Search

In this article, wave propagation in a one-dimensional (1-D) composite periodic frame structure is analyzed using spectral finite elements (SFE) method together with Bloch's theorem. Each element in the periodic frame structure is modeled as a first-order shear deformation theory (FSDT) beam element and wave equations for the beam elements are derived using FSDT considering axial, flexural, and shear deformations. Next, these equations are solved using the frequency domain SFE method to obtain an elemental dynamic stiffness matrix which on assembly gives the dynamic stiffness matrix for the unit cell of the periodic structure. A polynomial eigenvalue problem is formulated thereafter using Bloch's theorem to evaluate the dispersion coefficients and wave amplitude ratios. Finally, the entire periodic frame is modeled as homogenized two-noded elements capturing the wave response of the PS with a drastic reduction in computational cost. The results obtained using the present method are validated with finite element simulation using ANSYS mechanical Ansys Parametric Design Language (APDL). The frequency band gaps observed in the frequency domain responses are investigated and corroborated with those predicted by the dispersion relations. This is followed by a detailed parametric study on the influence of different parameters on the band gap characteristics. The present method provides a scheme of wave propagation analysis of composite periodic frames with substantial computational efficiency. [ABSTRACT FROM AUTHOR]

This paper reports a detailed numerical investigation on the buckling aspects of laminated composite shell panels of three forms (cylindrical, spherical and hyperbolic paraboloid) with five support conditions exposed to linearly varying in-plane edge load employing eight nodded isoparametric finite element formulation. The impacts of different parameters including ply orientation, load factor, shell forms, aspect ratio, modulus ratio, curvature ratio, width-to-thickness ratio and angle of lamination on the buckling load of shell panels are examined. It is found that the various parameters addressed in this study have a remarkable impact on the buckling phenomena of laminated composite shell panels. Further, a comparison is made showing the effects of five types of compressive edge loads like uniform, triangular, parabolic, partial edge load and point load on the buckling phenomena of laminated shell panels with respect to five support conditions. [ABSTRACT FROM AUTHOR]

In this study, the mechanical performances of glass fiber-reinforced notched and pin-connected composite plates were investigated experimentally and numerically. For this purpose, composite plates with a circular hole, semicircular double-edge notched, U-edge notched, and single and double pin joints were prepared from [ 0 ° ] 8 layer glass fiber composites. Tensile tests were carried out on the obtained specimens. The effect of notch type, number of pins, and position of pins on plate damage load and type was investigated for linear and non-linear material behavior. Progressive failure analysis was performed using the Hashin damage criteria. Subprogram codes were written in the Ansys program using the finite element method. According to the obtained data, it was determined that the type of notch and the number of pins have a significant effect on the damage loads of the plates and the behavior of the material is important in terms of convergence to the experimental results in numerical solutions. In single-pin composites, the type of damage changed from net-tension to shear out as the pin approached the free edge of the plate. It was observed that the distance between the pins did not have any effect on the damage type of the composites in the double-pin joint structure. Compared to single-pin joint composites, double-pin joint composites were found to carry a maximum of 34% more damage load. The convergence rate of experimental and numerical data was obtained as a minimum of 92.1% for nonlinear material behavior and a minimum of 73.4% for linear material behavior [ABSTRACT FROM AUTHOR]

Composite driveshafts have emerged as a potent substitute for traditional driveshafts because of their excellent strength-to-weight and stiffness-to-weight ratios. At the same time, usage of multi-walled carbon nanotubes (MWCNTs) as a reinforcement has gained a great momentum due to their superb mechanical, electrical, and thermal characteristics. In this work, a micromechanical model combining the rule of mixtures and the Halpin-Tsai (H-T) model was used to calculate elastic constants of MWCNTs-added carbon fiber reinforced epoxy resin. This micromechanical model considers the effect of agglomeration, aspect ratio, waviness, and random orientation of MWCNTs. Elastic constants of MWCNTs/epoxy resin calculated by using micromechanical model was compared by experimental results available in the literature. Moreover, finite element analysis (FEA) was carried out to predict the critical torsional buckling load of composite driveshafts for various MWCNTs concentrations and fiber orientation angles. The FEA results were compared with the results obtained theoretically. The results showed that Young's modulus of MWCNTs/epoxy resin calculated by using the micromechanical model follows the experimental findings. When compared to pure carbon fiber-reinforced epoxy resin, E1, E2, E12, and G23 (elastic constants of composite lamina) showed improvements of 0.66%, 27.80%, 49.02%, and 37.50%, respectively, in the case of 10vol.% MWCNTs addition. The ply orientation angle has a more dominant effect on Tcr than the Doi: 10.24012/dumf.1336638 MWCNTs concentration. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Considering the effect of different moulding processes, this paper studies the curing deformation of laminated composites of stiffened panel structures. The curing deformation is assessed after the stiffened panel structures of carbon fiber/epoxy resin composites are created through vacuum bag pressing process by co-curing, co-bonding, and secondary bonding and curing. For different moulding processes, by using an instantaneous linear elastic curing constitutive model and taking residual curing stresses as pre-stress, a finite element simulation method considering different curing methods is proposed, and is also compared and verified with the experimental results. The influences of factors such as moulding processes, layup methods and stiffener thickness on the curing deformation of the stiffened panel structures are analyzed. The results show that moulding processes, layup and stiffener thickness have a great influence on the curing deformation of the structures. The deformation of composite stiffened panel structures decreases considerably by increasing stiffener thickness and adopting an appropriate moulding process through a reasonable layup. [ABSTRACT FROM AUTHOR]

This paper presents an innovative methodology employing the One-dimensional Convolutional Gated Recurrent Unit neural network (1D-CGRU) algorithm for the analysis of laminated composites using the Refined Zigzag theory (RZT). The RZT methodology is utilized to assess laminated plate structures and generate essential data, forming the basis for training the 1D-CGRU model. The synergistic application of RZT and 1D-CGRU demonstrates exceptional global–local accuracy in predicting the mechanical behavior of laminated composite plates. For efficient data generation, RZT not only provides high precision, but also exhibits computational efficiency, making it suitable for finite element simulations with a C0-continuous kinematic approximation. Additionally, the 1D-CGRU model integrates the strengths of a One-dimensional Convolutional Neural Network (1D-CNN) for spatial feature extraction and dimensionality reduction, coupled with a Gated Recurrent Unit (GRU) network for discerning temporal relationships and mapping them to the target domain. Furthermore, quantitative accuracy measurements, including Mean Squared Error (MSE), Root Mean Squared Error (RMSE), and Mean Absolute Error (MAE), are used to validate the superior performance of the 1D-CGRU model compared to other surrogate models. For angle-ply and cross-ply composite laminates, the 1D-CGRU model achieves remarkable accuracy (98.15% and 99.45%, respectively) with low RMSE values. These results highlight the potential of the proposed framework to enhance predictive analysis for laminated composite structures, offering valuable insights for engineering applications and design optimizations. [ABSTRACT FROM AUTHOR]

Laminated composite honeycomb cellular core sandwich panels are widely utilized in various industries due to their exceptional stiffness-to-weight ratio and strength characteristics. Current analytical models often simplify honeycomb cores as homogenized continua, effectively predicting stiffness but falling short in capturing crucial failure modes, particularly shear buckling of honeycomb core walls. Existing theoretical studies on shear buckling are limited to isotropic materials and specific honeycomb geometries. While numerical models can simulate cell wall buckling, their computational demands render them impractical for large structures employing sandwich panels. This paper introduces a novel, simplified semi-analytical approach that accurately predicts the shear buckling load of laminated composite honeycomb cellular cores. The model accounts for bend-twist coupling effects and rotational restraints at laminate wall boundaries. To validate the proposed approach, predictions are compared with finite element analysis results for hexagonal honeycomb cores and cores of varying shapes, incorporating diverse fibre lay-up configurations. The findings demonstrate excellent agreement between the proposed approach and finite element analysis, indicating its reliability in predicting shear buckling. This research addresses the gap in existing methodologies by offering a practical and efficient tool for predicting shear buckling in laminated composite honeycomb cores, extending applicability beyond isotropic materials and specific honeycomb geometries. The proposed approach holds promise for optimizing the design and structural integrity of sandwich panels, impacting industries relying on these lightweight and high-performance structures. [ABSTRACT FROM AUTHOR]

• FMC is used for translaminar fracture toughness characterisation. • Glass fibre/PA6 laminated composites by varying the thickness are considered. • The experimental campaign is numerically simulated. • Considerations on fracture toughness dependence on specimen sizes are provided. This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness. [ABSTRACT FROM AUTHOR]

• Study focuses on analyzing the free vibrations of doubly curved laminated shells. • C ° finite element based on MHOZT is used for the analysis. • Model incorporates higher order displacement kinematics and accounts for both transverse normal and shear strains. • The formulation includes extended thickness criteria. • Numerical results closely resemble those from 3D elasticity solutions. In this study, the analysis of free vibrations for doubly curved laminated shells has been performed with modified higher order zigzag theory (MHOZT). This approach incorporates higher order displacement kinematics and considers both transverse normal and shear strains. The model assumes that the displacement fields within the plane are a combination of a global cubicly varying field and a locally zigzag linearly varying field. On the other hand, the out-of-plane displacement field varies quadratically with shell thickness coordinates. This formulation considers extended thickness criteria, ensuring the inclusion of the ratio of thickness to the radius of curvature (z / R) in strain displacement relations. Additionally, this model guarantees that there is no transverse shear stress at the extreme surfaces of the shell and that inter-laminar shear stress at interfaces is continuous. To implement this formulation effectively, a C ° finite element is used. The outcomes are compared against a three-dimensional (3D) elasticity solution, as well as other pertinent results available in the literature. The suggested model accurately predicts the vibration characteristics of laminated shells, showing good agreement with the 3D elasticity solutions. [ABSTRACT FROM AUTHOR]

This study presents a free vibration analysis of three different curved laminated composite plates having end-to-end decomposition under fixed opposing straight edges. The curved structures have been mathematically modeled by employing the Classical Laminated Plate Theory and the Finite Element Method to perform the location-based effect of decomposition. Besides, the relation among the decomposition, curvature characteristics, and stacking sequences is examined in terms of natural frequencies. For this purpose, the endto- end decompositions are defined in two different levels and re-positioned along the curved edge for each vibration analysis. The frequency ratio is obtained by proportioning the natural frequency of the damaged structure to that of the healthy structure and considered to interpret the effects of the decomposition location. Cross-ply and angle-ply structures having elliptic, circular, and parabolic curvatures are considered. It is concluded that the effect of the end-to-end decomposition on the natural frequencies varies to its level, the stacking order, and the bending regions of the relevant mode shape. [ABSTRACT FROM AUTHOR]

This paper reports for the first time the experimental investigation on the free vibration characteristics of angle-ply laminated composite stiffened plates along with the numerical investigation. The natural frequencies of these plates are computed experimentally using an FFT analyzer and numerically by employing the finite element method with combination of isoparametric nine nodded plate and three nodded beam elements. Angle-ply laminated stiffened plates are fabricated using woven glass fiber fabrics and epoxy by hand layup technique. The effects of various support conditions; number, orientation and types of stiffeners; aspect ratios of plates and different fiber orientations on the fundamental frequencies of the angle-ply laminated stiffened plates are investigated. These parameters significantly influence the natural frequencies. It is found that there is a very good agreement observed between the fundamental frequencies obtained from both experimental and numerical investigation. Mode shapes are also presented for angle-ply laminated square stiffened plates with three different support conditions to justify the trend of increasing/decreasing of the modal frequency with the addition of stiffeners. It is observed that the enhancement of the frequencies of the angle-ply plates due to addition of stiffeners is influenced significantly by the position of stiffeners and consequently mode shapes. As the research on the free vibration behavior of angle-ply stiffened plates with experimental analysis is very rare, this study can be considered as the benchmark for future research. [ABSTRACT FROM AUTHOR]

Propagation of Lamb waves in both laminated and functionally graded (FG) composites is analyzed. Anomalous dispersion at high frequencies is observed revealing substantial discrepancy in the high frequencies asymptotes for quasi-flexural and quasi-symmetric fundamental modes. The applied methodology is based on a variant of sextic complex formalism. [ABSTRACT FROM AUTHOR]

Composites have been extensively used in the modern era in wide range of applications. This article deals with the study of vibration characteristics of natural fiber reinforced composite beam in which Aloe vera fiber is reinforced in epoxy matrix and is used in combination with glass-epoxy. Finite element method of analysis is adopted using Ansys software. Effects of several parameters like laminate stacking sequence, support conditions, material hybridization, and number of layers, etc. on the natural frequency of natural fiber reinforced composite beam are analyzed. Experimental study on Aloe vera fiber reinforced composite beam is also conducted for validation. [ABSTRACT FROM AUTHOR]

In this study, the composite parts subjected to tensile load were combined with a doubleacting adhesive connection and analyzed using the 3D finite element method (FEM). The joint design is important to ensure that the joint is durable, does not take up too much space and has a long service life. In the analysis, carbon / epoxy (AS4 / 3501-6) composite parts with different orientation angles were used and DP410 was used as adhesive. Models for numerical analysis were created using ANSYS 14.5 package program. Finite element analyzes were performed to determine the damage loads. In general, because the damages occur in the adhesive region, the stresses in all directions on the adhesive, shear stresses, von-Mises stress and peel stresses were obtained at the specified failure loads. As a result, the effects of orientation angles, overlap dimensions of the bonded area and adhesive layer were investigated. The most effective parameters were determined for the composite parts joined with embedded double-acting adhesive. Furthermore, it is stated that embedded adhesive connection is important for industrial applications. [ABSTRACT FROM AUTHOR]

In this research, buckling behavior of rectangular plates of symmetric and antisymmetric laminated composite having centered circular hole under in-plane static loadings is analyzed with the aid of first shear deformation theory and the finite element method is used to find critical loads. The presence of hole may cause redistribution of stresses in plates with reduction of stability. The aim of the current paper is to find critical buckling load. The loads depend on many parameters like geometric aspect ratios (a/b) and (d/b), plate thickness (t), diameter of the circular hole (d), orientation of ply and boundary conditions. Numerical simulations for various boundary conditions obtained are shown in tables and graphical forms and compared with each other. [ABSTRACT FROM AUTHOR]

Laminated composite shells are used as roofing units in Civil Engineering applications and hypar shells are most popular because of their ease of construction and aesthetic elegance. The aim of the present study is to analyse higher mode free vibration of composite hypar shells. The purpose is to obtain some design guidelines for the practising engineers dealing with such structures. The methodology adopted here is the finite element method based on first order shear deformation theory. Effect of cross curvature is included in the formulation. The isoparametric finite element consists of eight nodes with five degrees of freedom per node is considered. Three noded beam elements with four degrees of freedom per node are used for stiffeners. The generalised Eigen value solution is chosen for the un-damped free vibration analysis. The formulation is validated first by solving standard problems from literature and then new results are obtained for varying boundary conditions, ply orientation and curvature of the shell. The first five modes of natural frequency are presented. In general, it is observed that fundamental frequency increases with the increase in the number of support constraints. There are, however, few departures from this general tendency when two shells of different laminations are compared. Sometimes lamination order may influence the frequency of stiffened composite shell with cut-out more significantly than its boundary conditions. Symmetric lamination exhibits reasonably good performance and may be adopted for all practical purposes. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the eigenfrequencies of rotating laminated composite (LC) and sandwich microbeams with different boundary conditions (BCs) are studied. The size-dependent variational formulation of the problem is obtained based on the Modified Couple Stress Theory (MCST) by employing a transverse shear-normal deformable beam theory and finite element method (FEM) formulation. The convergence and verification studies of the developed code are carried out and computed results in terms of dimensionless fundamental frequencies (DFFs) are compared with the available ones in the open literature. Various BCs, aspect ratios, fiber orientation angles, thickness to material length scale parameter (MLSP) ratios, core thickness to face layer thickness ratios, dimensionless rotation speeds (DRSs) and hub ratios are employed for the extensive analyses. It is found that the DFFs of the LC microbeams are highly affected by the small size effect accompanying with the orthotropy ratios, DRSs, hub ratios and fiber orientation angles. The effect of the small size on the DFFs of the rotating clamped-clamped LC microbeams is more pronounced than on those of the rotating clamped-free LC microbeams. The hub ratio has a significant effect on the DFFs of the rotating LC microbeams than the rotation speed. [ABSTRACT FROM AUTHOR]

Abstract This paper develops a formulation for displacement-only beam elements based on isogeometric analysis, with intended application to laminated composite members. The main purpose of the current study was to overcome some deficiencies of commonly used beam theories, such as shear-locking, the lacking relevance of isotropic materials for multi-layer composites, the incompatibility with other continuum elements, and the limited continuity in interpolation. A bi-variable non-uniform rational B-spline (NURBS) beam element with complete plane-stress elasticity terms and geometrical expressions was developed. Shear-locking, interlaminar stresses, the deep-beam situation, and vibration features were evaluated for several aspect ratios, ply orientations, and NURBS degrees, in order to verify the efficiency and accuracy. h -, p - and k -refinements were used to improve the displacement field. The validity of the solutions was measured based on results from plane-stress finite element analysis, and compared to the alternative Carrera unified formulation. Results show that the isogeometric displacement-only beam theory can provide the interlaminar stress distribution, gives high accuracy for mid and high-range eigen-frequencies, and avoids the shear-locking phenomenon. Highlights • A displacement-only beam element was formulated based on an IGA-approach. • In-plane elasticity was used for a bi-variate NURBS form. • h-, p- and k-refinements were studied for improving results. • Interlaminar stresses in a laminated composite beam could be evaluated. • Formulation gave good accuracy for static and vibration problems. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the Wave Finite Element (WFE) approach based on the finite element model and periodic structure theory, is extended in time domain to study the impact damage behavior of laminated composite structures. The targeted application is the damage detection of laminated E-glass/epoxy beam subjected to a transverse low velocity impact. The proposed strategy consist of a dynamic stress analysis using WFE approach and a damage analysis which is performed using Tsai–Wu quadratic failure and Hashin's failure criteria. Numerical simulations and comparison with the classical finite element prediction were performed to verify the high accuracy of the present method which provides extremely accurate solutions with much smaller system size and lower computational cost. [ABSTRACT FROM AUTHOR]

Abstract We in this study present a mixed solid-shell finite element formulation for laminated shell analysis. With the commonly adopted truncations applied to the strain components and the Jacobian determinant, a generalized stiffness matrix is established. Discrete shear gap (DSG) technique together with assumed natural strain (ANS) method is employed in order to alleviate shear locking and trapezoidal locking. Stiffness matrix formulation is analytically calculated based on the edge-based cell backgrounds, which result in simple and efficient computation. The proposed formulation does not require using cross-diagonal meshes, which can be an obstacle for several existing three-node degenerated shell elements. This aspect makes the present method much more appealing than others through examples tested. Numerical validations show that the present method performs well for both structured and unstructured triangular meshes. [ABSTRACT FROM AUTHOR]

In this study, geometrically nonlinear dynamic behavior of laminated composite super-elliptic shells is investigated using generalized differential quadrature method. Super-elliptic shell can represent cylindrical, elliptical or quasi-rectangular shell by adjusting parameters in super-ellipse formulation (also known as Lamé curve formulation). Geometric nonlinearity is taken into account using Green–Lagrange nonlinear strain–displacement relations that are derived using differential geometry and theory of surfaces. Transverse shear effect is considered through the first-order shear deformation theory. Equation of motion is obtained using virtual work principle. Spatial derivatives in equation of motion is expressed with generalized differential quadrature method and time integration is carried out using Newmark average acceleration method. Several super-elliptic shell problems under uniform distributed load are solved with the proposed method. Effects of layer orientations, boundary conditions, ovality and ellipticity on dynamic behavior are investigated. Transient responses are compared with finite element solutions. [ABSTRACT FROM AUTHOR]

Abstract The current work deals with the assessment of dynamic stability behavior of laminated composite and sandwich plates subjected to in-plane static and periodic compressive loads based on a recently developed zigzag theory by the authors. This theory satisfies the traction-free boundary conditions at top and bottom surfaces of the laminate as well as the inter-laminar stress continuity at layer interfaces. Also, it obviates the need of artificial shear correction factor. The theory is based upon shear strain shape function assuming non-linear distribution of transverse shear stresses. An efficient C0 continuous, eight-noded isoparametric element with seven field variables is employed for the dynamic stability analysis of laminated composite and sandwich plates. The boundaries of principal instability domains are obtained following Bolotin's approach and are represented either in the non-dimensional load amplitude-excitation frequency plane or load amplitude-load frequency plane. A series of numerical examples on the dynamic stability analysis of laminated composite and sandwich plates are studied to demonstrate the effects of modular ratio, span to thickness ratio, boundary conditions, thickness ratio, static load factor and various load parameters on the principal instability regions. The predicted results are compared with the available existing results in order to ensure the performance of the proposed model. [ABSTRACT FROM AUTHOR]

Analytical electromechanical solutions to the interfacial stresses in the adhesively bonded composite joints integrated with piezoelectric actuator are presented in this paper within the framework of full layerwise theory. Two lap joints with and without interfacial void are studied, and the edge effects near the end-points of the bondline as well as around the void are investigated. Sets of fully coupled governing equations of equilibrium are derived using the principle of minimum total potential energy and are simultaneously solved using the state space approach. It was observed that the edge effects results in significant interfacial stress concentrations around the void edges that may cause propagation of microcracks and debonding. [ABSTRACT FROM AUTHOR]

A new numerical method for the waves-damage interaction and the post-failure response analysis of laminated composite beams under an impact load is presented in this paper. The studied structure is made of E-glass/epoxy and it is decomposed in undamaged and damaged substructures. The material properties in the damaged substructure are modified according to sudden material property degradation rule. The damage describes the creation of micro-discontinuities in the structure during the loading. The enhanced formulation considered in this paper can be used to target this problem. The numerical method combines the Finite Element (FE) method to model the discontinuous regions, impact region and damaged region, and the wave finite element (WFE) to accurately model the periodic substructures (intact substructures). This hybrid method enables the calculation of the waves-damage interaction scattering coefficients and the response of the whole structure in both the frequency as well as in the time domain and it provides the reduction of the computational cost of analyses in space and time. Several numerical simulations have been performed, first to validate the accuracy of the results predicted by the proposed formulation and second to investigate the damage effect on the dynamic behaviour of the structure. [ABSTRACT FROM AUTHOR]

Vibration characteristics of laminated composite beams with magnetorheological (MR) layer are investigated using layerwise theory. In most studies, shear strain across the thickness of MR layer has been considered as a constant value, which does not precisely describe the shear strain. In this study, layerwise theory is employed to develop a finite element formulation to investigate MR-laminated beams. Experimental tests under different magnetic fields are carried out to verify the numerical results. Layerwise numerical results are compared with the experimental results and other theories. An empirical expression for complex shear modulus is presented. The effects of MR layer thickness on vibration of MR-laminated beams are examined. [ABSTRACT FROM PUBLISHER]

Honeycombs are versatile structures. They have been widely employed in industries where the characteristics of high stiffness, high buckling resistance, large shock absorption and light weight are required. To explore the potential of honeycombs in various mechanical applications, this paper proposes a novel honeycomb with composite laminate cell walls in order to provide wider selection of constituent materials, improved specific stiffness and distinct cell wall surfaces. Analytical homogenization model of this special type of honeycombs is established by modeling the locally heterogeneous honeycomb as a homogeneous orthotropic bulk. Both full-detailed and homogenized models are built and tested using finite element analysis, and the results showed that the analytical model has excellent accuracy in property prediction at a relatively small computational cost. Parametric studies are also conducted to investigate the effect of thickness and elastic moduli of the cell wall plies on the structure’s overall mechanical response. Based on the results, suggestions on property optimizations are discussed. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) Finite element (FE)-based progressive damage model, which considers the interface matrix layer between two neighboring laminae as a layer of cohesive elements, is proposed to analyze laminated composite plates. An elasto-plastic damage model is integrated with the FE-based program ABAQUS that uses user-defined material subroutine. The present damage model includes fiber failure, matrix failure, and delamination effects. A cohesive zone model, which is available in ABAQUS and uses cohesive elements, is combined with the proposed model to address the delamination damage in the interface layers. 3D solid brick elements are used to model composite layers, and cohesive zone elements are used in between two composite layers to model the adhesive layers. The proposed model has been applied for the progressive damage simulation of AS4/PEEK composite laminates under in-plane and uniaxial tensile loading. [ABSTRACT FROM AUTHOR]

In this paper, a new higher-order layerwise finite element model, developed earlier by the present authors for the static analysis of laminated composite and sandwich plates, is extended to study the free vibration behavior of multilayer sandwich plates. In the present layerwise model, a first-order displacement field is assumed for the face sheets, whereas a higher-order displacement field is assumed for the core. Thanks for enforcing the continuity of the interlaminar displacement, the number of variables is independent of the number of layers. In order to reduce the computation effort, a simply four-noded C0 continuous isoparametric element is developed based on the proposed model. In order to study the free vibration, a consistent mass matrix is adopted in the present formulation. Several examples of laminated composite and sandwich plate with different material combinations, aspect ratios, boundary conditions, number of layers, geometry and ply orientations are considered for the analysis. The performance and reliability of the proposed formulation are demonstrated by comparing the author's results with those obtained using the three-dimensional elasticity theory, analytical solutions and other advanced finite element models. From the obtained results, it can be concluded that the proposed finite element model is simple and accurate in solving the free vibration problems of laminated composite and sandwich plates. [ABSTRACT FROM AUTHOR]

The residual thermal stresses of MoSi 2 -SiC p + refractory metal foil laminated composites are estimated, in this paper, by both finite element methods (FEMs) as well as analytical expressions. It is observed in the present study that the refractory metal foils are found to possess compressive stresses, while the MoSi 2 -SiC p matrix layer is under tensile stresses. The Nb foil reinforced laminated composite is found to possess the lowest residual stresses owing to a lower thermal expansion mismatch between MoSi 2 -SiC p matrix and the Nb foil as compared to the Mo and Ta foils. [ABSTRACT FROM AUTHOR]

This article presents the vibro-acoustic modeling and analysis of un-baffled laminated composite flat panels subjected to harmonic point load under various support conditions. The frequency values of the panel are obtained by using simulation model through the commercial finite element package (ANSYS) via batch input technique. Initially, the rate of convergence of the current simulation results is established by solving different examples under various edge supports. Further, the natural frequencies and corresponding modes are computed and compared with available published and experimentally obtained values. Then, the modal values are exported to LMS Virtual.Lab environment for the computation of acoustic responses of the vibrating laminated plate structure. Further, an indirect boundary element approach has been adopted to extract the coupled vibro-acoustic responses. Subsequently, the radiated sound power of the structure and the sound pressure level within the acoustic medium are computed using the present scheme and compared with the published numerical results and in-house experimental data, respectively. Finally, a comprehensive study has been performed to highlight the effect of different structural parameters (thickness ratio, aspect ratio, modular ratio and lay-up scheme), support conditions and the composite properties on the acoustic radiation responses of the laminated plate structure. [ABSTRACT FROM AUTHOR]

Light weight laminated composite materials have seen dramatic increase in civil, aerospace, marine and other weight sensitive engineering applications due to their design versatility and high stiffness-to-weight and strength-to-weight ratios. Naturally different behavioural aspects like failure of composites gained importance as research areas for confident use of these materials. Failure in composites starts with the failure of the weakest lamina and may propagate in different directions due to reduction of stiffness thus introduced leading to progressive failure of the structure. In the present study composite shell structures are solved for failure using an eight noded isoparametric shell bending element. Failure behaviour of cross and angle ply, symmetrically laminated graphite-epoxy composite shell roofs are reported. [ABSTRACT FROM AUTHOR]

In this study, estimation of some physical properties of a laminated composite plate was conducted via the inverse vibration problem. Laminated composite plate was modelled and simulated to obtain vibration responses for different length-to-thickness ratio in ANSYS. Furthermore, a numerical finite element model was developed for the laminated composite utilizing the Kirchhoff plate theory and programmed in MATLAB for simulations. Optimizing the difference between these two vibration responses, inverse vibration problem was solved to obtain some of the physical properties of the laminated composite using genetic algorithms. The estimated parameters are compared with the theoretical results, and a very good correspondence was observed. [ABSTRACT FROM AUTHOR]

The paper presents an improved technique and the results of strength analysis for the aircraft structural elements with a structural defect like an arbitrary shape delamination. [ABSTRACT FROM AUTHOR]

In this study, an inverse trigonometric shear deformation theory developed by the authors is extended to assess the flutter behavior of multilayered composite plates subjected to yawed supersonic flow. The shear deformation is considered in terms of an inverse cotangent function which yields non-linear distribution of shear stresses. A generalized finite element formulation is presented to consider the shear strain function based theories. The displacement field is modified by a precise involvement of additional field variables to ensure the implementation of C 0 continuous finite element. First order piston theory is employed to consider the aerodynamic load. The applicability, validity and accuracy of the present mathematical treatment are ascertained by performing various numerical tests and comparing the present results with the existing results. The influences of various parameters such as lamination sequences, boundary conditions, material anisotropy, flow angles, etc. on the free vibration and flutter behavior are examined and significant conclusions are made. It is concluded that flow angles, lamination sequence and material anisotropy should be considered as essential design parameters for enhanced flutter boundary of supersonic vehicles. [ABSTRACT FROM AUTHOR]

Laminated composite structures operating in a marine environment are subject to moisture ingress. Due to the slow diffusion process of moisture, the distribution of moisture is not uniform so that the laminates can develop hygrothermal stresses. An accurate prediction of the moisture concentration and the associated hygrothermal stress is vital to the understanding of the effect of marine environment on failure initiation. The present paper investigates the time-dependent moisture diffusion and the stress distribution in carbon fibre reinforced polymeric (CFRP) composites by means of experimental study and Finite Element Analysis (FEA). Samples were made from CFRP pre-preg autoclave-cured, and then immersed in fresh water and sea water at a constant 50 °C for accelerated moisture diffusion. Laminates with [0] 16 , [90] 16 , [±45] 4s lay-up sequences were investigated. A multiscale 3D FEA model was developed to evaluate the interfacial stresses between polymer matrix and carbon fibre and the stress distribution in the composite laminates. The analysis revealed that both the stress distribution and stress level are time-dependent due to moisture diffusion, and the interphase between fibres and matrix plays an important role in both the process of moisture diffusion and the stress/strain transfer. The interlaminar shear stresses of the laminates induced by hygrothermal expansion exhibited a significant specimen edge effect. This is correlated with the experimental observations of the flexural failure of laminates. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to develop a general mathematical model for laminated curved structure of different geometries using higher-order shear deformation theory to evaluate in-plane and out of plane shear stress and strains correctly. Subsequently, the model has to be validated by comparing the responses with developed simulation model (ANSYS) as well as available published literature. It is also proposed to analyse thermal buckling load parameter of laminated structures using Green–Lagrange type non-linear strains for excess thermal distortion under uniform temperature loading. Design/methodology/approach – Laminated structures known for their flexibility as compared to conventional material and the deformation behaviour are greatly affected due to combined thermal/aerodynamic environment. The vibration/buckling behaviour of shell structures are very different than that of the plate structures due to their curvature effect. To model the exact behaviour of laminated structures mathematically, a general mathematical model is developed for laminated shell geometries. The responses are evaluated numerically using a finite element model-based computer code developed in MATLAB environment. Subsequently, a simulation model has been developed in ANSYS using ANSYS parametric design language code to evaluate the responses. Findings – Vibration and thermal buckling responses of laminated composite curved panels have been obtained based on proposed model through a customised computer code in MATLAB environment and ANSYS simulation model using ANSYS parametric design language code. The convergence behaviour are tested and compared with those available in published literature and ANSYS results. Finally, the investigation has been extended to examine the effect of different parameters (thickness ratios, curvature ratios, modular ratios, number of layers and support conditions) on the free vibration and thermal buckling responses of laminated curved structures. Practical implications – The present paper intends to give sufficient amount of numerical experimentation, which may lead to help in designing of finished product made up of laminated composites. Most of the aerospace, space research and defence organisation intend to develop low cost and high durable products for real hazard conditions by taking combined loading and environmental conditions. Further, case studies might lead to a lighter design of the laminated composite panels used in high-performance systems, where the weight reduction is the major parameter, such as aerospace, space craft and missile structures. Originality/value – In this analysis, the geometrical distortion due to temperature is being introduced through Green–Lagrange sense in the framework of higher-order shear deformation theory for different types of laminated shells (cylindrical/spherical/hyperboloid/elliptical). A simulation-based model is developed using ANSYS parametric design language in ANSYS environment for different geometries and loading condition and compared with the numerical model. [ABSTRACT FROM AUTHOR]

A structure with periodic dynamic load may lead to dynamic instability due to parametric resonance. In the present work, the dynamic stability analysis of laminated composite and sandwich plate due to in-plane periodic loads is studied based on recently developed inverse trigonometric zigzag theory (ITZZT). Transverse shear stress continuity at layer inteifaces along with traction-free boundary conditions on the plate sutfaces is satisfied by the model obviating the need of shear correction factor. An efficient C° continuous, eight noded isoparametric element with seven field variable is employed for the dynamic stability analysis of laminated composite and sandwich plates. The boundaries of instability regions are determined using Bolotin's approach and the first instability zone is presented either in the nondimensional load amplitude-excitation frequency plane or load amplitude-load frequency plane. The influences of various parameters such as degrees of ortliotropy, span-thickness ratios, boundary conditions, static load factors, and thickness ratios on the dynamic instability regions (Dills) are studied by solving a number of problems. The evaluated results are validated with the available results in the literature based on different deformation theories. The efficiency of the present model is ascertained by the improved accuracy of predicted results at the cost of less computational involvement. [ABSTRACT FROM AUTHOR]

Due to their low weight ratio, excellent damping behavior, and high strength characteristics, composite materials are widely used in different industries, including aerospace. Despite the excellent mechanical behavior, most of these materials suffer from damages such as delamination when undergoing low-energy impacts. In the present study, repairing the composite structures using the resin injection into the damaged zone is analyzed. In some samples, initial delamination is included during the manufacturing process using the Teflon film, while the other samples are left to be intact. Furthermore, the delamination inside the composite sample has been simulated using the cohesive zone method (CZM) using ABAQUS software. The samples with delamination were repaired with the resin injection method. Finally, all samples underwent the buckling test, and the buckling process of the samples was monitored using the acoustic emission method. The amounts of damage mechanisms of delamination growth, fiber breakage, and matrix cracking were calculated using the wavelet method. The results show a good agreement between the experimental results with both the finite element method (FEM) and the acoustic emission results. Besides, the restoration percentages of compressive strength in samples repaired with stacking sequence [0] 8 , [90] 8 , and [0/90] 8 were 88%, 87%, and 91.7%, respectively. [ABSTRACT FROM AUTHOR]

A frequency domain spectral finite element formulation is presented for the wave propagation analysis of laminated composite curved beams using the first order shear deformation theory (FSDT) and the classical laminate theory (CLT). The elements are derived from the exact solution of the governing equation of motion in frequency domain, obtained through Fourier transformation of the time domain equation. The formulation is validated by comparing the results for natural frequencies with the published results. The new elements are then employed to perform dispersion and wave propagation analyses of curved composite beams. The numerical results reveal that the wavenumbers predicted by the CLT show large deviation from those of the FSDT even for thin beams, and the deviation increases and occurs at lower frequencies with the increase in the thickness to radius ratio. The orthotropy ratio of the composite has a significant effect on the wavenumbers for tangential and mid-surface rotation modes. The wave propagation response predicted by the CLT differs widely from the FSDT prediction, for thin and thick, and shallow and deeply curved beams at both low and high frequencies. Thus, the CLT should not be used for wave propagation analysis of even thin curved laminated beams. [ABSTRACT FROM AUTHOR]

In this paper, a new layerwise plate formulation based on a C 0 higher-order finite element model is presented for static and free vibration analyses of laminated composite and sandwich plates. The proposed layerwise theory which is developed for a three layered composite plates, assumes higher-order displacement field for middle layer and first-order displacement field for top and bottom layers. Compatibility conditions are imposed at the layer interface to satisfy the interlaminar displacement continuity. An eight-noded isoparametric element is used to model the plate. The accuracy of the proposed formulation is assessed for linear static and free vibration analyses by comparing the authors’ results with available 3D elasticity, finite element and analytical solutions. It has been shown here that the present finite element formulation is much simpler, straightforward and accurate for static and free vibration analyses of laminated composite and sandwich plates. [ABSTRACT FROM AUTHOR]

In this work, inverse hyperbolic zigzag theory and inverse trigonometric zigzag theory, recently developed by the authors, are extended for the free vibration analysis of the laminated composite and sandwich plates. The developed plate models satisfy the condition of transverse shear stress continuity at the layer interfaces and the zero traction boundary conditions on the surfaces of the plate obviating the need of shear correction factor. They consider shear strain shape function assuming the nonlinear distribution of transverse shear stresses. The less numbers of independent variables makes the solution computationally effective. An efficient C0 continuous isoparametric serendipity element is employed for the usual discretization of the plate structure. In order to demonstrate the capabilities of the developed models in predicting the structural free vibration response, some representative results are obtained covering different features of laminated composite and sandwich structures such as boundary conditions, aspect ratios and span-to-thickness ratios and the results are compared with those in the literature wherever available. The excellent agreement of the evaluated results with the three-dimensional exact results conclude that the presented models are not only accurate but also efficient. [ABSTRACT FROM AUTHOR]

Laminated polymer matrix carbon fiber composites have poor thermal conductivity in through thickness direction as all the conductive fibers are within the plane. One can increase the through thickness thermal conductivity by introducing conductive fibers in that direction or by modifying the form, direction and architecture of the fiber network. In this paper we conduct a parametric study using finite element analysis to investigate the relation between the local fiber architecture and its effective through-thickness thermal conductivity. The role of the fiber tow orientation, volume fraction and stacking sequence is explored. Unidirectional laminates containing fiber tows aligned in the same direction for all laminae exhibit higher through thickness thermal conductivity than the stacking sequence with other orientations. A conductive coating surface layer enhances the thermal conductivity of laminates independent of fiber orientation configuration. A geometric scalar parameter is proposed to correlate laminate through-thickness thermal conductivity with fiber tow stacking sequence. The influence of different boundary condition types on the through-thickness thermal conductivity is also assessed. [ABSTRACT FROM AUTHOR]

Usually a three-dimensional (3D) finite element model is used for analyzing laminated composite bolted joints, because the stress and strain vary in all directions due to factors such as bolt bending and tilting, bolt pre-load and secondary bending. In general, the advantage of symmetry can greatly reduce the modeling and computational time in a 3D analysis. However, due to different lamination angles in laminated composite structures, symmetric model may not always be possible in most of the cases. To overcome this problem, an equivalent homogeneous 3D elasticity model is developed and presented in this paper for simplified analysis of laminated composite bolted joints. This type of model is beneficial for determining the basic mechanical behaviors of a laminated composite joint with significantly lesser computational effort. The present formulation is based on Mindlin–Reissner plate theory which takes into account the effect of transverse shear deformation in composite laminates. The present method is capable of finding equivalent homogeneous model for the laminated composite joints having any type of lamination scheme. This homogenization scheme is also useful for developing simplified analytical models (e.g., spring based models) for laminated composite bolted joints. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to improve the conventional electrodynamic shaker's performance at low frequency through the optimization of its support spring. It is acknowledged that to improve its low frequency performance, a shaker's support spring has to be lightweight and simultaneously of high lateral but low axial rigidity. Meanwhile it should have few resonance points in the useable frequency range. But both experimental modal analysis (EMA) and finite element analysis (FEA) in this study indicated that of the support spring of conventional shaker presents undesirable humps in its frequency response (FR) in low frequency area. The first order resonance frequency of the shaker (whose value decides the minimum of the shaker's useable frequency range) also turned out big. Hence a new support spring plate of laminated composite structure embedded with viscoelastic damping material is proposed in this study whose parameter values are further optimized. The optimization adopts damping thickness, angle and thickness of composite layer as the design variables. It targets at achieving minimum weight while satisfying the shaker's first order elastic natural frequency and the plate's intensity. The optimized support spring plate is then put to frequency response analyses. The findings indicate that it not only can suppress the humps in low frequency area, but also widens the shaker's useable low frequency range. Meanwhile it reduces the shaker's additional rigidity on the test object. Hence it can ensure the shaker's performance at low frequency. [ABSTRACT FROM AUTHOR]