Short Fiber Research Articles

Novel effective spectrum broadening technology pumped by 2 μm picosecond laser for mid-infrared supercontinuum generation

Using thulium-doped fiber laser to pump fluoride fiber is one of the most common methods to generate mid-infrared supercontinuum (SC). But it is difficult to generate SC spectrum with wavelength more than 4 μm by directly pumping short fluoride fiber with 2 μm picosecond (ps) laser. Although some studies with SC exceeding 4 μm have also been reported, the proportion of spectral power in the long-wavelength region is not very high. To address this issue, a novel and simple approach to solve low peak power of 2 μm ps pump sources is introduced by adding a short piece of holmium-doped fiber. This method can make full use of the gain bandwidth of Ho3+ and soliton self-frequency shift effect to enhance soliton energy and promote spectral broadening. The effectiveness of the approach is verified by constructing a theoretical model to solve the generalized nonlinear Schrödinger equation. We demonstrate through simulations that addition of holmium-doped fiber can yield significantly improved output spectral range, power ratio in the long-wavelength region and optical–optical conversion efficiency compared to the previous technical. Especially, the implementation of the new technology can effectively expand the SC long-wavelength edge by ∼470 nm after applying a 3 dB gain, and can easily build a simple, compact and low-cost mid-infrared light source system.

Framework for the Generation of 3D Fiber Composite Structures from 2D Observations

AbstractSynthetic generation of realistic materials for testing of process–structure–property (PSP) relationships in computational materials science has gained significant traction over the past two decades. Generation tools continue to lag in some aspects of realism, leading to uncertainty and errors in simulating material response. The experimental collection of information to guide generation of 3D synthetic structures remains costly, time consuming, and challenging. These challenges are compounded by limitations of stereology, which permits estimation of 3D microstructural statistics from 2D observations under restrictive assumptions on constituent morphologies and size distributions and can be difficult to apply to microstructure metrics like constituent orientation distribution and clustering. This work seeks to overcome these challenges by introducing a framework for learning probable 3D microstructure statistics by minimizing the loss determined by matching statistics obtained from 2D observations via synthetic microstructure generation software (e.g. Dream.3D) and stereological principles. This framework is applied to short carbon fiber composite structures printed from an additive manufacturing process, Direct Ink Writing, with the hope that the framework could generalize to other particulate structures as well as allow for simulation and design of materials structure.

Characterization of holocellulose extracted from agricultural and food processing byproducts via ecofriendly delignification pulping process

AbstractThis study investigated an ecofriendly peracetic acid delignification process to extract holocellulose from various fiber rich plant‐based byproducts (coconut palm spathe/leaf, apple pulp, wine grape pomace, hazelnut shell, and hemp fiber/hurd), and evaluated their physicochemical, morphological, and thermophysical properties in comparison with commercial cellulose nanofibers produced from wood. Holocellulose from coconut palm spathe has long fiber (~846.7 μm), whereas that from wine grape pomace and hazelnut shell exhibits a cylinder shape of particles with short fiber length (~123.8 and ~ 71.1 μm, respectively). Biofilms cast from apple pulp and hemp fiber holocellulose have higher degradation temperature (361 and 358°C, respectively) than biofilms from other materials, thus more thermally stable. All biofilms demonstrate high UV absorbance, and the biofilm cast from apple pulp holocellulose is transparent with smooth surface. Fourier‐transform infrared spectroscopy analysis confirms the presence of cellulose and hemicellulose as the main components in the biofilms, along with traces of residual lignin that remained after the extraction process. This study demonstrates that holocellulose with varied cellulose morphology and polymeric characteristics could be extracted depending on the type of byproducts and be employed to produce sustainable packaging materials.

Free vibration analysis of laminated anisotropic doubly-curved shell structures reinforced with three-phase polymer/CNT/fiber material

The present work investigates the vibrational response of laminated anisotropic doubly-curved shell structures reinforced with Carbon Nanotubes (CNTs) short fibers. The fundamental equations are derived from a curvilinear reference system of principal coordinates, employing the Equivalent Single Layer (ESL) methodology. Furthermore, a general variation in laminate thickness is considered. The unknown field variable is described using higher order theories through the unified formulation, taking into account a general interpolation of the unknown variables with Lagrange polynomials across the physical domain. The Hamiltonian Principle is adopted for the derivation of the dynamic equilibrium equations, which arediscretized numerically by using the Generalized Differential Quadrature (GDQ) method. In addition, an efficient isogeometric NURBS-based mapping is adopted for the distortion of the physical domain. The boundary conditions of the differential problem are modelled through a general distribution of linear elastic springs along the lateral surfaces of the three-dimensional doubly-curved solid. The theory is then applied to study the vibrational modes of structures with different curvatures and lamination schemes, taking into account a general distribution of CNTs along the thickness direction. The homogenized properties of CNTs layers are obtained from the Mori-Tanaka procedure, which accounts for the agglomeration effects of the dispersed nanofibers within the matrix. Unlike previous studies focusing on doubly-curved shells reinforced with composite materials and CNTs, the present formulation enables to derive the vibration characteristics of structures made of generally anisotropic materials with general orientations. Furthermore, the calibration of the parameters for the linear elastic springs’ distribution leads to general external constraints within a single element, thus reducing the computational cost of the problem.

A short banana fiber—PLA filament for 3D printing: Development and characterization

AbstractThis study aims to develop a 3D printable composite filament using short banana fiber and polylactic acid (PLA). The filament was acquired through a single screw extruder, employing various blending techniques. Various fiber loadings were examined, impacting PLA's mechanical, thermal, and printability properties. The results revealed altered mechanical characteristics, with reduced tensile and flexural properties compared with pure PLA. However, these values are at an acceptable level for non‐structural applications. Compared with previous works, the filament developed in the present work is found out to be second strongest among the cellulose fiber‐reinforced PLA filaments. 3D printing with the composite filament encountered no significant issues. A modified mixing method improved mechanical characteristics, although 3D‐printed samples showed deteriorated mechanical characteristics due to poor interfacial bonding. This research introduces an environmentally viable strategy for advancing 3D printing technology by integrating banana fibers into PLA filament. The proposed strategy can be effectively utilized in making cellulose/PLA filaments for 3D printing applications. This innovative approach preserves PLA's natural biodegradability while carefully managing the integration of banana fibers and their potential effects on mechanical properties.Highlights Fiber loading influences mechanical, with minimal impact on thermal properties. Solution casting improved fiber/matrix bonding and filler homogeneity. Plasticizing effect reduces the tensile strength. Modified mixing resulted in even filament diameter and improved tensile properties.

Valorisation of Agricultural Residue Bio-Mass Date Palm Fibre in Dry-Blended Polycaprolactone (PCL) Bio-Composites for Sustainable Packaging Applications

Abstract Purpose This study experimentally developed and characterised dry-blended Polycaprolactone (PCL)/date palm fibre biodegradable composites for sustainable packaging applications. Date palm fibres are collected from date palm trees as by-products or waste materials. They will be valorised in bio-composite application to promote fibre-based sustainable packaging items over their non-biodegradable synthetic polymer based conventional packaging products. In the dry-blending process, fibre and polymer are mixed with a shear mixer, while, in a melt-blending process, an extruder is used to extrude fibre/polymer blends after applying heating and high shear pressure to melt and mix polymer with fibres. Dry-blending process offers many comparative advantages, such as less equipment, steps, cost, process degradation, energy consumption and hence, lower harmful environmental emissions; while, a proper fibre/polymer mixing is a challenge and it needs to be achieved properly in this process. Therefore, it is important to understand the effects of dry-blending process on manufacturing of PCL/date palm fibre bio-composites for packaging applications, before promoting the dry-blending as a suitable alternative to the melt-blending process. Methods Short chopped fibres were grinded as powders and dry-blended at a ratio of (0 − 10%) (w/w) with PCL polymer using hand and a shear mixer for 30 min, following a compression moulding process to produce bio-composite samples. Tensile, water contact angle, SEM, TGA, DSC and DMA tests and analysis were conducted. The dry-blended PCL/date palm fibre composites’ properties were compared with reported melt-blended samples’ results found in literature. Results Dry-blended samples showed an increase in tensile modulus values (up-to 20%) with fibre inclusion and these values were found close to the melt-blended samples in the literature. Tensile strength and strain values were reduced which could be related to the poor fibre/polymer interface. Fibre addition affected the thermal, thermo-mechanical and crystallisation processes in PCL polymer matrix. Conclusion Dry-blending is capable of producing bio-composites with a very comparable properties to melt-blended counterparts, although a more details study is needed to conduct in future. The results of this study, could be used carefully to design dry-blended PCL/date palm fibre bio-composites for possible packaging applications. The irregular fibre distribution in dry-blended samples could be improved in different ways which should be investigated in future. Graphical Abstract

Novel sustainable steel fiber reinforced preplaced aggregate concrete incorporating Portland limestone cement

This study proposes a novel approach by adding Portland limestone cement (PLC) to preplaced aggregate steel fiber reinforced concrete (PASFRC) to create a sustainable concrete that minimizes CO2 emissions and cement manufacturing energy usage. The method involves injected a flowable grout after premixing and preplacing steel-fibers and aggregates in the formwork. This study evaluates the mechanical properties of a novel sustainable concrete that uses PLC and steel fibers. To achieve the intended objective, long and short end-hooked steel fibers of 1%, 2%, 3%, and 6% were incorporated in PASFRC. Also, Analysis of variance (ANOVA) was used to examine the data. Results indicated that PLC and higher fiber doses increased the mechanical properties of PAC. At 90 days, PASFRC mixtures containing 6% long steel fibers demonstrated superior compressive, tensile, and flexural strengths, registering the highest values of 49.8 MPa, 7.7 MPa, and 10.9 MPa, respectively and differed by 188%, 166%, and 290%, respectively from fiberless PAC. The study confirmed the suitability and effectiveness of using PLC with steel fibers in PAC which significantly improved the mechanical properties of PASFRC. This was verified through analytical analysis and new empirical equations were proposed to predict the mechanical properties of PASFRC.

Fiber Quality of Colored Cotton As a Function of Potassium Fertilization in the Semi-Arid Region

ABSTRACT Naturally colored fiber cotton is an essential alternative green and organic for the textile industry, as it does not require chemical dyeing. However, the low availability of potassium during production can directly affect the quality of the fiber. Based on this, this study aimed to evaluate the fiber quality in naturally colored cotton cultivars submitted to potassium fertilization in a semi-arid region. The experimental design was in randomized blocks, with four replications, and the treatments were arranged in split plots. In the plot, the following were allocated: five K rates (0, 60, 120, 180, and 240 kg ha−1 of K2O); and in the subplots, the four colored cotton cultivars (BRS Rubi, BRS Safira, BRS Topázio, and BRS Verde). The results showed that K is involved in the length, uniformity, short fiber index, micronaire index, and reliability index of naturally colored cotton fibers. A longer fiber length of 30.45 mm was obtained at a dose of 240 kg ha−1 of K2O for the cultivar BRS Topázio. In addition, a higher uniformity (84.95%) was achieved with the dose of 240 kg ha−1 of K2O for BRS Verde. The dose of 240 kg ha−1 of K2O reduced (8.62% and 11.28%) the short fiber index in the cultivars BRS Rubi and BRS Safira, respectively.

On-Chip Supercontinuum Generation Pumped by Short Wavelength Fiber Lasers

Supercontinuum (SC) generation pumped by fiber lasers with short wavelengths below 2.0 μm is important since it can provide a compact light source for various applications. We review the progress of SC generation in various materials regarding the formation of the waveguides and point out the existing issues in the current investigations and possible solutions in the future.

Mechanical and piezoresistive performance of additively manufactured carbon fiber/PA12 hybrid honeycombs

This study investigates a novel self-sensing honeycomb composite structure composed of two distinct cellular layers with differing unit cell architectures, specifically hexagonal and re-entrant designs. Short carbon fiber (CF)/polyamide 12 (PA12) composite filaments with 0, 5 or 15 wt.% CF content were utilized to additively manufacture the honeycomb structures via Fused Filament Fabrication (FFF), and their mechanical and piezoresistive self-sensing characteristics were experimentally investigated under quasi-static in-plane and out-of-plane compression at both room temperature and elevated temperatures. The results reveal that the hybrid hexagonal/re-entrant (HR) honeycombs mechanically outperform their non-hybrid double-layer and single-layer counterparts under in-plane loading, reporting an increase in collapse strength and energy absorption by factors of 1.64 and 2.25, respectively. These improvements are attributed to the mechanical interactions occurring at the interface between the auxetic and non-auxetic layers within the hybrid structure, effectively enhancing its structural attributes. Furthermore, the double-layer honeycombs display excellent strain-sensing capabilities within the elastic regime, with gauge factors reaching values as high as 146. Mechanical tests conducted at elevated temperatures reveal that the CF/PA12 honeycombs retain a significant portion of their elastic modulus, strength and energy absorption even at 125 °C, while maintaining high gauge factors of up to 72.4. These honeycombs also exhibit pronounced thermoresistive behavior, evidenced by a decrease in electrical resistance of up to 41.3 % with increasing temperatures from 25 to 125 °C. Considering their exceptional combination of thermo-mechanical, thermoresistive and piezoresistive characteristics, these hybrid double-layered CF/PA12 honeycombs hold promise for potential applications in multifunctional lightweight structures, offering integrated temperature and strain-sensing capabilities.

Radiation-induced graft copolymerization of a phosphonate monomer onto short flax fibers and Miscanthus x giganteus stem fragments: Influence of substrate composition

The functionalization of Miscanthus x giganteus stems fragments (R-MSF) by dimethyl(methacryloyloxy)methyl phosphonate (MAPC1) using pre-irradiation was studied. The influence of the composition and the structure of the substrate on the grafting efficiency was investigated by comparing the results with short flax fibers (SFF) and bleached Miscanthus x giganteus stems fragments (B-MSF). The lignocellulosic substrates were irradiated at several target doses ranging from 11 to 108.1 kGy using e-Beam. Electron Paramagnetic Resonance spectroscopy (EPR) highlighted major differences in terms of radical nature between R-MSF, SFF, and B-MSF samples. Following the polymerization reactions, washing, and drying steps, the phosphorus contents were measured by X-ray fluorescence spectrometry (XRF). Unlike Flax, pre-irradiation grafting was not efficient on R-MSF. The role of lignin content on grafting reactions was then evaluated by comparing R-MSF with SFFand B-MSF), showing only a minor impact. Using a reducing agent, it was possible to reach a phosphorus content of about 1.4 wt% for R-MSF and up to 4.0 wt% for B-MSF for a 100 kGy dose. Furthermore, phosphorus mapping using scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) highlighted a homogeneous dispersion of the grafted macromolecules. This demonstrates the possibility of conducting pre-irradiation grafting on lignin-rich substrates without bleaching. Efforts were then made to optimize the operating conditions in terms of storage temperature, reaction temperature and Fe2+ concentration. Finally, the fire behavior of treated Miscanthus x giganteus stem fragments was evaluated by pyrolysis-combustion flow calorimetry (PCFC).

Electric-driven shape memory deformation control and verification of composite films based on PVA/WPU/SCFs

Based on the research of Polyvinyl alcohol (PVA)/Waterborne Polyurethane (WPU)/Short Carbon Fibers (SCFs) novel electrochemically shape memory composites, this study delved into an exploration of factors influencing the shape memory deformation of shape memory film samples when subjected to voltage stimulation. These main affecting factors encompassed sample thickness, activation voltage, and wire layout. Subsequently, based on the above conclusions, the viscoelastic constitutive model of PVA/WPU/SCFs composite was established based on Maxwell model and the deformation deflection of the composite film was predicted by shape memory recovery, and the electrothermal coupling simulation analysis and shape memory recovery and deformation simulation verification were carried out. Finally, based on the shape memory recovery performance of the composite film, a new reciprocating moving deformation structure was conceptualized, characterized by distinct cycles of motion, each analyzed individually.

Activating Macrophage Continual Efferocytosis via Microenvironment Biomimetic Short Fibers for Reversing Inflammation in Bone Repair.

Efferocytosis-mediated inflammatory reversal plays a crucial role in bone repairing process. However, in refractory bone defects, the macrophage continual efferocytosis may be suppressed due to the disrupted microenvironment homeostasis, particularly the loss of apoptotic signals and overactivation of intracellular oxidative stress. In this study, a polydopamine-coated short fiber matrix containing biomimetic "apoptotic signals" to reconstruct the microenvironment and reactivate macrophage continual efferocytosis for inflammatory reversal and bone defect repair is presented. The "apoptotic signals" (AM/CeO2) are prepared using CeO2 nanoenzymes with apoptotic neutrophil membrane coating for macrophage recognition and oxidative stress regulation. Additionally, a short fiber "biomimetic matrix" is utilized for loading AM/CeO2 signals via abundant adhesion sites involving π-π stacking and hydrogen bonding interactions. Ultimately, the implantable apoptosis-mimetic nanoenzyme/short-fiber matrixes (PFS@AM/CeO2), integrating apoptotic signals and biomimetic matrixes, are constructed to facilitate inflammatory reversal and reestablish the pro-efferocytosis microenvironment. In vitro and in vivo data indicate that the microenvironment biomimetic short fibers can activate macrophage continual efferocytosis, leading to the suppression of overactivated inflammation. The enhanced repair of rat femoral defect further demonstrates the osteogenic potential of the pro-efferocytosis strategy. It is believed that the regulation of macrophage efferocytosis through microenvironment biomimetic materials can provide a new perspective for tissue repair.

Amazon açaí fiber-Portland cement compatibility: a challenge to produce cement-bonded fiberboards?

The açaí waste from Amazon contains short fibers that show potential for reinforcing cement-bonded fiberboards (CBFBs), although their compatibility with cement matrix is still unknown. This work aimed to characterize raw and pretreated açaí fibers and analyze their compatibility with Portland cement by different techniques, besides developing a CBFB. The fibers were subjected to thermal (180, 200, and 220 °C), cold and hot water, alkaline (NaOH), and bleaching (NaOH-H2O2) pretreatments. The chemical and water pretreatments raised the fiber crystalline indexes (28%-57%). The chemical pretreatments individualized the fiber bundles and removed hemicelluloses. Alkali-pretreated and raw fibers had the highest (96%) and lowest (65%) cement compatibility indexes. Portlandite and ettringite appeared after 24 h for most pastes but were delayed for raw and 220 °C-pretreated fibers. In contrast, only the raw fiber specimens reached the required compression strength of 34 MPa after 28 days; hence, they were chosen to produce a CBFB. The boards showed proper thickness swelling (1.4%), but low bending strength (MOE = 647.8 MPa; MOR = 1.9 MPa). Overall, the fiber modifications improved the compatibility with cement, but not the composite's mechanical strength. Açai-fiber CBFB is a promising building material, but future studies must overcome its poor mechanical performance.

A sponge-like nanofiber melatonin-loaded scaffold accelerates vascularized bone regeneration via improving mitochondrial energy metabolism

Electrospun nanofibers have been widely employed in bone tissue engineering for their ability to mimic the micro to nanometer scale network of the native bone extracellular matrix. However, the dense fibrous structure and limited mechanical support of these nanofibers pose challenges for the treatment of critical size bone defects. In this study, we propose a facile approach for creating a three-dimensional scaffold using interconnected electrospun nanofibers containing melatonin (Scaffold@MT). The hypothesis posited that the sponge-like Scaffold@MT could potentially enhance bone regeneration and angiogenesis by modulating mitochondrial energy metabolism. Melatonin-loaded gelatin and poly-lactic-acid nanofibers were fabricated using electrospinning, then fragmented into shorter fibers. The sponge-like Scaffold@MT was created through a process involving homogenization, low-temperature lyophilization, and chemical cross-linking, while maintaining the microstructure of the continuous nanofibers. The incorporation of short nanofibers led to a low release of melatonin and increased Young's modulus of the scaffold. Scaffold@MT demonstrated positive biocompatibility by promoting a 14.2 % increase in cell proliferation. In comparison to the control group, Scaffold@MT significantly enhanced matrix mineralization by 3.2-fold and upregulated the gene expression of osteoblast-specific markers, thereby facilitating osteogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs). Significantly, Scaffold@MT led to a marked enhancement in the mitochondrial energy function of BMMSCs, evidenced by elevated adenosine triphosphate (ATP) production, mitochondrial membrane potential, and protein expression of respiratory chain factors. Furthermore, Scaffold@MT promoted the migration of human umbilical vein endothelial cells (HUVECs) and increased tube formation by 1.3 times compared to the control group, accompanied by an increase in vascular endothelial growth factor (VEGFA) expression. The results of in vivo experiments indicate that the implantation of Scaffold@MT significantly improved vascularized bone regeneration in a distal femur defect in rats. Micro-computed tomography analysis conducted 8 weeks post-surgery revealed that Scaffold@MT led to optimal development of new bone microarchitecture. Histological and immunohistochemical analyses demonstrated that Scaffold@MT facilitated bone matrix deposition and new blood vessel formation at the defect site. Overall, the utilization of melatonin-loaded nanofiber sponges exhibits significant promise as a scaffold that promotes bone growth and angiogenesis, making it a viable option for the repair of critical-sized bone defects.

The moisture absorption of 3D printed short carbon fibre reinforced polyamide

Polymer composites are commonly exposed to humid conditions and undergo reductions in mechanical properties. It is challenging to describe the moisture absorption dynamics of 3D printed parts due to manufacture-induced microstructures. This work investigates the moisture absorption of 3D printed short carbon fibre reinforced polyamide with varied microstructures and resulting influence on mechanical properties. The printed composites have inferior microstructures compared to the polyamide and diffusivity increases with the number of interlayer interfaces by up to 119 % (three times that of compression moulded composite). The microstructure is permanently aggravated by moisture resulting in more significant and irreversible reductions in yield stress (39 to 59 %) and tensile modulus (65 to 79 %) compared to injection moulded samples. Additionally, the shear modulus of printed polyamide and composites decrease by up to 63 % and 74 %, respectively. The results are helpful for prediction, evaluation, and maintenance of 3D printed applications subject to moisture environment.

Enhancing mechanical properties of mortar with short and thin banana fibers: A sustainable alternative to synthetic fibers

The use of fiber in mortar/concrete is now common for enhancing the flexural and ductility properties of structures. However, the utilization of synthetic fibers contributes to the emission of harmful greenhouse gases. Replacing these synthetic fibers with natural fibers derived from waste plants is imperative for sustainable development. The objective of this study was to evaluate the performance of short and thin banana fibers in enhancing the mechanical properties of fiber-reinforced mortar, specifically in terms of compressive, flexural, and splitting tensile strengths. The base mortar, with a water-cement ratio of 0.30 and a unit water content of 298 kg/m3, was employed. The banana fibers were manually extracted from banana stalks, dried in an oven, and then cut into 10 mm fibers. The fibers were not treated with alkali. The fiber content was varied at 0 %, 0.125 %, 0.25 %, 0.5 %, and 0.75 % by weight of cement. Initially, the fibers were mixed into the viscous mortar along with the first portion of water and a superplasticizer. Subsequently, workability was improved by incorporating the second portion of water. The optimal content of banana fiber was determined to be 0.25 %, which increased the 28-day compressive, flexural, and splitting tensile strengths by 18.7 %, 29.9 %, and 41.1 %, respectively, compared to the base mortar. These findings suggest that the short and thin banana fiber has the potential to serve as a sustainable alternative to synthetic fibers. However, it is essential to conduct a thorough assessment of durability properties before implementing it in actual structures.

Biotribological properties of 3D printed high-oriented short carbon fiber reinforced polymer composites for artificial joints

Short carbon fiber (SCF) reinforced polymer composites are expected to possess outstanding biotribological and mechanical properties in certain direction, while the non-oriented SCF weakens its reinforcing effect in the matrix. In this work, high-oriented SCF was achieved during nozzle extrusion, and then SCF reinforced polyether-ether-ketone (PEEK) composites were fabricated by fused deposition modeling (FDM). The concrete orientation process of SCF was theoretically simulated, and significant shear stress difference was generated at both ends of SCF. As a result, the SCF was distributed in the matrix in a hierarchical structure, containing surface layer I, II and core layer. Moreover, the SCF was oriented highly along the printing direction and demonstrated a more competitive orientation distribution compared to other studies. The SCF/PEEK composites showed a considerable improvement in wear resistance by 44 % due to self-lubricating and load-bearing capability of SCF. Besides, it demonstrated enhancements in Brinell hardness, compressive and impact strength by 48.52 %, 16.42 % and 53.64 %, respectively. In addition, SCF/PEEK composites also showed good cytocompatibility. The findings gained herein are useful for developing the high-oriented SCF reinforced polymer composites with superior biotribological and mechanical properties for artificial joints.

Direct validation of 3D meso-scale fracture modelling of UHPFRC by in-situ micro X-ray CT wedge-split tests and parametric studies

3D meso-scale finite element models of ultra high performance fibre reinforced concrete (UHPFRC) based on in-situ micro X-ray Computed Tomography (CT) images are developed and validated in this study. The CT images at 16.9 μm voxel resolution from a progressive wedge-split test were converted into meso-scale 3D tetrahedron meshes. The short fibres, embedded in the mortar matrix, were modelled by truss elements with equivalent elastoplastic constitutive laws transformed from single fibre pullout load–displacement curves, so as to indirectly model the fibre–matrix interfaces. A concrete damage plasticity model was used to simulate damage and fracture in the mortar. The simulated load–displacement curves, final crack patterns, and load-crack opening curves were found in good agreement with the in-situ CT test results, and the non-vertical crack path was significantly affected by the overall orientation of fibres bridging the crack. Further simulations with all the fibres perpendicular to the tensile splitting direction showed that the peak load and fracture energy increased by 42 % and 45 % respectively from 1 % to 3 % fibre volume fraction. This indicates the need to optimize the fibre orientation for best mechanical performance according to the loading conditions.

Preparation of ultra-high-strength alumina microspheres based on fiber reconstruction via multistage low-carbon alcohol elution

Catalytic reactions play a central role in chemical production, wherein the strength of the catalyst support is key to long-term stable operation. Simple and efficient strength enhancement methods for heterogeneous catalysis have received significant attention. Herein, we developed a variable-temperature gradient elution technology for low-carbon alcohols to improve the crushing strength of microspheres prepared using the sol–gel method in a microfluidic system. Based on gel fiber growth and rearrangement utilizing the hydrogen-bonding effect between low-carbon alcohols and pseudo-boehmite, the pore structure and fiber network can be reconstructed. Low-carbon alcohols with strong hydrogen bonds and low steric hindrance are more conducive to the formation of short fibers when constructing a dense gel network coordinated with higher alcohols. By combining long and short fiber cross-linked networks, the crushing strength of microspheres is significantly improved, and a dense pore structure with a small pore volume forms. After gradient elution, a crushing strength of up to 71.78 N/mm2 can be achieved with a high specific surface area of 254.27 m2/g, which significantly exceeds that of commercial alumina supports with the same pore volume. This efficient method provides an important solution for the long-term, stable operation of catalysts.