Carbon Fiber Reinforced Polymer Materials Research Articles

Investigation of the effectiveness of CFRP strengthening of concrete made with recycled waste PET fine plastic aggregate.

In recent decades, several studies have considered the use of plastic waste as a partial substitute for aggregate in green concrete. Such concrete has been limited to non-structural applications due to its low strength. This raises whether such concrete can be enhanced for use in some structural applications. This paper reports an attempt to develop a structural-grade concrete containing plastic waste aggregate with high proportions of substitution and confined with carbon fiber reinforced polymer (CFRP) fabrics. Experimental research was conducted involving the casting and testing 54 plain and confined concrete cylinders. A concrete mixture was designed in which the fine aggregate was partially replaced by polyethylene terephthalate (PET) waste plastic at ratios of 0%, 25%, and 50%, and with different w/c ratios of 0.40, 0.45, and 0.55. The results show that confinement has a substantial positive effect on the compressive behavior of PET concrete. The enhancement efficiency increases by 8-190%, with higher enhancement levels for higher substitution ratios. Adding one layer of CFRP fabric raises the ultimate strength of samples that have lost compressive strength to a level close to that of unconfined samples not containing PET. This confinement is accompanied by an increase in the slope of the stress-strain curve and greater axial and lateral strain values at failure. For the specimens confined by CFRP fabric, PET aggregate can be used as a partial substitute for sand at a replacement ratio of up to 50% by volume for structural applications. This paper also considers the ability of existing models to predict the strength of confined-PET concrete circular cross-sections by comparing model predictions with experimental results. The strength of confined PET concrete elements can't be accurately predicted by any of the models that are already out there. It's important to come up with a new model for these elements.

Static and Vibration Analyses of a Composite CFRP Robot Manipulator

This paper reports analyses of a 5-degrees-of-freedom (5-DOF) carbon fiber-reinforced polymer (CFRP) robot manipulator, which has been developed for farm applications. The manipulator was made of aluminum alloy (AA) and steel materials. However, to check the effectiveness of CFRP materials on the static and free-vibration performance of the manipulator, the AA parts were replaced with CFRP. For this purpose, the effects of various cross-sections and layups on three design criteria—deflection, load-carrying capacity, and natural frequency—were investigated. Two types of thin-walled laminated sections, specifically the I section and rectangular tubular sections, were used for the composite parts. These parts were made from three hollow square section (“SSS” section) beams and three I section (“III” section) beams. These multi-cell beams were modeled using the finite element (FE) method. Three configurations were selected for analysis based on the manipulator’s most common operating conditions. The results indicated that the use of CFRP increased the manipulator’s natural frequencies, increased the load-carrying capacity, and decreased the manipulator’s tip deflection when compared with its AA counterpart. An analysis showed that using CFRP in the manipulator’s structure could improve static and vibrational performances. It was observed that the “SSS” section beams were 1.17 times stiffer, could carry a 1.20 times higher load, and were 1.40 times heavier than the “III” section beams. Also, decreasing the fiber direction in angle-ply layups from 90° to 0° and adding 0° plies, while keeping the total number of layers constant, decreased the manipulator’s tip deflection and increased its natural frequencies.

Numerical Simulations of Lightning Strikes to Carbon Fiber Reinforced Polymers Using a Multi-Variable Approach

Carbon fiber-reinforced polymer (CFRP) composite materials are being employed widely in the manufacturing of next-generation aircraft because of their superior mechanical properties compared to those of metallic-based materials. Owing to growing interest in CFRP materials from large commercial and military aircraft manufacturers, such as Boeing and Airbus, research that investigates lightning strikes and associated damage is of paramount importance, as the fiber-polymer composite is highly resistive to electrical current. The high resistivity of traditional CFRP materials means that they are susceptible to extreme damage caused by the Joule effect, also known as resistive heating. The aim of the study presented in this paper is to determine and quantify the effectiveness of a developed multi-variable pyrolysis approach to model the transient material degradation during a lightning strike event. The study employs the finite element method (FEM) in the form of a coupled thermal–electrical analysis in conjunction with a user subroutine available in Abaqus. A parametric study was conducted to compare three different peak current values (20[Formula: see text]kA, 30[Formula: see text]kA and 40[Formula: see text]kA) based on a model that utilized pyrolysis-dependent material constituents as well as a novel model for specific heat capacity. The study also included a heat transfer step for a cool-down process. The results obtained from the model developed have strong agreement with the surface damage area and depth of damage compared with those from experimental analysis in literature.

Numerical analysis of sandwich panels under high-velocity impact

Composites are gaining importance in aircraft structures, due to their high specific strength, stiffness, and low weight. There are different types of composites used in aircraft structures out of which carbon fiber reinforced polymer (CFRP) serves best in the aircraft industry. Half of the weight of the Boeing 787 is made of CFRP and other composites that reduced the weight of the aircraft by 20% as compared to the conventional design with aluminum alloy. Similar to CFRP the recent trend focused on the usage of sandwich structures in aircraft design. Sandwich structure is a composite material made of the lightweight thick core placed between the thin face sheets made of CFRP or Glass fiber reinforced polymer. During service, aircraft panels are subjected to severe structural, aerodynamics loads, and impact loads. These loads cause severe damage to the structure that affects the residual strength. The impact is the more susceptible damage in composite panels. In this paper, a numerical impact analysis of the sandwich panel is carried out. There are different parameters that influence the impact strength of sandwich panels are face sheet material, core material, and thickness of the core. In this paper, finite element-based parametric analysis is carried out by varying face sheet materials such as CFRP, GFRP, Al alloy, Ti alloy, and core materials (such as honeycomb structure and PVC foam). Further, in this work, the combined MADM method using TOPSIS and AHP is applied to find out the optimal face sheet material for the sandwich panel. The attribute data for applying the MADM method is obtained from finite element analysis (FEA).

Electroluminescent strain sensing on carbon fiber reinforced polymer

The present paper demonstrates an inexpensive and less labor-intensive machine vision-based strain and damage visualization technique compared to traditional carbon fiber reinforced polymer material inspection methods. This technique is used to characterize the fracture and failure properties upon progressive axial loading in textile carbon fiber reinforced polymer (CFRP) lamina with non-intrusive smart electroluminescent (EL) integration. The smart EL structure utilizes CFRP's unique conductive and piezoresistive properties to visualize deformation and cracks through brightness change. Two fiber orientations (±45° and 0°/90°) of twill-weave CFRP lamina are fabricated according to a modified ASTM D3039 for linear and fatigue loading in uniaxial mechanical tests to analyze both fiber and matrix-induced EL responses. The EL-strain visualization method is validated with standardized digital image correlation (DIC) utilizing the natural speckling pattern of the EL CFRP lamina. The axial EL-strain results for both static and cyclic loading highly agree with the strain extracted planar conventional DIC strain field on standard and damaged CFRP samples in terms of spatial resolution and sensitivity. This novel strain and damage visualization method aims to be a portable, low-cost, and real-time alternative to non-destructive testing methods commonly used in the composite industry. Instead of periodic checkups, EL architecture allows for real-time strain and damage visualization of composite structure. • Fabrication and tensile testing of strain sensing EL illuminating woven CFRP in [±45°] and [0°/90°] fiber orientations. • Visual damage and strain detection are achieved with EL CFRP structure. • Planar DIC strain fields produced on EL illuminating and conventional airbrushed patterns show strong correspondence. • Variations in piezoresistive and luminance response exhibit correlation with strain.

Influence of Pulse-Pause Sequences on the Self-Heating Behavior in Continuous Carbon Fiber-Reinforced Composites under Ultrasonic Cyclic Three-Point Bending Loads.

Several studies have been conducted in the Very High Cycle Fatigue (VHCF) regime on Carbon Fiber Reinforced Polymers (CFRP) in search of their fatigue limit beyond their typical service life, which is itself in the order of 108 loading cycles. The ultrasonic fatigue test (UFT) method has been recently gaining attention for conducting fatigue experiments up to 109 loading cycles. This can be attributed to the reduction of testing time, as the testing facility operates at a cyclic frequency of 20 kHz. The fatigue loading in UFT is usually performed in a pulse–pause sequence to avoid specimen heating and undesirable thermal effects. For this study, the pulse–pause combination of the UFT methodology was explored and its influence on the self-heating behavior of the CFRP material was analyzed. This was realized by monitoring the temperature evolution in the CFRP specimens at different pulse–pause combinations and correlating it with their final damage morphologies. From the obtained results, it is concluded that the specimen heating phenomenon depends on several variables such as cyclic loading amplitude, the pulse–pause combination, and the damage state of the material. Finally, it is proposed that the test procedure, as well as the testing time, can be further optimized by designing the experiments based on the self-heating characteristic of the composite and the glass transition temperature (Tg) of the polymer matrix.

Numerical Investigation of HSC Columns Retrofitted by CFRP Materials under Combined Load

Repairing and retrofitting old civil engineering structures based on reinforced concrete represents a challenge for civil engineering societies all over the world. Environmental impacts such as corrosion and natural disasters like earthquakes can considerably weaken those structures. Reinforced concrete confinement technique using carbon fiber-reinforced polymers (CFRP) is considered as an innovative solution to strengthen the old and damaged structures. In this paper, a numerical simulation was carried out to evaluate the impact of the CFRP jacket as a confining composite material on the compressive strength and the ultimate strain of confined reinforced concrete. A FE model was developed, validated by comparing its results with the available experimental measurements, and finally assessed by performing a parametric study. Indeed, the parametric investigations had as their purpose the evaluation of the level of confinement (different number of plies), namely without plies, one plie, and three plies configuration, that were subjected to different eccentric loading modes e=0, e=25 and e=50 mm, in order to assess the interaction between the combined load that can be represented by compressive and flexural effect. The numerical results were, in fact, in good agreement with the experimental data. In addition, CFRP wrapping had a significant effect on the maximum load of eccentrically loaded columns compared to concentrically loaded columns by increasing the compressive strength with a value of 15% gain compared to the unconfined column. Doi: 10.28991/CEJ-2022-08-04-011 Full Text: PDF

Thermodynamic simulation, surface morphology and bending property of carbon fiber reinforced polymer composite material subjected to laser cleaning

Carbon fiber reinforced polymer (CFRP) has been regarded as an important candidate as structural components in structural engineering. With purpose of removing the epoxy resin and contaminants and in turn enhancing the bonding strength between CFRP and other materials, a nanosecond laser was used to remove the epoxy resin and contaminates on CFRP composites. A thermodynamics model was established to investigate the temperature field distribution, influences of laser power density and laser scanning speed on the cleaning effect, and therefore provide theoretical reference for cleaning experiments. The results showed that the laser power density of 8.8 kW.cm−2 and scanning speed of 1000 mm/s are preferred for an excellent cleaning effect. The cleaned surface presented a higher surface free energy, which in turn improved the tensile shear strength and bending strength. The failure mechanisms for the joints between TC4 and CFRP depend on laser power density for laser cleaning treatment.

Parts Consolidation of Automotive Front Crossmember: From Two-Piece CFRP Design to One-Piece Design

<div class="section abstract"><div class="htmlview paragraph">As demand for fuel efficiency rises, an increasing number of automotive companies are replacing their existing metal designs with carbon-fiber-reinforced polymer (CFRP) redesigns. Due to the handling and manufacturing processes associated with CFRP materials, engineers have more design freedom to create complex, light-weight designs, which would be infeasible to manufacture using metal. Additionally, it is likely that by redesigning with CFRP, many steel assemblies can be consolidated to significantly fewer parts, simplifying or potentially eliminating the assembly process. When designing an automotive crossmember using CFRP materials, designers often aim for a two-piece design (top and bottom), while utilizing reinforcement material where needed. The joining of these two pieces is typically accomplished with many mechanical fasteners and adhesives, significantly increasing the part count and the manufacturing complexity. The objective of this research project is to redesign an existing steel front crossmember to a one-piece CFRP design, removing the need for most of the mechanical fasteners and adhesives. While a reduction in stiffness was observed in the final design, strength requirements were met, and the overall mass was reduced by over 25%. This work shows that a one-piece CFRP crossmember is possible and should be further explored in the automotive industry.</div></div>

Measurement of Elastic Constant Matrix of Carbon Fiber Composites With an Ultrasonic 2D-Array Transducer

The use of carbon fiber reinforced polymer (CFRP) composites is gaining popularity in various industries. Due to its anisotropic nature, the characterization of the mechanical properties of CFRP is challenging. The current practices for determination of the elastic properties of CFRP materials are through destructive testing methods, which is not feasible in many <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> scenarios. This paper presents an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> and non-destructive method to characterize elastic properties of CFRP plates by using an ultrasonic 2D-array transducer. The ultrasonic 2D-array transducer was made of 64 piezoelectric elements and the measurement is automated by an advanced ultrasonic system. An automated time-of-flight extraction algorithm was used based on peak detection of ultrasonic signals. The elastic constants of the CFRP plates were calculated based on the Christoffel equation. This method was validated by ultrasonic through-transmission method by using two discrete ultrasonic transducers. Complete elastic constant matrix measurements for unidirectional and quasi-isotropic CFRP plates were demonstrated using the proposed method. This method has higher positional accuracy, faster testing speed, and better consistency compared to through-transmission method. This work can also be applied for in-situ structural health monitoring of elastic properties changes of materials and structures.

Application of edge detection based on hexagonal image structure to delamination detection of carbon fiber reinforced polymer material

Delamination is one of the most critical damage modes in carbon fiber reinforced polymer (CFRP) materials, and is invisible to the naked eye. Although delamination defect images of CFRP materials can be obtained through ultrasonic tomography, it is still difficult to accurately identify the position and contours of defect images. In this study, four different delamination defect images of CFRP composite plates were obtained through a finite element simulation and fan-beam ultrasonic tomography. A hexagon algorithm based on interpolation is proposed that transforms the reconstructed defect images from square pixels into hexagonal pixels. The interpolation algorithm is based on the overlap between the square and hexagonal pixels. As the experiment results verify, the use of the hexagonal structure-based morphological method for edge detection significantly reduces the recognition error from 7.74% to 0.148% in comparison with a traditional quadrilateral structure. The experimental results also showed that this method can effectively reduce the artifact interference and obtain complete and accurate target edge information more effectively than a square structure.

Application of Edge Detection Based on Hexagonal Image Structure to Delamination Detection of Carbon Fiber Reinforced Polymer Material

Abstract Delamination is one of the most critical damage modes in carbon fiber reinforced polymer materials, and is invisible to the naked eye. Although delamination defect images of carbon fiber reinforced polymer materials can be obtained through ultrasonic tomography, it is still difficult to accurately identify the position and contours of defect images. In this study, four different delamination defect images of carbon fiber reinforced polymer composite plates were obtained through a finite element simulation and fan-beam ultrasonic tomography. A hexagon algorithm based on interpolation is proposed that transforms the reconstructed defect images from square pixels into hexagonal pixels. The interpolation algorithm is based on the overlap between the square and hexagonal pixels. As the experiment results verify, the use of the hexagonal structure-based morphological method for edge detection significantly reduces the recognition error from 7.74% to 0.148% in comparison with a traditional quadrilateral structure. The experimental results also showed that this method can effectively reduce the artifact interference and obtain complete and accurate target edge information more effectively than a square structure.

Comparison of Prestressing Methods with CFRP and SMA Materials in Flexurally Strengthened RC Members.

Over the years, prestressing concrete has become a well-known technique to improve the ultimate and serviceability state of RC members. Besides steel reinforcement, relatively new materials such as carbon fiber reinforced polymers (CFRP) or especially shape memory alloys (SMA) can be used to active strengthening. The main scope of this paper is to compare various prestressing methods using carbon composites and memory steel alloys. A description of SMA, shape memory effect, its utilization for prestressing, and CFRP materials are presented in the paper. Moreover, current state-of-the-art developments in the field of both materials, considering prestressing systems and available anchorage, material behavior, creep and stress relaxation, durability issues, thermal compatibility with concrete, and fire behavior, are described. A general revision of previous studies based on flexural strengthening using both materials is conducted and the selected results of these studies are briefly presented. The behavior of RC beams after strengthening with mentioned techniques is compared and discussed. Selected on-site applications are described to confirm the feasibility and practicality of the strengthening systems. Finally, the main advantages and disadvantages of CFRP and SMA materials for prestressing concrete structures are summarized and further recommendations for the future research are listed.

Experimental and finite element analysis of CFRP strengthened aluminum tubes flexure behavior

This study investigates the effect of carbon fiber reinforced polymers (CFRP) sheets on the flexure behavior of structural square cross-sectioned aluminum tubes. The specimens were extruded from an aluminum alloy 6063-T6 and shaped into hollow square tubes. Four-point bending tests were performed on three samples with different CFRP wrapping that included; (1) virgin (not strengthened), (2) strengthened with two layers of CFRP, and (3) strengthened with four layers of CFRP. Experimental tests were conducted and compared with finite element analysis. The load was applied by bearing plates that acted across each specimen section’s full flange width. The results showed that wrapping CFRP on the aluminum structures increases the flexural strength of the aluminum by approximately by three times. A finite element model (FEM) was developed to simulate the four-point bending experimental tests for the three specimens. FEM results depicted that the use of CFRP materials is a powerful technique for strengthening aluminum structural members, which results in an increase in the load-carrying capacity and an increase in stiffness. The finite element analysis depicted good agreement with the experimental results.

Shear strengthening and rehabilitating of reinforced concrete T-beams using externally carbon fiber reinforced polymer sheets

The shear behavior of reinforced concrete (RC) T-beams using externally bonded carbon fiber-reinforced polymers (CFRPs) composites is investigated experimentally and theoretically in this research. Nine RC T-beams were cast and tested under monotonic one-point loading. The variables used in this study are: the situation of specimens (strengthened or rehabilitated); type of CFRPs material (laminate or sheet); and the CFRPs configuration (inclined or horizontal). The experimental results were compared to theoretical results from nonlinear finite element (FE) models for T-beams using ABAQUS software. The experimental results showed that using different CFRPs materials in various configurations effectively improved shear capacity for strengthening and rehabilitating RC T-beams. Compared to the control beam, the three schemes used to strengthen the shear of RC T-beams were successful in increasing the maximum load capacity by a range of 13.6 to 36.4%, and by 4.6 to 27.3% for rehabilitate T-beams. The included horizontal strips of CFRPs laminates achieved the highest increase in the shear capacity for strengthened T-beams. While, for the rehabilitated T-beams the results showed that the CFRP scheme that included full wrap of the Web with CFRPs sheets was the best. A good agreement was found between the experimental and theoretical results. The differences in the ultimate loads and mid-span deflections were in the range of 0.33% to 26%, and 0.32% to 6.6%, respectively.

ANALYSIS OF THE AIRFRAME REPAIR NODE

Polymer composite materials can be used both for the production of semi-monocoque structures and for the repair of aircraft airframes. Of all the elements of the semi-monocoque structure, the airframe skin is most often damaged during operation. The fragments of the skin between the frame elements of the semi-monocoque structure are considered as a thin-walled plate. The paper presents an analysis of the repair node of a metal plate subjected to uniform shear. The model of the repaired plate made in the Ansys Workbench environment was used for the analysis. The boundary conditions were defined by means of an articulated frame using the possibilities of the computing environment in the scope of, defining elements among others. The model was initially verified experimentally, assuming that it can be used to carry out a comparative analysis of two methods of repairing a damaged plate, using CFRP (Carbon Fiber Reinforced Polymer) and GFRP (Glass Fiber Reinforced Polymer) materials. Analyzing the obtained results, it was found that the repair does not restore the original strength of the damaged structure, however, it reduces the stress of the plate material around the opening by 10%.

Fatigue and Damage Assessment of CFRP Material Using Digital Image Correlation

Fatigue testing of a Carbon Fiber Reinforced Polymer (CFRP) in tension-tension loading has been conducted. In-situ surface strain measurements were performed to examine the gradual elongation of the specimen as this relates to stiffness loss and fatigue damage. A methodology capturing the specimen at peak load has been developed, including an automated trigger mechanism that activates the camera at the desired cycle count. The material tested was a Unidirectional (UD) Non-Crimp Fabric (NCF) with carbon fibers and an epoxy matrix. The fatigue test results revealed a wide scatter in the mid-range of the high cycle fatigue region. By studying the strain in the early fatigue loading cycles and the stiffness loss over time, benchmark of the fatigue performance between different material samples could be carried out, explaining the scatter in the fatigue testing. It could be observed that the fatigue limit of the UD CFRP material in the fiber direction is in the magnitude of 80 % of the material's Ultimate Tensile Strength (UTS).

Simulated thermal image based on finite element models for a layered composite structures

This research aims to develop a simulation technique to predict the experimental results of the transient Thermal Nondestructive Test (TNDT) on Carbon fiber-reinforced polymer (CFRP) materials that have defects in them. This simulation uses finite element method-based software to solve the temperature distribution on the material surface. Such an approach is not only flexible but also essential to the successful implementation of TNDT procedures. The developed CFRP material model is made up of multiple layers with several depths of defects. The defects are represented by the material-inserted isosceles triangle and the voids isosceles triangle. Heat is applied to the model front surface for some time and then released and the model cools down naturally. The temperature distributions of the model's surface are measured during the heating and cooling process. The simulation results show that simulation can detect the existing defects, their location, and their relative depth. The thermography experiment was carried out to verify the simulation results. The experimental results were analyzed using the local differential temperature signal parameter. This simulation will streamline the desired experimental design.

Determination of the interfacial properties of carbon fiber reinforced polymers using nanoindentation

The mechanical properties of the interphase play a key role in determining the overall performance of carbon fiber reinforced polymer (CFRP) composite materials. For this reason, it is important to develop a method to easily and precisely investigate the mechanical performance of the interphase of CFRP materials. In this work, the surface topography of the CFRP material was examined using scanning probe microscopy (SPM), which revealed the polished flat sample can meet the requirements of the nanoindentation testing. The local mechanical performance of the interphase of the CFRP was determined using nanoindentation based on the continuous stiffness measurement (CSM) method. The results show that the size of the interphase between the carbon fiber and the matrix is about 1.5 μm, and the corresponding modulus and hardness values were estimated to be 5–11 and 0.4–3.3 GPa, respectively, considering the fiber-bias effects. Mapping of the local mechanical properties of a selected area revealed that nanoindentation reproduced excellently the surface topography and characterized precisely the properties of the interphase between the carbon fibers and the matrix.

Helical drilling of carbon fiber reinforced polymer by a femtosecond laser.

Carbon fiber reinforced polymer (CFRP) has been widely used in the aerospace industry and other fields, but its processing is still subject to many restrictions. A femtosecond laser helical drilling device is proposed. It can realize beam deflection and translation through a scanning galvanometer and a pair of lenses, respectively, and finally obtain the effect of beam oblique focusing. With the combination of a spiral scanning path and focus feed, the non-taper and high-quality drilling of materials can be realized. CFRP materials were processed through this method, and the influences of process parameters on the heat affected zone and machining taper were studied. The distribution and influence degree of the heat affected zone and the formation mechanism of the machining taper were analyzed. Finally, a high-quality straight hole processing effect of CFRP with up to a 9.7: 1 aspect ratio, less than 15 µm heat affected zone outside the hole, and no delamination in the hole was realized. This new drilling method is expected to further expand CFRP applications.