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This paper attempts to validate the application of the Virtual Isotropic Material Concept (VIMC) in combination with the average strain energy density (ASED) criterion to predict the critical load in notched laminated composites. This methodology was applied to E/glass–epoxy-laminated composites containing U-notches. For this purpose, a series of fracture test data recently published in the literature on specimens with different notch tip radii, lay-up configurations, and a number of plies were employed. It was shown that the VIMC–ASED combined approach provided satisfactory predictions of the last-ply failure (LPF) loads (i.e., critical loads).

The relations between the stiffness components of a symmetrical or unsymmetrical laminate having trans-verse matrix cracks only in the 90-degree laminas are explored in this work. The crack closure condition for these laminates under membrane and bending deformations is established to obtain the interrelationships. These equations also link the in-plane equivalent Young’s moduli and the Poisson’s ratios of balanced symmetric laminates. Cracks in off-axis laminas are not considered here. The present relations are validated using numerical data reported in the literature. Each inter-relationship can be used to obtain one elastic property when other property was experimentally measured or analytically calculated. Fil: Barulich, Nestor Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentina Fil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; Argentina Fil: Dardati, Patricia Mónica. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina

This study focuses on the dynamic modelling and analysis of the wind turbine blades made of multiple layers of fibre reinforced composites and core materials. For this purpose, a novel three-dimensional analytical straight beam model for blades is formulated. This model assumes that the beam is made of functionally graded material (FGM) and has a variable and asymmetrical cross section. In this model, the blades are assumed to be thin, slender and long with a relatively straight axis. They have two main parts, namely the core and the shell. The so-called core consists of a lightweight isotropic foam material, which also adds significant damping to the system. The core material is covered by the shell, which is modelled using homogenous and orthotropic material assumptions as the structure is reinforced with continuous fibres. Therefore, the blades are modelled under a straight beam with varying cross-section assumptions, in which the effective elastic properties are acquired by homogenizing the cross section. The beam formulation for modelling the system is performed both analytically and numerically with the finite element method. The results of both methods are in well agreement. The maximum deviation between the results is found below 4%.

Recycled newspaper (NP)/high density polyethylene (HDPE) laminated composite can reach the physical and mechanical criteria for most industrial applications, which shows the potential of using solid-state waste paper in engineering materials. Herein, the effects of splicing pattern and size on the physical and mechanical properties of the laminated composite were investigated with the ultimate purpose to fabricate a large-scaleale composite. The laminated composite with a stair-like splicing had better physical and mechanical properties than that with a vertical splicing. An efficient stress transfer could be guaranteed when the distance between the two adjacent junctions were greater than a critical proportion of 1/32 of the length at longitudinal direction. The tensile and flexural properties of the large-scaleale composite with a stair-like splicing, which was fabricated at the splicing ratio of 1/32, were 109 &plusmn, 4.2 MPa (MOR), 9836 &plusmn, 411 MPa (MOE), 119 &plusmn, 7.1 MPa (MOR) and 10002 MPa &plusmn, 347 (MOE).

This paper presents a new four-variable refined plate theory for free vibration analysis of laminated piezoelectric functionally graded carbon nanotube-reinforced composite plates (PFG-CNTRC). The present theory includes a parabolic distribution of transverse shear strain through the thickness and satisfies zero traction boundary conditions at both free surfaces of the plates. Thus, no shear correction factor is required. The distribution of carbon nanotubes across the thickness of each FG-CNT layer can be functionally graded or uniformly distributed. Additionally, the electric potential in piezoelectric layers is assumed to be quadratically distributed across the thickness. Equations of motion for PFG-CNTRC rectangular plates are derived using both Maxwell&rsquo, s equation and Hamilton&rsquo, s principle. Using the Navier technique, natural frequencies of the simply supported hybrid plate with closed circuit and open circuit of electrical boundary conditions are calculated. New parametric studies regarding the effect of the volume fraction, the CNTs distribution, the number of layers, CNT fiber orientation and thickness of the piezoelectric layer on the free vibration response of hybrid plates are performed.

In this study, the effect of graphene nanoplatelets reinforcement on the flexural strength of E-glass/epoxy laminated composite material was investigated experimentally. [0⁰/90⁰]3S oriented composite materials with and without graphene nanoplatelets reinforcement were manufactured by using hand lay-up and vacuum bagging method. Graphene nanoplatelets at three different ratios (0.25, 0.5 and 1 wt.%) were added to the epoxy. The produced plates were cut with a water jet cutting machine to obtain three-point bending specimens. Then, three-point bending tests were performed according to the ASTM D790 standard. The span between the centers of support cylinders/composite specimen thickness ratio (s/t) was selected as 16 in all the tests. Results indicate that the addition of graphene nanoplatelets to the epoxy matrix increased the flexural strength of the laminated composite material. When the graphene nanoplatelets at ratios of 0.25, 0.5 and 1 wt.% were added to the epoxy matrix, the flexural strengths increased by 4.32%, 12.88% and 7.03% respectively.

An innovative experimental methodology for the nondestructive assessment of local elastic properties of composite materials is proposed in this paper. A local region of rectangular shape is isolated on the investigated laminate with a proper clamping system. The first resonant frequency of the retained region with clamped boundaries is determined through the Impulse Excitation Technique. In order to take into account the anisotropy of the composite laminate, values of the resonant frequency are measured after rotating the clamping system with respect to the composite plate. The material constants are finally obtained from the measured frequencies through an inverse optimization algorithm based on Finite Element analysis. The proposed methodology is validated on a unidirectional composite plate with known elastic properties. Boundaries of the investigated region are clamped by pressing two rectangular frames to the plate through a testing machine, thus localizing the measure of the resonant frequencies. The first resonant frequency is measured at different angles (0°, 30°, 60° and 90°) between fibers direction and main axis of the rectangular region. Dynamic elastic properties are finally assessed through the proposed inverse optimization algorithm. The small differences between the nominal and the estimated mechanical properties prove the effectiveness of the proposed methodology.

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.

The structural integrity of composite structures depends on the use of appropriate damage detection and structural health monitoring methods in design and operation stages. In this paper, the initiation and propagation of delamination in laminated composite materials are investigated by performing Double Cantilever Beams (DCBs) tests. Acoustic Emissions (AEs) are used to characterize the delamination crack tip during DCB tests. For this purpose, a combination of AE signal localizations and scattering reduction procedure is implemented to determine the delamination tip position. Besides, bi-linear and tri-linear Cohesive Zone Models (CZMs) are implemented to investigate the initiation and propagation of delamination. The results show that the tri-linear CZM can accurately determine both the initiation and propagation of delamination in the existence of fiber bridging while bi-linear CZM fails to do so. It is also found that AE is a powerful approach in determining the position of the delamination crack tip.

RESUMO Neste trabalho foram desenvolvidos compósitos poliméricos epoxídicos laminados a base de cortiça e microesferas ocas de vidro. Os compósitos laminados foram confeccionados manualmente e avaliados quanto às características morfológicas em microscópio eletrônico de varredura e a influência da incorporação das cargas foi avaliada por meio da densidade e da resistência à flexão. De um modo geral, foi observada boa dispersão tanto do pó de cortiça como das microesferas ocas de vidro nas camadas centrais do laminado, porém os núcleos a base de cortiça apresentaram melhor adesão à matriz. Foi observada ainda a redução na densidade de todos os compósitos com relação à matriz pura e que os módulos de flexão dos compósitos a base de cortiça e os com microesferas ocas de vidro, mesmo com valores próximos, foram superiores ao módulo de flexão do sistema epóxi puro. Compósitos laminados com núcleo com incorporação de cortiça poderão ser aplicados como alternativa onde houver a necessidade de redução de peso e também onde houver a expectativa de solicitações de flexão superiores às suportadas pela resina pura. ABSTRACT In this work, epoxy polymer composites laminated with cork and hollow glass microspheres were developed. The laminated composites were manually made and evaluated for the morphological characteristics of the scanning electron microscope and the influence of the incorporation of the fillers was evaluated by means of density and flexural strength. In general, good dispersion of both the cork powder and the hollow glass microspheres was observed in the central layers of the sheet, but the cork-based cores presented better adhesion to the matrix. It was also observed the reduction in the density of all the composites with respect to the pure matrix and that the flexural modulus of cork-based composites and those with hollow microspheres of glass, even with close values, were superior to modulus of bending of the pure epoxy system. Core laminates with cork incorporation may be applied as an alternative where weight reduction is required and also where there is the expectation of bending stresses higher than those supported by the pure resin.

A new shear-corrected Reissner-Mindlin model is presented. The method reduces the modeling error of the classical model without affecting the form of the classical plate equations. Therefore, implementation on an existing software for the Reissner-Mindlin plate model is simple. The principle of virtual work and an explicit set of kinematic and kinetic assumptions is used in derivation. There, displacement assumption of the classical model is enhanced by a warping part which is eliminated to end up with equations for the classical part only. The equations differ from the classical ones in shear correction factors, modification in the source term, and stress expressions.

In order to understand the physics of the delamination onset in laminated composites, an experimental investigation of delamination growth is presented. The main objective of this paper is to demonstrate that delamination onset occurs at lower values than Gc defined by the ASTM standards, and that the strain energy release rate level at which the crack growth onset occurs under any mixed mode I/II loading is governed by the critical strain energy density (SED) approach. Quasi-static delamination experiments have been performed under mode I, mode II and mixed mode I/II loadings. The value of the strain energy release rate at the observed crack onset and the angle of the initial crack growth were correlated with the SED theory to test the validity. The acoustic emission was also used to provide more insight into the physics of the delamination growth. The investigation shows that the onset of delamination growth occurs at the strain energy release rate levels predicted by the critical SED approach, and well before reaching the critical strain energy release rate determined via delamination tests following the ASTM standards. Moreover, results indicated that the predicted angle of the initial crack for delamination onset was in a good agreement with the experimental data

In this article, a displacement model for micro and nano laminated composite Timoshenko beam is presented. The layer-wise displacement model is refined in order to calculate interlaminar stresses c...

The free vibration analysis of laminated nanocomposite plates and shells using first-order shear deformation theory and the generalized differential quadrature method is presented. Each layer of the laminate is modeled as a three-phase composite. An example of such composite material is given by a polymeric matrix reinforced with carbon nanotubes (CNTs). CNTs enhance the mechanical properties of the polymer matrix and the nanocomposite is treated as an isotropic material; a micromechanics model is used to compute the engineering constants of the isotropic hybrid material. This approach based on the Eshelby–Mori–Tanaka scheme takes into account the agglomeration of the nanoparticles in the matrix. The second step consists in combining this enriched matrix with unidirectional and oriented reinforcing fibers to obtain a fibrous composite with improved mechanical features. The overall mechanical properties of each orthotropic ply are evaluated through different micromechanics approaches. Each technique is illustrated in detail and the transversely isotropic properties of the three-phase layers are completely defined. The effects of both CNTs agglomeration and the mass fraction of these particles are investigated comparing with the results obtained by various homogenization techniques. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

In this paper, comparative assessment of failure fatigue lives of thin laminated cementitious composites (LCCs) modeled by two modeling approaches&mdash, double-parameter Weibull distribution model and triple-parameter distribution model&mdash, was carried out. LCCs were fabricated of ordinary Portland cement (OPC), fly ash cenosphere (FAC), quartz sand, and reinforcing meshes and fibers. The failure fatigue life assessment at various probabilities by the two-parameter model was based on numerical calculations whereas the three-parameter model was applied by an open source program&mdash, ProFatigue&reg, Respective parameters, shape and scale parameters in the two-parameter Weibull distribution model while shape, scale, and location parameters in three-parameter model were determined, and the corresponding probabilistic fatigue lives at various failure probabilities were calculated. It is concluded that the two-parameter model is more accurate in probabilistic fatigue life assessment of double-layer mesh-reinforced LCCs, whereas for single-layer reinforced LCCs, both models could be used at a fair confidence level.

In this paper, by considering the absorbed energy in the fracture process zone and extension of the minimum strain energy density theory for orthotropic materials, a new mixed mode I/II failure criterion was proposed. The applicability of the new criterion, to predict the crack growth in both laminated composites and wood species, was investigated. By defining a suitable damage factor and using the mixed mode I/II micromechanical bridging model, the absorbed energy in the fracture process zone was considered. It caused the new criterion to be more compatible with the nature of the failure phenomena in orthotropic materials, unlike available ones that were conservative. A good agreement was obtained between the fracture limit curves extracted by the present criterion and the available experimental data. The theoretical results were also compared with those of the minimum strain energy density criterion to show the superiority of the newly proposed criterion.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. In this paper, a three-dimensional numerical solution for the bending study of laminated composite doubly-curved shells is presented. The partial differential equations are solved analytically by the Navier summation for the midsurface variables; this method is only valid for shells with constant curvature where boundary conditions are considered simply supported. The partial differential equations present different coefficients, which depend on the thickness coordinates. A semi-analytical solution and the so-called Differential Quadrature Method are used to calculate an approximated derivative of a certain function by a weighted summation of the function evaluated in a certain grin domain. Each layer is discretized by a grid point distribution such as: Chebyshev-Gauss-Lobatto, Legendre, Ding and Uniform. As part of the formulation, the inter-laminar continuity conditions of displacements and transverse shear stresses between the interfaces of two layers are imposed. The proper traction conditions at the top and bottom of the shell due to applied transverse loadings are also considered. The present results are compared with other 3D solutions available in the literature, classical 2D models, Layer-wise models, etc. Comparison of the results show that the present formulation correctly predicts through-the-thickness distributions for stresses and displacements while maintaining a low computational cost. Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica

Purpose: The purpose of this paper investigates to stiffness behavior of hybrid laminated composites with surface crack. Design/methodology/approach: Hybrid laminated composites has 18 layers and 90x25 mm size with two different layers line up. The low velocity impact test of hybrid laminated composites carried on 3 m/sec with a/t=0.4 and a/c=0.4 surface crack parameters. Findings: The results are presented as the change of force-time and force-displacement graphs. As a result of this study, effects of stacking sequence on hybrid composite plates were analysed. Research limitations/implications: The research of stiffness behavior or dynamic response of hybrid laminated composites can contribute to developing new composite materials. Practical implications: These hybrid laminated composites materials could be used for different aviation areas. Originality/value: This paper is based on studies from Selçuk University and all the experiments and results were conducted by me. © by International OCSCO World Press. All rights reserved. 2016., British Association for Psychopharmacology: 12401029, 11101033, funded by Sel?uk University (BAP) Baltic-American Partnership Fund under grant numbers 12401029 and Baltic-American Partnership Fund 11101033.

The present paper proposes a multi-objective optimization technique for smart laminated composites to maximize two conflicting objectives. The first objective is the performance of active vibration control of smart composite with piezoelectric (PZT) actuators. The second is the fundamental frequency of smart structures related to the performance of passive vibration control. Both performances of active and passive vibration control are maximized simultaneously. The vibration suppression of smart structures strongly depends on both actuator placements and vibration mode shapes. It is possible to design vibration mode shapes for laminated fibrous composites since their anisotropy for whole thickness is tailorable by arranging fiber orientation angle in each layer. This allows the smart structure with laminated composite to archive higher performance of vibration suppression than those with isotropic materials. However, the optimized structure results in lower natural frequencies than composites with typical fiber orientation angles since an effective input of control force from actuators is realized for the structure with lower stiffness. This reveals that there is a trade-off relation for smart composite structures between the performance of active vibration suppression and natural frequencies. To disclose this relation, the present study applies the effective multi-objective optimization technique, the refined non-dominated genetic algorithm (NSGAII), and obtains Pareto optimal solutions. Calculated results are successfully validated by a comparison with those from the real-time control experiment where a laser excitation technique which is effective to small sized structures is used.

Complex composite structures manufactured using a low-pressure vacuum bag-only (VBO) method are more susceptible to defects than flat laminates because of the presence of complex compaction conditions at corners. This study investigates the contribution of multivariate processing parameters such as bagging techniques, curing profiles, and laminate structures on laminates&rsquo, shape conformation. Nine sets of laminates were produced with a concave corner and another nine sets with a convex corner, both with a 45&deg, inclined structure. Three-way analysis of variance (ANOVA) was performed to quantify thickness variation and spring effect of laminated composites. The analysis for concave and convex corners showed that the bagging techniques is the main factor in controlling the laminate thickness for complex shape applications. The modified (single) vacuum-bag-only (MSVB) technique appeared to be superior when compared to other bagging techniques, exhibiting the least coefficients of variation of 0.015 and 0.016 in composites with concave and convex corners, respectively. Curing profiles and their interaction with bagging techniques showed no statistical significance in the contribution toward laminate thickness variation. The spring effect of laminated composites was investigated by calculating the coefficient of determination (R2) relative to that of the mold. The specimens exhibited a good agreement with R2 values ranging from 0.9824 to 0.9946, with no major data offset. This study provides guidelines to reduce thickness variations and spring effect in laminated composites with complex shapes by the optimum selection of processing parameters for prepreg processing.

This paper discusses the robustness of plate elements based on Mixed Interpolation of Tensorial Components (MITC) technique and the variable kinematics approach of Carrera Unified Formulation (CUF) with respect to the problem of distorted meshes. MITC was originally proposed for Reissner-Mindlin type plates to develop shear locking free plate elements. In the present framework, refined plate elements are obtained by referring to high-order Equivalent Single Layer as well as Layer-Wise models expressed in CUF for the analysis of multilayered anisotropic structures. Four-node and nine-node elements are considered and some applications are developed for both isotropic and multilayered composite plates. Results related to the MITC approach are compared to the isoparametric elements, including selectively reduced quadrature schemes, for both, the static and free-vibration analysis. They show that CUF-MITC elements maintain their effectiveness also in the case of distorted meshes, for all the materials studied and kinematic models considered: the obtained elements are robust as free from shear locking and spurious zero-energy modes.

This paper demonstrates how the critical strain energy density in the delamination tip vicinity may be used to explain the physics of delamination growth under mixed mode I/II. A theory previously proposed to physically relate mode I and mode II delamination growth is further extended towards describing the onset of mixed mode I/II delamination. Subsequently, data from the literature is used to demonstrate that this new concept of the critical strain energy density approach indeed explains, based on the physics of the problem, the strain energy release rate level at which crack onset occurs. This critical strain energy density for the onset of delamination appears to be independent of the opening mode. This means that, in order to characterize the fracture behaviour of a laminate, fracture tests at only one loading mode are necessary. Because the load level at which the physical delamination onset occurs at the microscopic level is much lower than the traditional engineering definition of macroscopic onset, further work must reveal the relationship between the macroscopically visible delamination onset, and the microscopic onset.

This paper presents some solutions for mechanical responses of angle-ply laminated plates under transverse distributed loads, which are obtained by using refined finite element models adopting variable kinematics based on Carrera’s Unified Formulation (CUF). Plates with several types of stacking sequence under different boundary conditions are considered. Layer-wise (LW) models based on Chebyshev polynomials (first kind) and Equivalent Single Layer (ESL) models based on Trigonometric series are used in the analysis. To compare the performances of different displacement-based kinematic models, a set of simply supported boundary conditions and mixed clamped-free boundaries are adopted in the numerical study. A nine-node MITC (Mixed Interpolated of Tensorial Components) plate element is employed to contrast the shear locking phenomenon of thin plates. CUF-based variable kinematic models are used in the numerical study and the number of expansion terms in the thickness direction is increased until the requisite numerical accuracy is achieved. By comparing the numerical results obtained with CUF-based refined models and ABAQUS 3D models as well as reference solutions from literature, the effectiveness of the adopted models is verified. The newly studied numerical cases can be taken as benchmarks for future research.

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.

The optimal design of viscoelastic laminated composite panels with active piezoelectric patches is addressed in this paper. Constrained optimization is conducted to determine optimal distributions of piezoelectric patches on the top and bottom surfaces of laminated plates with viscoelastic layers. The design variables are the number and position of these patches, and the objectives are the minimization of the number of patches, the maximization of the fundamental modal loss factor and the maximization of the fundamental natural frequency. The problem is solved using the Direct MultiSearch (DMS) solver for derivative-free MultiObjective Optimization (MOO). The objective functions are evaluated by a finite element model that was developed for laminated sandwich plates incorporating piezoelectric or viscoelastic layers. Trade-off Pareto optimal fronts and the respective optimal active patch configurations are obtained and the results are analyzed and discussed. info:eu-repo/semantics/publishedVersion

Laminated Ti/Al 2 O 3 composite was fabricated by tape casting and vacuum hot-pressing sintering with intent to research mechanical properties including the fracture strength and toughness. The results showed that the flexural strength and fracture toughness improved according to the amount of layers. When the amount of layers was 35, the flexural strength and fracture toughness reached 361 MPa and 9.72 MPa m 1/2 , respectively. Based on the observation of microstructures, it was concluded that the improvement of mechanical properties was attributed to various crack propagation (such as crack deflection, crack bifurcation, crack termination and interface dissociation). The characterization of EDX and XRD at interfaces indicated that the initiative diffusion of O 2− from Al 2 O 3 to Ti layer led to the passive diffusion of Al 3+ (aggregating near the interface) and reacted with Ti to form Ti 3 Al, Ti[O] and AlTiO 2 solid solution.

A two-stage numerical model is developed to understand the energy transmission characteristics through a finite double-leaf structure placed in an infinite baffle subjected to an external excitation and subsequently the sound radiation behavior of the same into the semi-infinite receiving side. In the first stage, a mobility-based coupled finite element–boundary element (FE–BE) technique is implemented to model the energy transmission from the primary panel to the secondary panel through an air gap. In the second stage, a separate boundary element (BE)-based model is developed to estimate the sound power radiated by the radiating (secondary) panel into the receiving side which is assumed to be semi-infinite. The advantage of the proposed approach is that it is sufficient to mesh the structural panels alone, thereby reducing the problem dimensions and the difficulty in modeling. Moreover, the developed model can be easily implemented for structures made up of various constituent materials (isotropic or laminated composites) with complex boundary conditions and varying panel geometries. Numerical experiments are carried out for different material models by varying air-gap thicknesses and also by introducing alternate energy transmission path in terms of mechanical links and the obtained results are discussed.

In the present study, extended isogeometric analysis (XIGA) is used to analyse cracks in orthotropic media. NURBS and T-splines geometric technologies are used to define the geometry and the solution. Knot insertion and order elevation are used in NURBS models, while a new local refinement algorithm is applied to T-spline models. In XIGA, the basic idea of the extended finite element method (X-FEM) is used along with isogeometric analysis for modelling discontinuities by including enrichment functions. Special orthotropic crack tip enrichments are used to reproduce the singular fields near a crack tip, and fracture properties of the models are defined by the mixed mode stress intensity factors (SIFs), which are obtained by means of the interaction integral (M-integral). Results of the proposed method are compared with other available results.

In the present work, the influence of strain on phase formation at the Al/Ni interface was investigated during cold roll bonding and annealing. A sandwich sample composed of an Al-Ni-Al stack was cold rolled with reductions in the range of 50% to 90%, followed by annealing at 450 °C for 60 min. The crystallography of the annealed sandwich samples was analyzed by XRD (X-ray diffraction), whereas the microstructure was studied by scanning electron microscopy, equipped with EDS (energy dispersive spectrometer) analysis, and optical microscope. In the annealed samples, the intermetallic phase Al3Ni has formed at the Ni/Al interface, preferentially on the Al side of the interface. It is found that the applied strains did not have an effect on the type of intermetallic phase that was formed. However, the rolling reduction has a significant effect on the morphology of the intermetallic layer, as it was observed that after the lowest reduction of 50% only some scattered intermetallic nuclei were present, whereas at the highest rolling reduction of 90% a continuous intermetallic layer of 4.1 μm was exhibited. The formation of the intermetallic layer is discussed in terms of Al and Ni diffusion at the interface and irregular nature of the Al/Ni bonded interface after rolling reductions.

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. © 2017, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

The effects of thermoplastic polyimide (PI) and polypropylene (PP) fibers and areal density of toughened layer on interlaminar fracture toughness and impact performance of carbon fiber/epoxy (CF/EP) laminated composites were studied. Mode I interlaminar fracture toughness (GIC) was analyzed via double cantilever beam (DCB) tests. When comparing for the toughener type, PI played a positive role in enhancing the mode-I fracture toughness, while PP was not effective due to the less fiber bridge formed during composite curing. The toughening effects of areal density of PI were further investigated by end notched flexure (ENF) testing and low velocity impact testing to better understand the toughening mechanisms. The results revealed that the toughening effect reached its best effectiveness when the areal density of toughened layer was 30 g/m2. Compared with the control group, GIC and GIIC of CF/EP laminated composite were increased by 98.49% and 84.07%, and Fmax and Ee were enhanced by 92.38% and 299.08% under low velocity impact. There is no obvious delamination phenomenon on the surface of laminates after low velocity impact, indicating the improved interlaminar and impact performance of laminated composite.

The stress and strain recovery procedure already applied for solving doubly-curved structures with variable radii of curvature has been considered in this article using an equivalent single layer approach based on a general higher-order formulation, in which the thickness functions of the in-plane displacement parameters are defined independently from the ones through the shell thickness. The theoretical model considers composite structures in such a way that employs the differential geometry for the description of doubly-curved, singly-curved, revolution with variable radii of curvature and degenerate shells. Furthermore, the structures at hand can be laminated composites made of a general stacking sequence of orthotropic generically oriented plies. The governing static equilibrium equations are solved in their strong form using the local generalized differential quadrature (GDQ) method. Moreover the generalized integral quadrature (GIQ) is exploited for the evaluation of the stress resultants of the model under study. Several numerical applications are presented and the local GDQ results are compared with finite element method (FEM) commercial codes.

The present article illustrates a general formulation for a higher-order layer-wise theory related to the analysis of the free vibrations of thick doubly-curved laminated composite shells and panels. The theoretical framework relates to the dynamic analysis of shell structures by using a general displacement field based on the Carrera Unified Formulation (CUF), including the stretching effect for each layer. The order of the expansion along the thickness direction is taken as a free parameter. The starting point of the present general higher-order layer-wise formulation is to propose a kinematic assumption, with an arbitrary number of degrees of freedom. The main aim of this work is to determine the explicit fundamental operators that can be used for the layer-wise (LW) approach. These fundamental operators are obtained for the first time by the author and are related to motion equations of doubly-curved shells described in an orthogonal curvilinear co-ordinate system. The free vibration shell and panel problems are computationally solved using the generalized differential quadrature (GDQ) and generalized integral quadrature (GIQ) techniques. The numerical results are compared with recent papers in the literature and commercial finite element codes.

Purpose: The purpose of this paper researches to effect of different surface crack depth on hibrid laminated composites under low velocity impact forces. Design/methodology/approach: Hybrid laminated composites have 90x25 mm size and 18 layers with two different stacking sequence. Low velocity impact test of hybrid laminated composites with surface crack have been investigated with different a/t surface crack parameters and 3 m/sec velocity. Findings: The results are presented force-time and energy-time graphs than effects of different crack parameters were observed. As a result of this study, effects of surface crack depth on hybrid composite plates were analysed. Research limitations/implications: The research of dynamic behavior of hybrid laminated composites with surface crack can contribute to literature searches. Practical implications: These hybrid laminated composites materials could be used for different aviation areas. Originality/value: This paper is based on studies from Selçuk University and all the experiments and results were conducted by me. © International OCSCO World Press. All rights reserved. 2016.

In the present work, Cu-Pb-Sn and Q235 laminated composite were fabricated by a horizontal semisolid rolling procedure. The interfacial structure, elemental distribution, and properties of the composite were investigated. Finite-element simulation was conducted to analyze the temperature field and solidification process during the semisolid rolling. An appropriate semi-solid region was observed at a pouring temperature of 1598 K in the simulation, which would effectively kept fluidity and avoided casting defects. The experimental results showed that good interface between Cu-Pb-Sn alloy and Q235 steel was achieved by the proposed process at 1598 K, without casting defects or excessive deformation. The Cu and Fe alloys were bonded mainly by the diffusion of Fe into Cu matrix, and a handful of microscopic Pb-rich layer. Fine Pb-rich precipitates were uniformly distributed in the Cu-Pb-Sn alloy, and were considered to be advantageous to the self-lubrication property. The average tensile-shear strength of the interface was higher than 57.68 MPa at a pouring temperature of 1598 K, which fulfilled the requirements for a further extrusion process.

A multilayered plate theory which takes into account transverse shear and normal stretching is presented. The theory is based on a seven-unknowns kinematic field with five warping functions. Four warping functions are related to the transverse shear behaviour, the fifth is related to the normal stretching. The warping functions are issued from exact three-dimensional solutions. They are related to the variations of transverse shear and normal stresses computed at specific points for a simply supported bending problem. Reddy, Cho-Parmerter and (a modified version of) Beakou-Touratier theories have been retained for comparisons. Extended versions of these theories, able to manage the normal stretching, are also considered. All these theories can be emulated by the kinematic field of the present model thanks to the adaptation of the five warping functions. Results of all these theories are confronted and compared to analytical solutions, for the bending of simply supported plates. Various plates are considered, with special focus on very low length-to-thickness ratios: an isotropic plate, two homogeneous orthotropic plates with ply orientation of $0$ and $5$ degrees, a $[0/c/0]$ sandwich panel and a $[-45/0/45/90]_s$ composite plate. Results show that models are more accurate if their kinematic fields (i) depend on all material properties (not only the transverse shear stiffnesses) (ii) depend on the length-to-thickness ratio (iii) present a coupling between the $x$ and $y$ directions., Comment: arXiv admin note: text overlap with arXiv:1311.1463

International audience; Recent progress in sensor technologies, signal processing and electronics made it possible to fulfil the need for the development of in-service structural health monitoring (SHM) systems. An experimental study of local damage materials using acoustic emission (AE) has been conducted to characterize the mechanic behavior of E-glass/epoxy unidirectional composites instrumented by piezoelectric implant. A series of specimens of composite laminates with and without embedded piezoelectric were tested in static loading while constantly monitoring the response by AE technique. The acoustic signals were analyzed by the classification multi-parameters method available on NOESIS (k-means) in order to identify the different damage and to follow the evolution of these various mechanisms for both types of materials (simple and instrumented). The results show that integration of the sensors presents advantages of the detection of the acoustic events and also show the presence of three types of damage during tests. Comparing embedded sensor to sensor mounted on the surface, the embedded sensor showed a much higher sensitivity.

An efficient computational approach based on a generalized unconstrained approach in conjunction with isogeometric analysis (IGA) are proposed for dynamic control of smart piezoelectric composite plates. In composite plates, the mechanical displacement field is approximated according to the proposal model using isogeometric elements and the nonlinear transient formulation for plates is formed in the total Lagrange approach based on the von Karman strains and solved by Newmark time integration. Through the thickness of each piezoelectric layer, the electric potential is assumed linearly. For active control of the piezoelectric composite plates, a close-loop system is used. An optimization procedure using genetic algorithm (GA) is considered to search optimal design for actuator input voltages. Various numerical examples are investigated to show high accuracy and reliability of the proposed method.

The optimum design of laminated composite structures in terms of their strength is a complex task because many different mechanisms are involved in the damage and rupture to which these materials are subject. The great diversity of the damage mechanisms and their patterns of evolution makes it extremely difficult to estimate the strength margins. It is still impossible, for instance, to perform simulations on industrial structures made of unidirectional ply laminates up to rupture. The strategy adopted in this study on designing laminated composite structures is based on the choice of materials (woven or unidirectional plies) and the use of simple models (focusing on the rupture of the first ply) with which industrial structure analyses can be carried out. The choice of materials (woven or unidirectional plies) does not depend only on mechanical criteria but also on the simplicity of the corresponding modelling procedures.

A model of interlaminar fatigue crack growth based on damage accumulation ahead of the crack is proposed. Linear cumulative assumption is used for damage estimation, and a quadratic failure criterion is applied for complex interlaminar loading. Model parameters are determined from mode I and mode II fatigue tests, and used to predict mixed-mode delamination propagation rate. Comparison of theoretical prediction with mixed-mode test results for different brittle graphite FRP at several mode- and load ratios show reasonable agreement.

High-performance composite are fabricated by hot isostatic pressing of matrix and fibers. The cooling conditions in the forming process (Resin Transfer Molding, Structural Resin Injection Molding, Laying-up) play an important part in the thermal residual stress distribution. The existence of residual stresses, combined with mechanical loads, could considerably decrease the durability of laminate structures by leading matrix cracking, fibres breaking and interface delamination initiation. The objective of this study is to investigate the influence of residual stresses on the mechanical behavior of composite laminates. Incremental hole-drilling method combined with 3D FE analysis is used to performed the internal strains in laminate plates [0 2 /90 2 ] s polymerized with different cooling conditions (fast, normal and slow). The emission acoustic events system was used during static tensile tests and the signal interpretations are given by a schematic classification in order to estimated the damage initiation between interfaces. The results of this study show that the general level of the residual stresses changes appreciably with the conditions processing and prove that this new method gives a new prospect for the study of the residual stresses distribution in advanced composites parts.

Equal channel angular extrusion (ECAE) is a promising technique for production of ultrafine grained (UFG) materials of few hundred nanometers size. In this research, the grain refinement of copper strip is accelerated to ultrafine range by sandwiching it between two aluminum strips and then subjecting the three strips to ECAE process simultaneously. After passing the aluminum–copper–aluminum laminated billet through ECAE die up to 8 passes, tensile properties of the copper layer are evaluated. The optical, scanning and transmission electron microscopes, differential scanning calorimeter, and X-ray diffraction were used to characterize the microstructural changes. The results show that the yield stress of the middle layer (Cu) is increased significantly by about eight times after application of four consecutive passes of ECAE and then it is slightly decreased when more ECAE passes are applied. An ultrafine grain within the range of 150 to 200 nm is obtained in the Cu layer.