Discontinuous Fiber Research Articles

Microscopic stresses of discontinuous fiber reinforced composites under thermal and mechanical loadings – Finite element simulations and statistical analyses

The microscopic stresses of the discontinuous fiber reinforced composites under thermal and mechanical loadings have not been intensively studied as they cannot be directly measured. Thus, a finite element simulation associated with a suitable analysis strategy is required to reveal the microscopic stresses of these composite materials, though it is challenging owing to the randomly distributed fibers. In this study, the microscopic stresses in an actual composite are simulated by using finite element method and combining techniques of morphology transformation, massively parallel computing, and edge effect removal. The probability density of the von Mises stress of the resin exhibits a single peak and covers a wide range, following the Burr statistic model regardless of the loading type. The external mechanical loading and material modulus, rather than the thermal loading, are the main factors affecting the probability density. The reason for the appearance of the lower and upper values of the von Mises stress of the resin is also discussed. The characteristics of the discontinuous fiber reinforced composite evaluated in this preliminary study are beneficial to understand the mechanical properties of such new composites.

Achieving synergy of load-carrying capability and damage tolerance in a ZrB2-SiC composite reinforced through discontinuous carbon fiber

Achieving synergy between load-carrying capability and excellent damage tolerance is one of the most concerned issues in the ultra-high temperature ceramic field. Herein, ZrB2-SiC-Cf composite with homogenous architecture was constructed by a novel pressure filtration and slurry infiltration accompanied by low-temperature hot pressing. The composite exhibited a typical non-brittle fracture feature owing to crack deflection, crack bifurcation and fiber pull-out mechanisms, resulting in a reliable specific flexural strength of 75 MPa/(g/cm3) and superior work of fracture of 672 J/m2.

Effect of alkaline treatment on mechanical properties of composites: Unsaturated polyester reinforced ZrO2/jute and sisal

Alkali treated (5 wt. % alkali was used on the total weight of the alkali solution and the treatment time was 2 h) discontinuous cellulosic fiber (jute and sisal were used as cellulosic fibers and 35 wt. % filler content was incorporated) reinforced chemically modified ZrO2 (ZrO2 was used as 10 wt. % of total filler content. In this context, it is worthwhile to mention that when both fillers were used, the fiber content was taken in the weight ratio of 1:1.) dispersed hybrid unsaturated polyester composites were fabricated by a compression molding technique. The mechanical behavior of the fabricated composites was evaluated at the sub-micron scale by nanoindentation (indentation with an applied load on the composites surface at the nano-metric range) or depth-sensing instrumented indentation technique. The significant effect of incorporation of the dispersing phases within the unsaturated polyester matrix with respect to mechanical properties at microstructural length scale was observed. A marked improvement in the nanoindentation-derived parameters viz. , nanohardness, reduced modulus, elastic recovery, and indentation creep was observed which may be attributed due to the influence of fillers inclusion within the unsaturated polyester matrix. An extensive effort was laid to analyze the dynamic mechanical properties using the sinus indentation mode associated with nanoindentation measurements to further correlate the influence of fillers addition with the indentation-derived parameters.

Mechanical behavior of cellulosic fiber-incorporated modified fly ash-dispersed polymeric composites

Alkali-treated discontinuous cellulosic fibers (jute and sisal)-based heat-treated silanized fly ash-dispersed hybrid polyester composites were fabricated using a compression molding technique. The morphological features were observed using a scanning electron microscope and a high-resolution transmission electron microscope. The bulk mechanical testing namely, microhardness, tensile, flexural as well as Izod impact was successfully executed. The significant effect of the filler (cellulosic fibers as well as modified fly ash) dispersion within the polymeric matrix with respect to mechanical properties was thoroughly examined in this present investigation.

Cellulose-derived flexible carbonized paper for high-performance electromagnetic interference shielding

In this study, we describe the fabrication of flexible carbonized paper (f-CP) from toilet paper samples using a sandwich-type installation technique in a thermal chemical vapor deposition system. During the reaction, the substrate was heated up to 1000 °C at a rate of ~20 °C/min and naturally cooled down to room temperature in an Ar gas environment without temperature holding. The f-CP sample thus obtained contained continuous carbon fibers similar to the native toilet paper sample while carbonized paper (CP) fabricated using the conventional installation technique contained discontinuous carbon fibers. Compared to CP, f-CP exhibited higher electrical conductivity, mechanical flexibility, and shielding effectiveness (SE) against electromagnetic radiation. Even after bending the f-CP sample several hundred times, its SE decreased only slightly. Multi-layered f-CP (mf-CP; 3 mm thickness and 0.053 g/cm3 density) fabricated by stacking f-CP samples showed a remarkably high SE of 58 dB in the operating frequency range of 8.2–12.4 GHz. Therefore, f-CP and mf-CP, which exhibit excellent electromagnetic shielding characteristics, may potentially be used in electronic devices.

Evaluation of Discontinuous Carbon Fiber Reinforced Thermoplastics by General Measurement Systems

Evaluation of Discontinuous Carbon Fiber Reinforced Thermoplastics by General Measurement Systems

Modeling Short-Range Interactions in Concentrated Newtonian Fiber Bundle Suspensions

Abstract Sheet Molding Compounds (SMC) offer a cost efficient way to enhance mechanical properties of a polymer with long discontinuous fibers, while maintaining formability to integrate functions, such as ribs, beads or other structural reinforcements. During SMC manufacturing, fibers remain often in a bundled configuration and the resulting fiber architecture determines part properties. Accurate prediction of this architecture by simulation of flow under consideration of the transient rheology and transient fiber orientations can speed up the development process. In particular, the interaction of bundles is of significance to predict molding pressures correctly in a direct simulation approach, which resolves individual fiber bundles. Thus, this work investigates the tangential short-range lubrication forces between fiber bundles with analytical and numerical techniques. A relation between the effective sheared gap between bundles and the bundle separation distance at the contact point is found and compared to experimental results from literature. The result is implemented in an ABAQUS contact subroutine to incorporate short-range interactions in a direct bundle simulation framework.

The Effect of Alkali Treatment on Physical, Mechanical and Thermal Properties of Kenaf Fiber and Polymer Epoxy Composites.

The use of kenaf fiber as a reinforcement material for polymer composites is gaining popularity, especially in the production of automotive components. The main objective of this current work is to relate the effect of alkali treatment on the single fiber itself and the composite material simultaneously. The effect of temperature condition during mechanical testing is also investigated. Composite materials with discontinuous natural kenaf fibers and epoxy resin were fabricated using a compression moulding process. The epoxy composites were reinforced with 50 wt% untreated and treated kenaf fibers. The kenaf fiber was treated with NaOH solution (6% by weight) for 24 h at room temperature. Kenaf fiber treated with NaOH treatment had a clean surface and no impurities. For the first time we can see that alkali treatment had a damaging effect on the mechanical properties of kenaf fibers itself and the treated kenaf/epoxy composites. The composite reinforced with untreated kenaf fiber and treated kenaf fiber showed increased tensile strength (72.85% and 12.97%, respectively) compared to the neat epoxy. Reinforcement of the composite with treated kenaf fiber decreased the tensile strength due to the fiber pull out and the formation of voids which weakens the adhesion between the fibers and matrix. The temperature conditions also play an important role in composites with a significant impact on the deterioration of composite materials. Treated kenaf fiber has thermal stability and is not sensitive to temperature and as a result reinforcement with treated kenaf gives a lower loss value of 76%.

An experimental investigation on low-velocity impact response and compression after impact of a stochastic, discontinuous prepreg tape composite

The present paper investigated the impact and compression after impact behavior of thin carbon fiber epoxy plates manufactured from prepreg platelet molding compound (PPMC) with two different discontinuous fiber length, 25.5 mm and 12.7 mm, and compared it with the behavior of continuous fiber quasi-isotropic composite laminate with a similar plate thickness. The results of dynamic testing showed that PPMC/12.7 mm exhibited larger amount of absorbed energy, which correlated with larger damage area measured by ultrasonic inspection. Micro-CT analysis showed that a discontinuous fiber composite developed significant amount of through-thickness damage. C-scan measured damage area correlated well with the compression after impact testing results, which indicated that longer fibers provide for better damage tolerance.

EXPERIMENTAL STUDY AND NUMERICAL MODELLING FOR FLEXURAL CAPACITY OF FRC STRUCTURAL ELEMENTS

Concrete reinforced by short steel fibres is typical brittle matrix composite, in which fibres are impeding cracks growth, such way increasing material’s tensile strength. The use of steel fibre reinforced concrete (SFRC) in structures with high physical and mechanical characteristics makes possible to reduce their weight and cost, to simplify their production technology, to reduce or eliminate reinforcement labour, at the same time increasing reliability and durability. Randomly distributed discontinuous fibres are bridging the crack’s flanks providing material’s “ductility”- like non-linear behaviour at cracking stage. The current study is focused on one formulation of a specific type of concrete matrix with added fibres and without fibres. Concrete cubes and prisms without fibres and having in every situation the same content of 60 mm long fibres were fabricated. Cubes (100×100×100 mm) were tested in compression and beams (100×100×400 mm prisms) were tested under four-point bending (4PBT). Fracture process (crack growth) in the material was modelled, based on experimental results (part of experimental data was used). Finite element method (FEM) using the ANSYS program analysis were realized modelling stress distributions in the broken beams with the goal to predict fracture process. Model’s prediction was validated.

A novel discrete–continuous material orientation optimization model for stiffness-based concurrent design of fiber composite

The cooperation of tailoring fiber angles and designing its macro layout is an excellent approach to improve the performance of composite structures and achieve lighter weight. This article proposes a novel discrete–continuous optimization model for the concurrent optimization of the macro structural topology and local fiber angle for the fiber-reinforced composite structure. Therein, the novel modeling consists of a two-step strategy, where the normal distribution function is adopted to form the discrete material interpolation scheme firstly and then the continuous angle design on fine angle subintervals is conducted. Because it requires the fixed discrete design variables regardless of the number of angle subintervals and simultaneously achieves the continuous fiber angle design, it can save computational cost and provide an infinite design domain. Furthermore, the subdividing angle interval reduces the risks of falling into the local optimum solution for continuous angle design. Besides, the fiber discontinuity may cause stress concentration and manufacturing problems in the intersection of discontinuous fiber paths. Therefore, a linear density technique is used to achieve fiber continuity. Finally, a concurrent topology optimization model is built based on the proposed novel model. And several numerical examples are well-organized and presented to illustrate the validity of the proposed model.

Crashworthiness of recycled carbon fiber composites

The crashworthiness of discontinuous recycled carbon fiber composites was studied. Sinusoidal crush specimens were manufactured of acrylonitrile butadiene styrene, polyphenylene sulfide, and a common structural epoxy reinforced with recycled carbon fibers. Samples were tested at a range of strain rates and temperatures representative of automotive conditions. Crush debris size was quantified using sieving to correlate with energy absorption. The effect of manufacturing flaws such as embedded foreign objects, porosity, and ductile tearing was studied by comparing x-ray computed tomography images with crush test data gathered using digital image correlation. The results show great promise for discontinuous fiber organosheet composites as a novel material for automotive crash structures, exceeding the energy absorption capabilities of many continuous fiber thermosets.

Energy absorption and self-sensing performance of 3D printed CF/PEEK cellular composites

We report the energy absorption and piezoresistive self-sensing performance of 3D printed discontinuous carbon fiber (CF)-reinforced polyetheretherketone (PEEK) cellular composites. Experiments conducted on three different 2D lattices with hexagonal, chiral and re-entrant topologies of the same relative density (33%) and CF loading (30 wt%) reveal that the CF/PEEK hexagonal lattice (HL), due its relatively brittle response, shows about 40% and 9% decrease in specific energy absorption (SEA) under in-plane and out-of-plane compression, respectively, compared with PEEK HL. While the collapse response of PEEK HL is nearly insensitive to the strain-rate over 43 ≤ ε̇ ≤ 106 s−1, we observe a twenty-fold increase in peak stress and a five-fold increase in SEA under in-plane impact loading over the same range of strain-rates for the CF/PEEK HL. The CF/PEEK lattices exhibit pronounced piezoresistive response under both in-plane and out-of-plane compression with maximum sensitivity of 3.1 and 5.2, respectively, for the re-entrant lattice, offering insight into the damage-state. Higher damage sensitivity indicates faster percolation of new contacts due to folds forming between the cell walls within the lattice under compression. The energy-absorbing and strain- and damage-sensing nature of 3D printed CF/PEEK lattices demonstrated here offers insight into the design of lightweight, high-performance multifunctional lattices.

Analytical Study on Reinforced Concrete Beam With Carbon, Steel and Glass Fibers

Reinforced concrete mostly used in construction materials in the world. Fibre reinforced concrete in which small and discontinuous fibres are dispersed commonly. Fibre reinforced concrete used in fibres may be in different materials like carbon, steel and glass fibres etc. In addition of these fibres increases the compressive strength, tensile strength, flexural strength, and impact strength of concrete. carbon fibre reinforced concrete (CFRC) containing fibres of 1.5% and 0.2 of poisons ratio and steel fibre reinforced concrete (SFRC) containing fibres of 1.5% and 0.21 of poisons ratio and Glass fibre reinforced concrete (GFRC) containing fibres of 1.5% and 0.2 of poisons ratio. The results that comparing normal beam with fibre beam results. Its type and dimensions are selected based on preliminary study using ANSYS Software.

Substitution of virgin carbon fiber with low-cost recycled fiber in automotive grade injection molding polyamide 66 for equivalent composite mechanical performance with improved sustainability

Recycled carbon fiber has historically proven challenging to integrate into composite manufacturing due in no small part to the low-density, randomly oriented, discontinuous fiber format that results from typical recycling. Discontinuous fiber requires the use of alternative technologies than those traditionally applied to continuous fiber (e.g., hand lay-up, winding). Extrusion compounding is one such applicable technology, but material transfer into the system requires alternative feeding equipment or the use of an altered procedure as trialed in this research. In this study, an injection molding compound for automotive applications was prepared with recycled carbon fiber and compared against an existing commercial compound. Input fibers and molded compound were evaluated for mechanical performance, while relevant variables such as compounded fiber alignment and aspect ratio were compared to the existing baseline material to confirm a like-for-like composite material structure. Analysis indicates that recycled fiber performs similarly to virgin fiber reinforcement, demonstrating that recycled fiber may be a viable drop-in replacement for short-fiber discontinuous applications.

Prediction of strength and modulus of discontinuous carbon fiber composites considering stochastic microstructure

Modeling the mechanical behavior of discontinuous fiber composites has long been a challenge for the composites community and is of increasing interest due to recent interest for automotive lightweighting. Micromechanical models typically predict the stiffness accurately, but reliable strength models have been largely elusive due to the highly stochastic microstructure. This paper presents a stiffness and strength laminate analogy model for discontinuous fiber composites using stochastic fiber orientation, length, fiber volume fraction, and void volume fraction. For the first time, the master ply invariant approach has been applied to discontinuous fiber composites and shows good agreement in modeling the stiffness. A strain energy density-based laminate failure condition successfully predicts the tensile strength of these composites. This paper demonstrates accurate, first-order strength and stiffness predictions for discontinuous fiber composites using constituent properties readily obtained from material datasheets.

Multilevel Analysis of Strain Rate Effect on Visco-Damage Evolution in Short Random Fiber Reinforced Polymer Composites

Abstract In this study, the strain rate sensitivity of a discontinuous short fiber reinforced composite and the strain rate effect on the damage evolution are investigated. The studied material is a polymeric composite with a polyamide 6.6 matrix reinforced with oriented randomly short glass fibers at a 50% weigh ratio (PA6.6GF50). Tensile tests at low and high strain rate are conducted. In addition, interrupted tensile tests are carried out to quantify the damage at specific stress levels and strain rates. To perform the interrupted tensile tests, an intermediate fixture is realized via double notched mechanical fuses with different widths designed to break at suitable stress levels. The damage is estimated by the fraction of debonded fibers and matrix fractures. Based on the experimental observations, it is concluded that the ultimate stress and strain, and the damage threshold are mainly governed by the strain rate. Furthermore, it is established that the considered composite has a non-linear dynamic behavior with a viscous damage nature.

Theoretical approximation of hydrodynamic and fiber-fiber interaction forces for macroscopic simulations of polymer flow process with fiber orientation tensors

Flow processes of discontinuous fiber reinforced polymers (FRPs) are the essence of several polymer-based manufacturing processes. FRPs show a transient chemo-thermomechanical matrix behavior and fiber-induced anisotropic physical properties. Therefore, they are one of the most complex materials used in volume production. The general flow behavior is influenced by fibers and their interactions with the matrix and other fibers. The consideration of individual fibers is numerically not capable for process simulation of FRP parts. Therefore, orientation tensors are used in macroscopic simulations, leading to a loss of information about the fiber network. Within this work, novel approximation schemes are presented to determine hydrodynamic and fiber-fiber contact forces with information provided by the second order fiber orientation tensor. Approximation of these forces can henceforth facilitate fiber breakage modeling in macroscopic process simulations. The results are verified by numerical simulations with individual fibers of different orientation states and lengths, showing good agreement with the verification results.

Effects of heat treatment on interfacial characteristics and mechanical properties of titanium matrix composites reinforced with discontinuous carbon fibers

Weak interfacial bonding was a significant problem in titanium matrix composites (TMCs) reinforced with carbon fibers (CFs). In this study, heat treatment (HT) up to 1000 °C was applied on powder metallurgy Ti-6Al-4V matrix composites reinforced with discontinuous CFs to obtain different interfacial structures. Mechanical tests at both room-temperature and 500 °C showed that the best mechanical properties were attained at HT temperature of 900 °C. To understand the underlying mechanism, the phase structure, grain morphology and interfacial microstructure were examined. It was found that as HT temperature was increased, the interface thickness increases continuously and obvious grain growth happens at 1000 °C. Suitable interfacial reaction and fine grain size are identified as critical structural parameters to obtain high-performance CFs/TMCs. This study may provide new insight into the role of interfacial structure played in the strengthening effect of CFs/TMCs.

Analysis of the wool thickness and medullation characteristics based on sex and color in a herd of alpacas in Poland.

The objective of this study was to analyze the thickness and medullation characteristics of the wool of a herd of Huacaya alpacas kept in Poland. Wool samples were collected from 36 adult alpacas, including 22 females and 14 males. Light (15 animals) and dark (21 animals) color varieties of wool were considered in this research. A projection microscope was used to measure the fiber diameter and assess the medullation. Each fiber was categorized according to the medulla as a non-medullated, discontinuous medullated or continuous medullated fiber. The mean fiber diameter (MFD), standard deviation (SD), coefficient of variation (CV), comfort factor (CF) and prickling factor (PF) were determined for each sample. The MFD, SD and CV were also determined for the abovementioned fiber categories. The mean fiber diameter of all alpacas tested was 25.31 . The CF and PF were 77.79 % and 22.21 %, respectively. The medullation percentage in the wool of the study alpacas was 68.91 %. The mean fiber diameter was larger in males () than in females. There were no differences between males and females in terms of the proportion of fibers with a diameter 30 (CF) and 30 (PF). The non-medullated fibers in the wool of females were thinner () than in the wool of males. The wool of males also had a larger degree of medullation. Light wool was thinner () than dark wool. The discontinuous and the continuous medullated fibers were thicker () in dark wool than in light wool. In dark wool, the share of discontinuous fibers was higher () and the share of the non-medullated fibers was lower () than in light wool. The presence of various types of medulla or the absence of medulla was noted in fibers with smaller and larger diameters, regardless of the sex of the animals or the color of the wool.