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Composite materials are often exposed to repeated impact in their industrial applications, which can have serious consequences on their mechanical performance. Therefore, the key purpose of this investigation is to study experimentally and numerically the response of laminated composites and sandwich composites. This involves evaluating their mechanical response and the damage accumulation under repeated impacts. The numerical models developed using the ABAQUS/Explicit software were validated against experimental data obtained through a modified Charpy test, where initial impact energies of 30 J, 40 J, and 50 J were applied to the two composite types under investigation. This was achieved by comparing commonly used parameters such as absorbed energy and induced energy. The results confirm that the first impact is responsible for the damage and that the repetition of the impact has no fundamental effect on the shape of the damage, but slightly increases its surface area. The numerical results made it possible to accurately predict the absorbed energy values and traces of damaged areas observed experimentally. [ABSTRACT FROM AUTHOR]

This paper evaluates the fracture of notched epoxy matrix composites using the Brazilian disk (BD) test from both numerical and experimental points of view. The study began with a comprehensive experimental program covering three different composite lay-ups (quasi-isotropic, unidirectional, and cross-ply) and various geometries of U and V notches. Specifically, the BD samples combined the three layouts, four different notch angles, and three notch radii with three specimens per combination, leading to an overall number of 108 fracture tests. The experiments showed the appropriateness of the BD test for the study of the fracture behavior of composite materials and provided a good pool of data for further investigations. Subsequently, the virtual isotropic material concept (VIMC) was applied in combination with two fracture criteria to theoretically predict the experimentally acquired fracture loads. This study demonstrated that using the VIMC approach can provide robust predictions while incurring much lower computational costs compared to the conventional approaches found in the literature. [ABSTRACT FROM AUTHOR]

The problem of effective elastic properties of stochastic laminated composite is solved. The imperfect interface conditions between the reinforcement and the matrix are assumed to have the form of porous interlayers between the matrix and reinforcement, which are considered as the third component. These layers are perfectly bonded to the matrix and reinforcement, which is expressed as continuity of displacements and surface stresses. The approach is based on the stochastic equations of elasticity for a structurally inhomogeneous material, where the tensor of elastic moduli is a random function of one coordinate and the problem of effective elastic properties has an exact solution. The dependence of the effective elastic properties on the volume fraction of the reinforcement and the porosity of the interlayers is studied. [ABSTRACT FROM AUTHOR]

Abstract Helicopter power transmission systems consist of aluminum drive shafts which are connected together with flexible couplers to accommodate misalignment and hanger bearings to secure each drive shaft to the airframe. The development of carbon fiber composites have resulted in designs which reduce the weight of the system as well as eliminate parts which can be integrated into the composite material itself. The reduction in weight and parts provide transmissions which are more maintenance cost conscious as downtime related to manual part inspection for defects and damage is reduced. One barrier to fielding composite systems is impact qualification to ensure passing of survival standards. Some certainty that a design will not increase the vulnerability of a vehicle must exist and this paper provides an impact study for flexible composite drive shafts and performs a design analysis on tradeoffs between weight, and residual strength. 16 drive shafts with two different thicknesses and the optimized lamination [±45 6 /±40 2 ] were manufactured and impacted with either 7.62 or 12.7 mm projectiles while under 252 N-m of torque. [ABSTRACT FROM AUTHOR]

Abstract In this study, the size and location of delamination effects to layered composites' mechanical properties in buckling behavior are inspected experimentally. Composite plates were produced in accordance with the different dimensions of delaminations and the positions between the layers. These plates consist in delamination rates of a / L = 0.3 , 0.5 , 0.7 (a : Delamination width and L : Buckling length). The specimens were subjected to buckling tests with placed on its two edges, while the others are free. In the experiments two results are considered. First, we determined load-displacement graphs. Critical buckling loads (P c r) were determined from the obtained load-displacement graphs. Second, we acquire lateral displacements, which occurred with the effect of applied load in the delamination area in direction of plate thickness. By comparing P c r with each other, an optimum delamination dimension was determined for composite materials with delamination zones. In the applications, the negative effect on the mechanical properties due to delaminations can be seen, proportionally according to the delamination location. [ABSTRACT FROM AUTHOR]

In this work, two new shear deformation theories namely Trigonometric Deformation Theory (TDT) and Trigonometric-Hyperbolic Deformation Theory (THDT) are developed and implemented for the analysis of laminated and three dimensional braided composite plate. Both models are based upon shear strain shape function which yields non-linear distribution of transverse shear stresses and these models also satisfy the traction free boundary conditions on top and bottom surfaces of the plate. Virtual work principle is used to obtain the governing differential equations and boundary conditions. Both the proposed theories are formulated and validated for the free vibration and buckling of laminated and Three Dimensional (3D) braided composite plate. From the obtained results, the proposed theories are more accurate in predicting the response for free vibration and buckling analysis of laminated and 3D braided composite plates. Intensive numerical studies of 3D braided composite are performed in detail. It is further observed that the geometric parameter (aspect ratio), boundary conditions, fiber volume fraction and braiding angle have significant effect on the free vibration and buckling response of the 3D braided composite plates. In the framework of finite element analysis, both proposed theories anticipate exemplary results for the laminated and braided composite plates compared to existing theories. [ABSTRACT FROM AUTHOR]

Composite materials have many advantages when compared to metallic structures due to their better mechanical properties such as high specific stiffness and strength, high fatigue endurance and better impact properties. In addition, they offer higher corrosion and chemical resistance, better dimensional stability and design flexibility over metallic materials. Especially, in aerospace industry carbon fiber reinforced polymer (CFRP) composite is widely used because of its lightweight and high fatigue strength properties. The work presented in this study includes the effect of different size cutouts at both sides of the CFRP composite cylinder under pure bending. The results of a parametric study, concerning on the effects of a pair of cutouts symmetrically located at ±90° positions with respect to the vertical axis perpendicular to the bending axis, varying size of the cutouts and evaluating their effects on the buckling and maximum load levels of circular cylindrical shell were presented. The analysis methods that were used for the evaluation of the buckling and failure characteristics of shells include linear buckling analysis and nonlinear failure analysis using Riks method. During the nonlinear analysis, the imperfections coming from the buckling eigenvalue analysis were included at rates of 1%, 2.5%, 5% and 10% of the shell thickness to investigate the effect of imperfections. Analyses were performed using the commercial FEM solution ABAQUS. In that model, the stacking sequence was defined to be 24 layers of conventional fiber orientation angles. [ABSTRACT FROM AUTHOR]

The macrostructure and mechanical properties of Al/Cu/Sn multi layered composite produced by room temperature accumulative roll bonding (ARB) is studied. The necking and separation of the reinforcement layers are the main macrostructure evolutions took place during the intermediate cycles. With the increase in the number of the cycles, a uniform distribution of the segmented layers in the matrix is achieved. In addition, the high amount of imposed strain provide higher and faster diffusion path due to increase in dislocation density thus trigger the formation of Cu 6 Sn 5 intermetallic compound. This directly affects the strength and ductility values of the processed work piece. Despite the increasing trend of hardness in Al and Cu layers, the hardness of tin layer remains un-changed due to the high potential of which for dynamic recovery. The tensile strength also increases with the number of cycles, however a decreasing trend can be recognized from the second cycle to the fifth cycle. Surprisingly, the strength again starts to increase continuously up to the eighth cycle. These variations of strength and ductility are properly addressed considering the macrostructure evolution of the laminated composite. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A thermal buckling analysis is presented for laminated cylindrical shells with surface mounted piezoelectric actuators under combined action of thermal and electrical loads. Derivations of the equations are based on the classical laminated shell theory, using the Sanders nonlinear kinematic relations. The analysis uses the Galerkin method to obtain closed form solutions for the buckling loads of shallow and nonshallow piezolaminated cylindrical shells. Temperature dependency of material properties is taken into account. Illustrative examples are presented to verify the accuracy of the proposed formulation. The effects of the various design parameters on thermal buckling loads are investigated. [ABSTRACT FROM PUBLISHER]

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 Mo/Ti 3 SiC 2 laminated composite is prepared by spark plasma sintering at 1300 °C under a pressure of 50 MPa. Al powder is used as sintering aid to assist the formation of Ti 3 SiC 2 . The fabricated composites were annealed at 800, 1000 and 1150 °C under vacuum for 5, 10, 20 and 40 h to study the composite's interfacial phase stability at high temperature. Three interfacial layers, namely Mo 2 C layer, AlMoSi layer and Ti 5 Si 3 solid solution layer are formed during sintering. Experimental results show that the Mo/Ti 3 SiC 2 layered composite prepared in this study has good interfacial phase stability up to at least 1000 °C and the growth of the interfacial layer does not show strong dependence on annealing time. However, after being exposed to 1150 °C for 10 h, cracks formed at the interface. [ABSTRACT FROM AUTHOR]

We report on specific features of the dielectric and magnetic properties as well as magnetoelectric coupling coefficients ( α ME ) of the La 0.7 Ba 0.3 MnO 3 (L)-BaTiO 3 (B) 2–2 type ceramic composite. The powder of L and B was synthesized by two different methods (solid state reaction and Pechini). Orthorhombic and tetragonal phases were observed for the separated phases L and B of the composite, respectively, for both synthesis methods. The characteristics of grain size and interfacial interdiffusion in the L–B–L composite obtained for different synthesis method were studied, showing that diffusion was a typically physical migration, which can be mainly controlled by the grain size. Anomalies in the observed dielectric behavior are attributed to the internal residual stresses and chemically inhomogeneous regions. The existence of a broad magnetic transition observed in the pure L phase and laminated L–B–L composite was also attributed to its small grain size. A comparison of the maximum transversal ( α 31 ME ) and longitudinal ( α 33 ME ) ME coupling coefficients, at room temperature, is also shown. [ABSTRACT FROM AUTHOR]

Transmission structures such as transmission towers or transmission poles were designed to endure multiple combinations of acting force. However, these current structures that were made from concrete and metal are heavyweight materials that cause difficulties in handling during assembly, maintenance and reinstallation purposes. The other problem is vandalism issues on the metallic bracing of the transmission towers. Glass fiber reinforced polymer, (GFRP) is a type of fiber reinforced composites that combine the continuous high strength reinforcing fiber material and lightweight properties of polymeric matrix, thus offers an alternative solution for those problems. In this paper, a laminate design of GFRP samples were simulated using CompositeStar© software to determine the mechanical strength and its reserve factor. The composite panels were varied in term of fiber direction and it was designed to withstand a distributed load of 5 kN service load in longitudinal (x-axis) and transverse (y-axis) direction on samples with thickness range between 4.00 to 4.20 mm. From the simulated results, it shows that the panels with fiber orientation in bi-direction and quasi-direction display a balance strength and acceptable reserve factor in both x-direction and y-direction. Therefore the properties and reserve factors of laminate design simulated from this software can be used as a benchmark in designing a laminated composite. [ABSTRACT FROM AUTHOR]

A previous paper stated the method of determination of the neutral surface of a composite monolithic, laminate composite, organizing some of the component layers, go to the method of distribution of tasks developed in one given case. This regard illustrates several possible options of which results can enable a proper assessment of the maximum strains and alignment layers, ensuring a maximum lifting capacity. The study can be developed to optimize the organization of layers, depending on the practical purpose of using the composite structure (mechanical, thermal and / or sound). [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]

A modified Fourier series method is applied to study the free vibration of laminated composite and four-parameter functionally graded sector plates with general boundary conditions. The first-order shear deformation plate theory is employed to include the effects of rotary inertias and shear deformation. Regardless of the boundary conditions, each of the displacement and rotation components of the sector plates is described as a linear superposition of a double Fourier cosine series and several supplementary functions introduced to accelerate the convergence of series representations. The Rayleigh–Ritz procedure based on the energy functions of the sector plates is adopted to solve the exact solutions. In order to verify the accuracy and reliability of the present method, comparisons of the present results with those published are presented. New numerical results for laminated composite and functionally graded sector plates with elastic restraints are given. The effects of the boundary conditions and material and geometrical properties on the frequencies of the sector plates are investigated. [ABSTRACT FROM AUTHOR]

This article focuses on geometrically nonlinear transient analysis of thick deep laminated composite curved beams with generalized differential quadrature method. Generalized differential quadrature method is coupled with the weak form of the equation of motion. Virtual work principle is used to derive the equation of motion. Spatial derivatives in the equation of motion are expressed with generalized differential quadrature method. Geometric nonlinearity is considered through Green–Lagrange nonlinear strain–displacement relations that are derived using elasticity theory equations. First-order shear deformation theory is used to consider the transverse shear effect. Time integration of the equation of motion is carried out using Newmark average acceleration method. Several problems from the literature are solved with the proposed method and results are compared. [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]

The results of an investigation of impact fracture in laminated composite material are presented in this paper. Low velocity impact fracture tests were carried out on single edge notched three-point bending (SENB) specimens using a drop-weight rig. An inclined notch was introduced in the SENB specimen in order to generate mixed-mode I/II crack loading conditions. Different mixed-mode ratios were obtained by varying the notch inclination from 10° to 90° with a step of 10°. The SENB specimens were subjected to various impact potential energies by varying the drop-height in order to determine the critical impact potential energy at which the crack growth initiates from the initial notch tip position for each of the considered notch inclinations. The mechanical response of the SENB specimen to impact loading was analyzed using a two-dimensional linear-elastic finite element model. Good agreement was obtained between the predicted contact force -- time curve and the measured one at various impact potential energy levels and notch inclinations. The strain energy release rate mode components were computed by the virtual crack closure technique. The composite fracture toughness under impact loading was characterized in terms of the critical dynamic strain energy release rate at the onset of crack growth. It was found that the fracture toughness under impact loading increases with decreasing the notch inclination. This finding was attributed to the increase of mode II component of crack loading. A comparison of the fracture behaviour under impact and static loading was performed. It was found that the fracture toughness under impact loading was between 19% and 23% lower than the static one for the different notch inclinations. Therefore, it was concluded that static fracture toughness should not be used in the fracture mechanics based design of composite structures which are subjected to impact loading during their lifetime. [ABSTRACT FROM AUTHOR]

This paper presents the uniaxial and biaxial buckling analysis of rectangular plates based on new trigonometric shear and normal deformation theory. The theory accounts for the cosine distribution of the transverse shear strain through the plate thickness and on the free boundary conditions on the plate surfaces without using the shear correction factor. Governing equations and boundary conditions of the theory are derived by the principle of virtual work. The Navier type solutions for the buckling analysis of simply supported isotropic, transversely isotropic, orthotropic and symmetric cross-ply laminated composite rectangular plates subjected to uniaxial and biaxial compressions are presented. The effects of variations in the degree of orthotropy of the individual layers, side-to-thickness ratio and aspect ratio of the plate are examined on the buckling characteristics of composite plates. The present results are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT) and exact three-dimensional (3D) elasticity theory wherever applicable. Good agreement is achieved of the present results with those of higher order shear deformation theory (HSDT) and elasticity theory. [ABSTRACT FROM AUTHOR]

This article is about a layerwise finite element which is developed for the linear static analysis of laminated composite plates. In the first part; the paper presents a review of the literature involving the available theories and their drawbacks for multilayered composite plates. A second part reviews a relevant keypoint (zig-zag form of the displacement field in the thickness direction) that should be considered for an accurate stress and strain field. In the third part, the paper explains the layerwise finite element and the derivation of its stiffness matrix. The final part of the paper is devoted to giving a comparison of selected results that can be acquired either by layerwise finite element(Genson) or the other available theories in the literature. [ABSTRACT FROM AUTHOR]

Abstract: A stress function-based approach is proposed to analyze the free-edge interlaminar stresses of piezo-bonded symmetric laminates. The proposed method satisfies the traction free boundary conditions, as well as surface free conditions. The symmetric laminated structure was excited under electric fields that can generate induced strain, resulting in pure extension in the laminated plate. The governing equations were obtained by taking the principle of complementary virtual work. To verify the proposed method, cross-ply, angle-ply and quasi-isotropic laminates were analyzed. The stress concentrations predicted by the present method were compared with those analyzed by the finite element method. The results show that the stress function-based analysis of piezo-bonded laminated composite structures is an efficient and accurate method for the initial design stage of piezo-bonded composite structures. [Copyright &y& Elsevier]

This article presents the efficient mixed model analysis, often called global–local approach, to obtain interlaminar stresses at free edges in the laminated composite system under extension and flexure. For the proposed analysis, first, the discrete-layer elements are adopted as three-dimensional elements in the local region. Second, the equivalent single-layer elements are considered as two-dimensional elements in the global region. Finally, the mixed-dimensional transition elements are formulated to connect two different element types used in the global as well as the local regions, respectively. All the elements have higher order shape functions derived from the Lobatto shape function. Modes of the elements are classified into nodal and nodeless modes. The nodal modes have physical meaning, while nodeless modes with respect to the increase of order of the Lobatto shape function do not have physical meaning but improve accuracy of analysis. Therefore, fixing mesh arrangement of present analysis, the quality of the analysis can be enhanced without remeshing work. Some results obtained by the proposed approach are verified with comparison with published references. Also, efficiency of the mixed model analysis using the mixed-dimensional transition element is shown through comparison with numerical results obtained by the single model analysis using only discrete-layer elements. [ABSTRACT FROM PUBLISHER]

The so-called bi-value coding parameterization (BCP) method is developed for the simultaneous optimization of layout design and discrete fiber orientations of laminated structures related to the compliance minimization and natural frequency maximization. Both kinds of problems are transformed into a discrete material selection problem that is then solved as a continuous topology optimization problem with multiphase materials. A new form of the volume constraint is introduced in accordance with the BCP to control the material usage and material removal in the corresponding problem formulation. The BCP scheme assigning the integer value of +1 or -1 to each design variable for the unique “coding” is efficiently used to interpolate discrete fiber orientations and to identify the presence and removal of materials. Meanwhile, a general set-up strategy is proposed by assigning “uniform” weight values in BCP to ensure the feasibility of the initial starting point. Numerical tests illustrate that the BCP is efficient in dealing with both kinds of design problems including the volume constraint. [ABSTRACT FROM AUTHOR]

Highlights: [•] Composite optimization often produces a continuous representation of the ply numbers. [•] An integer representation is obtained by the lamination parameter matching. [•] A permutation GA is used to achieve the matching. [•] A wing box benchmark problem is used to demonstrate the potential of the technique. [Copyright &y& Elsevier]

Highlights: [•] A model was developed for elastoplastic analyses of metal matrix composites. [•] It was applied for multiscale analysis by linking constituent and composite levels. [•] Thermal or mechanical residual stresses were computed at both levels. [•] Various examples were provided to demonstrate the developed model. [ABSTRACT FROM AUTHOR]

The present investigation is devoted to the development of new optimal design concepts that exploit the full potential of advanced composite materials in the upper covers of aircraft lateral wings. A finite-element simulation of three-rib-bay laminated composite panels with T-stiffeners and a stiffener pitch of 200 mm is carried out using ANSYS to investigate the effect of rib attachment to stiffener webs on the performance of stiffened panels in terms of their buckling behavior and in relation to skin and stiffener lay-ups, stiffener height, and root width. Due to the large dimension of numerical problems to be solved, an optimization methodology is developed employing the method of experimental design and the response surface technique. Minimal-weight optimization problems were solved for four load levels with account of manufacturing, repairability, and damage tolerance requirements. The optimal results were verified successfully by using the ANSYS and ABAQUS shared-node models. [ABSTRACT FROM AUTHOR]

Abstract: In present study, a new inverse hyperbolic shear deformation theory is proposed, formulated and validated for a variety of numerical examples of laminated composite and sandwich plates for the static and buckling responses. The proposed theory based upon shear strain shape function yields non-linear distribution of transverse shear stresses and also satisfies traction free boundary conditions. Principle of virtual work is employed to develop the governing differential equations assuming the linear kinematics. A Navier type closed form solution methodology is also proposed for cross-ply simply supported plates which limits its applicability. However, it provides accurate solution which is free from any numerical/computational error. It is observed that the present theory can be more accurately applied for the modeling of laminated composite and sandwich plates at the same computational cost as that of other shear deformation theories. [Copyright &y& Elsevier]

Abstract: This paper examines the problem of the torsional loading of a composite strip composed of eleven layers of unidirectionally reinforced elements that are fully bonded. The shear moduli are obtained from the experimental torsional stiffnesses (T/ϕ) and data reduction techniques based on the orthotropic rectangular strip torsion model by Lekhnitskii. The stacking of laminae is also used to construct a computational model of the strip. [Copyright &y& Elsevier]

A proposed damage model is used for investigating the deformation and interfacial failure behavior of an adhesively bonded single-lap thick joint made of S2 glass/SC-15 epoxy resin composite material. The bonding material is 3M Scotch-Weld Epoxy Adhesive DP405 Black. Continuum damage mechanics models are used to describe the damage initiation and final failure at or near the interface. The effect of adhesive overlap length, thickness, and plasticity on the interfacial shear and normal stresses is studied. Experimental and analytical data are used to validate the proposed damage models. [ABSTRACT FROM AUTHOR]

Abstract: Vacuum brazing of Ni–NiCr laminated composite to Cr18–Ni8 steel was carried out using Ni–Cr–Si–B amorphous foil. Microstructure characteristic of the brazed joints was investigated by scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), field-emission scanning electron microscope (FE-SEM) and microsclerometer. Ni–Cr–Si–B amorphous foil exhibited good wettability on Ni–NiCr laminated composite. The brazed region consisted of γ-Ni solid solution and Ni–B eutectic. An excellent bonding with shear of 170 MPa was obtained. An interface of Ni3B precipitated in Ni cover layer near the brazed region. Microhardness of the interface was 500 HV. There was an interface consisting of fine boride granules in Cr18–Ni8 steel close to the brazed region and microhardness of the interface was 250 HV. Bonding behavior of the brazed joint was described according to the microstructure characteristic. [Copyright &y& Elsevier]

Abstract: Ferromagnetic shape memory alloy Ni49Fe18Ga27Co6 was used in a laminated composite with Pb(Zr0.52Ti0.48)O3 for studying the converse magnetoelectric (CME) effect. The CME properties with the frequency of driving electric voltage, bias magnetic field, and dc bias electric voltages were investigated in detail. A large value of α B of 1.05G/V at the resonance frequency 89kHz is observed under a low optimum H bias of 100Oe. The maximum values of α B at 1kHz can be tuned from 8.7 to 25mG/V by increasing dc voltage bias from −100 to 100V, exhibiting a giant tunable range in α B values. This composite exhibits promising applications in electrically controlled magnetic force devices. [Copyright &y& Elsevier]

Abstract: Vacuum brazing of super-Ni/NiCr laminated composite and Cr18–Ni8 steel was performed using NiCrP filler metal. Microstructure, elemental distribution, microhardness and shear strength were investigated by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electromechanical universal testing machine. An excellent joint was obtained at 1040°C for 20min and the shear strength was as high as 137MPa. The brazed region was divided into solid solution zone and eutectic zone. Elemental distribution indicated that P mainly concentrated in the eutectic zone in the form of Ni3P. Ni2Cr particles precipitated in NiCr base layer under the influence of thermal cycling. [Copyright &y& Elsevier]

The studies on the deformation and short- and long-term damage of homogeneous and composite materials are systematized. In the case of short-term damage, a single microdamage is modeled by an empty quasispherical pore formed in place of a microvolume damaged in accordance with the Huber-Mises or Schleicher-Nadai failure criterion. The ultimate microstrength is assumed to be a random function of coordinates. In the case of long-term damage, the damage of a single microvolume is characterized by its stress-rupture strength determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength. The equation of porosity balance at an arbitrary time and the equations relating macrostresses and macrostrains constitute a closed system. Algorithms of calculating the dependence of microdamage and macrostresses on time and macrostrains are developed. The effect of temperature and the resistance of particles of damaged material on the curves is studied [ABSTRACT FROM AUTHOR]

The studies of mathematical models for the coupled processes of deformation and long-time damage of stochastic composite materials are systematized. Damage is modeled by stochastically arranged micropores. The damage of a single microvolume is characterized by its stress-rupture strength determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength, according to the Huber-Mises or Schleicher-Nadai criteria, and assumed to be a random function of coordinates. The equation of damage balance at an arbitrary time and the equations relating macrostresses and macrostrains constitute a closed system. Algorithms of calculating the time dependence of microdamage and macrostresses are developed. The effect of temperature and nonlinearity on the curves is studied [ABSTRACT FROM AUTHOR]

This article aims at optimizing laminated composite plates taking into account uncertainties in the structural dimensions. As laminated composites require a global optimization tool, the Particle Swarm Optimization (PSO) method is employed. A new Reliability Based Design Optimization (RBDO) methodology based on safety factors is presented and coupled with PSO. Such safety factors are derived from the Karush-Kuhn-Tucker optimality conditions of the reliability index approach and eliminate the need for reliability analysis in RBDO. The plate weight minimization is the objective function of the optimization process. The results show that the coupling of the evolutionary algorithm with the safety-factor method proposed in this article successfully performs the RBDO of laminated composite structures. [ABSTRACT FROM AUTHOR]

The problem of bifurcational instability of cylindrical shells made of laminated composite materials with components subject to long-term damage is formulated and solved [ABSTRACT FROM AUTHOR]

The structure and vibration control system of smart laminated composites consisting of graphite–epoxy composites and piezoelectric actuators are designed for optimum vibration suppression. The placement of piezoelectric actuators, the lay-up configurations of laminated composite plates, and the H2 control system are employed as design variables and they are optimized simultaneously by a simple genetic algorithm. To reduce complexity, only pre-selected families of lay-up configurations are considered. An objective function is the H2 performance with respect to the controlled response for vibration suppression. A multidisciplinary design optimization is performed with the above three design variables and then the output feedback system is reconstructed with a dynamic compensator based on a linear matrix inequality approach. The validity of the modeling and calculation technique is confirmed experimentally. Optimization results show that optimized smart composites with the present approach successfully realize vibration suppression and it is confirmed that the proposed multidisciplinary design optimization technique enhances the vibration suppression of smart composites. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents nonlinear static analysis of a rectangular laminated composite thick plate resting on nonlinear two-parameter elastic foundation with cubic nonlinearity. The plate formulation is based on first-order shear deformation theory (FSDT). The governing equation of motion for a rectangular laminated composite thick plate is derived by using the von Karman equation. The nonlinear static deflections of laminated plates on elastic foundation are investigated using the discrete singular convolution method. The effects of foundation and geometric parameters of plates on nonlinear deflections are investigated. The validity of the present method is demonstrated by comparing the present results with those available in the literature. [Copyright &y& Elsevier]

For a variety of modern industries, interfacial delamination is a critical issue for the design and application of laminated composite structures. Numerous global experimental studies have been conducted to characterize the toughness of adhesively bonded composite structures. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions. The local interfacial traction-separation laws as the fundamental input are crucial for the successful applications of CZMs. Several local tests have also been conducted to determine the interfacial traction-separation laws in adhesively bonded joints. However, very few tests have been employed to investigate the dependency of the local interfacial traction-separation laws on the bondline thickness, particularly, for the laminated composite joints under Mode-II loading conditions. In this work, the effects of bondline thickness on the interfacial behavior have been systematically investigated at various typical bondline thicknesses (from 0.1 to 0.8 mm). The effects of adhesive thickness on the interfacial toughness, interfacial strength, and shapes of the local interfacial traction-separation laws have also been evaluated. The test results indicated that the measured Mode-II (shear test) interfacial shear strength of the composite joints increases as the adhesive layer becomes thicker. It was found a significant dependency of the measured shapes of the Mode-II interfacial laws on the bondline thickness. Several other interesting issues were also reported in this work. This work may provide valuable baseline test data for analytical and numerical modeling of fracture and failure of laminated composite structures. [ABSTRACT FROM AUTHOR]

This study has been designed to experimentally assess the changes of buckling loads of the E-glass fiber/epoxy composite laminates impacted at different impact energy levels. With the experiments conducted, the effects of the geometry parameters such as the ratio of impact point to the length of buckling (G = y/L) have been examined. According to the results of the experiments made, when the ratio of impact position is 0.2, buckling behaviors of the impacted specimens made at the energy levels of and under 10 J have been determined to be almost the same as the buckling behaviors of the non-impacted specimens. Generally, it has been found out that buckling behaviors of the impacted specimens made at the energies under such levels of energy as 15 J increase with the impact point ratio, and when the ratio is 0.2, buckling behaviors have been observed to be maximum. [ABSTRACT FROM AUTHOR]

Super Ni laminated composite and 1Cr18Ni9Ti stainless steel were welded by the tungsten inert gas process with the Cr25-Ni13 filler alloy. The microstructure, element distribution and phase formation near the fusion zone were evaluated by standard technique. Results indicated the formation of four main regions: the fusion transition region on the 1Cr18Ni9Ti steel side, the fusion transition region on the super Ni laminated composite side, a columnar crystal weld region and the weld centre region. The microstructure on either side of the weld was characterized by strong directionality and changed from columnar austenite to equiaxed austenite in the weld centre. A Ni, Fe and Cr element transition region, about 30 μm wide, was formed at the fusion zone on the super Ni side. The phase formed into welded zone was composed mainly of austenite, δ-Fe, γ-Ni(Cr, Fe) and FeNi intermetallic compounds. [ABSTRACT FROM AUTHOR]

Abstract: Baffles are used effectively to reduce the sloshing response of liquid in the liquid storage containers. In this paper, the dynamic interaction that exists between the liquid and elastic tank–baffle system has been considered to evaluate the coupled response of liquid and tank–baffle system using the finite element method. The baffle and tank wall are made up of lightweight laminated composite materials. The liquid is assumed to be incompressible and inviscid, and the flow is irrotational. The finite element equations of motion of liquid and structure domains are numerically integrated by Newmark’s integration scheme. The interaction effect between the two fields is studied by transferring the structural normal acceleration to the liquid domain and liquid pressure to the structure domain. Effects of different parameters, such as being composite baffles, lamination scheme on the slosh frequencies and coupled vibration frequencies in the liquid filled composite tanks have been studied. The effects of composite baffle parameters, such as being its dimensions and position in the tank wall, on the sloshing response of liquid and structural response of liquid filled composite tank are studied under translational base excitation. [ABSTRACT FROM AUTHOR]

Abstract: With assumption of material inhomogeneity on meso level, a three-point bending beam model has been adopted to simulate crack propagation in two dimensional laminated composite and to verify the toughening mechanism of energy dissipation and crack deflection along the weak interlayer. Moreover, the effect of strength, elastic modulus and thickness of the weak interlayer on both strength and toughness of the laminated composite have also been investigated in this paper. [Copyright &y& Elsevier]

A nine noded flat plate element, considering first order transverse shear deformation and rotary inertia with five degrees of freedom per node, is used to compute element stiffness and mass matrices for composite plates. Drilling degrees of freedom are introduced to account for three translations and three rotations per node, and transformed to obtain the global matrices for computing the dynamic response of stiffened laminated composite and sandwich folded plate structures. The stiffeners are visualized as parts of the folded plate. The formulation works well. New results for stiffened folded plates are reported with different arrangements of stiffeners to observe their effects. [ABSTRACT FROM AUTHOR]

The main objective of the present investigation was to examine how the damping properties of laminated composite plates vary with changes in the plate dimensions. Also, it was very important for plates with different ply-orientations to see how the dynamic characteristics vary from one plate to another or when the fibre-orientation was changed. The theoretical prediction of the natural frequency, mode shape and specific damping capacity for each mode obtained using the finite element method was to be compared with experimental results. [ABSTRACT FROM AUTHOR]

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites. [ABSTRACT FROM AUTHOR]

A general constitutive relationship for describing the inelastic and strength behavior of laminated composites reinforced with various fiber preforms was presented in References. The relationship is consistent in that when the fiber disappears or becomes the same as the matrix, the nonlinear constitutive equations of the resulting composite deteriorate to those of the isotropic matrix material. One of the best benefits of the constitutive relationship is that all the formulas involved are in explicit form and only the properties of the constituent fiber and matrix of the composite are required as input material data. This will significantly simplify a finite element analysis for a laminated structure. In the present paper, the general constitutive relationship for tape laminates was programmed into a user subroutine, UGENS, of the commerciaI finite element (FE) software ABAQUS, Several laminated structures including a complicated bone plate were then analyzed, and good correlation between the numerical results and available experimental data was found. A list of the original computer code together with an input data file was summarized in the appendixes of the paper. [ABSTRACT FROM AUTHOR]