Fiber Volume Fraction Research Articles

A creep/recovery model of dry fiber fabric during compaction considering temperature and in‐plane tension

AbstractIn the manufacturing of fiber‐reinforced composite materials, the preforming stage of dry fiber fabric entails compaction operations carried out under constant pressure, a specific preforming temperature, and in‐plane tension. Throughout this process, permanent deformation and creep/recovery behavior are observed in the fabric, correlating with factors such as time, sustained pressure, temperature, and in‐plane tension. Effective control of fiber volume fraction and material composition necessitates a thorough comprehension of these phenomena as well as the capacity to predict them with accuracy. To solve this, a viscoelastic‐plastic model was put forth, which provides an account of the viscous effects on the fabric during its stages of compression and recovery. The proposed model incorporates changed Burgers units to manage time‐dependent deformations and plastic units to address permanent deformations. Through the application of a single set of parameters, the model precisely and comprehensively characterizes through‐thickness creep/recovery behavior of preformed dry fiber fabrics under varying conditions, including creep stress, temperature, and in‐plane tension. To enhance the practical utility of the model, an application has been developed and validated against experimental data conducted under diverse test conditions. The results demonstrate consistency between experimental curves and model‐predicted curves across various compression scenarios.Highlights A viscoelastic‐plastic model was proposed with a single parameter set. Stress, temperature, and in‐plane tension all exacerbated creep/recovery. Model captures temp. and time‐related creep/recovery with in‐plane tension. The model has been transformed into a practical application tool.

Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers

Abstract This study combines two types of waste materials to achieve sustainable lightweight concrete (LWC) including agricultural and industrial wastes that hold high potential to reduce global environmental pollution. A novel application of 35% treated date seed (DS) wastes as partially replaced by volume to natural coarse aggregate in producing sustainable LWC was investigated. Calcium hydroxide solution was utilized as a treatment to extract cellulose from the achieved hemicelluloses of the DS. Fourier transform infrared spectroscopy was utilized to analyze the structural characteristics of the isolated cellulosic samples before and after treatment. Then different volume fractions of steel fibers (0.5, 0.75, and 1%) recycled from scrap tires were added to the LWC with 35% DS. Several experimental tests, including slump test, compressive strength, oven-dry density, split tensile strength, flexural strength, and water penetration depth, were carried out in this investigation. The results demonstrate that concrete containing 35% DS and reinforced with 1% recycled steel fibers show enhancement in the compressive, tensile, and flexural strengths by about 15.2, 32.6, and 58.2%, respectively, and reduces the permeability by 16.1% relative to the reference concrete mixture.

Flexural performance of bamboo fiber‐reinforced concrete mixed with seawater and sea sand

AbstractIn the face of the huge consumption of fresh water and river sand by the concrete industry and the poor flexural performance of plain concrete, it is theoretically feasible and environmentally friendly to use bamboo fiber as a replacement to reinforce concrete mixed with seawater and sea sand. In this research, taking the volume fraction (0.6%, 1.2%, and 2.4%), aspect ratio (10, 20, and 30) and diameter (1.0, 1.5, and 2.0 mm) of bamboo fibers as parameters, 15 groups of bamboo fiber‐reinforced concrete (BFRC) prisms and one control group of plain seawater sea sand concrete prisms were subjected to four‐point bending test, followed by analyzing the crack pattern, ultimate load, mid‐span deflection and strain. Under the condition of 1.2% volume fraction, 20 aspect ratio, 1.5 mm diameter, and 30 mm length, the maximum increase rate of flexural strength in this research was obtained, and then it was compared with that of flexural strength of concrete prisms reinforced by various natural fibers. In addition, relevant fitting equations and theoretical calculation formulas were derived, laying a foundation for the subsequent research and application of BFRC.

Synthesising realistic 2D microstructures of unidirectional fibre-reinforced composites with a generative adversarial network

The microstructure governs the behaviour of unidirectional fibre-reinforced composites. In this study, we developed a Deep Convolutional Generative Adversarial Network (DCGAN) to generate realistic 2D transverse microstructures of such composites. We evaluated the DCGAN-generated microstructures using three different methods: Fréchet inception distance, walking through the latent space, and feature matching. The results from these evaluations confirmed that the generated microstructures are distinct and not simply a replication of the training data. The generated microstructures were then compared to real microstructures, confirming that they match qualitatively and quantitatively with respect to detailed statistical characteristics, including fibre diameters, fibre volume fraction, fibre spatial distribution, and resin-rich pockets. We also found that microstructures created by traditional generators could not capture the real resin-rich pockets. This illustrates the capability and value of DCGAN to generate realistic transverse microstructures and provides insights for modelling methods based on real images.

A novel FFT framework with coupled non-local elastic-plastic damage model for the thermomechanical failure analysis of UD-CF/PEEK composites

A novel FFT-based computational framework for coupling non-local elastic-plastic damage model is proposed in this paper, which is employed to accurately simulate the transverse tensile behaviors of unidirectional (UD) CF/PEEK composite materials under different temperatures. To address the distinct material properties exhibited by different microscopic constituents within the composite, two approaches are employed: (i) an integral-type regularized traction-separation damage model is applied to the interphase debonding, and (ii) an implicit gradient regularization technique for Lemaitre-type damage (matrix cracking) of the PEEK. By coupling the non-local damage model capable of accurately characterizing different failure modes within composites with an FFT computational framework, accurate predictions of the transverse tensile performance of UD-CF/PEEK composites at different temperature conditions can be achieved. Furthermore, the influence of non-local feature parameters and interphase mechanical properties on the composite's mechanical behavior is thoroughly discussed. Comparisons with experimental results affirm the accurate prediction of the transverse tensile behavior of UD-CF/PEEK composites through the proposed computational framework. Ultimately, based on this framework, the transverse tensile modulus and strength of UD-CF/PEEK composites, considering different fiber volume fractions and temperatures, are predicted, successfully demonstrating the effectiveness and applicability of the proposed approach in forecasting the mechanical behavior of composites.

A strength optimization approach for manufacturable 3D printed variable stiffness laminates with a strain-based approximation

The 3D printed continuous carbon fiber reinforced polymers (CFRP) are promising lightweight structures with outstanding mechanical performance. In this work, we propose a structure-manufacture integrated optimization approach for strength maximization of variable stiffness 3D printed CFRP composites by tailoring the steered printing paths. The rule of mixture is modified to evaluate material properties and strength of the printed laminates considering the effect of fiber volume fraction. To make this approach applicable to CFRP with asymmetric layups, a strain-based two-level convex approximation for the failure index based on the Tsai–Wu failure criterion is proposed, which can take the tension-bending coupling effect into consideration. The local failure indices are aggregated using the p-norm formula to reduce the size of the strength optimization model. In order to guarantee the manufacturability of the optimal design, the curvature of the steered printing fiber paths is constrained using a hybrid control method within the approach. The numerical cases show that the strength enhancement of the 3D printed variable stiffness laminates depends on the load, where an improvement between 35% and 46% can be achieved under the tension. Moreover, the proposed method can not only converge stably, but also be capable of optimizing structures with complex geometry.

Short fibre/unidirectional hybrid thermoplastic composites: Experimental characterisation and digital analysis

This paper explores the use of compression moulding to produce structural hybrid composites based on short-fibre composites, combining a short-fibre core and uni-directional (UD) skins. A parametric study on processing parameters found low consolidation pressures provided a higher repeatability of the manufacturing process. The best mechanical response of the hybrid laminate was obtained through a 2-step consolidation process due to an increased fibre volume fraction. Despite a moderate 21.5% increase in cost compared to the short fibre material, the hybrid panels showed large increases in mechanical properties with an outstanding increase in flexural modulus of 330.4%. A semi-analytical constitutive model of the short fibre composite was developed to determine the variability in the mechanical response due to the stochastic microstructure. The results predicted a low scatter in strength, compatible with the requirements of structural applications. This study opens the path to the development of sustainable thermoplastic composites from recycled short-fibre compounds.

Novel method for fiber volume fraction of carbon/glass hybrid fiber composites

Because the physical properties of carbon fiber and glass fiber are very different, the fiber volume fraction in carbon/glass hybrid fiber composites cannot be tested by burning method or digestion method, respectively. Furthermore, these methods partially consume the fiber, especially for carbon fibers. To investigate the fiber volume fraction in carbon/glass hybrid fiber composites correctly, the test method is put forward. The burning method and the digestion method were combined to calculate the volume fraction of carbon fiber and glass fiber, respectively. The results show that the relative error between the measured value and the theoretical value is very small. The result of the present work implies that the feasibility and accuracy of this method through experimental verification.

VERIFICATION OF LAMINATE COMPOSITEPLATE SIMULATION UNDER COMBINED LOADINGS THERMALSTRESSES

This study deals with thermal cyclic loading phenomena of plates which were fabricated from composite materials (woven roving fiber glass + polyester) were exposed to (75 C°) temperature gradient thermal shock for ten times in different stage of conditioning times due to the effect of thermal fatigue using the method of Levy solution and compared these results with both results from experimental published work and (ANSYS Ver. 9) program. A composite laminate plate with fiber volume fraction (υf =25.076%) is selected in this study and applying the combined loadings like bending moment (Mo), and in-plane force (Nxx) beside the effect of thermal fatigue. It involves multi theoretical and finite element fields; but the theoretical one contains the derived equation of stresses distribution and evaluating the normal deflection of a middle point for dynamic analysis applying different boundary conditions for heating and cooling. The main present numerical results for a composite plate with (80%) fiber volume fraction claim that the relative reduction in normal deflection and dynamic load factor are (78.593%) and (9.421%) during cooling to (-15 respectively.

Single Curvature Bending of Structural Stitched Textile Reinforcements Part I: Experimental Work

Aerospace structural components made from polymer matrix composites (PMCs) offer numerous advantages. Their high stiffness and high strength combined with low densities enable lower fuel consumption coupled with higher payloads. As a result, PMCs provide an important economic advantage over typical metallic airframes. Textile reinforcements for PMCs are made by assembling reinforcement fibres, typically carbon. Then, the textile reinforcements are typically cut into smaller pieces, stacked, draped and assembled into a dry assembly called a preform, the shape of which generally approaches that of the PMC part to be made. This manufacturing process is labour intensive and expensive.Novel thick, net-shape, drapable, high fibre volume fraction (vf) textile reinforcements used toward manufacturing aerospace PMCs are being developed at the University of Ottawa. The technology enables the manufacturing of flat, drapable multilayered near net-shape preforms. The bending and in-plane shear behaviours of such novel thick reinforcement textiles was investigated to understand and define the behaviour of such thick fabric reinforcements when formed into required shapes. A bending apparatus was developed for investigating the bending behaviour of these novel thick reinforcement fabrics.

Study on thermal expansion coefficient and absorbing properties of fiber reinforced resin-based absorbing composites

In this paper, non-woven fabric and glass fiber fabric were used to prepare resin-based absorbing composite. The thermal expansion coefficient and the microwave absorbing properties of the absorbing composites with different glass fiber volume fraction were studied. The results show that the simulation results of the thermal expansion coefficient calculated by Schapery model are inconsistent with the experimental results, the metallographic results were studied to reveal that it is the added absorbent in the composite that partially replaced the resin at the interface between resin and fiber bundle causes the parameters of the material substituted in the Schapery model to be improper. A different simulation model was proposed to introduce a set of different parameters of the material to reduce the error between simulation and experiment results and the simulation results show that the error is reduced from a maximum of 53 % to a minimum of 3 %. Meanwhile the microwave absorbing properties show that the absorbing peaks of the composite materials move to low frequency with the increasing glass fiber volume fraction and the minimum reflection loss (RL) first increase and then decrease. The metallographic results show that the different distribution of absorbent in the composites within different reinforced fibers causes the movement of the absorbing peaks and the change of its minimum RL. Those research results lay a foundation for the further popularization and application of the absorbing composites.

Analytical assessment of wave dynamics for natural fibre-reinforced composite plates

This study presents a mathematical modelling to investigate the wave propagation behaviour in laminated natural fibre-reinforced composite plates integrated with surface bonded piezoelectric materials. To model wave dynamics, the constitutive relations, and governing equations of wave motion are derived based on different plate theories and Maxwell's electricity equation due to the surface bonded piezoelectric materials with the closed-circuit electrical boundary condition and transverse poling direction. The influence of natural fibres, as the reinforcing material of the host laminated composite plate, on wave propagation is studied and compared with the effects of synthetic fibres (i.e., carbon, Kevlar, and E-glass). The effects of other factors such as fibre volume fraction, laminate stacking sequence, and the presence of piezoelectric materials on wave dynamics are also investigated. The results of the wave propagation analysis reveal that the impact of different parameters on wave dynamics depends on the range of wavenumbers and wave mode numbers considered. It is found that some parameters may exhibit a noticeable influence on wave velocities, while others may have a negligible effect. The effect of piezoelectric materials on wave velocities in composite plates reinforced with natural fibres e.g., bamboo fibres, may differ from that observed in synthetic fibre-reinforced composite plates.

A statistical-experimental study to investigate the optimal parameters of fibres made from waste PET bottles for strengthening concrete

This research investigated using waste polyethylene terephthalate (PET) bottle fibres in concrete. Experimental tests were conducted to evaluate the mechanical properties of PET fibre-strengthened concrete. The effects of the fibre volume fraction and fibre length were studied to obtain optimal values. Moreover, a thorough statistical analysis was performed to identify the parameter that impacts the inclusion of PET fibres in concrete. Furthermore, the study explored the effect of PET fibres on reinforced concrete beams of shear failure mode. The results showed that incorporating PET fibres significantly enhances the ductility of the concrete material and reduces shrinkage. It also promotes the initial stiffness, the inelastic absorbed energy and the ductility of steel-reinforced concrete beams.

Investigation of shear response due to variation of fiber volume fraction, transverse steel, and placement method on short span R/UHPC beams

This study investigates the response of small-scale, reinforced ultra high performance concrete beams. Seven specimens were cast and experimentally tested. Steel fiber volume fraction, amount of longitudinal and transverse steel reinforcement, and casting direction varied between specimens. High longitudinal reinforcement ratios of 4.1% and 9.5% were expected to drive relatively large shear demands and low steel fiber volume fractions of 0.5% and 1% were expected to decrease the UHPC’s ability to resist tension, shear, and compression. Specimens were either cast at one end or mid-span. All specimens failed in shear, as expected. R/UHPC beams with only 0.5% fibers and a stirrup spacing equal to half the beam’s depth carried more ultimate load than beams with 1% fibers and twice the stirrup spacing. At a 0.5% fiber volume fraction, UHPC performed well, exhibiting fiber bridging in tension and resisting spalling in compression. As longitudinal reinforcement ratio increased from 4.1% to 9.5%, load carrying capacity generally increased, but not proportional to the increase in steel. Placement method did not influence fiber orientation in the R/UHPC beams when measured in 2D planes transverse or longitudinal to the specimens’ major axis. The longitudinal and transverse reinforcement interrupted fiber flow and prevented significant fiber alignment; combined with the short span of the beams, these factors mitigated the influence of placement method.

Mechanism and Kinetics of Water Absorption of Plantain Fibre Reinforced Bio-Composites

Mechanical characteristics, dimensional stability, and bonding strength are all impacted by water sorption in polymer filler materials. The diffusion coefficient (D) of water through polymer composite, should be determined to understand the impact of the deterioration on service life and micro-leakage. In this study, the kinetics and properties of water absorption by short-term immersion in room-temperature plantain fibre reinforced epoxy bio-composites (PFRC), were studied. 5, 10, 20, and 30 percent, plantain fiber (PF) volume fractions of bio-composite specimens were made. Due to the high cellulose content of natural fibers (NF), the percentage of moisture absorption grew as the PF volume fraction increased. The mechanism and kinetics of PFRC's water absorption were found to follow the Fickian diffusion mode and had the propensity to behave in the Fickian mode.

Effect of hybrid ratio on the flexural properties of Arenga Pinnata fiber/E-glass fiber/polyester hybrid composites

Hybrid ratio effect on flexural properties of sugar palm/E-glass fiber hybrid-reinforced polyester composites has been investigated. Before being embedded, the sugar palm fiber was taken off from its original mesh, washed, alkali-treated, and chopped into ~10 mm long. The specimens were cut from composite plates having different hybrid ratios, fabricated using cold pressed technique. The total fiber volume fraction was kept at ~0.21, where four hybrid ratios, and two span-to-depth ratios were used. The E-glass was arranged unidirectionally and placed right on the surface of a bottom mold and wetted using the matrix, and the SPF was then evenly poured on the wet E-glass arrangement in randomly oriented pattern. Specimen preparation and testing were carried out according to the ASTM D790 standard, where the E-glass sides were placed in tension sides of the beams. It was found that flexural strength, and strain at maximum stress significantly increase with the increase of hybrid ratio.

Effect of thermal-mechanical conditions on strength of silanized Al alloy/CFRTP hybrid joint made by thinning-controlled hot pressing

The strength of thermal-assisted joined metal and carbon fiber-reinforced thermoplastics (CFRTP) is dependent on physical and chemical interactions at the joining interface, which are strongly influenced by heat and pressure. Currently, there is a lack in deep research on effect mechanism of changeable pressure on the joining quality, limiting the joining condition optimization of the thermal-assisted joining process. In this study, an improved hot-pressing joining process with added thinning displacement control was adopted to study the effect of the joining pressure on the structure and strength of the interface between a silane-treated Al alloy and three CF-Polyamide-6 (CF/PA6). A high-strength, thinning-controlled lapped joint of Al and CF/PA6 could be realized by the proposed process, regardless of the fiber volume fractions in CF/PA6. At temperatures above the melting point of PA6, higher pressure typically resulted in higher interface strength. However, as the temperature approached the decomposition temperature, the joints under higher pressure tended to exhibit lower strength. The underlying mechanism of the interface strength variation with pressure was investigated by analyzing the effects of the joining conditions on the chemical reaction conditions, the resolidified-resin structure near the interlayer, and the existence of defects. These findings lay the foundational groundwork for future endeavors in metal/composite joining, offering potential benefits for industrial applications and environmental sustainability in the automotive sector.

Numerical Study of Thin-Walled Polymer Composite Part Quality When Manufactured Using Vacuum Infusion with Various External Pressure Controls.

The article presents the results of modeling various modes of vacuum infusion molding of thin-walled polymer-composite structures of arbitrary geometry. The small thickness of the manufactured structures and the fixation of their back surface on the rigid surface of the mold made it possible to significantly simplify the process model, which takes into account the propagation of a thermosetting resin with changing rheology in a compressible porous preform of complex 3D geometry, as well as changes in boundary conditions at the injection and vacuum ports during the post-infusion molding stage. In the four modes of vacuum-infusion molding studied at the post-infusion stage, the start time, duration and magnitude of additional pressure on the open surface of the preform and in its vacuum port, as well as the state of the injection gates, were controlled (open-closed). The target parameters of the processes were the magnitude and uniformity of the distribution of the fiber volume fraction, wall thickness, filling of the preform with resin and the duration of the process. A comparative analysis of the results obtained made it possible to identify the most promising process modes and determine ways to eliminate undesirable situations that worsen the quality of manufactured composite structures. The abilities of the developed simulation tool, demonstrated by its application to the molding process of a thin-walled aircraft structure, allow one to reasonably select a process control strategy to obtain the best achievable quality objectives.

Elastic moduli prediction of a short fiber composite with interface debonding at fiber ends

This work deals with the fiber ends debonding-induced elastic moduli degradation of a short fiber reinforced composite (SFRC). The strain fields of the matrix in a representative volume element (RVE) of the SFRC are determined from an imaginary fiber technique. By using the debonding boundary conditions, the debonded modulus of the composite is derived, which is affected by not only the far-field but also the transient solutions for the longitudinal strain of the matrix. Particularly, the imaginary fiber technique provides unbounded solution for a moderately large fiber aspect ratio. This is resolved by separating the RVE along the fiber direction into two domains. Combining the longitudinal strains in both domains, the longitudinal modulus is determined, and the longitudinal bridging tensor element in the micromechanics Bridging Model is amended. Five elastic moduli of an SFRC after the fiber end debonding are obtained on the amended Bridging Model. The effects of the fiber volume fraction, fiber aspect ratio, and fiber-to-matrix modulus ratio on the end-debonded longitudinal modulus, transverse modulus, and longitudinal Poisson’s ratio are investigated.

Toughness of Natural Hydraulic Lime Fibre-Reinforced Mortars for Masonry Strengthening Overlay Systems

Masonry structures are susceptible to damage and collapse due to seismic actions, a problem in many urban areas. To address this issue, researchers are studying the use of fibre-reinforced mortars as overlay strengthening systems. This study assessed the use of synthetic polyacrylonitrile (PAN) fibres as reinforcement of natural hydraulic lime mortar, focusing on their influence on fresh behaviour and mechanical properties. Natural hydraulic lime (NHL) was chosen for its compatibility with typical older ceramic and natural stone structural masonry and contemporary ceramic brick infill masonry substrates, as well as for the sustainability benefits. The study also assessed the contribution of the PAN fibres to toughness enhancement in the developed formulations. The fresh behaviour of fibre-reinforced mortar (FRM) was found to be adequate for applications with fibre volume fractions below 0.50%. The compressive and flexural strengths were affected differently by the increase in fibre volume fraction, with compressive strength decreasing and flexural strength increasing. The maximum compressive strength of 13.3 MPa was obtained for 0.25% of fibres, while for flexural strength a maximum of 6.70 MPa was achieved with 1.00% of fibres. The compressive and flexural toughness, related to the post-cracking responses, increased with the fibre fraction, and even for fractions as low as 0.25%, an important increment of the capacity to dissipate energy was achieved.