Fiber Dimensions Research Articles

Microstructural Analysis of the Transverse and Shear Behavior of Additively Manufactured CFRP Composite RVEs Based on the Phase-Field Fracture Theory

Due to the versatility of its implementation, additive manufacturing has become the enabling technology in the research and development of innovative engineering components. However, many experimental studies have shown inconsistent results and have highlighted multiple defects in the materials’ structure thus bringing the adoption of the additive manufacturing method in practical engineering applications into question, yet limited work has been carried out in the material modelling of such cases. In order to account for the effects of the accumulated defects, a micromechanical analysis based on the representative volume element has been considered, and phase-field modelling has been adopted to model the effects of inter-fiber cracking. The 3D models of representative volume elements were developed in the Abaqus environment based on the fiber dimensions and content acquired using machine learning algorithms, while fulfilling both geometric and material periodicity. Furthermore, the periodic boundary conditions were assumed for each of the representative volume elements in transversal and in-plane shear test cases,. The analysis was conducted by adopting an open-source UMAT subroutine, where the phase-field balance equation was related to the readily available heat transfer equation from Abaqus, avoiding the necessity for a dedicated user-defined element thus enabling the adoption of the standard elements and features available in the Abaqus CAE environment. The model was tested on three representative volume element sizes and the interface properties were calibrated according to the experimentally acquired results for continuous carbon-fiber-reinforced composites subjected to transverse tensile and shear loads. This investigation confirmed the consistency between the experimental results and the numerical solutions acquired using a phase-field fracture approach for the transverse tensile and shear behavior of additively manufactured continuous-fiber-reinforced composites, while showing dependence on the representative volume element type for distinctive load cases.

Transparent and Cell-Guiding Cellulose Nanofiber 3D Printing Bioinks.

For three-dimensional (3D) bioprinting to fulfill its promise and enable the automated fabrication of complex tissue-mimicking constructs, there is a need for developing bioinks that are not only printable and biocompatible but also have integrated cell-instructive properties. Toward this goal, we here present a scalable technique for generating nanofiber 3D printing inks with unique tissue-guiding capabilities. Our core methodology relies on tailoring the size and dispersibility of cellulose fibrils through a solvent-controlled partial carboxymethylation. This way, we generate partially negatively charged cellulose nanofibers with diameters of ∼250 nm and lengths spanning tens to hundreds of microns. In this range, the fibers structurally match the size and dimensions of natural collagen fibers making them sufficiently large to orient cells. Yet, they are simultaneously sufficiently thin to be optically transparent. By adjusting fiber concentration, 3D printing inks with excellent shear-thinning properties can be established. In addition, as the fibers are readily dispersible, composite inks with both carbohydrates and extracellular matrix (ECM)-derived proteins can easily be generated. We apply such composite inks for 3D printing cell-laden and cross-linkable structures, as well as tissue-guiding gel substrates. Interestingly, we find that the spatial organization of engineered tissues can be defined by the shear-induced alignment of fibers during the printing procedure. Specifically, we show how myotubes derived from human and murine skeletal myoblasts can be programmed into linear and complex nonlinear architectures on soft printed substrates with intermediate fiber contents. Our nanofibrillated cellulose inks can thus serve as a simple and scalable tool for engineering anisotropic human muscle tissues that mimic native structure and function.

DENSIDADE BÁSICA DA MADEIRA, DIMENSÕES DAS FIBRAS E COMPOSIÇÃO QUÍMICA DA MADEIRA DE QUATRO ESPÉCIES DE Eucalyptus PLANTADAS NO SUL DO BRASIL

ABSTRACT In the Brazilian planted forest sector, most of the species used are from the genus Eucalyptus. Even though Southern Brazil has a suitable climate for species of the genus Pinus, the planting of frost-resistant Eucalyptus species has been increasing annually. The objective of this study was to evaluate the basic density, fiber dimensions, and chemical composition of Eucalyptus benthamii, Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus cloeziana woods. The trees used were from a six-year-old experimental plantation located in Canoinhas, state of Santa Catarina. For each species, three trees were selected, and discs were removed from each tree at 0%, 25%, 50%, 75%, and 100% of the commercial stem height. To evaluate the quality of the wood, the basic wood density, fiber dimensions, and chemical composition of the wood were determined by comparing the values between species and between the heights in the stem. The highest basic density was that of the wood of E. cloeziana; this species also had the greatest length and width of fibers. E. dunnii had the lowest levels of lignin and the highest levels of holocellulose. The highest lignin content was found in the wood of E. benthamii, E. saligna, and E. cloeziana. The relationship between wood properties and stem height was not relevant. The results highlight the tendency for higher extractives to be found at taller heights (100%), and holocellulose and lignin content are similar at all heights.

Mechanical and thermal stability improvement of cellulosic fiber products derived from waste poplar boards under UV irradiation via lignin retention

As a derivative of agriculture crops and forestry cultivated plants, cellulosic fiber product (CFP) is of much industrial interest deemed a promising alternative to wooden composites and plastics owing to the low environmental impact. The high-performance CFP was fabricated via a facile molding and hot-pressing process without using adhesives. The UV aging test was carried out to evaluate the physical and mechanical stability before and after delignification. The tensile strength was increased from 41.3 MPa to 53.7 MPa, and the flexural strength was increased from 72.3 MPa to 85.4 MPa as the lignin was removed from 11.7% to 3.0%. The holocellulose content and crystallinity of fibers were increased, and the fiber dimensions were correspondingly decreased after delignification. However, the delignified specimens exhibited a faster reduction in mechanical strength than that of lignin-rich products (e.g., 0.074 vs 0.041 in the slope rate of fitting curves) throughout the UV irradiation, and the thermal stability was also decreased from 317.2 ℃ to 311.3 ℃ in onset decomposition temperature due to the delignification. Moreover, the lignin-rich CFP was superior to that of typical plastics (e.g., PP and epoxy resin) and wooden composites (e.g., WF/PP) in mechanical and thermal stability under UV irradiation through the comparison. • Cellulosic fiber product (CFP) developed using waste poplar boards via facile process. • Lignin-rich CFP exhibited higher mechanical stability than delignified products. • CFP was superior to that of plastics in properties stability under UV irradiation.

Abrasive blasting of the teeth of linter saws with the aim of their activation

The article presents materials on the effective use of abrasive blasting of the side surfaces of the teeth of saw blades in order to activate them during lightering. The scraping action and cutting of short fibers from seeds is enhanced by microroughnesses of the formed micro profile after impact interaction of an abrasive particle with a metal surface. Using atomic force microscopy, we obtained the height and step parameters of the roughness of the machined tooth surface, which are compared with the transverse dimensions of the cotton fibers, and thus a model for the intensification of the littering process is proposed.

Exploration of the Effect of Carbon Fiber Ratio and Dimensions on Electrical Conductivity in Mortars

This study was carried out on Class F and C fly ash reinforced, carbon fiber added mortar samples as a substitute for PÇ42,5 cement. Carbon fiber was added in different sizes at rates of 0.5%, 1%, and 3% in order to investigate the effects of the size and ratio of carbon fiber on electrical conductivity. 33 different series were formed such as obtained Class F; without fly ash 10%, 20% and Class C; without fly ash, 10%, 20% with samples without carbon fiber and with carbon fiber having dimensions 5 mm and 10 mm. The water/cement ratio was prepared to take the value of 22-23cm in the flow table test.,A viscosity regulator of 0.1% of the fine material was used in order to ensure homogeneous distribution of carbon fiber in the mortar. 3 samples were prepared for each series in order to reduce the margin of error. Electrical conductivity, compressive and tensile strength tests were applied to the oven dry and naturally moist conditions of the samples that completed their 7, 28 and 56 days curing periods. Increasing the carbon fiber size increased the tensile strengths and increasing the carbon fiber ratio increased the tensile strengths. It has been observed that carbon fiber increases the electrical conductivity, but the conductivity decreases depending on time, and as the sizes and proportions of the carbon fiber fibers increase, the compressive strength decreases due to the void effect in the mortar, while the compressive strength increases with the increase in the fly ash ratio. The microstructure and carbon fiber distribution of the samples were examined using SEM (Scanning Electron Microscopy) and it was seen that the carbon fiber distribution was in a way that supports the electrical conductivity measurement. The study allowed the size and proportion effect of carbon fiber in mortars to be compared with C and Class F reinforced mortar samples.

Fiber Quality of Yellow Bamboo (Bambusa vulgaris vitata) from Forest Area with Special Purpose Pondok Buluh, Simalungun Regency, North Sumatera Province

Forest Area with Special Purpose (FASP) Forest Training Pondok Buluh has a forest area of around 1.272 ha, with much plant species diversity, such as Yellow Bamboo. Bamboo can be used as a material that has the potential as a raw material to replace wood in several uses, one of which is pulp and paper. This study aims to analyze the dimension and derivation of fiber dimensions of the yellow bamboo that grows in FASP Pondok Buluh. The method used in this study is to get the maceration process of the bamboo sticks from yellow bamboo, then observe under a microscope to see the dimension of the fiber, then calculate the value of the derivative of its fiber dimensions. The results of this study obtained the average dimension of yellow bamboo fiber is 1945 μm in fiber length, fiber diameter is 12.75 μm, lumen diameter is 4.20 μm, and fiber wall thickness is 4.28 μm. Then calculated the fiber dimension derivative and obtained a Runkle ratio of 2.32, felting power of 152.61, muhlsteph ratio of 88.73%, coefficient of rigidity of 0.34, and flexibility ratio of 0.32. Based on the result of the derivative of the fiber dimensions, yellow bamboo gets a score of 225-275, which is included in quality class II. This means that the yellow bamboo that grows in the Pondok Buluh area can be used as a raw material for pulp and paper.

Fiber Quality of Betung Bamboo (Dendrocalamus asper) from Forest Area with Special Purpose (FASP) Pondok Buluh, Simalungun, North Sumatera

The FASP Pondok Buluh is located in Dolok Panribuan District, Simalungan Regency, Sumatera Utara, which has uniqueness due to the number of bamboo species found in this area, such as Betung Bamboo. This bamboo has a long fiber and is suitable for pulp and paper materials. This research aims to measure the dimension of Betung Bamboo and its fiber derivatives value for the eligibility of pulp and paper material. A total of 3 stems of Betung Bamboo were cut, and samples were taken in the form of a disc with a length of 5 cm at heights of 1, 3, 5, 7, 9, 11, 13, and 15 meters. Then the sample was cut into sticks, and separated fibers were made using the maceration process. Furthermore, the dimensions of the sample were measured using a light microscope, namely fiber length, fiber diameter, and fiber wall thickness, and then the measurement for the fiber derivatives value of the bamboo fiber. The results of this research obtained the average dimension of bamboo fiber is 2402 μm for fiber length, fiber diameter is 18.18 μm, lumen diameter is 8.73 μm, and fiber wall thickness is 4.91 μm. The fiber length graph shows the decreased fiber length along the bottom to the top of the bamboo culm and the wavy trend for the fiber diameter on some bamboo heights. The measurement of the fiber derivatives values obtained the average Runkle ratio 1.15, felting power 133.63, mulhsteph ratio 76.91%, rigidity coefficient 0.27, and flexibility ratio 0.48. Then the quality class of bamboo fiber was determined. A score of 275-325 was obtained with quality class II, meaning that Betung Bamboo is grown in the Pondok Buluh area. It is suitable for use as raw material for pulp and paper because it has long fibers, is easy to flatten when milled, and has good fiber bonds.

Anatomical properties of branches and twigs mangrove woods

In order to optimize the utilization of mangrove woods, particularly branches and twigs parts, this research was conducted to investigate anatomical properties of three species of mangrove woods, namely api-api (Avicennia marina), bakau minyak (Rhizopora apiculata), and berembang (Sonneratia caseolaris). The properties were comprised of both microtome sections and macerations dimensions. Procedure for microtome followed Sass method, resulted in three sections for each part, namely cross-section (L/longitudinal), radial/R section, and tangential/T section. Technical procedure for maceration based on Forest Product Laboratory (FPL) method, resulted in measurement of fiber dimension and derivative of fiber dimension. In term of microtome, the anatomical features between branches and twigs for each species in L, R, T sections are similar, but their quantitative anatomical observations between twigs and branches have differences in the vessel, rays and fiber parameters statistically. In term of fiber dimension and its derivatives (Runkel Ratio, Felting Power, Mulhstep Ratio, Coefficient Rigidity, Flexibility Ratio) both branches and twigs showed same quality class, namely 3rd class with scored 150-175 points.

Tapered MMF sensor fabrication using SnO2-NPs for alcohol sensing application

Metal oxide coated fiber optic sensor is proposed and experimentally characterized for alcohol sensing. The sensor probe design is based on the cladding removed methodology, done via tapering of the fiber. Chemical etching process was used to taper a section of multimode fiber (MMF) and the region was coated by tin dioxide nanoparticles (SnO2-NPs), which were synthesized by the sol–gel method. The sensing principle relies on the refractive index (RI) modification of SnO2 after being in contact with isopropanol solution leading to modulated output response. XRD structurally characterized SnO2-NPs and their crystallite size was found to be 19.88 nm. The prepared fiber dimension, nanoparticles morphology and the elemental composition were confirmed by FESEM and EDX characterization. A maximum average sensitivity with good linear behavior was found to be 22 counts/ppm for the wide range of concentrations (0–500 ppm). Along with excellent sensitivity, sensor shows nice reversibility and repeatability characteristics. A sensor combining optical fiber and metal oxide as sensing elements provides advantages of a miniaturized probe, low cost, ruggedness, online monitoring and remote sensing.

Wood quality of residual branches of Hymenaea courbaril L. from logging in the Amazon rainforest

Abstract Branches remain in the forest environment as logging activity residue. Considering the large size of many Amazonian trees, their branches have considerable dimensions and can contribute to a sustainable wood alternative for various applications. Due to the formation of reaction wood in the branches, relevant macro and ultrastructural changes can occur in its characteristics in relation to the trunk wood. However, the woods of the branches are not technologically well known. Therefore, this work aimed to evaluate the wood quality of branches of Hymenaea courbaril L., comparing it with wood of trunks. The extractives and lignin contents, basic density, shrinkage, fiber biometry, microfibril angle and mechanical resistance to compression parallel to the fibers were analyzed. The branch wood had smaller fiber dimensions and a higher microfibril angle than the trunk wood. The basic density was similar between these materials. The linear and volumetric shrinkages were smaller in the branch wood than in the trunk, while the axial shrinkage was higher in the branch. The parallel compressive strength was also lower in the branch wood than in the trunk. The branch wood has properties suitable for products with higher added value such as furniture, decorative objects, floors and utensils in general.

Substrate-free self-assembly of peptides nano-particles through acoustic levitation

Peptides self-assembled into nano-structures such as nano-tubes have shown to have great potential in different biomedical applications. However, when it comes to interacting with biological environment, the need for substrate (e.g. glass, silicone, and gold) during the self-assembling process, can have potential impeding effects, both on the resultant nanostructures as well as the very diligent biological subparts such as cells. This work, for the first time, shows the possibility of a substrate-fee peptide self-assembling process, through acoustic levitation. A pair of transducers was used to create standing acoustic waves at a high frequency of 40KHz to levitate water-based droplets. Two independent control variables of the self-assembling process were considered, namely the peptide concentration level and the velocity amplitude of the acoustic wave, to understand their effects on controlling the morphology, alignment and dimensional properties of the resultant nano-structures. The results showed that, at low concentration level of 1 mg/ml and independent of the velocity amplitude, no clear nano-structure was developed under the levitation conditions. However, at the concentration levels above 1.5 mg/ml, self-assembly of the peptide nano-particles do happen while the velocity amplitude can significantly affect the resultant nano-structures, in terms of fiber morphology, fiber dimension and fiber alignment. We also found that under levitation conditions, there is a preferred length for the resultant nano-fibers which is independent of the control variables, while the number of nano-fibers with that dominant size depends on the concentration level.

Wood Fiber Characteristics of Underutilized Poplar Species and Comparision with P. deltoides in Terms of their Pulp and Paper Quality

The pulp and Paper industries are growing at a tremendous rate. To satisfy the raw material supply and sustainability of their future industries need an alternative resource from fast-growing tree species. Poplar is one of the world’s fastest-growing lightwood trees with its used in several industries. The present work relies on the comparative fiber morphological dimensions of four species of poplar i.e. Populus alba L, Populus ciliata Wall. ex Royle, Populus euphratica Oliv, and Populus nigra L. The quality of pulp and paper was directly related to the fiber dimensions i.e., fiber length, fiber lumen diameter, and fiber wall thickness. A number of wood properties related to paper quality were also derived from the fiber dimensions including the Runkel ratio, flexibility coefficient, solid factors, luce’s-shape factors, slenderness ratio and wall coverage ratio. The mean value of fiber length, fiber diameter, fiber wall thickness and basic density of these four species ranged from 919-1425 μm, 19.71-25.85 μm, 2.72-4.99 μm and 0.38-0.54 g cm⁻¹ respectively. The prominent objective was to compare the fiber quality of these four poplar species within among self and also with an exotic poplar species Populus deltoides and other fast-growing tree species.

Effect of Alkaline Concentration Treatments on the Chemical, Physical and Thermal Characteristics of Cellulose from Tapioca Solid Waste

Tapioca solid waste (TSW), as a source of natural fiber, is produced in abundance, but its utilization is minimal and even has the potential to pollute the environment. Unfortunately, TSW fiber has low physical, mechanical, and thermal characteristics that limit its application. Therefore, one way to improve the characteristics of TSW so that the fiber can be applied in various fields is by using the modified alkalization method. This study aims to determine the effect of alkali concentration on cellulose's chemical, physical, and thermal characteristics from TSW. Alkali treatment used NaOH solution of 0%, 5%, 10%, 15%, and 20% (v/w). The chemical characteristics of the fiber were analyzed for moisture, starch, lignin, hemicellulose, and cellulose content. Fiber surface morphology was analyzed by scanning electron microscopy (SEM), functional group changes with Fourier transform infrared (FTIR), degree of crystallinity with X-ray diffraction (XRD), and thermal stability with thermogravimetric analysis (TGA). The results showed that alkaline treatment affected changes in the chemical, physical, and thermal characteristics of cellulose from TSW. The increasing concentration of NaOH causes the water and cellulose content to increase, while the starch, hemicellulose, and lignin content decrease. Surface morphology is getting rougher, fiber dimensions increase to 10% NaOH concentration, but at higher concentrations, it causes a decrease in dimensions. FTIR analysis showed that the intensity of the hemicellulose and lignin functional groups decreased with increasing NaOH concentration. The degree of crystallinity and crystal size increased until the NaOH concentration was 10%, but at higher concentrations, it tended to decrease. Meanwhile, d-spacing increased with increasing NaOH concentration. The thermal stability of the fiber tends to decrease with increasing NaOH concentration. Alkalized cellulose from TSW has the potential to be used in a wider field, such as adsorbent and composite reinforcing agent.

Evidence for helical microstructure of aragonite fibers in pteropod shells

Planktonic gastropods of the suborder Euthecosomata (order Pteropoda) secrete a unique microstructure made of tightly interlocked, space-filling helically coiled aragonite fibers. This material has a high degree of ordering because all fibers are in phase at a given growth plane. The recognition of the helical nature from mere scanning electron micrographs is somewhat uncertain. In addition, three-dimensional (3D) reconstructions of individual helices are hindered by the small dimensions of fibers, and the virtual absence of intervening organic interphases. Here, we (1) reexamine the morphological characteristics of the fibers in fracture and find them compatible with a helical model, (2) provide direct evidence of the helical mode of coiling in the form of anaglyphs, and (3) develop a 3D model, which is fully consistent with the patterns observed in fractures and polished sections. Proposals based on motifs different from helices are not congruent with the observations.Graphical abstractImpact statementSome planktonic gastropods of the order Pteropoda secrete a unique microstructure that was originally described as made of tightly interlocked helically coiled continuous aragonite fibers. Despite this material having been described 50 years ago, there is still debate as to the helical design of such fibers. We provide additional unambiguous evidence that fibers describe true helical trajectories during growth. Establishing their true nature is essential in order to know the spectrum of calcified biomaterials produced by molluscs. This is also a prerequisite for future biomimetic studies aiming at producing bioinspired highly functional materials.

A novel polysulfate hollow fiber membrane with antifouling property for ultrafiltration application

To tailor the morphology and performance of membrane precisely, exploring the principle in the phase separation process of a certain polymer is a crucial step. In this work, a novel polysulfate (PSE) was employed to fabricate a hollow fiber membrane via NIPS method for use in ultrafiltration. The PSE concentration in the dope was varied to thoroughly investigate the phase separation process from both thermodynamic and kinetic aspects. The dimension and skin morphology of the PSE hollow fiber was tuned by altering air gaps during spinning to receive a better ultrafiltration ability. The optimized PSE hollow fiber achieved a pure water flux of 83.2 L˙m−2˙h−1 (LMH), a BSA rejection of 97.9%, and a flux recovery rate of 92%, demonstrating that PSE is a novel polymer with a promising application in ultrafiltration hollow fiber membrane.

Optimizing Fabrication of Electrospinning Nanofiber Membranes for Water Filtration using Response Surface Methodology

Nanofiber Polyethersulfone (PES) membrane fabrication using the electrospinning method incorporating dry/wet phase inversion was investigated. The electrospinning process is a straightforward and versatile method to produce one-dimensional nanostructures, especially nanofibers. The electrospun’s outcome can be affected by the various process parameters and solution parameters, making it an interesting study subject and an opportunity for customized nanofiber membrane. In this work, the analysis includes dope formulation and electrospinning parameter influence to membrane morphology dimensional structure based on Scanning Electron Microscopy (SEM) and filtration capability. Fibrous membranes were electrospun at 1 to 3 ml/h feeding rate and at 12 to 25kV voltage rate in a fixed 10 to 12 cm distance between the filter membrane and the syringe needle tip. The PES dope solution with N-methyl-2-pyrrolidone (NMP) as solvent electrospun onto a wet filter base membrane (5A 90 mm Advantec Filter Paper) to refine the fabricated fibrous membrane and to induce the dry-wet phase inversion process. The results indicate that the PES fiber dimension reduced at a lower feeding rate and higher voltage rate. In terms of liquid separation performance, experimental results showed that pure water permeation flux was reduced with the increased flow spinning rate of 1 to 3ml/hr but triple times higher than the increased concentration PES formulation, even at higher voltage spinning. The electrospun performance of polyethersulfone was also explained using Response Surface Methodology (RSM). It focused on the polymer content, tip-to-collector distance, and flow rate parameters toward fiber diameter and contact angle. Among these factors, the effect of PES content (f-value = 65.87) was the most significant, followed by tip-to-collector distance (f-value = 11.26) and flow rate (f-value = 2.59).

Acoustic optimization of a flow through sonicator for fibrillation of cellulose fibers

Fibrillation is identified as the most energy intensive process step in pulp and paper manufacturing and improved energy efficiency is the motivation for development of alternative technologies. The aim of this study is to explore the potential of a new refining concept based on cavitation, focusing on the optimization of acoustic cavitation efficiency of the proposed flow-through sonicator concept. The simulations utilize the linearized wave equation in the frequency domain with an addition of nonlinear attenuation introduced by cavitation bubbles. Verification is made by pressure measurements, calorimetry, and foil tests. The fibrillation capability was validated on chemi-thermo mechanical pulp fibers at low consistencies. Fiber properties was characterized by ultrasonic spectroscopy, fiber analysis and SEM. The objective is to optimize the energy transfer efficiency from electrical input power to acoustic cavitation intensity for efficient fibrillation of cellulose fibers. Results showed changes in fiber dimensions and fiber morphology, however, improvements in tensile strength index, measured and predicted by ultrasonic spectroscopy, was limited to 20 % at an energy level of 804 kWh/bdt. To enhance energy efficiency and paper strength properties, it is suggested to add a hydrodynamic cavitation device prior to the sonicator to initiate cavitation bubbles and to increase turbulence intensity.

Evaluation of fiber characteristics and basic density of Acacia melanoxylon (R.Br.) grown in Ethiopia for pulp and paper making

The fiber characteristics and basic density of Acacia melanoxylon were investigated for its potential as a raw material for pulp and paper production. Six trees from the even-aged stand and similar diameter class were selected randomly from the Chencha district of Ethiopia. Wood disks were systematically cross-cut from a log along tree height levels, at the bottom (10%), middle (50%) and top (90%) of the merchantable height and blocks of wood (2 cm x 2 cm x 2 cm) were taken from pith to periphery at near pith (10%), middle (50%) and near bark (90%) of disk radius. Fiber maceration and basic density were determined, by 50% nitric acid solution and water displacement method respectively. All the data were analyzed using a two-way analysis of variance at α = 0.05. The fiber characteristics of the selected trees; the fiber length, fiber diameter, lumen diameter and cell wall thickness were measured while the-slenderness ratio, Runkel ratio, flexibility coefficient and wall coverage ratio of the fibers were derived from the measured fiber dimensions. The result showed that- the overall mean were, 1.04 mm, 21.60 µm, 15.36 µm, 3.75 µm, 0.48, 48.05%, 71.10%, 0.34 and 0.56 g/ml, for fiber length, fiber width, lumen diameter, cell wall thickness, Runkle ratio, slenderness ratio, flexibility ratio, wall coverage ratio and basic density, respectively. Generally, Acacia melanoxylon wood is suitable for pulp-and-paper-production, to due-to-its adequate-fiber dimension, derived fiber value and basic density. Therefore, attention should be given to tree growers, government and non-governmental organizations on the plantation expansion of Acacia melanoxylon.

Torsional behavior of ultra-high performance concrete (UHPC) rectangular beams without steel reinforcement: Experimental investigation and theoretical analysis

Steel fiber is the main reinforcing fiber of ultra-high performance concrete (UHPC) and could greatly improve its tensile strength and toughness. As a result, steel fiber has a significant influence on the structural behavior of UHPC beams under pure torsion. However, related research in this regard is severely insufficient. To fill in this research gap, this paper presents an extensive investigation to explore the effect of steel fiber property on the torsional performance of UHPC beams without steel reinforcement. A total of 8 UHPC rectangular specimens (including one control beam without steel fibers) were tested under pure torsion until failure. The variables in the specimens included the volume fraction, type, dimension and hybrid effect of steel fibers. The failure modes, torque versus angle of twist curves, torque versus strain curves and distribution of cracks for all specimens were acquired based on the torsion tests. Results show that the addition of steel fibers significantly increased the cracking and ultimate torques of UHPC beams, with maximum increases of 79 % and 159 %, respectively. The volume content, shape and dimension of steel fibers exhibited significant influence on the torsional performance of UHPC beams, including torsional capacity, ductility and cracking pattern. The shape and dimension of steel fibers both affected the post-cracking load-carrying capacity of UHPC beams. The cracking and ultimate torques of the two UHPC beams with hybrid steel fibers were higher than those containing single type of steel fiber, both exhibiting positive hybrid effects. Based on the experimental results of this study, the hybrid use of 1 % end-hooked and 1 % long straight steel fibers is recommended in UHPC beams by comprehensively considering the torsional performance and the cost. Finally, by fully considering the excellent tensile behavior of UHPC, theoretical formulas were proposed for calculating the cracking and ultimate torques of UHPC beams without steel reinforcement based on the Bredt thin-tube theory. Comparison between the experimental and theoretical results on 36 UHPC torsional beams demonstrated the feasibility of the proposed formulas.