Fiber Composite Structures Research Articles

3D nanoprinted kinoform spiral zone plates on fiber facets for high-efficiency focused vortex beam generation.

In this paper, we propose and demonstrate an all-fiber high-efficiency focused vortex beam generator. The generator is fabricated by integrating a kinoform spiral zone plate (KSZP) on the top of the composite fiber structure using fs-laser two-photon polymerization 3D nanoprinting. The KSZP with spiral continuous-surface relief feature is designed by superimposing a spiral phase into a kinoform lens, which can efficiently concentrate and transform an all incident beam to a single-focus vortex beam, without the undesired zero-order diffracted light and extra high-order focus. Under arbitrary polarized light incident conditions, experiment results show that the focusing efficiency and vortex purity of the all-fiber generators are over 60% and 86%, respectively, which is much higher than that of a traditional binary SZP integrated on an optical fiber facet. In addition, characteristics of the generated vortex beam, such as focal spot, focal length and vortex topological charge are numerically designed and experimentally investigated. The experimental results agree well with the numerical simulation model using the FDTD algorithm. Due to the compact size, flexible design, polarization insensitivity, high focusing efficiency and high vortex purity, the proposed all-fiber photonic devices have promising potential in optical communication, particle manipulation and quantum computation applications.

Super-Variable Focusing Vortex Beam Generators Based on Spiral Zone Plate Etched on Optical Fiber Facet

In this article, an all-fiber super-variable focusing vortex beam generator is proposed and demonstrated, the focal point of which can be drastically relocated by varying the wavelength of the incident light. The all-fiber generator is fabricated by etching a spiral zone plate (SZP) on the top of the composite fiber structure composed of a single mode fiber and a quarter pitch graded index fiber using focused ion beam lithography. Numerical simulation and experimental measurements have been applied in investigation of all-fiber output light field characteristics, such as the focal spot, focal length, and vortex topological charges. Results show that these parameters can be controlled by flexibly adjusting the design parameters of SZP microstructure. In particular, the position of the donut-shaped focus spot can be dynamically tuned in a wide range by varying the incident laser wavelength with the focal spot profile remains constant. The all-fiber generator can be potentially applied in particle manipulation, high capacity communication, and fiber optic endoscopic imaging, all of which require ultra-compact, multi-dimension, and flexible focusing schemes.

Surface Treatments Effect on Carbon Fiber Composite-Different Alloy Adhesion Performance

Carbon fiber reinforced composites have a wide range of uses, especially in aviation and aerospace, marine and automotive. The adhesion properties of these high-tech materials with other materials are critical. Adhesive selection, surface treatment type and surface preparation procedures control adhesion performance. In this study, the effect of surface treatments that increase adhesion strength in carbon fiber composite (CFRP) structures was investigated. In order to improve the adhesion properties of carbon fiber composite materials with different metals, mechanical and physical surface treatment techniques have been used. 7075 aluminum alloy (Al) and 304 stainless steel alloy (SS) were subjected to sandblasting and plasma activation processes after surface cleaning in experimental studies. After surface activation processes, the surface wetting angle was measured and adhesion tests were carried out. In experimental results, it has been observed that plasma and sandblasting processes increase adhesion strength by 30-50%.

Experimental and Numerical Buckling Analysis of Carbon Fiber Composite Lattice Conical Structure before and after Lateral Impact

In this research, the numerical and experimental analysis of the carbon fiber composite lattice conical structure has been performed to assess the buckling stability of the structure before and after the lateral impact. In the experimental analysis, the carbon fiber composite lattice conical structure was constructed with the winding method and using elastic molds and metal mandrel. In order to investigate the buckling stability of the structures before each lateral impact, they are subjected to be compressive-axial loading. The rest of the structures first subjected under the axial-compressive loading, then in the next step, a compressive loading is applied to determine the effect of the impact on the compressive strength of the damaged structures. In the numerical analysis, the Abaqus software is used to modeling and performing the mentioned analysis. Finally, the comparison of the results shows that the effect of the lateral impact causes how many reductions will be occurred in the buckling strength. So, it should be considered during the design of the applied structures. On the other hand, the low difference between the numerical and experimental simulations shows that the experimental and numerical methods can be used to analyze the structures with different geometric characteristics and material.

Ply-drop design of non-conventional laminated composites using Bayesian optimization

Automated Fiber Placement (AFP) technology enables the efficient production of large carbon fiber reinforced composite structures with complex surfaces. AFP has a wide range of tow placement angles, and the users can design layup angles so that they can tailor the performance of the structure. However, despite the design freedom, the industry generally adopts a layering of 0°, 90°, and ±45°ply-drop angles. Here, we demonstrate the optimization of ply-drop angles of non-conventional composites. Specifically, we use classical laminate theory and Bayesian optimization to achieve better layup angles in terms of stiffness, Tsai–Wu failure criteria, and manufacturing time. Our approach shows its effectiveness in designing carbon fiber composite structures using unconventional angles in their mechanical properties and production efficiency. Our method has the potential to be used for more complex scenarios, such as the production of curved surfaces and the utilization of finite element analysis.

Progressive damage and failure modeling in composite cylindrical pyramidal lattice structure

In this paper, the mechanical behavior of a carbon fiber composite cylindrical pyramidal lattice structure has been predicted based on initial failure criteria and progressive damage under compressive loading. For this purpose, the three-dimensional Hashin failure criteria with instantaneous and gradual unloading models have been employed by the user subroutine UMAT in ABAQUS/Standard. In the instantaneous and gradual unloading models, progressive damage has been controlled by binary and exponential damage functions, respectively. Besides, to validate finite element models, the results have been compared with the experimental tests. Therefore, a new mold has been designed and manufactured for the experimental test of composite cylindrical pyramidal lattice structures. The new mold allows the use of the maximum inherent strength of the fiber-reinforced composite. The predicted force–displacement curves are in good agreement with the experimental test results. Hence, it is possible to use these FE models in the design of ultra-lightweight structures.

Development of a flame spraying coating–based fiber composite structure: A thermo-mechanical finite element study

The optical fiber smart composite structures have been widely applied for the structural health monitoring, and the packaging technique of integrating optical fiber sensor with host structure is one of the key issues. The flame spraying coating provides strong adhesive strength with good heat resistance, which is particularly suitable for the packaging applications in harsh environments. However, the elaboration process of flame spraying coating–based fiber composite structure faces great challenges due to the flame spraying mechanisms. This study evaluates numerically an overall effect of flame spraying coating formation process on the structural and the optical properties of the embedded fiber optic based on a three-dimensional finite element model. First, the lumped capacitance method is used; both the average heat flux density in the whole spraying process and the specific heat flux density of each torch sweep are estimated to initialize the thermo-mechanical modeling. Then, the stress distributions in both radial and axial directions of the embedded fiber are discussed separately. Next, the variation of refractive index of the embedded fiber optic due to the residual strain is also investigated. Finally, the elaboration parameters including torch displacement and velocity are evaluated and optimized. The simulation results show that the embedded fiber optic maintains good structural and optical properties with the presented elaboration conditions, and therefore its transmission and sensing performance can be ensured.

A 2-D Radon Transformation for Enhancing the Detection and Imaging of Embedded Defects in Layered Composite Structures Using Millimeter-Wave System

This paper aims to tackle the challenge of detecting the presence of embedded defects in layered composite structures using imaging techniques including a 2D Radon transformation. The proposed technique aims at enhancing the detection and imaging of embedded defects in layered composite structures that is captured using a millimeterwave (MMW) radar system. A 94 GHz MMW system is used in the near field to detect defects such as disbond and delamination embedded in complex glass fiber composite structures. In order to simplify the detection in glass fibers, measurement data attained using a MMW radar are plotted as images using MATLAB. A stable detection and identification of these defects from the collected images is proposed using a robust two-stage algorithm. The Weiner filter-based deconvolution technique is used for the reflectivity deconstruction in the image and a two-dimensional Radon transformation called back-projection is used to as an additional filtering step enhance the detection of the embedded defects. The proposed method allows defects that are embedded 24mm below the surface of the scanning probe to be detected and identified in terms of location. Our results show potential in the proposed method to be employed in accurately imaging defects in composites that are used in the aerospace and civil infrastructure industries.

Comparison of various uncertainty models with experimental investigations regarding the failure of plates with holes

Predicting ultimate limit states and failure mechanisms in real technical systems is essential. This task is a real challenge because of a variety of uncertainties. The result often depends very much on the way these uncertainties have been described. This contribution is a study of how the uncertainty models can affect such predictions and how well a prediction matches the behavior of a real system. Three uncertainty models are compared to a series of experiments on Plexiglas® plates with holes under uniaxial tension regarding the failure mechanism and the associated ultimate load. A plate with holes can represent many technical applications, such as the behavior of adhesive bonds in fiber composite structures with air voids. A stochastic model, a model based on fuzzy-set theory and a polymorphic uncertainty model are applied to point out the individual usefulness and the informative value of the resulting numerical predictions. The comparison shows that the polymorphic uncertainty model is more costly but simultaneously contains both information of the monomorphic uncertainty models. In order to overcome the computational costly uncertainty propagations, a surrogate model based on Artificial Neural Networks (ANN) is constructed independently of the uncertainty model.

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications.

Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Design of the hybrid FRP/concrete structures for bridge constructions

The current paper deals with the analysis of the hybrid FRP/concrete structures for bridge constructions. The glass fiber composite structure connected with the reinforced concrete was analyzed numerically. The detailed analysis of the material properties was conducted and then used in the design process of the final construction. The different loading conditions were investigated taking into account nonlinear concrete material model. The preliminary parametric optimization was applied including the different distance between bridge supports and different support shapes. Besides, the influence of two different effects of the concrete shrinkage on the strength properties of the hybrid structure was verified.

Design and Test of a Student Hybrid Rocket Engine with an External Carbon Fiber Composite Structure

The development of hybrid rockets offers excellent opportunities for the practical education of students at universities due to the high safety and relatively low complexity of the rocket propulsion system. During the German educational program Studentische Experimental-Raketen (STERN), students of the Technische Universität Braunschweig obtain the possibility to design and launch a sounding rocket with a hybrid engine. The design of the engine HYDRA 4X (HYbridDemonstrations-RaketenAntrieb) is presented, and the results of the first engine tests are discussed. The results for measured regression rates are compared to the results from the literature. Furthermore, the impact of the lightweight casing material carbon fiber-reinforced plastic (CFRP) on the hybrid engine mass and flight apogee altitude is examined for rockets with different total impulse classes (10 to 50 kNs). It is shown that the benefit of a lightweight casing material on engine mass decreases with an increasing total impulse. However, a higher gain on apogee altitude, especially for bigger rockets with a comparable high total impulse, is shown.

Piezoelectric energy harvesting using macro fiber composite patches

Over the last decade, vibration energy harvesting has received substantial attention of many researchers. Piezoelectric materials are able to capture energy from ambient vibration and convert it into electricity which can be stored in batteries or utilized to power small electronic devices. In order to benefit from the 33-mode of the piezoelectric effect, interdigitated electrodes have been utilized in the design of macro fiber composites which are made of piezoelectric fibers of square cross sections embedded into an epoxy matrix material. This paper presents an analytical model of a macro fiber composite bimorph energy harvester using the 33-mode. The mixing rule is applied to determine the equivalent and homogenized properties of the macro fiber composite structures. The electromechanical properties of a representative volume element composed of piezoelectric fibers and an epoxy matrix between two successive interdigitated electrodes are coupled with the overall electro-elastodynamics of the harvester utilizing the Euler–Bernoulli theory. Macro fiber composite bimorph cantilevers with diverse widths are simulated for power generation when a resistive shunt loading is applied. Stress components in the Kapton layers, which are typically a part of any macro fiber composite patch, and in the bonding layers have been included in the model contrary to previously published studies. Variable tip mass, attached at the free end of the beam, is utilized in this paper to tune the resonance frequency of the harvester. The generated power at the fundamental short circuit and open circuit resonance frequencies of harvesters having three different widths is analyzed. It has been observed that higher electrical outputs are produced by the wider macro fiber composite bimorph using (M8528-P1 patches).

Manufacturing of Hybrid Yarn Thermoplastic Composites by the Method of Filament Winding

Filament winding is a manufacturing method to produce composite materials with a thermosetting or thermoplastic matrix impregnated continuous fibers. Due to the high melt viscosity of thermoplastics, some problems such as inadequate fiber dispersion in the structure, low wetting ability, and interface quality problems between matrix and fiber might emerge. Preforms can be used in order to solve these problems in the continuous fiber reinforced composite manufacturing; division of the polymer can be made using either powder or fiber form. In this study, polyethylene/E-glass fiber and polypropylene/E-glass fiber hybrid yarns were used as materials to produce thermoplastic composite structures. Firstly, plate samples were produced at various temperatures, periods of time and different thicknesses of ply. After the preparation of samples tensile test, 3 point bending flexural test, and calcination test were applied and Scanning Electron Microscopy (SEM) observations were also performed to these samples, and then the production parameters were optimized. After that, cylindrical shaped samples were produced by a laboratory-type manual filament winding device and ring stiffness tests were performed. According to the test results of the plate samples, the optimum production conditions were determined as 200 °C for 5 minutes for polyethylene/E-glass fiber composite structure and 220 °C for 5 minutes for polypropylene/E-glass fiber composite structure. Mechanical test results of plate samples revealed that polypropylene composites presented slightly better results than polyethylene ones. Additionally, in the cylindrical specimens, close results to the ring stiffness values determined by the standards were obtained.

Trial Manufacturing of Jelly-Rolled Nb/Al Monofilamentary Wire with Very Small Diameter below 50 microns

Jelly-rolled Nb/Al composite monofilamentary wires having an outer diameter of 50 microns and more than 100 meters in length were successfully fabricated. Moreover, some of these thin wires were additional drawn to 30 microns in outer diameter in this study. We recognized again that jelly-rolled Nb/Al composite monofilamentary wires have excellent cold workability and drawability. The transmission electron microscopic observation revealed that the niobium and aluminum laminations retained a nano-scaled fiber composite structure in the longitudinal direction like the microarchitecture of Japanese bamboo, even in the very thin wire with an outer diameter of 30 μm. The thickness of the aluminum sheet is approximately 70 nm, which is almost comparable to the value calculated from the reduction ratio. The critical temperature of 16.2 K (on set) and 15.7 K (off set) were obtained after the diffusion reaction at 850°C for 10 h. The transport critical currents in liquid helium (4.2 K) under external magnetic fields of 1 T and 8 T are 7.2 A and 0.7 A, corresponding to non-Cu critical current densities of 15,000 and 1,500 A/mm2, respectively. These values are greater than those of industrial Nb-Ti and MgB2 commercial multifilamentary wires.

Influence of critical parameters on UHPFRC structural elements subjected to blast loading

Response of structures subjected to blast loading is a highly complex phenomena involving time-dependent deformation, geometric and material nonlinearities and loading rate based material properties. During an explosion, blast loads act as an impulsive load of very short duration developing enormous heat and pressure. With increasing terrorist threats, attention is needed to study dynamic response of structures under blast loading. Ultra high strength concrete (UHPC) has been found to considerably enhance strength, member size, weight reduction and workability and is now a day used due to improved energy absorption capacity, workability and anti-abrasion ability. Investigations conducted by several researchers to study blast-resistant capacities of UHPC have demonstrated possibilities of using the material in structures susceptible to terrorist attack. The present paper provides comprehensive review of published research to study blast loading effect on Ultra high performance fibre reinforced concrete (UHPFRC) structural elements in terms of variables like standoff distance, charge weight, types of blast loadings, grades of UHPFRCs, etc., both analytically and experimentally. UHPFRC slab panels, beams, columns, and other fibre composite structures have been studied at structural level to draw fruitful inferences and conclusions. It has been found that UHPFRC possesses increased capacity to disseminate large amount of energy during blast loading and demonstrates better performance after blast damage contrasted with normal strength concrete and High strength concrete. Detailing in UHPFRC structural elements under seismic condition offers improved blast performance, and UHPFRC can more effectively resist compression and shock waves. Low Strength and low ductility fibres added to UHPFRC further illustrates minimal influence on the blast performance and fracture energy. Shear failure is also found to be one of the dominant modes in UHPFRC under blast loading at close standoff. Based on extensive review, further research is proposed to solve complex problems to achieve appropriate design of structural UHPFRC members.

The compressive behavior of a composite cylindrical pyramidal lattice structure manufactured with a new production methodology

In this paper, a new manufacturing method of pyramidal lattice cells has been suggested to produce lattice composite cylinders. Moreover, the effect of fiber volume fraction, vacuum molding, and fiber pre-tension has been investigated on the load-carrying capacity of the cylindrical pyramidal lattice structure of a carbon fiber composite. The carbon fiber composite cylindrical pyramidal lattice structure has been manufactured with laying fibers along the grooves of a silicone mold. Then, it has been subjected to the axial compressive test. Furthermore, to make pre-tension in fibers, a metal mold has been designed. Fiber pre-tension ensures the alignment of the fibers is straight between two nodal points. Additionally, the structure has been analyzed by the finite element buckling procedure. Experimental tests on the structures show that using a metal mold compare to the silicone molding method increases load-carrying capacity up to 48% without significantly varying the weight. Therefore, this method can be used for manufacturing pyramidal lattice structures in the hand layup process.

Impact Damage Resistance and Post-Impact Tolerance of Optimum Banana-Pseudo-Stem-Fiber-Reinforced Epoxy Sandwich Structures

Banana fiber has a high potential for use in fiber composite structures due to its promise as a polymer reinforcement. However, it has poor bonding characteristics with the matrixes due to hydrophobic–hydrophilic incompatibility, inconsistency in blending weight ratio, and fiber length instability. In this study, the optimal conditions for a banana/epoxy composite as determined previously were used to fabricate a sandwich structure where carbon/Kevlar twill plies acted as the skins. The structure was evaluated based on two experimental tests: low-velocity impact and compression after impact (CAI) tests. Here, the synthetic fiber including Kevlar, carbon, and glass sandwich structures were also tested for comparison purposes. In general, the results showed a low peak load and larger damage area in the optimal banana/epoxy structures. The impact damage area, as characterized by the dye penetration, increased with increasing impact energy. The optimal banana composite and synthetic fiber systems were proven to offer a similar residual strength and normalized strength when higher impact energies were applied. Delamination and fracture behavior were dominant in the optimal banana structures subjected to CAI testing. Finally, optimization of the compounding parameters of the optimal banana fibers improved the impact and CAI properties of the structure, making them comparable to those of synthetic sandwich composites.

A Refined Model for Predicting the 31-Coupling Effect of Piezoelectric Structural Fiber Composites

A refined model is proposed to predict the 31-coupling effect of a piezoelectric structural fiber (PSF) and PSF composites. The PSF model consists of a piezoelectric shell, inner and outer electrode layers, and a piezoelectric inactive core fiber. The inner and outer electrodes provide a radial electric field passing through the piezoelectric shell, which leads to the axial deformation of the piezoelectric shell, the piezoelectric inactive core fiber provides the mechanical support to the brittle piezoelectric shell. Analytical expressions of the effective piezoelectric coefficient d31 of the single PSF and the PSF composites are derived, the influences of aspect ratio of the piezoelectric shell, thickness of the electrode layer and PSF volume fraction, on the effective piezoelectric coefficient d31 are demonstrated. The numerical results show that the model without electrode layers may lead to a significant error.

Failure analysis and bending performance of carbon fiber composite sandwich structures with corrugated cores

In recent years, composite materials have been more widely used in sandwich structures, which have been proved better performance in sandwich structures than other materials in some cases. In this paper, an analytical model is developed to predict the key stress, failure modes, and failure loads of the composite corrugated-core sandwich structures under three-point bending in both longitudinal and transverse directions. Then a three-dimensional finite element model by using Hashin’s model to predict fiber composite laminates and cohesive zone model to predict extra epoxy layer of fiber composite laminates is developed and validated by the corresponding experiments. The analytical model is also validated through both simulation and experiment. Finally, the failure mechanism maps and effects of orientation angles on failure have been further studied based on the analytical model.