Fiber Assembly Research Articles

JNK2 silencing lipid nanoparticles for elastic matrix repair.

The over-expression of c-Jun N-terminal kinase (JNK2), a stress activated mitogen kinase, in the aortic wall plays a critical role in the formation and progression of abdominal aortic aneurysm (AAA). This triggers chronic downstream upregulation of elastolytic matrix metalloproteinases (MMPs), MMPs2 and 9 to cause progressive proteolytic breakdown of the wall elastic matrix. We have previously shown that siNRA knockdown of JNK2 gene expression in an AAA culture model stimulates downstream elastin gene expression, elastic fiber formation, crosslinking and reduces elastolytic MMPs2 and 9. Since naked siRNA poorly routes to intracellular targets, has poor stability in blood, and could be potentially toxic and immunogenic, this project is aimed to develop PEGylated lipid nanoparticles (LNPs) for delivery of JNK siRNA and to generate evidence of successful JNK2 knockdown and downstream attenuation of MMP2 gene and protein expressions. LNPs were formulated using thin-film hydration technique and had the size of 100-200 nm with zeta-potential ranging between 30 and 40 mV. JNK siRNA loaded PEGylated LNPs successfully knocked down JNK2 in cytokine-activated rat aneurysmal smooth muscle (EaRASMC) cultures. This resulted in a downstream decrease in MMP2 gene and protein expression and an upward trend in expression of genes for proteins critical for elastic fiber assembly such as elastin (ELN) and lysyl oxidase (LOX). Our result indicates cationic LNPs to be potential carriers for JNK siRNA delivery improving potency for elastin homeostasis required for AAA repair which could possibly provide benefits in preventing the progression of small AAAs.

Hollow Microfiber Assembly-Based Endocrine Pancreas-on-a-Chip for Sugar Substitute Evaluation.

With the increasing demand for low-sugar, low-calorie healthy diets, artificial sweeteners are widely used as substitutes for sugar in the food industry. Therefore, developing models that can better predict the effects of sugar substitutes on the human body is necessary. Here, a new type of endocrine pancreas-on-a-chip is developed based on a microfiber assembly and its stimulation of pancreatic secretion by glucose or sugar substitutes is evaluated. This new endocrine pancreas-on-a-chip is assembled using two components: (1) a cell-loaded hollow methacrylate gelatin (GelMA)/calcium alginate (CaA) composite microfiber prepared by microfluidic spinning to achieve vascular simulation and material transport, and (2) a 3D pancreatic islet culture layer, which also serves as a fiber assembly microchip. Using this established organ chip, the effects of five sweeteners (glucose, erythritol, xylitol, sodium cyclamate, and sucralose) were investigated on pancreatic islet cell viability and insulin and glucagon secretion. The constructed endocrine pancreas-on-a-chip has potential for the safety evaluation of sugar-substituted food additives, which can expand the application of organ chips in the field of food safety and provide a new platform for evaluating various food additives.

3D Electrospinning of Al2O3/ZrO2 fibrous aerogels for multipurpose thermal insulation

Ceramic aerogels are excellent ultralight-weight thermal insulators yet impractical due to their tendency towards structural degradation at elevated temperatures, under mechanical disturbances, or in humid environments. Here, we present flexible and durable alumina/zirconia fibrous aerogels (AZFA) fabricated using 3D sol–gel electrospinning — a technique enabling in situ formation of 3D fiber assemblies with significantly reduced time consumption and low processing cost compared to most existing methods. Our AZFAs exhibit ultralow density (> 3.4 mg cm−3), low thermal conductivity (> 21.6 mW m−1 K−1), excellent fire resistance, while remaining mechanically elastic and flexible at 1300 °C, and thermally stable at 1500 °C. We investigate the underlying structure-thermal conductivity relationships, demonstrating that the macroscopic fiber arrangement dictates the solid-phase thermal conduction, and the mesopores in the fiber effectively trap air thereby decreasing the gas conduction. We show experimentally and theoretically that directional heat transport, i.e., anisotropic thermal conductivity, can be achieved through compressing the fiber network. We further solve the moisture sensitivity problem of common fibrous aerogels through fluorination coating. The resulting material possesses excellent hydrophobicity and self-cleaning properties, which can provide reliable thermal insulation under various conditions, including but not limited to high-temperature conditions in vehicles and aircraft, humid conditions in buildings, and underwater environments for oil pipelines.Graphical

Investigation of Basic Characteristics of Waterproof-Breathable Nonwoven Nano-Fabric Manufactured by Improved Melt-Blowing Method

In recent years, materials with both waterproof and breathability have also been marked with the eye-catching slogan of "waterproof-breathable" on the commodity such as personal protective equipment or sportswear. Regarding the application of nanofiber non-woven fabric as waterproof and breathable materials for functional textile, although there are previous reports regarding conventional micro-fabrics, the relationship between the compositions of the fiber aggregate, waterproof and breathable properties remain unclear regarding nanofabrics. Therefore, this study shows investigation of influence of fiber diameter, bulk density and thickness of the woven nanofabric on waterproof-breathable ability with experiment and CFD (computational fluid dynamics) model. As a result, the average fiber diameters, bulk densities, and thicknesses to achieve waterproofness and air permeability were numerically obtained respectively. From the results, it can be found that, these parameters can be used as a reference for manufacturing high-performance waterproof permeable materials with both high waterproofness and high air permeability.

The Novel Yersinia enterocolitica Telomere Phage vB_YenS_P840 Is Closely Related to PY54, but Reveals Some Striking Differences.

Telomere phages are a small group of temperate phages, whose prophages replicate as a linear plasmid with covalently closed ends. They have been isolated from some Enterobacteriaceae and from bacterial species living in aquatic environments. Phage PY54 was the first Yersinia (Y.) enterocolitica telomere phage isolated from a nonpathogenic O:5 strain, but recently a second telomeric Yersinia phage (vB_YenS_P840) was isolated from a tonsil of a wild boar in Germany. Both PY54 and vB_YenS_P840 (P840) have a siphoviridal morphology and a similar genome organization including the primary immunity region immB and telomere resolution site telRL. However, whereas PY54 only possesses one prophage repressor for the lysogenic cycle, vB_YenS_P840 encodes two. The telRL region of this phage was shown to be processed by the PY54 protelomerase under in vivo conditions, but unlike with PY54, a flanking inverted repeat was not required for processing. A further substantial difference between the phages is their host specificity. While PY54 infects Y. enterocolitica strains belonging to the serotypes O:5 and O:5,27, vB_YenS_P840 exclusively lyses O:3 strains. As the tail fiber and tail fiber assembly proteins of the phages differ significantly, we introduced the corresponding genes of vB_YenS_P840 by transposon mutagenesis into the PY54 genome and isolated several mutants that were able to infect both serotypes, O:5,27 and O:3.

Simulation of fiber configuration in the sliver with the straightness and separation degree

The fiber straightness and separation degree have the important influences on sliver properties. In this work, an innovative model of the fiber configuration considering straightness was presented and optimized by taking the fiber separation degree into account. The new developed model could simulate fiber assemblies and all kinds of separated fibers, including hooked fibers and straight fibers. Furthermore, some thin and thick segments were presented in the optimized simulated sliver with consideration of the fiber separation degree, and the simulated sliver irregularities were close to the actual ones. The relative errors between tested sliver irregularities and simulated ones were reduced from around 80% to less than 30%. Besides, the influence of each fiber parameter on the sliver irregularity could be drawn from the novel model of fiber configuration in the sliver, which verified the necessity of the applications of the straightness and separation degree. Therefore, it could be concluded that the introduction of the fiber straightness and the consideration of the fiber separation degree made more accurate and reasonable simulation of the fiber configuration in the sliver. Moreover, the straightening process of the hooked fibers and the random combination between thick fragments and thin fragments during the drawing simulation could be realized based on this model in the future.

Increased expression of phosphodiesterase 4 in activated hepatic stellate cells promotes cytoskeleton remodeling and cell migration.

Activation and transdifferentiation of hepatic stellate cells (HSC) into migratory myofibroblasts is a key process in liver fibrogenesis. Cell migration requires an active remodeling of the cytoskeleton, which is a tightly regulated process coordinated by Rho-specific guanine nucleotide exchange factors (GEFs) and the Rho family of small GTPases. Rho-associated kinase (ROCK) promotes assembly of focal adhesions and actin stress fibers by regulating cytoskeleton organization. GEF exchange protein directly activated by cAMP 1 (EPAC1) has been implicated in modulating TGFβ1 and Rho signaling; however, its role in HSC migration has never been examined. The aim of this study was to evaluate the role of cAMP-degrading phosphodiesterase 4 (PDE4) enzymes in regulating EPAC1 signaling, HSC migration, and fibrogenesis. We show that PDE4 protein expression is increased in activated HSCs expressing alpha smooth muscle actin and active myosin light chain (MLC) in fibrotic tissues of human nonalcoholic steatohepatitis cirrhosis livers and mouse livers exposed to carbon tetrachloride. In human livers, TGFβ1 levels were highly correlated with PDE4 expression. TGFβ1 treatment of LX2 HSCs decreased levels of cAMP and EPAC1 and increased PDE4D expression. PDE4 specific inhibitor, rolipram, and an EPAC-specific agonist decreased TGFβ1-mediated cell migration in vitro. In vivo, targeted delivery of rolipram to the liver prevented fibrogenesis and collagen deposition and decreased the expression of several fibrosis-related genes, and HSC activation. Proteomic analysis of mouse liver tissues identified the regulation of actin cytoskeleton by the kinase effectors of Rho GTPases as a major pathway impacted by rolipram. Western blot analyses confirmed that PDE4 inhibition decreased active MLC and endothelin 1 levels, key proteins involved in cytoskeleton remodeling and contractility. The current study, for the first time, demonstrates that PDE4 enzymes are expressed in hepatic myofibroblasts and promote cytoskeleton remodeling and HSC migration. © 2023 The Pathological Society of Great Britain and Ireland.

Potential Use of COVID-19 Surgical Masks and Polyethylene Plastics in Developing Sustainable Concrete

Managing disposable waste surgical face masks and plastic made from polyethylene (PE) resin is a real challenge. Thus, these are considered a great threat to the environment. Generally, surgical face masks are made of microplastic made of polypropylene materials. Both polypropylene and PE are not easily decomposable in the soil. Consequently, the presence of these waste materials can have detrimental effects on terrestrial and aquatic ecosystems, exacerbating the ongoing crisis faced by the animal kingdom and the broader biosphere. Hence, it is imperative to identify alternate and efficient methods for waste management. Given its significant economic importance, the construction industry holds a prominent position among many industries globally. Consequently, waste masks within the construction sector might assume a crucial role in mitigating plastic pollution. Concrete, one of the most widely used construction materials, is being adapted with various waste materials as the partial or complete substitutes for natural constituents, such as cement and aggregates. This study focused on using different percentages of used COVID-19 surgical masks in fiber form and PE as partial replacements of natural coarse aggregates in producing sustainable concrete. Mask fibers were used in concrete production at percentages of 0%, 0.5%, 1%, 1.5%, and 2% of the total volume of concrete. Similarly, PE aggregates replaced the coarse aggregates by volume at 0%, 5%, 10%, and 15% in concrete. The results showed that the strength of concrete reduced as the percentages of mask fiber and PE aggregates increased. However, the strength and crack-bridging capability of mask concrete are still acceptable for some structural and non-structural applications. The results obtained from this research could also help engineers to design sustainable concrete materials with mask fibers.

Releases of microplastics and chemicals from nonwoven polyester fabric-based polyurethane synthetic leather by photoaging

The nonwoven PET fabrics are chemically, mechanically and thermally treated fiber aggregate without weaving, knitting or braiding, which could be used as a base to make polyurethane (PU) synthetic leather through a series of processing. Our research systematically compared the photoaging behaviors of pure non-woven PET base fabric (NPET-P) and PU synthetic leather (nonwoven PET-base fabrics with PU coating, NPET-U), and their possibilities for microplastic fibers (MPFs) generation and chemical transformation in water. NPET-U was photoaged to a higher oxidation degree with higher O/C ratios and more distinct changes in chemical structures. The amount of MPFs released from NPET-U (1.98 × 107 g/fibers) was significantly lower than that from NPET-P (4.76 × 107 g/fibers) after 360 h light irradiation (p value <0.05) with a slower degradation rate and delayed MPFs release. The lengths and diameters of released MPFs from NPET-U varied within a smaller range than that from NPET-P exposed to UV light irradiation. Natural sunlight aging of fabrics for 365 days was found to be equivalent to approximately 85.3–127.2 h UV aging in the laboratory, which indicated the lab accelerated experiments was extraordinarily intense to simulate natural sunlight aging. Furthermore, abundant calcium and sulfur-contained chemicals were detected in original fabrics and the leachate of 360 h light-aged fabrics using the inductively coupled plasma optical emission spectrometer (ICP-OES). The organic components of the leachate were separated according to their molecular weight with the changes of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and the UV response over aging time. UV stimulation aggravated the role of plastic polymers as disinfection by-product (DBP) precursors. Nevertheless, although NPET-U could produce more nitrogen-contained chemicals, it had similar formation potentials of nitrogen-containing DBPs as NPET-P. The discussion lucubrated the potential risks of the production of MPFs and chemical release in the leachate with regard to combined plastic pollution.

Mechanisms of damage and fracture of aramid fibers: Focus on the role of microfibril cooperativity in fracture toughness

AbstractPushing the limits of synthetic polymers in terms of stiffness and strength, aromatic polyamide fibers–like Kevlar®–are used for demanding applications in the form of fiber assemblies as ropes. The unique mechanical performance of aramid fiber is intimately linked to its hierarchical structure and orientation, induced during the spinning process. Surprisingly, after nearly 60 years of heavy use, very little is known about damage mechanisms and rational explanation of such high resistance. We report an experimental investigation of the fiber damage mechanisms at the single fiber scale (diameter ≅ 10 μm) with the aim to establish a link with the microstructure. Damage mechanisms and crack propagation are observed in situ for the first time and unveil a widespread damage over the entire length of the fiber in the form of a network of transverse and longitudinal cracks. These observations make it possible to draw a novel scenario of fracture that mitigates the small strain failure hypothesis. To shed light on the crucial role of microfibril cooperativity in fracture toughness, a slight twist is applied to the single fiber to promote tortuosity and frictional contacts between microfibrils. Statistical fracture analysis demonstrated the beneficial impact of such torsion on early failure events, since lowest fracture stresses are shifted to higher stresses.

Effect of disaggregation and activation of sepiolite on interfacial interaction and mechanical properties of natural rubber/sepiolite composites prepared by latex compounding method

AbstractThe demand for environmentally friendly and non‐petroleum based natural rubber products is on the rise. Sepiolite, a one‐dimensional clay mineral, has been found to be a suitable reinforcement for natural rubber through latex compounding. However, the aggregation of fibers and minerals may impact the overall properties of natural rubber composites. To overcome this challenge, the study utilized ultrasonic disaggregation and oxalic acid activation to prepare stable sepiolite suspensions with varying specific surface areas and surface activities. These suspensions were then mixed with natural rubber latex to prepare NR/sepiolite composites. The results showed that the dispersibility and bonding ability of sepiolite with natural rubber were improved due to the increased specific surface area and surface activity, resulting in more bonding sites. The mechanical properties of the composites were also found to be improved, with a significant increase in tear strength (from 61.9 to 67.6 N·mm−1) and tensile strength (from 23.0 to 29.5 MPa). This research lays a strong foundation for the utilization of sepiolite in rubber materials.

Injectable hydrogel made from antler mesenchyme matrix for regenerative wound healing via creating a fetal-like niche.

Scar formation and loss of cutaneous appendages are the greatest challenges in cutaneous wound healing. Previous studies have indicated that antler reserve mesenchyme (RM) cells and their conditioned medium improved regenerative wound healing with partial recovery of cutaneous appendages. To develop hydrogels from the antler RM matrix (HARM) and evaluate the effect on wound healing. We prepared the hydrogels from the HARM via enzymatic solubilization with pepsin. Then we investigated the therapeutic effects of HARM on a full-thickness cutaneous wound healing rat model using both local injections surrounding the wound and topical wound application. The results showed that HARM accelerated wound healing rate and reduced scar formation. Also, HARM stimulated the regeneration of cutaneous appendages and blood vessels, and reduced collagen fiber aggregation. Further study showed that these functions might be achieved via creating a fetal-like niche at the wound site. The levels of fetal wound healing-related genes, including Collagen III and TGFβ3 treated with HARM were all increased, while the expression levels of Collagen I, TGFβ1, and Engrailed 1 were decreased in the healing. Moreover, the number of stem cells was increased in the fetal-like niche created by HARM, which may contribute to the regeneration of cutaneous appendages. Overall, we successfully developed an injectable hydrogel made from antler RM matrix for the regenerative repair of full-thickness cutaneous wounds. We uncovered the molecular mechanism of the hydrogels in promoting regenerative wound healing, and thus pave the way for HARM to be developed for the clinic use.

Reflectivity and fluffiness coupled optical algorithm for colored cotton fibrogram of random-beard image method

Insufficient studies of reflectance and fluffiness effects on optical density caused large derivation and limited the application of fibrogram methods in colored cotton fiber length tests for decades. A coupled optical method was proposed here to solve this issue, named reflectivity and fluffiness coupled optical algorithm of the random-beard image method. In this algorithm, a defined theoretical reflectance was declared with an iteration method for optical linear density on the optical analysis of the derived Kubelka–Munk law, which satisfied its assumption of excluding reflected light at the interface with air. Meanwhile, an apparent polynomial relationship was revealed between the actual density and optical densities of fiber assemblies at different fluffiness. Its accuracy on weighted mean fiber length was demonstrated, referred to as advanced fiber information system, using 10 kinds of dyed cotton slivers and 12 kinds of naturally colored lint fibers whose mean and maximum absolute errors are 0.59 mm and 1.6 mm, respectively. Furthermore, their excellent agreement on fibrograms and the weighted mean length was confirmed by Bland–Altman analysis, correlation analysis and the T-test. Finally, an exceptionally high linear correlation (r2 = 0.93) was achieved on their weighted mean length and had no statistical difference with insignificant deviation under a significance level of a = 0.01. This new algorithm, featured fast and low cost, could provide accurate mean fiber length of colored or dark cotton, exhibiting valuable guidance in the potential application of the fiber trade and the quality control of colored cotton fibers or primaries in blending assemblies and yarn.

A refined finite element model for UHPC-filled FRP tube column

A sound finite element model is essential for the nonlinear structural analysis of FRP tube-confined UHPC columns, wherein an accurate constitutive model to characterize the mechanical behavior of UHPC under passive constraints is of utmost importance. This study presents a refined finite element modeling methodology for the UHPC-filled FRP tube column. The constitutive model for UHPC under passive constraint is developed, in which the yield criterion, hardening/softening law, plastic flow rule, and damage evolution law are determined based on the experimental results of UHPC under multiaxial loading conditions. Furthermore, a solid element model of FRP tube with definable layer information is utilized to simulate the behavior of FRP tubes under complex stress states. The proposed finite element model is implemented in ABAQUS and verified through available experimental results. The results indicate that the proposed model can accurately predict the stress–strain behavior of confined UHPC with varying fiber and coarse aggregate contents, and describe the damage progression of UHPC and FRP tubes. Particularly, the interaction process between FRP and UHPC can be well reflected. The proposed finite element model serves as a paradigm for numerical analysis of UHPC-filled FRP tube elements and provides a reference for simulations of UHPC structures.

Deformation-dependent permeability of fibrous materials

Fluid flow in fibrous materials depends on volumetric deformation, distortional deformation and fibre reorientation. The latter two effects introduce anisotropy in the hydraulic permeability. Motivated by the study of biological tissues, this work aims to develop an analytical model for evaluating the deformation-dependent permeability of fibrous materials. The material consists of a three-dimensional assembly of long fibres of a single type, with the fluid flowing through the interstices between the fibres. The macroscopic deformations are related to the deformation of a cylindrical representative element of volume (REV), comprised of a fibre surrounded by a cylindrical jacket of fluid. The effect of fibre orientation is modelled using an orientational probability distribution function (OPDF), and the REV permeability tensor is then evaluated using previously developed methods, accounting for the macroscopic deformation. Finally, the overall permeability tensor is calculated via directional averaging of the REV permeability tensor, in which the fibre OPDF serves as the weighing function. The model is validated numerically via a uniaxial contraction (confined compression) test performed for the case of an OPDF that is isotropic in the reference (undeformed) configuration, and is found to qualitatively reproduce experimental findings. The proposed model offers an analytical tool for evaluating the permeability of fibrous materials under large deformations, based on structural information such as fibre volumetric fraction, diameter and spatial orientation.

Synthesis of a polyester with a liquid crystalline silsesquioxane-contained backbone Chain

A one-pot multistep growth melt procedure utilizing multistep feeding has been developed to enable the synthesis of thermoplastic polymers based on 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA)with greater numbers of alternating units in their backbone chains. The decreased melting point (Tm) and glass transition temperature (Tg) indicated that the multistep feeding procedure helped to enhance the flexibility of the backbone chain due to the increasing number of alternating blocks, due to a reduction in the stacking between different main-chains, thus enabling the formation of liquid crystalline polyester (LCP) fibers with oriented structures. The covalent incorporation of rigid cage-like silsesquioxane groups led to a significant reduction of the melting point, resulting from the inevitable transformation of the original symmetrical backbone structure to a less ordered structure, due to the steric effect and hybrid feature of silsesquioxane. The presentation of silsesquioxane groups also enhanced the aggregation of ultrafine fibers with well-aligned orientation in the molten state and produce stronger fiber bundles.

Pulse EPR spectroscopy and molecular modeling reveal the origins of the local heterogeneity of dietary fibers

Optimizing human diet by including dietary fibers would be more efficient when the fibers' chain interactions with other molecules are understood in depth. Thereby, it is important to develop methods for characterizing the fiber chain to be able to monitor its structural alterations upon intermolecular interactions. Here, we demonstrate the utility of the electron paramagnetic resonance (EPR) spectroscopy, complemented by simulations in probing the atomistic details of the chain conformations for spin-labeled fibers. Barley β-glucan, a native polysaccharide with linear chain, was utilized as a test fiber system to demonstrate the technique's capabilities. Pulse dipolar EPR data show good agreement with results of the fiber chain modeling, revealing sinuous chain conformations and providing polymer shape descriptors: the gyration tensor, spin-spin distance distribution function, and information about proton density near the spin probe. Results from EPR measurements point to the fiber aggregation in aqueous solution, which agrees with the results of the dynamic light scattering. We propose that the combination of pulse EPR measurements with modeling can be a perfect experimental tool for in-depth structural investigation of dietary fibers and their interaction under such conditions, and that the presented methodology can be extended to other weakly ordered or disordered macromolecules.

High resolution monitoring of valvular interstitial cell driven pathomechanisms in procalcific environment using label-free impedance spectroscopy.

Fibro-calcific aortic valve disease has high prevalence and is associated with significant mortality. Fibrotic extracellular matrix (ECM) remodeling and calcific mineral deposition change the valvular microarchitecture and deteriorate valvular function. Valvular interstitial cells (VICs) in profibrotic or procalcifying environment are frequently used in vitro models. However, remodeling processes take several days to weeks to develop, even in vitro. Continuous monitoring by real-time impedance spectroscopy (EIS) may reveal new insights into this process. VIC-driven ECM remodeling stimulated by procalcifying (PM) or profibrotic medium (FM) was monitored by label-free EIS. Collagen secretion, matrix mineralization, viability, mitochondrial damage, myofibroblastic gene expression and cytoskeletal alterations were analyzed. EIS profiles of VICs in control medium (CM) and FM were comparable. PM reproducibly induced a specific, biphasic EIS profile. Phase 1 showed an initial impedance drop, which moderately correlated with decreasing collagen secretion (r = 0.67, p = 0.22), accompanied by mitochondrial membrane hyperpolarization and cell death. Phase 2 EIS signal increase was positively correlated with augmented ECM mineralization (r = 0.97, p = 0.008). VICs in PM decreased myofibroblastic gene expression (p < 0.001) and stress fiber assembly compared to CM. EIS revealed sex-specific differences. Male VICs showed higher proliferation and in PM EIS decrease in phase 1 was significantly pronounced compared to female VICs (male minimum: 7.4 ± 4.2%, female minimum: 26.5 ± 4.4%, p < 0.01). VICs in PM reproduced disease characteristics in vitro remarkably fast with significant impact of donor sex. PM suppressed myofibroblastogenesis and favored ECM mineralization. In summary, EIS represents an efficient, easy-to-use, high-content screening tool enabling patient-specific, subgroup- and temporal resolution.

Mechanical model of stiffness coefficients prediction of curved fiber reinforced composites considering fiber distribution and aggregation

In this paper, a mechanical model is built to numerically predict the stiffness coefficients of curved fiber reinforced composites. Aiming to quantitatively describe the geometrical morphology of a curved fiber, a curve parameter and an orientation angle are both defined. For a composite with abundant curved fibers, distribution functions are introduced to describe the various curve parameters and angles. To quantitatively express the probability and degree of fiber aggregation, a probability function and an aggregating parameter are also proposed. Validation examples for composite with unidirectional straight fibers, orthogonal distributed straight fibers or unidirectional curve fibers are given to verify the correctness and accuracy of the current model as well as the numerical process. Numerical examples considering composites with ordered and disordered distributed fibers are carried out to show the predicted stiffness coefficients of typical curved fiber reinforced composites. Universality of the model is obvious through the numerical examples.

Effect of process parameters on the mechanical properties of fiber‐reinforced thermoplastics fabricated by direct fiber feeding injection molding

AbstractGlass fiber‐reinforced polypropylene composites (GF/PP) were fabricated in this study by direct fiber feeding injection molding technology (DFFIM) equipped with specially designed plasticizing units. By analyzing the fiber length distribution, scanning electron microscopy micrographs, and the mechanical properties of GF/PP composites, the effect of three process parameters, namely the number of fiber bundles, screw rotational speed, and injection pressure, on the properties of GF/PP composites fabricated by DFFIM were investigated. The results show that the mechanical properties of GF/PP composites gradually increase as the fiber content increases and the screw rotational speed decreases; however, when the fiber content exceeds a certain range, the enhancement effect of mechanical property is reduced due to the increase of fiber breakage and fiber aggregation. Appropriately increasing the injection pressure can increase the fiber length and make the fiber and PP more tightly bonded, and the mechanical properties of GF/PP composites gradually improve, but the fiber breakage phenomenon is more severe under excessive injection pressure, the mechanical property enhancement effect is reduced or even the mechanical property is decreased due to the decrease of the fiber length.