Sandwich Structures

This paper presents the time history response of a sandwich beam with a porous core subjected to two moving harmonic loads with opposite directions. In the modelling, the beam is combined of two isotropic face sheets and a porous core with symmetric porosity distribution. The quasi-3D shear deformation beam theory in conjunction with Hamilton's variational principle is utilized to set up the governing equations of motion. The Navier solution is used to obtain the displacement field. The accuracy of the study is validated by comparing with existing results in the literature for specific cases. Effects of the velocity and excitation frequency of the moving loads on the deflection-time history are investigated and discussed. Numerical results reveal that in the case of the doublemoving harmonic loads in the antiphase, the resonance phenomenon cannot occur when the excitation frequency approaches the natural frequency of the beam.

This paper is a presentation of the process used for the manufacture of ultra-high-performance concrete (UHPC) Cladding Panel with Complex Geometry. It discusses the basic principles, mixing proportions, mixing techniques, molding materials, and pouring techniques to produce high-quality UHPC. The high proportion of ultrafine particles used in UHPC enables optimal packing to minimize composite porosity using a very low water-binder ratio. Molding materials used successfully in the manufacture of UHPC precast elements are steel, silicone, polyurethane, lexan, glass, epoxy-painted wood, and Teflon. UHPC, also known as [1] reactive powder concrete, is characterized by its high strength and ductility due to the presence of metallic or non-metallic fiber reinforcement. The manufacturing process followed in this paper aims to optimize the mix for the most appropriate water:cement ratio and superplasticizer:cement ratio to achieve the target strength and workability. UHPC is a material that is currently gaining momentum in terms of research and implementation due to its outstanding qualities and superiority in comparison with conventional and high-strength concrete.

In this research, a hexagonal honeycomb core under a compressional load is studied numerically from the initial elastic regime to the fully crushed state using the Abaqus finite-element modelling. Two modelling approaches, i.e., a static analysis and an explicit non-linear analysis are applied to a 3D model of an aluminium honeycomb core. This honeycomb structure is compressed quasi statically using rigid plates and displacement control. Moreover, the crushing of the honeycomb-core structure and the failure due to buckling are verified numerically, and a study is also performed to show how different densities, cell sizes and specimen sizes can affect the average crush force and plateau force. A comparison between experimental and numerical results is drawn, showing that the numerical models can effectively predict the mean crushing force and mechanical behaviour with a good accuracy.

In this paper, nonlinear stability of axially compressed cylindrical panels simply supported according to two types of boundary conditions (with possible or limited circumferential displacements of unloaded sides) is presented. Panels made of functionally graded materials (FGMs) of two constituents (metallic and ceramic phases) are treated as multi-layered composite structures with transverse inhomogeneity. Volume fractions of ceramics and metal distribution throughout the layer thickness are described by a simple power law. The influence of the transverse inhomogeneity of FGM panels on unsymmetrical stable post-buckling paths is shown. Special attention is paid to effect of the imperfection sign on post-buckling paths of investigated FGM panels. Some validations of the finite element analysis are discussed for isotropic panels compressed according to two (force and kinematic) loading schemes.

Structural sandwich beams are widely used because of their high specific stiffness and strength, noise reduction, thermal insulation and impact energy absorption characteristics. Conventional manufacturing method of composite sandwich structures is completed by a separate adhesive joining stage by which the composite faces are joined to the core. In this investigation, liquid phase sintering in the Al-Zn alloy system was used in order to form a diffusion bond between metallic foam and plate. Joining treatment was conducted at 610 o C for 30 minutes in an inert atmosphere. The shear strength of the joint was measured to be about 4.8 kPa.

This paper aims to characterise the mechanical behaviour of folded timber sandwich structures developed using integral rotational press-fit (RPF) joints. Six folded arches are tested to failure, under three load cases designed to induce different sagging and hogging conditions at internal joints. Experimental testing showed failures occurring at joint locations with maximum hogging moment, with two failure types observed as FRP tensile fracture and core compressive rupture. A nonlinear static analysis and simplified 2D frame model is proposed to predict moment distribution and failure load for FRP fracture modes. This model characterises the RPF joint as a nonlinear semi-rigid hinge, with assigned bilinear moment-curvature relation obtained from analysis of joint strain data collected during arch testing. Core compressive failures are shown to occur as an inelastic core buckling behaviour when there is misalignment between assembled core segments.

Functionally gradient materials are one of the most widely used materials in various applications because of their adaptability to different situations by changing the material constituents as per the requirement. Nowadays it is very easy to tailor the properties to serve specific purposes in functionally gradient material. Most structural components used in the field of engineeringcan be classified as beams, plates, or shells for analysis purposes. In this paper static analysis of functionally gradient material plate is carried out by sigmoid law and verified with the published results. The plate is modeled in step wise variation of the properties in thickness direction. The convergence study of the results is optimized by changing the mesh size and layer size. Power law and exponential laware applied for the same material and set of conditions. Results have been presented comparing with each other and the published results. Keyword: Functional composites, elastic properties, finit...

Existing sandwich structures failure maps are confined only to data from the quasi-static bending tests even for describing failure modes due to the impact event. Strengths of the constituent layers, which are not well-described by these maps, can reasonably change especially under the repeated impact load case. Hence, a new series of more realistic failure mode maps have been developed from the experimentally and numerically obtained observations on recently proposed bio-inspired dual-core sandwich beams in the presence of repeated low-velocity impacts of different energy levels. The beams consist of top and bottom carbon fiber reinforced polymer skins sandwiching the rubber and aluminum honeycomb cores. Departing from the modified Gibson model, an actual presentation of skin and core behaviors has been modeled following the trend of strengths variations for the construction of the failure mode maps when subjected to numerous impact numbers and energies. The produced maps offer the flexibility to accommodate the changes in strengths due to deterioration or densification of constituent layers after impact, and hence following more favorably the physical failure description of the sandwich beams. Accompanying these maps, a general set of mathematical expressions have also been produced for practical convenience. It is found that the failures from observations are within the proposed map boundaries with accuracies ranging from 85.7% to 100%.

The present paper deals with the influence of the axial extension mode on static and dynamic interactive buckling of a thin-walled beam-column with imperfections subjected to uniform compression when the shear lag phenomenon and distortional deformations are taken into account. A plate model (2D) is adopted for the beam-column. One-and two-dimensional models of the elements are compared, too. The structure is assumed to be simply supported at the ends. Equations of motion of the component plates are obtained from Hamilton's Principle, taking into account all components of inertia forces. Within the frame of the first order nonlinear approximation, the dynamic problem of modal interactive buckling is solved by the transition matrix using the perturbation method and Godunov's orthogonalization.

Fibre metal laminates (FMLs) have been widely used to manufacture airframe components. This work describes novel sisal fibre reinforced aluminium laminates (SiRALs) that have been prepared by cold pressing techniques and tested under tensile, flexural and impact loading. The pristine sisal fabric and the sisal fibre reinforced composites (SFRCs) were also tested to understand the difference in mechanical performance of the sisal fibre metal laminates. The SiRALs achieved not only the highest modulus and strength, but also the highest specific properties. The mean specific tensile strength and modulus of the SIRALs reached increases of 132% and 267%, respectively, when compared to the sisal fibre reinforced composites (SFRCs). Moreover, the mean specific flexural strength and modulus of the SiRALs were significantly higher than SFRCs, revealing increases of 430% and 973%, respectively. A delamination fracture mode was noted for SiRALs under bending testing. The SiRALs can be considered promising and sustainable composite materials for structural and multifunctional applications.

This book, written in Persian, covers classical materials and theories of plates and shells, as well as more advanced topics such as higher-order theories and non-homogeneous and non-isotropic structures. It also includes information on plates and shells made from smart materials such as FGMs, composites, piezoelectrics, porous materials, and sandwich panels, suitable for applications at macro, micro, and nano scales. The book is comprehensive and suitable for undergraduate, master's, and doctoral students, presenting concepts clearly and logically for educational and practical purposes. With twenty-four chapters, it provides a study of the mechanics of plates and shells based on basic concepts and simple methods, offering necessary formulas for the analysis and design of engineering structures and mechanical parts.

در این کتاب که شامل بیست و چهار فصل می‏باشد، مطالعه مکانیک ورق ‏ها و پوسته‏ ها بر مبنای مفاهیم بنیادی و با روش‏های ساده‏ای انجام شده ‏است. بدین ترتیب تمامی فرمول ‏های لازم با روشی گویا، منطقی و واضح به‏ دست آورده شده و می ‏توان آن‏ ها را برای تحلیل و طراحی سازه‏ های مهندسی و قطعات مکانیکی مورد استفاده قرار داد.
در این کتاب به طور جامع علاوه بر مطالب و تئوری ‏های کلاسیک ورق و پوسته، مباحث و تئوری ‏های پیشترفته ‏تری نظیر تئوری ‏های مرتبه بالاتر، همچنین ورق‏ های غیرهمگن و غیرایزوتروپ، ورق‏ها و پوسته‏ هایی از جنس مواد هوشمند که به تازگی به شدت مورد توجه محققان و دانشمندان قرار گرفته‏ اند نظیرورق از جنس تابعی مدرج، ساختارهای کامپوزیتی، پیزوالکتریک‏ ها، مواد متخلخل یا پروالاستیک و نیز ساندویچ پانل‏ ها که قابلیت کاربرد برای مقیاس ‏های مایکرو، میکرو و نانو را دارا می‏باشند، گردآوری و ارائه شوند. این کتاب به دلیل روان بودن متن که موجب جذابیت ناشی از انتقال مفاهیم می‏شود، پیوستگی، گستردگی و نیز تنوع مطالب جهت استفاده برای دانشجویان مقاطع کارشناسی، کارشناسی ارشد و دکتری از جنبه آموزشی و نیز کاربردی بسیار مناسب و جامع ارزیابی می‏شود.

This paper illustrates the effectiveness of two functionally graded (FG) layers on a homogenous circular plate for bending analysis. The classical plate theory (CPT) serves as the basis of the analysis. Differential quadrature method (DQM) as semi-analytical method is employed to solve the governing equations. The material properties is varied to obey power law in terms of the plate thickness direction. The plate is subjected to uniform transverse loading and resting on Winkler elastic foundation. In this study, the effect of the different profile of the plate thickness, elastic foundation coefficient, the volume fraction FG index, and effect of the boundary conditions, namely, simply supported and clamped edge on static response are demonstrated. The results are compared with finite element method and published literature that observed to be in accordance with each other.

In this paper, the supersonic flutter of Magneto-rheological fluid-based adaptive plates is considered. The structural formulation is based on the classical plate theory, the MR fluid core is modeled as a first order Kelvin-Voigt material and the quasi-steady first order supersonic piston theory is employed to describe the aerodynamic loading. The critical dynamic pressures at which unstable plate oscillations occur, are obtained via p method for selected applied magnetic field strengths and different base layer's materials and thicknesses.

In this paper, hexahedral piezoelectric solid-shell finite element formulations, with linear and quadratic interpolation, denoted by SHB8PSE and SHB20E, respectively, are proposed for the modeling of piezoelectric sandwich structures. Compared to conventional solid and shell elements, the solid-shell concept reveals to be very attractive, due to a number of well-established advantages and computational capabilities. More specifically, the present study is devoted to the modeling and analysis of multilayer structures that incorporate piezoelectric materials in the form of layers or patches. The interest in this solid-shell approach is shown through a set of selective and representative benchmark problems. These include numerical tests applied to various configurations of beam, plate and shell structures, both in static and vibration analysis. The results yielded by the proposed formulations are compared with those given by state-of-the-art piezoelectric elements available in ABAQUS; in particular, the C3D20E quadratic hexahedral finite element with piezoelectric degrees of freedom.

The aim of this work is to propose vibration modeling of sandwich structures with soft core using solid-shell finite elements. Several approaches have been adopted in the literature to accurately model this type of structures; however, they show some limitations in certain configurations of high contrast of material properties or geometric aspect ratios between the different layers. In such situations, it is generally well-known that the use of higher-order or three-dimensional finite elements is more appropriate, but will generate a large number of degrees of freedom and, thereby, large CPU times. In this work, an alternative method is proposed by considering a recently developed linear hexahedral solid-shell element. This solid-shell element is implemented into Matlab in order to use the so-called solver Diamant, which couples Asymptotic Numerical Method (ANM) and Automatic Differentiation (AD). Numerical tests, including various cantilever sandwich beams as well as a simplified pattern of rail on sleepers, are performed to show the efficiency of the proposed approach.

Composite sandwich panels are progressively being employed in the aircraft industry for floor panels, compartment partitions, bulkheads and even the skin and wings of aircraft. Lightweight structures are essential for aircraft operations because they allow for faster takeoff and landing. The sandwich panel comes into play in this situation. Composites with stiff, high-strength skin facings are bonded to a low-density core to form multi-layered materials with a high mechanical strength. Using finite element analysis and experimental equipment, composite sandwich panels are constructed, tested and evaluated under various load circumstances. The panel's expected compressive strength and flexural stiffness values were then calculated for various operating conditions. A mean difference of 0.28 is seen between the stresses in both x and y directions of the panel over a loading range of 1kg to 60kg. The standardised values of the strains were used to compare them using Bayesian estimation, which outperforms the t test. Ec increases by nearly 20 times when the side length is increased by 10% compared to when the side length is increased by 50%. For a given span length and when an is fixed, the flexural stiffness at f1=0.002 is nearly 2 times higher than that at f1=0.006. Although there are differences in the displacements and strains, the overall trend is fairly pleasing. The exact numerical conditions were not produced due to the experimental challenges, but the loading and displacements were equal.

Composite sandwich structures are usually utilized in aviation application, transport building, connect, and so on because of their low weight and superb solidarity to weight proportion. In the most recent decades, light-weight center materials, for example, honeycomb, wood, foam center have been utilized in make sandwich structures dependent on required. For this situation, sandwich structure with jute epoxy composite honeycomb center and carbon fiber face sheet is to be displayed, created, manufactured. The composite sandwich structures were made utilizing hand lay-up and vacuum sacking producing process. Design of honeycomb structure is performed in CATIA and analysis in ANSYS software. The practices of these structures under threepoint bending is to be explored. Flexural conduct of these structures has been tentatively and limited component researched. IndexTerms FEA, Sandwich composite Panel, UTM.

The active flutter control of supersonic sandwich panels with regular honeycomb interlayers under impact load excitation is studied using piezoelectric patches. A non-dominated sortingbased multi-objective evolutionary algorithm, called non-dominated sorting genetic algorithm II (NSGA-II) is suggested to find the optimal locations for different numbers of piezoelectric actuator/sensor pairs. Quasi-steady first order supersonic piston theory is employed to define aerodynamic loading and the p-method is applied to find the flutter bounds. Hamilton's principle in conjunction with the generalized Fourier expansions and Galerkin method are used to develop the dynamical model of the structural systems in the state-space domain. The classical Runge-Kutta time integration algorithm is then used to calculate the open-loop aeroelastic response of the system. The maximum flutter velocity and minimum voltage applied to actuators are calculated according to the optimal locations of piezoelectric patches obtained using the NSGA-II and then the proportional feedback is used to actively suppress the closed loop system response. Finally the control effects, using the two different controllers, are compared.

The objective of the welding simulation is to study the temperature generated during the welding process and investigate residual stresses in the component after welding. Such results give the possibility to determine properties of materials in welding zones, stress and strain state of welded parts. From other side it is possible to perform optimization process looking for welding parameters (welding speed, welding power source etc.) or initial shape of welded sheets according to displacement state (welding of thin metal sheets with stiffeners – T joints). Those results are the base for fatigue analysis too.

The aim of this work is to propose vibration modeling of sandwich structures with soft core using solid-shell finite elements. Several approaches have been adopted in the literature to accurately model this type of structures; however, they show some limitations in certain configurations of high contrast of material properties or geometric aspect ratios between the different layers. In such situations, it is generally well-known that the use of higher-order or three-dimensional finite elements is more appropriate, but will generate a large number of degrees of freedom and, thereby, large CPU times. In this work, an alternative method is proposed by considering a recently developed linear hexahedral solid-shell element. This solid-shell element is implemented into Matlab in order to use the so-called solver Diamant, which couples Asymptotic Numerical Method (ANM) and Automatic Differentiation (AD). Numerical tests, including various cantilever sandwich beams as well as a simplified pattern of rail on sleepers, are performed to show the efficiency of the proposed approach.

The aim of this work is to propose vibration modeling of sandwich structures with soft core using solid-shell finite elements. Several approaches have been adopted in the literature to accurately model this type of structures; however, they show some limitations in certain configurations of high contrast of material properties or geometric aspect ratios between the different layers. In such situations, it is generally well-known that the use of higher-order or three-dimensional finite elements is more appropriate, but will generate a large number of degrees of freedom and, thereby, large CPU times. In this work, an alternative method is proposed by considering a recently developed linear hexahedral solid-shell element. This solid-shell element is implemented into Matlab in order to use the so-called solver Diamant, which couples Asymptotic Numerical Method (ANM) and Automatic Differentiation (AD). Numerical tests, including various cantilever sandwich beams as well as a simplified pattern of rail on sleepers, are performed to show the efficiency of the proposed approach.

Being able to provide outstanding performances under out-of-plane loading, sandwich structures offer great flexibility for the design of lightweight structural systems. However, they can be affected by macroscopic and microscopic damages, which may trigger catastrophic failure modes. As a consequence, a detailed understanding of the propagation of macro-cracks in the core as well as of delamination phenomena at face-to-core interfaces are aspects of great computational interest. Moreover, linking sophisticated numerical models with the measurement of the mechanical properties of materials is fundamental in view of actual engineering applications. The elastic and fracture characterization of the core is particularly relevant because its cracking strongly reduces the capacity of the sandwich structures to carry out loads. To this end, PVC foams typically used as inner core in structural application are investigated over a range of foam densities. Firstly, the elastic properties of foams under compressive uni-axial loading are measured using the full-field methodology. Subsequently, Asymmetric Semi-Circular Bend (ASCB) specimens are tested varying the position of supports to generate all range of mixed fracture modes. Finally, some of the mostly recognized fracture criterions have been considered, and their capability to compute the crack propagation angles in PVC foams have been evaluated. The parameters experimentally determined have been used to test the accuracy of the response provided by a numerical model developed by the authors.

The aim of this study was the analysis of the bending and the low-velocity impact response of aluminium foam sandwich reinforced by the outer skins made of glass fiber reinforced epoxy matrix and the results were compared with those obtained for aluminium foam sandwiches without glass fiber skins. Static bending tests were carried on panels with the same nominal size at different support span distances in order to analyze the collapse modes and their capacity of absorbing energy, while the energy amount absorbed under dynamic loading was evaluated by means of impact tests. The experimental investigation has particular importance for applications which require lightweight structures with a high capacity of energy dissipation, such as transport industries. 1 Introduction Sandwich structures, consisting of glass fiber reinforced plastic (GFRP) skins bonded onto low density cores, offer great potential for use in various high performance composite structures which are nowadays widely used in aerospace, marine, automobile, windmills, transport, shipbuilding, defense because of their high specific stiffnesses and strengths, excellent thermal insulation, acoustic damping, fire retardancy, ease of machining and forming among others. It is important to choose high-quality core material in the optimal design of sandwich. Most current sandwich structures are based on polymeric foams (such as PVC, PUR) and aluminium honeycomb bonded to GFRP skins. Recently a great number of metal foams have been developed to replace polymer foams in applications where multifunctionality is important. For instance, acting as a structural component in a sandwich composite but also as an acoustic damper, fire retardant or heat exchanger [1]. As a new multi-function engineering material, aluminium foams have many useful properties such as low density, high stiffness, good impact resistance, high energy absorption capacity, easy to manufacture into complex shape, good erosion resistance, etc. [2, 3]. This fact opens a wide range of potential applications for sandwich structures with aluminium-foam core. Aluminium foam sandwiches (AFS) [4, 5], obtained by combining metal face sheets with a lightweight metal foam core, are suitable for applications in automotive industry and ship construction

This paper shows the application of refined finite element model developed by that are, equilibrium equation, constitutive equation and kinematic equation to be satisfied explicitly at considers the equilibrium equation for the refinement element model by choosing stress and displacement as on approximation function. Ramtekkar [1] variation from displacement derived space, by imposing the elastic relations on Energy Principle to obtain the governing differential equation. In present work also by considering the body forces as variables inthe formulation which enables the model to satisfy the equilibrium equation explicitly at the node. The formulation is validated by the elastic beam problem solvedby Pagano obtained are very accurate and also shows faster convergence over the Ramtekkar

Multi-term extended Kantorovich method (MTEKM) is used to solve the bending problem of thin skew (parallelogram) functionally graded plate resting on the Winkler elastic foundation under uniformly distributed transverse load. Formulations are based on the classical plate theory (CPT) with the physical neutral surface is considered as the reference plane. Various configurations of clamped, simply supported and free edges are considered. By implementing the concept of Galerkin's weighted residual method, the fourth-order partial differential governing equation and boundary conditions are converted into two sets of ordinary differential equations (ODE), which are then solved numerically using ''Chebfun" numerical computation package. Convergence and accuracy of MTEKM are investigated. Results obtained with MTEKM are compared to finite element method (FEM) solutions. FEM has been implemented using ANSYS software, in which the plate is modeled with shell elements, while the elastic foundation is modeled as a pair of contact/target elements. In addition, the effects of both the Winkler foundation stiffness and material power index have been investigated. Applying MTEKM in bending analysis of thin skew plates offered more accurate results than the single-term EKM but with the cost of more computation time but still provides simplicity and rapid convergence. It is found that MTEKM well suits the bending problem of skew FGM plates resting on elastic foundation.

Space telescopes for Earth observation will require data of increasingly high quality. The resolution of Earth observation has reached several tens of cm. Because resolution is proportional to the diameter of mirrors, larger and larger mirrors are required. Space astronomy telescopes also require increasingly high resolution and large mirrors. The James Webb Space Telescope has been already advanced to the developing phases and the deployable main mirror of 6 m in diameter is being manufactured [1]. Although the structure of telescopes is based mainly on system design, the selection of material is a key issue on points of high dimensional accuracy and stability, especially with regard to weight. Carbon fiber-reinforced composite (CFRP) has a high stiffness-to-weight ratio and can be designed to have nearly zero thermal expansion [2]. That makes CFRP one of the most promising materials for optical mirrors of space telescopes.

A new simple “four-variable shear deformation” plate model is proposed in this work to demonstrate the hygro-thermal environment effects on dynamic and buckling of functionally graded material “sandwich plates” supported by “Winkler–Pasternak” elastic foundations. Equations of motion are obtained from Hamilton’s principle containing the hygro-thermal influences. This model uses only “four variables” and considers trigonometric variation of “transverse shear stress.” In addition, these stresses become zero at the upper and lower surfaces of the “sandwich plate.” The novelty of this formulation is the addition of the integral term in the field of displacement, which leads to a reduction of the number of unknowns and basic equations. Various kinds of functionally graded material “sandwich plates” are examined in this study. To verify the validity of the model, the calculated results are compared with the existing results. Comparison investigations reveal that the computed results of th...

In this study, experimental mechanical and modal analyses of nano-Al 2 O 3 ceramic powder reinforced polyurethane foam core sandwich composites was carried out along with the investigation of vibration, buckling and compression responses. The reinforcement ratio of Al 2 O 3 ceramic powder was varied from 0 to 10 % by weight. The morphological effect of Al 2 O 3 powder reinforcement on the polyurethane microstructure was also investigated by benefitting from an optical microscope. Significant improvements in the damping response and the buckling behavior of the Al 2 O 3 sandwich specimens were observed. In this context, a 38.3 % increase in the damping ratio was observed for 2% Al 2 O 3 reinforced specimens compared to the neat specimens and the specimens with 1% and 3% Al 2 O 3 reinforcement showed 31.4 % and 26.8 % increase, respectively. Similarly, a 6% increase in the buckling peak load was observed for specimens with 5% reinforcement compared to the neat specimens. However, the compression peak load was observed to decrease linearly with an increase in the reinforcement ratio for all the reinforced specimens. TG-DTG, DSC and FTIR analysis of PUF cores with different reinforcement ratios were also performed within the scope of this study. It was observed in the TG graphs that the weight loss decreased with an increase in the reinforcement ratios. The glass transition temperatures of all the PUF core specimens were found by performing DSC analyses whereas, the structural bonds were detected by using the FTIR technique. Composite foam cores showed the existence of a dominant polyurethane structure.

Woven glass fiber reinforced with epoxy matrix composites are manufactured considering different glass/epoxy proportions and vibration analyses of the laminated composite plates subjected to free vibrations have been examined. The tensile and flexural strength of composites were evaluated by following ASTM standards. Free vibration of the composite specimen characteristics is studied using a Fast Fourier Transform analyzer, accelerometer using impact hammer excitation. The fast response functions are studied in order to clearly understand the vibration characteristics of the specimens. The experimentally obtained results of the rectangular composite plates are compared with the analytical results obtained from Nastran. The results showed a good agreement. It was observed that as the number of layers of the composite specimen increased, the frequency response also increased.

In recent years sandwich structures have been widely used in marine industry; such reason has lead to the study of mechanical properties of the above mentioned structures through the evaluation of the effects induced by different technological procedures. Therefore, this work presents unsymmetrical sandwich structures realised using both lay up and vacuum bag technology. In order to find a static characterisation of the sandwich structure, firstly flatwise and edgewise compressive tests were performed. Afterwards, a three point flexural test was realised in order to examine the different effects of a load, which has been applied to either one or the other side of an unsymmetrical sandwich structure. Thanks to the above mentioned tests, it has been possible to find out and interpret a number of fracture mechanisms that take place when the load conditions change and/or when the technological procedure used to produce the samples varies. Moreover, a theoretical model capable of predicting the stresses inside the sandwich sample is proposed.

In this research, we proposed coupling the Laplace transform method and the homotopy Perturbation Method (LHPM). We employed the fusion of the Laplace method to make up for the shortcomings of other semi-analytical approaches like the homotopy perturbation method, variation iteration method, and the Adomian decomposition method. We aim to obtain an approximate and semi-analytic solution of the n-dimensional system of nonlinear partial differential equations. N-dimensional partial differential equations with nonlinear terms are known as nonlinear partial differential equations. They have been used to solve mathematical problems like the Poincar e conjecture and the Calabi-Yau conjecture and describe physical systems, from gravity to fluid dynamics. Therefore, we proffer a semi-analytic solution in the form of a Taylor multivariate series of displacements x, y, and time t using the proposed method. A sideby-side comparison was carried out to compare the exact solution with the new solution using 3-dimensional graphs, and thus the graph analysis followed. Results show excellent agreement, and the emergence of this method as a viable alternative demonstrates its viability by requiring fewer computations and being much easier and more convenient than others, making it suitable for widespread use in engineering as well.

The nature of charge injection has been investigated across the Au-poly(3-hexylthiophene-2,5-diyl) (P3HT) interface of two kinds: P3HT on Au (bottom contact) and Au on P3HT (top contact). The J-V characteristics of a Au(bottom)/P3HT/Au(top) sandwich cell are analyzed by using the Fowler–Nordheim model and the hole barrier height at the top and bottom contacts has been estimated. The top contact showed a higher barrier height in comparison to the bottom contact. The quenching of photoluminescence spectra and the disappearance of characteristic P3HT peaks from the absorption spectra for the top contact supports that the ionically sputtered gold atoms on the polymer give rise to greater density of interfacial trap sites than those at bottom interface.

The sandwich panel exhibits higher stiffness than simple panels. The specific stiffness of sandwich panels depends on various factors like width, length, panel's thickness, thickness of the face plate and core's thickness of panels and type of materials used. Because of interaction effect between core and face plate, there is possibility of getting higher stiffness in multi-layered sandwich panels. In addition, incorporation of faceplate and core in the core structure varies the shear modulus and elastic modulus of core of the sandwich. However very limited research has been conducted on analytical modelling of multi-layered sandwich panels for their designing. In the present work analytical model has been developed to analyse the multilayer sandwich panels in terms of shear rigidity. flexural rigidity and deflection as a function of face plate thickness, core thickness, number of layers and beam width. Four types of specimens, those are single layer, double layer, triple layer and quadruple layer sandwich beam were prepared for this study. The deflection of the sandwich beam was measured by UTM (ultimate tensile machine). For core, Al-foam has been used and the theoretical values of elastic modulus and shear modulus were taken from the data available for cores of Al-foam synthesized at AMPRI, Bhopal. The deflection at 1000 N calculated theoretically for single layer and quadruple layer was 14.966 mm and 0.559 mm respectively. The practical calculation of deflection was 15.608 mm for single layer and 0.557 mm for quadruple layer. The practical and theoretical calculations were in well agreement. Further, it was understood that multi-layered sandwich panels are much more advantageous in terms of low deflection than single layer or double or triple sandwich panel.

Considering a stiffened panel made from an elastic homogeneous and isotropic material which suffers a single localized initial geometric imperfection, assessment of the buckling limit state under in-plane uniform axial compression in the direction of stiffeners was performed. Giving a topological configuration of the stiffened plate, focus was aimed at the combined effect resulting from geometrical dimensions and localized defect characteristics. The perfect stiffened plate taken as reference and diverse imperfect stiffened plates suffering a single localized initial geometric defect of the form of a square depression were analyzed in this work. Extensive parametric finite element simulations were performed according to full factorial design of experiment tables that were built on key intervening factors. It was found that the main parameters controlling the buckling stress for the perfect plate are the plate width, then the web height and width, then finally the interaction between...

Integration of lightweight and sustainable solutions in marine structures design is essential to achieve weight reduction goals and improve structural response. A key step to assess the reliability of innovative structural solutions is represented by large-scale experimental investigation. The current paper deals with the analysis of a lightweight ship balcony overhang, which includes an aluminium honeycomb sandwich structure and bimetallic welded joints. The design of the ship balcony overhang was previously performed, as an illustrative example, with the aim of suggesting the replacement of common marine structures with more green and lightweight alternatives. In order to validate the design procedure and to assess the feasibility of the suggested solution, an experimental investigation on a large-scale structure was performed. The ship balcony overhang was tested under bending with a configuration representative of severe loading conditions for ships balconies. The experimental a...

This paper focuses on the parametric instability of a functionally graded (FG) cylindrical thin shell under both axial disturbance and thermal environment. Based on Love's thin shell theory, and considering the temperaturedependent properties of FG cylindrical shell, the dynamic equations of the FG cylindrical shell are derived by Hamilton's principle. The multiple scales method is performed to obtain the instability boundaries of the shell with axial disturbance. The primary and combination instabilities of the shell are studied systematically. Moreover, numerical simulations are utilized to discuss the influences of axial disturbed amplitude, material heterogeneity and thermal effects on instability regions, frequency characteristics of the shell. Specially, some numerical results are given to illustrate the combined influence of axial disturbed amplitude and temperature variation on instability regions.

Honeycomb sandwich panels are investigated for a broad range of areas as protective structures that can withstand blast loading. The advantage of these panels is that they are light in weight when compared to solid metal plates due to the hollow core and have high energy absorption capabilities. Due to their high bending stiffness, honeycomb sandwich panels have found applications in aerospace, automotive, marine, defense, and railway industries. In order to analyze the effect of blast loading on sandwich panels the experiments that need to be conducted are costly as well as time-consuming. Also, while conducting experiments with explosives, human safety is a major concern. Taking the aforementioned parameters into consideration, modeling and simulation of honeycomb sandwich panels is the better alternative. ABAQUS software has been used in this paper to study the behavior of metallic honeycomb sandwich panels (MHSP) with squared, hexagonal, and circular cores when subjected to blas...

Two types of sandwich panels are designed by using the periodic structure theory. A double-wall panel with mechanical links and a sandwich panel with rectangular core are studied. An oriented optimization of the elastic bending waves' propagation versus the acoustic wavenumbers is achieved by using shifted core walls and by keeping the mass and stiffness of the system constant. Standard and optimized configurations are 3D-printed and sound transmission measurements are carried out by using a facility with an uncoupled reverberant-anechoic configuration. The experimental evidences of enlarged bending band-gaps and deformation mechanisms are proved using a reverse approach based on the acoustic radiation of the panels.

In this paper, a new technique for analysing functionally graded material (FGM) beams using the Chebyshev polynomials and Lagrange multipliers with various beam theories is presented. By utilizing the inner products and the Chebyshev polynomials' orthogonality properties incorporated with Lagrange multipliers, we can combine the governing equation and boundary conditions to yield the matrix equations with explicit weighting coefficients. Numerical examples are provided for vibration analysis of various beam theories and assumptions. Based on numerical evaluations, it is revealed that the proposed technique can efficiently achieve good agreement with those of the references.

This paper addresses the problem of optimal positioning of surface bonded piezoelectric patches in sandwich plates with viscoelastic core and laminated face layers. The objective is to maximize a set of modal loss factors for a given frequency range using multiobjective topology optimization. Active damping is introduced through co-located negative velocity feedback control. The multiobjective topology optimization problem is solved using the Direct MultiSearch Method. An application to a simply supported sandwich plate is presented with results for the maximization of the first six modal loss factors. The influence of the finite element mesh is analyzed and the results are, to some extent, compared with those obtained using alternative single objective optimization.

This paper shows the application of refined finite element model developed by that are, equilibrium equation, constitutive equation and kinematic equation to be satisfied explicitly at considers the equilibrium equation for the refinement element model by choosing stress and displacement as on approximation function. Ramtekkar [1] variation from displacement derived space, by imposing the elastic relations on Energy Principle to obtain the governing differential equation. In present work also by considering the body forces as variables inthe formulation which enables the model to satisfy the equilibrium equation explicitly at the node. The formulation is validated by the elastic beam problem solvedby Pagano obtained are very accurate and also shows faster convergence over the Ramtekkar

Being able to provide outstanding performances under out-of-plane loading, sandwich structures offer great flexibility for the design of lightweight structural systems. However, they can be affected by macroscopic and microscopic damages, which may trigger catastrophic failure modes. As a consequence, a detailed understanding of the propagation of macro-cracks in the core as well as of delamination phenomena at face-to-core interfaces are aspects of great computational interest. Moreover, linking sophisticated numerical models with the measurement of the mechanical properties of materials is fundamental in view of actual engineering applications. The elastic and fracture characterization of the core is particularly relevant because its cracking strongly reduces the capacity of the sandwich structures to carry out loads. To this end, PVC foams typically used as inner core in structural application are investigated over a range of foam densities. Firstly, the elastic properties of foams under compressive uni-axial loading are measured using the full-field methodology. Subsequently, Asymmetric Semi-Circular Bend (ASCB) specimens are tested varying the position of supports to generate all range of mixed fracture modes. Finally, some of the mostly recognized fracture criterions have been considered, and their capability to compute the crack propagation angles in PVC foams have been evaluated. The parameters experimentally determined have been used to test the accuracy of the response provided by a numerical model developed by the authors.