Carbon Fiber Reinforced Plastic Layers Research Articles

Seismic performance enhancement of underground structure influenced by CFRP wrapping schemes

The seismic failure mechanism of underground structures showing structural collapse is attributed to the deformation incompatibility between the central columns and the sidewalls, especially the insufficient deformation capacity of the central columns. Therefore, the approaches to improve the seismic performance of underground structures mainly aim at avoiding the damage of central columns. This paper presents a comparative study on the seismic performance of underground structures with the central columns retrofitted with different numbers of Carbon Fiber Reinforced Plastics (CFRP) layers. Seismic capacity of the CFRP retrofitting reinforced concrete (RC) columns was explored in detail through experimental and numerical approaches. Then numerical models were built and verified to simulate the behaviors of the CFRP retrofitting RC columns, and the seismic performance of the CFRP retrofitting underground structures was numerically simulated. Based on the numerical results, the damage of the CFRP retrofitting underground structures was calculated, and damage classification illustrated that the seismic performance of underground structures was enhanced remarkably. Finally, parametric studies were conducted to discuss about how the number of CFRP layers and the earthquake intensity affect the earthquake-induced damage of underground structures. Conclusions from this study could be referenced for seismic retrofitting of existing underground structures.

Buckling behavior analysis of corrugation reinforced composite pressure shell: Analysis of the influence of corrugation structural parameters

Based on CFRP(Carbon Fiber Reinforced Plastics) cylindrical pressure shell, the CFRP circumferential corrugation pressure shell is proposed in this study. The structure can further improve the buckling resistance capacity of CFRP pressure shell. Five CFRP circumferential corrugation pressure shells with varying corrugation structure parameters are designed and compared with CFRP cylindrical pressure shell. The buckling behaviors of the shells are analyzed in detail by nonlinear finite element method. The result show that reasonable corrugation structure can significantly improve the resist buckling capacity of CFRP cylindrical pressure shell. However, the increase of corrugation structure parameters will exacerbate the damage to the CFRP layers outside the pressure shell. Ultimately, pressure shell N2 with the best buckling resistance capacity is selected for hydrostatic pressure test, and the experimental results are found to align with the numerical simulation results. This study offers a novel approach for the design of deep-sea pressure shell structures.

Study on Axial Compression Performance of Corroded Reinforced Concrete Columns Strengthened by Concrete Canvas and Carbon Fiber Reinforced Plastic under Secondary Corrosion

To investigate the effects of concrete canvas (CC) and carbon fiber reinforced plastic (CFRP) reinforcement on the mechanical properties of corroded reinforced concrete columns (compressive strength, flexure strength, strength of extension, and so on), 42 columns in four groups were designed and axial compression experiments were carried out. For the corroded reinforced concrete columns reinforced with CC and CFRP, the effects of initial corrosion rate (5%, 10%), secondary corrosion time (15 d, 30 d), number of CC layers (0, 1), and number of CFRP layers (1, 2, 3) on the failure morphology, load carrying capacity, and ductility of concrete columns were analyzed. The test results show that the properties of the single layer CC confined specimens are improved to a certain extent, and the ductility properties are enhanced. The properties of the CC–CFRP composite constrained specimens are greatly improved, the plastic deformation ability is enhanced, and the typical ductile damage characteristics are shown. The corrosion inhibition of CC for specimens with a theoretical corrosion rate lower than 20% showed an increasing trend, and the corrosion inhibition rate ranged from 23.0% to 31.2%. CC and CFRP restrain the concrete jointly, hindering the expansion inside the concrete, and the peak strain of the joint restraint specimen itself changes greatly, while the overall peak strain of the corrosion specimen is very small under the action of the joint steel bar. Finally, according to the existing peak stress–strain model and the experimental data in this paper, a peak stress–strain model suitable for corroded reinforced concrete columns is established. The established calculation model has a high accuracy, which provides a certain theoretical basis for subsequent research.

Effective mechanisms responsible for increased strength and fracture strain of carbon fiber-reinforced plastic/steel hybrid laminates

The tensile properties of carbon fiber-reinforced plastic (CFRP)/steel laminates have been observed to exceed the expected values predicted by the rule of mixture. While the CFRP/steel laminate is expected to fail at the failure strain of the CFRP lamina, it was observed that hybridization with a steel lamina improves the failure strain. This study investigates numerically and analytically the roles of each influential mechanism responsible for this enhancement, including the thermal residual strain, bridging effect, effect of compressive transverse stress on CFRP layers, and effect of tensile transverse stress on steel layers. To assess these mechanisms, multiple finite-element and analytical models were developed. A mesoscale finite-element model was proposed, which uses novel random fiber distribution algorithm capable of reproducing random fibers with high fiber volume fractions exceeding 65%. Rather than the meso-scale model, macro finite-element models and analytical relationships were developed to assess each hybrid mechanism. Analysis showed 6% increase of the failure strain due to thermal effect and up to 11% increase of strength due to multiaxial stress in steel layer. The results of this study contribute to a deeper understanding of the role of each phenomenon that contributes to improved tensile properties in hybrid CFRP/metal laminates.

Qualitative evaluation of the moisture absorption rate in adhesive layers of carbon fiber reinforced plastic joints using electromagnetic induction testing

Herein, we developed and tested a method for moisture absorption rate measurements in the adhesive layers of carbon fiber reinforced plastic (CFRP) joints using electromagnetic induction testing (EIT). The proposed method relied on permittivity changes in the adhesive layer resulting from moisture absorption, which were evaluated by EIT. Moreover, the effects of changes in the thickness, conductivity, and permittivity of the CFRP and adhesive layer on the EIT output were evaluated by finite element analysis. Moisture absorption tests were conducted on the adhesive, CFRP, and CFRP single-lap joints, and a method was developed to record the permittivity changes in the adhesive layer of the CFRP joint, considering the influencing factors. The proposed method was found to be capable of qualitatively evaluating the moisture absorption rate in the adhesive layer of a CFRP joint from the central to the late moisture absorption period.

FINITE ELEMENT ANALYSIS OF UHPFRC CYLINDERS CONFINED WITH CFRP SHEETS

Many recently developed materials have proven their capability as retrofitting materials for different applications. These materials include carbon fiber-reinforced plastic (CFRP) and ultra-high-performance concrete with steel fiber reinforcement (UHPFRC). In this work, the influence of wrapping the UHPFRC cylinders with CFRP was investigated numerically. Different parameters were considered, including the grades of UHPFRC and configurations of CFRP. A 3D finite element model (FEM) of UHPFRC cylinders wrapped with CFRP under static loading was developed using nonlinear finite element software (ABAQUS). The model was first verified using the experimental results provided in the literature. After that, parametric studies were carried out to study the impact of grades of UHPFRC and the different confining CFRP schemes (fully and partially) on the overall behavior of strengthened cylindrical UHPFRC, as well as the impact of increasing the thickness of CFRP layers on the strength and ductility ratio of the confined specimens. The results indicated that using CFRP to warp the UHPFRC specimens significantly improved their strength and ductility. As expected, the use of CFRP to partially wrap specimens did not show a significant enhancement in the strength of the confined specimens when the CFRP layers were less than 60% of the height.

Effect of size on the eccentric compression performance of damaged square RC columns strengthened with CFRP: An experimental study

The objective of this study was to experimentally analyze the effect of size on the eccentric compression performance of damaged square Reinforced concrete (RC) columns reinforced with Carbon Fiber Reinforced Plastic (CFRP) in a bid to improve the rationality of the design of CFRP-reinforced large concrete members. In the experiment, 18 square RC columns with proportional sizes were prepared, and the principle of the proportional changes in the size was strictly controlled. The effects of the size, eccentricity, pre-damage, and number of CFRP layers were considered in the experiment, and the bearing capacity, lateral deflection, rebar strain, CFRP strain, and failure modes of RC columns of different sizes before and after the reinforcement were studied. The experimental results showed that the CFRP reinforcement could improve the bearing capacity and deformability of damaged square RC columns under small eccentric compression; however, the reinforcement effect gradually decreased with increasing size. When the cross-sectional dimensions were 100, 200, and 300 mm, the bearing capacity increased by 26.17%, 17.27%, and 12.98%, respectively, and the ductility coefficient increased by 104%, 44.80%, and 35.20%, respectively.

Comparison of stacking sequence on the low‐velocity impact failure mechanisms and energy dissipation characteristics of CFRP/Al hybrid laminates

AbstractCompared with the resin‐based composite laminates, fiber metal laminates (FMLs) have superior impact resistance. In this study, investigations were made to reveal the effects of stacking sequence on the low‐velocity failure mechanisms and energy dissipation characteristics of carbon fiber reinforced plastics (CFRP)/Al hybrid laminates with same areal density. Experiments were carried out to characterize the typical mechanical responses. Failure morphologies were evaluated by X‐ray computed tomography scanning techniques. Then numerical simulations based on three‐dimensional progressive damage analysis were applied to reveal the dynamic evolution process and energy dissipation characteristics. Results indicated that plastic deformation of aluminum layers acted as the dominant factor in energy dissipation. Stacking aluminum layers on the exterior surface could increase the absorbed impact energy and reduce the fracture behavior of the component layers. The specimens with more CFRP layers stacked on the surface exhibited more severe fracture behavior of component layers and larger delamination areas, thus promoting the energy dissipated by CFRP cracking and delamination. This work intended to provide practical guidance for the structural design of fiber reinforced polymer/metal hybrid protective structures.

Strength evaluation of CFRP structure of high pressure hydrogen tank based on mesoscale analysis

For designing with rigorous cost reduction and safety, high pressure hydrogen tanks manufactured from carbon fiber reinforced plastic (CFRP) of fuel cell vehicles, a method that can precisely predict the burst pressures of the tank is urgently needed. CFRP layers of tanks are formed with complicated mesostructured consisting of carbon fiber bundles and matrix resin using a filament winding process. A methodology that approaches by using cross shaped specimens to present fiber bundle conditions in CFRP layer of the tank is scrutinized. From the analysis and experiment with the specimen, it was found that strain rate dependency and tensile compression asymmetry of the resin have a great influence in addition to the fiber strength in the fiber direction on the CFRP fracture process. Burst pressures were predicted by CFRP mesoscale model with the load and boundary condition from macroscale analysis of conventional axisymmetric continuum model of the tank and validated through an actual tank burst test. As the results, we found the burst pressure of tank could be accurately predicted based on carbon fiber ruptures in the mesoscale model.

Analysis of multilayered carbon fiber winding of cryo-compressed hydrogen storage vessel

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.

Mathematical modeling of the eddy current testing of delamination cracks in multilayer CFRP objects

We propose an approximate mathematical model making it possible to obtain estimates of the change in the eddy current signal under the influence of delamination in multilayer carbon fiber reinforced plastic (CFRP) objects. We give the dependences of the change in the eddy current signal on delamination in the CFRP objects for a new flaw detection method based on the comparison of eddy current signals from CFRP layers grouped by angular orientation.

Cyclic Loading Behaviour of Externally Bonded CFRP Reinforced Concrete Beam-Column Joint

Cyclic loading behaviour of RC beam-column joints strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) was analysed through Abaqus CAE software. Effect of the number of CFRP layers and the strengthening technique on failure modes, hysteretic curves, skeleton curves, ductility, and energy dissipation capacity were studied. The results show that the strengthening of RC beam-column joints by externally bonded CFRP can effectively improve the cyclic loading behaviour. Strengthening the joint by fiber bands enhances ductility and energy absorption capacity. The increase in the number of CFRP layers leads to enhance energy absorption capacity significantly as compared to ductility.

A CFRP/PZT laminated piezoelectric motor with high force density

This work presents a laminated piezoelectric (PZT) motor to achieve high force density, high strength, and compact structure. The oscillator consists of vibration units and a driving foot. Each of the vibration units is formed by symmetrically bonding two PZT ceramics on a carbon fiber-reinforced plastic (CFRP) layer to improve its strength. The oscillator works in hybrid mode of the first longitudinal vibration (L1) and second bending vibration (B2). The finite-element method is adopted to tune the resonance frequencies of the two modes, and the vibration characteristics are experimentally analyzed. The strength test shows that the presence of the CFRP layer can increase the overall strength of the oscillator by 28% compared with a pure PZT motor. To evaluate the performance, the load characteristics of the fabricated prototype (with a size of 39 × 10 × 4.6 mm3 and weight of 10.6 g) are tested on a designed testbed. The single-phase driving method is used to drive the motor, and the best performance is obtained at the B2-mode frequency. The maximum thrust force, no-load speed, and output power reach 17 N, 335 mm s−1, and 775 mW, respectively, at a drive voltage of 100 Vp. Meanwhile, a thrust density of 1604 N kg−1 and an output power density of 73.11 W kg−1 are achieved. The thrust density is much higher than that of the other motors that operate in the same modes.

Pilot Demonstration of a Strengthening Method for Steel-Bolted Connections Using Pre-Formable Carbon Fiber Cloth with VaRTM

In recent years, many seismic retrofitting methods have been performed to improve the structural performance and prevent the brittle failure of structural members. In the case of steel structures, slender seismic braces have been widely used for buildings, towers, and bridges. The brace connections should resist the full plastic axial tension load to ensure adequate plastic deformation performance for vibration energy absorption. However, certain connections do not satisfy these requirements. Recently, carbon fiber reinforced plastic (CFRP) has been used extensively to strengthen existing structures because of its high-strength, high elastic modulus, and light-weight characteristics. In this paper, we investigate the applicability of CFRP strengthening for brace connections and gusset plates with stepped surfaces using the vacuum-assisted resin transfer molding technique as a pilot demonstration. Stepped surfaces can be eliminated by using alternative CFRP layers to straighten the structural CFRP layers in order to effectively transfer the axial stress. Eventually, it is shown that CFRP strengthening can improve the connection strength and plastic deformation with 3% elongation, even if the CFRP is molded on the stepped surface.

Theoretical, emulation and experimental analysis on auxetic re-entrant octagonal honeycombs and its applications on pedestrian protection of engine hood

In this article, a novel re-entrant octagonal honeycomb (ROH) with negative Poisson's ratio (NPR) configuration is proposed owing to its superior energy absorption and lightweight design performances. Regarding the effects of adjacent unit cells, a mechanics-based homogenization approach is put forward and employed to derive static mechanical properties including elastic modulus and Poisson's ratio of two-dimensional (2D) and three-dimensional (3D) ROHs under axial loading. Based on above, the predominant compression failure mode is explored. Then, the static mechanical properties and finite element model of ROH are validated by experiment and demonstrate high accuracy. Subsequently, to obtain dynamic responses of the ROH under dynamic impact loading, the relations among dynamic plateau stress and quasi-static plateau stress, initial density, dense strain and impact velocities are established under the conditions of mass conservation and momentum theorem based on one-dimensional shock wave theory and ideal rigid-perfectly plastic material model. Besides, dynamic energy absorption models of the ROH under dynamic loading are acquired in consideration of the effects of impact velocities on dense strain, the results show that theoretical models agree quite well with simulation results. On this basis, the application of ROH on automotive energy absorber is studied with the purpose of acquiring superior energy absorption and satisfying lightweight requirements simultaneously. Based on the decoupling thought of stiffness and pedestrian protection, a new design method of carbon fiber reinforced plastics (CFRP) hood with ROH is put forward in consideration of energy absorption and lightweight requirements. Of this, ROH is regarded as sandwich structure to meet the demands of energy absorption, CFRP plates are treated as outer and inner skins to satisfy the needs of stiffness. Firstly, multi-objective optimization models are set up under the constraints of reasonable structural parameters and negative Poisson’s ratio. Then, the NSGA-Ⅱalgorithm is adopted to achieve the optimal Pareto fronts with the targets for maximum unit mass energy absorption and minimum density. Afterwards, the optimization on thicknesses of CFRP layers is carried out to achieve minimum mass under the constraint conditions that the static stiffness of CFRP hood is larger than that of steel hood. In addition, the layering sequence of inner and lower skins are also optimized. Finally, improved overall stiffness, optimized HIC values and similar lightweight space of CFRP hood with ROH are achieved in comparisons with CFRP hood without ROH. Compared with steel hood, the pedestrian protection performance of CFRP hood with ROH is greatly enhanced, 1st free mode increases by 33.9%, and torsional stiffness and bending stiffness increase by 23.1% and 30.8%, respectively. While the weight decreases by 40.1%. The results indicate that the CFRP hood with ROH presents outstanding advantages of pedestrian protection and lightweight design in terms of HIC and stiffness performance.

Mechanical properties and bearing capacity of CFRP confined steel reinforced recycled concrete columns under axial compression loading

To study the axial compression behavior of carbon fiber reinforced plastics (CFRP) confined steel reinforced recycled concrete (CSRRC) columns, 11 specimens of CSRRC columns were manufactured and tested under axial compression loading. The design variables in the experiments included the replacement percentage of recycled coarse aggregate (RCA), layers of CFRP, strength of recycled aggregate concrete (RAC), profile steel ratio and slenderness ratio. Subsequently, the failure process and modes, load-displacement curves, stress-strain curves, transverse deformation coefficient and stiffness degradation of the specimens were obtained and analyzed in detail. The experimental results showed that the profile steel yielded before the steel rebars in the columns, then the RAC was crushed, and finally the CFRP broke under axial compression loading. The axial bearing capacity of CSRRC columns decreased with the increase of replacement percentage of RCA and slenderness ratio, respectively. However, the CFRP can give full play to its high-strength confinement performance and effectively improve the axial bearing capacity and deformability of columns. Moreover, the profile steel ratio and strength of RAC have significant effects on the initial stiffness of CSRRC columns, and the stiffness degradation rate of columns decreases with the increase of these parameters. Overall, the CSRRC columns exhibit high axial bearing capacity and good ductility deformation ability. Based on ACI 440.2R-08, the modified formula on the nominal axial bearing capacity of CSRRC columns was proposed in this study. The accuracy on the modified formulae was evaluated by the comparison between the calculated values and test values.

Measurement of directionality in carbon fiber reinforced plastic composite with eddy current testing

In carbon fiber reinforced plastic (CFRP) composite, the alignment of continuous carbon fibers guides the directional flow of eddy currents, which is beneficial to the structural and damage detection. In this study, for the purpose of impact damage repair, the transmitter-receiver (T-R) and the flat-tangent eddy current probes are used to determine the fiber orientations and stacking sequence in the CFRP laminate by surface scanning. Theoretical analysis shows that the T-R probe can flexibly pick up the magnetic field generated by the stretched eddy current in CFRP layers. In the meanwhile, the flat-tangent probe possesses layer selective characteristics. By calculating the fiber distribution images of individual directions based on two-dimensional fast Fourier transform (2D-FFT) and comparing the order of pixel intensity values of these images, the fiber orientation and the stacking sequence in the laminate plates can be obtained simultaneously, which provides guidance for damage detection and repair of the CFRP structures.

Numerical Investigation on Dynamic Response of RC T-Beams Strengthened with CFRP under Impact Loading

To precisely evaluate the retrofitting effectiveness of Carbon Fiber Reinforced Plastic (CFRP) sheets on the impact response of reinforced concrete (RC) T-beams, a non-linear finite element model was developed to simulate the structural response of T-beams with CFRP under impact loads. The numerical model was firstly verified by comparing the numerical simulation results with the experimental data, i.e., impact force, reaction force, and mid-span displacement. The strengthening effect of CFRP was analyzed from the section damage evaluation. Then the impact force, mid-span displacement, and failure mode of CFRP-strengthened RC T-beams were studied in comparison with those of un-strengthened T-beams. In addition, the influence of the impact resistance of T-beams strengthened with FRP was investigated in terms of CFRP strengthening mode, CFRP strengthening sizes, CFRP layers and FRP material types. The numerical simulation results indicate that the overall stiffness of the T-beams was improved significantly due to external CFRP strips. Compared with the un-strengthened beam, the maximum mid-span displacement of the CFRP-strengthened beam was reduced by 7.9%. Additionally, the sectional damage factors of the whole span of the CFRP-strengthened beam were reduced to less than 0.3, indicating that the impact resistance of the T-beams was effectively enhanced.

On crushing responses of filament winding CFRP/aluminum and GFRP/CFRP/aluminum hybrid structures

This study aims to explore the crushing characteristics and failure modes of multiple filament winding hybrid tubes. Two types of hybrid tubes, namely Glass fiber reinforced plastics (GFRP)/carbon fiber reinforced plastics (CFRP)/aluminum (Al) hybrid tubes and CFRP/Al, were fabricated by the filament winding process. The typical load-displacement curves, failure modes, effects of winding plies, winding angle and interaction on crashworthiness were explored. It showed that the failure modes of hybrid specimens were predominated by progressive brittle crack, delamination mode in CFRP layers and diamond failure mode in aluminum tube. Increasing hybrid plies increased the specific energy absorption (SEA), energy absorption (EA) and peak crushing force (PCF). The PCF of the hybrid tubes decreased with increasing CFRP winding angle from 30° to 60° (winding angle of 0° was along the axial direction of the tube) while the hybrid tubes with the winding angle of 45° showed the highest SEA and EA. A theoretical analysis was conducted on the effect of interaction on load bearing capacity and it is showed that the interactions between different materials can effectively enhance energy absorption. A comparison among the filament winding, vacuum bag forming and nested manufacturing processes was performed and the filament winding technique exhibited the highest improvement in crashworthiness of CFRP/Al hybrid tubes.

Automated removal of carbon fiber reinforced plastic layers for the repair by adhesive bonding

For the industrial repair of carbon fiber reinforced plastics (CFRP), scarfing is used to re-establish the load path. In the industry today, the state of the art removal of CFRP layers for a repair process is done mainly manually, leading to a time-consuming process. Therefore, an automation of this process is desirable. Today, vacuum suction blasting is used to pre-treat CFRP surfaces only for the superficial removal of impurities or the removal of the cover layer before bonding. With the common used blasting agents and nozzle geometries, the even removal of larger areas together with the fiber was not possible. This work shows that the technology of vacuum suction blasting was adapted to be used as an automated scarfing method. A combination of blasting parameters, especially the nozzle geometries together with a blasting agent were found to be able to remove CFRP layers precisely, detecting and correcting errors in-line with a line scanner-measuring unit. The presented method allows treating large-scale surfaces, scarfing the area one single layer at a time, increasing the removal rate in comparison to common blasting. With vacuum suction blasting the grinding dust emissions and process forces are low, post cleaning or further surface activation are not necessary and the removal results can directly be controlled. Challenges still exist with inaccurate removal due to interruptions in the blasting program and the generation of sharp edges for a stepped scarf.