Impregnation Behavior Research Articles

Study on short fiber reinforcement mechanism for mechanical performance improvement of 3D‐printed short‐continuous carbon fiber reinforced thermoplastic composites

Abstract3D printing of continuous carbon fiber reinforced thermoplastic (C‐CFRTP) composites is a promising fabricating process to achieve complex lightweight structures within a short time; nevertheless, low mechanical performance between printed layers is always a limitation. Adding short carbon fibers during C‐CFRTP fabrication could achieve short‐continuous carbon fiber reinforced thermoplastic (S/C‐CFRTP) composites with enhanced mechanical properties. However, the underlying reinforcement mechanism is not well understood, which hinders the optimization of 3D printing process for S/C‐CFRTP. This paper investigates reinforcing behavior of short carbon fibers and impregnation behavior of the matrix (short carbon fiber reinforced PA6) under various 3D printing conditions. The results indicate that promoting both reinforcing and impregnation behaviors during S/C‐CFRTP 3D printing can improve mechanical performance. As short carbon fiber content increases, the mechanical performance initially experiences enhancement caused by the reinforcing behavior of short fibers, followed by a decline attributed to the insufficient impregnation of the molten matrix. Higher nozzle temperatures facilitate the impregnation behavior of the molten matrix, resulting in superior mechanical performance. Moreover, by leveraging the reinforcement mechanism, the optimal parameter combination is proposed to improve tensile, flexural, and interlaminar shear strengths of the 3D‐printed S/C‐CFRTP to approximately 368.27, 319.80, and 20.09 MPa, respectively.Highlights Reinforcement mechanism is revealed by reinforcing and impregnation behaviors. Short carbon fiber content affects both reinforcing and impregnation behaviors. Beyond 15 wt%, short carbon fiber content shows adverse effects on performance. High nozzle temperature promotes impregnation behavior to improve performance. Optimal parameters raise 19.8% tensile, 39.9% flexural and 161.2% shear strength.

Magnetic Properties of Ferrofluid Change Over Time: Implications for Magnetic Pore Fabric Studies

AbstractThe anisotropy of magnetic susceptibility of ferrofluid‐impregnated samples is an efficient and powerful proxy for pore space anisotropy and preferred flow directions. One of the main assumptions in pore fabric studies is that all pores >10–20 nm are homogeneously filled with ferrofluid, and that the ferrofluid has constant properties throughout the pore space and over time. If only part of the pore space is filled, this can lead to artifacts. Additionally, because magnetic anisotropy of a given pore space depends on fluid susceptibility, quantitative interpretations may be affected by the interval between impregnation and measurement time, or by the age of the ferrofluid during impregnation, unless fluid properties remain constant. A careful investigation of the time variation of ferrofluid properties and magnetic pore fabrics in synthetic and natural samples shows time‐dependence of susceptibility and hysteresis properties, related to dissolution of particle surfactants, and deterioration of colloidal stability. The latter leads to particle aggregation and sedimentation, which changes the anisotropy properties, and also affects impregnation behavior. Natural samples impregnated by oil‐based ferrofluid also experience a 2.5–3‐fold increase in mean susceptibility, with important consequences for the susceptibility‐based determination of impregnation efficiency. Based on our results, we recommend that ferrofluid properties are determined at the time of impregnation, and that samples are measured shortly after impregnation.

Enhanced impregnation behavior and interfacial bonding in CF/PEEK prepreg filaments for 3D printing application

The high specific strength and modulus of carbon fiber-reinforced poly-ether-ether-ketone composites (CF/PEEK) have made them particularly useful for structural applications. However, undesired defects are derived from the incompatibility between the thermoplastic matrix and the thermoset-based sizing agent at the CF/PEEK interface. This issue is further aggravated by three-dimensional (3D) printing fabrication for incomplete impregnation during the printing process. Herein, we introduce a thermoplastic-based sizing treatment into CF/PEEK prepreg filament preparation in order to reduce or eliminate the defects from the material and process sources of (3D) printing. We evaluate the influence of the sizing treatment on the impregnation and compatibility behavior of the CF/PEEK prepreg filaments. In comparison to the unsized CF/PEEK composites, the tensile strength of the polyether imide- and PEEK-sized CF composites increased by 47.6% and 54.0%, respectively. In combination with the thermoplastic-based sizing treatment and prepreg filament approach, 3D printing has the potential to create structural parts with favorable interfacial bonding.

Development of a Test Bench for the Investigation of Thermoplastic-Thermoset Material Combinations in Additive Manufacturing

To enhance the mechanical properties of fused filament fabricated parts, the process integrates continuous fibers. Currently, fibers are impregnated either with thermoplastics or with thermoset material, which is completely cured before printing and later combined with thermoplastic filament during the coextrusion process. A major problem about using cured thermoset matrix for the fibers is an insufficient bond between the fiber matrix and the thermoplastic material. A new approach proposed by the authors combine uncured thermoset matrices with thermoplastic filaments to form a substance-to-substance bond. To investigate the material and bonding behavior, a test bench is constructed. Its main purpose is to replicate the coextrusion of thermoplastic filament and thermoset impregnated continuous fibers. Parameters, such as temperature, tension and extrusion speed can be adjusted within the setup to accurately simulate the additive manufacturing process. Aluminum blocks including heater cartridges and thermocouples act as hot ends and impregnation units. Heated blocks compact the fiber strands. We tested different heating blocks containing flat and curved geometries including actual additive manufacturing nozzles to evaluate the impregnation behavior of the dry carbon fiber filaments. Approaches with additive manufacturing nozzles show the most promising results regarding fiber impregnation with thermoplastic material.

Transverse permeability in Eucalyptus nitens wood specimens

ABSTRACT Permeability functionalities are noticeable in the wood drying and impregnation processes because it has an effect on the bulk flow of a fluid through the wood structure. The aim of this work was to measure the radial and tangential specific gas permeability of Eucalyptus nitens wood for 10 different provenances. Furthermore, the effect of the radial position (defined as inner-wood, middle-wood, and outer-wood) on the measurements was investigated. The specific gas permeability of E. nitens ranged in order of magnitude from 10−20 to 10−16 m2. The results showed that the radial position had a statistically significant effect on the specific permeability in both flow directions and, in general, the permeability values increased from inner-wood to outer-wood. Moreover, the scanning electron microscopy images showed obstruction of vessels by tyloses which explained the lower permeability values obtained in the inner-wood of E. nitens. Differences in the magnitude of the permeability values could explain the diverse drying and impregnation behavior according to the wood zones, the low permeability values in the internal wood-zone could suggest an opportunity for improving it, through chemical modification or structural changes to introduce new functionalities of this radial wood-zone in Eucalyptus nitens.

Study on preparation of composite carbon rod for high-power electrode from coke with different structural characteristics

Different from lithium-ion batteries, composite carbon rod for high-power electrode was widely used in high-end manufacturing industry due to its good conductivity and low CTE. In this study, semi cokes with different structural characteristics was used as aggregate and coal tar pitch was adopted as binder and impregnant to prepare composite carbon rod for high-power electrode, and the bonding and impregnation behavior was also investigated. It was found that calcination promoted ordered stacking of planar aromatic lamellae of acicular domain texture and aggravated the structural defects of mosaic texture. Coal tar pitch with low aromaticity and high toluene insoluble (TI) as bonded and impregnated pitch possessed higher adhesion but low weight gain ratio after calcination. While higher TI content of coal tar pitch enhanced the weight gain ratio, but the adhesion of composite carbon rod declined. In addition, the carbonaceous sheets derived from coal tar pitch gradually extended and covered the surface of orderly graphited sheets generated from acicular domain texture and contributed to the lowest CTE of 1.43 * 10−6·℃−1 as well as the lowest specific resistance of 6.03μΩ·m. While the structural defects and voids generated from disordered mosaic texture could not be completely filled, thereby resulting in highest CTE of 2.20 * 10−6·℃−1 and highest specific resistance of 9.55μΩ·m.

Influence of preheating temperature and printing speed on interlaminar shear performance of laser‐assisted additive manufacturing for CCF/PEEK composites

AbstractContinuous carbon fiber reinforced poly‐ether–ether–ketone (CCF/PEEK) shows great potential in engineering applications attributed to superior mechanical properties together with excellent thermal and chemical resistance. In this study, a laser‐assisted additive manufacturing device was established to accurately collect and control the preheating temperature based on a coaxial infrared temperature measurement system. The influence on laser power consumption, interlaminar shear performance, and failure mechanism was investigated in condition of different preheating temperatures and printing speeds. Results indicated that the laser‐preheated specimens showed much higher ILSS with maximum values and increasing percentage reached 33.48 MPa and 157.0% compared to unpretreated specimens. With the increase of preheating temperature and printing speed, more laser power was consumed, while the ILSS and increasing percentage increased firstly and then decreased. The strengthening effect on the interlayer bonding was ascribed to promoting the penetration of PEEK molecular chain ends between adjacent layers, increasing the fluidity and enhancing the bonding effect between adjacent filament together with improving the impregnation behavior of the inner fibers. The proposed interlaminar strengthening method based on laser‐assisted preheating provides potential application prospects in aerospace and automotive industries.

The influence of fabric architecture on impregnation behavior and void formation: Artificial neural network and statistical‐based analysis

AbstractThis work proposes an approach combining artificial neural networks (ANN) with statistical models to predict injection processing conditions for four reinforcement architectures: plain weave, bidirectional noncrimp fabrics, unidirectional fabrics (Uni) and random fiber mats (Random). Key results allow evaluating the velocity of the flow front by combining processing parameters and creating a three‐dimensional response surface based on a properly trained ANN. This investigation is based on a large number of experimental results. The key role played by some physical parameters was associated with predicting the impregnation behavior (velocity of the flow front) during resin injection. The main outcome aims to provide a better control of void content in terms of size and position to the four fibrous reinforcements considered.

Correlation between Pitch Impregnation Pressure and Pore Sizes of Graphite Block.

This study aimed to investigate the effect of impregnation pressure on the decrease in porosity of impregnated bulk graphite. The correlation between pitch impregnation behavior and the pore sizes of the bulk graphite block was studied to determine the optimal impregnation pressure. The densities and porosities of the bulk graphite before and after pitch impregnation under various pressures between 10 and 50 bar were evaluated based on the Archimedes method and a mercury porosimeter. The density increased rates increased by 1.93–2.44%, whereas the impregnation rate calculated from the rate of open porosity decreased by 15.15–24.48%. The density increase rate and impregnation rate were significantly high when the impregnation pressures were 40 and 50 bar. Compared with impregnation pressures of 10, 20, and 30 bar, the minimum impregnatable pore sizes with impregnation pressures of 40 and 50 bar were 30–39 and 24–31 nm, respectively. The mercury intrusion porosimeter analysis results demonstrated that the pressure-sensitive pore sizes of the graphite blocks were in the range of 100–4500 nm. Furthermore, the ink-bottle-type pores in this range contributed predominantly to the effect of impregnation under pressure, given that the pitch-impregnated-into-ink-bottle-type pores were difficult to elute during carbonization.

Preparation of CCF/PEEK filaments together with property evaluation for additive manufacturing

Additive manufacturing technology has been increasingly applied to fabricate continuous fiber reinforced thermoplastic composites for its potential in fabricating complex structures. Owing to the limited thermal and mechanical properties of the matrix, it is a critical trend to develop high-performance thermoplastics to widen engineering applications. This study aims to comprehensively investigate the properties of the prepared CCF/PEEK filaments together with their printed composites. The filaments were fabricated via a thermo-mechanical coupling process and were characterized by micromorphology observation, thermal and mechanical test. It was found that the impregnation behavior, thermal stability and mechanical performance of the filaments were improved with the increase of mold temperature and decrease of traction speed. The performance of printed specimens was evaluated by mechanical test and fracture analysis. It was concluded that the additive manufacturing process promoted the secondary impregnation behavior of the filaments. Higher nozzle temperature and bed temperature together with lower layer thickness and printing speed enhanced the tensile strength of printed specimens with maximum value reached 509.56 MPa. Besides, the analysis of failure mechanism indicated that filament fracture, horizontal cracks and filament pullout together with fiber breakage, fiber pullout, unimpregnated fibers and pores were the dominant failure modes for all printed specimens.

Resin impregnation and interfacial adhesion behaviors in carbon fiber/epoxy composites: Effects of polymer slip and normalized surface free energy with respect to the sizing agents

Herein, we report the effect of sizing agents on carbon fiber (CF)/epoxy interfacial interaction. In addition to the relationships between sizing agents and composite interfacial properties, which have been the focus of previous studies, this study deals with the effect of sizing agents on the resin impregnation behavior in vacuum assisted resin transfer molding (VaRTM), which affects the productivity of composite manufacturing. For this purpose, CFs treated with different sizing agents were compared. CF surface characteristics were investigated via various analyses. Surface free energy, a parameter of the fiber/matrix adhesion, was measured. Dynamic contact angles were measured to understand the CF wettability. VaRTM tests were performed. Interfacial shear strength (IFSS) of CF/epoxy composites was evaluated via micro-droplet tests. Finally, resin flow characteristics with polymer slip at the CF surface were studied, and the normalized surface free energy, considering the specific surface area, was suggested as the key parameter of IFSS.

Study of the Impregnation of Power-Transformer Cellulosic Materials With Dielectric Ester Oils

The application of alternative dielectric oils as esters in power transformers is hindered by the lack of knowledge regarding their properties and respecting which are the best techniques to ensure their proper performance. In this sense one of the fields needing an impulse is the impregnation processes of transformers cellulosic materials with these alternative oils, currently impregnated in most of the cases with mineral oils. This paper studies the impregnation behavior of eight usual dielectric solids, with two esters and a traditional mineral oil. Empirical equations of the impregnation evolution with time have been obtained, from these the rigid cellulosic materials present in the transformers and the viscosity of the dielectric oils have been identified as the key materials and properties to consider during impregnation. An adaptation of the current impregnation processes to the alternative oils have been proposed by increasing their temperature from ambient temperature up to 61-74°C, depending on the viscosity of the oil used.

Impregnation behaviour of regenerated cellulose fabric Elium® composite: Experiment, simulation and analytical solution

Filling time and volume fill prediction of long and complex parts produced using the method of resin infusion is of prominent importance. Fibre volume fraction, reinforcement type and composite laminate thickness significantly affect the manufacturing behaviour. It is crucial to have an estimate of fabrication parameters such as filling time. The PAM-RTM (resin transfer moulding) commercial software package makes it possible to characterize the production parameters in connection with lab scale experiments. In this work, simulation tools demonstrate an accurate prediction of the resin infusion process of pulp-based fabrics and characterization of the dynamic phenomena are verified using the analytical solution for a simple part. The accurate prediction for fabrication of pulp-based fabric Elium® composite demonstrated here can be beneficial for scaling up the composite part size and production speed. The filling time was accurately predicted until 270 s for the volume fill of 10–100% using the software tool and analytical solution. This proves the rayon fabric processing capabilities as a reinforcement for industry related projects and opens for the possibility of infusion process optimization.

Response surface optimization for improving the processing behavior of melamine formaldehyde impregnation resins

AbstractMelamine‐formaldehyde resins are widely used for decorative paper impregnation. Resin properties relevant for impregnation are mainly determined already at the stage of resin synthesis by the applied reaction conditions. Thus, understanding the relationship between reaction conditions and technological properties is important. Response surface methodology based on orthogonal parameter level variations is the most suitable tool to identify and quantify factor effects and deduce causal correlation patterns. Here, two major process factors of MF resin synthesis were systematically varied using such a statistical experimental design. To arrive at resins having a broad range of technological properties, initial pH and M:F ratio were varied in a wide range (pH: 7.9–12.1; M:F ratio: 1:1.5–1:4.5). The impregnation behavior of the resins was modeled using viscosity, penetration rate and residual curing capacity as technological responses. Based on the response surface models, nonlinear and synergistic action of process factors was quantified and a suitable process window for preparing resins with favorable impregnation performance was defined. It was found that low M:F ratios (~1:2–1:2.5) and comparatively high starting pHs (~pH 11) yield impregnation resins with rapid impregnation behavior and good residual curing capacity.

Fiber–matrix impregnation behavior during additive manufacturing of continuous carbon fiber reinforced polylactic acid composites

Abstract Continuous carbon fiber reinforced thermoplastic (C-CFRTP) composites have been broadly applied in key industries due to their excellent material properties. Fused filament fabrication (FFF), as a material extrusion additive manufacturing (AM) technology, can be applied to fabricate C-CFRTP parts with complex structures. However, the underlying fiber–matrix impregnation behavior during FFF of C-CFRTP composites, which is a key factor to bridge process parameters and mechanical properties, is still unknown. In this paper, we developed a theoretical model to discern the impregnation process at different parametric conditions. The microscopic measurement of continuous carbon fiber reinforced polylactic acid (PLA) specimens was conducted to characterize the impregnation percentage for the model verification. The results indicated that almost all predicted values agreed well with the experimental results. Additionally, the increase in impregnation percentage was found to improve the tensile strength. The findings in this work provide insights into the process-impregnation-property relationship and promote the effective FFF fabrication of C-CFRTP components.

Creep behavior of polyetherimide semipreg and epoxy prepreg composites: Structure vs. property relationship

In the present study, the creep behavior of polyetherimide semipreg and epoxy prepreg composites was studied using dynamic mechanical analyzer and focused on structure vs. property relationships in glassy, glass transition, and elastomeric regions. The main contribution to the field is to study pre-impregnated materials concerning creep behavior, mainly based on different analytical models, and microstructure. Two different reinforcements were used (carbon fiber and glass fiber) for each matrix. Findley, Burger, and Weibull analytical models were applied with an excellent fit for the most of them. The impregnation quality, verified by C-scan and the void content by acid digestion, shows different impregnation behaviors, mainly for epoxy/CF, which also influenced molecular motion behavior. The creep behavior was mainly influenced by matrix type than reinforcement architecture and void content. In addition, the creep was higher for epoxy in the glassy region; however, in the glass transition region, higher deformation was found for polyetherimide composites. Previous behavior is mainly attributed to higher energy storage in the glassy region which plays a significant role in the dissipation (glass transition energy), resulting in the energy loss or the drop of storage modulus in a narrow temperature range – more abrupt. This behavior was corroborated by time-temperature superposition curves in which the low deformation obtained for polyetherimide composites at low temperatures is maintained only until the glass transition temperature. Epoxy composites showed a higher initial creep deformation, but the values were almost constant with temperature, even when the temperature passes by the glass transition temperature.

Impregnation and resin flow analysis during compression process for thermoplastic composite production

Impregnation and in-plane resin flow of film-stacking material under compression process were investigated. The understanding of this phenomenon is the key to optimize the impregnation process under pressure rollers in a double-belt press for organo-sheet production. The stack of carbon fiber woven fabrics and viscous fluid were compressed in a flat open-edge mold under various controlled conditions using a testing machine. The impregnation, in-plane flow, and pressure profile were characterized from the experimental observations. Furthermore, a theoretical model was developed to describe the impregnation and in-plane flow behavior. The model prediction showed decent agreement with the experimental data. The developed model will be useful to optimize the process parameters of double belt press process.

Atmospheric impregnation behavior of calcium phosphate materials for antibiotic therapy in neurotrauma surgery.

As part of a verification model of antibiotic therapy in cranioplasty, we evaluated the impregnation efficiency of interporous calcium phosphate materials with saline under atmospheric pressure and compared it to the efficiency of using the decompression method established by the Japanese Industrial Standard, under which pressure is reduced by 10 kPa. Five types of material formed in 1 mL cubes were selected as test samples: two consisting of hydroxyapatite (HAp) with 85% and 55% porosity and three of β-tricalcium phosphate (β-TCP) with 75%, 67%, and 57% porosity. All test samples showed an impregnation ratio of more than 70%, except for the HAp sample with 55% porosity, which had a ratio of approximately 50%. These high ratios were achieved at only 15 min. The impregnation effects were likely dependent on porosity and were independent of base material, either HAp or β-TCP. Obtaining sufficient impregnation and antimicrobial efficacy in materials with low porosity, which are commonly used in cranioplasty, would require an increased volume of antibiotics rather than increased duration of impregnation. Our findings will enable the simple preparation of drug-impregnated calcium phosphate materials, even in operating rooms not equipped with a large decompression device.

A mechanistic model for tensile property of continuous carbon fiber reinforced plastic composites built by fused filament fabrication

Lightweight and high-strength continuous carbon fiber reinforced plastic (C-CFRP) composites have become promising materials for aerospace, automotive, and sports applications. Recently, fused filament fabrication (FFF) technology enables the production of geometrically complex C-CFRP components that are difficult to fabricate using conventional manufacturing processes. In this study, a novel mechanistic model to predict tensile strength and elastic modulus of C-CFRP parts built by a co-extrusion based FFF process was developed for the first time. The fiber-matrix impregnation behavior, physical gap ratio, and fiber orientation within the as-built C-CFRP were also considered. In order to verify the model, C-CFRP parts were fabricated using different matrix materials including PA, PC, PETG, PLA, and short carbon fiber reinforced PA (SCF/PA) for tensile testing. The comparative results showed that the prediction errors for tensile strength and elastic modulus were less than 5 % and 10 %, respectively. C-CFRP with the matrix of SCF/PA exhibited the largest tensile strength of 288.65 MPa, while C-CFRP with PLA matrix possessed the highest elastic modulus of 29.12 GPa. This study provided an insight into the material-process-impregnation-property relationship during co-extrusion based FFF of C-CFRP components.

Modeling transverse micro flow in dry fiber placement preforms

Dry fiber placement has a large potential for manufacturing preforms for primary-load components at minimum scrap rate and fiber crimp. Yet, challenging impregnation behavior due to low permeability of these preforms during liquid composite molding imposes a need for further research to optimize preform structure for higher permeability. For full understanding of flow behavior within these preforms, flow has to be considered on micro scale (in between single fibers), on meso scale (in between single rovings or strands), and on macro scale (on scale of parts to be manufactured). While macro and meso scale can be measured in experiments or derived from filling times in real processes, micro scale is usually not easily assessable and accessible for standard textile materials. Analytical approaches are limited to regular fiber arrangements (square and hexagonal) that are strongly differing from real arrangements. The present work deals with application of a numerical solver to random fiber arrangements to determine micro permeability transverse to the fiber orientation, for later use in meso- and macro-scaled models. As a premise for reliable calculation, guidelines for boundary conditions as well as size and resolution of the representative volume element are elaborated in the course of this work. Calculated out-of-plane micro permeabilities are subsequently compared to real experiments and show good accordance. The influence of binder particles on micro permeability has not yet been conclusively clarified.