Carbon Fiber Sheets Research Articles

Joining processes of CFRP‐Al sheets in automobile lightweighting technologies: A review

AbstractAccording to the development trend of modern car body, the future car body will be composed of steel, aluminum‐magnesium alloy, plastic, carbon fiber reinforced polymer (CFRP), and other lightweight materials. Hybrid material body represents the latest development trend of car body structure in the future. With the development of lightweight technology, the application of carbon fiber composite material in automobile bodies is increasing due to its exceptional performance. Therefore, the joining of carbon fiber sheets with dissimilar sheets process in the hybrid material body is a key technical problem that needs to be solved. In this paper, the existing joining processes of adhesive process, mechanical joining, welding process, and hybrid joining for carbon fiber composites are reviewed; the principle, development, advantages, and shortcomings of each process for carbon fiber composites joining processes are systematically described; and the latest progress of the joining process are introduced. The purpose is tantamount to broaden the application range of carbon fiber sheets with dissimilar sheets and provide reference for its extensive application in the development of hybrid car body and lightweight.

Additive manufacturing of high density carbon fibre reinforced polymer composites

Additive manufacturing (AM) of carbon fibre reinforced thermoplastic composites can offer advantages over traditional carbon fibre manufacturing through improved design freedom and reduction in production time and cost. However, the carbon fibre composites produced using current state-of-the-art AM approaches generally possess high porosity (18–25 %) compared to those produced by conventional manufacturing (1 %). An approach known as composite fibre additive manufacturing (CFAM) is presented, involving selectively printing a binder and polymer powder onto discontinuous carbon fibre sheets, which are then compressed, heated and post-processed to form net shape components. The results demonstrate a correlation between compaction pressure applied and porosity/fibre volume fraction within components. Composite components were produced containing porosity of 1.5 % and fibre volume content of 15 % with 97 MPa tensile strength and 8.9 GPa elastic modulus, presenting a new approach for production of discontinuous carbon fibre reinforced polymer parts with mechanical properties exceeding those of state-of-the-art AM.

Flow Behaviour of Carbon Fibre Sheet Moulding Compound

The growing popularity of SMC compression moulding in the automotive industry has led to great interests in process simulation model development. Existing process simulation models are commonly adapted from models originally developed for short fibre composites and lacking experimental validation data. A novel material model specifically developed for SMC flow simulation is proposed in this paper, where the experimental material characterisation is performed using the squeeze flow testing method. The model is validated through simulation of the squeeze flow testing and the accuracy of the model is assessed by comparing the predicted compression forces against experimental data collected from the squeeze flow testing. The proposed new model has demonstrated significant improvement in comparison to existing commercial models in term of compression force prediction, but the predicted compressive forces diverted away from the experimental values towards the end of the test. The predicted cavity pressure distribution has also been investigated and compared to observations reported in the literature where good correlation between predicted pressure distribution and the literature have been achieved.

Investigation of the Compressive Strength of CFRP Wrapped Nylon Fiber Reinforced Concrete Cylinders

Nylon fibers are found to increase the mechanical properties of structural concrete like compressive and tensile strength when introduced into the concrete matrix by partially replacing fine aggregates. Since Nylon fibers are cheap waste materials, properly controlling their percentage into the matrix results in higher strength as well as cost control. This study discusses the compressive strength of nylon fiber induced concrete cylinders by wrapping them with 200gsm carbon fiber sheets as well as records the failure pattern, which is done by comparing the compressive strength of control specimens with sets of cylinders which are induced with nylon fiber and wrapped around with zero, one and three layers of CFRP laminates. Alongside the compressive test results, this study also reflects on several tensile tests carried out on CFRP strips which can be used as a measure to check hardener bond strengths in field. For that purpose, five coupons were prepared for flat tensile test and another five for overlap splice tensile test, stress-strain data were recorded; and the tests followed the guidelines stated in ACI code. The recorded tensile test data was found satisfactory with the recommended values for ACI 440.3R-04 and better compression capacity for cylinders were found with increasing CFRP layers. Journal of Engineering Science 13(1), 2022, 31-39

Process-induced failure mode transition of compression molded discontinuous carbon fiber composites: From coupon to component level

Discontinuous carbon fiber composites have been reported to be damage tolerant materials with insensitivity to notches and defects. Meso-scale damage mechanisms and crack arresting are responsible for high apparent fracture toughness and pseudo-ductility. This work studies the effect of manufacturing and structure formation on the mechanical behavior of stochastic carbon fiber sheet molding compounds based on thermosetting prepreg platelets with a fiber length of 50 mm. The process–structure–property–performance relationship is analyzed by non-destructive characterization and mechanical bending tests on the component level. Model components of various preform and stack placement scenarios were compression molded to investigate different flow conditions, weld lines and artificially introduced defects. The experimental findings revealed a process-induced failure mode transition from pseudo-ductile to brittle failure behavior. Low-flow scenarios showed a highly non-linear response with large deflection values and high energy absorption. Higher in-mold material flow and weld lines caused brittle failure at significantly lower deflections with a considerable reduction of energy absorbing capacity. Increased material flow also reduced component stiffness and maximum load values. Weld lines exhibited major strength reduction compared to the pristine material configuration. Full-scale and high-resolution X-ray computed tomography scans revealed differences in local fiber orientation state, increased levels of fiber waviness and porosity, as well as asymmetric distribution of defects.

Investigation on Silver Modification of Different Shaped Filler on the Heat Conduction Performance Improvement for Silicone Elastomer

The continuous miniaturization and multi-function of electronic devices have put forward high requirements for the effective removal of the heat generated in the system. Developing thermally conductive polymer composite-based thermal interface materials is becoming the research hotspot. In addition to the usually concerned intrinsic thermal conductivity of the filler itself, surface modification is one of the important ways to form an effective heat conduction pathway and improve the overall thermal conductivity of materials. In this work, we used silicon rubber as the polymer matrix and achieved the thermal conductivity increment via various fillers with different shapes. The adopted fillers are spherical aluminum oxide (Al2O3), linear carbon fiber and boron nitride sheets, which can be considered as zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) fillers respectively. We also prepared the silver-modified fillers and investigated the influence on the formation of heat conduction pathways and interfacial thermal resistance of different shaped fillers. An obvious increment in thermal conductivity of the composite with silver-modified fillers was observed compared to the composite with pristine fillers. Furthermore, through the practical thermal management performance investigation, we found the thermal conductivity increment did improve the actual heat transfer performance of composite elastomers functioning as thermal interface materials

Mechanism and performance evaluation of FeSe2 and MoS2-loaded carbon fiber sheet as a novel heterogeneous Fenton-like catalyst

A novel non-woven carbon fiber sheet-supported FeSe2 and MoS2-loaded Fenton catalyst (MoS2@FeSe2@CFS) was synthesized by a two-step hydrothermalprocess. The MoS2@FeSe2@CFS exhibited an excellent performance on hydrogenperoxide (H2O2) activation at different conditions. Removal efficiency of methyleneblue (MB) reached 99.7% within 20 min and the rate constant was higher than those of the most reported iron-containing catalyst/H2O2 systems for MB degradation. The possible activation mechanism of H2O2 by MoS2@FeSe2@CFS in heterogeneous system was proposed·H2O2 was activated to ·OH by Fe2+, and generated Fe3+ was reduced to Fe2+ by Mo4+. Besides, MoS2 has great adsorption performance and can aggregate MB near the catalyst, shortening the mass transfer distance. Therefore, the heterogeneous Fenton catalyst MoS2@FeSe2@CFS has excellent catalytic property. Notably, it was discovered that S might participate in the Fe3+/Fe2+ cycle, which has not been reported in literature. Moreover, MoS2@FeSe2@CFS have good long-term stability and repeatability because of its highstrength and chemicaldurability. Overall, this work expands the environmental application of iron-containing catalyst and provides a promising heterogeneous Fenton system for removal of contaminants from water.

A use of natural sisal and jute fiber composites for seismic retrofitting of nonductile rectangular reinforced concrete columns

Given a size of low-rise residential buildings located in seismic-prone areas, it is difficult to rationalize the application of Carbon Fiber Sheet Polymer (CFRP) sheets for the sake of seismic strengthening. Consequently, this study aimed at finding alternate solutions that could justify the cost without compromising on the performance of strengthened buildings. The potential of sisal and jute fibers was investigated in preventing brittle shear failures of short RC columns. A total of 6 RC columns furnishing typical old non-seismic details with a shear span-to-depth ratio of 2.35 were tested in this study. One column served as control whereas one column was strengthened with 2 layers of CFRP sheets. Rest of the 4 columns were strengthened with 2 and 4 layers of sisal and jute fiber composite sheets. Structural performance in terms of failure modes, ductility, energy dissipation, and peak lateral loads was summarized. It was established that both the natural fiber composites could enhance the structural performance of RC columns to a level comparable to that established by CFRP sheets. This too was achieved by reducing the strengthening cost per column relative to CFRP by 35 and 15% for sisal and jute, respectively.

Experimental feasibility and environmental impacts of compression molded discontinuous carbon fiber composites with opportunities for circular economy

Compression molding of carbon fiber sheet molding compounds (CF-SMC) is a promising technology to reduce the waste of carbon fiber composites and to drive sustainable development in lightweight applications. Both, the production waste of prepreg scrap and the end-of-life waste of carbon fiber components can be used efficiently in the recycling process with an apparent sandwich structure of virgin and recycled materials. This contribution investigates the technology on the example of a structural automotive component (transmission crossmember). A one-shot compression molding process was developed which enables cost-efficient, large-scale manufacturing with cycle times of about two minutes. The process–structure–property–performance relationship was experimentally characterized with manufacturing studies and prototype tests. A multilayered hybrid structure of virgin and recycled carbon fiber materials maintains the manufacturability and the mechanical performance compared to primary CF-SMC. The environmental impacts were assessed within a comparative life cycle assessment (LCA). Different material and recycling scenarios were analyzed for the components produced. It revealed lower environmental impacts than an industrially used reference version in aluminum in most impact categories. The combination of the compression molding technology with multilayered hybrid carbon fiber composites reveals opportunities for circularity and the multistage use of industrial recyclates for varying quality requirements in lightweight applications.

Advanced process simulation of compression molded carbon fiber sheet molding compound (C-SMC) parts in automotive series applications

The following paper focuses on the development of a 3D virtual process chain (VPC) for parts made from Carbon Fiber Sheet Molding Compounds (C-SMC). The VPC consists of two modules addressing the compression molding and warpage simulation of parts made from two different high fiber volume fraction C-SMC materials. The press simulation module applies a solid mechanics material modelling approach within the Coupled Eulerian-Lagrangian (CEL) simulation framework available in ABAQUS/Explicit. Through a combination of flow characterization experiments and numerical simulations, local mechanical properties and fiber orientation information can be predicted from numerically simulated local flow strains. A warpage simulation module has also been developed in ABAQUS/Standard together with a data processing/transfer interface implemented in ANSA. With these highly integrated numerical tools, process characteristics such as press forces, flow fronts and weld-line development based on material amount, insert geometry and placement position in the mold can all be predicted and analyzed.

High strength composites of carbon fiber sheets-veneers sandwich-structure for electromagnetic interference shielding materials

Due to the advantages of porous structure, anisotropy, and fiber composition, wood possesses great potential to be a high-strength electromagnetic interference (EMI) shielding material. This study used vacuum assisted resin transfer molding (VARTM) technology to fabricate EMI shielding composite material by combining carbon fiber sheets and wood veneers via infusion of epoxy resin. The shielding effectiveness of the composites against electromagnetic waves in the 8.2–12.4 GHz (X-band) can reach 40 dB. The flexural and tensile strength (i.e., 442.3 and 195.5 MPa, respectively) of the composite were 6-fold and 3-fold higher than natural poplar (i.e., 69.8 and 55.6 MPa, respectively), respectively. The composites possessed superior thermal conductivity (0.91 W m-1 K-1) compared to poplar, good water resistance and surface hydrophobicity. The addition of carbon fiber sheets not only improved the mechanical performance of samples, but also made samples possessing the ability to shielding electromagnetic waves. This work provides a novel technology to make a natural bio-based high-strength composite material for the EMI shielding applications.

Flexural performance of ECC-concrete composite beams strengthened with carbon fiber sheet

In order to study the strengthen effect of carbon fiber sheet (CFS) on steel reinforced engineering cemented composite (ECC)-concrete composite beams. Three groups with totally 12 specimens of steel reinforced ECC-concrete composite beams strengthened by CFS were made and their static flexural experiments were conducted. The effects of ECC replacement heights, layers of CFS pasted and CFS hoops on flexural behavior of ECC-concrete composite beams were investigated, in terms of strain, load bearing capacity, deflection, crack and failure pattern. The results show that compared with unstrengthened specimen, the crack width of CFS strengthened specimen was reduced and load bearing capacity was enhanced. The maximum improvement of load bearing capacity is 63%. Compared with strengthened specimen without CFS hoop, the load bearing capacity of strengthened specimen with CFS hoops improved 9%. Based on reasonable assumptions and materials simplified constitutive model, load bearing capacity of CFS strengthened concrete beam and ECC-concrete composite beam are developed. The values predicted by the formulas are in good agreement with the results tested, indicating the validity of formulae proposed and can be used in engineering practice.

Fibre alignment and mechanical performance of carbon fibre Sheet Moulding Compounds under different preform compaction

This work investigates the effect of preform compaction on the mechanical performance and flow-induced fibre alignment of carbon fibre reinforced Sheet Moulding Compounds (SMCs). Two groups of panels have been compression moulded from reclaimed carbon fibre tows in vinyl-ester resin with low (0.5 MPa) and high (10 MPa) preform compaction pressure Additionally, a low-cost fibre orientation analysis method has been further improved in terms of reliability, and a novel flow assessment method has been developed for carbon fibre SMCs. This approach revealed greater fibre alignment with the flow direction in the lower faces of panels as a result of greater contact time with the heated mould and a lower charge viscosity at the time of pressing. As expected, greater fibre alignment in the flow direction was observed outside the initial charge coverage area in both types of panels, where the flow was greatest. Due to additional fibre flow during the high-pressure compaction stage, the mean degree of flow alignment in the high compaction panel was 47% higher than that of the low compaction panel. Improvements in the tensile stiffness (8%) and strength (32%) were also observed as a result of the high-pressure compaction stage and associated flow alignment.

Integration of Energy Oriented Manufacturing Simulation into the Life Cycle Evaluation of Lightweight Body Parts

Recent years introduced process and material innovations in the design and manufacturing of lightweight body parts for larger scale manufacturing. However, lightweight materials and new manufacturing technologies often carry a higher environmental burden in earlier life cycle stages. The prospective life cycle evaluation of lightweight body parts remains to this day a challenging task. Yet, a functioning evaluation approach in early design stages is the prerequisite for integrating assessment results in engineering processes and thus allowing for a life cycle oriented decision making. The current paper aims to contribute to the goal of a prospective life cycle evaluation of fiber-reinforced lightweight body parts by improving models that enable to predict energy and material flows in the manufacturing stage. To this end, a modeling and simulation approach has been developed that integrates bottom-up process models into a process chain model. The approach is exemplarily applied on a case study of a door concept. In particular, the energy intensity of compression molding of glass fiber and carbon fiber sheet molding compounds has been analyzed and compared over the life cycle with a steel reference part.

Application of Microwave Polarimetry to the Characterization of Fiber Misalignment in Composites

In this paper synthetic aperture radar (SAR) polarimetry techniques are applied to detect and characterize fiber misalignment in both carbon fiber sheets and glass fiber reinforced polymer (GFRP) composites. The principle behind SAR polarimetry technique to characterize fiber orientation is described, making use of the fact that carbon and glass fibers are polarizing when irradiated with a microwave signal. The difficulties in using 2D polarimetry techniques to make the 3D orientation measurements, required to characterize out-of-plane fiber misalignment, are discussed as well. Subsequently, the feasibility of a recently-developed 3D SAR polarimetry method for this purpose is demonstrated. Several carbon fiber sheet and glass fiber reinforced polymer (GFRP) samples were manufactured with both in-and out-of-plane fiber misalignment. Polarimetric SAR images of the samples were then produced to show the spatially-varying relative orientation (both in-plane and out-of-plane) of the fibers for each sample. These images can be used to both detect and characterize any fiber misalignment, successfully demonstrating the potential for SAR polarimetry as a tool for the inspection of carbon and glass fiber reinforced composites.

Study on strengthening effect of prestressed cfrp sheet on steel box girder

The finite element software Abaqus is used to simulate the reinforcement of the steel box girder with CFRP sheets. The wave anchor anchorage system clamps the carbon fiber (CFRP) sheets and anchors them in the tensile zone at the bottom of the steel box girder. The temperature method is used to simulate the prestress applied to the steel box girder in the actual project, and the stress of the steel box girder in the project example is compared to analyze the mid span deflection of the steel box girder; With the change of stress and strain, the mid span deflection of prestressed CFRP sheet to steel box girder is analyzed; Stress; The improvement of strain sum shows that prestressed CFRP has good reinforcement effect for flexural members.

Hybridization Process of Carbon Fibre Sheet Moulding Compound with Carbon Fibre Prepregs: a Case Study

The main objective of this work was to show the technical viability of a traditional Sheet Moulding Compound process hybridized with Carbon fibre prepreg reinforcements, in a demonstrative car seat structure. The new reinforced seat is lighter, has better mechanical resistance to impact and the typical carbon fibre visual aspect in the reinforced areas. Currently, the seat structure is composed by the hybrid solution with the matrixes of both materials being epoxy, therefore compatible which promotes a good adhesion under the correct processing conditions. To ensure the viability of this hybridization, an extensive laboratorial test campaign was conducted in a laboratorial hot plate press to study the Sheet Moulding Compound flow dynamics during the moulding process and how it interacts with the prepreg preforms. The cure process of both materials was also analysed to establish the optimal temperature profiles. Finally, mechanical tests were performed according to ASTM D 5868-01 to evaluate the mechanical properties of the bonding between the two materials. The reinforced car seat prototype was validated according to the ECE-R17 and FMVSS202a impact tests on the head rest and a 25% reduction in overall weight was achieved. The life-cycle cost and the visual aspect benefits are expected to compensate the slightly higher manufacturing cost in relation to the original part due to the cost of the prepreg material. Further research will be needed to in terms of process automation to ensure the required process quality.

Squeeze flow rheometry and data analysis of carbon fiber sheet molding compounds

The compression molding process of carbon fiber sheet molding compounds (CF-SMC) is characterized by a squeeze flow of the material. There are no standardized measurement methods to characterize the flow behavior of CF-SMC and conventional methods of shear-flow dominated plastics processing are not suitable to describe the elongational deformation mode during compression molding. The objective of this work was to develop a methodology to determine the rheological properties of two CF-SMC materials. This included the development of the squeeze flow measurement device and the necessary software tools to efficiently analyze the data. The experimental findings were used to calibrate rheological power law models for both materials and validated with numerical compression molding simulations.

Damage location sensing in carbon fiber composites using extrusion printed electronics

Structural Health Monitoring (SHM) uses sensors in advanced engineering structures to evaluate integrity and detect damage or deformation affecting structural performance, e.g. cracks, holes, or corrosion. Carbon fiber (CF) textile composites are commonly used to reinforce structures such as aircraft, vehicles, or bridges due to their high tensile strength to weight ratio, chemical resistance, and thermal and electrical conductivity. Printing electronics on textiles is a scalable manufacturing technology combining the physical properties of textile materials with the added functionality of electronic elements making them self-sensing. Extrusion printing is a contactless digital printing method to print electrical conductors and passive circuit elements. This paper proposes to combine conventional CF composite manufacturing processes with printed conductors to create self-sensing CF textile composites. Damage is sensed by measuring resistance changes in a CF sheet. Contacts are extrusion printed directly on woven CF sheets using silver flake ink. A multiplexed Kelvin Double Bridge circuit is the read-out interface. This allows small resistance changes due to damage to be measured in a four-point configuration. The circuit is connected to the printed contacts on the CF sheet through multiplexers to detect damage in different locations. This 2D digital sensor can detect the location and size of damage holes for SHM. The resolution of the sensor is controlled by the location and spacing of the silver electrodes, which were studied experimentally and by simulation. The resolution is 26 mm in the current direction and 16 mm in the orthogonal direction. The threshold of detectable damage is 4 mm2. Simulation of the sensor as an isotropic 2D conductor shows good agreement with experimental results for the orthotropic fabric. The resultant sensing device could be integrated into many composite structures as one of its layers or simply printed on the surface to create smart structures.

Electrochemical noise analysis of cathodically protected steel reinforcement in concrete using carbon fiber sheet as anode

This paper presents an efficiency and mechanism analysis of impressed current cathodic protection (ICCP) for corroded steel reinforcements in concrete by means of electrochemical noise (EN), which is an advanced technique that allows real-time monitoring without any disturbance. The considered variables include protection method (non-protection, ICCP) and current density of ICCP (30 mA/m2, 90 mA/m2). In the cases of ICCP, carbon fiber sheet is adopted as the anode thanks to its good electrochemical properties and durability. Electrochemical potential noise (EPN) and electrochemical current noise (ECN) of steel reinforcement in concrete are measured every 30 d during the 120-d exposure period and analyzed from the perspectives of time and frequency domains. The results show that ICCP treatment with a current density of 30 mA/m2 leads to slighter fluctuations in ECN signals, an improvement in noise resistance Rn, and decreases in the low frequency plateau WL in power density diagram (PSD) of ECN signals. It indicates that the corrosion of steel is alleviated. However, the results of the specimen protected with a current density of 90 mA/m2 are the opposite, which is overprotected and hydrogen corrosion may happen. Compared to the specimen with no protection, the specimen treated with 30 mA/m2 ICCP shows an evident increase in energy proportion of d1-d3 wavelet crystals. Additionally, with increasing the treatment duration, the energy proportion of d1-d3 wavelet crystals increases. This illustrates that ICCP is more effective in inhibiting general corrosion than pitting corrosion. Extra caution should be paid to EPN signals of specimens subjected to ICCP, namely polarization, because EPN signals may anomalously exhibit severer fluctuations as a result of insufficient depolarization. It is suggested to use ECN signals instead of EPN signals to analyze the corrosion behavior of specimens subjected to ICCP.