Polymer Laminates Research Articles

Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading.

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

Nonlinear Analytical Procedure for Predicting Debonding of Laminate from Substrate Subjected to Monotonic or Cyclic Load

The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements' strength and stiffness. However, premature laminate-substrate debonding is commonly observed in laboratory tests, which prevents the laminate from reaching its ultimate strength, and this creates uncertainty with respect to the level of strengthening that can be achieved. Therefore, for the safe and effective application of this technology, a close estimate of the debonding load is necessary. Towards this end, in this paper, a new, relatively simple, semi-analytic model is presented to determine the debonding load and the laminate stress and deformation, as well as the interfacial slip, for concrete substrates bonded to SRP/FRP and subjected to monotonic or cyclic loading. In the model, a bond-slip law with a linearly softening branch is combined with an elasto-plastic stress-strain relationship for SRP. The model results are compared with available experimental data from single-lap shear tests, with good agreement between them.

Experimental characterization and numerical study on the interlaminar fracture toughness of carbon fibre reinforced polymer laminates reinforced with carbon nanotubes

AbstractThe present study is focused on the nanoreinforcement of carbon fiber reinforced polymer laminates to evaluate its effect on delamination growth in double cantilever beam specimen. Multi‐walled carbon nanotubes were sprayed on the laminate interface using air‐brush spraying technique. Three nanofiller contents of 0.05 wt.%, 0.1 wt.%, and 0.5 wt.% were examined to evaluate the mode I fracture toughness (GIC) in a double cantilever beam specimen and the results were compared with the base laminate (0.0 % carbon nanotubes). The average mode I fracture toughness of composite laminates increased from 180.6 J/m2 to 270.92 J/m2 due to the addition of 0.05 wt.% multi‐walled carbon nanotubes, and to 268.27 J/m2 for 0.1 wt.% multi‐walled carbon nanotubes. Mechanisms for the increase in GIC of the nanofiller reinforced laminates are discussed based on the experimental results and microscopic study of fractured specimen surfaces from scanning electron microscopy. Energy dissipation from carbon nanotube bridging ahead of the crack front is the major toughening mechanism resulting in improved fracture toughness. Numerical simulations of delamination growth were performed as well by using virtual crack closure technique analysis in Abaqus. The R‐curve behaviour from the experiments is implemented in the finite element modeling of delamination growth to validate the effect of nanoreinforcements.

Engineering uniformity in mass production of MWCNTs/epoxy nanofibers using a lateral belt-driven multi-nozzle electrospinning technique to enhance the mechanical properties of CFRPs

Electrospinning is one of the most diverse, cost-effective, and ecologically renowned methods for generating continuous nanofibers, but electrospinning of thermosetting polymers like epoxy and their mass volume productions have been a major challenge in recent years. This study proposes a fabrication method by addressing electrospun MWCNTS/epoxy (CNT/epoxy) nanofiber's volume processing, reproducibility, and accuracy issues in an effective manner. Lateral belt-driven (LBD) multi-nozzle electrospinning is here newly adopted to enhance the mechanical properties of the carbon fiber-reinforced polymer (CFRP) laminates. With the LBD approach, the electric field can be uninterruptedly distributed to deposit a uniform layer of CNT/epoxy scaffolds over the entire width of CFRP prepreg. This study optimizes the distance between two nozzles, the motion of the lateral belt, and the electrospinning period. The laminates made of coated CFRP show enhanced mechanical properties when compared to pristine CFRPs. Under high-stress conditions, these CFRP laminates' interlaminar shear strength (ILSS) and fatigue performance demonstrated 29% and 27% improvements, respectively. This study, which demonstrated the success of using an LBD multi-nozzle system, has enormous opportunities to produce thinner and continuous fibers with more concentrated collections at a faster rate, which is critical for commercial applications.

Examining slow crack growth metrics and competing failure modes in IM7/5320-1 carbon fiber reinforced polymer laminates with pre-existing damage states

The growing use of composites in aircraft structures has necessitated a slow growth criteria to assess the life of these materials and an appropriate similitude parameter. Due to the simplified stress state and inherent interactions of intralaminar and interlaminar damage progression in multi-directional ply layups, there have been questions about the applicability of double cantilever beam specimens to aerospace applications. This study examines these interconnected damage growth mechanisms in [±453]s and [±452/902]s layups via compact tension specimen geometries, with and without pre-existing damage, in order to examine the efficacy of proposed similitude parameters in capturing slow crack growth. The change in stored potential strain energy per cycle provided the most unified results across the 18 tests under different loading and pre-existing damage conditions. Via microscopy of the specimens after damage progression, the similitude parameters were connected to overall trends in the damage mechanisms. The fatigue results, coupled with the microscopy of the interactions amongst the complex damage mechanisms, demonstrates the need to analyze proposed similitude parameters across various sample geometries and stress states, which will be more enable an understanding of composite material fatigue performance in aerospace applications.

Parametric analysis on the flexural behaviour of RC beams strengthened with prestressed FRP laminates

In this paper, the effectiveness of reinforced concrete (RC) beams strengthened with prestressed basalt fibre-reinforced polymer (BFRP) laminates was parametrically studied through discrete displacement-coordinated finite element (FE) method. Three dimensional (3D) FE models were established based on experiments, and the reliability of the FE model was verified. The influences of material properties, prestress load level, reinforcement ratio, and shear span on the overall behavior were investigated. The results demonstrated that the optimal capacity of strengthened beam can be achieved in large shear span with low reinforcement ratio and high-strength concrete. The cracking load of RC beams was also significantly increased by strengthening with prestressed BFRP laminates. Then, polynomial equations were fitted to quantify the influences of different parameters on capacity enhancement. The shear span ratio was found to be the most important factor. In addition, the utilisation efficiency of BFRP is much higher than that of carbon FRP (CFRP) with the same section and prestress level due to the strong deformation ability.

Fatigue response of RC beam strengthened by BFRP laminate

Strengthening RC structures become more essential due to its deterioration, updating in new design codes, lack of quality control, and changes in the use of the structure. The technique of external bonding fiber reinforced polymer is recognized as a convenient method for repairing existing reinforced concrete structures and provides immediate shelter rather than replacement of the whole existing structure. Basalt Fiber Reinforced Polymer gaining more demand in recent research due to its eco-friendly properties. In this regard, this research investigates the efficaciousness of externally bonded Basalt Fiber Reinforced Polymer (BFRP) laminates in the reinforced concrete beam under repeated load. BFRP is externally bonded at the soffit of reinforced concrete (RC) beams to enhance its fatigue resistance. The load-deflection relationship, stiffness, crack pattern, and energy dissipation capacity of the BFRP-reinforced concrete beams are experimentally investigated and validated with the ANSYS simulated results. The experimental results exhibits that the BFRP reinforced concrete beams enhances the fatigue response, load carrying capacity and prevention of premature failure. The numerical results are validated with the experimental results which are found to be correlated with negligible deviation. Also, both investigations reveal the failure mode of RC beams, which helps fatigue life prediction in its application.

Influence of fabric areal density in woven GFRP laminate on abrasive water jet drilling responses

ABSTRACT The objective of this investigation is to find out the effect of the woven glass fiber reinforced polymer (GFRP) laminates with different glass fiber densities, such as 610 GSM and 210 GSM, and manufactured by the hand layup technique, supported by compression molding on mechanical properties and abrasive water jet (AWJ) drilling responses. During the investigation, the woven GFRP with a fiber density of 610 GSM has been found to display greater flexural strength, interlaminar strength (ILSS), and tensile strength as compared to the woven GFRP with a fiber density of 210 GSM. The woven GFRP with a fiber density of 610 GSM has also displayed reduced drilling damage in the surface region and less delamination compared to the woven GFRP with a fiber density of 210 GSM. The results of both types of composites prove that the TR and JP considerably impact the delamination extent (DE) and surface roughness (SR). A decrease in the TR and an increase in the JP are primarily responsible for optimizing the desired machining performances. Finally, a FESEM analysis has been done to examine the machined surfaces’ morphology.

Interlaminar fracture toughness of carbon fibre composites with electrospun nanofibrous interleaves of polystyrene and cellulose nanocrystals

Polystyrene nanofibres reinforced with cellulose nanocrystals have been produced by electrospinning. Two different orientations of the nanofibres were produced, namely aligned and random, and these nanofibrous interleaves were investigated both as-spun and after thermal treatment. Aligned nanofibres exhibited a 2500% increase in their Young’s modulus compared to the randomly orientated materials, while the ultimate tensile strength increased by up to 300%. It is also demonstrated that crazing occurs in the nanofibres, which is thought to enhance the fracture properties of the materials. Interleaves of both orientations were then included in a carbon fibre-reinforced polymer laminate. The fracture toughness of the laminate was determined under both mode I and mode II testing. No increases in mode I toughness were observed. It was, however, found that the aligned interleaves increased the mode II toughness of the composite laminate (from 1.9 ± 0.3 to 2.7 ± 0.2 kJ m−2). This increase is demonstrated to be due to a combination of nanofibre bridging and the formation of microcracks in the resin under applied tensile and shear load.

A Strain Rate Dependent Damage Model for Evaluating the Dynamic Response of CFRTP Laminates with Different Stacking Sequence

Carbon fiber reinforced thermoplastic polymer (CFRTP) laminates can be used in packaging electronics components to reduce weight and shield external disturbance. The CFRTP structures in operation are inevitably to suffer dynamic loading conditions such as falling rocks, tools and impacts. In this study, a strain rate dependent material model for accurately evaluating the dynamic response of CFRTP laminates with different stacking sequence was proposed. The model was composed of three components: a strain rate dependent constitute model, a strain rate related damage initiation model and an energy-based damage evolution model. The strain rate effect of modulus and strength was described by a stacking sequence related matrix, and the damage initiation model could describe the matrix, fiber and delamination damage of CFRTP laminates without introducing cohesive elements. The material model was implemented into finite element software ABAQUS by user defines subroutine VUMAT. The low velocity impact tests of CFRTP laminates with quasi-isotropic and angle-ply stacking sequence were used to provide validation data. The dynamic response of CFRTP laminates from numerical results were highly consistent with the experimental results. The mechanical response of CFRTP laminates were affected by stacking sequence and impact energy, and the numerical error of proposed material model significantly decreased with the increasing impact energy especially for the laminae with damage occur.

Evaluation of Tensile and Flexural Properties of Unidirectional Glass-Epoxy Laminate with Aluminium Oxide and Magnesium Hydroxide as Filler Materials

Low weight is one of the most important factors in the design process of road and flight vehicles. The design engineers are careful with regards to the weight decrease without thinking twice about the primary strength. The composite is a lightweight material that has decent underlying properties and it is generally utilized. Fiber-supported polymer composites assumed a prevailing part for quite a while in an assortment of uses for their high explicit strength. The current work portrays the turn of events and the portrayal of another arrangement of GFRP. Experiments are carried out to study the effect of the addition of fillers by varying their percentages. The present work focus on the effect of the fillers on properties of Glass fiber epoxy laminates with aluminum oxide and magnesium hydroxide powders as the fillers. In the present work, fabrication and experimental investigation on unidirectional glass epoxy composites are carried out. Initially, glass fiber reinforced polymer laminate fabricated without filler material, hand layup followed by vacuum bagging methods are used . Then, by adding Aluminium oxide and Magnesium hydroxide as a filler material with different percentages like 5%, 10%, and 15% by weights and laminates are fabricated and experimental investigation is conducted to study their mechanical behavior. The comparative studies on the laminates are carried out and the obtained results are analyzed and those are quite interesting.

Effects of Elastic Couplings in a Compressed Plate Element with Cut-Out.

Analytical calculations were performed on carbon fiber-reinforced polymer (CFRP) laminates in an asymmetrical configuration. The asymmetric configuration of composites was investigated, where extension-twisting and extension-bending couplings were used to obtain the elastic element. Analysis of the presence of elastic couplings was conducted according to Classical Laminate Theory (CLT). Components of matrices A, B, and D, as well as the parameters Dc and Bt, were obtained using the MATLAB software environment. The results show that couplings between the extension and bending, as well as between the extension and twisting, were strongly dependent on specimen plies' orientation. Moreover, additional analysis was performed on the influence of layer angle on the terms which are components of the Bt and Dc coefficients. The results indicate that the angle of laying fibers around 45-50° significantly amplifies the effects of elastic couplings.

Investigating the Bond Strength of FRP Laminates with Concrete Using LIGHT GBM and SHAPASH Analysis.

The corrosion of steel reinforcement necessitates regular maintenance and repair of a variety of reinforced concrete structures. Retrofitting of beams, joints, columns, and slabs frequently involves the use of fiber-reinforced polymer (FRP) laminates. In order to develop simple prediction models for calculating the interfacial bond strength (IBS) of FRP laminates on a concrete prism containing grooves, this research evaluated the nonlinear capabilities of three ensemble methods-namely, random forest (RF) regression, extreme gradient boosting (XGBoost), and Light Gradient Boosting Machine (LIGHT GBM) models-based on machine learning (ML). In the present study, the IBS was the desired variable, while the model comprised five input parameters: elastic modulus x thickness of FRP (EfTf), width of FRP plate (bf), concrete compressive strength (fc'), width of groove (bg), and depth of groove (hg). The optimal parameters for each ensemble model were selected based on trial-and-error methods. The aforementioned models were trained on 70% of the entire dataset, while the remaining data (i.e., 30%) were used for the validation of the developed models. The evaluation was conducted on the basis of reliable accuracy indices. The minimum value of correlation of determination (R2 = 0.82) was observed for the testing data of the RF regression model. In contrast, the highest (R2 = 0.942) was obtained for LIGHT GBM for the training data. Overall, the three models showed robust performance in terms of correlation and error evaluation; however, the trend of accuracy was obtained as follows: LIGHT GBM > XGBoost > RF regression. Owing to the superior performance of LIGHT GBM, it may be considered a reliable ML prediction technique for computing the bond strength of FRP laminates and concrete prisms. The performance of the models was further supplemented by comparing the slopes of regression lines between the observed and predicted values, along with error analysis (i.e., mean absolute error (MAE), and root-mean-square error (RMSE)), predicted-to-experimental ratio, and Taylor diagrams. Moreover, the SHAPASH analysis revealed that the elastic modulus x thickness of FRP and width of FRP plate are the factors most responsible for IBS in FRP.

Convolutional neural network method for damage detection of CFRP in electrical impedance tomography

Damage detection is vitally important for carbon fiber reinforced polymer (CFRP) laminates. When CFRP laminates are damaged, its impedance property is changed. Based on the electrical properties of CFRP laminates, the changed conductivity distribution can be reconstructed with the electrical impedance tomography (EIT) method. The detection method is attractive due to its simple equipment, low cost, and easy operation. However, image reconstruction of EIT faces a serious ill-conditioned nonlinear inverse problem. In order to solve this problem, a feature fusion convolutional neural network based on the dense connection (FF-D) method is applied in EIT to establish the mapping relationship between voltage measurement and conductivity distribution in this paper. The optimization can extract and utilize features to a greater degree and improve reconstruction accuracy and robustness. For the purpose of simulating the electrical properties of CFRP better, the conductivity values measured by an impedance analyzer are used as the data set. The correlation coefficient (CC) and root mean square error (RMSE) are used as indicators to evaluate the quality of image reconstruction. The simulation and experimental results suggest that the FF-D method can reconstruct images better than typical algorithms based on deep learning and conventional algorithms of EIT.

Experimental and analytical study on the effect of different repairing and strengthening strategies on flexural performance of corroded RC beams

This paper reports the results of a study conducted to investigate the flexural behavior of corroded reinforced concrete (RC) beams that were first repaired with different types of cover repairing materials and then strengthened with the carbon fiber-reinforced polymer (CFRP) laminates. Thirteen RC beam specimens were prepared. One specimen was used as a control beam (un-corroded, unrepaired, unstrengthened), and the reinforcing bars in twelve specimens were corroded using an accelerated corrosion setup. While five corroded specimens (two unrepaired and three repaired) were tested without strengthening using CFRP laminates, the other seven corroded specimens (two unrepaired and five repaired) were strengthened with one and two layers of CFRP laminates before testing under flexure. For the RC beams subjected to 10 and 20% corrosion of steel bars (by mass), strengthening using one layer of CFRP laminate enhanced the load-bearing capacities by 89 and 73%, respectively, while strengthening with two CFRP layers improved the load-carrying capacity by 162 and 154%, respectively. Repairing the damaged cover of the corroded RC beams using ultra-high-performance concrete (UHPC) was found to be most effective in enhancing the load-bearing capacity and stiffness, whether the corroded beams were strengthened with CFRP laminates or not. Repairing of the cover using commercial repair material also enhanced the load-carrying capacity and stiffness, with ductility more than that of UHPC. Strengthening of the corroded beams further improved the load-carrying capacity. An analytical model was developed that can predict the load-bearing capacity of the beams with a fair degree of accuracy.

Two-dimensional demixing within multilayered nanoemulsion films.

Benefiting from the demixing of substances in the two-phase region, a smart polymer laminate film system that exhibits direction-controlled phase separation behavior was developed in this study. Here, nanoemulsion films (NEFs) in which liquid nanodrops were uniformly confined in a polymer laminate film through the layer-by-layer deposition of oppositely charged emulsion nanodrops and polyelectrolytes were fabricated. Upon reaching a critical temperature, the NEFs exhibited a micropore-guided demixing phenomenon. A simulation study based on coarse-grained molecular dynamics revealed that the perpendicular diffusion of oil droplets through the micropores generated in the polyelectrolyte layer is crucial for determining the coarsening kinetics and phase separation level, which is consistent with the experimental results. Considering the substantial advantages of this unique and tunable two-dimensional demixing behavior, the viability of using the as-proposed NEF system for providing an efficient route for the development of smart drug delivery patches was demonstrated.

An experimental study on fatigue debonding growth of RC beams strengthened with prestressed CFRP plates

Externally bonded Fiber Reinforced Polymer (FRP) laminates are increasingly used to strengthen Reinforced Concrete (RC) members. However, FRP debonding remains a major drawback of this strengthening method. To better understand the mechanisms of FRP debonding, six RC beams strengthened with prestressed or non-prestressed Carbon Fiber Reinforced Polymer (CFRP) plates were subjected to static and fatigue loading. CFRP plate debonding was observed in both cases. However, the mechanism of debonding differed: under cyclical fatigue loading, debonding was initiated under both loading points simultaneously and propagated synchronously towards the nearest support whereas in static tests debonding began under a single loading point and progressed suddenly towards its adjacent support. The results also showed that stress redistribution induced coupling between accumulated fatigue damage in the steel reinforcement and fatigue debonding of the CFRP plate, accelerating the fatigue failure of the specimens.

Strategies for strengthening of corroded reinforced concrete beams using CFRP laminates and UHPC jacketing

AbstractThis article aims to investigate the flexural behavior of strengthened corroded reinforced concrete (RC) beams using carbon fiber‐reinforced polymer (CFRP) laminates and using a hybrid system of CFRP laminates and ultrahigh‐performance concrete (UHPC) layers. A total of 15 RC beam specimens were prepared, out of which one specimen was uncorroded–unstrengthened, and 14 specimens were corroded using accelerated corrosion set up to cause a significant reduction in the load‐carrying capacity of the RC beams. The damaged covers of the corroded RC beam specimens were first repaired and then strengthened with different strengthening strategies involving CFRP laminates alone as well as the CFRP laminates and UHPC jacketing together. The experimental results obtained by testing the strengthened RC beam specimens in flexure showed a significant enhancement in the load‐carrying capacity and stiffness of the strengthened corroded RC beams. The number of CFRP laminates, hybridization of the CFRP laminates and UHPC layer, and the thickness of the UHPC layer all significantly improved the load‐carrying capacity and stiffness of the strengthened corroded RC beams indicating the possibility of selecting an optimal strategy out of different options for strengthening the corroded beams to achieve a targeted degree of the efficacy of the strengthening. The analytical model developed in this study to estimate the flexural capacity of the strengthened RC beams was found to predict the values of the load‐bearing capacity of the RC beams strengthened using different strategies very close to their respective experimental values.

A Thermoplastic Elastomeric Nanofibrous Membrane as CFRP Modifier to Boost Both Delamination and Damping Performance

AbstractIn the present work, thermoplastic elastomeric nanofibers made up of a homogenous blend of nitrile butadiene rubber (NBR) and Ppolycaprolactone (CL), with 80% wt of rubbery component, are used to modify a carbon fiber reinforced polymer (CFRP) laminate with the aim of improving its delamination and damping behavior at the same time. Since the nanofibrous membrane is not chemically cross‐linked, the fibrous morphology is lost during composite curing owing to its melting. Nonetheless, the nanomodified CFRP displays an impressive ability to improve the delamination resistance in mode I and also an enhanced damping capacity at low temperature. The use of nanofibrous membranes allows for modification of specifically selected areas, thus maximizing the toughening and damping behavior where most required, without necessarily affecting the whole bulk of the resin. Both PCL and NBR components contribute to the final performance; however, the very high amount of rubber leads to a membrane difficult to handle whose final performance in CFRP modification is not superior to membranes up to 60% wt NBR that are instead more stable and easier to deal with. Overall, the proposed results are nonetheless very promising, taking into account also that the improved delamination resistance in mode I and enhanced damping are obtained without significantly sacrificing the weight and overall dimension of the obtained composite.

Three-dimensional numerical investigation of mixed-mode debonding of FRP-concrete interface using a cohesive zone model

• A 3D mixed-mode cohesive zone model of the FRP-concrete interface is proposed. • The mixed-mode damage factor based on the exponential softening relationship is clearly expressed. • The friction in the interface is considered independently by considering the interface sliding. • The simulation results fit well with the experimental ones in different validation cases. • The shear-peeling debonding behavior of the interface with different peeling angles is analyzed particularly. As a low-cost high-performance method for concrete structural reinforcement and repair, the external bonding (EB) of fiber-reinforced polymer (FRP) laminates has gradually become popular. But these FRP-reinforced structures usually fail prematurely due to the interfacial debonding. Thus, the mixed-mode debonding behavior of the FRP-concrete interface by a 3D cohesive zone model (CZM) will be analyzed in this study. The 3D CZM provided a detailed description of interfacial damage propagation and friction-sliding evolution during the whole debonding process. Based on the program coding which implements the proposed CZM, numerical models will be built according to the previous experiments. By comparison, the numerical and experimental results showed a good agreement. Besides, the key parameters, which include peeling angle, strength ratio, energy ratio, and friction coefficient, will also be investigated to assess their effect on the interfacial bond capacity.