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Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: 10 June 2025 | Viewed by 8836

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Special Issue Editors

Dr. Aliakbar Gholampour

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Guest Editor

College of Science and Engineering, Flinders University, Adelaide, Australia
Interests: co-friendly and sustainable composites; waste-based concrete; nanocomposite; lightweight foam composite; high-performance and ultra-high performance composite; fiber-reinforced polymers
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Togay Ozbakkaloglu

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Guest Editor

Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA
Interests: structural engineering; construction materials; smart and high-performance infrastructure materials; high-strength and high performance concretes; waste-based concretes; geopolymers; fiber reinforced polymers (frps); composites incorporating recycled materials; green composites; biocomposites; structural applications of composites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Owing to their excellent strength-to-weight ratio, fiber-reinforced polymers and composites have received significant attention in different applications, e.g., automotive, marine, aerospace and construction. This Special Issue of Materials is dedicated to the recent advances in the experimental investigation and computational modeling of fiber-reinforced polymers and composites. We are expecting to receive papers dealing with cutting-edge issues on the research and application of polymers and composites containing internal fibers in different applications.The topics included in this Special Issue include but are not limited to the mechanical, durability, thermal, fire microstructural, and long-term properties of the composites manufactured using different types of internal fibers (including recycled, natural and synthetic fibers) and nanomaterials. Both original contributions and reviews are welcome.

Dr. Aliakbar Gholampour
Prof. Dr. Togay Ozbakkaloglu
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

fiber-reinforced polymers
fiber-reinforced composites
internal fibers
durability properties
thermal properties
mechanical properties
fire-resistant
nano
natural fibers
recycled fibers
synthetic fibers
modeling
concrete
microstructure

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Published Papers (8 papers)

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Research

11 pages, 3586 KiB

Open AccessArticle

Effect of Clamped Member Material and Thickness on Bolt Self-Loosening Under Transverse Loads

by Rashique Iftekhar Rousseau and Abdel-Hakim Bouzid

Materials 2025, 18(2), 462; https://doi.org/10.3390/ma18020462 - 20 Jan 2025

Viewed by 501

Abstract

Bolted joints, prevalent in industrial applications for component fastening, are susceptible to self-loosening—a critical issue resulting in a gradual reduction in clamping force. Gaining insight into the underlying mechanisms of self-loosening is crucial. While prior research has largely focused on evaluating component stiffness, limited attention has been given to its impact on the self-loosening behavior of bolted joints under transverse cyclic loading. This study investigates how component stiffness influences self-loosening in bolted joints by varying the material and thickness of clamped members. An experimental setup replicating real-world conditions is devised to simulate loosening caused by cyclic lateral displacement. Tests are conducted using steel and high-density polyethylene (HDPE) clamped members of different grip lengths to explore the relationship between stiffness and self-loosening. Key parameters measured include bolt axial load, transverse force on clamped members, relative displacement, and rotation between the bolt and nut. The findings provide valuable insights into the effects of stiffness across various clamped member materials and grip length combinations, which can enhance the understanding of conditions that promote loosening resistance. Moreover, by highlighting stage-II or rotational loosening, with each test resulting in complete preload loss, the study provides a comparative analysis of the influencing factors. This enables the identification of distinct loosening patterns and supports the development of improved bolted joint designs to reduce loosening. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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17 pages, 6922 KiB

Open AccessArticle

Mechanical Properties of Ultra-High-Performance Concrete with Steel and PVA Fibers

by Ana Elisabete P. G. A. Jacintho, André M. dos Santos, Gilvan B. Santos Junior, Pablo A. Krahl, Grazielle G. Barbante, Lia L. Pimentel and Nádia C. S. Forti

Materials 2024, 17(23), 5990; https://doi.org/10.3390/ma17235990 - 6 Dec 2024

Viewed by 606

Abstract

Ultra-high-performance concrete (UHPC) has gained worldwide popularity due to its high mechanical performance. This research studied the influence of adding a mixture of two fibers (steel and PVA) on the compressive strength, modulus of elasticity, and flexural tensile strength of UHPC. The mixtures were prepared by adding steel fibers and PVA fibers using a standard procedure defined in the research, which is the time to mix the dry materials and the time to mix the admixture and water. The Central Composite Rotational Design (CCRD) methodology was used for the experimental design of the compressive strength and longitudinal deformation modulus tests. The results were analyzed using statistical software to investigate the influence of fibers on these two mechanical properties of UHPC. With this technique, an optimized design for the study of flexural tensile strength was arrived at. It was found that the standardized equations for the modulus of elasticity, directed to conventional concrete and high-strength concrete, are inadequate for estimating the modulus of UHPC in this research. Statistical analysis indicated that the range of fiber amounts analyzed did not significantly affect the compressive strength and modulus of elasticity. Regarding the optimized mixture, its flexural tensile strength indicated that the fiber content should be higher for UHPC to be suitable for structural use. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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16 pages, 4191 KiB

Open AccessArticle

Deep Learning-Based Microscopic Damage Assessment of Fiber-Reinforced Polymer Composites

by Muhammad Muzammil Azad, Atta ur Rehman Shah, M. N. Prabhakar and Heung Soo Kim

Materials 2024, 17(21), 5265; https://doi.org/10.3390/ma17215265 - 29 Oct 2024

Viewed by 696

Abstract

Fiber-reinforced polymers (FRPs) are increasingly being used as substitutes for traditional metallic materials across various industries due to their exceptional strength-to-weight ratio. However, their orthotropic properties make them prone to multiple forms of damage, posing significant challenges in their design and application. During the design process, FRPs are subjected to various loading conditions to study their microscopic damage behavior, typically assessed through scanning electron microscopy (SEM). While SEM provides detailed insights into fracture surfaces, the manual analysis of these images is labor-intensive, time-consuming, and subject to variability based on the observer’s expertise. To address these limitations, this research proposes a deep learning-based approach for the autonomous microscopic damage assessment of FRPs. Several computationally efficient pre-trained deep learning models, such as DenseNet121, NasNet Mobile, EfficientNet, and MobileNet, were evaluated for their performance in identifying different damage modes autonomously, thus reducing the need for manual interpretation. SEM images of FRPs with five distinct failure modes were used to validate the proposed method. These failure modes include three fiber-based failures such as fiber breakage, fiber pullout, and mixed-mode failure, and two matrix-based failures such as matrix brittle failure and matrix ductile failure. The entire dataset is divided into train, validation, and test sets. Deep learning models were established by training on train and validation sets for five failure modes, while the test set was used as the unseen data to validate the models. The models were assessed using various evaluation metrics on an unseen test dataset. Results indicate that the EfficientNet model achieved the highest accuracy of 97.75% in classifying the failure modes. The findings demonstrate the effectiveness of employing deep learning techniques for microscopic damage assessment, offering a more efficient, consistent, and scalable solution compared to traditional manual analysis. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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21 pages, 3647 KiB

Open AccessArticle

Constitutive Damage Model for Rubber Fiber-Reinforced Expansive Soil under Freeze–Thaw Cycles

by Rongchang Wang, Zhongnian Yang, Xianzhang Ling, Wei Shi, Zhenxing Sun and Xipeng Qin

Materials 2024, 17(20), 4979; https://doi.org/10.3390/ma17204979 - 11 Oct 2024

Viewed by 1034

Abstract

To elucidate the degradation mechanism of expansive soil–rubber fiber (ESR) under freeze–thaw cycles, freeze–thaw cycle tests and consolidated undrained tests were conducted on the saturated ESR. The study quantified the elastic modulus and damage variables of ESR under different numbers of freeze–thaw cycles and confining pressure, and proposed a damage constitutive model for ESR. The primary findings indicate that: (1) The effective stress paths of ESR exhibit similarity across different numbers of freeze–thaw cycles, the critical stress ratio slightly decreased by 8.8%, while the normalized elastic modulus experienced a significant reduction, dropping to 42.1%. (2) When considering the damage threshold, the shear process of ESR can be divided into three stages: weak damage, damage development, and failure. As strain increases, the microdefects of ESR gradually develop, penetrating macroscopic cracks and converging to form the main rupture surface. Eventually, the damage value reaches 1. (3) Due to the effect of freeze–thaw cycles, initial damage exists for ESR, which is positively correlated with the number of freeze–thaw cycles. The rubber fibers act as tensile elements, and the ESR damage evolution curves intersect one after another, showing obvious plastic characteristics in the late stage of shear. (4) Confining pressure plays a role in limiting the development of ESR microcracks. The damage deterioration of ESR decreases with an increase in confining pressure, leading to an increase in ESR strength. (5) Through a comparison of the test curve and the theoretical curve, this study validates the rationality of the damage constitutive model of ESR under established freeze–thaw cycles. Furthermore, it accurately describes the nonlinear impact of freeze–thaw cycles and confining pressure on the ESR total damage. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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21 pages, 11489 KiB

Open AccessArticle

Experimental Investigations on the Application of Natural Plant Fibers in Ultra-High-Performance Concrete

by Linus Joachim and Vincent Oettel

Materials 2024, 17(14), 3519; https://doi.org/10.3390/ma17143519 - 16 Jul 2024

Cited by 4 | Viewed by 1776

Abstract

Due to its high strength, the use of ultra-high-performance concrete (UHPC) is particularly suitable for components subjected to compressive loads. Combined with its excellent durability, UHPC can be used to produce highly resource-efficient components that represent a sustainable alternative to conventional load-bearing structures. Since UHPC fails in a brittle manner without the addition of fibers, it is typically used in conjunction with micro steel fibers. The production of these steel fibers is both expensive and energy-intensive. Natural plant fibers, due to their good mechanical properties, cost-effective availability, and inherent CO₂ neutrality, can provide a sustainable alternative to conventional steel fibers. Thanks to the low alkaline environment and dense matrix of UHPC, the use of natural plant fibers in terms of durability and bond is possible in principle. For the application of natural plant fibers in UHPC, however, knowledge of the load-bearing and post-cracking behavior or the performance of UHPC reinforced with natural plant fibers is essential. Currently, there are no tests available on the influence of different types of natural plant fibers on the load-bearing behavior of UHPC. Therefore, five series of compression and bending tensile tests were conducted. Three series were reinforced with natural plant fibers (bamboo, coir, and flax), one series without fibers, and one series with steel fibers as a reference. Under compression loads, the test specimens reinforced with natural plant fibers did not fail abruptly and exhibited a comparable post-failure behavior and damage pattern to the reference specimens reinforced with steel fibers. In contrast, the natural plant fibers did not perform as well as the steel fibers under bending tensile stress but did show a certain post-cracking bending tensile strength. A final life cycle assessment demonstrates the superiority of natural plant fibers and shows their positive impact on the environment. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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26 pages, 7235 KiB

Open AccessArticle

Influence of Confining Element Stiffness on the In-Plane Seismic Performance of Confined Masonry Walls

by Muhammad Mubashir Ajmal, Asad Ullah Qazi, Ali Ahmed, Ubaid Ahmad Mughal, Syed Minhaj Saleem Kazmi and Muhammad Junaid Munir

Materials 2024, 17(13), 3100; https://doi.org/10.3390/ma17133100 - 25 Jun 2024

Cited by 1 | Viewed by 844

Abstract

Confined masonry (CM) construction is being increasingly adopted for its cost-effectiveness and simplicity, particularly in seismic zones. Despite its known benefits, limited research exists on how the stiffness of confining elements influences the in-plane behavior of CM. This study conducted a comprehensive parametric analysis using experimentally validated numerical models of single-wythe, squat CM wall panels under quasi-static reverse cyclic loading. Various cross-sections and reinforcement ratios were examined to assess the impact of the confining element stiffness on the deformation response, the cracking mechanism, and the hysteretic behavior. The key findings included the observation of symmetrical hysteresis in experimental CM panels under cyclic loading, with a peak lateral strength of 114.3 kN and 108.5 kN in push-and-pull load cycles against 1.7% and 1.3% drift indexes, respectively. A finite element (FE) model was developed based on a simplified micro-modeling approach, demonstrating a maximum discrepancy of 2.6% in the peak lateral load strength and 5.4% in the initial stiffness compared to the experimental results. The parametric study revealed significant improvements in the initial stiffness and seismic strength with increased depth and reinforcement in the confining elements. For instance, a 35% increase in the lateral strength was observed when the depth of the confining columns was augmented from 150 mm to 300 mm. Similarly, increasing the steel reinforcement percentage from 0.17% to 0.78% resulted in a 16.5% enhancement in the seismic strength. These findings highlight the critical role of the stiffness of confining elements in enhancing the seismic performance of CM walls. This study provides valuable design insights for optimizing CM construction in seismic-prone areas, particularly regarding the effects of confining element dimensions and reinforcement ratios on the structural resilience. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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22 pages, 7923 KiB

Open AccessArticle

Mechanical, Durability, and Microstructure Assessment of Wastepaper Fiber-Reinforced Concrete Containing Metakaolin

by Mohammad Valizadeh Kiamahalleh, Aliakbar Gholampour, Mohsen Rezaei Shahmirzadi, Tuan D. Ngo and Togay Ozbakkaloglu

Materials 2024, 17(11), 2608; https://doi.org/10.3390/ma17112608 - 28 May 2024

Cited by 3 | Viewed by 1026

Abstract

This study evaluates the potential use of discarded plasterboard paper as fibers from buildings to reinforce concrete. Various concentrations of wastepaper fibers (0.5%, 1%, 1.5%, 2%, and 2.5% by weight of the binder) were investigated in this research. To mitigate the water absorption effect of the paper fibers, metakaolin was employed as a partial cement replacement. The results demonstrate that the inclusion of the wastepaper fiber enhances the mechanical and durability performance of the concrete. The optimal fiber proportion was identified as 1%, leading to a 29% increase in the compressive strength, a 38% increase in the splitting tensile strength, a 12% decrease in the water absorption, and a 23% decrease in the drying shrinkage with respect to the concrete containing 20% metakaolin. However, exceeding this optimal fiber content results in decreased mechanical and durability properties due to the fiber agglomeration and non-uniform fiber distribution within the concrete matrix. Based on the microstructural analysis, the improved performance of the concrete is ascribed to decreased porosity, more refined pore structure, and reduced propagation of microcracks within the concrete matrix in the presence of wastepaper fiber. According to the results, concrete containing 20% metakaolin and 1% wastepaper fiber exhibits durability and mechanical properties comparable to those of the traditional concrete. This finding highlights the significant promise of reducing dependency on conventional cement and incorporating suitable recycled materials, such as discarded plasterboard, and secondary by-products like metakaolin. Such a strategy encourages the preservation of resources, reduction in carbon dioxide emissions, and a decrease in the ecological footprint resulting from concrete production. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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25 pages, 10159 KiB

Open AccessArticle

Mechanical and Durability Characterization of Hybrid Recycled Aggregate Concrete

by Rashid Hameed, Muhammad Tahir, Safeer Abbas, Haseeb Ullah Sheikh, Syed Minhaj Saleem Kazmi and Muhammad Junaid Munir

Materials 2024, 17(7), 1571; https://doi.org/10.3390/ma17071571 - 29 Mar 2024

Cited by 6 | Viewed by 1338

Abstract

The recycling of construction and demolition waste (CDW) for the extraction of recycled concrete aggregates (RCAs) to be used to produce recycled aggregate concrete (RAC) is widely acknowledged internationally. However, CDW not only contains concrete debris but may also contain burnt clay bricks. The recycling of such CDW without the segregation of different components would result in recycled aggregates having different proportions of concrete and brick aggregates. The utilization of these aggregates in concrete requires a detailed investigation of their mechanical and durability properties. In this regard, the present study focused on investigating the mechanical and durability properties of hybrid recycled aggregate concrete (HRAC) made by the 100% replacing of natural aggregates with recycled brick (RBAs) and RCA in hybrid form. The partial replacement of cement with fly ash was also considered to reduce the corban footprint of concrete. An extensive experimental program was designed and carried out in two phases. In the first phase, a total of 48 concrete mixes containing coarse RBA and RCA in mono and hybrid forms were prepared and tested for their compressive strength. The test results indicated that the compressive strength of HRAC is greatly affected by the proportion of coarse RBA and RCA. In the second phase, based on the results of the first phase, eight concrete mixes with the most critical proportions of RBA and RCA in hybrid form were selected to evaluate their mechanical and durability performance. In addition, four mixes with natural aggregates were also prepared for comparison purposes. To evaluate the mechanical properties of the concrete mixes, compressive strength and modulus of rupture (MOR) tests were performed, while for the evaluation of durability properties, water absorption and behavior after exposure to aggressive conditions of acidic and brine solutions were studied. The results revealed that a 20% replacement of cement with fly ash resulted in acceptable mechanical and durability properties of HRAC intended to be used for making concrete bricks or pavers. Full article

(This article belongs to the Special Issue Advances in Experimental Investigation and Computational Modeling of Fiber Reinforced Polymers and Composites)

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