Web-core Sandwich Plates Research Articles

Comparative investigation on ultimate strength of hull girder with laser-welded web-core sandwich deck

This paper numerically studies the ultimate strength characteristics of the hull girder with the upper deck made of the laser-welded web-core sandwich plates subjected to the vertical bending, the horizontal bending, the torsion and the combined loads among them. The hull girder with the upper sandwich deck is designed from the typical midship section of a light cargo ship as the prototype on the basis of equal cross-sectional area. Compared with the prototype hull girder, the advantages of the hull girder with the upper sandwich deck in the ultimate strength are fully demonstrated in this paper. The results show that by using the laser-welded web-core sandwich deck, the stiffness of the hull girder under sagging has been improved. The sagging ultimate strength of the hull girder can be increased by 15%, and the horizontal bending ultimate strength can be increased by 6.2%. The finite laser weld rotation stiffness has no significant effect on the ultimate strength of the hull girder with the upper sandwich deck. Based on the numerical results, the ultimate strength interaction relationships for the hull girders under the combined two or three moments are established with high accuracy.

Ultimate strength characteristics and assessment of laser-welded web-core sandwich plates under combined biaxial compression and lateral pressure

The ultimate strength and the collapse characteristics of laser-welded web-core sandwich plates subjected to the combined biaxial compression and lateral pressure are investigated by the finite element method. The finite T-joint rotation stiffness is considered, which is derived from the published experimental data. The results show that the finite T-joint rotation stiffness will result in a maximum of 23% decrease in the transverse ultimate strength, much larger than that in the longitudinal ultimate strength. The decrease of the transverse shear stiffness accounts for the reduction of the load-carrying capacity. The lateral pressure reduces the ultimate strength of the sandwich plates, and the reduction in the ultimate strength dominated by the longitudinal compressive collapse is more significant than that in the ultimate strength dominated by the transverse compressive collapse. The applied compressive stress ratios determine the collapse modes of the sandwich plates, which explains the difference in the degree to which the lateral pressure reduces the ultimate strength under the biaxial compression. Based on the numerical results, a preliminary formula is proposed in this paper to assess the load-carrying capacity of the laser-welded web-core sandwich plate subjected to the combined biaxial compression and lateral pressure.

Ultimate strength behavior of laser-welded web-core sandwich plates under in-plane compression

This paper numerically investigates the ultimate strength behavior of the laser-welded web-core sandwich plates under in-plane compression. Both geometric nonlinearity and material nonlinearity are taken into consideration. Besides the global deflection of the sandwich plate, the local deflections of the face plates are also introduced in the ultimate strength analyses to study the influence of the local buckling on the ultimate strength. The influence of the magnitudes of the initial deflections on the ultimate strength of the web-core sandwich plates is studied. Four boundary conditions are considered, and the result shows that the boundary conditions on the unloaded edges, i.e. the simply supported or clamped boundary conditions, have little effect on the ultimate strength of the sandwich plate. The ultimate strength of the sandwich plates shows a reduction when the laser weld rotation stiffness is accounted for, and transverse shear stiffness has a large effect on the ultimate strength. The contact between the web plates and face plates in the joints increases the ultimate strength of the sandwich plates, and the smaller root gap results in the higher ultimate strength.

Design space for bifurcation buckling of laser-welded web-core sandwich plates as predicted by classical and micropolar plate theories

The strength of laser-welded web-core sandwich plates is often limited by buckling. In design of complex thin-walled structures the combination of possible structural and material combinations is basically infinite. The feasibility of these combinations can be assessed by using analytical, numerical and experimental methods. At the early design stages such as concept design stage, the role of analytical methods is significant due to their capability for parametric description and extremely low computational efforts once the solutions have been established for prevailing differential equations. Over the recent years significant advances have been made on analytical strength prediction of web-core sandwich panels. Therefore, aim of the present paper is to show impact of this development to the design space of web-core sandwich panels in buckling. The paper reviews first, briefly the differential equations of a 2-D micropolar plate theory for web-core sandwich panels and the Navier buckling solution for biaxial compression recently derived by Karttunen et al. (Int J Solids Struct 170(1):82–94, 2019) by exploiting energy methods. By comparing the micropolar and widely-used classical first-order shear deformation plate theory (FSDT) solutions, it is shown that the different equivalent single layer (ESL) formulations and plate aspect ratios have a significant impact on the practical outcomes of the feasible design space and this way motivating further developments for micropolar formulations from practical structural engineering viewpoint.

Post-buckling of web-core sandwich plates based on classical continuum mechanics: success and needs for non-classical formulations

The paper investigates the post-buckling response of web-core sandwich plates through classical continuum mechanics assumptions. The compressive loading is assumed to be in the direction of the web plates. Equivalent Single Layer (ESL) plate formulation is used with the kinematics of the First order Shear Deformation Theory (FSDT). During the initial, membrane-dominated loading stages, it is observed that the effect of finite size of the periodic microstructure is barely influences the plate responses. At the higher loads, when bending is activated, the finite size of the microstructure activates secondary shear-induced bending moments at the unit cells of the plate. A method to capture the envelope of the maximum values of these bending moments is presented. The findings are validated with the shell element models of the actual 3D-geometry. Finally, the physical limits of the classical continuum mechanics are discussed in the present context.

Geometrical parameters influence on the stiffness of steel sandwich plates with web-core

Laser welded sandwich plates with web-core have found their position in the marine and land vehicles. To implement such design accurately, knowledge about the influence of geometrical parameters on the stiffness is necessary. In this paper, the over-hanging three points bending tests were performed on the laser welded web-core steel sandwich plate under quasi-static conditions, together with the finite element (FE) simulations. The following parameters were analysed: the thickness of the face plate, the spacing of the two core plates and the height of the core plates. The agreement between experimental measurements and FE results was considered to be good. It is shown that changes of these parameters can contribute to increase or decrease of the stiffness of web-core sandwich plate, but the height of the core plate has no effect on the shear stiffness as the spacing of the two core plates is known. There are linear, exponential and polynomial fitted relationships between the geometrical and the stiffness of the web-core sandwich plates.

Accurate analytical solutions for shear-deformable web-core sandwich plates

An accurate discrete model and analytical solutions thereof are presented for shear-deformable web-core sandwich plates. The face-plates are analyzed using the equations of three-dimensional elasticity, while the webs are accurately modelled using the classical plate theory with a plane stress solution for transverse bending and a Levy-type methodology for lateral bending. It is shown that this obviates the need for a complete three-dimensional analysis of the sandwich plate. Results obtained by this approach are used to highlight the effect of shear deformation of the face-plates.

An accurate discrete model for web-core sandwich plates

An accurate discrete model is presented here for the analysis of simply supported web-core sandwich plates. In this model, the face plates are analysed using the equations of 3D elasticity and for the webs a plane stress idealization is used to model the kinematics of transverse bending while simple one-dimensional classical models are employed for lateral bending and torsion. Thus, this model accounts for the non-classical effects of transverse shear deformation and transverse thickness-stretch in the face-plates and the webs. It is shown that this model is capable of accurately capturing the effects of secondary local bending of the face-plates between the webs on the displacement and stress fields. Results obtained by this rigorous approach are used to highlight the errors of the commonly used model based on the classical hairbrush hypothesis for the face-plates.

Analysis and Experiment on Bending Performance of Laser-Welded Web-Core Sandwich Plates

The bending performance is the main performance index of the sandwich structure. This paper is used to analyse and test showing that: the range of the elastic limit and the maximum bearing capacity is 25 ∼ 30kN and 34.9 ∼ 54.8kN, respectively; the average of bending stiffness and shear stiffness measured by test is 810kN. m and 1717kN/m, respectively; In elastic stage (U2 = 6mm), plate material in the weld junction of web (n = 5)and face plates appear local yield, which shows that the most unfavorable area of sandwich panels is the weld junction of web and face plates.

Bending Properties of Laser Welded Web-Core Steel Sandwich Plates

This paper presents a detailed discussion of the bending properties of laser welded web-core steel sandwich plates and the influence of weld width on stiffness and strength. The over-hanging three point bending test was conducted on the laser welded web-core steel sandwich plates with various welds width by self-designed device, together with the finite element simulations. A good agreement is obtained between the 2D FE analyses and experiment results. The stiffness and strength of the sandwich plates increased with the increasing of weld width, especially for the weld width lower than 60% thickness of the core plate. It is necessary to consider the weld width in the design and evaluation of the stiffness and strength of the laser welded web-core sandwich plate. Base on the results, the FEM is the priority to analysis bending properties of laser welded web-core steel sandwich plates.

Influence of general corrosion on buckling strength of laser-welded web-core sandwich plates

The strength of a web-core steel sandwich plate is potentially reduced in a corrosive environment. This study is dedicated to the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich plate buckling strength and first-fibre failure. Two scenarios are investigated in which corrosion reduces the thickness of (a) the outer sides of the face plates and (b) all surfaces, including the core. The laser weld between the face sheets and the core is assumed to be intact. The assumptions are made on the basis of earlier experimental findings. Critical buckling and geometric non-linear analysis are carried out with the finite element method, with the kinematics being represented using two approaches: (1) equivalent single-layer with first-order shear deformation theory, and (2) a three-dimensional model of the actual geometry of the structure, modelled using shell and connector elements. The former is used to identify the effect of corrosion on the stiffness coefficients and, consequently, the buckling strength. The latter is used for verification and for stress prediction during post-buckling. A rapid decrease in the buckling strength was found for corrosion affecting the outer sides of the sandwich plate. The decrease in the buckling strength doubled in the case of the diffusion of moisture (water) into the core. The shear-induced secondary bending of the faces was found to affect the first-fibre yield.

The Strength of Laser Welded Web-Core Steel Sandwich Plates

All steel laser welded sandwich plates have found their position in the marine and land vehicles. To implement such design accurately, knowledge about its strength properties and the influence of laser weld dimensions on strength is necessary. In this paper, the over-hanging three point bending tests were conducted on the laser welded web-core steel sandwich plate with various weld dimensions by self-designed device, together with the finite element simulations. The results show that the joint is formed on the first plastic hinge when the load is no longer a linear relationship with the deflection, and the joint cracking when the load reaches the maximum bearing capacity of sandwich plate. The joint yield load and the maximum bearing capacity of the sandwich plates increased with the increasing of weld width. Meanwhile, the mode of failure of sandwich plates also changed: When the weld width is smaller, the mode of failure is joint yield, When the weld width is greater than 3mm, the mode of failure is the combination of partial joint yield, face plate and core plate local yield, while the face plate and core plate yield exists in the whole weld joint. It is necessary to consider the weld width in the design and evaluation of the strength of the laser welded web-core sandwich plate.

Load-carrying behaviour of web-core sandwich plates in compression

This paper investigates theoretically the compressive load-carrying behaviour of geometrically imperfect web-core sandwich plates. Slender plates, which first buckle globally, are considered. The study is carried out using two approaches, both solved with the finite element method. The first is the equivalent single-layer theory approach. First-order shear deformation theory is used. The second approach is a three-dimensional shell model of a sandwich plate. Plates are loaded in the web plate direction. Simply supported and clamped boundary conditions are considered with a different level of in-plane restraint on the unloaded edge. The results show that the behaviour of the sandwich plate is qualitatively equal to the isotropic plate of the same bending stiffness for deflections lower than the plate thickness. As the deflections increase, the lower in-plane stiffness of the sandwich plate results in lower post-buckling stiffness. Local buckling of face plates in the post-buckling range of the sandwich plate further reduces the structural stiffness.

Influence of weld stiffness on buckling strength of laser-welded web-core sandwich plates

This paper investigates the influence of weld rotation stiffness on the global bifurcation buckling strength of laser-welded web-core sandwich plates. The study is carried out using two methods, the first is the equivalent single-layer theory approach solved analytically for simply supported plates and numerically for clamped plates. First-order shear deformation theory is used. The second method is the three-dimensional model of a sandwich plate solved with finite element method. Both approaches consider the weld through its rotation stiffness. The weld rotation stiffness affects the transverse shear stiffness. Plates are loaded in the web plate direction. Four different cross-sections are considered. Weld stiffness is taken from experimental results presented in the literature. The results show a maximum of 24% decrease in buckling strength. The strength was affected more in plates with high reduction of transverse shear stiffness and high bending stiffness. Furthermore, clamped plates were influenced more than simply supported. The intersection between buckling modes shifted towards higher aspect ratios, in the maximum case by 24%. The results show the importance of considering the deforming weld in buckling analysis.

Interaction between laser-welded web-core sandwich deck plate and girder under bending loads

Present paper investigates the interaction between laser-welded web-core sandwich deck plate and supporting girder under bending loads. The study is based on two linear-elastic Finite Element (FE) approaches, i.e. one using beam elements to model the girder and shell elements to model the homogenized web-core sandwich plate. With this approach the obtained FE model is considerably smaller than in the case of modeling the full, periodic, 3D geometry with shell elements. The FE solution results in stress resultants for beam and shell elements. These stress resultants do not describe accurately the periodic stress response of the sandwich plate or shear stress distribution at girder web. Therefore, the paper utilizes analytical methods to calculate these stress components from the obtained Finite Element solution. The second computational approach is based on modeling the actual 3D topology with shell elements. The two approaches are shown to be in very good agreement. The investigation shows that the effective flange width of the sandwich is different for the top and bottom face plates indicating that the interaction is different for these face plates. The present study also shows that this difference between the two faces depends strongly on the orientation of the web plates of the sandwich with respect to girder axis and the stiffness of the girder. The investigation also shows that the normal stress response in bending is dominated by the interaction between the sandwich plate and the girder, but also by the shear-induced normal stresses at the outer surface of the plate.

Design Optimization of Steel Sandwich Hoistable Car Decks Applying Homogenized Plate Theory

This paper describes an approach for concept design of laser-welded web-core steel sandwich panels. The method uses a newly developed theory for the bending response of laser-welded web-core sandwich plates. Structural optimization is carried out using enumeration and newly developed vectorization-based genetic algorithm. To demonstrate these concepts, a case study in design of a hoistable car deck is considered. Finally, the optimization is conducted considering the objectives of deck weight.

Bending response of web-core sandwich plates

Bending response of web-core sandwich plates

Laser-welded web-core sandwich plates under patch loading

This paper presents an approach to the structural analysis of patch-loaded, laser-welded web-core sandwich plates. This approach is especially suitable for the concept design phase of ship structures. The method consists of two parts; the global bending response is evaluated using sandwich plate theory and the local response of the patch-loaded face plate is determined with the help of basic plate theory. Both analyses utilise analytical and numerical methods and include the effect of the rotation stiffness of the laser-welded T-joint between the face and web plate. Combining the results of these two analyses gives the total response of the web-core sandwich plate. The results of the proposed approach are compared to those given by 3D solid and shell element FE analyses and the agreement of deflections and normal stresses is found to be good. The sensitivity of the response to patch-load size, T-joint rotation stiffness, and plate aspect ratio is studied. The main benefits of the proposed approach are its short analysis time and the good accuracy of deflections and stresses. This considered advantageous when applied to the design of large ship structures such as hoistable car decks.

Bending response of web-core sandwich beams

This paper presents a new analytical solution for the bending response of a web-core sandwich beam. The beam is a transverse cut from the sandwich plate. The method is based on the plane frame analysis, where the response of the beam is divided into local and global components. The Clebsch’s method is used to calculate the deflection of the face plates. The validation of the plane frame method is carried out with FE-analyses based on the shell element formulation. Also a comparison is made with the method based on homogenized beam. Periodic stress distributions in the face plates are revealed with the plane frame analysis and are supported by the FE-analysis. The existing methods based on homogenized beam are not able to predict these stresses. The plane frame analysis can benefit the development of the theory related to web-core sandwich plate.