Hybrid FRP Research Articles

Hygrothermal aging and durability prediction of 3D-printed hybrid fiber composites with continuous carbon/Kevlar-fiber and short carbon-fiber

Hybrid Fiber Reinforced Polymers (HFRP) have excellent mechanical properties. However, preparation with 3D-printing technology is prone to hydrothermal aging compared to conventional method. Currently, complex hygrothermal aging and degradation mechanisms of 3D-printed HFRP are still unclear. Thus, hygrothermal aging and durability prediction of 3D-printed HFRP with continuous carbon/Kevlar-fiber and short carbon-fiber are studied, which considers four typical stacking sequences. All experimental samples are manufactured by Fused Deposition Modeling (FDM) 3D-printing. The artificial accelerate aging testing is conducted on samples at different times, and then flexural testing is adopted to evaluate the residual mechanical properties and failure modes. The results show that the stacking sequence significantly influences the moisture absorption behaviors, and [OC4O2K4]S absorbed more moisture than [OK4O2C4]S. During the aging process, the flexural properties of the 3D-printed HFRP first decrease rapidly and then keep stable. Among them, [OK4O2C4]S have the fastest degradation but possessed the highest residual strength. OC8O4K8O possess the slowest degradation but have a lower residual strength. The morphologies and micro failure modes/mechanisms are analyzed to explain the significant mechanical degradation. Finally, the Arrhenius relationship is adopted to accurately predict and analyze the degradation evolution process of specimens. This work offers a novel perspective on the hygrothermal aging and durability of 3D-printed HFRP.

Development and analysis of Fe-doped ZnO nanoparticle-infused sisal fiber reinforced hybrid polymer composites for high-performance sound absorption and thermal insulation applications

In the current study, sisal fiber-reinforced hybrid composites have been developed by integrating a bidirectional mat with a blend of epoxy using Fe-doped ZnO (IDZO) nanoparticles at concentrations of 0.2, 0.4, 0.6, and 0.8 wt%. Hand-lay-up approach was used to create the composites. The composites were characterized through a comprehensive analysis of their density, water absorption, elasticity, thermogravimetric analysis, mechanical resistance, thermal conductivity, microhardness, and propagation of sound properties, including sound absorption coefficients and sound transmission class ratings. As filler loading increased, the bio-composite sample’s hardness increased under the density and void volume fraction values, with 0.8 wt% composite sample showing the superior micro-hardness. A positive correlation was observed between the ZnO nanoparticle weight percentage and thermal conductivity, with improve nanoparticle content leading to improved thermal performance. Composites containing 0.4 wt percent nanoparticles showed superior tensile strength (66.8–84.16 MPa), flexural strength (97.69–120.02 MPa) and flexural modulus (3.56–7.68 GPa). It has been observed that the weight percentage of IDZO filler greatly influences the sound absorption efficiency of the current composites. These findings highlight the promising potential of these novel biocomposites in advanced engineering applications, emphasizing their usefulness in demanding environments with biodegradability and high-performance thermal, mechanical, and acoustic properties. Based on the sound transmission class ratings, the sisal fiber biocomposites have been regarded as great adoptions for use as sound-absorbing materials such as wall partitions, doors, enclosures, and structural components, thermal insulation systems, and electrical insulation.

Enhancing compressive behaviour of seawater sea sand concrete filled hybrid carbon-glass FRP tubes exposed to seawater: Effect of thickness

This study presents a novel investigation into the impact of tube thickness on the residual compressive strength of sea water sea sand concrete (SWSSC) filled filament wound hybrid fibre-reinforced polymer (HFRP) tubes, positioning them as innovative alternatives to traditional concrete-filled steel tubes in corrosive marine environments. The research explores tube thicknesses of 2 mm, 3 mm, and 4 mm, employing a unique hybrid configuration of 50 % carbon fibre reinforced polymer (CFRP) internal layers and 50 % glass fibre reinforced polymer (GFRP) external layers. This study examines the effect of these configurations on compressive mechanical properties, microstructural characteristics, and damage progression under alkaline and seawater conditions. Additionally, the research evaluates cross-ply and hoop orientations as variables in filament winding fibre orientation. A comprehensive set of 108 hybrid tubes were filled with an alkaline solution to simulate the SWSSC environment and exposed to seawater at varying temperatures and durations. Accelerated aging experiments were conducted in the laboratory to assess the long-term compressive performance of SWSSC-filled HFRP tubes exposed to seawater. Long-term compressive strength predictions were made using the Arrhenius theory, based on short-term accelerated aging data. The accelerated test data revealed maximum compressive strength reductions of 33 %, 15 %, and 17 % for 2 mm, 3 mm, and 4 mm cross-ply HFRP tubes, respectively, after 150 days of exposure at 60 °C. For hoop HFRP tubes, the corresponding reductions were 19 %, 18 %, and 17 %. Thicker tubes (3 mm and 4 mm) with sufficient internal CFRP layers protect external GFRP layers from alkaline damage, akin to pure CFRP tubes. Thinner tubes (2 mm) exhibit similar performance to GFRP tubes as alkaline damage spreads from their less substantial internal CFRP layers to the outer GFRP layers. For cross-ply tubes, the recommended strength reduction factors are 0.6 for 2 mm, 0.8 for 3 mm, and 0.8 for 4 mm thicknesses. For hoop tubes, the suggested factors are 0.7 for 2 mm, 0.7 for 3 mm, and 0.8 for 4 mm thicknesses. This study shows the innovative potential of tailored hybrid HFRP tubes in enhancing the durability and performance of marine infrastructure.

Prediction of Tensile Properties of Natural Fiber Reinforced PP Hybrid Composites by Facca-Kortschot-Yan (FKY) and Palsule Equations

Abstract Natural fiber reinforced polymer hybrid composites are advanced materials for commercial and engineering applications. Rule of hybrid mixtures has been applied to develop Facca-Kortschot-Yan (FKY) Equation and Palsule equation for predicting tensile strength and modulus of these hybrid polymer composites. This study predicts the values of tensile strength and modulus of a few natural fibers reinforced polypropylene hybrid composites by these two equations and compares them with the reported experimental values.

Experimental investigation on tensile strength and impact strength of palmyra palm leaf stalk – Sisal fiber reinforced polymer hybrid composite

Natural fiber-reinforced polymer composites are the most widely used materials and preferable in terms of biodegradability, cost production, recyclability, and low density. The main aim of this study is to conduct an experimental investigation on tensile strength and impact strength of palmyra palm leaf stalk fiber (PLSF) and sisal fiber reinforced polymer hybrid composite. The composite material was fabricated using hand lay-up techniques. The working parameters are mass fraction ratio of PLSF/sisal fiber and volume fiber fraction with the matrix. Tensile strength and impact energy resistance tests were experimentally conducted according to the ASTM standard dimensions. The results revealed that the addition of sisal fiber to PLSF enhanced the tensile strength by 12.850 %, 26.540 %, and 30.630 % respectively compared to pure Palmyra palm leaf stalk fiber reinforced composite (PPFRC). Whereas, the addition of PLSF to sisal fiber improved the impact of energy by 20.980 %, 13.610 %, and 11.880 % compared to pure sisal fiber reinforced composite (PSFRC). The tensile strength with 20 % fiber volume fraction is improved by 53.996 % and 12.188 % compared to 10 % and 15 % of fiber respectively. The impact strength was also enhanced by 24.931 % and 10.030 % compared to 10 % and 15 % of volume fiber fraction respectively. The tensile strength and impact energy of the treated fiber composite increased by 62.243 % and 22.478 % respectively compared to the untreated hybrid Palmyra palm leaf stalk and sisal hybrid fiber reinforced composite (UHPSFRC). Generally, the HPSFRC-2 (Palmyra palm leaf stalk/sisal fiber) (P/S ratio 50/50 % ratio with 20/80 % ratio of fiber/matric percentage reinforced polymer hybrid composite) has good tensile strength and impact energy. Therefore, the mechanical property of the (Palm/Sisal) hybrid composite can be used for the manufacturing of the automotive interior parts like door panel, dash board, seat back, and automotive roof.

Hybrid rehabilitation of 3D RC beam-column joints using UHP-HFRC and FRP wrapping: Experimental evaluation and theoretical analysis

Beam-column joints are crucial elements in reinforced concrete (RC) structures subjected to seismic loading, as they are vulnerable elements prone to significant damage during earthquakes. Due to extensive structural damage, various methods have been developed to strengthen beam-column joints. However, research on rehabilitation and repair methods has been limited, with most studies focusing on 2-D joints and overlooking the confinement effect of corner beams on the joint core. This study aims to investigate novel hybrid rehabilitation systems, including ultra-high performance hybrid fiber-reinforced concrete (UHP-HFRC) and fiber-reinforced polymer (FRP) systems, alongside embedding reinforcement into heavily damaged 3-D beam-column joints subjected to pre-cyclic loading and subsequent cyclic loading. Parameters related to hysteresis response were obtained and discussed, such as ductility, lateral stiffness, dissipated energy, equivalent hysteresis damping, and pinching ratio of the tested specimens. The experimental findings revealed that utilizing an FRP and UHP-HFRC hybrid rehabilitation system enhanced ductility, dissipated energy, and lateral stiffness of heavily damaged joints by 25 %, 73 %, and 81 %, respectively, compared to the undamaged reference specimen. Additionally, a simplified design model was developed to predict the shear resistance of beam-column joints, incorporating principles of strut-and-tie. The theoretical design model was also validated against the experimental database, demonstrating a good accuracy with MV and COV of 0.97 and 13 %, respectively.

Evaluation of Mechanical and Thermal Properties of Alkali-Treated Sisal, Bamboo, and Hybrid Fiber-reinforced Polymer Composites

Evaluation of Mechanical and Thermal Properties of Alkali-Treated Sisal, Bamboo, and Hybrid Fiber-reinforced Polymer Composites

Bond performance between sand coated hybrid glass-carbon FRP tubes and seawater sea sand concrete after exposure to elevated temperatures

Employing hybrid glass-carbon FRP tubes in concrete-filled FRP tubes for marine applications offers a balance between durability and cost-effectiveness, making them ideal for harsh, corrosion-prone environments. The investigation aimed to explore the bond-slip characteristics of sand-coated hybrid carbon-glass FRP tubes filled with seawater sea sand concrete (SWSSC) subjected to varying high temperatures. Elevated temperatures can affect the bond by causing thermal expansion and altering material properties, while sand coating enhances the bond by increasing surface roughness and improving mechanical interlocking. Utilising a push-out test, the study addresses this crucial but insufficiently studied aspect of the interface between SWSSC and FRP tubes. Thirty-three sand coated hybrid tubes were tested experimentally, with temperature being the sole variable. The samples underwent testing at eleven different temperature levels (ranging from 25°C to 250°C) to investigate the relationship between temperature fluctuations and bond-slip behaviour. The results highlighted three key factors influencing bond performance. Two factors had a positive influence: firstly, the expansion of the tube due to increased temperatures, promoting better interlocking among the concrete, sand coat, and tube; secondly, resin’s mechanical properties as a result of post-curing. Conversely, a negative impact was observed due to sand coating detachment and tube degradation resulting from elevated temperatures. Analysis of the findings revealed a pattern in bond strength retention: a decrease to 77 % renetion up to 80°C, followed by an increase to 108 % up to 220°C, and finally a decrease again to 83 % at 250°C. The findings from this study enhance the progress and utilisation of hybrid FRP tubes together with SWSSC in producing environmentally sustainable construction materials, all the while ensuring they meet the necessary structural standards.

Numerical and machine learning modeling of GFRP confined concrete-steel hollow elliptical columns

This article investigates the behavior of hybrid FRP Concrete-Steel columns with an elliptical cross section. The investigation was carried out by gathering information through literature and conducting a parametric study, which resulted in 116 data points. Moreover, multiple machine learning predictive models were developed to accurately estimate the confined ultimate strain and the ultimate load of confined concrete at the rupture of FRP tube. Decision Tree (DT), Random Forest (RF), Adaptive Boosting (ADAB), Categorical Boosting (CATB), and eXtreme Gradient Boosting (XGB) machine learning techniques were utilized for the proposed models. Finally, these models were visually and quantitatively verified and evaluated. It was concluded that the CATB and XGB are standout models, offering high accuracy and strong generalization capabilities. The CATB model is slightly superior due to its consistently lower error rates during testing, indicating it is the best model for this dataset when considering both accuracy and robustness against overfitting.

Multi-scale moisture diffusion modeling and analysis of carbon/Kevlar-fiber hybrid composite laminates under the hygrothermal aging environment

Hybrid fiber reinforced polymer (HFRP) can have more complex micro moisture diffusion process than single fiber composite, owing to diverse hygroscopic properties of dissimilar fibers. Thus, elucidating the multi-scale moisture diffusion mechanism of HFRP through experimental method becomes a challenging endeavor. To this end, a multi-scale moisture diffusion modeling approach is proposed to investigate the moisture diffusion behavior of carbon/Kevlar HFRP under the hygrothermal aging environment. Leveraging Fick's law as a foundation, a combination of multi-scale moisture diffusion model and finite element method is employed. To validate the effectiveness of model, accelerated aging experiments are conducted on HFRP samples with various stacking sequences. By SEM characterization, the surface aging on aged Kevlar fibers and the debonding of aged fiber/matrix interface are conspicuously observed. Based on this model, the moisture diffusion behaviors in different HFRP configurations are simulated and analyzed to reveal the micro-, meso‑ and macro-scale moisture diffusion and resistance mechanisms. Our findings highlight the profound influence of factors such as fiber type, fiber content, fiber placement, hygroscopic properties of constituents, and their synergistic effects on moisture absorption and saturated moisture absorption rates. Finally, the hygroscopic properties of HFRP laminate with different stacking sequences are predicted by multi-scale model. This work endeavor furnishes valuable insights and guidelines for the design and analysis of moisture-resistant HFRP.

Thermite frass biomass and surface modified biowaste coir fiber reinforced biocomposites-Conversion of waste to useful products.

Polymer composites are known for its light weight and specific mechanical characteristics. This study examines sodium hydroxide (NaOH)-treated coir fiber, an agro-leftover, stuffed in a polyester matrix with termite frass powder, a bio-leftover for possible use in light-weight structural applications. Composite samples were made using compression molding and NaOH-treated coir fiber reinforced hybrid polymer composite (TCRHPC) with 40 wt% treated coir fiber and 1, 2, 3, and 4 wt% termite frass powder. TCRHPC samples mechanical, water captivation, tribological, and thermal properties were affected by termite frass powder wt%. The TCRHPC sample with 3 wt% termite frass powder has excellent mechanical properties, which improved by tensile (41.6%), flexural (28.57%), impact (43.7%), and hardness (18.84%) properties. With perfect water captivation and low weight increases in normal water (0.017 g), seawater (0.015 g), and NaOH solution (0.010 g), the identical composite sample with thermal stability up to 238°C also reduced wear mass by 5.27%. Conversely, filler agglomeration and heterogeneous dispersion in composite sample impair thermo-mechanical characteristics of TCRHPC containing 4 wt% termite frass powder. The bonding among polyester, treated coir fiber, and termite frass powder in composites were appraised with the aid of fractographic images of TCRHPC samples. The results show that TCRHPC material suits well for support structures requiring lesser weight.

Investigation on the damage mechanisms using acoustic emission method and damping characteristics of hybrid flax‐glass composites

AbstractFiber‐reinforced polymers (FRP) feature high strength‐to‐weight ratio amongst the emerging class of natural composites. This paper presents the impact of the glass fiber on the tensile strength of the flax epoxy laminate. The mechanical behavior and damping characteristics of flax fiber reinforced polymer (FFRP) and the hybrid flax‐glass fiber reinforced polymer (HFRP) are experimentally investigated. Both the flax and hybrid FRPs are made using vacuum infusion process. The specimens without and with holes of 4, 5, and 6 mm in diameter are subjected to tensile test using acoustic emission monitoring and free vibration test. In the former testing, HFRP resulted in higher peak frequencies and cumulative counts. Also, the natural frequency and damping factor of HFRP vary proportionately with the hole size, as identified in the latter tests. Different damage mechanisms during the tensile test revealed that the presence of glass fibers in HFRP increased resistance for certain damage mechanisms.Highlights Adding glass fiber to flax fiber reinforced polymer (FFRP) creates a hybrid FRP (HFRP) with increased resistance to damage and improved damping characteristics. HFRP exhibits a distinction in failure mechanisms compared to FFRP. The study utilizes acoustic emission (AE) to identify various damage mechanisms in the material, providing a more detailed information. The addition of glass fibers in HFRP leads to a more pronounced increase in damping factors.

Experimental and numerical investigation on short CHS steel columns restrained with HFRP under axial compressive loading

Fiber-reinforced polymer (FRP) is a practical approach to delay or even suppress the deformation of steel structures. However, their application has been constrained by brittle damage and low strengthening efficiency. This paper presents an investigation of the mechanical behavior of short circular hollow section (CHS) steel columns restrained with hybrid fiber-reinforced polymer (HFRP) composed of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) under axial compression. The results show that the restraint effect of HFRP composed of one layer of transverse CFRP as the middle layer and two layers of transverse GFRP as the inner and outer layers is better than two layers of transverse CFRP, with peak load and ductility increased by 7.29 % and 12.36 % over the latter. Then, a simplified method for simulating HFRP and single FRP restrained short CHS steel columns is proposed and verified by experimental results. Moreover, a parametric study is performed to discuss the effect of the diameter-to-thickness ratio on the bearing capacity. Finally, a universal method is proposed to calculate the ultimate bearing capacity of HFRP and single FRP restrained short CHS steel columns, for which the average error and standard deviation from the measured values are 2.27 % and 0.024, respectively.

Axial compressive behavior of low-alkalinity seawater sea-sand concrete column reinforced with hydrophobic longitudinal SFCBs and FRP hoops

To address corrosion problem of steel bars and shortage of freshwater and river sand in marine and offshore structures, a novel hydrophobic-modified longitudinal steel-FRP composite bars (SFCB) and FRP hoops reinforced low-alkalinity seawater sea-sand concrete (SWSSC) is developed. However, axial compressive behavior of hybrid SFCB and FRP reinforced columns is not clear and the applicability of existing design methods is low. Here, nine hybrid reinforced columns have been designed and tested. Typical failure modes of columns and axial compressive behavior of constituent materials (i.e., hydrophobic reinforcements and low-alkalinity SWSSC) are investigated. It is found that the synergistic confining effect formed by hybrid reinforcement are significant. The mesh confinement formed by densely distributed FRP hoops and longitudinal SFCBs improves the local buckling behavior, and effectively constrains the lateral expansion of concrete core, resulting in improved compressive strength and ductility of column. The compressive contribution of single longitudinal SFCB to ultimate load capacity of column can be enhanced effectively, up to 36.3 %, by increasing steel content of SFCB. Based on this, a prediction model of hybrid reinforced columns is proposed, which can accurately evaluate the ultimate load capacity. This work provides valuable experimental observations and load capacity model for hybrid reinforced column, which promote its design and application in marine engineering.

On the low-velocity impact properties of CFRP/HAFRP interlayer hybrid fibre composite laminates

Hybrid fibre-reinforced polymer composites have been increasingly utilised in key engineering fields, such as the manufacture of aerospace structures, due to their high specific strength, stiffness, and design flexibility. This paper attempts to investigate the low-velocity impact performance and residual strength after impact of hybrid composites consisting of carbon fibre-reinforced polymer (CFRP) and heterocyclic aramid fibre-reinforced polymer (HAFRP). Since carbon fibres are brittle and vulnerable to impact loading despite their ultra-high strength, the aim of this study was to enhance the impact resistance of CFRP by hybridising it with high-toughness heterocyclic aramid fibres. The influence of hybrid layup configuration on the performance of both low-velocity impact and compression after impact (CAI) was explored. Four types of specimens, including pure CFRP and hybrid CFRP/HAFRP laminates with different layups, were manufactured and tested. Drop-weight impact tests were conducted on the specimens under impact energies of 25 J, 30 J and 40 J to measure the impact response, such as force-displacement and energy absorption curves. The internal impact damage was then assessed by ultrasonic C-scan method. The compressive strengths of specimens were measured both before and after low-velocity impact. The results indicated that hybrid laminates had better impact resistance than pure CFRP specimens, and the reduction in the compressive strength after impact for pure CFRP specimens was 2–4 times that of hybrid specimens. Therefore, hybridisation of heterocyclic aramid fibre with carbon fibre in composite laminates can retain high strength of carbon fibre while benefiting from the excellent fracture toughness of heterocyclic aramid fibre.

Flexural behavior of historical RC beams strengthened with hybrid FRP sheets

Historical reinforced concrete (RC) buildings are culturally and aesthetically significant and require conservation due to aging. Strengthening RC buildings often requires the use of Fiber Reinforced Polymer (FRP) sheets, however distinct material properties of historical RC buildings have not been systematically considered yet. This study investigates the flexural behavior of historical RC beams strengthened by hybrid FRP sheets. A total of 11 beam specimens with varying FRP sheet configurations were tested using a four-point bending test to assess their flexural behavior, including failure mode, cracking pattern, load-deflection behavior, strain distribution, and ductility. The results showed that hybrid FRP sheets increased the maximum bearing capacity of strengthened specimens up to 30.2 %. An optimal fiber sheet configuration (T-3) is identified. 45-degree incline installation contributes to a 4.5 % increase in the bearing capacity of specimens. The average ductility loss of hybrid FRP sheets strengthened specimen (except for double-layer strengthened specimen) is 42 %, while an increase of sheet layer post adverse effect on ductility. Strain distribution conforms to the plane-section assumption. Additionally, a maximum bearing capacity calculation model was proposed, aiding the understanding of FRP strengthening in historical RC buildings.

A novel crimped composite spline joint for pultruded FRP tubes: Conceptual design and tensile properties

Creating an effective composite joint between fiber-reinforced polymers (FRPs) and metallic profiles poses a significant challenge for heavy-loaded and lightweight emergency truss bridges. A novel crimped composite spline joint (CCSJ) was developed to achieve satisfactory engineering performance. Comparative tensile tests were conducted to evaluate the tensile properties and load-carrying mechanism of the CCSJ in comparison to those of joints without splines. Finite element (FE) analysis considering the crimping process and tensile loading was simultaneously executed and calibrated by experiments. Parametric simulation was supplemented to explore the key factors influencing the ultimate bearing capacity. The results indicated that the novel CCSJ features a simple preparation process, high connection efficiency, and large bearing capacity. A 60×6 mm hybrid FRP tube can withstand a maximum tensile load of 804 kN, achieving a connection efficiency of 61.3 % without the need for any secondary processing of the FRP tube. The CCSJ demonstrates a significantly higher connection efficiency of approximately 20 % compared to joints without splines. The ability of the CCSJ to effectively transfer significant axial loads through the interfacial friction effect is attributed to the increase in the interfacial contact area and preloading radial pressure resulting from the incorporation of pre-crimping splines. A typical failure mode involves interfacial slippage, resulting in satisfactory ductile behavior. The ultimate bearing capacity of the CCSJ is positively correlated with the crimping variables, friction coefficient, spline length, and number of splines. The FE model demonstrates sufficient accuracy in predicting the key behavioral indicators of the composite joint.

Study on mechanical properties and molecular simulation of nano‐SiO2‐modified hybrid fiber reinforced polymer bar under the dry and alkaline environment

AbstractFiber reinforced polymer (FRP) bars have received extensive promotion and application in the structural engineering. However, due to the limitations inherent in using single material, FRP reinforced concrete structures often encounter issues, such as brittle failure and inadequate energy dissipation, particularly in complex natural environments and under various loading conditions. In this study, the preparation of nano‐SiO2‐modified carbon/basalt hybrid FRP bars was carried out using the pultrusion‐winding process and ultrasonic treatment. The objective was to investigate the influence of the fiber volume ratio and mass fraction of nano‐SiO2 on the mechanical properties of FRP bars under drying and alkaline conditions. Molecular dynamics simulations were performed to construct interface models between fibers and epoxy resin in order to elucidate the toughening mechanism of nano‐SiO2 and the degradation mechanism in alkaline conditions. The research results show that elevating the substitution rate of carbon fibers and incorporating nano‐SiO2 doping bring about alterations in the brittle fracture characteristics of BFRP bars and enhance the post‐yield performance and interlaminar shear properties of hybrid FRP bars, concurrently mitigating the degradation of mechanical properties induced by exposure to alkaline solutions. MD simulations indicate that the addition of nano‐SiO2 improves the binding rate of hydrogen bonds between BF and epoxy resin, resulting in a higher interfacial energy between BF/epoxy resin compared to CF/epoxy resin. Moreover, nano‐SiO2 effectively mitigates the impact of alkaline solutions on the formation of interfacial hydrogen bonds. The findings of this study serve as a valuable reference for the design and application of FRP reinforced concrete structures.Highlights Nano‐SiO2 modified B/CFRP bars made via extrusion‐winding & ultrasonic treatment. Improved mechanical properties and plastic deformation in Nano‐SiO2 modified B/C FRP bars. Nano‐SiO2 inhibits B/CFRP bars degradation in alkaline solution. Nano‐SiO2 bind more at BF/epoxy than CF/epoxy interface. Nano‐SiO2 reduces alkaline solution effect on interfacial H‐bonding.

Inter-layer failure and toughening mechanisms of carbon/aramid hybrid fiber composites interleaved with micro/nano pulps under low-velocity impact load

Hybrid fiber-reinforced polymer (HFRP) composites are widely used in aerospace structures because of their excellent overall performance. However, it is still challenging to address the issue of high sensitivity to delamination between dissimilar material interlayers in HFRP composites. This study combines experimental and numerical simulation to analyze the low-velocity impact behavior and interlaminar damage of two types of HFRP. Based on a micromechanical model, an equivalent aramid pulp (eAP) toughening laminate model is developed. The impact behavior of the HFRP toughen by eAP only in dissimilar material interlayers is simulated based on the model. The effect of eAP areal density on the impact behavior and evolution of interlaminar damage is analyzed. Results show that the maximum force and impact stiffness of eAP-toughened HFRP increase initially with the increase in eAP areal density, and then decrease slowly. The area and extent of damage of dissimilar material interlayers in eAP toughened laminates is significantly reduced. Finally, the interlaminar toughening and failure mechanisms by eAP-toughening only in dissimilar material interlayers of the HFRP composites are systematically revealed from fiber bridging and damage transfer perspectives.

Manufacture and structural performance of modular hybrid FRP–timber thin-walled beams

Developed to fulfil the rising societal demand for sustainable constructions, Modular Hybrid Fibre-reinforced polymer-Timber (MHFT) thin-walled sections are lightweight timber-based composite structures manufactured through a modular assembly method. Motivated by prior research on MHFT columns characterized by efficient load-carrying capacity, this paper conducted a thorough investigation into the manufacture and structural performance of MHFT beams. Experimental, analytical and numerical studies were conducted for beams subjected to four-point bending load, with parametric analyses of four distinct beam types to investigate design parameter influence on flexural performance. The experimental study demonstrated the structural efficacy of MHFT beams, as evidenced by increased moment of inertia and enhanced resistance to edge split failures, as compared to previously studied folded HFT beams. MHFT beams also exhibited a comparable strength-to-weight ratio compared to their structural steel counterparts. Both numerical and analytical methods provided acceptable predictions for flexural strength and material failure modes of MHFT beams, with strength predictions varying by less than 22% compared to experimental averages. The numerical method reliably predicted flexural stiffness and load–displacement responses, with discrepancies within 12%. The parametric analyses further revealed that the thickness of glass fibre-reinforced polymer (GFRP) layers and cross-sectional geometric profile were most strongly influenced beam parameters. Specifically, the use of 3-layer GFRP material resulted in a strength increase of over 17% and a stiffness increase of over 19% compared to 1-layer material, effectively mitigating the occurrence of local buckling and edge split failures.