Discontinuous Fiber Research Articles

SPH Simulation for Short Fibre Recycling Using Water Jet Alignment

ABSTRACT This work presents a computational model for a discontinuous fibre composite manufacturing process. The alignment mechanism of this novel process, called the High Performance Discontinuous Fibre (HiPerDiF) method, involves highly coupled fluid–structure interactions. Fibres with a length on the order of a few millimetres are placed in a water suspension, sprayed between two parallel plates and deposited on a moving belt to make an aligned discontinuous fibre tape. This technology can be used as part of a composites recycling process to remanufacture reclaimed fibres into valuable recycled composite feedstock by ensuring a high level of alignment. This work aims to model the alignment mechanism using smoothed particle hydrodynamics in order to inform the design of the industrial machine. The results reveal the influence of jet angle and fibre length on the overall quality of fibre alignment.

A review of the mechanical properties of additively manufactured fiber reinforced composites

Recent developments in additive manufacturing technologies have made it possible to print fiber reinforced composite materials that have reasonable mechanical performance. In this paper, a brief review of the additive manufacturing technologies for composites are presented. The focus is the mechanical properties of both discontinuous and continuous fiber reinforced composites fabricated by state-of-the-art additive manufacturing technologies. The deformation mechanisms are also briefly discussed. In addition, recommendations for future work are made.

Development and calibration of a structural simulation method of CF-SMC composite parts processed by compression molding

The need for the reduction in CO2 production in automotive field increasingly leads manufacturers to consider fiber-reinforced composite materials that are however costly to processes. Discontinuous fiber composite materials, like CF - SMC, are a competitive candidate because they are transformed by the high productivity compression molding technology. On the negative side, their structural complexity introduces high variability in the mechanical performance that needs to be considered at the design stage. This contribution describes the development of a structural modeling strategy for parts made of CF-SMC processed by compression molding. It is based the statistical material model proposed by Feraboli implemented here in a FEA-based structural analysis procedure. After validation and calibration of a specific CF-SMC material, the proposed procedure is applied to the simulation of the structural response of a compression molded part of complex geometry subjected to know loading conditions.

Asymmetric flexural process and fracture behaviors of natural bamboo node with gradient discontinuous fibers

Natural bamboo node samples bended from two opposite radial directions (Type I and Type II) displayed asymmetric flexural fracture process and behaviors. The real-time flexural process and fracture behaviors were observed and analyzed with the aid of optical video microscopy and acoustic emission (AE). Results indicated there are three kind of fracture behaviors within bamboo node during the deformation and fracture process, which are parenchyma cells failure, fiber dissociation and fiber breakage. They showed different sequences due to the gradient discontinuous fibers within bamboo node. The toughening mechanisms within bamboo node are concluded as cellular-fibrous effect, crack deflection, fiber bridging/pull-out and the induced avalanche delay.

Masonry buildings strengthened with textile-fiber composite (TRC) layers and fiber-reinforced cementitious (FRC) layers

In June 2015, the authors published a paper titled “Brief Report of Shaking Table Test on Masonry Building Strengthened with Ferrocement Layers” [1]. The authors suggested in that paper to replace the traditional way of constructing masonry houses using the so called practical columns and beams (herein after called traditional masonry houses) with bandaging using ferrocement layers on both sides of the walls as skin facings and brick wall as core. Since then, many masonry houses bandaged with ferrocement layers are built in Indonesia. Apart from constructing new earthquake resistant houses, ferrocement bandaging is also used for retrofitting existing as well as damaged houses after earthquakes. In the past decades, continuous fiber mesh was introduced to replace the steel wire mesh in a cementitious matrix. Since the early 2000, textile-based composites were used in the field of strengthening and seismic retrofitting of masonry as well as concrete structures. Originally these new “textile fiber composite” materials are called “Textile Reinforced Concrete” (TRC) in Europe. However, in the USA, the term used is “Fiber Reinforced Cementitious Matrix systems” (FRCM). Extensive research on FRCM / TRC were conducted. A wide variety of publications on the subject matter are now available worldwide. Apart from TRC, many technical studies are published addressing fiber reinforced cement and concrete composite. The term “Fiber Reinforced Cementitious” (FRC) is used and defined as concrete and/or cementitious matrix with suitable discontinuous fibers added to it for the purposes of achieving a desired level of performance in a particular property, such as modulus elasticity, tensile strength, and ductility [2]. Lately, the use of discontinuous fibers as reinforcement for concrete and cementitious matrix FRC are introduced by many practitioners and civil engineers. Adding fibers in concrete / cementitious matrix mixer simply like adding sand or admixtures, to create a homogenous, isotropic, strong, tough, durable, and moldable structural materials [2]. In this paper the authors used the terms of TRC and FRC as defined by Naaman [2, 3], namely TRC for fiber-cement with fiber-mesh and FRC for fiber-cement with discontinuous fiber. This paper provides a simplified global analysis of the overall structure strengthened with FRCM / TRC as well as strengthened with FRC.

A brief review on mechanical properties of Al-MMCs fabricated by stir casting route & applications

Aluminium metal matrix composites are pretty much important in the different demanding sectors such as in the field of medicine and engineering like automobiles, aerospace, defence, dental and consumer goods. The need arises due to its huge calibre in industrial need of good materials with lighter weight, excellent properties and economical in cost demanded the researchers or scientists research on composite materials. The AMMCs or Al-MMCs consists of an apex variety of mechanical properties which is directly proportional to the chemical composition of the Aluminium matrix. To enhance strength the reinforcement plays a key role in AMMCs could be in the form of continuous/ discontinuous fibres, whiskers & particulate as the second phase depending on their applications and property requirements. In addition to it, various strength enhancers are reinforcements such as fly ash, TiC, SiC, Al2O3, TiO2, B4C etc. This paper attempts to review the different combinations in the processing of aluminium metal matrix composites along with their properties and their applications.

Long fiber thermoplastic pellets of glass fiber/polypropylene from pultrusion process

Long fiber thermoplastic pellets (LFTP) are composite materials that consist of thermoplastic and discontinuous reinforcement fibers with an aspect ratio more than critical aspect ratio. LFTP are high modulus, high strength and excellent impact resistance. Normally, commercial LFTP were produced by hot melt impregnation process or combinding between pultrusion and extrusion process. In this research, Thermoplastic pultrusion process was used for production of LFTP. The thermoplastic pultrusion process is uncomplicated process and machine less than hot melt impregnation process. The glass fibers were used in LFTP as a reinforcement and polypropylene (PP) fibers were used as a matrix of LFTP. General full factorial design of experiment was used to determine the optimal condition for un-impregnation on specimen from pultrusion process of LFTP. The study focused on three factors including the filling ratio, the molding temperature and pulling speed. The specimens were investigated on impregnation of resin in LFTP by microscope. The results show that un-impregnation decreased with an increase of filling ratio. Un-impregnation decreased with an increase of molding temperature. Finally, un-impregnation had increased with an increase of pulling speed. However, the void content has a little effect to molding temperature and pulling speed, or they have not almost effect. From statistical analysis, the optimal condition for the pultrusion process of LFTP was filling ratio of 104.73 %, molding temperature of 230 °C and pulling speed of 10 cm/min, which was given the lowest un-impregnation value of 5.85 %.

Effect of Fractal‐Based Fiber Clustering on Tensile Properties of BFRP

To explore the clustering phenomenon of discontinuous fibers in composite materials, this paper deduces the fiber uniform distribution coefficient and analytical expressions of fiber clustering content based on fractal theory and establishes a tensile strength prediction model of fiber/epoxy resin composite materials containing cluster fibers. With basalt fiber/epoxy resin composites (BFRP) as an example, this paper analyzes the tensile strength law of BFRP under fiber clustering effect. The results show that when the fiber volume fraction is constant, the tensile strength of the composite in the presence of agglomerated fibers is only related to the fractal dimension of the circumference and cross‐sectional area of the inner fiber agglomerate. The calculated value of the composite tensile strength based on fractal theory is lower than the experimental value, but closer to the experimental value than the approximate method. The research conclusions can provide theoretical support for strength prediction of fiber/epoxy resin composites.

Repurposed/recycled discontinuous carbon fiber organosheet development and composite properties

The high cost of carbon fiber composites often limits their use in automotive applications. This paper describes the study of an emerging class of materials, chopped fiber reinforced thermoplastic (polyphenylene sulfide) organosheets that provide mechanical properties exceeding sheet molding compounds at low material and manufacturing cost with long shelf life at room temperature. The tensile and shear properties were found to be directionally-dependent, while the impact of void content on these properties was small. It was shown that tensile testing of the dry preforms can serve as a method of screening the degree of anisotropy, reducing the need for extensive processing trials. Due to the anisotropy and microstructure variance of these materials, designs must encompass laminate stacking sequence and the variability in mechanical properties. Monte Carlo simulations of composite lamination theory utilizing stochastic mechanical properties conservatively predict the mechanical properties of organosheet laminates. This paper offers one of the first in-depth evaluations of this novel new class of composite materials made of repurposed/recycled carbon fiber.

On the effective elastic properties based on mean-field homogenization of sheet molding compound composites

Fiber reinforced polymers, for example sheet molding compounds (SMC), have gained significant importance as lightweight materials. In this work, a SMC composite based on unsaturated polyester-polyurethane hybrid resin (UPPH) reinforced with discontinuous long glass fibers is considered. The mechanical behavior of this composite is highly governed by its microstructure. Based on samples extracted from compression molded sheets, the underlying microstructure is characterized by means of X-ray computed tomography (µCT) scans. Tensile tests are performed to investigate and characterize the elastic properties of this composite. A mean-field method is presented to approximate the effective elastic behavior. In this context, the tensile tests performed serve as validation data for the simulation results. The effective Young’s modulus is in good agreement with the experimentally obtained data with a deviation less than 15%.

Mechanical characterization of particulated FRP composite pipes: A comprehensive experimental study

Particulated fiber reinforced polymer (FRP) composite pipes encompass unidirectional continuous glass fibers (hoop glass), resin (thermoset polymer vinylester) matrix, chop glass (discontinuous short fibers), and particulate reinforcement (sand) impregnated into resin. They are categorized based on their nominal diameter, pressure class, and stiffness class. Mechanical characteristics of this class of composite materials have not, to date, been comprehensively studied. As such, this paper presents a systematic approach toward comprehensive experimental investigation into their mechanical characterizations in terms of the axial and hoop tensile strengths. The particulated FRP composite pipes used in the current study have glass fibers reinforced along the hoop direction at approximately 89° angle. To assure the experimental data accuracy and reliability, three batches associated with each pipe category were selected which slightly differ in the composition of their constituents. Three specimens per batch were selected and two types of tests were conducted on each specimen. 18 tests (2 × 3 batches × 3 specimens)) were conducted per pipe category (9 tests for hoop and 9 tests for axial). Therefore, 648 tests were conducted in total on 36 pipe categories. Instron 5569A and Instron 8801 universal testing machines were utilized for the axial tensile tests and a split disc hydraulic testing machine for the hoop tensile tests. The mean tensile and the hoop axial stresses and their associated standard deviations were calculated based on the Population Standard Deviation (PSD) equation and then plotted against the material constituents. The results demonstrated that an increase in the composition of particulate reinforcement results in a decrease in the axial and the hoop tensile strengths. However, increasing the ratio of resin, chop glass, and glass fibers contributes to the enhancement of the axial and the hoop tensile strengths. This study provides comprehensive design guidelines for engineers and manufacturing industries.

Polyetheretherketone and Its Composites for Bone Replacement and Regeneration.

In this article, recent advances in the development, preparation, biocompatibility and mechanical properties of polyetheretherketone (PEEK) and its composites for hard and soft tissue engineering are reviewed. PEEK has been widely employed for fabricating spinal fusions due to its radiolucency, chemical stability and superior sterilization resistance at high temperatures. PEEK can also be tailored into patient-specific implants for treating orbital and craniofacial defects in combination with additive manufacturing process. However, PEEK is bioinert, lacking osseointegration after implantation. Accordingly, several approaches including surface roughening, thin film coating technology, and addition of bioactive hydroxyapatite (HA) micro-/nanofillers have been adopted to improve osseointegration performance. The elastic modulus of PEEK is 3.7–4.0 GPa, being considerably lower than that of human cortical bone ranging from 7–30 GPa. Thus, PEEK is not stiff enough to sustain applied stress in load-bearing orthopedic implants. Therefore, HA micro-/nanofillers, continuous and discontinuous carbon fibers are incorporated into PEEK for enhancing its stiffness for load-bearing applications. Among these, carbon fibers are more effective than HA micro-/nanofillers in providing additional stiffness and load-bearing capabilities. In particular, the tensile properties of PEEK composite with 30wt% short carbon fibers resemble those of cortical bone. Hydrophobic PEEK shows no degradation behavior, thus hampering its use for making porous bone scaffolds. PEEK can be blended with hydrophilic polymers such as polyglycolic acid and polyvinyl alcohol to produce biodegradable scaffolds for bone tissue engineering applications.

A Force-Balanced Fiber Retardation Model to Predict Fiber-Matrix-Separation during Polymer Processing

The use of discontinuous fiber reinforced composites in injection and compression molding faces a number of challenges regarding process-induced changes in microstructure, which have a significant influence on the mechanical properties of the final component. The changes in final microstructure are caused by complex fiber movements, such as fiber orientation, attrition and accumulation during flow. While there are existing phenomenological prediction models for both fiber orientation and attrition, the prediction of fiber accumulation due to fiber-matrix separation is currently only possible with a complex mechanistic particle simulation, which is not applicable in industrial simulations. A simplified phenomenological model, the fiber retardation model (FRM), for the prediction of fiber-matrix separation in commercially available software tools is presented in this paper. The model applies a force balance onto an interacting two phase flow of polymer melt and fiber phase and applies a retardation factor Κ to calculate the slowing and accumulation of the fiber phase. The general model is successfully applied to a simple compression molding simulation.

Direct Fiber Simulation of a Compression Molded Ribbed Structure Made of a Sheet Molding Compound with Randomly Oriented Carbon/Epoxy Prepreg Strands—A Comparison of Predicted Fiber Orientations with Computed Tomography Analyses

Discontinuous fiber composites (DFC) such as carbon fiber sheet molding compounds (CF-SMC) are increasingly used in the automotive industry for manufacturing lightweight parts. Due to the flow conditions during compression molding of complex geometries, a locally varying fiber orientation evolves. Knowing these process-induced fiber orientations is key to a proper part design since the mechanical properties of the final part highly depend on its local microstructure. Local fiber orientations can be measured and analyzed by means of micro-computed tomography (µCT) and digital image processing, or predicted by process simulation. This paper presents a detailed comparison of numerical and experimental analyses of compression molded ribbed hat profile parts made of CF-SMC with 50 mm long randomly oriented strands (ROS) of chopped unidirectional (UD) carbon/epoxy prepreg tape. X-ray µCT scans of three entire CF-SMC parts are analyzed to compare determined orientation tensors with those coming from a direct fiber simulation (DFS) tool featuring a novel strand generation approach, realistically mimicking the initial ROS charge mesostructure. The DFS results show an overall good agreement of predicted local fiber orientations with µCT measurements, and are therefore precious information that can be used in subsequent integrative simulations to determine the part’s mesostructure-related anisotropic behavior under mechanical loads.

Fiber bundle tracking method to analyze sheet molding compound microstructure based on computed tomography images

Discontinuous fiber reinforced polymers (DicoFRP) like Sheet Molding Compounds (SMC) are frequently applied in modern lightweight designs, due to their good formability and mechanical properties at low density. The DicoFRP microstructure affects the mechanical properties and has to be taken into account in the design process. X-ray Micro-Computed Tomography (μCT) systems acquire volumetric images of microstructures in a non-destructive way. The fiber orientation is determined by using state-of-the-art image processing tools. The resolution of volumetric images and the specimen size are directly coupled due to the cone-beam μCT geometry. In order to identify all individual fibers, high resolution images are needed and consequently, only small specimen volumes are scanned. The present contribution makes use of the property that fibers are arranged as bundles within SMC. Consequently, fiber bundles instead of individual fibers are used to analyze microstructures in order to overcome the μCT-cone-beam-related conflict between sample size and image resolution. The fiber bundles are determined by means of orientation data and an introduced tracking method, facing the challenge of crossing fiber bundles. Subsequently, the tracked fiber bundles, which are related to the same mesoscopic fiber bundle are merged by using a hierarchical agglomerative clustering method. The presented method is applied to a typical SMC microstructure. This contribution introduces an image processing method for analyzing SMC microstructures based on fiber bundles, opening up the possibility to investigate large specimen volumes. This enables to characterize representative SMC microstructures and utilize the data for art modeling approaches.

Fabrication and Characterisation of Aligned Discontinuous Carbon Fibre Reinforced Thermoplastics as Feedstock Material for Fused Filament Fabrication.

In this work, aligned discontinuous fibre composite (ADFRC) tapes were developed and investigated as precursors for a novel 3D printing filament. ADFRCs have the potential to achieve mechanical performance comparable to continuous fibre reinforced composites, given sufficient fibre length and high level of alignment, and avoid many of the manufacturing difficulties associated with continuous fibres, e.g., wrinkling, bridging and corner radii constraints. Their potential use for fused filament fabrication (FFF) techniques was investigated here. An extensive down-selection process of thermoplastic matrices was performed, as matrix properties significantly impact both the processing and performance of the filament. This resulted in four candidate polymers (ABS, PLA, Nylon, PETG) which were used to manufacture ADFRC tapes with a Vf of 12.5% using the high performance discontinuous fibre (HiPerDiF) technology and an in-house developed continuous consolidation module. Tensile stiffness and strength up to 30 GPa and 400 MPa respectively were recorded, showing that a discontinuous fibre filament has the potential to compete with continuous fibre filaments.

Machine learning-based prediction for compressive and flexural strengths of steel fiber-reinforced concrete

Steel fiber-reinforced concrete (SFRC) has a performance superior to that of normal concrete because of the addition of discontinuous fibers. The development of strengths prediction technique of SFRC is, however, still in its infancy compared to that of normal concrete because of its complexity and limited available data. To overcome this limitation, research was conducted to develop an optimum machine learning algorithm for predicting the compressive and flexural strengths of SFRC. The resulting feature impact was also analyzed to confirm the reliability of the models. To achieve this, compressive and flexural strengths data from SFRC were collected through extensive literature reviews, and a database was created. Eleven machine learning algorithms were then established based on the dataset. K-fold validation was conducted to prevent overfitting, and the algorithms were regulated. The boosting- and tree-based models had the optimal performance, whereas the K-nearest neighbor, linear, ridge, lasso regressor, support vector regressor, and multilayer perceptron models had the worst performance. The water-to-cement ratio and silica fume content were the most influential factors in the prediction of compressive strength of SFRC, whereas the silica fume and fiber volume fraction most strongly influenced the flexural strength. Finally, it was found that, in general, the compressive strength prediction performance was better than the flexural strength prediction performance, regardless of the machine learning algorithm.

Effects of hygrothermal aging on the thermomechanical properties of a carbon fiber reinforced epoxy sheet molding compound: An experimental research

AbstractCarbon fiber sheet molding compounds (C‐SMCs) are discontinuous fiber reinforced composite materials. Among them, epoxy‐based C‐SMCs are becoming relevant materials due to their high thermomechanical performance and better formability than continuous fiber reinforced composites. The thermomechanical performance of epoxy resins and epoxy based continuous carbon fiber composites have shown to be influenced by hygrothermal aging. In this work, this influence is studied for an epoxy‐based C‐SMC. Epoxy‐based C‐SMC samples were hygrothermally aged by means of accelerated conditioning, exposing them to 65% relative humidity, and 80°C in a climatic chamber. The equilibrium moisture content, as well as the moisture diffusion coefficient has been determined. The thermomechanical properties of epoxy C‐SMC have been analyzed by dynamic mechanical analysis, tensile, 3‐point bending, and short beam tests in dry and aged samples. The results showed that epoxy C‐SMC is affected by hygrothermal aging in the cases of moisture intake and its effects on Tg value, but interestingly, the hygrothermal aging did not generate any degradation effects in the mechanical response of epoxy C‐SMC.

Effects of node with discontinuous hierarchical fibers on the tensile fracture behaviors of natural bamboo

Bamboo is widely planted in the world and many species of bamboo are intensively used as sustainable bio-composite materials in the construction of houses, pavilions, furniture and bridges, etc. The bamboo nodes play an important role on natural bamboo's strength. This paper is focused on the structure-property-fracture relations of the natural Moso bamboo with node. The inner structures are characterized by optical and scanning electron microscopy (SEM), which indicated that bamboo node has coarser fiber bundles, higher volumes of fibers and 3D woven hierarchical fibrous structures. Though the fibers on the out and inner skins of node are discontinuous, it has higher strength than internodes samples. There are three kinds of fracture behaviors within bamboo node during the tensile fracture process as detected by acoustic emission (AE), which are matrix (parenchyma cells) failure, fiber dissociation and fiber breakage. The AE results indicated bamboo node has much lower volumes of fracture behaviors, higher proportions of fiber dissociation and matrix failure due to its hierarchical fibrous woven structure. The strengthening effects within bamboo node are concluded as coarse fiber bundles, high volumes of fibers, fiber pull-out and crack deflections.

Fiber reinforcement of a resin modified glass ionomer cement

ObjectivesUnderstand how discontinuous short glass fibers and braided long fibers can be effectively used to reinforce a resin modified glass ionomer cement (RMGIC) for carious lesion restorations. MethodsTwo control groups (powder/liquid kit and capsule) were prepared from a light cured RMGIC. Either discontinuous short glass fibers or braided polyethylene fiber ribbons were used as a reinforcement both with and without pre-impregnation with resin. For the former case, the matrix was the powder/liquid kit RMGIC, and for the latter case the matrix was the capsule form. Flexural strength was evaluated by three-point beam bending and fracture toughness was evaluated by the single-edge V-notch beam method. Compressive strength tests were performed on cylindrical samples. Results were compared by analysis of variances and Tukey’s post-hoc test. Flexural strength data were analyzed using Weibull statistical analysis. ResultsThe short fiber reinforced RMGIC both with and without pre-impregnation showed a significant increase of ∼50% in the mean flexural strength and 160–220% higher fracture toughness compared with the powder/liquid RMGIC control. Reinforcement with continuous braided fibers gave more than a 150% increase in flexural strength, and pre-impregnation of the braided fibers with resin resulted in a significant flexural strength increase of more than 300% relative to the capsule control. However, for the short fiber reinforced RMGIC there was no significant benefit of resin pre-impregnation of the fibers. The Weibull modulus for the flexural strength approximately doubled for the fiber reinforced groups compared to the control groups. Finally, compressive strength was similar for all the groups tested. SignificanceBy using a RMGIC as a matrix, higher flexural strength was achieved compared to reported values for short fiber reinforced GICs. Additionally, the short fibers provided effective toughening of the RMGIC matrix by a fiber bridging mechanism. Finally, continuous braided polyethylene fibers gave much higher flexural strength than discontinuous glass fibers, and their effectiveness was enhanced by pre-impregnation of the fibers with resin.