RReliefF algorithm. On this basis, the damage degree prediction model of CFRP structure based on epsilon-support vector regression was established. Finally, the method proposed in this paper was experimentally verified. The results showed that the epsilon-support vector regression model can accurately predict the damage degree of unknown samples, and the absolute relative error of 27 experiments was less than 10% for 30 testing experiments. This paper provided a feasible method for predicting the damage degree of CFRP structures. [ABSTRACT FROM AUTHOR]

Highlights • Fracture mechanics of CFRP laminates are studied under static and dynamic loading conditions. • The vision-based method – DGS – is extended to study mixed-mode fracture behavior of orthotropic materials. • A methodology for extracting crack tip SIFs in orthotropic materials using optical measurements is outlined. • The loading rate effects on mixed-mode SIFs and energy release rates in the pre- and post-initiation regimes are quantified. • Differences in the static and dynamic fracture behaviors are explained. Abstract Crack initiation and growth in single-edge notched unidirectional T800s/3900-2 CFRP laminates are studied under stress wave and quasi-static loading conditions. An optical technique called reflection-mode Digital Gradient Sensing is also extended to study fracture mechanics of CFRP by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. DGS is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflection of light rays. A method for extracting crack-tip parameters – the instantaneous crack speed and stress intensity factor (SIF) histories – associated with the stationary and propagating cracks using measured surface slopes is presented. The effect of fiber orientation in the range 0°–60° relative to the initial notch and two loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode fractures ensue in others. Besides crack initiation occurrence at higher loads as fiber orientation increases, the SIF histories imply strong fiber bridging at low fiber orientations under quasi-static conditions. Furthermore, this CFRP shows significant loading rate dependence during crack growth. Unlike stress wave loading conditions, an increasing crack growth resistance immediately after crack initiation is seen under quasi-static conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The corrosion characteristics of CFRP/Al riveted structures were studied. • The variation trends of pit depth and weight with ageing time were obtained. • Relationship between microstructure and mechanical property of the joints was analyzed. • The corrosion mechanism of CFRP/Al riveted joints was analyzed. Abstract This paper investigated the microstructure and mechanical property evolution of CFRP/Al electromagnetic riveted structures exposed at a neutral salt spray environment. Electrochemical tests, microstructure observations, weight measurements and mechanical property tests were conducted. The observed results showed that corrosion pits on Al sheet were mainly located at the edge of the overlapping area due to the galvanic and crevice corrosion. Beside, visible cracks were observed on the surface of CFRP sheets after 3 weeks ageing. Maximum pit depth and weight evolution showed that the corrosion rate after the ageing time of 1 week was the fastest. The reason was that the corrosion products existed in pit and clearance effectively prevented oxygen and water contacting with Al matrix, which led to a decrease in the subsequent corrosion rate. The mechanical property tests results showed that the maximum shear loads after the ageing time of 1 week dropped the quickest due to faster corrosion rate at this stage. In addition, at the ageing time of 1 to 7 weeks, the maximum shear load after the ageing time of 3 weeks decreased faster. This was due to the surface of CFRP sheet was obviously damaged after the ageing time of 3 weeks, which further reduced the joint strength. In general, this work is expected to deeply understand the corrosion characteristics of the CFRP/Al electromagnetic riveted joints in engineering application. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigated the effect of two types of carbon fiber reinforced plastics (CFRPs) with different matrices, on the strength of a metal alloy–plastic composite joint made by the hot metal pressing (HMP) technique. One set of experiments was carried out with a PAN-type CFRP with a thermoplastic polyurethane (TPU) matrix, and the other with a PAN-type CFRP with a polyamide 6 (PA6) matrix. Both matrices were joined with either as-received or annealed AZ31 Mg-alloy sheets processed at different annealing durations to produce oxide layers on the alloy sheets. Due to the complete suppression of CFRP-resin decomposition at its joint interface, the CFRP with a PA6 matrix exhibited superior joint strength as compared to the TPU-matrix CFRP, which showed partial suppression of the CFRP-resin decomposition and bubble formation, with complete suppression characterized by microcracking at its joint interface. A reaction between C and MgO was observed at the joint interface for the TPU-CFRP but not for the PA6-CFRP. The melting/decomposition temperature of the matrix materials and the influence of the oxide layer on the conduction of heat between the materials were the key determinants of the AZ Mg alloy-CFRP joint strength. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastics (CFRPs) are being used in various applications due to their light weight and good mechanical properties. However, conventional hole making in CFRPs results in defects like delamination and fiber pullout. Literature confirms the feasibility of producing defect-free holes using electric discharge drilling (EDD). The researchers have studied macro EDD in CFRPs but drilling of micro holes in CFRPs using electric discharge drilling has not completely investigated. The present research endeavor is an attempt to experimentally investigate the micro EDD process for CFRPs. A tungsten carbide electrode of diameter 120 μm was used as a tool electrode. Several experiments were conducted using different tool geometries (i.e. solid, single notch and double notch) at different values of voltage, capacitance and tool speed. Single notch electrode was found to be the best electrode in getting high material removal rate (MRR), moderate tool wear rate (TWR) and high aspect ratio (29.17). At lower values of discharge energy, a better surface quality was observed during morphological analysis. A comparison was performed between the aspect ratio achieved in the present study and that available in the literature, the tabulated results highlight the achievements of the present experimental endeavor. [ABSTRACT FROM AUTHOR]

Materials play a fundamental role in defining the vibrational and acoustic characteristics of structures and their importance is even increasing because of the continuing demand for lightweight products. Carbon Fibre Reinforced Plastics (CRFP) components are becoming more and more popular because of their excellent mechanical properties but are unfortunately almost unable to dissipate energy. This is one of the reasons why their usage is limited to structural components and does not directly affect acoustic and vibrational response, which are among the factors responsible for harshness and comfort. In vehicles, for example, large panels of CFRP are as noisy as metallic panels so that this kind of lightweight structures is only used when a limited mass is of paramount importance, e.g. in racing cars. The chance of incorporating a damping material in the stacking sequence of CF layers that define a composite seems to be a viable solution to ameliorate the vibrational behaviour of composite materials. This configuration permits to cure the damping layers together with the resins, in order to obtain both free and constrained layer solutions. In this paper, the Oberst beam method has been chosen to determine the elastic modulus and loss factor of such materials, as a function of both frequency and temperature. Three nominally identical samples for each configuration have been tested in a temperature controlled environment, according to the Oberst beam test method. The effects of aging have been simulated by an accelerated standard procedure, with cyclically varying temperature and humidity for a total of 792 h (3 cycles x 264 h). The analysis of experimental data has been performed in the frequency domain by a least square fitting procedure, aimed at outperforming the simple half-power point method. An open source version of the fitting technique has also been implemented and can be obtained from the authors under the CC-by license. [ABSTRACT FROM AUTHOR]

The reduction of burr formation during machining of carbon fiber reinforced plastic composite is of great concern in many applications. This novel work presents the deburring of CFRP using ultrasonic-assisted electrical discharge machining. An L 18 array varying the input parameters, such as capacitance, pulse-on time, and ultrasonic voltage, was selected to assess the output performances like tool wear rate and burr removal rate. Multi-objective optimization was performed by the grey fuzzy logic method and the optimum input parameter was predicted based on the results of grey fuzzy reasoning grade. The significance of the process parameters on TWR and BRR were also analyzed using analysis of variance. The experimental results show that a capacitance of 10,000 pF, T ON of 200 µs, and V US of 150 V were the optimal input parameters to simultaneously minimize TWR and maximize BRR. The burr free exit side walls were observed by scanning electron microscopic image during machining at the optimum condition. However, the vaporization of the resin near the hole surface is unavoidable which is due to the electro-thermal effect of EDM process. The capacitance (63.58%), T ON (29.17%), and V US (2.76%) were found to be the factors most affecting the combined output responses. Finally, the verification of the results shows an overall improvement of 7.14% on TWR, 19.88% on BRR, and 1.3% on GFRG. [ABSTRACT FROM AUTHOR]

Precise knowledge of ultrasonic travel time in carbon fiber reinforced plastics (CFRP) is difficult to obtain due to the layered anisotropic nature. This paper proposes a model-based method to calculate the travel time of qP wave in CFRP laminates. The aim is to correct the time delays of total focusing method (TFM) applied to post-process the full matrix capture data for enhanced ultrasonic imaging. Experiments show that a 4.84 mm delamination is accurately sized by corrected TFM. The associated detection sensitivity is 46.0 dB and 3.6 dB above those of paintbrush acquisition and basic TFM, respectively. [ABSTRACT FROM AUTHOR]

The durability of hybrid carbon fiber reinforced plastics (CFRP)/aluminum alloy (Al) structures is receiving increasing attentions in engineering applications. In this paper, the mechanical performance of CFRP/Al electromagnetically riveted lap joints after exposure in neutral salt spray environment for various ageing time was studied. The shear and fatigue tests were conducted. The mechanical property degradation laws and failure mode evolution were obtained. The results showed that the shear and fatigue properties of the CFRP/Al electromagnetically riveted lap joints linearly decreased with the increase of ageing time. In addition, the fatigue test results showed that three weeks was the critical ageing time for failure mode changing. Fatigue crack initiated from the riveted hole (below 3 weeks) and the edge of the overlapping region (over 3 weeks) of Al sheet, respectively. Meanwhile, the fracture analysis showed that the cracks of specimens after long-time ageing (over 3 weeks) were initiated from the several corrosion pits simultaneously. [ABSTRACT FROM AUTHOR]

Laser ultrasonic testing (LUT) can realize contactless and instantaneous non-destructive testing, but its signal-to-noise ratio must be improved in order to measure carbon fiber reinforced plastics (CFRPs). We have developed a mid-infrared (mid-IR) laser source optimal for generating ultrasonic waves in CFRPs by using a wavelength conversion device based on an optical parametric oscillator. This paper reports a comparison of the ultrasonic generation behavior between the mid-IR laser and the Nd:YAG laser. The mid-IR laser generated a significantly larger ultrasonic amplitude in CFRP laminates than a conventional Nd:YAG laser. In addition, our study revealed that the surface epoxy matrix of CFRPs plays an important role in laser ultrasonic generation. [ABSTRACT FROM AUTHOR]

Electromagnetic riveting (EMR) has received increasing attention as a new kind of riveting technique in engineering industry. In this paper, EMR process was used to connect carbon fiber reinforced plastics (CFRP) and aluminum alloy (Al) hybrid joints. The mechanical behaviors (including static and fatigue properties) of the electromagnetic riveted lap joints were comprehensively investigated. The microstructure observation and the mechanical property tests were conducted to evaluate the joints performance. The mechanical test results showed that the failure modes of shear specimens were bending of the Al sheet and damage of the CFRP sheet, which was caused by rivet squeezing effect under static loading. However, the failure mode of fatigue specimens under each stress level was all ruptured at the Al sheet and the fracture analysis showed that cracks firstly initiated around the hole of Al sheet. This was caused by the fretting wear between Al sheet and rivet under cyclic loading. Two-parameter Weibull distribution was employed to analyze statistically fatigue cycles results. The S-N curves were drawn for different reliability levels (10%, 36.8%, 50% and 90%) for engineering applications. In addition, Hysteresis loop analysis implied that the specimens had no obvious flaw after EMR. [ABSTRACT FROM AUTHOR]

Electromagnetic riveting (EMR) process is suitable for composite joining due to small damage. In this paper, the EMR experiments were conducted to obtain the fatigue samples. Specimens with normalized driven head dimensions were tested to obtain the fatigue behaviors. The experimental results showed that the driven head dimensions had a remarkable effect on fatigue property. The fatigue life increased first and then decreased with the increasing of D/D 0 ( D and D 0 are the diameters of rivet driven head and original shaft, respectively). The electromagnetic riveted specimens with D/D 0 = 1.5 had the best fatigue properties. The fatigue failure analysis showed that the specimens had three typical fatigue failure modes: failure in the rivet, failure in the Al sheet and failure in the CFRP and Al sheets as influenced by driven head dimensions and stress levels. [ABSTRACT FROM AUTHOR]

The modern Industrial Furnace Technology is characterized by the design of new furnaces for high strength metals and carbon fibers for the light weight construction concepts in automotive industry. The furnaces for the annealing of modern high strength metals (steel, Al), are characterized by innovative cooling sections, with high cooling rates and a concomitant homogeneity, which are controllable for different steel or aluminum grades, variable widths and thicknesses for high productivity strips plants for products used in automotive industry. Resulting from this intensive research and development concerning the improvement of the local heat transfer knowledge for extremely high heat fluxes with gas, mist and/or water cooling is necessary. This research is driven by a competitive situation between steel and aluminum and since a few years also carbon fiber reinforced plastic (CFRP). On the other hand steels with a cheap alloying concept are used successfully in combination with the press hardening technology. The furnaces for the different applications in light weight design are very different between the materials (steel, Al, CFRP) due to different temperature ranges, principles of heat transfer and thermal operations. The environmental aspect of industrial furnaces requires the reduction of the specific CO 2 -Emissions which can be realized with advanced technologies improving the energy efficiency of fuel heated furnaces (high temperature air preheating with recuperative and regenerative burner concepts). For the overall CO 2 -emission reduction of 90 % up to 2050 related to 1990 actually no proved concepts are available. [ABSTRACT FROM AUTHOR]

This research is focused on the use of active infrared thermography as a non-destructive testing technique for damage detection in carbon fiber reinforced plastics (CFRPs). The aim of this study is to examine the efficiency of various mathematical methods in thermographic data processing, with respect to the thermal excitation method and the type of artificial defect in the CFRP specimens. We applied two techniques of active infrared thermography to CFRP samples with artificial cracks and internal delaminations at known locations. An infrared camera recorded the temperature field and generated a sequence of thermal images. To reveal the defects of the CFRP laminate, the thermograms were processed (a) as 2D images, and (b) as if each pixel was a 1D signal over time. We present representative experimental results, which illustrate that the depiction of the norm of the 1st spatial derivative of temperature and the 2D wavelet transforms proved to be most efficient for crack detection, whereas the 1D Fourier and 1D wavelet transforms did not yield clear results. In contrast, delamination damages could be identified through 1D techniques because the 1D Fourier transform as well as the 1D wavelet transform were very accurate. [ABSTRACT FROM AUTHOR]

This study proposes a skin-added X-lattice composite structure consisting of corrugated ribs and a very thin skin, as an alternative form of anisogrid composites, for the efficient light weight structural concept under compression loading. The high mechanical capability of skin-added X-lattice structures is numerically analyzed, followed by introduction of the related manufacturing method. This manufacturing process is composed of preparation of corrugation units and co-curing of the units with a thin skin. The results of compression tests of fabricated X-lattice panels agree with numerical predictions in terms of buckling loads and buckling modes, while skin-added X-lattice panels exhibited somewhat lower buckling load than the prediction. Feasibility of the proposed skin-added X-lattice is demonstrated in this work by fabrication and mechanical characterization. [ABSTRACT FROM AUTHOR]

The surfaces of carbon fibers were modified by hydrogen plasma treatment to investigate the consequent effects on reinforcement of polyetherimide (PEI) composites. The structural surface properties were characterized by Raman spectroscopy, XPS, FT-IR and SEM. The effectiveness of hydrogen and oxygen plasma treatments in improving the surface roughness, structure and mechanical properties of the composites was demonstrated. The results indicated that hydrogen and oxygen plasma treatment modified the carbon bonding structure and the surface roughness differently. Both an increase in the density of functional groups and changes in the carbon bonding contributed to the enhancement of the PEI matrix. SEM imaging confirmed decreased fiber pull-out for PEI reinforced with plasma-treated carbon fibers because of the enhanced adhesion between the carbon fibers and the PEI. Thus, hydrogen plasma treatment of the carbon fibers led to an enhancement of tensile properties at both room temperature and high temperature (150 °C). This study demonstrates that hydrogen plasma treatment is a promising technique for improving the mechanical properties of carbon-fiber-reinforced polymer composites. [ABSTRACT FROM AUTHOR]

It is important to know the electric current distribution in a laminated carbon fiber reinforced plastics (CFRP) plates for safety analysis of lightning strikes and for damage monitoring of plates based on changes in electrical resistance. An orthotropic electric potential function has been previously proposed, which was effective for modeling of a CFRP cross-ply laminate used in beam structures. However, that method is limited to cross-ply laminates that contain no angle plies, while CFRP plate structures typically feature angle plies. In the present study, a new analysis method is proposed for laminated CFRP plates that contain angled plies. In the new method, two or three angle plies are coupled and assumed to have orthotropic conductivity of double or triple thickness. A new method to calculate the equivalent conductivity is also proposed. The new method is applied to two types of laminates containing angle ply structures. The results obtained are compared with those from a finite difference method and from experimental measurements. The new method is shown to be effective for analysis of the electric current of laminates that contain angled plies. [ABSTRACT FROM AUTHOR]

In the present study, rotary ultrasonic machining (RUM) was adopted to perform drilling of carbon fiber reinforced plastics (CFRP) in a cryogenic environment. An L27 orthogonal array was selected to conduct experiments by varying the spindle speed (denoted as N), feed rate (denoted as f), and ultrasonic power (denoted as P). The thrust force (denoted as Fz), exit burr area, and surface roughness (denoted as Ra) were measured to evaluate the machining performance. The influence of process parameters and the regression model were derived for each output quality response. Additionally, multi-objective optimization was performed using desirability analysis, and the predicted levels were used for confirmation. The results indicated that the feed rate (f) contributed more to the thrust force (Fz) by 45.85% and a maximum thrust force was recorded at 0.1 mm/rev. A decrease in spindle speed (N) was associated with an increase in feed rate (f) and ultrasonic power (P), and it resulted in minimum exit burr area. The influence of ultrasonic power (P) was highly significant in reducing burrs with a contribution of 52.45%. Conversely, the surface roughness (Ra) of the drill holes decreased at 3000 rpm, and this was attributed to the brittle fracture of the fibers at a lower temperature. Both N (30.88%) and f (30.83%) had an equal influence on producing a better surface finish in the drill holes. Furthermore, the predicted optimal settings were used to validate the results and were found to be within 95% confidence and prediction interval. Finally, the microscopic images of tool wear, burr formation, and drill hole surface morphology were analyzed and examined. [ABSTRACT FROM AUTHOR]

In this paper, an ultrafast femtosecond laser was used to tailor the surface of the PEEK/CFRP (carbon fiber reinforced plastics with polyether ether ketone as resin matrix), using a nanosecond laser as a contrast. By analyzing the effect of femtosecond and nanosecond laser tailoring on the surface morphology, surface chemical composition and wettability of PEEK/CFRP, the internal reasons for the improved of bonding performance of heterojunction between PEEK/CFRP and Al–Li alloy by laser pretreatment were explored. As a result, the shear strength increased considerably from 4.9 MPa to 16.1 MPa and 29.5 MPa after nanosecond laser and femtosecond laser pretreatment, respectively. Finally, the fracture surface and failure modes of heterojunction bonded joints were compared, and the different mechanisms of femtosecond and nanosecond laser tailoring PEEK/CFRP surface were explained. Femtosecond laser tailoring is a competitive process for improving the bonding properties of the heterojunction between PEEK/CFRP and Al–Li alloys because of its productivity, controllability and lack of pollution. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastics (CFRP) are extensively used in aerospace, marine, and automotive fields. A variety of imaging methods for plate structures are proposed to find the damage as early as possible and ensure the safety of the structure. However, due to the anisotropy of CFRP, current methods still have some limitations for CFRP damage imaging, such as inaccurate localization, large spots and obvious artifacts. To improve the damage imaging performance of CFRP structures, a time-of-flight based weighted imaging method is proposed in this paper. First, a time-of-flight based weighted function is designed, which can be calculated according to the time-of-flight of potential scatterers and scattering signals. Then, the Hausdorff distance between the reference signal and the damage signal is implemented as damage influencing factor to characterize the impact of the damage on the sensing path. Finally, all time-of-flight based weighted functions are multiplied with damage influencing factors and fused for damage imaging and localization. The experimental results show that this method has less artifacts and lower positioning error, and can accurately locate crack damage with different states compared with other imaging methods. [ABSTRACT FROM AUTHOR]

In this study, compression properties of composite honeycomb sandwich panel and tube structures with S-shaped reinforced core was studied. The S-shaped reinforcements was machined from conventional honeycomb core. Quasi-static compression tests showed that the peak force and energy absorption of the proposed sandwich panels were enhanced by up to 85.28% and 31.41% respectively, in comparison to the carbon fiber/aluminum honeycomb sandwich panels. Based on the experimentally validated finite element model, the effects of number of S-shaped reinforcement structures, wall thickness and rotation direction were investigated for mechanical performance of the carbon fiber/aluminum honeycomb sandwich tubes under compression. Numerical results demonstrated that the S-shaped reinforcement structure could change the load transfer path effectively. The mechanical behavior and properties of the honeycomb core with S-shaped reinforcement were significantly influenced by changing the number and distribution of S-shaped reinforcements with different rotating directions. The homodromous structure caused shear damage, while the heterodromous structure showed more stability. • A honeycomb core with S-shaped reinforcements, which could effectively enhanced peak load and energy absorption, was proposed. [ABSTRACT FROM AUTHOR]

Potentials of integrating new technologies, particularly carbon fiber reinforced plastics, are not fully considered conventional reengineering processes. This paper firstly addresses the benefit by integration of functions, reduction of weight and fuel consumption, substitution of rare materials and customer individuality. Consequently, these aspects have been evaluated in three case studies, comprising representative cultural goods (eg. pipe organs), components of sport-aircraft (eg. ultralight helicopters) and urban-transport (eg. multifunctional stroller-bicycle trailer). Therefore, the following methods have been applied: functional analysis, reverse engineering and measuring technologies. [ABSTRACT FROM AUTHOR]

The influence of porosity on the ultrasonic wave propagation in unidirectional carbon-fiber-reinforced composite laminates is investigated based on the two-dimensional finite element analysis and measurements. Random distributions of pores with different contents and size are considered in the analysis, together with the effects of viscoelastic plies and interlaminar resin-rich regions. The transient reflection waveforms are calculated from the frequency-domain finite-element solutions by the inverse Fourier transform. As the measures for porosity characterization, the ultrasonic wave velocity, attenuation coefficient, and interlaminar interface echo characteristics are examined for 24-ply unidirectional composite laminates. As a result, the wave velocity decreases with the porosity content in a manner insensitive to the pore size. On the other hand, the attenuation coefficient increases both with the porosity content and with the pore size. The time–frequency analysis of the reflection waveforms shows that the temporal decay rate of interlaminar interface echoes at the stop-band frequency is a good indicator of the porosity content. The measured porosity-content dependence of the wave velocity is better reproduced by the numerical simulations when the interlayer interfacial stiffnesses are adjusted according to the porosity content, indicating that not only the porosity features but also the interlaminar interfacial properties vary with curing conditions. [ABSTRACT FROM AUTHOR]

The homogenization of material parameters layer by layer is a mostly sufficient method for the simulation of Lamb wave propagation in carbon fiber reinforced plastics. But since current experimental investigations of the wave behavior in undamaged CFRP structures reveal an effect called “quasi-continuous mode conversion”, which can not be reproduced with this layer-wise homogenization procedure, an improved material model for the finite element analysis of the Lamb wave propagation is presented in this work. The used 2D plane strain state model considers the random distribution of fibers in the matrix material on the microscale by homogenized subdomains and thereby properly capture the “quasi-continuous mode conversion” effect. Numerical investigations of the influence of the material model on the developing wave modes in a unidirectional layer will complete the work. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymers (FRPs) show advantageous physical-mechanical, thermal, and dielectric characteristics, making them promising candidates for weight reduction in structural applications. However, machinability is often difficult because of the specificity of their structure. This paper highlights the latest advances in CFRP drilling. Key papers are analyzed with respect to workpiece materials, geometrical tool features, and input variables (such as variation in process parameters). The influence of tool geometry and process parameters on workpiece delamination and hole quality/integrity represents the primary focus of this review. In addition, some new data are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper the effect of the embroidery based textile manufacturing technology Tailored Fiber Placement (TFP) on the stiffness and stress behavior of continuous fiber reinforced plastics is analyzed. Therefore the geometrical impact of the used stitching yarn on the fiber waviness is experimentally determined in a single unidirectional carbon fiber reinforced plastic layer made by TFP. Based on experimental data a parametrical three-dimensional representative unit cell (RUC) is developed to numerically determine the local fiber volume content as well as the stress and strain distribution under uniaxial loading. The numerical results are found in good agreement with the results obtained from tensile tests. A significant variation of local strain is found in fiber direction within the RUC while due to the effect of TFP the variation of global strain is observed to be insignificant. [ABSTRACT FROM AUTHOR]

In this study, a new cutting model for the machining of unidirectional CFRP laminates was developed to examine the mechanism for changes in the cutting forces with tool wear. This model is based on Zhang's model and divides the cutting zone into two characteristic deformation regions; chipping and pressing. Furthermore, CFRP milling tests were performed using two kinds of cutting tools: tungsten carbide (WC–Co) and polycrystalline diamond (PCD). Based on the experimental results with the developed cutting model, the net cutting forces to make a cut chip and press CFRP laminates under the flank surface of the tool were quantitatively evaluated. Consequently, it was found that the former does not depend on the progress of the tool wear, but the later increases with tool wear. Additionally, based on the results in this study, a new technique for reducing cutting forces during CFRP machining, which is based on the use of two layer tool that has a wear resistance distribution at around the tool edge was introduced. [ABSTRACT FROM AUTHOR]

The fracture toughness of carbon fiber reinforced plastic laminates was investigated in term of modifying the epoxy matrix with the pristine and functionalized stacked-cup carbon nanofibers. The results showed that the highest enhancements in Mode I (13.6%) and Mode II (45.3%) fracture toughness were achieved by adding 0.5 wt% and 1.0 wt% functionalized nanofibers, respectively. The toughening mechanism was analyzed based on the morphology evaluations of the fracture surfaces. The evidence of bridging, pull-out, peeling-off and unravelling of nanofibers were clearly observed, which contributed to dissipating more energy for crack propagation, resulting in the improvement of fracture toughness. [ABSTRACT FROM AUTHOR]

The increasing demand for products made of carbon fiber reinforced plastics (CFRP) raises the risk of damages occurring during their use in a large variety and number. Depending on the type of damage, the product cannot be used any longer. CFRPs are characterized by high manufacturing costs and geometric individuality of the products, which limits the availability of replacement. From an economic and ecological point of view, several repair methods especially in the aerospace industry have been developed in the last years. The decision, which of these repair techniques has to be applied, depends on the extent of damage and different requirements of the product. Parts made of CFRP can often be repaired by manual removing of the damaged area followed by a re-lamination. This paper shows an actual approach to the CFRP-repair. Thereby influencing factors like the material removal, surface pretreatment and material composition will be discussed. By comparing the major factors, which lead to an increase of mechanical properties, suitable repair techniques could be defined. The optimum was found by experimental methods. [ABSTRACT FROM AUTHOR]

Two-dimensional finite element simulations and experiments are presented to examine the ultrasonic wave propagation behavior in the corner section of CFRP (carbon fiber reinforced plastics) laminate structures. The numerical model consists of a right-angle corner section of CFRP laminate immersed in water and subjected to the ultrasonic wave incidence from its inner or outer side. The anisotropic stiffness constants of the unidirectional CFRP are identified experimentally and used to model the curved laminate structure. A commercial finite element analysis code is used to compute the reflection waveforms in the pulse-echo mode, and the effect of the laminate stacking sequence and the wave incidence direction is examined. It is shown that the reflection waveforms for the wave incidence from the outer side of the corner qualitatively resemble those for the plane laminate except that the echo signals of the former are substantially weaker. The numerical simulations are shown to well reproduce the qualitative features of experimental reflection measurements performed for the corner sections of 16-ply CFRP laminate. Experimental results indicate that the porosity content of the corner section can be estimated by the amplitude ratio of the surface and the back-wall echoes when a curvature-dependent calibration relation is properly used. [ABSTRACT FROM AUTHOR]

Within the aircraft industry, the use of composite materials such as carbon fiber reinforced plastics (CFRPs) is steadily increasing, especially in structural parts. Manufacturability needs to be considered in aircraft design to ensure a cost-effective manufacturing process. The aim of this paper is to describe the development of a new strategy for how SAAB Aerostructures addressing manufacturability issues during the development of airframe composite structures. Through literature review, benchmarking and company interviews, a design for manufacturing (DFM) strategy was developed. The strategy ensures that the important factors for successful DFM management are implemented on strategic, tactical and operational levels that contribute to a more cost-efficient product development process and aircraft design. [ABSTRACT FROM AUTHOR]

The present work intends to provide a numerical tool for the efficient design of the multidirectional carbon fiber reinforced plastic (CFRP) material using finite element simulation software ABAQUS ® . A 3D model has been established for simulation of the tensile test composite specimen which enables to understand the mechanical strength and strain at failure of the composite materials. 15 ply CFRP specimens with various stacking sequences were analyzed for their strength and displacement. Exhaustive parametric studies reveal the dependency of reinforcing material and ply orientation on the strength and stiffness of composite materials. Carbon fibers with cross ply lamination were found to be stiffer than angle ply glass fiber lamination. A fairly good comparison was obtained between the predicted results with available experimental and theoretical data in open literature [ABSTRACT FROM AUTHOR]

Abstract: This study was performed to investigate the feasibilities, characteristics and mechanisms of dissimilar joints between carbon fiber reinforced plastics (CFRPs) and zinc-coated steel using a continuous wave (CW) diode laser. Tensile shear tests show that the high strength joint with about 3300N could be produced. Many bubbles of sub-millimeter size inside the melted zone of CFRP at the cross sections of the joints were widely formed, and thin zinc-coated layer at the joint interface was partially fractured. Then, the melted plastic was filled closely to flow in the fractured zinc-coated layer, suggesting strong mechanical bonding. Furthermore, the joint was tightly bonded on atomic or molecular sized level between the melted plastic containing most carbon and nanometer thick zinc oxide film on the surface of zinc-coated layer, inducing strong possibility of physical and chemical bonding. It is consequently confirmed that a strong joint of CFRP to zinc-coated steel could be obtained by laser direct joining process. [Copyright &y& Elsevier]

Abstract: Novel addition-type imide oligomer (degree of polymerization: n =1–10) derived from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 2-phenyl-(4,4′-diaminodiphenyl ether) (p-ODA) which has asymmetric and non-planar structure, and 4-phenylethynylphthalic anhydride was synthesized for the matrix resin of high heat resistant carbon fiber-reinforced composites. The uncured imide oligomers (degree of polymerization: n =1–4) showed good solubility (more than 30wt.%) in aprotic solvents such as N-methyl-2-pyrrolidone (NMP). These imide oligomers also showed a very low viscosity. These data were accomplished by preventing the aggregation caused by the pendant phenyl group of p-ODA. The imide oligomers were successfully converted to cross-linked structures after curing at 370°C. The glass transition temperature and elongation at break of the cured imide resin were found to be very high (almost 360°C and >15%) respectively. [Copyright &y& Elsevier]

Abstract: Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates. [Copyright &y& Elsevier]