Symmetric Laminates Research Articles

Analytical and finite element analysis of the concrete stress intensity factor with carbon fibers

Concrete is a material with low tensile strength and fracture resistance. One way to improve these properties is through the insertion of synthetic fibers such as carbon fibers into the concrete. This work determined the stress intensity factor for concrete with aligned carbon fibers (laminate) using an analytical model and finite element methods – macro-mechanical analysis of the composite laminate using the ABAQUS finite element package. Symmetrical laminate models were used with carbon fibers ranging from ± 15° to ± 75°. A single-edge notch bending specimen geometry was used to determine the KI of the laminates. The mechanical properties of the laminate were obtained through analytical models of the laminate theory. Results indicate that the fiber angles influence the stress intensity factor. The behavior is practically linear and a strong correlation was observed between the angle of the fibers and the KI through Pearson’s r. The laminate with a fiber angle of ± 75° showed a higher KI value compared to the others (x14 about ± 15°). Comparisons of the analytical and numerical results showed good agreement in the determined KI.

Modelado micromecánico del comportamiento no lineal de laminados angle-ply ante diferentes estados de tensión plana

The non-linear behaviour ocurring in symmetrical angle-ply laminates formed by unidirectional layers of carbon fiber reinforced polymeric matrix (CFRP), known as pseudo-ductility, has been previously studied numerically and experimentally under different uniaxial, biaxial and bending loads. This phenomenon is associated with different mechanisms which affect the mechanical behaviour of the material: large permanent strains, fiber reorientation and matrix cracking. The present study is based on a microscale approach through simulations based on the Finite Element Method (FEM), with the aim of predicting the homogenized response of these laminates subjected to multiaxial in-plane. The micromechanical model is based on a Representative Volume Element (RVE) where Periodic Boundary Conditions (PBC) are applied, together with a non-linear material model of the matrix and a cohesive interface between fibre and matrix. In addition, the implementation of the model is updated to be able to reproduce any plane stress state in a [±45]S laminate, without the need to add other meso- or macroscale models.

The influence of manufacturing on the buckling performance of thin-walled, channel-section CFRP profiles—An experimental and numerical study

The aim of this study is to investigate the influence of manufacturing on the buckling and post-buckling behaviour of thin-walled, columns made from CFRP. Static compression was performed on channel-section profiles with dimensions equal to 80 mm × 38 mm × 240 mm (web × flange × length of profile) composed of an eight-layered symmetric laminate [45/−45/45/−45] and a thickness of 0.92 mm. The samples were manufactured by two distinct methods: 1) conventional lamination of a channel, and 2) by manufacturing a square cross-section and cutting it into two channels. Buckling tests showed that the second method is 2.5 times more material efficient and provides 18 % higher buckling resistance. Moreover, three finite element models were implemented—a​ model that did not include any prestress (residual stresses), and simulations of the channel and square cross sections where residual stresses were included. The conventional channels matched the numerical results of the model which did not include any prestress (nominal error of 1.8%). Whereas the buckling response of the square cross section samples were substantially influenced by the residual stresses (18.1% increase in buckling load). These results have significant implications for the design/production of CFRP channels with enhanced buckling performance.

The Influence of Ply Stacking Sequence on Mechanical Properties of Carbon/Epoxy Composite Laminates.

In this work, the effect of ply stacking sequence of carbon/epoxy laminates subjected to flexural, tensile and impact loading was investigated. Five laminates with different stacking configurations were produced using the hand-laying-up technique. This includes a unidirectional laminate, cross-ply laminates, and quasi-isotropic laminates. Following the autoclave curing process, the responses of the composites to bending, tension and impact force were determined according to ASTM standards, and their corresponding strength, stiffness as well as impact energy were evaluated. Likewise, the flexural failure mode associated with each laminate was characterised using an optical microscope. The unidirectional laminates have higher flexural and tensile strength compared to the cross-ply and quasi-isotropic laminates. Moreover, as a result of material symmetry, the flexural and tensile modulus of symmetric cross-ply laminate improved by 59.5% and 3.97% compared to the unsymmetric counterpart. Furthermore, the quasi-isotropic laminates with absorption energy of 116.2 kJ/m2 and 115.12 kJ/m2, respectively have higher impact resistance compared to other samples.

Analytical and Numerical Solutions to Static Analysis of Moderately Thick Cross-Ply Plates and Shells

This study aimed to provide a static solution to the boundary value problem presented by symmetric (0°/90°/0°) and antisymmetric (0°/90°) cross-ply composite, moderately thick shallow shells and plates (a special case of the shells) subjected to mixed-type unsolved boundary conditions. The boundary-discontinuous double Fourier series (BDM) method, in which displacements are expressed in trigonometric functions, is employed in a well-established framework. The analytical solution obtained using the BDM is compared with the successful integration of the generalized differential quadrature (GDQ) method for the static analysis of composite shells with a roller skate-type boundary condition prescribed on two opposite edges, while the remaining two edges are subjected to simply supported constraints. Comprehensive results are presented in order to show the effects of curvature on the deflections and stresses of moderately thick shallow shells made up of symmetric and antisymmetric cross-ply laminated composite materials. The validity of the proposed model is authenticated through the available HSDT-based literature review, and the convergence characteristics are demonstrated. The changing trends of displacements and stresses are explained in detail by investigating the effect of various parameters such as lamination, material properties, the effect of curvature, etc. Based on the results obtained using the proposed static solution, analytical BDM results were found to be in very close agreement with the numerical GDQ method, especially for symmetric lamination. However, the results obtained using the BDM and GDQ methods for antisymmetric lamination show differences, possibly due to the presence of a discontinuity in the derivatives originating from the bending–stretching matrix in antisymmetric lamination. Important numerical results presented include the sensitivity of the predicted response quantities of interest to material properties, lamination, and thickness effects, as well as their interactions. The results presented here may also serve as benchmark comparison points with numerical solutions such as finite elements, boundary elements, etc.

Castor Oil-Based Polyurethane/S2 Glass/Aramid Hybrid Composites Manufactured by Vacuum Infusion.

This study evaluates the hybridization effect of S2-glass/aramid on polyurethane (PU) composites produced by vacuum infusion. Different laminates were produced with similar thickness (around 2.5 mm), using, as reinforcement, only aramid fabrics (five layers, named as K5) or only S2-glass fabrics (eight layers, named as G8). Furthermore, hybridization was obtained by manufacturing symmetrical hybrid inter-ply laminates, with four S2-glass layers and two of aramid, (G2K)S and (KG2)S. The mechanical response of the laminates was evaluated in tensile, interlaminar shear strength, dynamical mechanical analysis and quasi-static indentation tests, and related to their morphological characteristics. The main results show that the pure glass composites presented less voids, but a higher density as well as higher tensile stiffness and strength. The aramid laminates showed a high capability for absorbing impact energy (ca. 30% higher than the pure glass laminates), and the hybrid laminates had intermediate properties. More importantly, this work shows the possibility of using a polyurethane matrix for vacuum infusion processing, effective even for aramid/S2-glass hybrid composites with thermoset polyurethane resin. This study is therefore promising for impact absorption in applications such as protective armor. The studied hybrid laminate may display a suitable set of properties and greater energy absorption capability and penetration resistance for impact applications.

Influence of shear direction on the buckling of CFRP composite perforated plate

The shear buckling performance of CFRP composite perforated plates taking due account of the influence of the flexural anisotropy is examined in this paper using the finite element analysis procedure. Typical laminated composite lay-up causes many complexities but can easily be dealt with in the numerical simulations. The results from the finite element models are shown to agree favourably with the buckling curves from the independent simulations using finite strip method of analysis. Results in the paper clearly show that care should be taken seriously for the case of composite structural members having opening in their webs. Depending on the nature of the applied shear loading, openings, and varied symmetric angle ply laminates, the buckling behavior and capabilities have also been altered.

A bi-stable nonlinear energy sink using the cantilever bi-stable hybrid symmetric laminate

This paper develops a new bi-stable nonlinear energy sink (BNES) only consisting of the cantilever bi-stable hybrid symmetric laminate (BHSL) and tip masses. This BNES has advantages of light weight, simple and reliable structure, since it does not need external devices or magnets to maintain its bi-stable characteristic. A finite element model (FEM) is developed to perform static and dynamic analyses of a harmonically excited linear oscillator coupled with BNES. An equivalent theoretical model is developed to model the coupled system based on the relationship between the restoring force and the displacement of BHSL. The Runge-Kutta method is used to perform direct numerical solutions. Different types of the steady-state response for BNES contain the local and global periodic motions, the local and global strongly modulated responses and chaos, while the primary object exhibits the periodic motion and the strongly modulated response. The effects of the excitation amplitude, the tip mass of BNES, the lay-up design and the length of BHSL are considered on the dynamic responses and vibration suppression efficiency of BNES. The results show adjusting these parameters and lay-up designs can improve the vibration suppression efficiency of BNES. In addition, the experimental prototype is prepared and verifies the rightness of the finite element model and theoretical model.

Damage evolution and failure mechanism of asymmetric composite laminates under low-velocity impact and compression after impact

The damage mechanisms of the balanced symmetrical laminates under low-velocity impact (LVI) and compression after impact (CAI) loading conditions are not fully applicable to composite stiffened panels. However, studies on LVI and CAI damage evolution and failure mechanism for asymmetric composite laminates are very rare, which poses challenges to the theoretical study, strength prediction, and application of composite structures, and increases the risk of sudden failure under load. In this study, the damage evolution and failure mechanisms of asymmetric composite laminates under LVI and CAI loading conditions were studied experimentally and numerically. Ultrasonic phased array C-scan technique was used to analyze damage state, damage size, and delamination damage induced by LVI under different impact energies in impact tests. Moreover, a three-dimensional digital image correlation (3D-DIC) technique was employed to monitor the evolution of full-field displacement and strain in the asymmetric composite laminates during the CAI tests. A three-dimensional damage model considering the interaction among the interlaminar delamination damage, intralaminar matrix damage, and intralaminar fiber damage was proposed, and an interface-based cohesive behavior embedded framework in ABAQUS/Explicit was used to define and capture the interlaminar damage. The damage initiation, evolution, and propagation behaviors of different damage modes were simulated to study the complex damage and failure mechanisms of the asymmetric laminates in the LVI and CAI processes. The relationships among the different impact energies and the impact damage modes, delamination morphologies, and compression damage propagation and failure modes were discussed.

Application of Aeroelastic Tailoring for Load Alleviation on a Flying Demonstrator Wing

This article presents the application of aeroelastic tailoring in the design of wings for a flying demonstrator, as well as the validation of the design methodology with flight test results. The investigations were performed in the FLEXOP project (Flutter Free Flight Envelope Expansion for Economical Performance Improvement), funded under the Horizon 2020 framework. This project aimed at the validation of methods and tools for active flutter control, as well as at the demonstration of the potential of passive load alleviation through composite tailoring. The technologies were to be demonstrated by the design, manufacturing and flight testing of an unmanned aerial vehicle of approximately 7 m wingspan. This article addresses the work towards the load alleviation goals. The design of the primary load-carrying wing-box in this task is performed using a joint DLR–TU Delft optimization strategy. Two sets of wings are designed in order to demonstrate the potential benefits of aeroelastic tailoring—first, a reference wing in which the laminates of the wing-box members are restricted to balanced and symmetric laminates; second, a tailored wing in which the laminates are allowed to be unbalanced, hence allowing for the shear–extension and bending–torsion couplings essential for aeroelastic tailoring. Both designs are numerically optimized, then manufactured and extensively tested to validate and improve the simulation models corresponding to the wing designs. Flight tests are performed, the results of which form the basis for the validation of the applied aeroelastic tailoring approach presented in the article.

Direct-write 3D printing of UV-curable composites with continuous carbon fiber

Continuous fiber-reinforced polymer composites, with their superior combinations of high stiffness, high strength, lightweight, and corrosion resistance, have been leading contenders in various applications ranging from aerospace to ground transportation. The integration with 3D printing allows the composite products to be customized quickly and fabricated inexpensively to meet unique specifications. However, the material-process-property relationships of 3D printed thermoset composites with continuous fiber are insufficiently explored in the field. In this work, a cost-effective 3D printing method is developed based on the direct ink writing method to print UV-curable composites reinforced with continuous carbon fiber. During the printing, the fiber tow is impregnated with an acrylate ink inside the printer head and then extruded onto the printer bed, where it is cured upon UV irradiation. The influences of different material and processing variables, such as the resin viscosity, nozzle size, printing speed, and substrate temperature, on the quality and mechanical properties of composites, are investigated. The porosity, stiffness, and strength of printed symmetric laminate are also examined. Finally, the 3D printing of composite structures and the conformal coating of curved surfaces along a defined printing path are demonstrated. The findings reported in this work could contribute to the rapid design and manufacturing of composite components with unprecedented mechanical properties and emerging functionalities for the automotive, defense, and aerospace industries.

The effect of load eccentricity on the compressed CFRP Z-shaped columns in the weak post-critical state

The study investigated short, thin-walled Z-shaped carbon-epoxy laminate columns. Two multi-layer composite lay-up configurations were tested [0/45/-45/90]s and [90/-45/45/0]s, each consisting of eight symmetric laminate layers. The Z-columns were loaded in compression, and the loading mode included the scenario of force application eccentric to the center of gravity of the column’s cross-section. The modeled boundary conditions corresponded to the ball-jointed support at the end sections of the column. The study set out to determine the effect of loading eccentricity on the buckling mode, the values of the buckling load (the perfect structure), and the critical force (the structure with initial imperfections). The critical force of the real structure was established using the approximation method, based on experimentally determined post-critical equilibrium paths of the structure. For the numerical finite element analysis (FEM), Abaqus software was employed. In the first step, the FEM solved the eigenvalue problem, which lead to establishing the mode of stability loss and the determination of the corresponding bifurcation load for the Z-column subjected to axial and eccentric loading. The second stage of analysis focused on the nonlinear behavior of the structure with initial imperfections. The critical force was derived from the results of approximation based on the numerical post-critical equilibrium paths. The experimental data then served as the base for the validation of the developed numerical models. The findings enabled determining the effect of the compressive load eccentricity on the buckling mode and the critical force values. The project/research was financed in the framework of the project Lublin University of Technology-Regional Excellence Initiative, funded by the Polish Ministry of Science and Higher Education (contract no. 030/RID/2018/19).

Wind-induced vibration behavior of bistable hybrid symmetric laminate

Bistable composite laminates have the potential advantage in the fields of wind energy harvesting and deformable wings, which involve many fluid–structure interaction issues. This paper presents the fluid–structure interaction analysis of a cantilevered bistable hybrid symmetrical laminate (BHSL) in the uniform wind. In this work, a finite element model based on the Lattice Boltzmann Method (LBM) is used to analyze the wind-induced response of the BHSL and its variations with respect to wind speed and laminate length. Then, the wind-induced vibration behavior of BHSL is verified by wind tunnel tests. The finite element analysis (FEA) results are in good agreement with the experimental results. The results show that as the wind speed increases, the BHSL transitions from a single-well vibration response to a cross-well vibration response. The wind-induced vibration analysis of BHSL will provide analytical methods for its application in deformable wings and energy harvesting for wind-induced vibration.

Investigation of the effect of steel fiber (200 mesh size) hybridization on properties of steel/glass fiber and steel/basalt fiber reinforced epoxy composite laminates

AbstractSteel fiber is the most common metal fiber used due to its cost‐effectiveness, high performance, and availability despite its heavyweight. This study is an attempt to evaluate the mechanical properties of steel/glass fiber and steel/basalt fiber‐reinforced epoxy composites. The symmetric hybrid laminates were produced by replacing the innermost 1, 2, 3, and 4 layers of steel fiber (200 mesh size) with basalt and glass fiber layers. The specimens were subjected to tensile, flexural, and Charpy impact tests in accordance with relevant ASTM standards. Moreover, fracture surfaces were analyzed, and the micrographs were obtained using a scanning electron microscope. The results showed that a high improvement in tensile strength was achieved with BS1–E (1 layer steel mesh–8 layers basalt) and GS1–E (1 layer steel mesh–8 layers glass) hybrid composites, with an increase of 528% and 233%, respectively, compared to steel fiber reinforced epoxy composites. Similarly, BS1–E and GS1–E hybrid composites showed the highest flexural strength increase of 82.2% and 66.8%, respectively, compared to steel fiber reinforced epoxy composites. Consequently, the potential to hybridize steel fiber with glass fiber and basalt fiber could create new materials with unique physical structures and synergistic effects on mechanical properties.

Numerical study on stability of composite cutter bar milling system in rotating coordinate frame

This paper studies the chatter stability of composite cutter bar milling system in rotating coordinate frame. The main contribution of this paper is establishing a continuous distributed chatter analysis model for a composite cutter bar milling system in rotating coordinate frame. The stability of the milling system with a rotary symmetric dynamic cutter bar is predicted using the semi-discrete time domain method. The effects such as internal damping, external damping, and symmetrical and asymmetric laminates on the stability of the milling system were analysed, and the results were compared between rotating and fixed coordinate frames. The results are consistent for symmetrical cutter bars in both the rotating and fixed coordinate frames. A new chatter instability zone appears at high rotating speeds due to the material internal damping of the rotating composite cutter bar.

A quasi-zero-stiffness vibration isolator using bi-stable hybrid symmetric laminate

The quasi-zero-stiffness (QZS) vibration isolator is usually composed of positive and negative stiffness elements in parallel. The negative stiffness element usually requires specific constraint boundaries to form negative stiffness characteristics, which cannot meet the lightweight design of spacecraft structures. So the bi-stable hybrid symmetric laminate (BHSL) is presented as a negative stiffness element. A finite element model (FEM) is developed to carry out static and dynamic analyses of this vibration isolator. An equivalent theoretical model is developed based on the restoring force–displacement curve of BHSL. The approximate analytical solutions and direct numerical solutions are obtained by employing the averaging method and the Runge-Kutta method, respectively. Different types of the steady-state response are obtained, namely the symmetrical multi-harmonic response, the asymmetric multi-harmonic response and the single-harmonic response. There exists a small gap between the analytical solutions and the Runge-Kutta solutions or the FEM results only at the low frequency excitation due to the super-harmonics. The displacement transmissibility is used to quantify the vibration isolation performance of this vibration isolator. The experiment is designed to verify the theoretical and FEM models from static and dynamic analysis perspectives. The results show adjusting geometric parameters and lay-up designs can improve the vibration isolation performance.

A variational approach for accurate prediction of stress and displacement fields and thermo-elastic constants in general symmetric laminates containing ply cracking and delamination under general triaxial loading

Delamination induced by ply cracking is an important damage mechanism that results in stress redistribution and degrades both the in-plane and out-of-plane laminate properties. In this work, a novel variational model is first developed that accurately predicts stress and displacement fields in arbitrary symmetric laminates, containing uniformly spaced ply cracks in a single orientation with delaminations on the interfaces between the plies at the tips of ply cracks, subject to general triaxial loading and thermal residual stresses. The model is then used to predict the dependence of the in-plane and out-of-plane laminate thermo-elastic properties on ply crack density and delamination length. The results are extensively compared with those obtained from refined finite element methods and available experiments, showing excellent accordance.

Effect of Non-Uniform Fibre Distribution along Thickness and Non-Uniform Ply Thicknesses on Frequencies of Symmetric Angle-Ply Laminates

Effect of Non-Uniform Fibre Distribution along Thickness and Non-Uniform Ply Thicknesses on Frequencies of Symmetric Angle-Ply Laminates

Computational model for predicting the low-velocity impact resistance and tolerance of composite laminates

We present a numerical model for predicting the low velocity impact resistance and tolerance of multidirectional carbon fiber-reinforced composite laminates made of non-crimp fabric. A finite element model is developed wherein the heterogeneous plies are replaced by equivalent homogeneous orthotropic plies. The low-velocity impact of a carbon–epoxy laminate is investigated using an explicit finite element model. Intralaminar failure and damage is evaluated using the 3D Hashin failure criteria and a surface-based cohesive behavior is implemented to capture the delamination between the plies. Following the low velocity impact, the finite element model is subjected to axial compression to investigate the compressive residual strength after impact, which is a measure of damage tolerance. The computational model is used to investigate the impact resistance and tolerance of a 24-ply multidirectional symmetric laminate reinforced with carbon fiber non-crimp fabric. The low velocity impact response and the compressive residual strength after impact are validated with experimental data for different levels of impact energy. It is found that the computational model can predict the impact resistance and damage tolerance for impact energies up to 50 J.

Study the internal cracks effect on vibration of laminated composite square plates

The study of cracks behaviour in a composite plate is of significant importance in the dynamics of the Mechanical parts in order to avoid design failures due to resonance or high amplitude vibrations. In this paper, a square glass-epoxy composite plate is adopted. The plate has four layers with symmetric and asymmetric lamination. Assuming the cracks are profound as defects. The results were obtained by using a numerical solution of mechanical APDL from ANSYS. It has been found for different boundary conditions that the rank of natural frequencies is decreased by increasing the crack ratio due to the reduction of the plate’s stiffness, whereas the crack direction has no mentioned effect for a small angle of rotation. The accuracy of results is verified by comparing a single case of the current work with other previous investigations. Evaluate the influence of the crack length ratio, angle of the crack rotation, boundary conditions and lamination angles on the natural frequencies of the square composite plate with glass-epoxy materials.