Fiber Angle Research Articles

Tunable Coefficient of Thermal Expansion of Composite Materials for Thin-Film Coatings

In most engineering applications, the coefficients of thermal expansion (CTEs) of different materials in integrated structures are inconsistent, especially for the thin-film multilayered coatings. Therefore, mismatched thermal deformation is induced due to temperature variation, which leads to an extreme temperature gradient, stress concentration, and damage accumulation. Controlling the CTEs of materials can effectively eliminate the thermally induced stress within the layered structures and thus considerably improve the mechanical reliability and service life. In this paper, randomly distributed fibers are incorporated into the matrix material and thus utilized to tune the material CTE from the macroscopical viewpoint. To this end, finite element (FE) modeling is proposed for fiber-reinforced matrix composites. In order to overcome the challenges of creating numerical models at a mesoscale, the random distribution of fibers in three-dimensional space is realized by proposing a fiber growth algorithm with the control of the in-plane and out-of-plane angles of fibers. The homogenization method is adopted to facilitate the FE simulations by using the representative volume element (RVE) of composite materials. Periodic boundary conditions (PBC) are applied to realize the prediction of the equivalent CTE of macroscopic composite materials with randomly distributed fibers. In the established FE model, the random distribution of carbon fibers in the matrix makes it possible to tune the CTE of the composite material by considering the orientation of fibers in the matrix. The FE predictions show that the volume fraction of carbon fibers in the composite materials is found to be crucial to macroscopic CTE, but results in minor variations in Young’s modulus and shear modulus. With the developed ABAQUS plug-in program, the proposed tuning method for CTE is promising to be standardized for industrial practice.

Nonlinear Buckling and Postbuckling Analysis of Tow-Steered Composite Cylinders with Cutouts

The buckling and postbuckling behavior of two composite tow-steered shells with cutouts of different sizes is assessed using nonlinear finite element analysis and compared to experimental measurements. The cylindrical shells are manufactured using an automated fiber placement system, where the shells’ fiber orientation angles vary continuously around the shell circumference from on the crown and keel to on the sides. One shell features thickness variations due to tow overlaps that result from application of all 24 tows during each pass of the fiber placement system. The second shell uses the system’s tow drop/add capability to achieve a more uniform wall thickness without overlaps. Unreinforced cutouts of two different sizes—the first smaller cutout representing a passenger door on a commercial aircraft and the second larger cutout a cargo door—were machined into each of the two cylinders resulting in a total of four test cases. These cylinders were tested in axial compression and buckled elastically in previous work and are now analyzed using nonlinear finite element models to compare bifurcation buckling loads as well as the load–displacement response in the prebuckling and postbuckling regimes. For all four shells analyzed, the prebuckling stiffness, buckling load, and deformation mode sequence throughout the loading–unloading cycle is accurately reproduced by the models. In particular, the shells first buckle locally around the cutouts in a stable (supercritical) manner with only a slight decrease in axial stiffness, which occurs due to the favorable load redistribution facilitated by tow steering. The shells then buckle globally in an unstable (subcritical) manner with diamond-shaped buckles forming to the left and right (circumferential direction) of the cutouts. The buckling load of all shells with cutouts is at least 82% of the buckling load of the pristine shells without cutouts. Overall, the ability to sustain local buckling phenomena, and the relatively small reductions in global buckling load compared to pristine shells without cutouts, demonstrates the great potential of using tow steering to mitigate the adverse effects of cutouts in axially compressed shell structures.

Alkali treatment influence on cellulosic fiber from Furcraea foetida leaves as potential reinforcement of polymeric composites

The present study explores the potential of the alkali-treated Furcraea foetida (FF) fibers as reinforcement materials in polymeric composites. The fibers were treated and soaked for 3 h in an alkali solution of different concentrations (3, 6, 9, 12, and 15 wt.%). The untreated and alkali-treated fibers were characterized, and their physical and mechanical properties were determined. The results revealed that the 9 wt.% alkali-treated FF fiber yielded superior mechanical strength and Young's modulus because of its relatively high cellulose fraction after removing non-cellulosic materials. The twisting behavior and increasing microfibril angle of the FF fiber were attributed to a non-linear region in the stress–strain curves after the alkali treatment. The Fourier-transform infrared and X-ray diffraction studies endorsed the removal of non-cellulosic materials on optimally treated fiber. Thermogravimetric analysis of the 9 wt.% alkali-treated FF fiber confirmed the increase in the degradation temperature (358 °C) and activation energy (145.29 kJ/mol). Scanning electron microscopy results confirmed that the fiber surface roughness is proportional to the alkali solution concentration. Then the results were compared with others previous studies. Thus, treating FF fibers with optimized alkali concentration at specified soaking period can enhance their performance as a viable reinforcement material in polymeric composites for low-load applications.

Elastic-Plastic Stress Analysis of Steel Fiber Reinforced Composite Plates Under Axial Load

Composite materials, obtained by combining two or more materials; It is defined as a new type of material with high strength, high rigidity and lightness. Composite plates are structural elements that are used in machines and structures under different loads, consist of at least two types of materials and can be produced in various constructions. In this study, elastic-plastic stress analysis of polymer matrix continuous fiber reinforced composite plate under axial load was solved with Airy Stress Function proposed as a 5th order non-uniform polynomial to solve the elasticity problem. Polyethylene matrix composite reinforced with steel fibers was taken as the plate material and the material was accepted as ideal elastic-plastic. Tsai-Hill Yield Criterion was used for the plastic solution. According to the results of the analysis, as the fiber angle increased in the composite plate, the plastic stress limit decreased, the increase in the fiber angle decreased the plastic stress limit, and the decrease in the plastic stress limit caused the residual stresses to increase.

Anisotropic bilinear flexural behavior and failure mechanism of parallel bamboo strand lumber plates

To investigate the plate behavior of parallel bamboo strand lumber (PBSL) plates, flexural experiments on four groups of PBSL plates with fiber direction changing from 7.5° to 45° were performed. All of these PBSL plates have progressive failure process, developing from initial matrix tensile fracture, succeeding fiber compression fracture, latter matrix tensile fracture and final punch failure. An orthotropic plate theory combining with composite failure theory was proposed to predict the elastic behavior, the cracking load and the ultimate load. The perdition error is acceptable for the PBSL with strong structural dispersion. It is revealed that the ultimate bearing capacity of the PBSL plate in this research has a slight decreasing trend with the fiber direction changing from 0° to 45° as fiber fracture controls the complete failure. The orthotropy makes the plate crack under relatively small load depending on the tensile strength of the matrix and the cracking load also has a slight decreasing trend with the increase of the fiber angle.

The Effect of Self-Myofascial Release on the Pennation Angle of the Vastus Medialis Oblique and the Vastus Lateralis in Athletic Male Individuals: An Ultrasound Investigation.

BackgroundMaintenance of patellar stability requires a balance between the vastus medialis oblique (VMO) and the vastus lateralis (VL). The imbalance between these muscles is thought to be implicated in the etiology of patellofemoral pain (PFP). Where there is hypertrophy of the VL in PFP patients, self-myofascial release (SMR) may be utilized for its management. However, there is no current evidence regarding SMR and its effects on VMO and VL architecture. The aim of this study, therefore, was to use ultrasound to gain further understanding of the effects of a program of SMR on the fiber angles of the VMO and VL.HypothesisThere will be a significant decrease in the pennation angles of the VMO and VL after seven weeks of SMR using a foam roller.Study DesignCohort StudyMethodsTwenty-five young, athletic, male participants were recruited to use a foam roller, along the full length of both anterior thighs, three times weekly, on three separate days, for seven weeks. Ultrasound was used to determine the initial and final VMO and VL pennation angles on both limbs. One eligible participant was chosen as an intra-rater control and did not partake in the SMR regimen.ResultsThere was a statistically significant (p < 0.001) decrease in the pennation angles of the VMO and VL after the SMR regime. Mean combined right and left VL angle change was -6.65° (-18% mean change) and the mean combined right and left VMO angle change was -7.65° (-11.5% mean change). A weak negative correlation was found between initial VMO fiber angle and the angle change (Rsquared = -0.21), as well as moderate negative correlation for the VL (Rsquared = -0.51).ConclusionA program of SMR on the anterior thighs of young, asymptomatic males resulted in changes to the fiber angles of both the VMO and VL. There was a significant decrease in pennation angle after seven weeks of SMR using a foam roller.

Buckling behavior of laminated composite stiffened cylindrical shell panels having cutout for different parametric variations

Buckling of composite stiffened cylindrical shell panels having cutout is analyzed using the finite element approach. Shell panel and stiffeners are modeled using first-order shear deformation theory and considering displacement compatibility at the stiffener-panel interface. Convergence and validation studies are conducted to establish the accuracy of the present approach. An attempt is made to maximize the uniaxial and biaxial buckling loads by varying the lamination, boundary conditions, load position, depth of stiffeners, and their arrangements. Parametric studies show that buckling load and mode shapes depend on the size of cutout, ratio of shell width to thickness, degree of orthotropy, and fiber orientation angle. The parametric variations considered here may help the practicing engineers to have an elaborate design aid for improving the buckling strength of such shell panels.

Experimental Analysis of Matrix Cracking in Glass Fiber Reinforced Composite Off-Axis Plies under Static and Fatigue Loading.

The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted white light imaging using a digital camera and LED illumination from the back of the specimen on a servo-hydraulic testing machine. Static and fatigue results were examined with respect to crack initiation and crack growth, considering the special case of bonding yarns parallel to the fiber directions. The bonding yarns act as stress concentrations, influencing the early cracking behavior, and complicate the detectability of cracks growing underneath or next to the bonding yarns. In cyclic loading, the influence of load level, load ratio, mean stress, fiber orientation, and ply thickness was the focus of the experimental campaign. Cyclic cracking behavior in terms of initiation and growth was analyzed based on the applied loading conditions and laminate configurations. It was found that halving the ply thickness nearly doubled the amount of microcracks in case of high loads. For low loads, no such effect was observed up to loading cycles. Experimental findings on individual crack growth confirmed that crack interaction started for crack spacings less than four times the ply thickness and that subsequent crack growth shifted into regions of larger local crack spacing.

Finite strip method based on Carrera unified formulation for the free vibration analysis of variable stiffness composite laminates

AbstractThis work presents a refinement of the finite strip method (FSM) based on the Carrera unified formulation (CUF) and is applied to free vibration analysis of variable stiffness composite laminated (VSCL) plates. VSCL plates considered here are composed of layers with curvilinear fibers in which their orientation angle changes linearly with respect to one of the in‐plane coordinates. The FSM permits the plate to be divided into some finite strips connected along the so‐called nodal lines. The conventional finite strip method involves an approximation of the solution of a plate problem by using continuously harmonic series in the longitudinal direction along the nodal lines and simple polynomial shape functions (the usual beam shape functions) in the transverse direction of the plate. However, refined finite strip model that presented in this paper allows one to express the unknown variables as a set of thickness functions that only depend on the thickness coordinate and the corresponding variable that depends on the in‐plane coordinates which involve continuously harmonic series and polynomial shape functions. Thanks to this new finite strip model, the shape functions used in the transverse direction can be chosen as 1D bar shape functions, and also, all three components of the displacement field are considered in each nodal line. Moreover, based on this approach, three‐dimensional displacement field is approximated in a compact form as a generic N‐order expansion. Therefore, explicit expressions of fundamental nuclei of finite strip matrices are obtained in a compact form and presented here. The results obtained by the present formulation for VSCL plates are compared with those obtained from published data. The results show that this kind of strip is efficient and useful. Further, several numerical examples are presented, and the effect of the order of expansion, the number of strips, curvilinear fiber angle, and various boundary conditions are examined.

A general higher-order shear deformation theory for buckling and free vibration analysis of laminated thin-walled composite I-beams

A general higher-order shear deformation theory for buckling and free vibration analysis of laminated thin-walled composite I-beams is proposed in this paper. It is based on a unified nonlinear variation of shear strains in the wall thickness and then theoretical formulation is derived in the general form which can recover the previous conventional theories such as classical and first-order thin-walled beam theory. Series-type solutions with hybrid shape functions are developed for different boundary conditions. Numerical examples are performed on laminated thin-walled composite I-beams with arbitrary lay-ups. Effects of transverse shear strains, fiber angles and slenderness ratio on the critical buckling loads and natural frequencies of the beams are reported.

Experimental Study on the Characterization of Orientation of Polyester Short Fibers in Rubber Composites by an X-ray Three-Dimensional Microscope.

Polyester-short-fiber-reinforced rubber composites have been detected by an X-ray three-dimensional microscope, and then the three-dimensional reconstruction of the image has been carried out to characterize the orientation of polyester short fibers in the composites for the first time. Based on the summary of three traditional methods and mechanisms of characterizing the orientation of polyester short fibers by the numerical parameter method, the direct test method, and the indirect test method, the method and mechanism of the X-ray three-dimensional microscope applied to the orientation characterization of polyester short fibers have been studied. The combination of the center point and threshold segmentation methods has been used to distinguish which fiber section belongs to the same fiber, and the identification of the whole short fiber in different slice images has been realized for the first time. Moreover, Avizo software has been used to realize the three-dimensional reconstruction of a polyester short fiber scanning image. The obtained data have been integrated and the orientation angle and orientation degree have been quantitatively characterized for the first time. This has filled the key technical problem of quantitative characterization of the orientation angle and orientation degree of polyester fibers. The image has been verified by 3Dmed software, and furthermore, the accuracy of the three-dimensional reconstruction results has been verified.

Fatigue life prediction and optimization of GFRP composites based on Failure Tensor Polynomial in Fatigue model with exponential fitting approach

In this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with [Formula: see text], [Formula: see text], and [Formula: see text] lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization.

A new light transmission method to evaluate the through thickness fibre alignment in transparent resin

This work presents a new method to analyse vertical alignment of short fibres inside transparent resin layers using in situ measuring of light transmission through the layer. In this method, a light source is placed on one side of the composite layer and on the opposite side, a phototransistor measures the transmitted light intensity. A feature of the alignment process causes increased light transmission with increased fibre alignment. Using this technique, alignment of short nickel coated carbon fibres inside epoxy resin layers under magnetic field were evaluated and the effect of fibre content, field strength, fibre length and resin thickness on the alignment quality were characterised. An important finding is that the ratio of fibre length and resin thickness showcases a limit to the alignment degree. Finally, an analytical model is introduced which aims to predict average fibre angles based on the sample configuration, showcasing good agreement with experimental results.

GA-based Optimization Method for Fiber Orientation Angle

GA-based Optimization Method for Fiber Orientation Angle

Global buckling and wrinkling of variable angle tow composite sandwich plates by a modified extended high-order sandwich plate theory

The advanced Automated Fibre Placement (AFP) manufacturing technologies make the synthesis of Variable Angle Tow (VAT) composites, which enable the design of lightweight sandwich structures to possess variable stiffness facesheets. However, both global and local instability phenomena of VAT sandwich plates under in-plane compressive loads are rarely explored till now. The objective of this article is to fill this gap by developing a Rayleigh–Ritz procedure based on a modified extended high-order sandwich plate theory (EHSAPT). The original two-dimensional EHSAPT proposed by Phan et al. (2012) is extended to a three-dimensional case with a minor modification that the first-order shear deformation theory instead of the classical Kirchhoff–Love hypothesis is adopted for each facesheet, which brings several merits such as the conciseness in derivation process and the easiness in program implementation. The Rayleigh–Ritz approach combined with the principle of minimum potential energy is employed to derive the eigenvalue equation that governs the instability problem of VAT sandwich plates under in-plane compressive loads. Both global buckling and wrinkling patterns of VAT sandwich plates can be captured under this proposed analytical model framework. Before instability analysis, the nonuniform prebuckling stresses over the entire sandwich plate are determined under the assumption of membrane prebuckling state. The usage of Lagrange multiplier method in the prebuckling regime removes the restrictions inherent in conventional Rayleigh–Ritz formulation and thus provides a general way to model in-plane boundary conditions. The accuracy and effectiveness of the developed Rayleigh–Ritz procedure are validated by comparing with previously published results and FE solutions given by ABAQUS. Effects of core thickness, core orthotropy, and fibre orientation angle of the facesheets on the instability behaviour of VAT sandwich plates are investigated. Finally, the mechanism of steering the fibre trajectory over the facesheets to improve the buckling resistance for the sandwich plate is studied and discussed.

Comparison of off-axis angle on the low velocity impact behaviors for carbon-fiber-reinforced polymer laminates

Three types of composite specimens with different off-axis angles after indentation were subjected to progressive tensile loading, and the results showed that although the tensile strength is reduced with an increase in off-axis fiber orientation angle, such off-axial structure can enhance the impact-resistance capacity. An acoustic emission (AE) signals analysis showed that data can be divided into categories that correlate with three damage modes. The AE peak frequency characteristics of each damage mode were also identified for both specimens with and without indentation, and the results also showed that indentation can change the order of appearance of different damage modes during loading. Additional characterization was provided by using Micro-computed tomography (Micro-CT) during a progressive tensile loading process, and the CT images provided visualization of damage location and evolution in the composites, with the data exhibiting good correlations with the AE data for defect prediction. The use of AE and Micro-CT technology was shown to effectively characterize composite damage evolution, and such data can potentially serve as a reference for the structural health monitoring (SHM) of such composites when used in structures.

Prediction of fracture toughness due to delamination in cross-ply composite laminates considering interlaminar and intralaminar cracking and inhomogeneous fiber-matrix modeling

In this study, a finite element strategy is implemented for more accurate simulation of nonlinear failure behavior in multidirectional laminated composites. The considered approach is based on the parameters which could affect the SERR2. Accordingly, interaction between delamination and matrix cracking as well as mixed stress distribution around the fiber due to mismatch in properties of adjacent plies with different fiber angle orientation influence the strain energy release rate. Thus, in the present research the prediction of the damage behavior of cross-ply laminates is improved considering the effects of matrix cracking and inhomogeneous fiber-matrix modeling. For simulation of the delamination and the matrix cracking damage, cohesive interface elements are implemented. They have been used perpendicularly inside the 90o plies for the matrix cracking. CZM3 approach, ABAQUS subroutine and Python programming were utilized for automatic modeling of matrix cracking. The resultant load–displacement curve in DCB4 test of cross-ply laminates indicated that by considering delamination and matrix cracking simultaneously, load–displacement curve of cross-ply laminates became nonlinear earlier and the obtained results had an acceptable compatibility with experimental results. The obtained results for double cantilever beam (DCB) test specimen with cross-ply lay-up indicate that the numerically reproduced GIc parameter of 90/0 interface can be improved about 20% using this simulation. Moreover, by simulating periodic matrix cracking inside 90o plies, crack jumping, stick-slip phenomenon and local hardening behavior are anticipated such as experiments.

Experimental analysis of fiber-reinforced laminated composite plates with embedded SMA wire actuators

Shape memory alloy (SMA) wires are effective smart actuators since they provide relatively large actuation force and strain in a very limited space. Embedding SMA wires in flexible laminated composite plates or shells allows for creating active structures for morphing applications. However, the design of such structures is challenging due to the nonlinear thermomechanical coupling of SMA materials, the adhesion of the SMA actuators to the resin, the effect of temperature on the adhesion strength, the heat transfer between the SMA wires and the surrounding laminate, and the convection boundary conditions. This paper presents an experimental analysis of smart fiber-reinforced composite laminated plates with embedded SMA wires, focusing on the relationship between the applied electric current, measured temperature of the SMA wires, and the resulting tip deflection. A temperature-based control method was developed to achieve the required wire temperature and tip deflection as quickly as possible. Results showed that the fiber-orientation angle of the composite plies and the convection boundary conditions have significant effects on the structure’s actuation. With cyclic actuation, damage starts around the heated SMA wires and can grow to cause delamination at areas between neighboring SMA wires and yielding of the matrix material, resulting in permanent deformation.

Effect of Fiber Orientation Angle on Stress Intensity Factor of Composite Plate Using Extended Finite Element Method (XFEM)

This paper presents the effect of fiber orientation angle on the stress intensity factor SIF for carbon epoxy composite plates with single-edge, center, and inclined cracks of varying lengths under tensile load. The stress intensity factor and shape factor were calculated individually for each case, with nine different fiber orientation angles computed using the extended finite element method XFEM concepts. It is found the stress intensity factor increases with increasing crack lengths while the shape factor decreases. In the case of single edge cracks, the SIF increases in the average value reached (173 %) for composite plates with different fiber orientation angles, while in the case of the center crack, the average value of SIF reaches (81 %). It was observed in this study that the increases in stress intensity factor and the decreases in the shape factor with different crack lengths were more stable in the composite plate with a fiber orientation angle of 75°. The higher values of SIF at an angle of 75° are because of the high probability of fiber slippage at 75° due to induced shear stresses in addition to the tensile stresses at the fiber-matrix interface. As a result, the crack tip has a high-stress intensity factor.

Testing and Evaluation of the Oil Absorption Characteristics of Cotton Fibers

ABSTRACT The wetting property to different oil of cotton fibers which come from different regions of China was studied. The surface adsorption characteristics of cotton fibers were characterized. It is found that the oleophilic and hydrophobic properties of all the raw cotton fibers are fantastic and the average static contact angle of cotton fibers to water is 135.36°, but it is less than 51° to different oil such as engine oil, waste oil and salad oil. In the dynamic spreading process, the droplets of water formed on the surface of cotton fibers and the contact angles of all the cotton fibers to water is not changing with time while the oil liquids were quickly and completely spread out almost in 2000 ms. The speed of spreading is closely relevant with the viscosity of oil and the higher oil viscosity, the slower wetting velocity. The contact angles of cotton fibers come from different regions to the same oil liquid had little changes, thus the adsorption velocity difference of cotton fibers to engine oil, waste oil and salad oil was not significant, respectively.