Dvir Elmalich

A high-order finite element for dynamic analysis of soft-core sandwich plates

The dynamic behavior of soft-core sandwich plates is investigated. A high-order finite element concept that has been developed for the dynamic analysis of multi-layered plate structures with stiff and compliant layers is applied to the soft-core sandwich plate. The application to sandwich plates aims to validate the general model through comparison with experimental and analytical benchmarks and to throw light on the unique structural response of the sandwich plate. The model introduces the core’s three-dimensional stress and deformation fields using a high-order kinematic assumption that is based on the closed-form solution of the static governing equations of the core. The first-order shear deformation laminated plate theory is used for the face sheets. The combination of the high-order theory with the finite element concept aims to extend the application of the theory to more general layouts, to reduce the computation effort needed for a three-dimensional analysis, and to address some of the obstacles due to differences in length scales and elastic properties. The validity and the capabilities of the formulation are examined through comparison with experimental and analytical results taken from the literature. In addition, the static, free vibration, and dynamic behaviors of an ‘L’ shaped sandwich plate subjected to localized loads and boundary conditions are numerically studied. The formulation, the comparison with experimental and analytical benchmarks, and the numerical study highlight the three-dimensional effects and reveal unique aspects of the dynamic response of soft-core sandwich plates.

Nonlinear Analysis of Masonry Arches Strengthened with Composite Materials

The nonlinear behavior of masonry arches strengthened with externally bonded composite materials is investigated. A finite-element (FE) formulation that is specially tailored for the nonlinear analysis of the strengthened arch is developed. The FE formulation takes into account material nonlinearity of the masonry construction and high-order kinematic relations for the layered element. Implementation of the above concept in the FE framework reduces the general problem to a one-dimensional nonlinear formulation in polar coordinates with a closed-form representation of the elemental Jacobian matrix (tangent stiffness). A numerical study that examines the capabilities of the model and highlights various aspects of the nonlinear behavior of the strengthened masonry arch is presented. Emphasis is placed on the unique effects near irregular points and the nonlinear evolution of these effects through the loading process. A comparison with experimental results and a discussion of the correlating aspects and the ones that designate needs of further study are also presented.

Twist in soft-core sandwich plates

This paper studies the twist behavior of soft-core sandwich plates. The paper adopts a comparative analytical approach, derives a geometrically nonlinear extended high-order sandwich plate theory, and compares this theory with the classical high-order one. The extended theory takes all stiffness components of the core and its Poisson effect into account and considers the direct contribution of the in-plane shear stresses in the core to the twist resistance mechanism. The classical high-order sandwich plate theory, which is presented for comparison, neglects the in-plane shear and normal stiffness of the core and attributes the twist mechanism to the composite action of the face sheets and to the ability of the core to resist out-of-plane shear and out-of-plane normal stresses. Both theories account for large displacements, moderate rotations, and small strains in the face sheets and serve as platforms for the development of specially tailored finite elements. Along with the development of the extended sandwich plate theory, the paper studies the twist behavior, compares the two theories, compares the results with experimental ones taken from the literature, and looks into the impact of the geometrical nonlinearity on the twist response.

Geometrically Nonlinear Behavior of Sandwich Plates

The geometrically nonlinear behavior of modern soft-core sandwich plates is studied. For this purpose, a specially tailored geometrically nonlinear finite element that is based on a high-order sandwich plate theory is developed. The theory uses a von Karman type of geometrical nonlinearity in the face sheets and account for shear and through the thickness deformability of the core. The conversion of the theory to a specially tailored finite element extends its applicability to a wide range of structural layouts, allows the use of standard numerical techniques, and simplifies the coupling with other elements. Yet it avoids the need for meshing through the thickness of the plate. The application of the specially tailored finite element to the geometrically nonlinear analysis of in-plane and out-of-plane loaded sandwich plates explores many interesting physical phenomena. Among them, the evolution of localized instabilities during a globally stable load-deflection behavior, the development of localized diago...

Localized Effects in Walls Strengthened with Externally Bonded Composite Materials

AbstractThe localized effects and, particularly, the stress and deformation concentrations near edges, mortar joints, and irregular points in walls strengthened with externally bonded composite materials are studied. To quantify the structural behavior and to cope with the coupling of large-scale and localized-scale effects, a substructuring procedure that uses a specially tailored high-order finite element is developed. The specially tailored element accounts for the bidirectional behavior of the wall and for the interfacial interaction between the adhesively bonded components. The formulation uses a first-order shear deformation orthotropic plate theory for the independent modeling of the existing wall and the composite layers and a high-order theory for the modeling of the displacement fields of the adhesive layers. A static condensation-based substructuring procedure is used for the formulation of a superelement. The computational strength and the convergence characteristics of the high-order superele...

Dynamic Geometrically Nonlinear Behavior of FRP-Strengthened Walls with Debonded Regions

AbstractThis paper studies the dynamic geometrically nonlinear behavior of walls that are strengthened with fiber-reinforced polymer (FRP) composite materials but include preexisting debonded regions. For that purpose, two specially tailored finite elements corresponding to the perfectly bonded regions and debonded regions within the layered wall are formulated under the umbrella of a dynamic analysis. The two finite elements are based on a high-order multilayered plate theory. The geometrical nonlinearity is introduced by means of the Von Karman nonlinear strains. The convergence and validity of the geometrically nonlinear dynamic model are studied for the case of a locally debonded FRP-strengthened wall under in-plane shear loads applied at a constant rate. The unified model of the strengthened wall with a local delamination is then used for studying the dynamic nonlinear behavior under different levels of shear loading rate. The dynamic results and the comparison with static analyses reveal the impact ...

Fiber Orientation Effect in the Dynamic Buckling of Debonded Regions in Laterally Loaded FRP Strengthened Walls

This paper studies the effect of lamination and fiber orientation on the geometrically nonlinear dynamic response of debonded regions in walls strengthened with FRP. The paper adopts an analytical/numerical approach and uses a specially tailored finite element formulation for the layered structure. By means of this analytical/numerical tool, two strengthening layouts for a wall segment subjected to a dynamic shear loading are compared. In the first layout, the fibers are oriented along the width and height of the segment and in the second one, they are oriented along its diagonals. The analysis reveals that the two layouts are involved with significantly different critical points and significantly different dynamic post-buckling behaviors. Specifically, it shows that the diagonal layout, which better serves the shear loading scenario, is involved with a much smaller critical displacement and a dynamic post-buckling behavior that is governed by the stiffer compressed and tensed diagonals.