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19 pages, 5500 KiB

Open AccessArticle

Development of Hybrid Composite Utilizing Micro-Cellulose Fibers Extracted from Date Palm Rachis in the Najran Region

by Hassan Alshahrani, Basheer A. Alshammari, Ahmer Hussain Shah and Abdul Qadeer Dayo

Polymers 2022, 14(21), 4687; https://doi.org/10.3390/polym14214687 - 3 Nov 2022

Cited by 5 | Viewed by 1747

Abstract

Environmental effects can be reduced by using renewable resources in various applications. The date palm fibers (DPF) used in this study were extracted from waste date ranches of the Najran region by retting and manual peeling processes. The biocomposites were developed by reinforcing [...] Read more.

Environmental effects can be reduced by using renewable resources in various applications. The date palm fibers (DPF) used in this study were extracted from waste date ranches of the Najran region by retting and manual peeling processes. The biocomposites were developed by reinforcing the silane-treated DPF (SDPF) at different wt.% in eugenol phthalonitrile (EPN) and difunctional benzoxazine (BA-a) copolymer. The impact strength, tensile, flexural, and dynamic mechanical properties and thermogravimetric analysis were evaluated to understand the mechanical, thermomechanical, and thermal properties. Results confirmed that 30 wt.% SDPF-reinforced poly (EPN/BA-a) composites produced the highest mechanical and thermomechanical properties, and were considered optimized SDPF reinforcement. Furthermore, hybrid composites with 30 wt.% SDPF and 15 wt.% silane-treated glass fibers (SGF) reinforcement having different lamination sequences were also studied. The lamination sequences showed a significant impact on the mechanical and thermomechanical properties, as properties were further enhanced by adding a core layer of SGF in hybrid composites. However, the thermal properties of SDPF/SGF laminates were higher than SDPF biocomposites, but the SGF lamination sequence did not produce any impact. According to the limiting oxygen and heat resistance indexes, the developed SDPF/SGF laminates are self-extinguishing materials and can be used in temperature-tolerant applications up to 230 °C. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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20 pages, 21214 KiB

Open AccessArticle

Study on Flexural Behavior of Glass Fiber Reinforced Plastic Sandwich Composites Using Liquid Thermoplastic Resin

by Hassan Alshahrani and Azzam Ahmed

Polymers 2022, 14(19), 4045; https://doi.org/10.3390/polym14194045 - 27 Sep 2022

Cited by 10 | Viewed by 2873

Abstract

Experimental and numerical studies of composite sandwich structures are warranted to reap the benefits of these materials when they are well designed. In the current research, new liquid thermoplastic and epoxy resins were used to fabricate four composite sandwich panels with two additional [...] Read more.

Experimental and numerical studies of composite sandwich structures are warranted to reap the benefits of these materials when they are well designed. In the current research, new liquid thermoplastic and epoxy resins were used to fabricate four composite sandwich panels with two additional foam types and different densities in the wind turbine industry. A comprehensive comparison of three-point bending test results was made. Finite-element-based simulations using the ABAQUS program with Hashin’s damage criterion were conducted to examine the failure behavior of the GFRP sandwich composites. The flexural behavior of the glass-fiber-reinforced plastic (GFRP) sandwich panels was investigated and compared with the experiments. The results show that the GF/PVC/Elium composite panel gives the highest load absorption, flexural strength, flexural modulus, core shear ultimate strength, and facing stress due to effect of the core foam and resin types. For the PVC foam core sandwich panel, using thermoplastic resin increased the flexural strength by 18% compared to that of the epoxy resin. The simulation results show excellent agreement between the finite-element-predicted failure loads and the experimental results. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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17 pages, 4428 KiB

Open AccessArticle

Tensile Behavior of 3D Printed Polylactic Acid (PLA) Based Composites Reinforced with Natural Fiber

by Eliana M. Agaliotis, Baltazar D. Ake-Concha, Alejandro May-Pat, Juan P. Morales-Arias, Celina Bernal, Alex Valadez-Gonzalez, Pedro J. Herrera-Franco, Gwénaëlle Proust, J. Francisco Koh-Dzul, Jose G. Carrillo and Emmanuel A. Flores-Johnson

Polymers 2022, 14(19), 3976; https://doi.org/10.3390/polym14193976 - 23 Sep 2022

Cited by 31 | Viewed by 7695

Abstract

Natural fiber-reinforced composite (NFRC) filaments for 3D printing were fabricated using polylactic acid (PLA) reinforced with 1–5 wt% henequen flour comprising particles with sizes between 90–250 μm. The flour was obtained from natural henequen fibers. NFRCs and pristine PLA specimens were printed with [...] Read more.

Natural fiber-reinforced composite (NFRC) filaments for 3D printing were fabricated using polylactic acid (PLA) reinforced with 1–5 wt% henequen flour comprising particles with sizes between 90–250 μm. The flour was obtained from natural henequen fibers. NFRCs and pristine PLA specimens were printed with a 0° raster angle for tension tests. The results showed that the NFRCs’ measured density, porosity, and degree of crystallinity increased with flour content. The tensile tests showed that the NFRC Young’s modulus was lower than that of the printed pristine PLA. For 1 wt% flour content, the NFRCs’ maximum stress and strain to failure were higher than those of the printed PLA, which was attributed to the henequen fibers acting as reinforcement and delaying crack growth. However, for 2 wt% and higher flour contents, the NFRCs’ maximum stress was lower than that of the printed PLA. Microscopic characterization after testing showed an increase in voids and defects, with the increase in flour content attributed to particle agglomeration. For 1 wt% flour content, the NFRCs were also printed with raster angles of ±45° and 90° for comparison; the highest tensile properties were obtained with a 0° raster angle. Finally, adding 3 wt% content of maleic anhydride to the NFRC with 1 wt% flour content slightly increased the maximum stress. The results presented herein warrant further research to fully understand the mechanical properties of printed NFRCs made of PLA reinforced with natural henequen fibers. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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21 pages, 9368 KiB

Open AccessArticle

Fatigue Analysis of CFRP-Reinforced Concrete Ribbed Girder Bridge Deck Slabs

by Shuai Tian, Xiaotao Zhang and Wenjing Hu

Polymers 2022, 14(18), 3814; https://doi.org/10.3390/polym14183814 - 12 Sep 2022

Cited by 3 | Viewed by 2236

Abstract

This study aims to improve the operational safety of reinforced concrete-ribbed beam bridge decks and prolong their service life by performing fatigue analysis of deck slabs reinforced with carbon-fiber-reinforced polymers (CFRP) and other materials. Based on a 16-m-span ribbed girder bridge, five test [...] Read more.

This study aims to improve the operational safety of reinforced concrete-ribbed beam bridge decks and prolong their service life by performing fatigue analysis of deck slabs reinforced with carbon-fiber-reinforced polymers (CFRP) and other materials. Based on a 16-m-span ribbed girder bridge, five test beams were designed: three reinforced (with CFRP cloth, CFRP mesh, and strip steel plates) and the remaining unreinforced. To simulate the real force of the bridge deck slabs, a PLS-500 electro-hydraulic servo dynamic and static test system was used and static load failure (monotonic graded loading) and fixed-point constant-amplitude fatigue loading tests (fatigue load of 0.515, loading frequency of 5 Hz) were performed. The main fatigue crack appeared when the number of load cycles exceeded 90% of the fatigue life. In the middle of fatigue, the reinforcement material can reduce the deterioration value of the bridge deck by approximately 50%. When it is reinforced at the cumulative damage degree of 0.4, its fatigue life extends by approximately 53.3–78.9%. The fatigue life of the bridge deck slabs reinforced with CFRP cloth or mesh was 22.1–25.6% more than that of those reinforced with strip steel plates. CFRP cloth is best suited for the reinforcement of bridge deck slabs. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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20 pages, 13552 KiB

Open AccessArticle

Effect of Fiber Wrapping on Bending Behavior of Reinforced Concrete Filled Pultruded GFRP Composite Hybrid Beams

by Lokman Gemi, Emrah Madenci, Yasin Onuralp Özkılıç, Şakir Yazman and Alexander Safonov

Polymers 2022, 14(18), 3740; https://doi.org/10.3390/polym14183740 - 7 Sep 2022

Cited by 49 | Viewed by 3160

Abstract

The application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0° fiber orientation in [...] Read more.

The application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0° fiber orientation in the drawing direction should be considered. In this direction, it is thought that the structural performance of the profiles produced by the pultrusion technique can be increased with 90° windings by using different fiber types. This paper presents experimental studies on the effect of FRP composite wrapping on the flexure performance of reinforced concrete (RC) filled pultruded glass-FRP (GFRP) profile hybrid beams with damage analysis. The hybrid beams are wrapped fully and partially with Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites. Hybrid beam specimens with 0° to 90° fiber orientations were tested under three- and four-point bending loads. Based on the experimental load–displacement relationship results, initial stiffness, ductility, and energy dissipation capacity were compared. The experimental findings revealed that the maximum load-carrying capacities of beams produced with pultrude profiles increased by 24% with glass wrapping and 64.4% with carbon wrapping due to the change in the damages. A detailed damage analysis is provided. Similarly, significant increases were observed in structural performance ratios such as initial stiffness and ductility ratio. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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12 pages, 5061 KiB

Open AccessArticle

The Reinforcing Effect of Waste Corrugated Paper Fiber on Polylactic Acid

by Jian Su, Zhiwei Jiang, Changqing Fang, Yamin Zheng, Mannan Yang, Lu Pei and Zhigang Huang

Polymers 2022, 14(17), 3562; https://doi.org/10.3390/polym14173562 - 29 Aug 2022

Cited by 7 | Viewed by 2161

Abstract

To improve the recycle value of waste paper and promote circular economic development, waste corrugated paper fiber (WCPF) was used as a reinforcing agent to prepare waste corrugated paper fiber/polylactic acid (WCPF/PLA) composites via dichloromethane solvent which can be reused. The WCPF in [...] Read more.

To improve the recycle value of waste paper and promote circular economic development, waste corrugated paper fiber (WCPF) was used as a reinforcing agent to prepare waste corrugated paper fiber/polylactic acid (WCPF/PLA) composites via dichloromethane solvent which can be reused. The WCPF in the waste corrugated paper is extracted by beating in a Valli beating machine for different time lengths and grinding in a disc grinder. The effects of beating time and the content of WCPF on the microstructure, mechanical properties, thermal decomposition process, and crystallization properties of the WCPF/PLA composite were studied. The result shows that the WCPF can be well separated from each other and can be evenly dispersed in the PLA matrix. When 25 wt% WCPF which was beat for 30 min was used, the composite has the greatest improvement in tensile property. This study provides a new process for the recycling of waste paper in the application of polymer reinforcement. The research on waste paper fiber and degradable polymer composite is of great significance for reducing environmental pollutants and developing circular economy. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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26 pages, 8384 KiB

Open AccessArticle

Effects of Polyoxymethylene Fiber on Mechanical Properties of Seawater Sea-Sand Concrete with Different Ages

by Fei Wang, Jianmin Hua, Xuanyi Xue, Neng Wang and Yunhang Yao

Polymers 2022, 14(17), 3472; https://doi.org/10.3390/polym14173472 - 25 Aug 2022

Cited by 12 | Viewed by 1889

Abstract

Workability and mechanical properties of the seawater sea–sand concrete (SWSSC) were similar to those of ordinary concrete made with freshwater and river sand, which had a wide application in structures. Since the polyoxymethylene (POM) fiber performed the outstanding alkali resistance and durability, POM [...] Read more.

Workability and mechanical properties of the seawater sea–sand concrete (SWSSC) were similar to those of ordinary concrete made with freshwater and river sand, which had a wide application in structures. Since the polyoxymethylene (POM) fiber performed the outstanding alkali resistance and durability, POM fibers were added in SWSSC in this study to enhance the mechanical properties. Moreover, the mechanical properties of concrete during the early age have significant effects on the construction phase. The experiment, including 96 test specimens, was conducted to clarify effects of POM fibers on mechanical properties of SWSSC with different ages. The cube compressive, axial compressive, splitting tensile, and flexural tests of NF and POM0.6 SWSSC were conducted. Based on test results, the predictive equations were proposed to quantify relations between concrete age and mechanical properties of NF and POM0.6 SWSSC. Effects of the concrete age on ratios f_tT/f_cT and f_fT/f_cT were investigated and quantified through proposed equations. Failure performances of NF and POM0.6 SWSSC specimens with different ages were analyzed. The microstructure of POM0.6 SWSSC specimens was observed, and the reinforcing mechanism of POM fibers was further explained. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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21 pages, 5649 KiB

Open AccessArticle

Effect of Temperature on Mechanical Behavior of Concrete Reinforced with Different Types of GFRP Bar

by Ruan Carlos de Araújo Moura, Paulo Roberto Lopes Lima and Daniel Véras Ribeiro

Polymers 2022, 14(17), 3437; https://doi.org/10.3390/polym14173437 - 23 Aug 2022

Cited by 3 | Viewed by 2469

Abstract

Glass fiber reinforced polymer (GFRP) bars have been increasingly used as reinforcement in concrete structures. However, when the bars are exposed to high temperatures, there is a change in the internal structure of the polymer which affects the tensile strength of the matrix [...] Read more.

Glass fiber reinforced polymer (GFRP) bars have been increasingly used as reinforcement in concrete structures. However, when the bars are exposed to high temperatures, there is a change in the internal structure of the polymer which affects the tensile strength of the matrix and its adhesion with the fibers, reducing the mechanical strength of the bar. In addition, with increasing temperature, the bar-concrete interface is also damaged by the decomposition of hydration products from the cement paste and the loss of surface adhesion. The intensity of these changes is associated with the type of resin used as a matrix since each polymer has its own molecular structure that provides a greater or lesser ability to resist the changes imposed by temperature. The present study evaluates the mechanical behavior of reinforced concrete containing different types of GFRP bars and subjected to temperatures of 150 °C, 300 °C, and 350 °C. The GFRP bars with three types of matrices (polyester, vinyl ester, or epoxy) were mechanically evaluated under tension in two conditions: isolated and inserted into reinforced concrete specimens with a thickness of 20 mm, using two types of concrete (with and without silica fume). Degradation mechanisms at the bar/concrete interface were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), differential thermal analysis (DTA), and bond techniques. The results showed that the type of matrix has a significant influence on the tensile behavior of GFRP bars, with the epoxy matrix showing the best performance, followed by bars with vinyl ester and polyester matrix resins. The use of silica fume improved the performance of the concrete coating and, consequently, improved the protection of GFRP bars, hindering the diffusion of oxygen and heat; bar/concrete adhesion was compromised by thermal degradation of GFRP bar ribs. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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17 pages, 8246 KiB

Open AccessArticle

Strain-Field Modifications in the Surroundings of Impact Damage of Carbon/Epoxy Laminate

by Jarmil Vlach, Radek Doubrava, Roman Růžek, Jan Raška, Jan Horňas and Martin Kadlec

Polymers 2022, 14(16), 3243; https://doi.org/10.3390/polym14163243 - 9 Aug 2022

Cited by 8 | Viewed by 1698

Abstract

The relationship between deformation and stress is crucial for any elasto-plastic body. This paper deals with the experimental identification of the basic parameters of the composite laminate model in relation to the finite element model. Standardized tensile, impact, and post-impact tests on a [...] Read more.

The relationship between deformation and stress is crucial for any elasto-plastic body. This paper deals with the experimental identification of the basic parameters of the composite laminate model in relation to the finite element model. Standardized tensile, impact, and post-impact tests on a carbon fiber-reinforced epoxy laminate were used. The method by which the elasticity and failure parameters were obtained from the initial components is described. In the article, the modes of initiation and complete failure of samples in tensile tests, which are compared with the simulation, are presented. Furthermore, the article deals with the issue of the generation and detection of damage by low-speed impact, which can be caused by contact with moving objects, due to improper handling or maintenance. The results of impact analysis simulations are shown in the context of strain-field distribution changes obtained with the help of digital image correlation. The results showed high agreement between the calculations and the experiments. Based on this agreement, simulations of impact damage for various energies were performed. These simulations were used to determine the approximate sizes of the affected zones in relation to the impact energy. The results are finally discussed in the context of the possible use of structural health monitoring based on strain modifications. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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21 pages, 3938 KiB

Open AccessArticle

Selection of Natural Fibre for Pultruded Hybrid Synthetic/Natural Fibre Reinforced Polymer Composites Using Analytical Hierarchy Process for Structural Applications

by Thinesh Sharma Balakrishnan, Mohamed Thariq Hameed Sultan, Jesuarockiam Naveen, Farah Syazwani Shahar, Muhammad Imran Najeeb, Ain Umaira Md Shah, Tabrej Khan and Tamer Ali Sebaey

Polymers 2022, 14(15), 3178; https://doi.org/10.3390/polym14153178 - 4 Aug 2022

Cited by 10 | Viewed by 2736

Abstract

Application of synthetic fibres in composites has been raising environmental issues due to carbon emissions from the production site and reliability on non-renewable resources upon production. Hence, this research sets as a preliminary study to select suitable natural fibres to be hybridized with [...] Read more.

Application of synthetic fibres in composites has been raising environmental issues due to carbon emissions from the production site and reliability on non-renewable resources upon production. Hence, this research sets as a preliminary study to select suitable natural fibres to be hybridized with glass fibres for the development of sustainable and high-performance hybrid composites as potential alternative to conventional pultruded fibreglass composites in structural profile applications. In this study, analytical hierarchy process (AHP) was conducted to select the ideal natural fibre as reinforcement in the hybrid pultruded FRP composites suitable for structural applications. Hence, 13 natural fibre candidates were selected as alternatives and six criteria were chosen and analysed to select the best candidate for pultruded hybrid FRP. Criteria such as tensile strength, tensile modulus, density, cellulose content, elongation, and availability of fibres were assigned as the standard of selecting natural fibres for the application intended in this study. Among the 13 alternatives, kenaf was found to be the most suitable reinforcement for the application as it yielded the highest priority vector at 0.1. The results were then validated by carrying out sensitivity analysis to ensure kenaf is the most suitable material for the research. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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15 pages, 3831 KiB

Open AccessArticle

Parameters Influence on the Dynamic Properties of Polymer-Matrix Composites Reinforced by Fibres, Particles, and Hybrids

by Zuzana Murčinková, Przemysław Postawa and Jerzy Winczek

Polymers 2022, 14(15), 3060; https://doi.org/10.3390/polym14153060 - 28 Jul 2022

Cited by 9 | Viewed by 2087

Abstract

In this paper, we present an extensive experimental study on the dynamic mechanical properties of composites with polymer matrices, as well as a quantification of the parameters that influence these properties. Polymer-composite matrices make it possible to form any reinforcement arrangement of fibres, [...] Read more.

In this paper, we present an extensive experimental study on the dynamic mechanical properties of composites with polymer matrices, as well as a quantification of the parameters that influence these properties. Polymer-composite matrices make it possible to form any reinforcement arrangement of fibres, particles, and layers, which makes it possible to form composite materials with certain dominant mechanical properties according to the internal arrangement for the application. In this study, we focused on the dynamic properties (i.e., damping parameters, such as the loss factor (tan d), logarithmic decrement (λ), storage modulus (E′), and loss modulus (E″)) of composites with polymer matrices, including parameters such as the fibre material, fabric weaving, fibre orientation, temperature, frequency, particle size, volume of short fibres, and epoxy resin type. If other articles focus on one type of composite and 1–2 parameters, then the benefit of this article lies in our analysis of 8 mentioned parameters in the experimental analysis of 27 different types of composites with polymer matrices. The tested fibre materials were glass, aramid, and carbon; the tested woven fabrics were twill, plain, unidirectional, and satin; the temperature range was from −50 to +230 °C; the frequency was 1 Hz and 10 Hz; the particle size was 0.1–16 mm; the volume percentages of the short fibres were 3, 6, and 12 vol.% of the hybrid polymer composites and the type of polymer matrix. We used the free-damped-vibration method with vibration dynamic signal analysis and the forced-damped vibration of dynamic mechanical thermal analysis for testing. We ranked the parameters that influence the dynamic vibration properties according to the effects. Among sets of results provided in the paper, considering the storage modulus, loss modulus, and loss factor, the best results of the fibre composites were for aramid-fibre-reinforced polymers, regardless of the weave type, with an advantage for unidirectional fabric. The best results of the particle composites were for those with fine filler sizes that incorporated the short fibres. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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12 pages, 5207 KiB

Open AccessArticle

Study on the Impact and Water Absorption Performance of Prosopis juliflora & Glass Fibre Reinforced Epoxy Composite Laminates

by Manoj Kumar Gurunathan, Navasingh Rajesh Jesudoss Hynes, Omar Ali. Al-Khashman, Michael Brykov, Nagasubramoniam Ganesh and Antoaneta Ene

Polymers 2022, 14(15), 2973; https://doi.org/10.3390/polym14152973 - 22 Jul 2022

Cited by 8 | Viewed by 1599

Abstract

Current global trends demand the replacement of synthetic fibres with natural fibres in polymeric composites. The present work makes use of Prosopis juliflora, a plant that is a threat to the environment as a partial replacement in a hybrid composite. Individual Prosopis juliflora [...] Read more.

Current global trends demand the replacement of synthetic fibres with natural fibres in polymeric composites. The present work makes use of Prosopis juliflora, a plant that is a threat to the environment as a partial replacement in a hybrid composite. Individual Prosopis juliflora fibres are added to matrices at ratios of 12, 6, 9 and 8 wt % and glass fibres are added discretely at ratios of 28, 24, 21 and 32 wt % into matrices as well. The composites are prepared with four different combinations and tested in terms of the mechanical benefits and water absorption performance. This work exploits the mechanical advantage of impact energy in addition to producing Prosopis juliflora particles, fibre glass mats, and resin appropriate for structural uses. Water absorption tests are conducted for four different compositions. Among the four samples, sample 3 (9 wt % Prosopis juliflora fibres and 21 wt % glass fibres) has a higher rate of water absorption than the others, although sample 2 (6 wt % Prosopis juliflora fibres and 24 wt % glass fibres) has a lower rate. The difference in the quantity of water absorption between the hybrid composites can be attributed to the weight percentage of fibres. On the other hand, sample 1 (12 wt % Prosopis juliflora fibres and 28 wt % glass fibres) is reported to have absorbed 2.6 J of energy in the impact strength test. The increase in impact strength is attributed to the increase in the weight percentage of glass fibres. A scanning electron microscope is employed to study the fractured surfaces of the composites. This study shows that the developed hybrid composite could be employed in structural and automotive applications because of its improved impact strength and water resistance. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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15 pages, 6731 KiB

Open AccessArticle

Study on Carbonization Characteristics and Deterioration Mechanism of Recycled Concrete with Tailings and Polypropylene Fiber

by Tao Li, Meng Zhan, Xiuyun Chen, Fan Xu, Sheliang Wang and Xinxin Liu

Polymers 2022, 14(14), 2758; https://doi.org/10.3390/polym14142758 - 6 Jul 2022

Cited by 12 | Viewed by 2001

Abstract

To improve the deformation performance of recycled concrete with tailings (TRC), its carbonization characteristics and deterioration mechanism with different polypropylene fiber content were analyzed macroscopically and microscopically. The results showed that the fiber had little effect on the compressive strength, which increased first [...] Read more.

To improve the deformation performance of recycled concrete with tailings (TRC), its carbonization characteristics and deterioration mechanism with different polypropylene fiber content were analyzed macroscopically and microscopically. The results showed that the fiber had little effect on the compressive strength, which increased first and then decreased, with the optimum content being 0.6%. The splitting tensile strength first increased and then tended to be stable, with the optimum dosage ranging from 0.6% to 0.9%. The more the content, the higher the peak strain and the lower the elastic modulus. The rising section of its constitutive curve changed little, while the falling section became more gentle. Carbonization made the relative dynamic elastic modulus change small with a trend of first increasing and then decreasing, and the optimum content was 0.6–0.9%. When the fiber content was small, the influence on the carbonization depth did not remain significant, but when it was large, the depth increased obviously, and this critical content was about 0.6%. Microscopically, through nuclear-magnetic resonance (NMR) and scanning electron microscope (SEM) analysis, due to the strong tensioning effect of the fiber, when a small amount was added, the porosity and pore structure had not been significantly changed, so the impact on its resistance to carbonization was not obvious. However, after excessive addition, the interface transition zone (ITZ) between different materials became larger, resulting in a significant increase of its harmful cracks and a great impact on the anti-carbonization ability, with the optimal content being about 0.6%. This study provides a theoretical reference for the deformation performance improvement measure of TRC, which would be helpful for the rapid promotion and application of green concrete in engineering practice. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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17 pages, 2847 KiB

Open AccessArticle

Micromechanical Model for Predicting the Tensile Properties of Guadua angustifolia Fibers Polypropylene-Based Composites

by Jorge I. Fajardo, Josep Costa, Luis J. Cruz, César A. Paltán and Jonnathan D. Santos

Polymers 2022, 14(13), 2627; https://doi.org/10.3390/polym14132627 - 28 Jun 2022

Cited by 7 | Viewed by 2152

Abstract

In this paper, the one-dimensional tensile behavior of Guadua angustifolia Kunth fibre/polypropylene (PP+GAK_S) composites is modeled. The classical model of Kelly–Tyson and its Bowyer–Bader’s solution is not able to reproduce the entire stress–strain curve of the composite. An integral (In-Built) micromechanical [...] Read more.

In this paper, the one-dimensional tensile behavior of Guadua angustifolia Kunth fibre/polypropylene (PP+GAK_S) composites is modeled. The classical model of Kelly–Tyson and its Bowyer–Bader’s solution is not able to reproduce the entire stress–strain curve of the composite. An integral (In-Built) micromechanical model proposed by Isitman and Aykol, initially for synthetic fiber-reinforced composites, was applied to predict micromechanical parameters in short natural fiber composites. The proposed method integrates both the information of the experimental stress-strain curves and the morphology of the fiber bundles within the composite to estimate the interfacial shear strength (IFSS), fiber orientation efficiency factor

η_{FOD}

, fiber length efficiency factor

η_{FLD}

and critical fiber length

l_{c}

. It was possible to reproduce the stress-strain curves of the PP+GAK_S composite with low residual standard deviation. A methodology was applied using X-ray microtomography and digital image processing techniques for the precise extraction of the micromechanical parameters involved in the model. The results showed good agreement with the experimental data. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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22 pages, 20877 KiB

Open AccessArticle

Experimental Analysis of Matrix Cracking in Glass Fiber Reinforced Composite Off-Axis Plies under Static and Fatigue Loading

by Gordon Just, Ilja Koch and Maik Gude

Polymers 2022, 14(11), 2160; https://doi.org/10.3390/polym14112160 - 26 May 2022

Cited by 5 | Viewed by 2168

Abstract

The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted [...] Read more.

The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted white light imaging using a digital camera and LED illumination from the back of the specimen on a servo-hydraulic testing machine. Static and fatigue results were examined with respect to crack initiation and crack growth, considering the special case of bonding yarns parallel to the fiber directions. The bonding yarns act as stress concentrations, influencing the early cracking behavior, and complicate the detectability of cracks growing underneath or next to the bonding yarns. In cyclic loading, the influence of load level, load ratio, mean stress, fiber orientation, and ply thickness was the focus of the experimental campaign. Cyclic cracking behavior in terms of initiation and growth was analyzed based on the applied loading conditions and laminate configurations. It was found that halving the ply thickness nearly doubled the amount of microcracks in case of high loads. For low loads, no such effect was observed up to

5 \times 10^{5}

loading cycles. Experimental findings on individual crack growth confirmed that crack interaction started for crack spacings less than four times the ply thickness and that subsequent crack growth shifted into regions of larger local crack spacing. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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11 pages, 8037 KiB

Open AccessArticle

Bearing Properties of CFRP Composite Laminates Containing Spread-Tow Thin-Plies

by Hassan Alshahrani and Tamer A. Sebaey

Polymers 2022, 14(10), 2076; https://doi.org/10.3390/polym14102076 - 19 May 2022

Cited by 3 | Viewed by 2018

Abstract

With the development of spread-tow, thin-ply technology, ultra-thin composite laminates could be produced. Composite bolted joints are commonly used on aircraft’s load-bearing structures and are considered the main cause of stress concentration. The aim of this research is to investigate the bolted joint [...] Read more.

With the development of spread-tow, thin-ply technology, ultra-thin composite laminates could be produced. Composite bolted joints are commonly used on aircraft’s load-bearing structures and are considered the main cause of stress concentration. The aim of this research is to investigate the bolted joint behavior of composite laminates that combine thin-plies and conventional thick-plies in a predetermined stacking sequence. The impact of thin-ply placement within the stack on bearing strength, including the onset of damages, is examined. The work involves mechanical tests and fractographic activities to understand the damage mechanisms of the plies and their interactions, and its reflections on the bearing load capacity of the joint for double-lap bolted joints. The results showed an improvement in the bearing strength of up to 19% by inserting the thin-plies inside the laminate. The visual examination of the specimens showed a bearing damage mode for all the tested specimens. The computed tomography scans showed damage mechanisms that mostly occurred with the normal plies, rather than breaking the thin-plies. For the specimens of traditional plies, delaminations were noticed at most of the interfaces. For the one with a block of thin-plies in the middle, all the delaminations were forced to the surface layers with an extra large size. Forspecimens with distributed thin-plies, a higher number of smaller delaminations was recognized. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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17 pages, 37036 KiB

Open AccessArticle

Effect of Embedded Thin-Plies on the Charpy Impact Properties of CFRP Composites

by Hassan Alshahrani and Tamer A. Sebaey

Polymers 2022, 14(9), 1929; https://doi.org/10.3390/polym14091929 - 9 May 2022

Cited by 5 | Viewed by 2361

Abstract

In this study, different configurations of epoxy composite laminates that contained thin plies were prepared and characterised for sudden impact load bearing applications. The primary aim of this investigation was to develop a hybrid epoxy-based thin ply composite for aerospace and automotive applications [...] Read more.

In this study, different configurations of epoxy composite laminates that contained thin plies were prepared and characterised for sudden impact load bearing applications. The primary aim of this investigation was to develop a hybrid epoxy-based thin ply composite for aerospace and automotive applications that would be tolerant of high impacts. The impact properties of the selected configurations were investigated both experimentally and numerically under low-velocity Charpy impact loading conditions. Furthermore, any damage to the laminates was evaluated with an emphasis on the identification of dominant damage mechanisms and locations. This included a comparison between the laminates that were made from traditional plies and the thin ply laminates in terms of their absorbed energy and failure modes. The results revealed that the integration of thin plies into normal ply had a major effect on the amount of absorbed energy under flatwise conditions: up to 8.7 J at a cut-off angle of 90°. However, edgewise conditions produced a maximum observed energy of 10.0 J for the thin plies that were surrounded by normal plies (Plate 3). The damage assessments showed the increased damage resistance of the hybrid thin ply composites due to their uniform stress distribution. The traditional ply composites incurred large deformations from the impact loads. Moreover, it was noted that delamination formed in the middle regions of the traditional plies. The FEM model analysis revealed that it was capable of accurately predicting the absorbed energy for different configurations of composites, which were prepared and analysed experimentally. Both the experimental and numerical values were very similar to each other. These impact damage assessments improved the thin ply composites so that they could be used as working materials for applications that are prone to high loads, such as the aerospace, defence, automotive and structural industries. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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20 pages, 3807 KiB

Open AccessArticle

Advanced Machine Learning Modeling Approach for Prediction of Compressive Strength of FRP Confined Concrete Using Multiphysics Genetic Expression Programming

by Israr Ilyas, Adeel Zafar, Muhammad Talal Afzal, Muhammad Faisal Javed, Raid Alrowais, Fadi Althoey, Abdeliazim Mustafa Mohamed, Abdullah Mohamed and Nikolai Ivanovich Vatin

Polymers 2022, 14(9), 1789; https://doi.org/10.3390/polym14091789 - 27 Apr 2022

Cited by 35 | Viewed by 3770

Abstract

The purpose of this article is to demonstrate the potential of gene expression programming (GEP) in anticipating the compressive strength of circular CFRP confined concrete columns. A new GEP model has been developed based on a credible and extensive database of 828 data [...] Read more.

The purpose of this article is to demonstrate the potential of gene expression programming (GEP) in anticipating the compressive strength of circular CFRP confined concrete columns. A new GEP model has been developed based on a credible and extensive database of 828 data points to date. Numerous analyses were carried out to evaluate and validate the presented model by comparing them with those presented previously by different researchers along with external validation comparison. In comparison to other artificial intelligence (AI) techniques, such as Artificial Neural Networks (ANN) and the adaptive neuro-fuzzy interface system (ANFIS), only GEP has the capability and robustness to provide output in the form of a simple mathematical relationship that is easy to use. The developed GEP model is also compared with linear and nonlinear regression models to evaluate the performance. Afterwards, a detailed parametric and sensitivity analysis confirms the generalized nature of the newly established model. Sensitivity analysis results indicate the performance of the model by evaluating the relative contribution of explanatory variables involved in development. Moreover, the Taylor diagram is also established to visualize how the proposed model outperformed other existing models in terms of accuracy, efficiency, and being closer to the target. Lastly, the criteria of external validation were also fulfilled by the GEP model much better than other conventional models. These findings show that the presented model effectively forecasts the confined strength of circular concrete columns significantly better than the previously established conventional regression-based models. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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17 pages, 7132 KiB

Open AccessArticle

Experiments and Finite Element Simulations of Composite Laminates Following Low Velocity On-Edge Impact Damage

by Wenjun Xu, Longquan Liu and Wu Xu

Polymers 2022, 14(9), 1744; https://doi.org/10.3390/polym14091744 - 25 Apr 2022

Cited by 5 | Viewed by 2140

Abstract

Composites are widely used in aircraft structures that have free edges and are vulnerable to impact events during manufacturing and maintenance. On-edge impact may have a great contribution in terms of the compression strength loss of composites, but the influence remains unclear. This [...] Read more.

Composites are widely used in aircraft structures that have free edges and are vulnerable to impact events during manufacturing and maintenance. On-edge impact may have a great contribution in terms of the compression strength loss of composites, but the influence remains unclear. This paper presents experiments and simulations of carbon-fiber-reinforced plastic (CFRP) materials with on-edge impact and compression after edge impact (CAEI). On-edge impact damage was introduced to the composite laminates through the drop weight method with 4, 6, 8 and 10 J impact energies, respectively. A special guide-rail-type fixture was used in the compression tests in which strain–force and load–displacement relationships were obtained. A continuous-step finite element model was proposed to simulate impact and compression. Continuum shell elements and Hashin failure criteria were used to simulate in-ply damage, and interlaminar damage was modelled by cohesive elements. The model was validated by correlating the experimental and numerical results. The investigation results revealed the relationships of the damage size and residual strength with the different impact energies. The crack length and delaminated area grow with the increase in impact energy. The residual compressive strength follows a downward trend with increasing impact energy. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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15 pages, 1909 KiB

Open AccessArticle

Optimization of Typha Fibre Extraction and Properties for Bio-Composite Applications Using Desirability Function Analysis

by Mahmudul Hasan, Mashiur Rahman, Ying Chen and Nazim Cicek

Polymers 2022, 14(9), 1685; https://doi.org/10.3390/polym14091685 - 21 Apr 2022

Cited by 14 | Viewed by 2102

Abstract

The effect of extraction time, temperature, and alkali concentration on the physical and mechanical properties of cattail (Typha latifolia L.) fibres were investigated using five levels of time (4, 6, 8, 10, and 12 h), four levels of temperature (70, 80, 90, [...] Read more.

The effect of extraction time, temperature, and alkali concentration on the physical and mechanical properties of cattail (Typha latifolia L.) fibres were investigated using five levels of time (4, 6, 8, 10, and 12 h), four levels of temperature (70, 80, 90, and 95 °C), and three levels of NaOH concentration (4, 7, 10%, w/v) in a 3 × 4 × 5 factorial experimental design. The extraction parameters were optimized for bio-composite application using a desirability function analysis (DFA), which determined that the optimum extraction time, temperature and NaOH concentration were 10 h, 90 °C, and 7%, respectively. A sensitivity analysis for optimal treatment conditions confirmed that the higher overall desirability does not necessarily mean a better solution. However, the analysis showed that the majority of optimum settings for time, temperature, and concentration of NaOH found in the sensitivity analysis matched with the optimum conditions determined by DFA, which confirmed the validity of the optimum treatment conditions. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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21 pages, 7012 KiB

Open AccessArticle

Mechanical Investigation on Fiber-Doped Cementitious Materials

by Yongcheng Ji, Yunfei Zou, Xucheng Wan and Wei Li

Polymers 2022, 14(9), 1663; https://doi.org/10.3390/polym14091663 - 20 Apr 2022

Cited by 10 | Viewed by 1773

Abstract

Cementitious materials can be reinforced by adding different fibers. However, the effect of different fiber reinforcements on the mechanical properties of cement-based materials remains to be further studied. This paper studies the influencing factors of different fiber cement-based materials by combining experimental and [...] Read more.

Cementitious materials can be reinforced by adding different fibers. However, the effect of different fiber reinforcements on the mechanical properties of cement-based materials remains to be further studied. This paper studies the influencing factors of different fiber cement-based materials by combining experimental and theoretical methods. The tests used carbon fiber, glass fiber, and polyvinyl alcohol (PVA) fiber-reinforced cement-based materials. The addition ratios of fibers are 0%, 0.5%, and 1% by volume respectively. The compressive strength, bending strength, and drying shrinkage are studied for 3 to 28 d. The relationship between bending strength, compressive strength, dosage, and shrinkage is analyzed. The test results show that carbon fiber cement-based materials’ bending, and compressive strength increase the fastest, followed by glass and PVA fibers. The presented mathematical model accurately predicted the strength of the three fiber cement-based materials at different curing times. Compared to glass fiber and PVA fiber, carbon fiber shrinks less. It can be shown that the fiber significantly affects the early strength change of the fiber cement-based material by changing the shrinkage size of the fiber-cement-based material. The bending strength of carbon fiber, glass fiber, and PVA fiber increases with the increase of fiber volume fraction. On the other hand, the compressive strength increases and then decreases. Mechanical tests show that carbon fiber has the best reinforcement effect. The number of fibers, center spacing, and ultimate tensile length are all important factors that affect the strength of different fiber cement-based materials. Moreover, applied ABAQUS software established compression and bending finite element models of fiber-cement composites. It can predict the mechanical performance concerning fiber cement-based materials’ different types and volume fractions. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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16 pages, 9222 KiB

Open AccessArticle

Sensitivity Analysis of Various Geometries of PCD and Cemented Tungsten Carbide Cutting Tools during the Milling of GFRP Composite

by François Ducobu, Eloïse Mélice, Edouard Rivière-Lorphèvre, Thomas Beuscart, Oihan Aizpuru, Aurélie Granjon, Paulo Flores, Denis Soriano, Mikel Cuesta and Pedro-Jose Arrazola

Polymers 2022, 14(8), 1524; https://doi.org/10.3390/polym14081524 - 9 Apr 2022

Cited by 7 | Viewed by 2189

Abstract

Although much research has been carried out in the field of the milling of GFRP (Glass Fibre Reinforced Polymer) composites, the complexity of the process is such that it is still not mastered in many industrial cases. The current work is aimed at [...] Read more.

Although much research has been carried out in the field of the milling of GFRP (Glass Fibre Reinforced Polymer) composites, the complexity of the process is such that it is still not mastered in many industrial cases. The current work is aimed at studying the influence of three different geometries of PCD (PolyCrystalline Diamond) and cemented tungsten carbide cutting tools during the up-milling of GFRP composites at fixed cutting conditions (v_c = 502 m/min and v_f = 420 mm/min). Delamination, cutting forces and tool wear are compared at the fresh and worn states, and the correlation between the lifespan and the cost of the cutting tool is analysed. The main wearing phase of the tools was performed under the conditions of production in the facilities of a company (Sobelcomp, Loncin, Belgium). The results indicate that the PCD tool with the straight edge, inclined peripheral tooth shape produces the smallest total cutting force and less delamination (shortest and lowest number of delaminated fibres) at both fresh and worn states. Moreover, the grinding ability of PCD makes the cutting tool cost per part lower than for cemented carbide. The PCD tool is therefore the best option to mill GFRP parts. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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15 pages, 4881 KiB

Open AccessArticle

Flexural Performance of Concrete Beams Reinforced with Continuous FRP Bars and Discrete Steel Fibers under Cyclic Loads

by Haitang Zhu, Chuanchuan Li, Shengzhao Cheng and Jiansong Yuan

Polymers 2022, 14(7), 1399; https://doi.org/10.3390/polym14071399 - 30 Mar 2022

Cited by 9 | Viewed by 3282

Abstract

This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm³ were constructed and tested to failure under [...] Read more.

This research investigated the flexural behavior of high-strength concrete beams reinforced with continuous basalt fiber-reinforced polymer (BFRP) bars and discrete steel fibers. Five concrete beams with the dimensions of 150 × 300 × 2100 mm³ were constructed and tested to failure under four-point bending cyclic loading. The specimens consisted of four BFRP-reinforced concrete beams with various reinforcement ratios (ρ_f), namely, 0.56%, 0.77%, 1.15%, and 1.65%, and one conventional steel-reinforced concrete beam for comparison purposes. The cracking behavior, failure modes, load-deflection behavior, residual deformation, and stiffness degradation of the beams were studied. Additionally, a deformation-based approach was used to analyze the deformability of the beams. The results show that an increase in the ρ_f effectively restrained the crack widths, deflections, and residual deformation while also enhancing the flexural bearing capacity of the beams. In comparison to the first displacement cycle, the bearing capacity dropped by 10% on average in the third cycle. The stiffness exhibited a fast to slow degradation trend until failure. The residual stiffnesses were higher in beams with a higher ρ_f. The over-reinforced beams had superior deformability than the under-reinforced beams, according to the deformability factors. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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15 pages, 2726 KiB

Open AccessArticle

Design and Analysis of CFRP Drilling by Electrical Discharge Machining

by Luis Roldan-Jimenez, Fermin Bañon, Ana P. Valerga and Severo R. Fernandez-Vidal

Polymers 2022, 14(7), 1340; https://doi.org/10.3390/polym14071340 - 25 Mar 2022

Cited by 13 | Viewed by 2348

Abstract

The novelty of EDM machining as a drilling operation for composite materials means that there is no consensus on the influence of the parameters that optimise the final quality. For these reasons, a characterisation of the EDM drilling process of a unidirectional composite [...] Read more.

The novelty of EDM machining as a drilling operation for composite materials means that there is no consensus on the influence of the parameters that optimise the final quality. For these reasons, a characterisation of the EDM drilling process of a unidirectional composite material has been developed. The influence of several cutting parameters has been related to the quality of the final hole obtained. Thus, macrogeometric aspects in terms of conicity and final diameter and microgeometric aspects in terms of surface quality have been evaluated. In addition, the final state of the material and the wear of the electrode have been evaluated by visual inspection, allowing the range of cutting parameters that offer the best performance to be established. Finally, a series of contour diagrams based on predictive models have been obtained to establish a direct relationship between input and output variables. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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Review

Jump to: Research

20 pages, 4800 KiB

Open AccessReview

Properties of Fiber-Reinforced One-Part Geopolymers: A Review

by Guoliang Guo, Chun Lv, Jie Liu and Li Wang

Polymers 2022, 14(16), 3333; https://doi.org/10.3390/polym14163333 - 16 Aug 2022

Cited by 20 | Viewed by 2550

Abstract

Geopolymers have the advantages of low carbon, being environmentally friendly and low price, which matches the development direction of building materials. Common geopolymer materials are also known as two-part geopolymers (TPGs). TPGs are usually prepared from two main substances, which are formed by [...] Read more.

Geopolymers have the advantages of low carbon, being environmentally friendly and low price, which matches the development direction of building materials. Common geopolymer materials are also known as two-part geopolymers (TPGs). TPGs are usually prepared from two main substances, which are formed by polymerization of a silicoaluminate precursor and an alkaline activator solution. The TPG has many limitations in engineering application because of its preparation on the construction site, and the use of solid alkaline activator in one-part geopolymers (OPGs) overcomes this shortcoming. However, the brittleness of OPGs such as ceramics also hinders its popularization and application. The properties of the new OPG can be improved effectively by toughening and strengthening it with fibers. This review discusses the current studies of fiber-reinforced one-part geopolymers (FOPGs) in terms of raw precursors, activators, fibers, physical properties and curing mechanisms. In this paper, the effects of the commonly used reinforcement fibers, including polyvinyl alcohol (PVA) fiber, polypropylene (PP) fiber, polyethylene (PE) fiber, basalt fiber and other composite fibers, on the fresh-mixing properties and mechanical properties of the OPGs are summarized. The performance and toughening mechanism of FOPGs are summarized, and the workability, macroscopic mechanical properties and durability of FOPGs are investigated. Finally, the development and engineering application prospect of FOPGs are prospected. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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29 pages, 3611 KiB

Open AccessReview

A Review on the Physical Parameters Affecting the Bond Behavior of FRP Bars Embedded in Concrete

by Boğaçhan Başaran, İlker Kalkan, Ahmet Beycioğlu and Izabela Kasprzyk

Polymers 2022, 14(9), 1796; https://doi.org/10.3390/polym14091796 - 28 Apr 2022

Cited by 21 | Viewed by 3877

Abstract

The present study is a detailed literal survey on the bond behavior of FRP (Fiber Reinforced Polymer) reinforcing bars embedded in concrete. There is an urgent need for the accurate assessment of the parameters affecting the FRP–concrete bond and quantification of these effects. [...] Read more.

The present study is a detailed literal survey on the bond behavior of FRP (Fiber Reinforced Polymer) reinforcing bars embedded in concrete. There is an urgent need for the accurate assessment of the parameters affecting the FRP–concrete bond and quantification of these effects. A significant majority of the previous studies could not derive precise and comprehensive conclusions on the effects of each of these parameters. The present study aimed at listing all of the physical parameters affecting the concrete-FRP bond, presenting the effects of each of these parameters based on the common opinions of the previous researchers and giving reasonable justifications on these effects. The studies on each of the parameters are presented in detailed tables. Among all listed parameters, the surface texture was established to have the most pronounced effect on the FRP–concrete bond strength. The bond strength values of the bars with coarse sand-coating exceeded the respective values of the fine sand-coated ones. However, increasing the concrete strength was found to result in a greater improvement in bond behavior of fine sand-coated bars due to the penetration of concrete particles into the fine sand-coating layer. The effects of fiber type, bar diameter and concrete compressive strength on the bar bond strength was shown to primarily originate from the relative slip of fibers inside the resin of the bar, also known as the shear lag effect. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymer Materials)

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