Straight Fibers Research Articles

The Influence of Materials on the Mechanical Properties of Ultra-High-Performance Concrete (UHPC): A Literature Review.

Ultra-high-performance concrete (UHPC) is a cementitious composite combining high-strength concrete matrix and fiber reinforcement. Standing out for its excellent mechanical properties and durability, this material has been widely recognized as a viable choice for highly complex engineering projects. This paper proposes (i) the review of the influence exerted by the constituent materials on the mechanical properties of compressive strength, flexural tensile strength, and elastic modulus of UHPC and (ii) the determination of optimal quantities of the constituent materials based on simplified statistical analyses of the developed database. The data search was restricted to papers that produced UHPC with straight steel fibers at a content of 2% by volume. UHPC mixture models were proposed based on graphical analyses of the relationship of constituent materials versus mechanical properties, aiming to optimize the material's performance for each mechanical property. The results proved to be in accordance with the specifications present in the literature, characterized by high cement consumption, significant presence of fine materials, and low water-to-binder ratio. The divergences identified between the mixtures reflect how the constituent materials uniquely impact each mechanical property of the concrete. In general, fine materials were shown to play a significant role in increasing the compressive strength and flexural tensile strength of UHPC, while water and superplasticizers stood out for their influence on the material's workability.

Combined effect of natural fibre and steel fibre on the thermal-mechanical properties of UHPC subjected to high temperature

This research investigates the combined effect of steel and natural fibre on the mechanical properties and spalling resistance of ultra-high performance concrete (UHPC) before and after exposure to elevated temperatures. The effects of two parameters, namely temperature (ambient temperature, 200 °C, 400 °C and 600 °C) and fibre type (solely macro end hooked steel fibre (MHS) and hybrid of micro straight steel fibre (MSS), macro end hooked steel (MHS) fibre and micro jute (MJ) fibre) on the mechanical properties, spalling resistance and mass loss of UHPC were studied.Micrographs from scanning electron microscope (SEM) test were utilized to appraise the steel fibre and jute fibre before and after exposure to elevated temperatures. The test results exhibited that the residual tensile strength and flexural strength were significantly declined after exposure to high temperatures for UHPC specimens reinforced with macro steel fibre only. Moreover, explosive thermal spalling occurred for this group of specimens under 600 °C. Whereas the combined use of jute fibre and micro-macro steel fibre was an effective approach to prevent the explosive thermal spalling under 600 °C and improve the residual tensile strength, flexural strength and toughness of UHPC. Furthermore, preliminary empirical expressions have been developed in this study to predict the residual mechanical properties of UHPC as a function of natural fibre content, steel fibre content and temperature.

A multiscale experimental study of CFRP-UHPFRC interfacial bond behaviour: Failure mechanisms and a fibre volume dependent bond-slip law

Carbon fiber reinforced polymer (CFRP) materials are being increasingly used with ultra high performance fiber reinforced concrete (UHPFRC) to construct composite structural members making use of their unique properties. As the interfacial bond behaviour between CFRP and UHPFRC plays a key role in the design of such members, it was investigated in detail by multiscale experiments of single shear pull-off tests of 26 CFRP-UHPFRC bonded joints with different bond lengths and widths of CFRP laminates and 0.5–4% volume fraction (Vsf) of straight high-strength steel fibers (length = 13 mm, diameter = 0.2 mm). 12 CFRP-normal strength concrete (NSC) bonded joints were also tested for comparison. The surface strain evolution and the interfacial debonding process were captured and analysed by the digital image correlation (DIC). The complex microscale failure mechanisms, such as the mortar cracking, the CFRP-UHPFRC interfacial debonding, and the steel fibers’ slipping and pulling out of the mortar, were visualised and analysed by the 3D micro X-ray Computed Tomography (μXCT) scanning. It was found that the debonded layer of mortar under the laminates was much thinner than that in the CFRP-NSC bonded joints, due to the lack of coarse aggregates in UHPFRC. The peak pulling forces for the specimens with Vsf = 0.5%, 1%, 2%, and 4% were 9%, 21%, 28%, and 29% higher than those without steel fibers, respectively. An empirical bond strength model and an interfacial bond-slip model were proposed based on the test results, accounting for Vsf, the material properties, and the laminate to UHPFRC width ratio. Finally, the proposed bond-slip model was applied in finite element modelling to simulate the flexural behaviour of an FRP-UHPFRC composite deck in the literature, with the interfacial debonding failure and the ultimate loads successfully predicted.

Utilization of Bamboo Roots as Reinforcing Composite Materials for Light Vehicle Dashboards

Bamboo roots are residual material from the utilization of bamboo trees’ waste. Bamboo roots utilize in engineering by making new materials in the form of composites. Bamboo roots are easy to get, and getting bamboo root fiber is relatively easy compared to getting bamboo stem fiber. Bamboo root fibers are used as reinforcement in composites with resin binders and catalysts as hardeners. The composite made by mixing the composition consists of 10% bamboo root fiber, 89% resin, and 1% catalyst from the weight of the specimen. This composition uses three variations of fiber direction; straight, random, and woven fiber—each variation tests tensile strength, impact, and bending strength. Those three test results show that the highest values come from the woven fiber, which are 21.04 MPa from the tensile strength, 0.0693 J/mm2 from the impact value, and 34.789 MPa from the bending strength value. The test result found that applying bamboo roots composite material suits dashboard material for light vehicles (cars and motorcycles). This test result meets the standard material for dashboard vehicles based on plastic material data ABS (Acrylonitrile butadiene styrene). This research on natural fiber composite material is novel and valuable as a waste utilization solution for engineering materials.

Variable angle tow composites in fibre-reinforced polymer bridges

Fibre reinforced polymers are increasingly used in bridge structures for reducing their environmental impact, extending the service life and saving costs. In this work, we propose the use of composite laminates called Variable Angle Tow (VAT) to realise bridge structures. In VAT composite laminates, the fibre orientation changes pointwise over the structure, enhancing stiffness tailoring capabilities with respect to traditional straight fibre (SF) laminates. In aerospace engineering, VAT composites have been successfully used to tailor structures’ stiffness to enhance linear elastic response, reduce buckling phenomena, and optimise the postbuckling behaviour. However, VAT laminates have never been applied in civil structures. This work shows how using VAT composite laminates in a bridge girder improves its buckling and postbuckling behaviours and increases its overall stiffness. A numerical investigation is conducted to assess the benefits given by VAT composite laminates to the structural performance of bridge girders. For different spans, results of a multi-objective optimisation considering both traditional SF and VAT laminates are presented. It is found that VAT laminates exhibit a buckling load up to 80% over SF laminates, with equal or lower deflections and without adding extra material, thereby opening new design scenarios for bridge structures.

Effect of steel fiber shape and content on printability, microstructure and mechanical properties of 3D printable high strength cementitious materials

This study investigates the effects of steel fiber shape (straight and hooked-end) and content (0, 0.5, 1.0, and 1.5 vol%) on rheological properties, printability, mechanical performance and microstructure of 3D printable steel fiber reinforced high strength concrete (3DP-SFHSC). The results indicate that the increase of fiber content improves the mechanical behaviors of 3DP-SFHSC, but the extrudability suffers from reduction when the fiber content exceeded 1.0 vol% due to the significant increase in yield stress. The addition of 1.5 vol% hooked-end fibers enhances the compressive strength of 3DP-SFHSC by 8%, 25.7%, and 40.4% in the X, Y, and Z directions, respectively. Additionally, it also improves the tensile strength in the X direction by 37.67%. The printed specimens exhibit weaker mechanical properties compared to the cast specimens. On the one hand, the lower fiber-matrix compactness resulting from the absence of vibration during printing leads to increased porosity and weak bonding between the steel fibers and matrix. On the other hand, the inconsistent movement between fibers and mortar matrix during extrusion process may also cause the formation of gaps around fibers. Straight fibers show pronounced enhancements in buildability, compressive strength and tensile strength compared to hooked-end fibers at the same fiber volume fraction. Straight fibers align easily during the extrusion process, contributing to a matrix with lower porosity and smaller average pore size.

Effects of the addition of short straight steel fibers on the strength and strains of high-strength concrete during compression

The article presents the effect of the addition of short straight steel fibers on the behavior of high-strength concrete (HSC) under compression (σ–ε curves). Deformations of cylindrical samples were measured simultaneously with the use of linear variable differential transformers (LVDT), strain gauges and the method of digital image correlation (DIC). The study showed that as the content of short straight steel fibers increases, both the composite compressive strength (fc) and strains (ε0), which correspond to the stress equal to the compressive strength, increase as well. To a lesser extent, the effect of short straight fibers on the descending part of the σ–ε curve was observed. An increase in the density and toughness ratio of the compressive strength of high-strength concrete with fibers compared to concrete without fibers was also observed. Moreover, compressive strength of the composite was estimated using the ultrasonic method. Based on the obtained results, a statistical analysis and an estimation of parameters fc and ε0 were carried out, and an analytical model was proposed to describe σ–ε relationship for HSC reinforced with short straight fibers under compressive loading. The results obtained for compressed fiber-reinforced concrete were compared with data available in literature.

Failure mechanism of steel fiber pullout in UHPC affected by alternating cryogenic and elevated variation

This paper investigates the pullout response of straight and hooked-end steel fiber embedded in Ultra-high Performance Concrete (UHPC) subjected to alternating cryogenic (−170 °C) and elevated (200 °C) temperature variation. The temporal evolution of Acoustic Emission (AE) parameters and failure behavior during the pullout process were monitored in situ using the AE test. Additionally, changes in the UHPC microstructure were also evaluated. Results showed that in addition to the UHPC matrices exposed to elevated temperature, the compressive and flexural strength of UHPC matrices subjected to single or multiple cycles were generally higher than those at ambient temperature. Whereas the bond strength/pullout energy of straight fiber increased with a single cycling exposure of UHPC specimens to either cryogenic or elevated temperature, the improvement in the pullout performance of the hooked-end fiber was obtained only after the post-cryogenic thawing of specimens. Moreover, the exposure to an increased number of temperature-variation cycles caused the pullout strength and energy of both fiber groups to gradually decrease. Nonetheless, the pullout performance of the hooked-end fiber was significantly and consistently superior to that of the straight fiber, regardless of the exposure temperature or cycles. The AE test confirmed that the pullout process of both fibers was mainly characterized by tensile failure, with a marginal occurrence of shear failure for the hooked-end fiber. When the UHPC was exposed to various temperatures, the fiber pullout behavior was predominantly influenced by the physical structure of the fibers, thermal deformation proclivity of the matrix, and the competition between mechanisms such as pore moisture phase change, secondary hydration, and the composition of hydrates.

High spatial resolution temperature variation detection in one direction with a fiber solenoid and RDTS system

Limited by the large bottom width of the pulsed light and the large sampling spacing of the data acquisition card in conventional Raman distributed temperature sensing (RDTS) systems, short straight fibers cannot acquire temperature measurements with high spatial resolution and high temperature accuracy in a single temperature variation region (TVR). In contrast, winding sensing fiber on a screwed tube as a fiber solenoid for temperature sensing can indirectly improve the spatial resolution of the system. However, as the radius of the screwed tube decreases, the ability of the screwed tube to improve the spatial resolution of the system will deteriorate. To break this limitation, we innovatively propose a signal processing scheme to first construct a three-dimensional surface of the sensing length of screwed tube-temperature-area value, then obtain the length of the TVR and the area value of the temperature rise curve generated from a single TVR, and finally demodulate the temperature of the TVR in the surface. The experimental results show that the proposed scheme improves the spatial resolution of the conventional screwed tube from 8 cm to 1 cm, and the average temperature accuracy of the three TVRs with the interval and length of the TVRs in the order of centimeters is ± 0.63 °C. The screwed tube can be used for axial temperature distribution measurements of liquids as well as solids, and the proposed method can further expand the application prospects of the RDTS system for continuous measurement of multiple TVRs with lengths and intervals of centimeters in one direction without changing the internal hardware.

First Advanced Bilayer Scaffolds for Tailored Skin Tissue Engineering Produced via Electrospinning and Melt Electrowriting

AbstractIn vitro skin models are validated methods for screening cosmetics and pharmaceuticals, but still have limitations. The bilayer poly(ε‐caprolactone) scaffold/membrane model described here overcomes some of these deficits by integrating a solution electrospun (SES) membrane at the dermoepidermal interface and a melt electrowritten (MEW) scaffold that provides an optimal open‐pore environment for the dermis. To the knowledge, this scaffold/membrane model is the only one capable of creating a properly differentiated, full thickness skin model with neosynthesized extracellular matrix (ECM) in only 18 days. Both the wavy and straight fiber scaffold designs create a well‐organized dermis, but dermal collagen organization differs between designs. Adding cells and vitamin C to the scaffolds improves the mechanical properties to more closely mimic native human skin. These findings establish bicomponent scaffolds as a promising advancement for rapidly creating different skin models with varied properties. The versatility and adaptability of the described model can be used for studying how the biological and physical microenvironment impact skin, and testing dermo‐cosmetics and pharmaceutical treatments on different ages of skin. Furthermore, it can be an excellent new tool for studying wound healing and development into its use as a graft or wound dressing is ongoing.

Open loop flutter control of optimally oriented smart variable stiffness plates under hygrothermal environment

The present study investigates the impact of hygrothermal effects on the free vibration and flutter characteristics of a smart variable stiffness composite laminate (VSCL). This research seeks to underscore the inherent advantages of VSCLs in contrast to conventional straight fibre constant stiffness composite laminates (CSCLs). Utilizing curvilinear fibres, VSCLs offer a heightened level of customization, culminating in notably enhanced structural performance. The Genetic Algorithm is employed to obtain optimal fibre paths for the variable stiffness laminates. Introducing an active fibre composite layer as an actuator atop the optimally oriented VSCL laminate enhances its capabilities. A parametric inquiry into the influence of hygrothermal loading on the smart structure's free vibration and flutter traits is undertaken. While hygrothermal loading imparts vulnerability to the laminate, the introduction of voltage to the active fibre composite layer counteracts this weakening effect, effectively augmenting stiffness and concurrently enhancing the flutter parameters (velocity, frequency) intrinsic to the plate structure.

Straight fiber bundles with non-uniform porosity: Shell-side hydrodynamics and mass transfer in cross flow

This study explores fully developed shell-side hydrodynamics and mass transfer past straight fiber bundles with non-uniform porosity in cross-flow. Simplified geometries made up by checkerboard arrays of alternately high and low porosity regions are considered. Simulations are performed for two domain sizes: a small geometry (26 fibers) and a large geometry (104 fibers). In the small geometry, the Darcy friction coefficient (fT) exhibits hydraulic isotropy at low transverse flow Reynolds numbers (ReT) but becomes dependent on the flow attack angle (θ) at higher ReT. In the large geometry, this dependency is observed at lower ReT. A non-uniform porosity reduces fT at almost all ReT and θ in the small geometry, with the large geometry exhibiting a more complex behavior. Regarding mass transfer, up to ReT≈1-10 (depending on θ), a non-uniform porosity leads to lower Sherwood numbers compared to regular square arrays. However, at higher ReT, it enhances mass transfer.

Abrasion resistance of milling steel fibre-reinforced ultrahigh-performance concrete

Ultrahigh-performance concrete (UHPC) is susceptible to various forms of abrasion during its service life. This study is an investigation of the abrasion resistance of UHPC, focusing on two primary causes of wear: dynamic traffic loads and hydraulic impacts. To enhance the material's resistance to abrasion, milling steel fibres were utilised. For comparative purposes, straight steel fibres and hybrid milling–straight steel fibres were also employed. The protective function of the steel fibres primarily comes into effect once the concrete cover has experienced wear. When subjected to traffic and hydraulic loads, UHPC containing milling fibres exhibited superior resistance, compared with that containing straight fibres, while maintaining favourable workability. Notably, the UHPC incorporating hybrid steel fibres, which form a composite skeleton, owing to the presence of two fibre types, demonstrated even greater effectiveness in resisting external abrasion. Furthermore, the abrasion resistances observed under both traffic and hydraulic conditions displayed a positive linear correlation, with R2 > 0.8. These findings suggest the feasibility of evaluating the material's abrasion resistance under various wearing causes using a single test method. The outcomes of this study hold promise in advancing the development of UHPC and promoting its utilisation in conditions characterised by severe abrasion.

On characteristic behavior and flattened chromatic dispersion properties of bent photonic crystal fibers

Abstract In this paper by using modified scalar effective index method, first effective refractive index of straight and bent photonic crystal fibers are determined and then propagation parameters, such as chromatic dispersions for different structural designs of PCF, are obtained. By changing the values of affecting parameters in the bent PCF, such as different bent radius, distance between air holes Λ $\Lambda $ and air-filling factor d / Λ , $d/\Lambda ,$ the chromatic dispersion is determined in terms of propagating wavelengths. The obtained results of bent PCF are compared with the results of straight PCF. The results of the present paper might be useful in designing optical devices and sensing systems.

Experimental Study on the Effects of Straight and Ring-Type Steel Fibres on the Bond Behaviour of Steel Bars in Rubber-Recycled Aggregate Concrete

The application range of rubber-recycled aggregate concrete (RRAC), a new type of green building material, is currently limited due to performance defects, including low hardness, high water absorption, and poor adhesion. To expand its application in reinforced concrete structures, it is crucial to enhance the bonding performance between RRAC and steel bars. In this study, the effects of adding straight steel fibres (SSFs) and ring-type steel fibres (RSFs) to RRAC were investigated, in order to enhance the bonding performance. To investigate the impact of steel fibres (SFs) on the bonding properties of RRAC and steel bars, a total of 51 specimens were subjected to pull-out tests to systematically examine the impact of SSF and RSF dosages on the bonding performance. The results demonstrated that incorporating the optimal amount of SSFs and RSFs can significantly improve the bond strength and bond stiffness. Moreover, the combined use of SSFs and RSFs yielded even better enhancement effects. The RRAC exhibited remarkable performance, when the total content of SFs was 1.2% and the proportion of RSFs 75%. In this case, the bond strength and bond stiffness were enhanced by 3.7% and 53.88%, respectively. Finally, a bond–slip constitutive model for RRAC and steel bar was established. The combined use of SSFs and RSFs minimizes the limitations of poor mechanical properties in traditional RRAC and holds significant value for the widespread adoption and application of RRAC.

Simultaneous optimization of fiber paths and geometric dimensions for fiber composite laminates using double neural network-surrogate model and genetic algorithm

CFRP is characterized by its anisotropic properties. Therefore, further structural weight reduction might be achieved by introducing the fiber direction as a design variable. For this study, steering fiber laminates defined by a Bezier curve are applied to a skin panel of CFRP stiffened panels. Then, simultaneous optimization of the fiber paths and stringer dimensions is performed to minimize the panel weight. We propose a new surrogate model that combines two neural networks and Latin hypercube sampling. Stiffness, manufacturability, and buckling load are introduced as constraints. Also, optimization is performed using the surrogate model and a genetic algorithm (GA). Furthermore, the stringer dimensions and fiber directions are optimized for straight fiber laminates. Comparison of steering fiber laminates and straight fiber laminates demonstrated that the introduction of steering layup into skin plates can reduce the stringer weight by up to 25.6%. An effective method for designing the geometric dimensions and layup path is provided.

Mechanical properties of twisted galvanized iron fiber reinforced concrete with different contents and pitches

Utilizing galvanized iron (GI) instead of expensive steel fiber has become a new technique in concrete construction to improve the mechanical properties of concrete. Tensile strength tests confirm that twisted GI fibers could serve as a viable alternative to steel fibers. Using deformed fiber instead of straight fiber increases the strength parameters of concrete significantly. As such, twisted GI fibers were employed in this study to improve the quality of the concrete. The GI fibers were mechanically twisted with varying twisting pitches (4, 6, and 8 turns per inch) to create rope-like fibers. Thirteen different concrete mixtures were prepared using three different fiber contents (1.0%, 1.5%, and 2.0% by weight), maintaining a constant 25.4 mm fiber length. Compressive strength, split tensile strength, flexural strength, toughness indices, and residual strength of GI fiber reinforced concrete (GIFRC) were determined. Employing GI fibers increased the compressive strength to a range from 13.4% to 28.9%, the split tensile strength from 18.8% to 42.5%, and the flexural strength from 11.5% to 46.0% compared to the control specimen. Besides, twisted GI fiber increased compressive strength from 1% to 7%, split tensile strength from 2% to 11%, and flexural strength from 3% to 13% than those of plain GIFRC. Toughness indices and residual strengths were significantly higher for GIFRC beams compared to the control specimen, which indicated greater energy absorption capacity of GIFRC. Additionally, strength prediction models were established to estimate different strength parameters with varying twisting pitch of GIFRC. Experimental results resembled the proposed strength models. Therefore, using twisted GI fibers in concrete can be an excellent choice to improve the mechanical properties of concrete.

Methodological Aspects and Mesh Convergence in Numerical Analysis of Athermal Fiber Network Material Deformation

A balance between model complexity, accuracy, and computational cost is a central concern in numerical simulations. In particular, for stochastic fiber networks, the non-affine deformation of fibers, related non-linear geometric features due to large global deformation, and size effects can significantly affect the accuracy of the computer experiment outputs and increase the computational cost. In this work, we systematically investigate methodological aspects of fiber network simulations with a focus on the output accuracy and computational cost in models with cellular (Voronoi) and fibrous (Mikado) network architecture. We study both p and h-refinement of the discretizations in finite element solution procedure, with uniform and length-based adaptive h-refinement strategies. The analysis is conducted for linear elastic and viscoelastic constitutive behavior of the fibers, as well as for networks with initially straight and crimped fibers. With relative error as the determining criterion, we provide recommendations for mesh refinement, comment on the necessity of multiple realizations, and give an overview of associated computational cost that will serve as guidance toward minimizing the computational cost while maintaining a desired level of solution accuracy.

Using recycled plastic waste as fiber reinforcement on limestone residue mortar

The main purpose of the paper is to study the effect of the geometry of recycled plastic fiber on the performance of mortar basing on natural limestone residue. The used fibers were collected from plastic waste of polypropylene, resulting from domestic sweeps fabrication. Two types of recycled fibers were used, straight and crimped fibers, which have the same length (20 ± 2 mm) and the same diameter (0.45 ± 0.07 mm). Four dosages of fibers were considered, 0.5, 1, 1.5 and 2 wt. %. The obtained results show that the geometry of recycled plastic fibers has an important effect on the performances of limestone residue mortar. The addition of recycled fibers to mortar decreases its workability and the decrease is higher with crimped fibers. The results revealed that the limit dosage of recycled plastic fiber necessary to obtain a workable mortar is 1 % and 0.5 % for straight and crimped fibers, respectively. The benefit of recycled plastic fibers is well observed on the flexural and compressive behavior of limestone residue mortar, but the strength’s values are higher in straight fibers mortar (SFM) than that in crimped fibers mortar (CFM). The microstructure analysis confirms the good performances of the fiber mortar.

The significance of growth shells in development of symmetry, transparency, and refraction of the human lens.

Human visual function depends on the biological lens, a biconvex optical element formed by coordinated, synchronous generation of growth shells produced from ordered cells at the lens equator, the distal edge of the epithelium. Growth shells are comprised of straight (St) and S-shaped (SSh) lens fibers organized in highly symmetric, sinusoidal pattern which optimizes both the refractile, transparent structure and the unique microcirculation that regulates hydration and nutrition over the lifetime of an individual. The fiber cells are characterized by diversity in composition and age. All fiber cells remain interconnected in their growth shells throughout the life of the adult lens. As an optical element, cellular differentiation is constrained by the physical properties of light and its special development accounts for its characteristic symmetry, gradient of refractive index (GRIN), short range transparent order (SRO), and functional longevity. The complex sinusoidal structure is the basis for the lens microcirculation required for the establishment and maintenance of image formation.