Straight Fibers Research Articles

Mechanical model of stiffness coefficients prediction of curved fiber reinforced composites considering fiber distribution and aggregation

In this paper, a mechanical model is built to numerically predict the stiffness coefficients of curved fiber reinforced composites. Aiming to quantitatively describe the geometrical morphology of a curved fiber, a curve parameter and an orientation angle are both defined. For a composite with abundant curved fibers, distribution functions are introduced to describe the various curve parameters and angles. To quantitatively express the probability and degree of fiber aggregation, a probability function and an aggregating parameter are also proposed. Validation examples for composite with unidirectional straight fibers, orthogonal distributed straight fibers or unidirectional curve fibers are given to verify the correctness and accuracy of the current model as well as the numerical process. Numerical examples considering composites with ordered and disordered distributed fibers are carried out to show the predicted stiffness coefficients of typical curved fiber reinforced composites. Universality of the model is obvious through the numerical examples.

Maximisation of Bending and Membrane Frequencies of Vibration of Variable Stiffness Composite Laminated Plates by a Genetic Algorithm

PurposeIn comparison to traditional, constant stiffness laminates, variable stiffness composite laminates (VSCL) with curvilinear fibres represent an extra analysis effort. It is the purpose of this work to present and test a relatively simple optimisation procedure, in order to find the maximum fundamental frequency of vibration in bending and in in-plane vibrations. It is also intended to explain why certain fibre paths lead to higher frequencies.MethodsThe optimisation is performed using a genetic algorithm (GA), which is described in detail. The bending and the in-plane plate models are based on the p-version Finite Element Method. Each model requires a small number of degrees of freedom, an important feature because applying the GA involves the solution of a large number of eigenvalue problems. In order to support the physical interpretation of the optimal designs, mode shapes and stress fields corresponding to some optimal solutions are illustrated.ResultsSingle- and multi-layer plates with different boundary conditions and fibre path types are studied. Fibre paths that lead to maximum fundamental frequencies are found and justified. The consequences that maximising the first frequency has on the higher-order modes of vibration are studied.ConclusionThe proposed optimisation and modelling methods are effective. Curvilinear fibres with the characteristics considered led to the maximum first natural frequency of vibration in a few cases, but not all. Particularly in in-plane vibrations, curvilinear fibres can provide major gains in comparison to straight fibres. The increase in the vibration frequency is accompanied by, overall, larger stresses.

Study on the Damage Characteristic of Ununiform Corroded SFRC by 3D Mesoscale Numerical Simulation

Steel fiber reinforced concrete (SFRC) will appear ununiform corrosion under chloride environment, resulting in corrosion-induced crack. However, the mechanism of corrosion-induced crack of ununiform corroded SFRC is not clear. In this paper, the 3D mesoscale numerical model of SFRC structure is established, the generation algorithm of round straight steel fiber is provided, and the corrosion-induced crack are simulated by XFEM, at the end the damage characteristic of ununiform corroded SFRC are studied. The result shows with the increase of rebar corrosion area, the number of corrosion-induced cracks increase gradually. The width of each corrosion-induced crack decreases linearly with the thickness of the protective layer, and the width of the penetrate crack decrease to 0.08 mm~1.2 mm.

Straight recycled green fibre pull-out behaviour in an ultrahigh performance concrete composite matrix UHPC

This article presents the study of the pull-out method and the behavior of the cementitious matrix under loading. Using finite element analysis to investigate the interfacial debonding performance allows us to grasp the experiment’s estimated values. The mechanical bonding is determined using a Scanning Electron Microscopy SEM image. The slippage during the pull-out load varies depending on the cementitious matrix grade and whether the recycled steel strand is hooked at specific angles (Inclination angle). The relationship between monotonic loading and steel fiber diameter was found to be a direct proportion. To comprehend the bonding and debonding between surfaces, as well as the shear experience under loading, both studies find the correlation between theoretical and experimental results to be satisfactory. All aspects were discussed in relation to the effective use of a finite element method in analysis.

Hydrodynamics and mass transfer in straight fiber bundles with non-uniform porosity

The present study investigates the effects of non-uniformity in a bundle’s porosity by considering a model channel made up of “dense” (low porosity) and “loose” (high porosity) regions. In a first, simplified, approach these regions are treated as non-interacting porous media and previously obtained computational results are used for the Darcy permeability and the Sherwood number. In a second, and more complete, approach 3-D CFD simulations are conducted for a checkerboard arrangement of alternately “dense” and “loose” regions with square-arrayed fibers, accounting for entry effects and for interactions between regions. Non-uniformity causes a significant increase of the permeability and a strong reduction of the Sherwood number. These effects are larger, approaching those obtained for non-interacting regions, if the regions’ length scale is large. The attainment of fully developed conditions is greatly shifted forward in non-uniform bundles and the mass transfer development length may largely exceed the physical length of most hollow-fiber devices.

Experimental tensile tests on carbon fibre cords with bond-type anchorages

Despite the potential interest for civil engineering structural applications, few studies have explored the feasibility of employing carbon fibre cords as prestressed elements in strengthening systems. This research presents a large experimental campaign to investigate the tensile behaviour of straight carbon fibre cords connected to a bond-type anchorage. Specifically, 78 tensile tests have been performed varying several parameters: anchorage geometry, resin type, cord cross sectional area, and fibre free-length and treatment (unimpregnated or impregnated with resin). The results shed light on their role on the structural response, and highlight the existence of size effects regarding fibre free-length and cross sectional area of the cord. These phenomena are magnified in unimpregnated specimens, and, de facto, may prevent their use in full-scale post-tensioned applications.

Experimental Investigation of Compound Effect of Flexural and Torsion on Fiber-Reinforced Concrete Beams

Fiber-reinforced concrete is widely acknowledged for its ability to resist cracking effectively and limit its propagation. By preventing cracks from spreading, the addition of fiber composites to concrete can enhance its extensibility and tensile strength, not only at the initial point of cracking but also at its maximum capacity. Additionally, the fibers in fiber-reinforced concrete are capable of binding the matrix, even when exposed to significant cracking. However, there is limited information available about the behavior of fiber-reinforced concrete under a bending moment combined with torsion. This study aims to investigate the structural behavior of fiber-reinforced concrete members subjected to a bending moment with a torsion to moment ratio equal to 1. Synthetic and steel fibers of 1.0% content with different lengths (19, 35, and 55 mm for synthetic fiber and 13 mm for straight and hook steel fibers) were mixed with concrete mixtures to examine the effects of fiber lengths and types on the concrete beam performance. Test results indicated that the fiber-reinforced concrete beams showed higher cracking moments than the normal-strength concrete beam. The steel fiber with a hooked configuration reinforced beam showed increased moment capacity and total torsional toughness higher than that of the straight steel fiber-reinforced beam. The synthetic fiber of a 55 mm length reinforced beam exhibited the highest first-crack and ultimate moment values among other tested beams. The test results were compared with past research models for the moment capacity of beams under the compound effect of bending and torsion and we modified these values with another factor that represented the fiber length influence on beam capacity, as suggested in past research. The comparison between the ultimate moment of the test results and the moment predicted from the modified past research model presented a good correlation.

Numerical Study of the Shear Behavior of Ultra-High-Performance Concrete Beams


 
 
 In the last decades, experimental and numerical studies on steel fiber-reinforced concrete have shown that providing suitable fiber content and distribution in the matrix can improve the post-cracking strength of concrete. Although there is a large database of experimental and numerical shear tests of steel fiber-reinforced concrete beams, there are not profuse test data and numerical models available for steel fiber-reinforced concrete beams with traditional transverse shear reinforcement (stirrups). In this work, the shear behavior of ultra-high-performance fiber-reinforced concrete beams is analyzed using the plastic damaged model developed in Abaqus. For this purpose, a comparative study is previously carried out by means of an experimental test available in the literature to validate the finite element model with conventional rebars. Then, the shear behavior of different ultra-high-performance concretes without fiber reinforcement, with the addition of 13 mm steel straight fibers, with 30 mm steel hooked-end fibers, and a mixture in 50% of 13 and 30 mm steel fibers are analyzed.
 
 

Efficient removal of methylene blue from aqueous solution by ZIF-8-decorated helicoidal electrospun polymer strips

Immobilization of metal-organic frameworks (MOFs) on electrospun products for wastewater treatment has garnered considerable attention in recent years. However, the effect of the overall geometry and surface-area-to-volume ratio of MOF-decorated electrospun architectures on their performances have rarely been investigated. Herein, we prepared polycaprolactone (PCL)/polyvinylpyrrolidone (PVP) strips with helicoidal geometries via immersion electrospinning. By regulating the weight ratio of PCL to PVP, the morphologies and surface-area-to-volume ratios of the PCL/PVP strips could be controlled precisely. Then, the zeolitic imidazolate framework-8 (ZIF-8) for removing methylene blue (MB) from an aqueous solution was immobilized on the electrospun strips, resulting in ZIF-8-decorated PCL/PVP strips. The key characteristics of these composite products, such as adsorption and photocatalytic degradation behavior toward MB in the aqueous solution, were carefully investigated. Owing to the desired overall geometry and high surface-area-to-volume ratio of the ZIF-8-decorated helicoidal strips, a high MB adsorption capacity of 151.6 mg g−1 was obtained, which is significantly higher than those with conventional electrospun straight fibers. In addition, higher MB uptake rates, higher recycling and kinetic adsorption efficiencies, higher MB photocatalytic degradation efficiencies, and faster MB photocatalytic degradation rates were confirmed. This work provides new insights to improve the performance of existing and potential electrospun product-based water treatment strategies.

Behavior and constitutive model of ultra-high-performance concrete under monotonic and cyclic tensile loading

Ultra-high-performance concrete (UHPC) holds great promise for constructing lightweight and high-performance concrete structures. Hence, the proportion of live load increases, in turn, leads to a higher live-to-dead load ratio. UHPC structures suffer from cyclic stress amplitude in higher possibility. Therefore, the behavior and constitutive model of UHPC under cyclic tensile loading is of significance for the understanding of bearing capacity and deformation property for structures subjected to cyclic loading, which, nevertheless, is seldomly reported. In this regard, the present study conducted direct tensile tests on 35 UHPC dog-bones with four steel fiber volume fractions (i.e., 0%, 1%, 2%, and 3%) and two fiber shapes (i.e., straight and hooked-end). A constitutive model for UHPC under tensile loading was proposed, implemented into OpenSees, and employed in numerical simulations of UHPC beams subjected to bending in cyclic loading. The numerical results were compared with test results on UHPC beams for model verification. The experimental and numerical results show that the UHPC with straight fiber volume fractions less than 1% demonstrated a brittle failure, whereas the UHPC with straight fiber volume fractions higher than 1% or with a hooked-end fiber volume fraction of 2% exhibited a ductile failure. The increase in fiber volume fraction resulted in great enhancements of the initial crack and peak stresses, and the peak and ultimate strains, and the energy absorption capacity. Besides, the use of hooded-end fibers also led to a slight improvement in tensile strain behavior of UHPC but negatively affected the initial crack stress and peak stress. It also provided sufficient bonding between fiber and matrix. The envelope curves and failure patterns for UHPC under monotonic and cyclic loading are close. The proposed constitutive model for UHPC under tensile loading is composed of an envelope curve that is assumed bi-linear for strain softening UHPC or tri-linear for strain hardening UHPC, an unloading curve and a reloading curve described by an exponential function, and a damage index defined as the reduction of unloading modulus. The proposed constitutive model for UHPC under tensile loading can provide acceptable results for the prediction of the bearing capacity and deformation property of UHPC beams without reinforcements subjected to bending in cyclic loading.

Effectiveness and response of replacing web reinforcements with steel fibers reinforced in shear for non-stirrup UHPC beams

This paper reports the shear behavior of non-stirrup ultra-high performance concrete (UHPC) beams to fully use the high strengths of UHPC. A total of nine simply-supported beams were entailed based on steel fiber contents (0%, 1%, 2%, and 3%), equivalent stirrup ratios (0.6%, 0.8%, and 1.1%), and shear span-to-depth ratios (1.0, 2.0 and 3.0). Test results indicate that the failure loads of specimens using steel fibers achieved about 1.5, 2.5, and 3.75 times the specimens with equivalent stirrups. Also, the shear cracking loads increased by 100%, 200%, and 250%; meanwhile 20% higher global stiffness was found relative to the specimens using stirrups. Note that the longitudinal crack along the tensile reinforcements at the shear span-to-depth ratio of 1.0 led to the anchorage failure whereby the used straight steel fibers and reduced interlock and/or friction along the shear crack enabled greater fiber-composite strain hardening. Additionally, replacing stirrups with steel fibers could decrease the maximum crack width from 0.04 to 0.01 mm despite carrying twice the cracking load. These findings demonstrated that substituting steel fibers for stirrups could improve the structural both service and ultimate performance. In closing, too-conservative predictions from the current codes warranted a rational theoretical method.

Bond performance of reinforcing bars in SFRC: Experiments and meso-mechanical model

The bond performance of reinforcing bars in steel fiber-reinforced concrete (SFRC) remains a topic of discussion in the community. The effect of deformed steel fiber types is not fully understood, and a rational mechanics-based model is required to consider this behavior. This study experimentally investigated the bond performance of steel rebars in SFRC containing milled-cut (M) fibers with proven high bridging capacity, namely MCSFRC. The results indicated that M fibers yielded a higher bond strength of rebars compared to hook-end (H), crimped (C), and straight (S) fibers from previous studies. This was attributed to the superior bond resistance of M fibers in the matrix, provided by the rough inner surface, stiff end hook, and longitudinal twist. A meso-mechanical model (rib and fiber scale) was then developed to effectively assess the bond strength of rebars in SFRC, accounting for rib-concrete interaction, as well as the fiber reinforcement differences including fiber–matrix interaction, fiber spatial distribution, content, and dimension. This model was applicable to rebars in SFRC with H, C, S, and M fibers, and the results showed good agreement with 301 tests in the established database. On that basis, a unified local bond-slip model for rebars in SFRC was proposed, which was able to suitably reproduce the entire bond-slip response under pull-out and splitting failures.

120 Determining moisture content in equine arena footing on-farm

Arenas are important fixtures on equine farms as they provide constant surfaces for horses to work and train on. Water serves to help control dust issues and increase the shear strength of the footing. Some footing companies indicate an optimal moisture content for their product, but without a method to determine the moisture content, arena managers and owners rely on dust production to decide when to add more water, which is an unreliable method. Oven drying of soil/arena footing is a common method for determining moisture content in the research settings but is not a practical solution on farms. This study sought to compare 3 different methods for determining moisture content in arena footing: oven drying, microwave drying, and a FieldScout TDR 350 Soil Moisture Meter. The 3 methods were tested with 3 footing types: a straight sand footing, a sand and fiber mixture, and a sand with organic material mixture. The oven drying method consisted of drying 3 samples of at least 30 g in a 100C oven for 24hrs, the microwave method also used 3 samples of at least 30 g that were dried in a standard microwave oven until all water evaporated, and the TDR moisture content method utilized the average of 3 TDR measurements in the footing. Paired t-tests were used to compare the microwave and the TDR methods to the oven drying method for each footing type. Though the paired t-test analysis for the microwave drying method determined statistically significant differences for the sand with fiber (P < 0.001)and the sand (P < 0.001), nominally the difference in the moisture contents of the 3 footings are unlikely to have an impact in on-farm use as all were within 0.6% of the oven-dried moisture contents. In comparison, all of the paired t-tests determined statistically significant difference for the TDR method (sand with organic material P < 0.001, sand with fiber P < 0.001, and sand P = 0.003). The TDR determined moisture contents were at least 1.6% higher than the moisture contents determined with the oven drying method. Overall, the microwave drying method provides a viable on-farm solution for determining the moisture content of footing, provided that the footing material is microwave safe.

Downtaper on Multimode Fibers towards Sustainable Power over Fiber Systems

This paper presents a transition taper for coupling light between optical fibers with different geometries and refractive index profiles used in Power over Fiber (PoF) systems. Global energy efficiency and costs are critical parameters when delivering high power to remote areas. High-power lasers have maximum coupling for large core fibers, while widespread multimode optical (OM1) fibers used in optical communications are cheaper. We study the optical losses between large core fibers (200 µm) and OM1 fibers (62.5 µm) theoretically and experimentally. We demonstrate that improvements of 2 dB can be obtained by adding the new tapered structure to the system, compared to the direct splice between both fibers. There is good agreement between measured and calculated loss values using a new Gaussian loss model to describe splices between tapered and straight fibers. The fabrication of the transition taper is also described. We also measure the numerical aperture (NA) changes in the downtaper zone and demonstrate that the lower the NA of the input light, the higher the efficiency improvement.

Optimization design of variable stiffness composite cylinders based on non-uniform rational B-spline curve/surface

Compared with a constant stiffness (CS) composite structure of traditional straight fiber path, a variable stiffness (VS) composite structure of curvilinear fiber path has a broader design space. Taking the performance of a CS cylinder as the baseline, two curved fiber formats of VS cylinders are investigated. One is that the fiber angle varies in circumferential direction (i.e., circumferential stiffness variation, VS-C), the other is that the fiber angle varies in both circumferential and axial directions (i.e., circumferential and axial stiffness variation,VS-CA). Non-uniform rational B-spline curve/surface is used to define the continuously varying fiber orientation angle, making the VS design come true. This paper focuses on the maximum buckling capacity of VS composite cylinders under two kinds of loading cases (pure bending moment at both ends, concentrated force at the middle of the axis), and the optimal fiber angles of VS-C and VS-CA cylinders are obtained. In order to improve the computational efficiency, the adaptive Kriging surrogate model is integrated with genetic algorithm to solve the above optimization problems. The results show that the anti-buckling performance of VS-CA structure is always better or close to VS-C structure under different loading conditions, and all are better than that of CS structure.

Axial impact behaviors of UHPC: The roles of nanomaterials and steel fibres

With the gradual maturity of nanotechnology, many nanomaterials have been used to modify ultra-high performance concrete (UHPC) to improve its performance. In the course of use, concrete structures will suffer from various forms of dynamic impact loads, resulting in serious damage. At present, the research on the dynamic properties of nanomaterials modified UHPC is still lacking. This study presents an experimental study on the axial impact behaviors of nanomaterials modified UHPC by Split Hopkinson Pressure Bar (SHPB). The effects of nanomaterials and steel fibres on failure patterns, dynamic compressive strengths, impact toughness, dynamic compression constitutive relationship and dynamic increase factor (DIF) of UHPC under different strain rates were analyzed and discussed. The results show that UHPC is strain rate sensitive. Steel fibre improves the dynamic compressive strength and impact toughness of UHPC, and reduces the strain rate sensitivity of UHPC. The effect of hook-end steel fibre on the impact performance of UHPC is generally better than that of straight steel fibre. Proper addition of nanomaterials can improve the axial compression impact properties of UHPC, but excessive nanomaterials will adversely affect the impact performance of UHPC. Under strain rate of 160 s−1, the dynamic compressive strength and impact toughness of UHPC were improved by 10.05 % and 5.70 % respectively by adding 2 % nano-CaCO3. Based on the experimental results, a recalibrated DIF model considering the coupling effect of nanomaterials and steel fibres is proposed for the UHPC, and it predicted the test results of the modified UHPC reasonably well.

Amplitude-frequency response of a helically-wound fiber distributed acoustic sensor (DAS)

The goals of this study were to analyze the capabilities of DAS (distributed sensors) in resolving mining problems, compare them with existing seismoacoustic data collection systems, and prepare the basis for conducting seismoacoustic studies with recording by a fiber optic distributed system. This paper considers the capabilities of recording seismoacoustic responses using fiber optic distributed acoustic systems (DAS). Based on physical and geometrical analysis, the amplitude-frequency responses (characteristics) of recorded longitudinal waves for straight and helically-wound fibers were obtained. In the case of helically-wound fiber, the frequency response depends on several key factors: integrating the measured value along the fiber based on the measurement; the angle of incidence on the cable; and the winding angle of the fiber in the cable. An increase in the winding angle increases the uniformity of the amplitude-frequency characteristics of longitudinal waves both in terms of frequencies and angles of incidence. At the same time, helical winding changes the effective response spacing (gauge length). This makes it possible, by summing the responses of the straight and helically-wound fibers due to the overlap of the spectra, to record frequencies that are suppressed in case of separate recording. Based on the study results, a cable design was proposed to record broadband seismoacoustic responses enabling a wide range of mining and engineering problems to be resolved, and for seismic surveys both in wells and on the surface to be carried out.

Amplitude-frequency response of a helically-wound fiber distributed acoustic sensor (DAS)

The goals of this study were to analyze the capabilities of DAS (distributed sensors) in resolving mining problems, compare them with existing seismoacoustic data collection systems, and prepare the basis for conducting seismoacoustic studies with recording by a fiber optic distributed system. This paper considers the capabilities of recording seismoacoustic responses using fiber optic distributed acoustic systems (DAS). Based on physical and geometrical analysis, the amplitude-frequency responses (characteristics) of recorded longitudinal waves for straight and helically-wound fibers were obtained. In the case of helically-wound fiber, the frequency response depends on several key factors: integrating the measured value along the fiber based on the measurement; the angle of incidence on the cable; and the winding angle of the fiber in the cable. An increase in the winding angle increases the uniformity of the amplitude-frequency characteristics of longitudinal waves both in terms of frequencies and angles of incidence. At the same time, helical winding changes the effective response spacing (gauge length). This makes it possible, by summing the responses of the straight and helically-wound fibers due to the overlap of the spectra, to record frequencies that are suppressed in case of separate recording. Based on the study results, a cable design was proposed to record broadband seismoacoustic responses enabling a wide range of mining and engineering problems to be resolved, and for seismic surveys both in wells and on the surface to be carried out.

Three-dimensional fine structures in deep fascia revealed by combined use of cryo-fixed histochemistry and low-vacuum scanning microscopy

Recent physiological studies have shown that the deep fascia has received much attention concerning clinical medicine; however, histological examination of the deep fascia has not been well established. In this study, we aimed to clarify and visualize the structure of the deep fascia by taking advantage of cryofixation techniques and low-vacuum scanning electron microscopy. As a result, the ultrastructural observations revealed three-dimensional stratification of the deep fascia composed of three layers: the first superficial layer consisting of collagen fibers extending in various directions with blood vessels and peripheral nerves; the second intermediate layer formed by single straight and thick collagen fibers with flexibility; and the third deepest layer, consisting of relatively straight and thin collagen fibers. We explored the use of two hooks to hold a piece of deep fascia in place through the course of cryo-fixation. A comparative observation with or without the hook-holding procedure would indicate the morphological adaptation to physiological stretch and contraction of the deep fascia. The present morphological approach paves the way to visualize three-dimensional ultrastructures for future biomedical studies including clinical pathophysiology.

Morphing characteristics and damage analysis of 3D printing variable stiffness bistable laminates based on continuous fiber thermosetting composites

The morphing characteristics and damage analysis of variable stiffness bistable laminate fabricated by continuous fiber 3D printing technology are systematically studied. Conventionally, bistable structures used in morphing applications are achieved with straight fibers. With the application of fiber placement technology, it is now possible to prepare variable stiffness laminates with different directions and layup angles of fibers. Moreover, the structure will be damaged with the increase in deformation times. How to effectively suppress the failure of laminates is also a highlight for this composite structure. In this paper, three curvilinear fiber paths are designed and compared. And a semi-analytical model based on the Rayleigh-Ritz method is used to predict the curvature of stable configuration. In particular, continuous fiber thermosetting resin matrix composites 3D printing technology is proposed for preparing variable stiffness laminates, which has several advantages compared to other traditional preparation methods of variable stiffness laminates. The corresponding finite element model is also developed to investigate the bistable behavior and damage analysis. In addition, the influence of different angle parameters and fiber paths on the stable configuration and the snap-load are also discussed. Finally, the damage evolution and mechanical properties of straight-fiber laminates and variable stiffness laminates in tension and compression are carried out based on the Hashin failure criteria.