Hybrid CFRP Research Articles

Study on out-of-plane tensile strength of angle-plied reinforced hybrid CFRP laminates using thin-ply

Thin-plies are generally defined as composites with ply thicknesses below 100 μm. These materials are rapidly gaining interest for high-performance applications, for example, the aerospace sector. Many practical techniques have been proposed to prevent delamination and improve the strength of composite laminates. A recent study has shown that the delamination could be postponed by replacing layers of CFRP with thin-ply in a unidirectional composite laminate, a configuration known as hybrid laminates reinforced with thin-plies. Since fiber orientation is known to be one of the most important parameters in composite laminate design, this study investigates the effect of oriented layers of thin-ply or both thin-ply and conventional CFRP in a hybrid laminate under out-of-plane tensile loading. A numerical Representative Volume Element (RVE) model for CFRP and thin-ply was generated, considering the unidirectional [0], cross-ply [45/−45], and [0/90] in order to better understand the effect of angle-plied hybrid composite laminates. Experimental results show that angle-plied composite laminates present higher failure load under out-of-plane tensile loading compared to the unidirectional ones. This can be attributed to the fact that an initiated crack is faced with a significantly more complex crack path in an angle-plied laminate to advance in the through-the-thickness direction.

On crushing behavior of square aluminum/CFRP hybrid structures subjected to quasi-static loading

Metal/composite hybrid thin-walled structures exhibit tremendous merits on the balance design among material costs, weight reduction and mechanical performances. In spite of these advantages, their underlying energy dissipating mechanisms and the influence law of key factors (such as mechanical properties, hybrid ratio, loading angle, etc.) on crushing behavior are still not well illustrated. This study aims to comprehensively explore the crushing deformation characteristics and underlying energy dissipating mechanisms of various square aluminum/CFRP hybrid structures (i.e., aluminum tube internally strengthened with CFRP namely CFRP/AL; aluminum tube externally strengthened with CFRP namely AL/CFRP tubes). Specifically, several axial quasi-static compression tests are performed to compare crushing behavior and performances of between hybrid tubes together with the corresponding net aluminum and CFRP tubes. Experimental results indicate that the total energy absorption of the CFRP/AL hybrid tubes is considerably higher than that of the summation of corresponding individual tubes. Subsequently, finite element models are developed for CFRP/AL hybrid columns to explore the underlying energy-absorbing mechanisms (the contribution of each constituent part on total energy absorption) and the influence law of key factors (mechanical properties, hybrid ratio, loading angle), which cannot be observed from experimental results. Numerical results indicate that the main reasons for the improvement in total energy absorption of CFRP/AL hybrid tubes are the altered deformation pattern of the outer aluminum tube and the significantly increased friction energy. Further, their outer aluminum tube seems to be more likely to generate plastic folding deformation rather than splaying progressive failure mode with increasing initial yield stress. The hybrid ratio and CFRP layer thickness jointly determine the deformation pattern of the CFRP/AL hybrid columns. Finally, it is also found that the load carrying capacity and energy-absorbing characteristics of CFRP/AL hybrid columns gradually reduce with increasing loading angle. The present study is expected to illustrate the potential of such hybrid structure as a crashworthy device and offer some design guidance for application and dissemination.

Effect of Alumina and Silicon Carbide Nanoparticle-Infused Polymer Matrix on Mechanical Properties of Unidirectional Carbon Fiber-Reinforced Polymer

Unidirectional carbon fiber-reinforced polymer nanocomposites were developed by adding alumina (Al2O3) and silicon carbide (SiC) nanoparticles using ultrasonication and magnetic stirring. The uniform nanoparticle dispersions were examined with a field-emission scanning electron microscope. The nano-phase matrix was then utilized to fabricate the hybrid carbon fiber-reinforced polymer nanocomposites by hand lay-up and compression molding. The weight fractions selected for Al2O3 and SiC nanoparticles were determined based on improvements in mechanical properties. Accordingly, the hybrid nanocomposites were fabricated at weight fractions of 1, 1.5, 1.75, and 2 wt.% for Al2O3. Likewise, the weight fractions selected for SiC were 1, 1.25, 1.5, and 2 wt.%. At 1.75 wt.% Al2O3 nanoparticle loading, the flexural strength modulus improved by 31.76% and 37.08%, respectively. Additionally, the interlaminar shear and impact strength enhanced by 40.95% and 47.51%, respectively. For SiC nanocomposites, improvements in flexural strength (12.79%) and flexural modulus (9.59%) were accomplished at 1.25 wt.% nanoparticle loading. Interlaminar shear strength was enhanced by 34.27%, and maximum impact strength was improved by 30.45%. Effective particle interactions with polymeric chains of epoxy, crack deflection, and crack arresting were the micromechanics accountable for enhancing the mechanical properties of nanocomposites.

Static and Dynamic Behavior of Circularized Reinforced Concrete Columns Strengthened with Hybrid CFRP

In this study, three strengthening techniques, near-surface mounted NSM-CRFP, NSM-CFRP with externally bonding EB-CFRP, and hybrid CFRP with circularization were studied to increase the seismic performance of existing RC slender columns under lateral loads. Experimentally, 1:3 scale RC models were studied and subjected to both lateral static load and seismic excitation. In the dynamic test, a model was subjected to El Centro 1940 NS earthquake excitation by using a shaking table. According to the test results, the strengthening techniques showed a significant increase in load carrying capacity, of about 86.6%, and 46.6%, for circularization and NSM-CFRP respectively, of the reference unstrengthened columns. On the other hand, columns strengthened with hybrid NSM-CFRP and EB-CFRP showed a different failure mode. Dynamically, the lateral drift was decreased by about 75%, 47%, and 49% for earthquake amplitudes of 0.05g, 0.15g, and 0.32g respectively. Finally, it was concluded, depending on the static and dynamic analyses, that the circularization process showed a significant increase in lateral load-bearing capacity.

Shear response of RC beams encompassing hybrid CFRP strips and steel stirrups: Beam depth effect

In this study, nonlinear finite element analysis (FEA) was conducted to investigate the shear behavior of reinforced concrete (RC) beams encompassing hybrid CFRP strips and steel stirrups. Primal FEA models were calibrated and verified by comparing the load–deflection response, cracking, and failure modes with the experimentally tested RC beams. A parametric case study was then implemented to evaluate the influence of critical parameters including: configurations of CFRP strips (strip width, orientation angle), size effect, and concrete compressive strength. The results showed that changing the individual CFRP strip width while maintaining a constant total width has no significant effect on the behavior of the RC beams. Increasing the concrete compressive strength improves the bond strength between the CFRP strips and concrete leading to higher load capacity. Changing the orientation angle of the CFRP strips up to 45° has minor effect on the RC beam shear capacity. The contribution of the CFRP strips was more pronounced as the beam depth increased. A comparison showed that internally-integrated CFRP strips leads to better enhancement in the shear strength of RC beams than externally strengthening with CFRP composites.

Fatigue behavior of hybrid and bonded single lap joints made of composite material

Joining of composite materials can be performed with different techniques and, in particular, trough mechanical fasteners, bonding, hybrid solutions. In last years, hybrid (bolted/bonded) joints are attracting the interest of several companies and scientific community, since the use of both techniques permit to overcome some critical aspects connected to the separate usage of adhesive and bolts, i.e., negative effects of the environmental conditions on adhesive, localized stresses at the notch. This paper aims to improve the knowledge about the fatigue behavior of hybrid CFRP (Carbon Fiber Reinforced Polymer) joints. For the purpose, experimental fatigue and static tests are performed on hybrid and bonded joints and the results herein discussed. Results are post-processed with the main goal to highlight the benefits led to the hybrid technique with respect to the bonding one.

STRESS DISTRIBUTION IN THE HOLLOW STIFFENED HYBRID LAMINATED COMPOSITE PANELS IN SHIP STRUCTURES UNDER SINUSOIDAL LOADING

A simplified hollow stiffened hybrid laminated plate model has been developed for the marine structures. The detailed stress analysis through the thickness of the stiffened plate based on the higher order shear deformation theory has been carried out under sinusoidal loading. The hybrid laminates are made by wrapping the GFRP laminates with CFRP at the outermost layers of the stiffened panel. This hybridization technique can be an optimum solution from the point of view of cost reduction as well as enhancement of strength properties. The layer-wise stresses for the stiffened plate have been calculated in the present paper. A 3D polynomial curve fitting technique has been used to obtain higher accuracy and consistency in the computation of stresses. The computer code has been developed using MATLAB considering the plates as eight noded isoparametric plate bending element and the stiffener has been modeled as three noded isoparametric beam element. The stiffened panel has also been analysed using the ANSYS14.0 software package considering 2D model. The results obtained from the present formulation have been compared with those available in the published literature to validate the present formulation. The stiffened panels made of GFRP, CFRP and GFRP-CFRP hybrid laminates have been studied here. An extensive parametric study has been carried out with varying fibre content in the laminates.

Mechanical Characterization of Hybrid CFRP Composite

Mechanical Characterization of Hybrid CFRP Composite

Behavior of Hybrid CFRP Laminated Thin-Walled Beams: Experimental, Numerical, and Analytical Evaluations

The aim of this paper is to assess the structural behavior of hybrid thin-walled beams which were fabricated using laminated carbon fiber reinforced polymer (CFRP). Seven hybrid (CFRP) I-beams were fabricated, instrumented, then have been tested under monotonic four-point loading in order to evaluate their behavior up to failure. In constructing the I-beam specimens which were evaluated in this study, plywood core was implemented on both the web and flanges. Several important parameters were conducted in this study considering changing both of the ply orientations and stacking sequences of laminated fibers, also changing the shear span-to-depth ratio (a/d) of the specimens. The experimental results showed that stacking sequence is the most significant parameter that influences both flexural strength and stiffness of the hybrid beams. Also, the experimental results promoted the effectiveness of the core material for enhancing the flexure (bending) stiffness of beams. Then, these results were compared with a previous simulated study which used the finite element modeling to model the beams. Also, in order to evaluate the efficiency of the CRFP beams, the results were compared to similar steel beams having the same dimensions of the CFRP beams. As compared to steel beams, the load carrying capacity of the laminated beams is being high compared with steel beams when taking into consideration their specific strength ratio.

Flexural behavior of reinforced concrete beam using CFRP hybrid system

This paper presents experimental and numerical study to investigate the flexural behaviour of strengthened RC beams using three CFRP techniques. Considered main variables were CFRP technique, amount of CFRP NSM and rope and cost/increase in strength effectiveness. Results indicate that using CFRP rope and sheet increased significantly maximum load and maximum strain of RC beams. Average increase in strength and maximum strain were 76.3% to 143.5% and 206% to 246% as the control RC beam. Moreover, RC beams strengthened with CFRP rope exhibited strength approximately similar to ones strengthened with CFRP strip. The cost/increase in strength ratio of specimens strengthened by CFRP rope is 61% higher than the ratio of specimens strengthened by CFRP NSM strip. Hence, the specimens strengthened by one layer of CFRP rope is the most economic techniques based in cost/increase in strength ratio even though it exhibited maximum load less than the specimens strengthened with two layers of CFRP rope or strip. CFRP rope was 40% lower than CFRP strip when same strengthening effect was achieved. Finally, complementary to experimental work a finite element model FEM was developed to investigate the flexural behaviour of beam. The FEA model showed somehow good agreement with the experimental results.

Effect of filaments diameter on the mechanical properties of wrap hybrid CFRP

In this paper, the vine-like structure of carbon bundles was designed through polyester fibre wrapping for better mechanical properties. The effect of wrapped hybrid structure and diameters of polyester fibre on the mechanical properties of carbon-polyester fibre/epoxy unidirectional composites was investigated experimentally. Five kinds of specimens with different polyester filament diameters were produced. The impact, tensile and unidirectional compressive properties of WHC (Wrap Hybrid Composite) were measured. Experimental results show that: it can be developed with strength and toughness properties far superior to those of their constituents, the compressive fracture morphology of specimens indicated that the fracture patterns of composites depend on wrapped hybrid structure, polyester fibres with higher tensile strengths provide better impact resistance, while thinner wrapping fibres enhance the compression properties of the composite material more effectively. The diameter of the wrapping fibre should be optimized as per the application of the composite material. The vine-like structure can provide a new design method for the structural design of continue fibre reinforced composite materials.

Enhancing the EB-FRP strengthening effectiveness by incorporating a cracking-control layer of ECC with different thicknesses

The multiple and tight cracking nature of engineered cementitious composite (ECC) under tension can significantly mitigate or eliminate the premature debonding of externally bonded (EB) fiber-reinforced polymer (FRP). This paper systematically investigates the flexural performance of concrete beams that were jointly strengthened by hybrid carbon FRP (CFRP) and ECC. The ECC layer realizes the dual-function of maximizing the strengthening effectiveness and contributing additional flexural strength. The test results indicate that the inclusion of an ECC layer changed the CFRP strip from debonding to rupture at the ultimate state, which in turn remarkably increased the member flexural capacity, the energy consumption capacity and ductility, compared to the EB-CFRP strengthened counterpart. The CFRP rupture occurred even though the ECC thickness was only half that of the concrete cover. Further increasing ECC thickness contributed marginally to the member load capacity and ductility until when the ECC total enwrapped longitudinal reinforcement. The optimal thickness of ECC was discussed. The crack width of the concrete block was considerably narrowed after applying the ECC layer. Finally, a model was developed to predict the flexural strength of CFRP-ECC jointly strengthened beams, providing good agreement between the predicted and experimental results.

Flexural behavior of RC continuous T-beams reinforced with hybrid CFRP/ steel bars (experimental and numerical study)

This study presents experimental and numerical investigations to understand the response and failure of hybrid RC continuous T-beams reinforced in flexure by both Carbon Fiber Reinforced Polymer (CFRP) bars and steel bars at sagging and hogging regions. Three RC continuous T-beams were constructed experimentally and studied to discuss three parameters which are the type of reinforcement material, the relation between sagging and hogging reinforcement, and the moment redistribution. The control beam was reinforced with steel rebars that have been designed to fail in flexure. The second beam was reinforced with hybrid CFRP/ steel bars at the sagging and hogging regions. The sagging region of the third one was reinforced with steel bars while the hogging region was reinforced with CFRP bars. All critical sections at the tested specimens are designed to have the same axial stiffness for the reinforcement bars. Experimental results revealed that the moment redistribution ratio and mode of failure depend on the type of reinforcement bars and using the hybrid bars at both critical regions helped to control the serviceability limits of the beams.This study also suggests and validates a 3D numerical model to simulate the performance and failure of hybrid reinforced RC continuous T-beams using the finite element (FE) software “ANSYS”. The results agreed with the experimental observations that indicated significant effect of the type of reinforcement material at sagging and hogging regions on the failure mode and the redistribution of the moment of the RC continuous beams.

Flutter study of flapwise bend-twist coupled composite wind turbine blades

Bending-twisting coupling induced in big composite wind turbine blades is one of the passive control mechanisms which is exploited to mitigate loads incurred due to deformation of the blades. In the present study, flutter characteristics of bend-twist coupled blades, designed for load alleviation in wind turbine systems, are investigated by time-domain analysis. For this purpose, a baseline full GFRP blade, a bend-twist coupled full GFRP blade, and a hybrid GFRP and CFRP bend-twist coupled blade is designed for load reduction purpose for a 5 MW wind turbine model that is set up in the wind turbine multi-body dynamic code PHATAS. For the study of flutter characteristics of the blades, an over-speed analysis of the wind turbine system is performed without using any blade control and applying slowly increasing wind velocity. A detailed procedure of obtaining the flutter wind and rotational speeds from the time responses of the rotational speed of the rotor, flapwise and torsional deformation of the blade tip, and angle of attack and lift coefficient of the tip section of the blade is explained. Results show that flutter wind and rotational speeds of bend-twist coupled blades are lower than the flutter wind and rotational speeds of the baseline blade mainly due to the kinematic coupling between the bending and torsional deformation in bend-twist coupled blades.

Experimental and numerical analysis of CFRP-SPCC hybrid laminates for automotive and structural applications with cost analysis assessment

The present study evaluated CFRP and SPCC hybrid laminates by combined experimental and simulation analysis. The results showed that the strength of hybrid laminate [SPCC/[0]n]S increased more than 100% from 1000 MPa (0.5 mm thickness) compared to 2000 MPa (2 mm thickness). Moreover, by setting the volume fraction of hybrid laminates, the strength can increase from under 500 MPa to more than 3000 MPa with a minimum changed in strain performance. In other results, the effect of temperature differences during the manufacturing process is investigated. The analysis related to the operational temperature that used different material combinations was also evaluated. The band of temperature is varying from as high as 45 °C to as low as −45 °C. The outcomes demonstrate that the range of maximum strain of laminate from 45 °C to −45 °C can up to 0.1% of strain. Further analysis with a comparison regarding the angle effect of hybrid laminates with residual compressive stress and the curing temperature was also evaluated. The waviness trend shows higher when the temperature is set higher, and vice versa. The experimental results indicate good agreement with simulation results. Moreover, the analysis based on cost assessment was included and compared with other mechanical properties.

Acoustic Emission Techniques for Evaluating Damage Modes in CFRP Hybrid Joints

The Acoustic Emission (AE) technique is one of the powerful Non-Destructive Evaluation (NDE) tools for predicting and assessing damages in composite structures. In this research work, the energy released during each acoustic event, as a function of the total number of counts, is used for evaluating the damage modes in CFRP hybrid joints. The damage modes identified using the AE parameter, Energy per Count () is compared with the waveforms of the acoustic events. Generally, the type of damage mode can be identified by postprocessing the acoustic waveforms. By comparing the waveforms with the , the damage mode has been evaluated. The technique introduced in this work will reduce the data storage and computation time for analyzing the waveforms. The damage modes can be identified during loading using this technique. In addition to that, the location of the generated acoustic events is used for identifying the critical failure areas in the CFRP hybrid joints. The attenuation of the AE events due to the distance between the sensors and the AE source is also considered for this study. From the observed results, the AE technique proves to be one of the formidable techniques for evaluating damage modes in composite structures.

Steel foil reinforcement for high performance bearing strength in Thin‐Ply composites

This study investigates the influence of local hybridization of Thin and Thick-Ply CFRP laminates on the open-hole and bearing properties. The area weight of the CFRP unidirectional prepregs used is 40 gsm in the case of Thin-Ply layers and 160 gsm in the case of Thick-Ply layers. The steel used is a 1.4310 stainless-steel foil with the same layer thickness as the prepregs. In the hybrid area, 90∘ layers were locally replaced by stainless steel patches. The local metal foil content varies from 6.25%, 12.5% to 25.0%. For notched laminates, the open hole tensile strength is significantly decreased with thinner layer thicknesses. The failure behavior changes from complex delamination dominated failure to brittle failure. By using stainless steel foils in the regions of stress concentrations, energy can be dissipated by plastic deformation of the steel foil and stresses can be deflected to neighbouring areas. For Thin-Ply samples with a local steel content of 25% the open hole tensile strength increases by 64% in comparison to the reference Thin-Ply specimens and the sensitivity towards stress concentrations decreases. The bearing strength of the hybrid CFRP laminates is increased by up to 54.6% in comparison to the reference material, due to the confinement of the steel foil and the resulting higher compressive strength and the plastic deformation at high stresses. The stress–strain diagrams and micrographs of the fibre metal samples reveal that damage is initiated before the maximum bearing strength. However, the damage offset bearing strength increase concerning the specific density of the material significantly.

Experimental and numerical investigation of ply size effects of steel foil reinforced composites

The effect of ply thickness on the notch sensitivity and bearing properties on carbon fibre reinforced polymer composites and their hybrid laminates with steel foils were studied. Laminates with ply thicknesses of 0.3 mm and 0.03 mm comprising of CFRP and hybrid laminates were manufactured and characterized using tension, open hole tension and double lap bearing tests. A 25% ply substitution was found to double the bearing load with extensive plastic deformation in the joint while maintaining high stress and maintaining constant cross-sectional thickness in the laminate. With a good agreement between the finite element predicted values and failure behaviour, the damage initiation and progression behaviour could be observed experimentally. We numerically captured (i) rapid failure of 0° plies in the thin ply CFRP hybrid and (ii) continuous delamination with significant plastic deformation for the thick ply CFRP hybrid. The numerical results significantly reduce future experimental work when designing hybrid laminates and could allow the laminate lay-up to be tailored for load cases. Both the experiments and numerical models underline the distinct size effects occurring with respect to the ply thicknesses when hybridising a very ductile metal with a brittle yet strong composite material.

Experimental study on cyclic response of concrete frames reinforced by Steel-CFRP hybrid reinforcement

A novel section with Steel-carbon fiber reinforced polymer (CFRP) hybrid reinforcement is introduced. CFRP longitudinal reinforcements are placed in the outer layer of the section, while steel reinforcements are arranged in the inner layer. The new type section is utilized to reduce the residual deformation of anti-seismic structures and improve the durability of structures. Cyclic loading tests are conducted on the four concrete frame structure with an axial compression ratio of 0.31. Seismic performances of concrete frames with steel reinforcements, steel-CFRP hybrid reinforcements and CFRP reinforcements are compared and studied. The major objectives of study are focus on the performance of CFRP reinforcements under the axial compression ratio of 0.31 and the ductility, energy dissipation, strength degradation, unloading stiffness, residual deformation of the frame structure with different reinforcement modes. Test results showed that as compared with the steel reinforced concrete frame, Steel-CFRP hybrid reinforced concrete frame exhibited excellent post-earthquake repairabilities, comparable hysteretic energy dissipation abilities and reasonable strength degradation. Furthermore, when the axial compression ratio is 0.31, the ultimate tensile strength of CFRP reinforcements calculated in accordance with the bearing capacity is 27.2%–32% of the static ultimate tensile strength. The concrete frame with ideal mechanical properties can be obtained by reasonable allocation of steel and CFRP reinforcement.

Graphitic nanoparticles functionalized with epoxy moiety for enhancing the mechanical performance of hybrid carbon fiber reinforced polymer laminated composites

AbstractExceptional properties and unique structural features of graphene make it a successful secondary reinforcing agent for the enhancement of mechanical performance of hybrid carbon fiber reinforced polymer (CFRP) composites. In this study, graphitic nanoparticles (GrNPs) were functionalized with the epoxy moieties through the traditional silanization method and an innovative approach of grafting with epichlorohydrin and then reinforced in epoxy system to prepare nanocomposites and hybrid CFRP laminated composites. The morphological, structural, and thermal investigation revealed the successful functionalization of GrNPs. The tensile strengths of the nanocomposites were found significantly enhanced by ~36% due to incorporation of silanized GrNPs and ~30% due to incorporation of epichlorohydrin grafted GrNPs compared to the neat epoxy. The tensile strengths of the resulting CFRP composites reinforced with silanized and epichlorohydrin grafted GrNPs showed ~37% and ~36% improvements, respectively, as compared to the control sample. Comparing the results of silanized and epichlorohydrin grafted GrNPs nanocomposites, it has been found that silanization has better potential to improve the mechanical performance of the hybrid CFRP composites as compared to epichlorohydrin grafting.