Fiber Angle Research Articles

Global sensitivity analysis of complex moduli of carbon fiber reinforced polymer

AbstractGlobal sensitivity analysis of complex moduli of carbon fiber reinforced polymer (CFRP) is performed by using variance‐based sensitivity analysis. Twelve material properties of matrix and fiber are selected as input arguments, including fiber volume fraction, three matrix properties, and eight carbon fiber properties. Ten thousand samples are generated with Sobol sequence. Based on the correspondence principle, six complex moduli of unidirectional CFRP, and two complex moduli of quasi‐isotropic laminate, orthogonal laminate, and symmetric laminate with different fiber angles are predicted using the generalized method of cells and classical laminate theory. The sensitivity indexes of all input arguments are calculated. The results show that the loss factors of CFRP are mainly affected by the matrix loss factor and fiber axial loss factor, and slightly affected by the fiber transverse loss factor.Highlights Sensitivity analysis reveals key factors influencing CFRP complex moduli. Impact of fiber and matrix properties on CFRP damping revealed. Insights for high‐damping and high‐stiffness CFRP development. Enhanced understanding of energy absorption mechanisms. Uncovering the dominant role of matrix and fiber axial properties in damping.

Geometric model of tufts based on the internal fiber configurations

Fiber tufts were modeled as random fibrous materials based on the statistical orientations of the observed fibers. The tufts with different fiber properties were analyzed experimentally and simulated well. It was found that the distribution of fiber orientation angles is not uniform. The simulations of tufts have confirmed that the sizes of tufts could also be affected by the orientation angle distribution of the constituted fibers. The model was verified by the simulated tufts and the tested ones. Good agreement was achieved between the sizes of simulations and the observed ones. The above model can further explore the underlying principles of carding in yarn manufacture. Furthermore, the modeling method can also be widely used to simulate other fibrous materials where fibers are highly tangled.

The Impact of Bend–Twist Coupling on Structural Characteristics and Flutter Limit of Ultra-Long Flexible Wind Turbine Composite Blades

Flutter is an instability phenomenon that can occur in wind turbine blades due to fluid–structure interaction, particularly for longer and more flexible blades. Aeroelastic tailoring through bend–twist coupling is an effective method to enhance the aeroelastic performance of blades. In this study, we investigate the impact of bend–twist coupling on the structural performance and flutter limit of the IEA 15 MW blade, which is currently the longest reference wind turbine blade, and determine the optimal layup configuration that maximizes the flutter speed. The blade is modeled by NuMAD and iVABS, and the cross-section properties are obtained by PreComb and VABS. The accuracy of the blade model is verified in terms of stiffness and frequency. The bend–twist coupling is implemented by changing the fiber angle of the skin and spar cap considering symmetric and asymmetric layups. The flutter limits of both the baseline and the bend–twist coupled blade are evaluated based on HAWC2. The results show that the angle of spar cap carbon fiber has a greater effect on the blade’s structural properties and flutter speed than the skin fiber. Varying the spar cap carbon fiber angle increases the flutter speed, with the effect being more significant for the symmetric layup, up to 9.66% at a fiber angle of 25 degrees. In contrast, the variation in skin fiber angle has a relatively small impact on flutter speed—within ±3%.

Deep reinforcement learning for stacking sequence optimization of composite laminates

Fiber reinforced polymer (FRP) composite laminates are increasingly used in a wide range of safety–critical products due to their excellent material properties. The stacking sequence of FRP composite laminates plays a critical role in the resulting part’s mechanical properties. Despite this, composite engineers still commonly fabricate parts with “classic” ply layups (e.g. four ply laminate with fiber orientation angles: [-45/0/45/90°]), which may have sub-optimal mechanical performance in the expected loading/use cases. Finding the composite stacking sequence that achieves the best material and mechanical properties possible is a challenging optimization problem characterized by the large domain space involved in solving an inverse design problem. This paper introduces a novel approach to optimizing stacking sequence for composite plate stiffness by applying off-policy deep reinforcement learning (DRL). We formulate the problem as a sequential decision making process. The state of the system is based on the stiffness of the composite for the currently selected stacking sequence and the action is to select a new stacking sequence using our reward function, formulated as the offset, normalized stiffness modulus. We compare our DRL model to two classical stacking sequences, a randomized baseline model, and a competitive genetic algorithm (NSGA-II). For maximizing longitudinal composite plate stiffness, the DRL model finds the optimum solution for all ply thicknesses and the genetic algorithm comes within 0.5% of the optimum. The DRL model determines the optimum stacking sequence significantly faster and is less sensitive to parameter tuning. The DRL model and the genetic algorithm both outperform the random baseline algorithm by over 5.7 standard deviations in the most conservative case. This research demonstrates the ability of DRL to effectively and efficiently optimize composite laminate stacking sequence.

Оценка качественных признаков древесины в селекционных программах (краткий обзор современной литературы)

The literature review concerning wood quality traits measuring in forest tree breeding programs is given. Methods of wood density measuring by Pilodin and different types of Resistograph are shortly described. Comparison study to measure Scots pine wood density by Pilodin and Resistograph revealed that Resistograph provide more precise wood density data than Pilodin. Method of measuring of wood stiffness an important wood mechanical property using acoustic velocity data is characterized. There is relationship between distortion of lumber and grain angle of wood fibers. Grain angle, i.e. spiral grain, refers to the degree of helical deviation from longitudinal arrangement of wood fibers. It can be measured with a wedge grain angle gauge hammered into a stem of a standing tree. It is shown, that microfibril angle (MFA), referring to the deviation of cellulose microfibrils in the layer of the secondary cell wall from the long axis of cell, is the main determinant of the mechanical properties of wood. There is shortly described the system of instruments with linked software (SilviScan), the main components of this system are optical cell scanner (for measurement of fiber size), X-ray densitometer (density profile and others) and X-ray diffractometer (microstructure traits). A minor negative relationship between growth and wood quality traits is noted, so the index selection is recommended under realization of tree breeding program. Some examples of genomic selection in tree breeding programs for wood quality are given.

Fractal interpolation-based micro-surface reconstruction method for composite pore walls

The pore wall morphology of carbon fiber reinforced composite (CFRP) laminates is one of the key factors to determine their service performance. However, due to the direction angle of the material fibers, the original micro surface morphology of the pore wall is complex and difficult to characterize. In this paper, a method to reconstruct the micro surface of the hole wall by fractal interpolation is proposed. By using a small number of data points extracted, the high-precision equivalent micro surface by fractal interpolation can be reconstructed, which can effectively characterize the composite joint surface. Firstly, the geometric features of micro surface are extracted by using the experimental measurement. Then, based on the model for fractal interpolation, an improved self affine fractal interpolation algorithm is used to reconstruct the original measured surface. Finally, the geometric and mechanical validity of fractal interpolation surface reconstruction is verified by combining geometric model and finite element model. The results show that when the sampling interval is 3~5, the geometric error and mechanical property error of the fractal interpolation method are below 10%, which can effectively characterize the original composite joint surface.

Topology Optimization of Minimum Compliance for Continuous Fiber-Reinforced Polymer

Continuous fiber-reinforced polymer (CFRP) has been paid more attention to due to its advantages of high strength, high stiffness, and lightweight. However, it is challenging for topology optimization to achieve CRRP structure design. A topology optimization (TO) model with minimizing structural compliance under volume fraction constraint is established based on the independent continuous mapping (ICM) method. The continuous fiber angle optimization (CFAO) method solves the fiber orientation. Meanwhile, the local optimal solution problem caused by the CFAO method is greatly avoided by the direction of principal stress. The effectiveness of the method is verified by classic numerical examples. This paper has a significant reference for the TO design of CFRP structure.

Space fractional-order modeling for the sintering process of metal fibers via Lattice Boltzmann method

Considering the abnormal diffusion phenomena in the forming process of the sintered junction of metal fibers, a spatial fraction-order differential model is proposed based on the geometrical model and the integer-order differential model in this work. Lattice Boltzmann method(LBM) is applied to numerically analyze the established fractional model. And the growth process of sintered junctions dominated by surface diffusion mechanism at different fiber angles and sections is characterized by numerical simulation. Besides, the effects of fractional order, diffusion coefficient, and skewing parameters on the sintered process of metal fibers are presented and discussed. The developed model is valid by comparing the outcomes of numerical simulations with those obtained from the scanning electron microscope(SEM). It is also demonstrated that the fraction-order model can accurately depict the sintering process of metal fibers, and the anisotropy of metal bars can be characterized via the proposed model during sintering.

Natural Frequencies Optimisation of Hybrid Composite Laminates using Response Surface Method

Natural frequency is an important property in designing structures, as resonance can induce catastrophic failure. Nevertheless, the vibration behaviour of hybrid composite laminates due to the hybridisation has still not been fully understood. This study aims to analyse and optimise the natural frequency response of hybrid composite laminates under free vibration due to the effect of various lamination schemes, plate thicknesses and hybridisation volume fractions. Initial stage involved mesh convergence analysis and numerical validation. Design of Experiments approach was employed to set up the important parameters and effective case studies. The natural frequencies for each case study were determined and analysed using finite element analysis software. The final stage involved optimisation using Response Surface Method. The results from the 34 case studies showed that the range of natural frequency was between 116.53Hz and 5598.4Hz. It was found that both symmetric and anti-symmetric laminates with 0° fibre angle produced the highest natural frequency of 5598.4Hz. Considering other parameters, the thicker plate and higher volume of carbon produced higher natural frequency. In conclusion, this study has contributed significant knowledge such as better understanding the effect of the studied parameters on the natural frequencies of hybrid composite laminates.

Evaluation of draping simulations by means of 3D laser scans and robot supported fiber angle scans

In order to demonstrate the accuracy of macroscopic finite element draping simulations it is necessary to compare the results with experiments. In this work, a compact overview of evaluation methods for draping simulations based on experiments, in the recent literature, is provided. Then, a method using state of the art 3D laser scans (RS6, Hexagon) and robot supported fiber angle scans (FScan, Profactor) is described. The presented comparison of draping results with the tool geometry in 3D allows for an evaluation of wrinkles and bridging areas. For the evaluation of the edge contour, the commonly used method of projecting the edge contour on a 2D plane is extended to a comparison in 3D space. To determine fiber orientations and compare them with the predictions from simulations, a robot supported fiber angle sensor and a script-based mapping and comparison algorithm are used. The results are further analyzed statistically, to derive comparative figures to other results found in the literature. The location and dimensions of macroscopic manufacturing effects such as fiber bridging and wrinkles could be predicted accurately. The final component contour could be on average predicted within 5.2 mm. The fiber orientation could be predicted with a deviation of less than 2° for approx. 65% and within 6° for 95% of the part surface for UD laminas. Cross-ply laminas showed larger deviations, only 40% of the part surface was within 2° and 80% within 6°, compared to the experiment. Overall, the results for the presented methods show good agreement between multi-ply draping experiments and macroscopic simulations conducted with the Abaqus Fabric material model.

A seven-parameter high-order finite element model for multi-stable analysis of variable stiffness laminated shells

Variable angle fiber composites provide large design space for multi-stable structures. However, they require reliable numerical models to accurately predict their mechanical behavior characterized by a complex material response and large deformation. To this end, we propose an accurate yet efficient model for stability analysis of variable angle fiber laminated shells. In this model, first a seven-parameter shell formulation with Equivalent Single Layer theory, which is suitable for three-dimensional constitutive laws, is utilized to accurately characterize the large deformation. The fiber orientation angle is described by a linear variation from the center to the end of the shell. Then, to improve the accuracy and to reduce the computational cost, the spectral/hp element with high-order polynomial basis functions is adopted for discretization. Finally, complex nonlinear equilibrium paths are effectively tracked by the Riks method. By comparison with ABAQUS solutions, the proposed model shows to be efficient and accurate for variable angle fiber laminates under various conditions, in which both the buckling, the snap-through and tristability behaviors are studied. Moreover, variable angle fiber shells provide more design possibilities than straight fiber shells. By opportunely varying the fibers angle of each lamina, it is possible to control the stable states as well as to obtain multiple stable configurations (bi- and tri-stability).

Fiber Angle influence and Toughness characterization of bioinspired discontinuous fiber helicoids composite materials produced via additive manufacturing

Over millennia nature has produced composite materials with excellent mechanical properties compared to the low properties of their base materials and has managed to obtain a good compatibility between stiffness and toughness; as a result, they are a good source of inspiration for material optimization for applications, such as increasing toughness and damage resistance, something that is difficult in conventional engineering materials. Nowadays eight structural elements are identified in biological materials: fibrous, helicoidal, gradients, layered, tubular, cellular, suture, and overlapping. Helical structures consist of stacks of ordered fibers that form layers that are rotated at a constant angle of inclination. These include plywood and Bouligand structures. Bouligand structures consist of an arrangement of fibrous laminates that completes a 180° turn and provides some biological materials with increased strength and toughness in multiple directions and exceptionally high fracture toughness. The classical composite materials mechanics provides some constitutive model approximations for this type of materials, but they still need to be studied and tested to properly understand their behavior. Injection molding, compression molding, hand layup, resin transfer molding, filament winding, pultrusion, and automated fiber placement are just a few of the traditional methods used to make fiber-reinforced polymer composites (FRPC). However, these traditional manufacturing techniques have a restriction on specific fiber alignment and demand expensive molds, dies, or lithographic masks. Additive manufacturing has the potential to replace many conventional manufacturing processes due to its ability to create complex geometries with customizable material properties and employ several materials simultaneously, among other things. Fused deposition modeling (FDM) is the most widely used manufacturing additive technique for manufacturing FRPC due to its low cost, low energy input, material consumption, and operation simplicity. This work presents three-dimensional models mimicking the Bouligand structures by turning the pitch angle of the layers and a analytical models comparison were made. The specimens were fabricated using the FDM technique. A thermoplastic polyurethane (TPU) was used for the matrix and polylactic acid (PLA) for the fibers. Tensile tests were used to mechanically characterize both the raw materials and the manufactured composites to examine the impact of the helical angle and the contribution of the matrix and fiber materials to the stiffness and toughness of the composite. Experiments and analysis revealed that high rotation angles improve the stiffness, strength, and toughness of the composite.

Nonlinear damping and forced vibration analysis of sandwich functionally graded material beams with composite viscoelastic core layer

In the present article, an analytical model is proposed to assess the nonlinear damping and frequency curves of the three layered sandwich beams, constituted with FGM faces and viscoelastic core layers. The proposed analytical model is formulated in the context of forced vibration analysis. The kinematical model developed for the purpose is based on the higher order zig-zag theories coupled with the higher order shear deformation theory (HSDT), employing shear functions, formulated by Timoshenko, Reddy, and Touratier. The frequency response curves and the nonlinear loss factors are provided by resourcing to analytical solution, derived from the harmonic balance technique coupled with the one mode of Galerkin’s method. The elastic moduli of the viscoelastic material are described with complex numbers in the frequency domain. The material proprieties of the FGM beams vary gradually along the thickness direction, transiting from metal to ceramic materials. The effect of the geometrical and material parameters of the FGM and viscoelastic composite layers on the damping and frequency response curves of the sandwich beams are studied according to the first and higher-order shear deformation theories. Basing on the proposed analytical model, numerical results are presented to study the effect of the FGM parameters and the fiber orientation angle of the composite core on the nonlinear damping evolution with the vibration amplitude and the frequency curves.

Ultrasonography of Knee Muscles During SLR With Different Positions of Hip and Ankle in Patellofemoral Pain Syndrome

Objective Due to the substantial prevalence of patellofemoral pain syndrome and the importance of quadriceps strengthening in knee rehabilitation, determining the best way to activate and strengthen the patella stabilizing muscles is considered as one of important keys of treatment. The aim of this study is to evaluate the effect of different hip rotations associated with ankle dorsiflexion during maximal straight leg raising (SLR) maneuver in the sitting position on thickness and fibers angle of vastus medialis oblique (VMO) and vastus lateralis (VL) muscles using ultrasonography. Materials & Methods This quasi-experimental study was performed on 40 individuals (healthy group: 20, patellofemoral pain syndrome [PFPS] group: 20). VMO and VL thickness and fiber angle were measured using ultrasonography during maximal SLR in 6 positions: hip internal, hip external, and neutral rotations with and without ankle dorsiflexion. Results In between-group comparison, no significant difference was found for all variables with different SLR maneuvers (P>0.05). In the within-group comparison, hip external rotation compared to other hip positions without ankle dorsiflexion resulted in a significant increase in VMO thickness and fiber angle in both groups (P<0.05). Also, adding ankle dorsiflexion to different hip rotations during SLR significantly increased the thickness and fiber angle of VMO and VL. Conclusion By changing hip rotations with or without ankle dorsiflexion during SLR, the trend of changes in VMO and VL thickness and fiber angle in the two groups followed the same pattern. Moreover, performing SLR in hip external rotation with ankle dorsiflexion can be recommendable for the rehabilitation of PFPS.

Experimental characterization of unidirectional carbon – Carbon composite laminate

Advanced polymeric Composites have wide applications in various industrial sectors of Missile System, Automobile, and Space Structures have been sound prominent and endlessly receiving the wide awareness for many industries. The structural engineer desires to be eminent with the belongings of the composite material structures. The performance of fiber reinforced polymeric composite material beneath dynamic load plays a crucial task in designing such structures. In the recent work, an attempt is made to determine optimum fiber angle and the behavior of the advanced polymeric composite material, i.e., Carbon – Carbon Composites under Tensile and Compressive loads. Mechanical properties, viz., Compressive and Tensile strength are determined by using experimentation method. Hand layup technique is used for fabricating the laminates. FE Analysis (Ansys) is carried out on various fiber angles likely be [0°-90°], [30°], [45°], [60°] to validate the results which is obtained from experimentation.

Moving Load Analysis of Laminated Porous Micro Beams Resting on Elastic Foundation

This research highlights dynamic displacements of laminated porous micro beams resting on elastic foundation under moving load. In the constituted equation of laminated micro scaled beam, the modified coupled stress theory is used in order to determine the size effect. Each layer is considered as identical and porosity distribution and assumed as uniform. Lagrange technique is applied in achieving governing equations, and Ritz method within algebraic polynomials is used for solution. For dynamic solution steps, Newmark average acceleration method is used within time domain. Influences of porosity coefficients, length scale parameter, foundation parameter, order of laminas, fiber orientation angles on dynamically deflections of laminated micro beam are investigated.

Nonlinear parametric resonances of a rotating composite thin-walled beam under aerodynamic force and hygrothermal environment

Considering combined effects of aerodynamic force and hygrothermal environment, the nonlinear parametric resonance of a composite thin-walled beam subjected to a time-dependent rotating speed is investigated in this work. The rotating speed is presumed to comprise a small disturbance harmonically changing one with a steady one. The dynamical model of the system is obtained with the help of established dynamic model in existing research. Then the nonlinear partial differential equation of the system is discretized by the Galerkin method. Afterwards, the low-frequency and high-frequency resonances of the system are analyzed via the multiple scales method to discuss the combined effect of rotating speed, pitch angle, setting angle, fiber orientation angle, temperature-humidity and inflow ratio on the amplitude-frequency responses and the unstable region. In addition, the Routh-Hurwitz criterion is employed to determine the stability conditions of the trivial and non-trivial solutions. The results show that both sub- and super-critical pitchfork bifurcations will occur to the system in parametric resonances regime, accompanied with stable and unstable non-trivial solutions simultaneously. Particularly, the mechanism of the influence of hygrothermal environment is deeply studied, which reveals a competitive relation between the change of mechanical properties and additional stress brought by the change of temperature and humidity.

Experimental examination of the axial compression conduct of filament-wound cylindrical composite tubes at different wall thicknesses and orientation angles

This study presents the results of experimental research on the behavior and stretching of hollow cylindrical epoxy tubes made of glass, carbon, and kevlar fibers subjected to axial compression load. Hollow cylindrical tubes were fabricated by fiber winding method using glass, carbon, and kevlar fiber-reinforced composite materials. In this study, hollow cylindrical composite tubes with constant outer (Ø17 millimeters), two different inner diameters (Ø12 and Ø13 millimeters; 2 ve 2,5 millimeters wall thickness), and 80 millimeters in height. Experimental research was carried out for two dissimilar wall thicknesses and four fiber orientation angles. The compressive strengths of all samples were investigated experimentally by applying loads in the axial direction. Twenty-four configurations of composite specimens were fabricated (three reinforcement materials, four winding angles, and two wall thicknesses) to research the impact of axial compression stress. Experimental results revealed that polymer reinforcement material, fiber winding angle, and wall thickness have a significant impact on the compressive stress of cylindrical composite tubes as a result of applied load in the axial direction. The conclusions show that the compressive stress of all reinforcement rises as the orientation angle and wall thickness increase under an axial compression load, and the compressive stress reaches a maximum when the orientation angle is 90° under an axial compression load. It was observed that the axial compressive stress was highest in glass/epoxy samples with 217 MPa, followed by carbon/epoxy samples with 173 MPa and kevlar/epoxy samples with 145 MPa, respectively. The axial compressive stress of all samples was highest at a 90° orientation angle and lowest at a 15° orientation angle. were found to have low values. It was observed that the axial compressive stress value increased in all reinforcement materials as the wall thickness increased.
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Composition, architecture and biomechanical properties of articular cartilage in differently loaded areas of the equine stifle.

Strategies for articular cartilage repair need to take into account topographical differences in tissue composition and architecture to achieve durable functional outcome. These have not yet been investigated in the equine stifle. To analyse the biochemical composition and architecture of three differently loaded areas of the equine stifle. We hypothesise that site differences correlate with the biomechanical characteristics of the cartilage. Ex vivo study. Thirty osteochondral plugs per location were harvested from the lateral trochlear ridge (LTR), the distal intertrochlear groove (DITG) and the medial femoral condyle (MFC). These underwent biochemical, biomechanical and structural analysis. A linear mixed model with location as a fixed factor and horse as a random factor was applied, followed by pair-wise comparisons of estimated means with false discovery rate correction, to test for differences between locations. Correlations between biochemical and biomechanical parameters were tested using Spearman's correlation coefficient. Glycosaminoglycan content was different between all sites (estimated mean [95% confidence interval (CI)] for LTR 75.4 [64.5, 88.2], for intercondylar notch (ICN) 37.3 [31.9, 43.6], for MFC 93.7 [80.1109.6] μg/mg dry weight), as were equilibrium modulus (LTR2.20 [1.96, 2.46], ICN0.48 [0.37, 0.6], MFC1.36 [1.17, 1.56] MPa), dynamic modulus (LTR7.33 [6.54, 8.17], ICN4.38 [3.77, 5.03], MFC5.62 [4.93, 6.36] MPa) and viscosity (LTR7.49 [6.76, 8.26], ICN16.99 [15.88, 18.14], MFC8.7 [7.91,9.5]°). The two weightbearing areas (LTR and MCF) and the non-weightbearing area (ICN) differed in collagen content (LTR 139 [127, 152], ICN176[162, 191], MFC 127[115, 139] μg/mg dry weight), parallelism index and angle of collagen fibres. The strongest correlations were between proteoglycan content and equilibrium modulus (r: 0.642; p: 0.001), dynamic modulus (r: 0.554; p < 0.001) and phase shift (r: -0.675; p < 0.001), and between collagen orientation angle and equilibrium modulus (r: -0.612; p < 0.001), dynamic modulus (r: -0.424; p < 0.001) and phase shift (r: 0.609; p < 0.001). Only a single sample per location was analysed. There were significant differences in cartilage biochemical composition, biomechanics and architecture between the three differently loaded sites. The biochemical and structural composition correlated with the mechanical characteristics. These differences need to be acknowledged by designing cartilage repair strategies.

Pore scale study of heat and mass transfer in ice-containing gas diffusion layer of polymer electrolyte membrane fuel cells

The liquid water transport and ice melting process in gas diffusion layer (GDL) are studied using the enthalpy-based multi-component multiphase flow lattice Boltzmann model. Then the heat and mass transfer process under different inlet heating temperatures, inlet flow velocities, rib-channel width ratios and contact angles of carbon fibers are discussed. The results show that heat convection and heat conduction areas are formed in the GDL, and the increase of the inlet heating temperature promotes ice melting, the heating temperature needs to be high enough to promote the reduction of the mixture content of water and ice. The inlet flow velocity has a great influence on both the ice melting efficiency and the discharge of liquid water. The reduction ratio of melting time from 0.5 m/s to 1.0 m/s is larger than that from 1.0 m/s to 1.5 m/s. The wider rib structure reduces the range of heat conduction region, so it has higher ice melting efficiency. The surface wettability of carbon fibers has no significant effect on ice melting rate in the heat convection area. Overall, the more hydrophilic the surface, the sooner the ice melts, but the more hydrophobic the surface, the more favorable the discharge of liquid water.