Fiber Defects Research Articles

Progressive Microstructural Deterioration Dictates Evolving Biomechanical Dysfunction in the Marfan Aorta.

Medial deterioration leading to thoracic aortic aneurysms arises from multiple causes, chief among them mutations to the gene that encodes fibrillin-1 and leads to Marfan syndrome. Fibrillin-1 microfibrils associate with elastin to form elastic fibers, which are essential structural, functional, and instructional components of the normal aortic wall. Compromised elastic fibers adversely impact overall structural integrity and alter smooth muscle cell phenotype. Despite significant progress in characterizing clinical, histopathological, and mechanical aspects of fibrillin-1 related aortopathies, a direct correlation between the progression of microstructural defects and the associated mechanical properties that dictate aortic functionality remains wanting. In this paper, age-matched wild-type, Fbn1C1041G/+, and Fbn1mgR/mgR mouse models were selected to represent three stages of increasing severity of the Marfan aortic phenotype. Ex vivo multiphoton imaging and biaxial mechanical testing of the ascending and descending thoracic aorta under physiological loading conditions demonstrated that elastic fiber defects, collagen fiber remodeling, and cell reorganization increase with increasing dilatation. Three-dimensional microstructural characterization further revealed radial patterns of medial degeneration that become more uniform with increasing dilatation while correlating strongly with increased circumferential material stiffness and decreased elastic energy storage, both of which comprise aortic functionality.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

Grading of Raw Jute Fibres Using Criteria Importance through Intercriteria Correlation (CRITIC) and Range of Value (ROV) Approach of Multi-criteria Decision Making

ABSTRACT In modern BIS system, a scientific approach is adopted for grading the raw jute fibers based on six apposite physical properties, namely fiber strength, defect, root content, fineness, color, and bulk density, of which the latter two parameters are still evaluated subjectively. Several researchers have attempted, over the years, many exponents of multi-criteria decision making (MCDM) approaches and got encouraging results. However, in all these approaches, subjective weighting methods have been used in the form of analytic hierarchy process (AHP). In this paper, a maiden integrated approach using criteria importance through intercriteria correlation (CRITIC) and range of value (ROV) is presented for grading jute fibers on the basis of abovementioned six attributes. Ranking performance of the present approach closely resembles with other approaches hitherto attempted by several researchers. The efficacy and robustness of the new approach are validated using sensitivity analysis through altering the weightage levels of the criteria. The rank correlation coefficients between the ranking patterns obtained in each of the weightage levels are, in most of the cases, 1 or very close to 1, which signifies no occurrence of rank reversal or change in ranking. During sensitivity analysis in dynamic decision conditions, the approach is stable up to certain level and then rank reversal takes place for some of the alternatives including the top ranked one. The uniqueness of the present study lies in the fact that here criteria weights are determined objectively using CRITIC and hence more reliable and devoid of influence/preferences of decision-makers (DMs). Moreover, the new approach is very simple with a few simple mathematical equations, albeit a potent tool of decision making with strong background logic.

Interconversion mechanisms of Ge-related oxygen deficient defects in germanium dioxide optical fiber

The interconversion mechanisms of Ge-related oxygen deficient defects including Ge-related oxygen deficient center (GeODC), Ge-related E' center (Ge-E') and germanium lone pair center (GLPC) have been investigated in germanium dioxide optical fiber. Our results revealed that the conversion paths from GeODC through Ge-E' centers, GLPC and then back to GeODC were similar in four- to six-membered rings. Furthermore, the transformation from Ge-E' to GLPC is spontaneous, indicating that it is the most likely to take place. We employed first-principles calculations to calculate optical properties and electronic properties of Ge-related oxygen deficient defects as well. All these models have a series of absorption peaks at 4-6 eV in the optical absorption spectrum, which may be related to the defect levels generated in the band gap. Our work provides a better understanding of the interaction among the three defects in germanium dioxide optical fiber.

Fatigue Damage Evaluation of Short Carbon Fiber Reinforced Plastics Based on Thermoelastic Temperature Change and Second Harmonic Components of Thermal Signal.

Short fiber reinforced plastics (SFRPs) have excellent moldability and productivity compared to continuous fiber composites. In this study, thermoelastic stress analysis (TSA) was applied to detect delamination defects in short carbon fiber reinforced plastics (SCFRPs). The thermoelastic temperature change ΔTE, phase of thermal signal θE, and second harmonic temperature component ΔTD were measured. In the fatigue test of SCFRP, it was confirmed that changes in ΔTE, θE, and ΔTD appeared in the damaged regions. A staircase-like stress level test for a SCFRP specimen was conducted to investigate the generation mechanism of the ΔTD. The distortion of the temperature change appeared at the maximum tension stress of the sinusoidal load—and when the stress level decreased, the temperature change returned to the original sinusoidal waveform. ΔTD changed according to the change in the maximum stress during the staircase-like stress level test, and a large value of ΔTD was observed in the final ruptured region. A distortion of the temperature change and ΔTD was considered to be caused by the change in stress sharing condition between the fiber and resin due to delamination damage. Therefore, ΔTD can be applied to the detection of delamination defects and the evaluation of damage propagation.

Bio‐Sourced Poly l‐Lactide‐Flax Composites with Close to Maximum Stiffness at Low Fiber Content through Two‐Stage Annealing

AbstractPoly l‐Lactide (PLLA) composites with short flax fibers (from 0 to 10 wt/wt%) with close to maximum theoretical stiffness are prepared by melt‐compounding and injection‐molding followed by a two‐step isothermal crystallization protocol that fully separates the nucleation and growth stages (Tammann). The use of fast chip scanning calorimetry for thermal characterization avoids the complicating issues of crystal reorganization during the cooling and heating steps between the isothermal stages. Flax fibers are very efficient and selective nucleating agents of PLLA favoring the ordered α form. The resulting morphology exhibits trans‐crystallization on the fibers surface, predominantly at fiber defects, with a clear reduction of crystal size and a very strong fiber matrix cohesion. Efficient nucleation further leads to a large reduction of the overall crystallization time. Avrami analysis evidences a reduction of crystal growth dimensionality, consistent with both optical and scanning electron microscopy. The high modulus of the composites is unambiguously related to the strong orientation of the fibers in the tensile direction, to their high aspect ratio and to the excellent matrix‐fibers cohesion. On the other hand, the tensile strength and hardness appear isotropic within experimental uncertainty and are unfavorably influenced by the presence of the fibers and by the two‐stage annealing.

Effect of Defects on Progressive Failure Behavior of Plain Weave Textile Composites.

Various types of internal defects occur during manufacturing and handling of composite materials. It is practically impossible to manufacture composite structures without defects, making it crucial to understand the effect of defects on their failure behavior to maintain structural safety. In this work, the effect of pre-defects on the failure behavior of plain weave textile composites was studied. Unit cell configurations with symmetric, in-phase, and shifted fiber tow arrangements were considered. Inter-laced warp and fill tows and matrix pockets of plain weave unit cells were modeled in three-dimensional finite elements, and cohesive elements were inserted between all bulk elements to account for the fracture modes of the fiber and matrix direction failure of warp and fill tows, matrix pocket failure, and interface failure. Unit cell models containing pre-defects of voids, tow-matrix pocket separation, warp-fill tow separation, and cracks in the warp and fill tows were analyzed, and their effects on progressive failure behavior were investigated in terms of the interaction between fiber tow arrangements and defects. Results indicated that initial failure occurred in matrix-direction failure mode in fill tows, whereas fiber tow-matrix pocket separation was the major failure mode under uniaxial tensile load. Furthermore, failure behavior was found to be highly dependent on the fiber tow arrangement pattern and the location of pre-defects.

Generating 3D digital material twins for woven ceramic‐matrix composites from μCT images

AbstractThis paper proposes a novel method for generating 3D digital material twins (DMTs) from μCT images for woven ceramic‐matrix composites. The key points to generating DMTs are the efficient and high‐precision identification and segmentation of fiber yarns, matrix, and defects in μCT images. Due to the low gray contrast among fiber yarns, traditional threshold segmentation methods cannot effectively obtain the corresponding woven structures. Therefore, a novel deep convolution neural network (DCNN) model with the U‐Net architecture is developed to overcome these difficulties. Based on this approach, cross sections and centerlines of fiber yarns are identified and used to reconstruct their 3D architectures. Defects are introduced through the spatial mapping between their locations in μCT images and the 3D meshes of the matrix. The DMTs of a C/SiC woven composite with quantitative matrix porosity defects are established, and a simulation of the composite under tension is presented. The DMTs approach provides new insights into damage and failure analyses of ceramic‐matrix composites.

Comprehensive approach to determination of space proton-induced displacement defects in silica optical fiber

Silica-based optical fibers presents a variety of applications used in radiation environments such as space, fusion facilities, accelerators and nuclear power plants. The radiation-induced displacement damage in optical fibers resulting in point defects may lead to attenuation signals that is a major concern for these applications. The present study proposes a computational approach to the calculation of the proton-induced displacement damage in vitreous silica. Therefore, Geant4 as a Monte Carlo particle transport code has been used to obtain the knock-on atom distributions caused by the interaction of space trapped proton with vitreous silica during an ISS mission. Moreover, molecular dynamics simulations using ReaxFF potential have been performed to produce the initial vitreous silica structure to evaluate the displacement damage cascades by LAMMPS package. The results show that ReaxFF has an appropriate potential to produce and evaluate the vitreous silica structure that provides better agreement with experimental data at both short-range and medium-range order. Furthermore, ODC(Si3) and NBOHC(O1) are dominant defect species created in the vitreous silica after trapped proton irradiation, where the total number of defects have increased on average by 94 for each keV increasing in PKA energy approximately.

A multiphasic model for determination of water and solute transport across the arterial wall: effects of elastic fiber defects.

Transport of solute across the arterial wall is a process driven by both convection and diffusion. In disease, the elastic fibers in the arterial wall are disrupted and lead to altered fluid and mass transport kinetics. A computational mixture model was used to numerically match previously published data of fluid and solute permeation experiments in groups of mouse arteries with genetic (knockout of fibulin-5) or chemical (treatment with elastase) disruption of elastic fibers. A biphasic model of fluid permeation indicated the governing property to be the hydraulic permeability, which was estimated to be 1.52×10-9, 1.01×10-8, and 1.07×10-8 mm4/μN.s for control, knockout, and elastase groups, respectively. A multiphasic model incorporating solute transport was used to estimate effective diffusivities that were dependent on molecular weight, consistent with expected transport behaviors in multiphasic biological tissues. The effective diffusivity for the 4 kDA FITC-dextran solute, but not the 70 or 150 kDa FITC-dextran solutes, was dependent on elastic fiber structure, with increasing values from control to knockout to elastase groups, suggesting that elastic fiber disruption affects transport of lower molecular weight solutes. The model used here sets the groundwork for future work investigating transport through the arterial wall.

Improvement in the Quantification of Foreign Object Defects in Carbon Fiber Laminates Using Immersion Pulse-Echo Ultrasound.

This research presents a new technique using pulse echo ultrasound for sizing foreign objects within carbon fiber laminates. Carbon fiber laminates are becoming increasingly popular in a wide variety of industries for their desirable properties. It is not uncommon for manufacturing defects to occur within a carbon fiber laminates, causing waste, either in the discarding of failed parts or the overdesign of the initial part to account for these anticipated and undetected errors. One such manufacturing defect is the occurrence of a foreign object within the laminate. This defect will lead to a localized weakness within the laminate including, but not limited to, stress risers, delamination, and catastrophic failure. This paper presents a method to analyze high-resolution c-scan full waveform captured data to automatically capture the geometry of the foreign object with minimal user inputs without a-priori knowledge of the shape of the defect. This paper analyzes twelve samples, each a twelve-lamina carbon fiber laminate. Foreign objects are made from polytetrafluoroethylene (PTFE) measuring 0.05 mm (0.002 in.) thick and ranging in diameter from 12.7 mm (0.5 in) to 1.588 mm (0.0625 in), are placed within the laminates during fabrication at varying depths. The samples are analyzed with a custom high-resolution c-scan system and smoothing, and edge detection methods are applied to the collected c-scan data. Results are presented on the sizing of the foreign objects with an average error of 6% of the true area, and an average absolute difference in the estimation of the diameter of 0.1 mm (0.004 in), an improvement over recently presented ultrasonic methods by a factor of three.

Characterization and Determination of the Biocompatibility of Porous Polytetrafluoroethylene Membranes Fabricated via Electrospinning

The structure and properties of polytetrafluoroethylene (PTFE) polymeric membranes obtained by electrospinning from a suspension of PTFE in a solution of polyvinyl alcohol (PVA) with subsequent thermal treatment were presented. The effect of the PTFE suspension ratio in spinning solutions on the morphology, crystal structure, chemical composition, strength, and cytotoxicity of the formed PTFE membranes was evaluated. We found that a decrease in the PTFE suspension content in spinning solutions leads to a decrease in the number of defects in the membrane fibers, which increasing the strength and elongation. Membranes made from spinning solutions with a lower content of PTFE suspension have a higher degree of crystallinity and a more perfect crystal structure. It has been suggested that the products of PVA destruction during the heat treatment of PTFE/PVA membranes are capable of plasticizing effects on PTFE particles, improving the strength of PTFE membranes. The membranes after thermal treatment were not cytotoxic regardless of the PTFE suspension content in the spinning solutions. High biocompatibility of membranes was established during implantation into soft tissues.

Effect of nickel electroplating followed by a further copper electroplating on the micro-structure and mechanical properties of high modulus carbon fibers

The nickel electroplating followed by a further copper electroplating process was conducted on high modulus carbon fibers (HMCFs), and the HMCFs were oxidized in nitric acid prior to the Ni-plating process. Effect of the electroplating process on the microstructure and mechanical properties of HMCFs was investigated. Uniform nickel particles were observed on the surfaces of Ni-plated HMCFs and fiber diameter increased from 5.0 μm to 6.1 μm. With a further Cu-electroplating process, the fiber diameter continued increasing to 7.5 μm. The Ni-plating process resulted in increased surface roughness, whereas the surface RMS and Ra values dropped significantly after the Cu-plating process. Owing to the Ni-plating treatment, the relative content of carbon element on fiber surfaces decreased from 96.54 % to 36.74 %. After a further Cu-plating process, the relative content of Cu element on HMCF surfaces was as high as 54.01 %. The electroplating process resulted in decreased tensile modulus from 415.71 GPa to 407.71 GPa. By contrast, the tensile strength of electroplated HMCFs increased by 1.1 % due to the reduction of fiber defects and stress concentration. Results also showed that both the Ni-plating and Cu-plating process could lead to significant decreases in the values of electrical resistance and resistivity.

Highly flexible and strong SiC fibre mats prepared by electrospinning and hot-drawing

ABSTRACT Silicon carbide (SiC) fibres are widely used as promising reinforcement in ceramic matrix composites due to their excellent mechanical and thermal properties. In this work, sub-micrometer SiC fibres were prepared by electrospinning using polycarbosilane as the precursor, followed by curing in air and pyrolysing at high temperatures. The effect of the microstructure of SiC fibres on mechanical properties was investigated and the SiC fibre mats prepared at 1300°C for 2 h exhibited a mechanical strength of 184.5 ± 19.4 MPa. Hot-drawing was conducted on as-spun fibres during the curing process and the strength, Young’s modulus, and flexibility of SiC fibre mats were improved. The strength with a drawing ratio of 200% reaches 243.0 ± 17.5 MPa. The enhancement of mechanical strength after hot-drawing is mainly attributed to the reduced defects in fibres, improvement in the orientation of the precursor fibres as well as the alignment of the molecular chains in the precursor fibres.

Effect of processing condition and antioxidants on visual properties of multilayer post-consumer recycled high density polyethylene films

Mechanical recycling is a promising approach to reduce the environmental impact of plastic packaging waste. However, the presence of defects in recycled materials results in final products with relatively poor visual and/or mechanical properties. In this work, the origin of the visual defects in post-consumer recycled HDPE (PCR HDPE), as well as the effects of processing method, processing condition and the addition of antioxidants on the visual defects were studied in multilayer flexible polyethylene films. The nature of the defects in the film samples were investigated by combining optical microscopy, energy dispersive X-ray (EDX), hot stage microscopy, solvent extraction, and differential scanning calorimetry (DSC) techniques. It was found that the defects in PCR film samples can be mainly categorized as fiber defects and point gels. Hot stage microscopy results show that point gels can be subcategorized in two groups: (a) non-melting, non-deformable gels, and (b) melting, deformable defects. In addition, it was found that deformation of molten, deformable defects increased at higher temperatures specifically above 200 °C. Further characterizations showed that the observed deformable defects are highly entangled high molecular weight HDPE. The effect of processing temperature, processing with a twin-screw extruder and the addition of antioxidant on the visual defects in film samples were also discussed in detail. It was shown that increasing processing temperature and using twin-screw extruders were two approaches that could reduce considerably the number of defects. The addition of antioxidants was also shown to improve the film quality especially at lower processing temperatures.

Study on production technology and surface morphology of carbon fiber

Since the 21st century, China’s carbon fiber industry has begun to develop rapidly. The research and development of carbon fiber is a major project related to national strategic security. Carbon fiber production technology has been mature, among which PAN based carbon fiber has the largest capacity. However, compared with the imported carbon fiber materials, there is still a certain gap in the performance of domestic carbon fiber materials. The purpose of this paper is to compare the properties of domestic carbon fiber and its composites. Firstly, the production process of carbon fiber is introduced, including monomer polymerization, spinning, oiling, preoxidation, carbonization, graphitization and other steps. Then, the T700 Carbon Fibers of Toray, Japan and two kinds of domestic T700 Carbon Fibers of Hengshen and Weihai were characterized and analyzed, and the surface morphology of three kinds of carbon fibers was compared. It is found that the domestic carbon fiber of Weihai adopts the similar technology of thousand spray wet spinning, and the fiber surface is smooth. However, Hengshen carbon fiber adopts the wet spinning process. There are grooves on the surface of the fiber, which will increase the mechanical meshing force between the fiber and the resin, and have a positive significance for the interface performance of the composite. However, it will increase the probability of fiber defects, such as fine lines, and have a negative impact on its tensile properties and other mechanical properties.

Effect on the processability, structure and mechanical properties of highly dispersed in situ ZnO:CS nanoparticles into PVA electrospun fibers

The main purpose of this work was to synthesize ZnO nanoparticles (NPs) in situ into a chitosan (CS) matrix to obtain highly dispersed antibacterial composites by the sol–gel technique. These composites were characterized by their thermal, structural, morphological and optical properties. NPs were subsequently used and added into polyvinyl alcohol (PVA) in order to obtain electrospun fibers. Previously, it was determined the adequate PVA/CS ratio and changes in their morphological features in dependence of molecular weight of PVA and electrospinning parameters to avoid the beads and spindle-like defects in the final fibers. Then, optimal conditions were used to fabricate PVA/in situ ZnO:CS nanofiber composites. The hydrogen bonding interaction governs the ZnO:CS system, which forms a combination between flower-type and agglomerated rod morphologies. It was found that CS promotes the crystallinity of ZnO NPs maintaining the hexagonal phase. The addition of ZnO into the CS matrix was performed via weak interactions by stabilizing the hybrid compound after the second decomposition stage when the mass loss is above 50%. Free-defects uniform fibers with an improvement in hardness as well as in the elastic modulus was obtained in the electrospun PVA/in situ ZnO:CS fibers. The presence of ZnO NPs improves the spinnability in the fiber nanocomposites with an average diameter of 223 nm. PVA/in situ ZnO:CS mats displayed an inhibition of bacterial growth of Escherichia coli and Staphylococcus aureus.

The Effect of Fiber Waviness on the Residual Stress State and Its Prediction by the Hole Drilling Method in Fiber Metal Laminates: A Global-Local Finite Element Analysis

In this paper, fiber waviness, as one of the most frequently occurring defects in fiber reinforced composites, is numerically investigated with regard to the formation of residual stresses in fiber metal laminates. Furthermore, the prediction of the residual stress state in the thickness direction by means of the simulated hole drilling method is studied. To this regard, a global-local finite element analysis based on the submodel technique is presented. The submodel technique essentially consists of two governing steps: In the first step, a global model is first utilized to calculate and analyze the residual stress distribution and deformation in the intrinsically joined hybrid structure. Effective cure-dependent thermo–elastic properties predicted by a numerical homogenization procedure were used to simulate the curing-process and analyze the residual stresses state. However, the dimension of the intrinsically manufactured hybrid plate is large compared to the diameter of the drilled hole (2 mm), so that a local model is necessary, which provides only a geometric partial portion of the global model. The local model takes the global stress state into account and is subsequently used to simulate the incremental hole drilling method with a refined mesh discretization. The production-related fiber waviness is modeled by an element-wise orientation approximating a sinus function. In order to validate the global-local modeling approach, a comparison between numerical results and experimental data from literature is presented. The comparison between global residual stress state (global model) and the simulated hole drilling method (local model) is used to assess the applicability and reliability of the hole drilling method in case of fiber waviness. It is found that an in-plane fiber waviness leads to a rather low variance of residual stresses over thickness. In case of an out-of-plane fiber waviness, oscillating residual stress fields occur over the entire thickness along the fiber direction. Moreover, the current limits of the incremental hole drilling method could be pointed out by the presented investigations. It is seen that the simulated results of the incremental hole drilling method are sensitive to waviness, even if the amplitude-wavelength-ratio is small. Without further adjustment of the calibration coefficients the oscillating stress and strain fields lead, in particular fiber waviness in thickness direction, to unreliable predictions. For the experimental application it can be concluded that the specimens have to be carefully examined with regard to fiber waviness.

Observation of Damage of Cotton Fiber in the Processes of Blowing, Cleaning and Carding

The quality of the produced yarn mainly depends on the properties of the raw material, its preparation for spinning, the condition of the equipment, and the preservation of the natural quality of cotton fiber during processing. The question of the number of defects in cotton fiber and their total content is a very important issue for cotton spinning. The non-standardized number of defects in the raw material reduces the quality indicators and yarn yield, which requires additional technological processes; therefore, on the part of production, the requirements for reducing the share of cotton fiber defects are constantly increasing. During processing in blowing and cleaning units and on carding machines, the cotton fiber is mechanically damaged. To observation the damaged fibers, we used the Congo-Roth red paint according to the method of Ch. Dore. Despite the carding is considered the last stage in the process of cleaning the fibers from impurities and defects in the spinning system, 30% of impurities and fiber defects still remain on the card sliver. Besides, it should be noted the carding machine is also considered an additional occurrence of defects, in particular (neps), which reduce the quality indicators of the card sliver and the finished product.

Causes of damage to the raw cotton in the pneumatic transport system and ways to reduce it

This article examines the occurrence of seed damage during the transportation of raw cotton to the production shops and the occurrence of defects that affect the quality of fiber on these indicators, and conducted research to reduce the increase in fiber defects.