Fiber Compaction Research Articles

Sposoby wytwarzania kompozytow jednopolimerowych

This paper constitutes a review of the literature on the single polymer composites (SPC), an interesting and useful group of new polymer materials. They are fully recyclable and have mechanical properties comparable to heterogeneous polymer composites. The most important preparation methods of these composites (hot compaction of polymer foils, fibres and tapes, infusion of polymer solution or powder, film-stacking method, co-extrusion technology, injection moulding) are presented.

고압 처리 후 가공한 반건조 병어의 품질특성과 저장성

Abstract We investigated the quality characteristics and resulting sensory evaluation of semi-dried silver pomfret treated with high hydrostatic pressure (HHP) processing and brining for 14 days at 4 and 10℃ to evaluate the effects of treatment with HHP processing. HHP treatment and brining could cause compaction of fibers and the space between muscle. The G' values of all samples were higher than the G values and the tan δ values of the tissue ranged from 0.222 to 0.251 with no further changes observed during storage. HHP treatment and brining significantly increased the total color difference, and the HHP and brine-treated group scored significantly higher than the others in terms of sensory evaluation. HHP treatment combined with brining could have a significant effect on the quality characteristics of the semi-dried products and their storage stability, and it is suggested from the results that they may have the potential to satisfy the requirements to produce commercially marketable food grade products.Key word: high hydrostatic pressure, brining, semi-drying, quality characteristics, storage stability

Cohesin-dependent globules and heterochromatin shape 3D genome architecture in S. pombe.

Eukaryotic genomes are folded into three-dimensional structures, such as self-associating topological domains, the borders of which are enriched in cohesin and CCCTC-binding factor (CTCF) required for long-range interactions1-7. How local chromatin interactions govern higher-order folding of chromatin fibers and the function of cohesin in this process remain poorly understood. Here we perform genome-wide chromatin conformation capture (Hi-C) analysis8 to explore the high-resolution organization of the Schizosaccharomyces pombe genome, which despite its small size exhibits fundamental features found in other eukaryotes9. Our analyses of wild type and mutant strains reveal key elements of chromosome architecture and genome organization. On chromosome arms, small regions of chromatin locally interact to form “globules”. This feature requires a function of cohesin distinct from its role in sister chromatid cohesion. Cohesin is enriched at globule boundaries and its loss causes disruption of local globule structures and global chromosome territories. By contrast, heterochromatin, which loads cohesin at specific sites including pericentromeric and subtelomeric domains9-11, is dispensable for globule formation but nevertheless affects genome organization. We show that heterochromatin mediates chromatin fiber compaction at centromeres and promotes prominent interarm interactions within centromere-proximal regions, providing structural constraints crucial for proper genome organization. Loss of heterochromatin relaxes constraints on chromosomes, causing an increase in intra- and inter-chromosomal interactions. Together, our analyses uncover fundamental genome folding principles that drive higher-order chromosome organization crucial for coordinating nuclear functions.

Factor XIII stiffens fibrin clots by causing fiber compaction

FactorXIII-induced cross-linking has long been associated with the ability of fibrin blood clots to resist mechanical deformation, but how FXIII can directly modulate clot stiffness is unknown. We hypothesized that FXIII affects the self-assembly of fibrin fibers by altering the lateral association between protofibrils. To test this hypothesis, we studied the cross-linking kinetics and the structural evolution of the fibers and clots during the formation of plasma-derived and recombinant fibrins by using light scattering, and the response of the clots to mechanical stresses by using rheology. We show that the lateral aggregation of fibrin protofibrils initially results in the formation of floppy fibril bundles, which then compact to form tight and more rigid fibers. The first stage is reflected in a fast (10min) increase in clot stiffness, whereas the compaction phase is characterized by a slow (hours) development of clot stiffness. Inhibition of FXIII completely abrogates the slow compaction. FXIII strongly increases the linear elastic modulus of the clots, but does not affect the non-linear response at large deformations. We propose a multiscale structural model whereby FXIII-mediated cross-linking tightens the coupling between the protofibrils within a fibrin fiber, thus making the fiber stiffer and less porous. At small strains, fiber stiffening enhances clot stiffness, because the clot response is governed by the entropic elasticity of the fibers, but once the clot is sufficiently stressed, the modulus is independent of protofibril coupling, because clot stiffness is governed by individual protofibril stretching.

Effects of stitch density and stitch thread thickness on mode II delamination properties of Vectran stitched composites

Mode II delamination properties of Vectran stitched composites were investigated, and tabbed end notch flexural specimen testing was used to prevent premature failure. The effects of stitch density and stitch thread thickness were explored, and fibre compaction due to the stitching process was also verified. The results show that, in moderately stitched laminates (low stitch density), the improvement in GIIC was negligible. Crack bridging by the stitch threads at the crack zone were mostly compensated for the effect of fibre compaction, which reduced the GIIC values. Conversely, in densely stitched laminates (high stitch density), GIIC values were improved significantly (2·4 times higher than those of unstitched laminates). The effects of stitch thread thickness appeared to be negligible in moderately stitched laminates. For densely stitched laminates, thicker stitch thread (500 denier) possessed GIIC values that were 45·7% higher than thinner stitch thread (200 denier).

Data on force-dependent structural changes of chromatin fibers measured with magnetic tweezers.

The compaction of chromatin fibers regulates the accessibility of embedded DNA, highly associated with transcriptional activities [1]. Single molecule force spectroscopy has revealed the great details of the structural changes of chromatin fibers in the presence of external exerted force [2–7]. However, most of the studies focus on a specific force regime [2,3,8,9]. The data here show force-extension (FE) traces of chromatin fibers as measured with magnetic tweezers, covering the force regime from 0 pN to 27 pN. Those traces provide information for further studies at varied force regimes.

Electrostatic effect of H1-histone protein binding on nucleosome repeat length

Within a simple biophysical model we describe the effect of electrostatic binding of H1 histone proteins on the nucleosome repeat length in chromatin. The length of wrapped DNA optimizes its binding energy to the histone core and the elastic energy penalty of DNA wrapping. The magnitude of the effect predicted from our model is in agreement with the systematic experimental data on the linear variation of nucleosome repeat lengths with H1/nucleosome ratio (Woodcock C L et al 2006 Chromos. Res. 14 17–25). We compare our model to the data for different cell types and organisms, with a widely varying ratio of bound H1 histones per nucleosome. We underline the importance of this non-specific histone-DNA charge-balance mechanism in regulating the positioning of nucleosomes and the degree of compaction of chromatin fibers in eukaryotic cells.

Optimization of fluid flow inside blowroom transport duct using CFD

The fiber characteristics go through a transformation in blowroom transport ducts, namely buckling of fibers and compactness of fiber tufts, as a result of flow characteristics in the duct. To understand the effect of flow, a detailed analysis of the air flow characteristics inside blowroom transport ducts using computational fluid dynamics has been carried out. Based on the analysis, the critical flow regimes within the transportation duct responsible for transformation of tuft openness have been established. Modification has been suggested to improve the flow characteristics in the duct. Flow analysis has been carried out by inserting plates (flow deflectors) by varying the inclination and proportion of area blockage created with a view to improve the flow. It is seen that 10% area blockage and inclination angle of 45° improve the flow significantly and experiments carried out with fiber showed significant reduction in compactness of fibers.

CENP-A Arrays Are More Condensed than Canonical Arrays at Low Ionic Strength

The centromeric histone H3 variant centromeric protein A (CENP-A), whose sequence is the least conserved among all histone variants, is responsible for specifying the location of the centromere. Here, we present a comprehensive study of CENP-A nucleosome arrays by cryo-electron tomography. We see that CENP-A arrays have different biophysical properties than canonical ones under low ionic conditions, as they are more condensed with a 20% smaller average nearest-neighbor distance and a 30% higher nucleosome density. We find that CENP-A nucleosomes have a predominantly crossed DNA entry/exit site that is narrowed on average by 8°, and they have a propensity to stack face to face. We therefore propose that CENP-A induces geometric constraints at the nucleosome DNA entry/exit site to bring neighboring nucleosomes into close proximity. This specific property of CENP-A may be responsible for generating a fundamental process that contributes to increased chromatin fiber compaction that is propagated under physiological conditions to form centromeric chromatin.

Reducing Railway Noise with Porous Sound-Absorbing Concrete Slabs

The effect of porous sound-absorbing concrete slabs on railway noise reduction is examined in this paper. First, the acoustical absorption coefficients of porous concrete materials with various aggregate types, gradations, fibre contents, and compaction indexes are measured in the laboratory. The laboratory results show that porous concrete that uses a composite of expanded perlite and slag as aggregate can not only obtain good acoustical absorption properties but also satisfy mechanical requirements. Also, the gradation of the combined aggregate has a significant effect on the acoustic absorption performance of the porous concrete, with an optimal aggregate gradation of 1~3 mm. Furthermore, the fibre content and compaction index affect both the strength and the acoustic absorption property of the porous concrete, with the optimum value of 0.3% and 1.6, respectively. Then, the findings from the laboratory studies are used to make porous sound-absorbing concrete slabs, which are applied in a test section. The measurements indicate that porous sound-absorbing concrete slabs can significantly reduce railway noise at different train speeds and that the amount of the noise reduction changes roughly linearly with speed when the train is traveling at less than 200 km/h. The maximum noise reduction is 4.05 dB at a speed of 200 km/h.

A physically motivated constitutive model for cell-mediated compaction and collagen remodeling in soft tissues

Collagen is the main load-bearing component of many soft tissues and has a large influence on the mechanical behavior of tissues when exposed to mechanical loading. Therefore, it is important to increase our understanding of collagen remodeling in soft tissues to understand the mechanisms behind pathologies and to control the development of the collagen network in engineered tissues. In the present study, a constitutive model was developed by coupling a recently developed model describing the orientation and contractile stresses exerted by cells in response to mechanical stimuli to physically motivated collagen remodeling laws. In addition, cell-mediated contraction of the collagen fibers was included as a mechanism for tissue compaction. The model appeared to be successful in predicting a range of experimental observations, which are (1) the change in transition stretch of periosteum after remodeling at different applied stretches, (2) the compaction and alignment of collagen fibers in tissue-engineered strips, (3) the fiber alignment in cruciform gels with different arm widths, and (4) the alignment of collagen fibers in engineered vascular grafts. Moreover, by changing the boundary conditions, the model was able to predict a helical architecture in the vascular graft without assuming the presence of two helical fiber families a priori. Ultimately, this model may help to increase our understanding of collagen remodeling in physiological and pathological conditions, and it may provide a tool for determining the optimal experimental conditions for obtaining native-like collagen architectures in engineered tissues.

Static and dynamic puncture behaviors of compound fabrics with recycled high-performance Kevlar fibers

An economical and flexible compound fabric was prepared using Kevlar fabric and glass fabrics as well as recycled Kevlar/Nylon/low-Tm polyester nonwovens via needle-punching and thermal-bonding processes. Effects of Kevlar staple fibers fraction, number of layers and inter-laminar bonding on the static and dynamic puncture resistances were comparatively studied. Findings indicate that increase of Kevlar staple fibers fraction improved static puncture resistance more significantly, but inter-laminar shear effect influenced on dynamic puncture resistance more evidently. With 20wt% recycled Kevlar fibers, static puncture resistance had linear relation to number of layers, but dynamic puncture resistance showed a parabolic relationship. The contacting pressure and friction strength of compound fabric to probe was to resist against static puncture resistance, but mechanism for dynamic puncture resistance was due to fiber elongation of fabric interlayer and compactness of compound fabric. Yarn brittle-breakage was the main dynamic puncture resistance mechanism for G-CF, but pushing fiber apart was for K-CF, besides of contact pressure of probe to compound fabrics. The improved both of static and dynamic puncture resistances were attributed to cut resistance of Kevlar fibers and compactness of fiber assembles. Comparatively, cut resistance property of Kevlar fibers related to dynamic puncture behavior more significantly, but fiber compactness affected static puncture resistance obviously.

Exploring the behavior of glass fiber reinforcements under vibration-assisted compaction

In this study, a new vibration-assisted approach is proposed for compacting dry fibrous reinforcements in liquid composite molding (LCM). The first steps of LCM processes involve fiber bed lay-up within a rigid mold, followed by the closure of the counter-mold and subsequent fiber compaction. Traditionally, static compaction has been applied to level the thickness of the reinforcement and achieve high fiber volume contents. However, fibrous materials under transverse compression exhibit viscoelastic characteristics that can be exploited through dynamic loading in order to achieve a higher level of compaction. In this work, a vibration-assisted compaction technique has been developed, in which static and dynamic stresses are combined to provide specific compaction conditions. A series of tests allowed exploring the impact of different loading conditions (i.e. static force, dynamic force, and vibratory frequency) on the compaction response of fibrous preforms. The effects of vibration-assisted compaction on various fabric architectures and different numbers of stacked layers were explored as well. The analysis of experimental outputs allows identifying the governing parameters of this new approach. The fiber volume contents obtained reveal that the use of a complex compressive load, composed of static and dynamic forces, can be very effective for the compaction of dry fibrous materials. Although vibration-assisted compaction remains a technology in its preliminary stage, this paper contributes to a better understanding of its potential and provides tools for eventual applications.

Effect of Resin Viscosity in Fiber Reinforcement Compaction in Resin Injection Pultrusion Process

In resin injection pultrusion, the liquid resin is injected through the injection slots into the fiber reinforcement; the liquid resin penetrates through the fibers as well as pushes the fibers towards the centerplane causing fiber compaction. The compacted fibers are more difficult to penetrate, thus higher resin injection pressure becomes necessary to achieve complete reinforcement wetout. Lower injection pressures below a certain range (depending upon the fiber volume fraction and resin viscosity) cannot effectively penetrate through the fiber bed and thus cannot achieve complete wetout. Also, if the degree of compaction is very high the fibers might become essentially impenetrable. The more viscous the resin is, the harder it is to penetrate through the fibers and vice versa. The effect of resin viscosity on complete wetout achievement with reference to fiber-reinforcement compaction is presented in this study.

The role of the nucleosome acidic patch in modulating higher order chromatin structure

Higher order folding of chromatin fibre is mediated by interactions of the histone H4 N-terminal tail domains with neighbouring nucleosomes. Mechanistically, the H4 tails of one nucleosome bind to the acidic patch region on the surface of adjacent nucleosomes, causing fibre compaction. The functionality of the chromatin fibre can be modified by proteins that interact with the nucleosome. The co-structures of five different proteins with the nucleosome (LANA, IL-33, RCC1, Sir3 and HMGN2) recently have been examined by experimental and computational studies. Interestingly, each of these proteins displays steric, ionic and hydrogen bond complementarity with the acidic patch, and therefore will compete with each other for binding to the nucleosome. We first review the molecular details of each interface, focusing on the key non-covalent interactions that stabilize the protein-acidic patch interactions. We then propose a model in which binding of proteins to the nucleosome disrupts interaction of the H4 tail domains with the acidic patch, preventing the intrinsic chromatin folding pathway and leading to assembly of alternative higher order chromatin structures with unique biological functions.

Capsular Contracture after Breast Reconstruction

Breast implant capsular contracture is a common complication of implant-based breast reconstruction. To develop nonsurgical interventions to combat breast capsular contractures, a clearer understanding of the process is required. Comparing breast implant-related capsular contracture to the fibrotic scarring process, the hypothesis is that these processes differ with regard to the compaction of collagen fibers within the connective tissue matrix. Morphologic differences in the connective tissue matrix by light, polarized light, and fluorescence microscopy documents these differences. Discarded Baker grade II and III periimplant capsules harvested during routine breast reconstructive operations were used for the evaluation. Within severe breast capsule contractures, light microscopy revealed the absence of mast cells, whereas polarized light microcopy showed that collagen fiber bundles were consolidated into thick cable-like structures. In less severe breast capsules, mast cells were present, whereas thick cable-like collagen structures were absent. By fluorescence microscopy, fibroblast populations associated with severe contractures were oriented perpendicular to the long axis, suggesting a spiral orientation in the compaction of these cable-like structures. These findings were absent in less severe contractures. To the authors' knowledge, these histologic findings in breast implant capsules are unreported and unique when compared with other fibrotic contractures. Elucidating the biological mechanisms involved in the reorganization of collagen fiber bundles that lead to implant-related capsular contracture is a critical step for developing strategies to treat and control breast capsule contractures.

Effect of consolidation pressure on volumetric composition and stiffness of unidirectional flax fibre composites

Unidirectional flax/polyethylene terephthalate composites are manufactured by filament winding, followed by compression moulding with low and high consolidation pressure, and with variable flax fibre content. The experimental data of volumetric composition and tensile stiffness are analysed with analytical models, and the composite microstructure is assessed by microscopy. The higher consolidation pressure (4.10 vs. 1.67 MPa) leads to composites with a higher maximum attainable fibre volume fraction (0.597 vs. 0.530), which is shown to be well correlated with the compaction behaviour of flax yarn assemblies. A characteristic microstructural feature is observed near the transition stage, the so-called local structural porosity, which is caused by the locally fully compacted fibres. At the transition fibre weight fraction, which determines the best possible combination of high fibre volume fraction and low porosity, the high pressure composites show a higher maximum performance in terms of tensile stiffness (40 vs. 35 GPa). The good agreement with the model calculations (fibre compaction behaviour, and composite volumetric composition and mechanical properties), allows the making of a property diagram showing stiffness of unidirectional flax fibre composites as a function of fibre weight fraction for consolidation pressures in the range 0–10 MPa.

Simulation of bleeder flow and curing of thick composites with pressure and temperature dependent properties

A two-dimensional transient heat transfer, one-dimensional compaction and two-dimensional resin flow analysis of a thick laminated composites fabrication assembly including the bleeders and vacuum bagging is carried out in a fully coupled manner. Resin distribution within the laminate and the bleeders is controlled by their respective compaction behavior as well as permeability of the fiber network. Compaction behavior of dry bleeders is obtained from compression experiments carried out in-house and the derived relevant empirical parameters are used in the numerical simulation. The variations in the resin volume fraction within the laminate due to the resin outflow to the surrounding bleeder were tracked and updated as a function of time in the cure simulation. Four case studies were performed with temperature dependent as well as independent resin properties and pressure dependent and also pressure independent resin volume fractions. These simulations were carried out to understand the behavior of resin flow through the bleeder and its impact on the local variations in the resin content of the laminate. The results obtained show a significant disparity in the thermal overshoot at the center of the laminate and the pressure distribution within the laminate and the bleeder, when a complete coupling and the parametric changes as in the real situation are ignored in numerical simulation. It is shown that the complete coupling of various real-time phenomena helps in accurate prediction of temperature, pressure, resin viscosity, bleeder and fiber compaction, resin flow and associated changes in fiber volume content, and degree of cure distributions for thick composites as they are cured.

Dextrocardia with Situs Inversus Associated with Non-Compaction Cardiomyopathy

Dextrocardia is a rare condition usually diagnosed incidentally and associated with other congenital anomalies. It is characterized by the position of the heart in the right hemithorax, with its base-apex axis directed to the bottom right. Its incidence associated with situs inversus, in the general population, is 1:10.0001. Non-compaction cardiomyopathy (non-compaction CMP), in turn, has an incidence ranging from 0.014 to 1.3%2, may occur alone or associated with other congenital defects and results from failure in the process of compaction of myocardial fibers, resulting in the persistence of trabeculations and deep recesses that communicate with the ventricular cavity2. A rare association of these two diseases is described. Cases similar to the one reported have not been found3-5.

Effect of stitch density on tensile properties and damage mechanisms of stitched carbon/epoxy composites

Experimental investigation is performed to study tensile properties, damage initiation and development in stitched carbon/epoxy composites subjected to tensile loading. T800SC-24kf dry preforms with tow orientation of [+45/90/−45/02/+45/902/−45/0]s are stitched using 200 denier Vectran® thread. Modified-lock stitch pattern is adopted, and stitch density is varied, viz. moderate density (stitched 6×6: stitch density=2.8cm−2) and high density (stitched 3×3: stitch density=11.1cm−2). The stitched preforms are then infiltrated by epoxy XNR/H6813 using resin transfer molding process. Tensile test is conducted to obtain in-plane mechanical properties (tensile strength, failure strain, tensile modulus and Poisson’s ratio). Effect of stitch density on the mechanical properties is assessed, and it is found that stitched 3×3 modestly improves the tensile strength by 10.4%, while stitched 6×6 reduces the strength by only 1.4%. In stitched 3×3 cases, the strength increase is mainly due to an effective impediment of edge-delamination. Tensile stiffness and Poisson’s ratio of carbon/epoxy are slightly reduced by stitching. Fiber misalignment in in-plane and out-of-plane directions is responsible for stiffness reduction, whilst reduction of Poisson’s ratio is probably caused by the orthogonal binding effect of modified-lock stitch architecture. Damage mechanisms in stitched and unstitched composites are studied using acoustic emission testing and interrupted test coupled with X-ray radiography and optical microscopy. The detailed damage observation reveals that stitch thread promotes early formation of transverse and oblique cracks. These cracks rapidly develop, and higher density of cracks ensues in stitched composites. Although this behavior triggers early formation of delamination, stitched 3×3 effectively impedes the growth the delamination. In contrast, stitched 6×6 is ineffective in suppressing the delamination yet the cracks are vast in this specimen. One of the plausible reasons of the rapid development of cracks in stitched composites is fiber compaction effect whereby fibers are compacted and the gap among fibers is reduced. The verification of compaction effect is done experimentally by performing burn-off test to measure the local fiber volume fraction. It is confirmed that fiber compaction indeed occurs as indicated by higher local fiber volume fraction between stitch lines.