81 research outputs found
Development of computational efficient shell formulation for analysis of multilayered structures subjected to mechanical, thermal, and electrical loadings
No full textThe aim of this work is the development of robust finite shell model suitable for numerical applications in solid mechanics with a remarkable reduction in computational cost. Two-dimensional (2D) structural models, commonly known as plates/shells, are for instance used in many applications to analyze the structural behavior of thin and slender bodies such as panels, domes, pressure vessels, and wing stiffened panels amongst others. These models reduce the three-dimensional 3D problem into a two-dimensional 2D problem, where variables depend on the in-plane axis coordinates. Two-dimensional elements are simpler and computationally more efficient than 3D (solid) models. This feature makes plate/shell theories still very attractive for the static, dynamic response, free vibration, thermo-mechanical and electro-mechanical analysis, despite the approximations which they introduce in the simulation. Nevertheless, analytical solutions for three-dimensional elastic bodies are generally available only for a few particular cases which represent rather coarse simplifications of reality. In most of the practical problems, the solution demands applications of approximated computational methods. The Finite Element Method (FEM) has a predominant role among the computational techniques implemented for the analysis of layered structures. The majority of FEM theories available in the literature are formulated by axiomatic-type theories. In this thesis, attention is focused on weak-form solutions of refined plate/shell theories. In particular, higher-order plate/shell models are developed within the framework of the Unified Formulation by Carrera, according to which the three-dimensional displacement field can be expressed as an arbitrary expansion of the generalized displacements. A robust finite shell element for the analysis of plate and shell structures subjected to mechanical, thermal, and/or electrical loadings is developed. A wide range of problems are considered, including static analysis, free vibration analysis, different boundary conditions and different laminations schemes, distributed pressure loads, localized pressure loads or concentrated loads are taken into account. The high computational costs represent the drawback of refined plate/shell theories or three-dimensional analyses. In recent years considerable improvements have been obtained towards the implementation of innovative solutions for improving the analysis efficiency for a global/local scenario. In this manner, the limited computational resources can be distributed in an optimal manner to study in detail only those parts of the structure that require an accurate analysis. In the second part of the thesis two different methodology are presented to improve the analysis efficiency, and at the same time keeping the finite higher-order plate/shell element accuracy. The two approaches can be collocated in the simultaneous multi-model methodologies. The first is the Mixed ESL/LW variable kinematic method, where the primary variables are described along the shell thickness selecting some plies with an ESL description and others with a LW behaviour by using the Legendre polynomials for both the assembling approaches. The second approach is a new simultaneous multi-model, here presented as Node-Dependent Variable Kinematic method. The shell element with node-dependent capabilities enables one to vary the kinematic assumptions within the same finite element. The expansion order ( along the shell thickness ) of the shell element is, in fact, a property of the FE node in the present approach. Different kinematics can be coupled without the use of any mathematical artifice. The theories developed in this thesis are validated by using some selected results from the literature. The analyses suggest that Unified Formulation furnishes a reliable method to implement refined theories capable of providing almost three-dimensional elasticity solution, and that the two simultaneous multi-theories methods are extremely powerful and versatile when applied to composite or sandwich structures subjected to various mutlifield loadings
Nonlocal analytical solution for multilayered composite shells
No full textAbstract In this work, an advanced nonlocal analytical formulation for the static analysis of composite
shell structures is proposed. The governing equations are derived from the Principle of Virtual
Displacement (PVD) [1] and are solved by the use of the Navier solution [2]. Layer-Wise models
related to linear up to fourth order variations of the unknown variables in the thickness direction are
treated. The modelization of multilayered structure materials takes into account the composite material
properties and the nonlocal behavior based on the work of Eringen [3]. In order to take into account
the nonlocality of the material, the Eringen’s stress-gradient model is employed [4]. The novelty and
innovation of this work is related to the development of an advanced nonlocal analytical formulation
for static analysis of composite shells structures by the use of stress-gradient model combined with
Layer-Wise kinematics. The accuracy of the present analytical formulation is validate through various
assessments. Isotropic, cross-ply composite and simply-supported shell structures are considered.
Different lamination sequences and different shell aspect ratios are taken into account to generalize
the obtained results. References [1] J.N. Reddy, An evaluation of equivalent-single-layer and layerwise
theories of composite laminates, Composite Structures, 25 (1993) 21–35. [2] A. Alaimo, C. Orlando,
S. Valvano, Analytical frequency response solution for composite plates embedding viscoelastic layers,
Aerospace Science and Technology 92 (2019) 429–445. [3] A.C. Eringen, D.G.B. Edelen, On nonlocal
elasticity, International Journal of Engineering Science, 10 (1972) 233–248. [4] J.N. Reddy, Nonlocal
theories for bending, buckling and vibration of beams, International Journal of Engineering Science, 45
(2007) 288–307
FBG-Embedded Sensors for Structural Health Monitoring in Missile Fixed Wings: Enabling Reusability of Solid Rocket Thrusters
No full textThe reusability of solid rocket thrusters is a critical objective in advancing the cost-efficiency and sustainability of aerospace systems. Structural Health Monitoring (SHM) is integral to achieving this goal by ensuring integrity and reliability of reusable components. This study proposes the integration of Fiber Bragg Grating (FBG) sensors into the fixed wings of missiles in order to monitor and assess structural health under extreme operational conditions in near real time. FBG sensors, known for their high sensitivity, lightweight, and immunity to electromagnetic interference, are strategically embedded within the composite structure of missile wings to detect strain, deformation, and temperature variations in real-time. A experimental framework is presented, including sensor placement, calibration processes, and data acquisition strategies tailored to the loads and thermal stresses experienced during missile flight. Finite Element Analysis (FEA) simulations validate the sensor placement by predicting stress values for twin digital modelling. The experimental results demonstrate the sensors’ capability to accurately capture strain profiles, providing actionable insights for maintenance and reuse planning
A free-vibration thermo-elastic analysis of laminated structures by variable ESL/LW plate finite element
No full textAnalysis of laminated composite structures with embedded piezoelectric sheets by variable kinematic shell elements
No full text In this article, the static analysis of multilayered shell structure embedding piezoelectric layers is performed using some advanced theories, obtained by expanding the unknown variables along the thickness direction using equivalent single-layer models, layer-wise models, and variable kinematic models. The variable kinematic models permit to reduce the computational cost of the analyses by grouping some layers of the multilayered structure with equivalent single-layer models and keeping the layer-wise models in other zones of the multilayer. This model is here extended to the static analysis of electro-mechanical problems. The used refined models are grouped in the Carrera Unified Formulation, and they accurately describe the displacement field, the stress distributions, and the electric potential along the thickness of the multilayered shell. The shell element has nine nodes, and the mixed interpolation of tensorial components method is used to contrast the membrane and shear locking phenomenon. The governing equations are derived from the principle of virtual displacement, and the finite element method is employed to solve them. Cross-ply plates and shells, with piezoelectric skins and simply supported edges, subjected to bi-sinusoidal mechanical or electrical load are analyzed. Various aspect ratios and radius-to-thickness ratios are considered. The results, obtained with different theories within Carrera Unified Formulation context, are compared with the elasticity solutions given in the literature. From the results, it is possible to conclude that the shell element based on Carrera Unified Formulation is very efficient in the study of electro-mechanical problems of composite structures. The variable kinematic models combining the equivalent single-layer with the layer-wise models permit to have a reduction of the computational costs, with respect to the full layer-wise theories, preserving the accuracy of the results in localized layers. </jats:p
MULTILAYERED PLATE ELEMENTS WITH NODE-DEPENDENT KINEMATICS FOR THE ANALYSIS OF COMPOSITE AND SANDWICH STRUCTURES
No full textIn this paper a new plate finite element (FE) for the analysis of composite and sandwich plates is proposed. By making use of the node-variable plate theory assumptions, the new finite element allows for a simultaneous analysis of different subregions of the problem domain with different kinematics and accuracy, in a global/local sense. In particular higher-order theories with an Equivalent-Single-Layer (ESL) approach are simultaneously used with advanced Layer-Wise (LW) models. As a consequence, the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states present a complex distribution. On the contrary, computationally cheaper, low-order kinematic assumptions can be used in the remaining parts of the plate where a localized detailed analysis is not necessary. The primary advantage of the present variable-kinematics element and related global/local approach is that no ad-hoc techniques and mathematical artifices are required to mix the fields coming from two different and kinematically incompatible adjacent elements, because the plate structural theory varies within the finite element itself. In other words, the structural theory of the plate element is a property of the FE node in this present approach, and the continuity between two adjacent elements is ensured by adopting the same kinematics at the interface nodes. According to the Unified Formulation by Carrera, the through-the-thickness unknowns are described by Taylor polynomial expansions with ESL approach and by Legendre polynomials with LW approach. Furthermore, the Mixed Interpolated Tensorial Components (MITC) method is employed to contrast the shear locking phenomenon. Several numerical investigations are carried out to validate and demonstrate the accuracy and efficiency of the present plate element, including comparison with various closed-form and FE solutions from the literature
A variable kinematic shell formulation applied to thermal stress of laminated structures
No full textA variable kinematic doubly-curved MITC9 shell element for the analysis of laminated composites
No full textThe present article considers the linear static analysis of composite shell structures with double-curvature geometry by means of a shell finite element with variable through-the-thickness kinematic. The refined models used are grouped in the Unified Formulation by Carrera (CUF) and they permit the distribution of displacements and stresses along the thickness of the multilayered shell to be accurately described. The shell element has nine nodes and the mixed interpolation of tensorial components (MITC) method is used to contrast the membrane and shear locking phenomenon. The governing equations are derived from the principle of virtual displacement (PVD) and the finite element method (FEM) is employed to solve them. Cross-ply spherical shells with simply-supported edges and subjected to bi-sinusoidal pressure are analyzed. Various laminations, thickness ratios, and curvature ratios are considered. The results, obtained with different theories contained in the CUF, are compared with both the elasticity solutions given in the literature and the analytical solutions obtained using the CUF and the Navier's method. From the analysis, one can conclude that the shell element based on the CUF is very efficient and its use is mandatory with respect to the classical models in the study of composite structures. Finally, shells with different lamination, boundary conditions, and loads are also analyzed using high-order layer-wise theories in order to provide FEM benchmark solution
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