Consolidation Of Composites Research Articles

Consolidation Enhancement of Weathered Coal Gangue Utilized for Aggregate Filling of Cement Pavement in Mining Area

The large-scale, open-air storage of coal gangue often leads to oxidation and decomposition due to natural weathering, resulting in decreased strength and instability, which limits its wider application in concrete pavement. To address these issues, this paper proposed a composite consolidation treatment for weathered coal gangue (WCG), assessing its effectiveness and enhancement mechanisms through aggregate performance tests, mixture performance tests, and microscopic visualization analyses. Results indicated that the initial and post-20 dry–wet cycle crushing values of WCG were 23.96% and 47.94%, respectively, failing to meet required standards. However, applying a composite consolidation treatment using a lithium curing agent and cement paste significantly improved WCG’s robustness and stability. After 4 days of treatment, the crushing value, impact value, and Vickers hardness of WCG had reached 18.3%, 6.58%, and 113.52 kgf/mm², respectively, fully meeting the standards for aggregate filling in mini concrete pavements. Furthermore, tests demonstrated that the lithium curing agent induced the formation of hydrated calcium silicate and calcium aluminate on both the surface and interior of the WCG, enhancing its structural stability. Approximately 5–12 wt.% of the curing agent penetrates and encapsulates the WCG, strongly bonding and reinforcing its internal weak surfaces. These findings offer potential solutions and technical insights for the large-scale management of weathered coal gangue.

Parametric process optimisation of automated fibre placement (AFP) based AS4/APC-2 composites for mode I and mode II fracture toughness

In-situ consolidation of thermoplastic composites using Automated Fibre Placement (AFP) technology is an emerging manufacturing technique, offering tailored composite properties through customised processing parameters. Multiple competing parameters during AFP manufacturing influence the quality and mechanical performance of the laminates. These lay-up parameters are interrelated, and often require comprehensive experimental characterisation which is costly and time-intensive. This study aims to optimise the fracture toughness of in-situ consolidated thermoplastic composite (AS4/APC-2) and investigate the mechanisms that contribute to it. Taguchi’s method is employed to efficiently analyse the effect of various process parameters at multiple levels. Based on the obtained results, a considerable effect of process parameters on Mode I and II fracture toughness is observed. The statistical analysis reveals that the Hot Gas Torch (HGT) temperature required for AFP processing significantly affects the Mode I fracture toughness, contributing to 33.8%. Whereas, the consolidation force, another key processing parameter in AFP notably affects Mode II fracture toughness, with the contribution of 81.8%. The analysis of variance (ANOVA) reveals interdependent processing parameter relations for both fracture modes. A validation test showed good agreement between the predicted fracture toughness and the experimental test.

Consolidation performance and mechanism of composite dust suppressant based on graft modification

AbstractTo solve the severe coal dust pollution and dust hazards in underground coal mines, this study utilized graft copolymerization modification technology and compound technology to develop a mining composite consolidation dust suppressant. On this basis, analysis of its consolidation wettability and dust suppression mechanism was conducted through characterization tests and molecular dynamics simulation methods. The results show that polyacrylamide (PAM) had been successfully grafted onto the soybean protein isolate (SPI) molecule, and form a SPI‐PAM complex. After the dust suppressant acted on the coal dust surface, it utilized its wealthy hydrophilic groups, for the adsorption of water molecules and the positive amide group for binding to produce a large area of agglomeration of coal dust particles at the interface, exhibiting good wetting and consolidation into a shell. At the same time, molecular dynamic simulation verified that the diffusivity of water molecules in the dust suppressant‐coal system was 0.30Å2/ps, decreased by 43.3%, and the interaction energy with coal molecules was −200.27 kcal/mol, absolute value increased by 41.35%, which made the dust suppressant molecules more easily adsorb and agglomerate on the surface, demonstrated an excellent solidification and dust suppression effect.

Prediction of the in-plane permeability and air evacuation time of fiber-placed thermoplastic composite preforms with engineered intertape channels

The two main void removal mechanisms during vacuum-bag-only (VBO) consolidation of thermoplastic composites are through-thickness diffusion and in-plane air evacuation. The automated fiber placement (AFP) process allows for the creation of preforms with an engineered intertape channel network by deliberately introducing spacing between the tapes that can facilitate air evacuation during the VBO consolidation. However, it is unclear what dimensions of the intertape channels allow for effective in-plane air evacuation. The current research presents a predictive simulation tool to optimize the intertape channel dimensions for effective in-plane air evacuation. An analytical method is developed to calculate the in-plane permeability tensors of the composite preform with uniform intertape channel dimensions. In addition, a more elaborate mesoscale method is developed that estimates the in-plane permeability tensor of the engineered intertape channel network based on the distributions in intertape channel dimensions. Finally, a finite difference model is implemented to calculate the time required for air evacuation as a function of the in-plane permeability tensors of the preform and its in-plane dimensions. The results from the models indicated that in-plane air evacuation through the engineered intertape channel network is quick, and it takes only a few minutes to evacuate 99% of the air from large preforms like fuselage panels.

Analysis of microstructure and mechanical properties of alumina composites reinforced with Ti2AlN MAX phases

This study presents new findings on nitride MAX phases addition to ceramic matrix. Synthesised Ti2AlN was incorporated into alumina matrix with the use of powder metallurgy. Due to the low thermal stability and tendency of MAX phases for decomposition, Spark Plasma Sintering (as rapid sintering method) was utilized for composites consolidation. In order to evaluate the possibility of adopting Ti2AlN as reinforcing phase, the emphasis of the research was placed on microstructural analysis. Additionally, mechanical properties and tribological performance of produced sinters were examined. Successful synthesis of Ti2AlN phase was confirmed by XRD and FTIR analysis. Moreover, performed observations revealed that MAX phase preserved it layered structure in prepared composites. In addition, obtained results showed an improvement in the mechanical properties within entire range of Ti2AlN addition. Highest Vickers hardness (1974 HV) was measured for sinters with 2 and 2.5 wt% addition, while indentation fracture toughness reached maximum value of 4.84–5.13 MPa*m1/2 for shares in the range of 1.5–3 wt%. In case of composites with Ti2AlN content above 3 wt% decrease in mechanical properties was observed. For these sinters, adopted MAX phase undergoes phase transformation and reactions, resulting in presence of TiN, Ti2Al and Ti3AlN in microstructure. Additionally, composites with addition of 2, 2.5 and 5 wt% of Ti2AlN, when tested under the load of 60 N, where characterised by lower wear rate than reference pure alumina sinter.

In-situ consolidation of thermoplastic composites by automated fiber placement: Characterization of defects

The emergence of automated manufacturing of composites has not only transformed the manufacturing of optimized and geometrically complex structures but has also expanded the promising prospect of in-situ manufacturing of thermoplastic composites (TPC), where both material placement and consolidation are carried out by automated fiber placement (AFP) equipment, streamlining the process into single step manufacturing. However, the inherent complexities in different aspects of robotic automation, imperfections in the supplied material, and the occurrence of multi-physical phenomena during in-situ consolidation introduce various manufacturing-induced defects. While the defects in thermoset composites (TSC) made by AFP have been widely studied in the past, this study explores the diverse defects at micro and macro scales for TPCs made by AFP, with a focus on carbon-fiber/poly-ether-ether-ketone (CF/PEEK) tapes consolidated using hot gas torch (HGT) heating system. An overview of defects and associated characteristics is presented across three phases: defects in supplied impregnated tapes, defects and limitations in performance of AFP system, and defects in the final in-situ consolidated composite. For the defects subject to studies in the past, the description is limited to a concise review, while those with limited understanding are supported by new empirical observations in this work.

In-situ infrared annealing for laser-assisted automated fiber placement to enhance interlaminar properties without sacrificing laydown efficiency

Laser-assisted automated fiber placement (LAFP) in-situ consolidation (ISC) of thermoplastic composites suffers from poor interlaminar bonding. Repass treatment improves interlaminar bonding but sacrifices laydown efficiency. Here we propose an in-situ infrared annealing (IIA) strategy that combines infrared heat treatment with a second pressure roller immediately following the LAFP ISC process. This approach causes repeated interlaminar melting and slower cooling, reducing the porosity by 57.9% and increasing crystallinity by 89.2% compared to LAFP-manufactured carbon fiber-reinforced polyether-ether-ketone composites. Moreover, it completes the crystallization process with only a single placement rather than multiple placements by repass treatment. Interlaminar shear strength and mode I interlaminar fracture toughness are improved by 239.7% and 292.4%, respectively. These improvements are comparable to those achieved by repass treatment with a near-infrared laser. Overall, the IIA strategy offers a promising alternative to traditional post-consolidation processes while maintaining laydown efficiency.

Grid stiffened panel made by Automated Fiber Placement (AFP) in-situ consolidation of thermoplastic composites

Grid stiffened panels offer significant potential for weight savings, which has led to an increased focus on their research. A novel method is presented for fabricating thermoplastic composites consisting of skins and grids through the Automated Fiber Placement technique and in-situ consolidation. The technique improves the flatness of the center in the cross-shaped structure. This step is critical since any irregularity in this area caused by material overlapping would negatively impact the mechanical functionality of such structures. The manufactured structure is subjected to a 5-point bending test to evaluate its mechanical properties and failure behaviour.

Three-dimensional finite element-based data-driven thermal model of in-situ automated fiber placement

This study proposes a data-driven model for thermal history prediction during in-situ consolidation of thermoplastic composites using Hot Gas Torch (HGT)-assisted Automated Fiber Placement (AFP). Temperature data was generated using a three-dimensional finite element (FE) model that was fitted to and validated with experimentally measured temperatures. Temperature curves for various combinations of heat source velocity and locations through the thickness and width were extracted from the fitted FE model. Three feedforward neural networks were trained to predict the temperature distribution during processing. The work demonstrates the effectiveness and potential of using neural networks for online prediction and optimization.

An embedded digital element model to simulate the wrinkle defects driven by the consolidation of composites

Understanding the mechanisms of fiber wrinkling during the compaction process is of paramount importance as fiber wrinkling significantly affects the mechanical properties of composite materials. This study introduces an embedded digital element model for simulating the consolidation process of prepreg. Flexible digital element chains are employed to simulate the reinforcing effect of fibers on resin, accounting for the viscoelastic constitutive behavior of uncured resin. The simulation captures intra-layer wrinkles and in-plane waviness defects in the consolidated prepreg, thereby uncovering the mechanism behind fiber wrinkle formation during composite material prepreg consolidation. The accuracy of the model is validated through compression experiments on flat plates and L-shaped structures. The results demonstrate that the proposed embedded digital element model accurately predicts wrinkle defects. Factors such as interlayer friction of the prepreg, consolidation temperature, and mold curvature radius significantly influence the shape and size of wrinkles.

Composite laminates reinforced by vertically aligned carbon nanotubes: Detailed manufacturing process, from nanotubes transfer to composite consolidation

Nano-constituent incorporation into composites has been extensively studied in the literature due to its improvement in static and dynamic mechanical properties, as well as its prevention from interlaminar crack initiation and propagation. This work introduces a detailed manufacturing process of nano-engineered composite laminates, from impregnation to consolidation, without damaging the initial morphology of carbon nanotubes transferred on prepreg interfaces. Based on prepreg and vertically aligned carbon nanotubes (VACNTs) synthesized on an aluminium alloy (Al) substrate, the impregnation step allows for the transfer of VACNTs onto the prepreg surface through partial resin-rising capillarity. The Al alloy substrate is then removed from the VACNTs through a separation step, ensuring highly effective and repeatable transfer with more than 80% VACNTs transferred onto the prepreg surface. This paper provides insight into the impregnation and transfer processes and guides the choice of process parameters to ensure minimal VACNTs buckling during the consolidation of the hybrid composites at high pressure in an autoclave.

The Influence of Processing Temperature on the Tensile Properties of Melt-Spun PLA Fibres and their Self-Reinforced Composites

The temperature during the consolidation of self-reinforced PLA composites has a significant effect on their mechanical properties. In the present work, the effect of the consolidation or processing temperature on the properties of melt-spun, highly oriented PLA fibres is experimentally studied through single fibre tests. It is shown that the Young’s modulus and strain to failure of PLA fibres increases with exposure to consolidation / processing temperature, and the strength decreases more drastically. Using these data and findings from earlier studies, it is demonstrated that the dependence of the tensile properties of self-reinforced PLA composites on the processing temperature can be directly predicted from the single PLA fiber properties as a function of the processing temperature. This prediction holds true provided that the tensile properties of both the PLA fibers and self-reinforced PLA composites are measured using the same cross-head speed or strain rate.

Experimental investigation and numerical modeling of mechanically alloyed Al-TiC composites

The present work studies the mechanical alloying, consolidation, evaluation, modeling, and optimization of the Al-TiC composites mixed at different milling times (MTs) of 6, 12, 24, and 48 h and reinforced with three TiC concentrations (3, 6, and 12 vol.%). The Al-TiC composites formed via the powder metallurgy method. The XRD of the mixed powder and the consolidated composites were investigated. Furthermore, density, wear, compressive strength, and hardness have been examined for the consolidated composites. Also, the worn surface of the wear-tested composites was studied utilizing SEM analysis. The response surface methodology (RSM) was involved to clarify the effects of mechanical alloying parameters of MTs and the TiC concentrations and their interaction towards achieving their optimum process factors to produce Al-TiC composites. The RSM results prove the applied factors’ importance in improving the consolidated composites’ properties. The optimization results show the optimum parameters to produce Al-TiC composites are 28.4 MTs and 12 vol.% TiC to produce Al-TiC composites with 304.4 ± 3 MPa compressive strength, 191.21 ± 2 HV hardness, 2.88 ± 0.008 g/cm3 density, and 9.7 ± 0.01 mg weight loss. The ANOVA analysis reveals that the suggested models can virtually expect the tested responses of density, hardness, compressive strength, and weight loss with a confidence level of over 90, 98, 95, and 95%, respectively.

Consolidation of Zn-Hydroxyapatite and Zn-Bioactive Glass Composites Using High-Pressure Torsion

There has been a great interest in developing zinc-based composites for biological applications. Mixing bioactive particles and obtaining a well-dispersed structure is not straight forward though. The present study reports a novel processing route in which zinc particles are mixed with hydroxyapatite and bioactive glass particles and consolidated at room temperature using high-pressure torsion. The composites display good dispersion of second phase particles, enhanced strength and an increased corrosion rate in the Hank’s balanced salt solution. The incorporation of these particles can be used to tailor the corrosion rate of zinc. It is shown that the surface layer of the corrosion product in the zinc-bioactive particle composites is richer in calcium and phosphorous than the pure zinc counterpart.

Vacuum-bag-only consolidation of C/PEKK fiber placed preforms with engineered gas evacuation channels

Vacuum-bag-only (VBO) consolidation of automated fiber placed (AFP) thermoplastic composites can be a cost-effective processing route for large and complex thermoplastic composite structures. This paper explores the possibility of two-step AFP and VBO consolidation of advanced thermoplastic composites. Two commercially available carbon fiber reinforced Poly-Ether-Ketone-Ketone (C/PEKK) thermoplastic tapes were evaluated. Different process parameters were needed for the two material systems. Further, for the first time, an attempt was made to create in-plane air evacuation channels by deliberately introducing gaps between the tapes in the preforms during the placement. In the case of one material system, the VBO consolidation of preforms with and without gaps yielded good consolidation quality with less than 1% voids. In the other case, VBO consolidation of preforms with gaps showed a improved consolidation quality with less than 1% voids than the preform without gaps, indicating that the gaps possibly help accelerate the gas evacuation process.

Consolidation of aerospace-grade high-temperature thermoplastic carbon fiber composites via nano-engineered electrothermal heating

A carbon nanotube (CNT) electrothermal heater is shown to enable consolidation of high-temperature thermoplastic composite laminates for the first time, leveraging the CNT film's stable operation in air above 500 °C. This out-of-oven (OoO) conductive heating method without applied pressure (i.e., vacuum bag only) is used to process aerospace-grade carbon fiber/polyether ether ketone (PEEK) composite prepreg, which requires heating to 380–400 °C and is normally processed with significant applied pressure (∼2 ± 1 MPa) via a hot-press or autoclave. Micro-computed tomography verifies that the processed laminates exhibit low porosity of ≤0.1 vol%, which more than meets the desired target of <1 vol% voids. A range of thermophysical (including degree of crystallinity) and mechanical (interfacial shear strength and bending) tests show equal or improved properties vs. both hot press and autoclave processing. The CNT heaters in the OoO approach are observed to most closely match the desired processing cycle, with the observed benefit of being the only process studied to hit the target range of % crystallinity. The energy consumption comparison indicates a 98% energy saving of the CNT heater compared to the hot press. This study demonstrates autoclave-quality processing of high-temperature thermoplastic composite structures via conformal CNT heaters that can be fabricated efficiently and effectively in an out-of-autoclave (OoA) process.

Applying the Taguchi to Optimization the densification, and flexural strength of ZrB2–SiC–ZrC-CNFs

The purpose of this research is to optimize the densification, microstructure and flexural strength of ZrB2-25 vol% SiC composites reinforced by carbon nano fibers (CNFs) and zirconium carbide (ZrC). Spark Plasma Sintering (SPS) was applied for composites consolidation. Taguchi orthogonal array L9 as the design of statistical experiments (DOE) was evaluated to optimize the additives, as well as SPS parameters (temperature and time). Three levels were defined for each factor. The relative density (R.D%) and flexural strength of the samples were calculated based on Archimedes' law and the three-point bending test. Moreover, analysis of variance (ANOVA) was utilized to determine the importance of effective parameters and to optimize the SPS variables and compounds (the amount of CNFs and ZrC). The microscopic structure of surfaces was examined through field emission scanning electron microscopy equipped with energy dispersive spectroscopy (FE-SEM, EDS). The results showed that the best output of relative density and flexural strength was equal to 99.8% and 610 MPa, respectively, with an average ZrB2 grain size of 9.6 μm in a composite containing 15 vol% CNFs and 10 vol% ZrC and SPSed at 1875 °C for 7 min.

Describing and Modeling Rough Composites Surfaces by Using Topological Data Analysis and Fractional Brownian Motion.

Many composite manufacturing processes employ the consolidation of pre-impregnated preforms. However, in order to obtain adequate performance of the formed part, intimate contact and molecular diffusion across the different composites' preform layers must be ensured. The latter takes place as soon as the intimate contact occurs and the temperature remains high enough during the molecular reptation characteristic time. The former, in turn, depends on the applied compression force, the temperature and the composite rheology, which, during the processing, induce the flow of asperities, promoting the intimate contact. Thus, the initial roughness and its evolution during the process, become critical factors in the composite consolidation. Processing optimization and control are needed for an adequate model, enabling it to infer the consolidation degree from the material and process features. The parameters associated with the process are easily identifiable and measurable (e.g., temperature, compression force, process time, ⋯). The ones concerning the materials are also accessible; however, describing the surface roughness remains an issue. Usual statistical descriptors are too poor and, moreover, they are too far from the involved physics. The present paper focuses on the use of advanced descriptors out-performing usual statistical descriptors, in particular those based on the use of homology persistence (at the heart of the so-called topological data analysis-TDA), and their connection with fractional Brownian surfaces. The latter constitutes a performance surface generator able to represent the surface evolution all along the consolidation process, as the present paper emphasizes.

Hot Isostatic Pressing Control of Tungsten-Based Composites

Metal-oxide composites are commonly used in high temperature environments for their thermal stability and high melting points. Commonly employed with refractory oxides or carbides such as ZrC and HfC, these materials may be improved with the use of a low density, high melting point ceramic such as CeO2. In this work, the consolidation of W-CeO2 metal matrix composites in the high CeO2 concentration regime is explored. The CeO2 concentrations of 50, 33, and 25 wt.%, the CeO2 particle size from nanometer to micrometer, and various hot isostatic pressing temperatures are investigated. Decreasing the CeO2 concentration is observed to increase the composite density and increase the Vickers hardness. The CeO2 oxidation state is observed to be a combination of Ce3+ and Ce4+, which is hypothesized to contribute to the porosity of the composites. The hardness of the metal-oxide composite can be improved more than 2.5 times compared to pure W processed by the same route. This work offers processing guidelines for further consolation of oxide-doped W composites.

Predictive Thermal Modeling and Characterization of Ultrasonic Consolidation Process for Thermoplastic Composites

Abstract Ultrasonic consolidation (USC) of thermoplastic composites is a highly attractive and promising method to manufacture high-performance composites. This work focuses on USC of dry carbon fiber (CF) fabrics with high-temperature polyphenylene sulfide (PPS) films. Experimental trials to assess feasibility of the process are time-consuming. Consequently, a predictive thermal model would facilitate process parameters selection to reduce expensive trial-and-error approaches. This paper presents a 2D finite element model of samples under consolidation, incorporating equations for viscoelastic heating, matrix phase change, and material properties. Theoretical temperature profiles for nodes of interest were compared to the corresponding experimental temperature curves for various control parameters (i.e., weld time and vertical displacement of sonotrode) and showed good agreement during heating phase. It was found that welding time values below 1750 ms were insufficient to reach melting temperature, whereas weld times above 3000 ms led to the lowest average void content (2.43 ± 0.81%). More specifically, the time the material spent above melting temperature, i.e., residence time, was established as a parameter that could estimate cases resulting in better consolidation and lower void content (time above 2600 ms for void content below 2.5%). X-ray diffraction (XRD) characterization revealed that the USC process led to mostly amorphous PPS, due to the high cooling rates (70 °C/s to 108 °C/s). Overall, the thermal model and micro-structural outcomes confirmed the feasibility of the USC process for layered composites made from dry fabric and high-temperature thermoplastic films.