Fiber-reinforced Composites Research Articles

Improving the joint strength of thermoplastic composites joined by press joining using laser-based surface treatment

Fibre-reinforced thermoplastic composites (TPC) provide an automated and cost-effective solution for their use in lightweight structures in series production. The combination of different material configurations allows the design of highly stress tolerant components. Previous studies demonstrated that the combination of TPC sheets, TPC hollow profiles and injection moulding compounds is even suitable for crash-relevant automotive parts. All three components are combined during the injection moulding process. To prevent collapse, the part must remain in a consolidated state and cannot be preheated. However, this results in poor adhesion between the hollow profile, the bulk material, and the TPC sheet. Previous studies have shown that the bonding strength between the hollow profile and the injection moulding compound can be increased by surface pre-treatment using laser structuring and plasma technology. In this work, laser structuring is employed to enhance the bonding strength between the hollow profile and the TPC sheet. Microscopy analysis is used to investigate the resulting surface morphology. Subsequently, single-lap-shear (SLS) specimens are produced by pressing the TPC sheets onto the flat part. The resulting bonding strengths are then evaluated by tensile shear tests. The study analyses the impact of various pre-treatment parameters on the bonding strength. Furthermore, it investigates the effect of sheet temperature on the bonding strength, including specimens without pre-treatment. Finally, the results of the surface treatment of hollow composite profiles are discussed.

Effects of nozzle geometry and fiber orientation on the tensile strength of 3D printed continuous fiber reinforced composites

In material extrusion (MEX) based 3D printing, inter-filament voids are intrinsic to printing process. The void orientation, volume and shape are affected by multiple factors including the nozzle shape, stacking sequence and printing direction. In this study, the adverse effects of the inter-filament voids on tensile properties and damage modes were investigated numerically on 3D printed acrylonitrile butadiene styrene-carbon fiber (ABS/CF) continuous fiber-reinforced composites (CFRCs). Uniaxial tensile simulations were performed considering various nozzle geometries (circular, square), fiber orientations (θ=0o,30o,45o,60o,90o) relative to loading direction, and a regular stacking sequence of extrudates. The extrudate cross-section was modeled either using elliptical or superelliptical extrudates deposited from a circular or square nozzle, respectively. Excellent agreement was seen when the simulated results were benchmarked against several published experimental and numerical work. Simulated results showed that changing the nozzle shape from circular to square improved the mechanical properties across all fiber angles by lowering the void content by 7−8% and increasing the ultimate tensile strength (σT) by 11−18%, tensile stiffness (ET) by 6−8%, and the tensile failure strains (ϵT,fail) by 1−11%. For superelliptical extrudates the number of observed damage modes also reduced, and this is due to a 37.2% and 58.2% improvement in the inter-filament and inter-layer bond lengths, respectively. Also, when fiber angle became increasingly off-axis to tensile load direction, the strengths, moduli, and failure strains reduced for both circular and square nozzles. The significance of using microstructure geometries and explicitly modeling inter-filament voids for simulating MEX printed CFRCs was highlighted by comparing these results with both analytical calculations and simulated results of homogeneous solid CFRC blocks without voids.

Process-structure–property study of 3D-printed continuous fiber reinforced composites

3D-printed fiber-reinforced composites hold many advantages compared to conventional composites in terms of individualization, mass customization, design freedom, and tailoring the composite geometry to load-bearing specifications. Among candidate continuous fibers for reinforcement, basalt fibers (BFs) serve as an eco-friendly alternative with excellent physical and thermal properties. However, the applicability of continuous BFs to be used for 3D-printed polymer composites was rarely addressed in existing literature. Especially, the effects of impregnation density during manufacturing and the influence of local fiber distribution on the fracture behavior of BF-reinforced composites remain unclear. In this study, a solution coating process was employed as a fiber pre-treatment to improve the packing density of BF in a polylactide (PLA) matrix. The effects of the resulting fiber volume fraction (8–31 %) and the local fiber distribution on the tensile fracture mechanisms of 3D printed BF/PLA samples are thoroughly analyzed using three-dimensional X-ray tomography. It was found that at a concentration of 3 wt-%, the coating solution uniformly dispersed optimally between the fibers, resulting in improved impregnation densities of the BF in the PLA matrix. Thus, the resulting composite exhibited a tensile strength of 175 MPa and a Young’s modulus of 6.2 GPa, respectively. A viscoelastic constitutive model incorporating damage is used for property prediction within a composite design framework to be applied to 3D-printed BF/PLA structures. The model is validated with experimental data from tensile tests. The obtained results demonstrate the applicability of eco-friendly BF/PLA composites for 3D printing of industrial high-performance applications with an individualized property profile.

A study on interactive fiber rubber composite structures subjected to bend-twist coupling

Abstract This paper investigates the deformation behavior of shape memory alloy (SMA)-integrated fiber-reinforced composites, with an emphasis on how different fiber orientations influence bend-twist coupling. The study combines experimental analysis, finite element simulations using Ansys, and analytical modeling via Classical Laminate Theory (CLT) to assess the mechanical response of these composites. The experiments revealed that composites with higher fiber angles (60°) exhibited dominant twisting behavior, while those with lower angles (30° and 45°) showed more pronounced bending deformation. The simulations corroborated these trends, offering detailed insights into the displacement behavior. The CLT model further predicted a decrease in deflection with increasing fiber angles, which was consistent with experimental results, although some deviations in Z-deformation were attributed to material and manufacturing factors. This research highlights the critical role of fiber orientation in achieving desired deformations in SMA-integrated composites, offering valuable insights for the design of adaptive structures. The findings demonstrate the potential for optimizing fiber configurations to tailor bend-twist coupling in advanced composite applications.

Efficient property-oriented design of composite layups via controllable latent features using generative VAE

Fiber-reinforced composites provide substantial tailoring potential, while the extensive parameters and complex coupling mechanisms pose formidable challenges to layup designs. This paper presents an efficient inverse design framework for composite layups utilizing a variational autoencoder (VAE), which is applicable to non-conventional laminates. By leveraging the VAE's exceptional feature extraction and generative capabilities, the decoder rapidly produces layups with desired properties through controllable feature vectors. Based on the stacking characteristics of layups, multi-scale one-dimensional convolutions precisely extract sequence features relevant to mechanical properties and specific manufacturing constraints. A customized loss function is formulated to constrain the latent features, while addressing the non-uniqueness problem for layups with certain mechanical properties. The developed property-oriented VAE can generate 100,000 layups in seconds, achieving an average success rate of 66.9% under comprehensive in-plane and bending stiffness design, and remains effective for 100-ply thick laminate. For comparison, the VAE model outperforms the genetic algorithm and the logic-based method in reinforced panel designs, reducing the retrieval error by 46.4% and 38.1%, respectively. The proposed approach demonstrates flexible and efficient design advantages using generative machine learning models, and is easily extendable to other inverse design scenarios.

An ANN-based concurrent multiscale damage evolution model for hierarchical fiber-reinforced composites

In this paper, an ANN-based concurrent multiscale damage evolution model is proposed, which is able to investigate the complex failure behaviors of hierarchical fiber-reinforced composites. In the framework of the proposed model, yarn damage evolution laws at the mesoscale are indirectly derived from the microscale representative volume element (RVE), using artificial neural networks (ANNs) as a surrogate model. A homogenized characterization method is proposed to derive the homogenized damage variables. The homogenized strain and damage variables of the microscale RVE are taken as inputs and outputs in ANNs, respectively. The dataset is generated by combining clustering with the finite element simulation. A typical kind of plain-woven composite is adopted as a benchmark material for numerical implementation and experimental verification. The numerical predictions, including the tensile properties and damage evolution, are consistent with the results from quasi-static tension experiments.

Examining the effect of the shear coefficient on the prediction of progressive failure of fiber-reinforced composites

The ultimate damage of composites under tension usually results from fiber damage, which includes both tensile and shear contributions. In this study, the shear coefficient α of the fiber yarn is incorporated into the failure criterion to consider the shear effect of the fiber yarn. An analytical model is then proposed that combines a homogenization method and the enhanced failure criterion to facilitate quick evaluation of the progressive damage and failure of the composite. The sensitivity of α on the behaviors of progressive damage and failure are comprehensively explored for different types of fiber-reinforced composites, including a laminate, a plain weave composite, a two-dimensional triaxially braided composite, and a three-dimensional woven composite. The results indicate that damage and failure behaviors are generally sensitive to the shear coefficient, and composites with more complex textile structure demonstrates greater sensitivity to the α. An analysis of the sensitivity of α for different failure criteria was also conducted, and the results reveal that the Hashin–Hou criterion shows more sensitivity to α than the Chang–Chang criterion, the Hoffman criterion, or the Tsai–Wu criterion. Therefore, the identification of the shear coefficient is significant for exploring the damage and failure behaviors of fiber-reinforced composites.

Vacuum Chamber Infusion for Fiber-Reinforced Composites

A new approach to an automatable fiber impregnation and consolidation process for the manufacturing of fiber-reinforced composite parts is presented in this article. Therefore, a vacuum chamber sealing machine classically used in food packaging is modified for this approach—Vacuum Chamber Infusion (VCI). Dry fiber placement (DFP) preforms, made from 30 k carbon fiber tape, with different layer amounts and fiber orientations, are infused with the VCI and with the state-of-the-art process—Vacuum Assisted Process (VAP)—as the reference. VCI uses a closed system that is evacuated once, while VAP uses a permanently evacuated open system. Since process management greatly influences material properties, the mechanical properties, void content, and fiber volume fraction (FVF) are analyzed. In addition, the study aims to identify how the complexity of a resin infusion process can be reduced, the automation potential can be increased, and the number of consumables can be reduced. Comparable material characteristics and a reduction in consumables, setup complexity, and manufacturing time by a factor of four could be approved for VCI. A void content of less than 2% is measured for both processes and an FVF of 39% for VCI and 45% for VAP is achieved.

Physical, Mechanical and Thermal Characterization of Areca, Pineapple and Glass Fiber Reinforced Polymer Composites for Aerospace Applications

In the current scenario, the focus on applying natural fiber-reinforced polymer composites in aerospace applications has increased tremendously due to their attractive characteristics such as lightweight, higher strength-to-weight ratio, good thermal stability at environmental temperatures, resistance to corrosion, sound absorbing capability and increased fuel efficiency. Further, studies on Bi-directionally oriented fiber composites have more advantages than the random or unidirectional orientation, such as uniform stress distribution and improved bonding at the interface. So, the present work focuses on using the Areca, Pineapple Leaf Fiber (PALF) and Glass fiber as the bi-directional fiber mat for reinforcing it into Epoxy polymer. The three different materials were fabricated by changing the fiber type with constant volume fraction and orientation. The martial characterization was done on the fabricated composites in order to evaluate their orientation effectiveness through density, moisture absorption, tensile, impact, hardness and thermal degradation. The bonding relationship was analyzed through a Scanning Electron Microscope. The results showed that the properties obtained were higher for the PALF composite than the areca composites due to the fact that the higher surface area of PALF fibers is confirmed through SEM analysis.

Material removal and damage formation mechanisms induced by periodic indentation during ultrasonic vibration-assisted scratching of SiCf/SiC composites

Fiber-reinforced ceramic matrix composites (CMCs) exhibit high hardness, brittleness, heterogeneity, and anisotropy. This study explores the material removal and damage formation mechanisms during ultrasonic vibration-assisted scratching of SiCf/SiC composites through experimental and micro-finite element simulations. The research reveals that high-frequency periodic indentation-separation of abrasive grain influences stress transfer and crack propagation, which are affected by the interfacial layer and fiber orientation. Crack deflection plays a crucial role in material removal and determines the amplitude of normal scratching force. Stress transfer interference primarily governs damage formation, with more severe damage occurring along the longitudinal and transverse fiber directions due to secondary stress concentration and crack deflection. In contrast, scratching along the perpendicular fiber direction requires higher normal forces due to residual adjacent phase materials, but results in more controlled material removal and less damage. The study provides insights into optimizing the ultrasonic vibration-assisted machining of CMCs to minimize damage.

Chemically Degradable Vitrimers Based on Divanillin Imine Diepoxy Monomer and Aliphatic Diamines for Enhanced Carbon Fiber Composite Applications

This study presents the development of a diglycidyl monomer containing two imine groups that can act as dynamic and reversible bonds. During the curing of the monomer with two different amine hardeners, we confirmed the formation of new imine groups due to the transamination reaction between the imine groups of the diepoxy monomer with the amine groups of the hardener. The effect of this structural change was observed in the stress relaxation behavior, resulting in the overlapping of two different relaxation modes. The analytical modelling was able to extract two distinct characteristic relaxation times using a double-element Maxwell model. A second characterization of the stress relaxation process by frequency sweep experiments was performed to corroborate the results obtained, confirming speedy stress relaxation. Acid-catalyzed hydrolysis was performed on the studied materials, demonstrating the complete degradation of the network. We finally confirmed that the synthesized diepoxy compound is suitable for preparing carbon-fiber-reinforced composite materials, demonstrating easy fiber impregnation, fast reshaping, and especially a total degradation of the polymer matrix that allows for the recovery of the carbon fibers in mild conditions. This epoxy–amine system is an excellent candidate for overcoming the traditional limits of thermosets in preparing fiber-reinforced composites.

Analysis of compact tension specimens with deflected cracks for orthotropic materials

Anisotropic materials, such as alloy, wood and fiber-reinforced composites, are widely used in load-bearing components. Accurately obtaining its fracture performance is crucial for safety assessment. However, existing testing methods based on compact tension (CT) specimen have not taken into account material anisotropic characteristics and crack deflection. In this work, the systematic finite element analysis (FEA) was conducted for CT specimens with deflected cracks made of orthotropic materials. A wide range of geometric (crack deflection angle, β, and ratio of crack length to width, ap/W) and orthotropic material (λ and ρ) parameters were discussed. Complete solutions of the stress intensity factor (KI and KII) and load-line compliance (C) were determined for the first time. The results showed that the geometric dimensions and material parameters have a significant coupling influence on the fracture parameters. The influence of the λ is generally greater than that of the ρ. Changes of material parameters can make fracture parameters’ dependence on β vary. The variation of β and ap/W could enlarge or minish even dismiss the impact of λ and ρ. In addition, to further verify the importance of the obtained fracture parameters, the CT fracture tests of carbon fiber-reinforced epoxy resin under various orientations were conducted. The solutions will promote the optimization of the fracture toughness testing standards for CT specimens made of anisotropy materials.

Optimizing dielectric constant of noncommercial biobased fibres - Acacia Nilotica, Acacia Leucophloea and Prosopis juliflora - For composite applications with selected fillers

In recent decades, most electrical/electronic products possess non – biodegradable components. The expanding consumption of these goods and their eventual disposal pose a serious environmental threat. To cope up with this issue, biodegradable electrical/electronic components using biobased fibres can be an alternative option. The novel exploration of this research work is the usage of underutilized biobased fibres, such as Acacia Nilotica, Acacia Leucophloea and Prosopis Juliflora, as sustainable alternatives to traditional synthetic fibres in natural fibre-reinforced epoxy composites. The novelty lies in the combination of these natural fibres with ceramic fillers like Silicon Carbide, Boron Nitride and Aluminium Oxide, aiming to enhance the composite properties. The objective of the study is to optimize the type of fibre, fibre content (2 wt%, 4 wt% and 6 wt%) and types of fillers (1 wt%) combinations using the Box-Behnken Design to improve the dielectric properties of these composites. Analysis of Variance (ANOVA) is used to evaluate the relevance of each parameter on dielectric constant of the biobased fibre reinforced epoxy composite. The significant outcome is identified that Prosopis Juliflora (6 wt%) combined with Boron Nitride (1 wt%) yields an optimal dielectric constant of 1.11, highlighting the potential of these biobased fibres to serve as effective substitutes for conventional glass and carbon fibres for electrical insulating materials used in switchboards and socket pins to prevent electrical conduction and ensure safety. This research not only contributes to the field of sustainable materials but also addresses critical environmental concerns associated with electric/electronic waste.

An Improved Mampel Model of the Non-Isothermal Crystallization Kinetics of Fiber-Reinforced Thermoplastic Composites.

Fiber-reinforced thermoplastic composites (FRTPs) are gaining increasing attention and widespread use in engineering applications due to their high specific strength and stiffness, excellent toughness, and recyclability. The mechanical properties of these composites are closely tied to their crystallization process, making it crucial to accurately describe this phenomenon. Existing theoretical models for analyzing the non-isothermal crystallization of thermoplastic composites often face challenges relating to the complexity of obtaining multiple parameters and the difficulty of achieving a final relative crystallinity of 1. To address these issues, this paper introduces a novel functional form of the crystallization rate parameter K(T), tailored for engineering applications, and proposes an improved Mampel model. This model assumes K(T) to be zero before the onset of crystallization and also to be linearly dependent on temperature thereafter, ensuring that the final relative crystallinity reaches 1. The model requires only two easily accessible parameters: the initial crystallization temperature (Ts) and the linear slope (k). The simplicity of the model makes it particularly well suited to engineering applications. This provides a straightforward and effective tool for describing the non-isothermal crystallization kinetics of fiber-reinforced thermoplastic composites.

Enhancing flame retardancy and mechanical strength of glass fiber-reinforced biomass polyamide composites with surface-functionalized black phosphorus

Fiber-reinforced polyamide exhibits exceptional mechanical properties and durability; however, its widespread application is impeded by potential fire hazards. In this study, a hybrid material consisting of black phosphorus (BP) and polyhedral oligomeric silsesquioxane (POSS) was synthesized, denoted as BP-CO-POSS. The fire safety of fiber-reinforced polyamide demonstrated significant enhancement upon the incorporation of aluminum diethyl phosphinate (Alpi) and BP-CO-POSS. This enhancement was evident in various aspects, including the suppression of heat release behaviors, reduction in the emission of toxic gases, and an increase in the UL-94 rating. Notably, with the additional inclusion of 0.5 wt% BP-CO-POSS, a substantial decrease in both heat release rate (31.15 %) and total heat release (37.59 %) was observed when compared to the application of Alpi and BP alone, thus affirming the existence of a synergistic effect. This observation was substantiated through a comprehensive analysis of results obtained from both gas and condensed phases. This study offers a practical methodology for the widespread utilization of phosphorus-rich advanced materials, thereby further enhancing the fire safety of fiber-reinforced polymers.

Exploring mechanical properties of eco-friendly hybrid epoxy composites reinforced with sisal, hemp, and glass fibers

It is now widely accepted that various subsets of hybrid fiber composites reinforced with combined natural and synthetic fibers can significantly expand the applicability of composite-based materials in design and technology practice. The already existing unnatural circumstances on the planet put natural fibers far ahead of traditions in the field of materials thanks to their biodegradability characteristics, availability and over-term endurance and corrosion resistance. At the same time, composites are rapidly taking their place in many industries and sectors of the economy as metals in as much as it is economically and energetically justified. This study evaluates the mechanical properties of hybrid composites reinforced with glass, hemp, and sisal fibers. Using a hand lay-up method with epoxy resin, composite laminates were fabricated and tested for tensile, flexural, impact strengths and hardness test in accordance with ASTM standards. The experimental results revealed that glass-sisal fiber composites achieved the highest tensile strength of 69.1 MPa, while glass-hemp-sisal fiber composites exhibited superior flexural strength of 15.22 MPa and impact strength of 137.45 kJ/m2 while best hardness value was 24.73 HV for glass-sisal fibre composite. These findings underscore the potential of glass-sisal-hemp fiber-reinforced epoxy composites as viable alternatives to traditional synthetic fiber-reinforced materials in automotive industry where there are no structural loadings i.e. automobile interiors; offering enhanced mechanical performance and sustainability.

Neural Network Prediction and Enhanced Strength Properties of Natural Fibre-Reinforced Quaternary-Blended Composites

Neural Network Prediction and Enhanced Strength Properties of Natural Fibre-Reinforced Quaternary-Blended Composites

Low-velocity impact (LVI) and compression after impact (CAI) of Double-Double composite laminates

Tailorability is a key advantage of fiber-reinforced composites over other material systems. While tailoring a single isolated laminate is relatively simple, challenges arise when designing larger integrated components while ensuring compatibility between laminates and avoiding sharp changes in local stiffness. The innovative Double-Double (DD) laminate design method simplifies the optimization and processing of laminates by incorporating 4-ply building blocks consisting of +ϕ, −ϕ, +ψ, and −ψ ply orientations. As a relatively new concept, DD laminate design requires careful assessment to ensure its performance is equivalent to that of conventional designs. The current study compares impact damage tolerance of quadriaxial (QUAD) laminates consisting of 0°, 90°, and ±45° ply orientations with equivalent DD laminates under Low-Velocity Impact (LVI) and Compression After Impact (CAI) loadings. To this end, a validated three-dimensional high-fidelity finite element model capable of capturing fiber breakage, splitting, kinking, as well as matrix cracking and delamination, was used. A computer tool was developed to identify equivalent DD laminates and to find the best stacking sequence for achieving layup homogenization. Three equivalent DD laminates were selected for the [0/45/90/−45]4s. The first laminate had an equal in-plane stiffness [A] matrix ([67.5/–22.5/22.5/−67.5]8T), the second laminate had an equal flexural stiffness [D] matrix ([64.5/−17/17/−64.5]8T), and the third laminate ([65.5/−18.5/18.5/−65.5]8T) had a similar [D] matrix while keeping the difference between each element of [A] matrices below 10 %. The results indicate that the QUAD laminates can be replaced by equivalent DD without compromising impact damage tolerance while benefiting from the improved design and manufacturing ease of the DD laminate configuration.

The Role of Glass Fiber-reinforced Composites in Maxillary Fracture Repair

The Role of Glass Fiber-reinforced Composites in Maxillary Fracture Repair

Bacterial adhesion and surface roughness of particulate-filled and short fiber-reinforced composites.

The objective of the study was to assess the initial adhesion of Streptococcus mutans (S. mutans) and surface roughness of different particulate-filled (PFC) and short fiber-reinforced (SFRC) composites. Five PFC composites (CeramX Universal, Filtek Universal, Omnichroma, Tetric Prime and Venus Diamond) and four SFRC composites (everX Posterior, everX Flow Bulk, everX Flow Dentin and experimental packable SFRC) were tested in this study. A non-contact 3D profilometer was employed to assess the surface roughness (Ra) of the polished specimens (using 4000-grit abrasive paper). For the bacterial adhesion test, the specimens (n = 5/group) were immersed in a solution of S. mutans to facilitate initial adhesion. To determine the number of cells on the surfaces of the discs as colony-forming units (CFU), the vials holding the microbial samples were highly agitated using a vortex machine. Subsequently, the samples were diluted multiple times and anaerobically incubated for 48h at 37°C on Mitis Salivarius Agar plates (Difco) supplemented with bacitracin. Bacterial adherence assessment was performed using SEM. The data were analyzed using ANOVA. All tested PFC and SFRC composites showed similar adhesion of S. mutan. The lowest Ra values (0.26µm) (p < 0.05) were found in the flowable SFRCs (everX Flow Bulk & Dentin), while the highest values (p < 0.05) were observed in CeramX and everX Posterior (0.42µm). Experimental SFRC had comparable Ra value (0.38µm) than other commercial composites. The presence of short microfibers in the composite appeared to have no adverse effects on the initial adhesion of bacteria or the surface roughness.