Nonlinear Behavior of Sandwich Panels With Delamination Inside Face Sheets Based on Refined Higher Order Core Theory

2000 ◽  
Author(s):  
R. Li ◽  
V. La Saponara ◽  
G. A. Kardomateas
Keyword(s):  
Sandwich Structure ◽  
Nonlinear Distortion ◽  
Eigenvalue Problems ◽  
Continuation Method ◽  
Nonlinear Behavior ◽  
Higher Order ◽  
The Core ◽  
Core Theory ◽  
The Face ◽  
Inside Face

Abstract Sandwich construction, consisting of two stiff face sheets and a soft core of a foam or low strength honeycomb type while designed principally as efficient integral structures, can lose this quality when delaminations occur inside the face sheets, especially under compressive loading condition. A refined higher order core theory is developed for the core that accounts for the nonlinear distortion of the plane of section of the core and the compressibility in the vertical direction, and for the skins in which part of the transverse deflections is related to the core nonlinear distortion. Based on this core theory, nonlinear behavior of sandwich beams/panels with delaminated faces is studied. The nonlinear governing equations, boundary conditions, and continuity conditions are formulated for the compressed sandwich structure which includes initial imperfection and delamination in the face sheets. Solution arc length parameterization within Newton continuation method is employed in solving the bifurcation and nonlinear eigenvalue problems for critical loads and postbuckling behavior of the sandwich structure. The results suggest that delaminations inside face sheets have considerable influence on the global and local behavior of the whole sandwich con structure.

Buckling and Postbuckling of Sandwich Beams With Delaminated Faces Based on Higher Order Core Theory

1999 ◽  
Author(s):  
R. F. Li ◽  
Y. Frostig ◽  
G. A. Kardomateas
Keyword(s):  
Nonlinear Distortion ◽  
Variational Principles ◽  
Vertical Direction ◽  
Initial Imperfection ◽  
Order Theory ◽  
Sandwich Beams ◽  
Postbuckling Behavior ◽  
The Core ◽  
Core Theory ◽  
The Face

Abstract Delaminations within the face sheets are often observed when a sandwich structure is exposed to impact loads. The buckling and postbuckling behavior of sandwich beams with delaminated faces is investigated in this work. The governing nonlinear equations, boundary conditions, and continuity conditions are formulated through variational principles. The beam construction consists of upper and lower, metallic or composite laminated symmetric skins, and a soft core of a foam or low strength honeycomb type. A high order theory is used for the core that accounts for the nonlinear distortion of the plane of section of the core and the compressibility in the vertical direction. The delamination considered is an interface crack, in which the substrate includes the transversely flexible core. The case of a debond at one of the skin-core interfaces is also included. The effects of the delamination length and location on the overall and local behavior are examined with an arbitrary initial imperfection.

Flexural Behavior of Sandwich Structure with AA 8011 Honeycomb Core and Al 1100 Face Skins

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
M.R. Ashok ◽  
M. Manojkumar ◽  
P.V. Inbanaathan ◽  
R. Shanmuga Prakash
Keyword(s):  
Finite Element Analysis ◽  
Sandwich Structure ◽  
Flexural Behavior ◽  
Bending Test ◽  
Honeycomb Core ◽  
Element Analysis ◽  
Three Point Bending ◽  
The Core ◽  
Flexural Testing ◽  
The Face

This paper details the fabrication and flexural testing of sandwich structure with Aluminium honeycomb core with Aluminium face skins. The material for the face skin is aluminium 1100 and for the core is Aluminium AA8011. The cell size obtained by fabrication is 7mm. The specimen is prepared and tested as per the ASTM standard C393/C393M-11 on a three-point bending test to obtain the ultimate core shear strength and the face skin strength. Finite element analysis is also carried out to validate the experimental test.

Implication of Anisotropy of Face-Sheets and Core Layer Materials on the Load Carrying Capacity of Advanced Sandwich Panels: Linear and Nonlinear Responses

2000 ◽  
Author(s):  
Liviu Librescu
Keyword(s):  
Carrying Capacity ◽  
Sandwich Structure ◽  
Sandwich Panels ◽  
Core Layer ◽  
Anisotropic Materials ◽  
Load Carrying Capacity ◽  
The Core ◽  
Load Carrying ◽  
The Face ◽  
Sandwich Shells

Abstract This paper deals with a comprehensive geometrically nonlinear theory of shallow sandwich shells that includes also the effect of the initial geometric imperfections. It is assumed that the face-sheets of the sandwich structure are built-up from anisotropic materials layers, whereas the core layer from an orthotropic material. As a result of its features the structural model can provide important information related to the load carrying capacity of sandwich structures in the pre- and postbuckling ranges. Moreover, by using the directionality properties of face-sheets materials, possibilities of enhancing the load carrying capacity of sandwich shells/plates are reached. Selected numerical illustrations emphasizing these features are presented and pertinent conclusions on the beneficial implications of anisotropy of face-sheets and core layer materials upon the load-carrying capacity of sandwich panels are emphasized. Under the present study, the sandwich structure consists of a thick core-layer bonded by the face-sheets that consist of composite anisotropic materials, symmetrically laminated with respect to the mid-surface of the core-layer. The initial geometric imperfection consisting of a stress free initial transversal deflection, will be also incorporated in the study. The loads under which the nonlinear response will be analyzed consist basically of uniaxial/biaxial compressive edge and lateral loads.

scholarly journals Connection Mechanism of Molten Pool during Laser Transmission Welding of T-Joint with Minor Gap Presence

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1823 ◽  
Author(s):  
Ke Xu ◽  
Haichao Cui ◽  
Fuquan Li
Keyword(s):  
Fluid Flow ◽  
Pore Formation ◽  
Sandwich Structure ◽  
Thermal Deformation ◽  
Three Dimensional ◽  
The Core ◽  
Transient Simulations ◽  
The Face ◽  
Face Plate ◽  
Bead Profile

Laser welding of T-joint transmitting from the face plate to the core is commonly used in the sandwich structure preparation. Minor gaps between the face and the core plate are inevitably present after several beads on the sandwich structure welding due to the thermal deformation. The effects of gap presence on fluid flow from the face to the core plate are rather significant, where the gas can be easily entrapped into the pool and form the pores. To this end, three-dimensional transient simulations based on VOF (volume of fluid) method were conducted to explore and ascertain the effect of fluid flow inside the pool on the pore formation due to the gap presence. It was found that minor gap within 0.2 mm will not reduce the welding quality. Under the effects of gravity and surface tension, the fluid from the face sheet will drop down to the core, which removes all the air out of the gap and the laser goes through the fluid of the gap and then shines on the core, which prevents the air from being entrapped into the pool. While the laser goes though gap, the wall of keyhole opens and closes continuously. The vibrating time of keyhole is approximately 0.029 s. After finishing the vibration, the welding is stable, which is the same as common unfull penetration. Finally, the simulated results are well verified through observing the plasma oscillating frequency in the gap and comparing to the pore-free bead profile. This paper supplies evidence that minor gap presence during laser transmitting welding on sandwich structure has nothing to do with pore formation.

Measurement and Simulation of the Performance of a Lightweight Metallic Sandwich Structure With a Tetrahedral Truss Core

2004 ◽  
Vol 71 (3) ◽  
pp. 368-374 ◽  
Author(s):  
H. J. Rathbun ◽  
Z. Wei ◽  
M. Y. He ◽  
F. W. Zok ◽  
A. G. Evans ◽  
...  
Keyword(s):  
Sandwich Structure ◽  
Sheet Material ◽  
Limit Load ◽  
Structural Performance ◽  
The Core ◽  
Truss Core ◽  
Element Simulation ◽  
The Face ◽  
Shear Characteristics ◽  
Constitutive Properties

Metallic sandwich panels with tetrahedral truss cores have been fabricated and their structural performance evaluated. A fabrication technique involving deformation-shaping and brazing has been used. The responses of the structure in core shear and panel bending have been measured. The results demonstrate robust behavior beyond the limit load. A finite element simulation of the core shear response duplicates the features found experimentally. When combined with the constitutive properties of the face sheet material, these shear characteristics have been shown to predict, with good fidelity, the limit load for panels in bending.

scholarly journals Honeycomb Composite Structures of Aluminum: Aerospace Applications

2019 ◽  
Author(s):  
D.L. Majid ◽  
Nor Hafizah Manan ◽  
Yee Ling Chok
Keyword(s):  
Composite Structure ◽  
Composite Structures ◽  
Sandwich Structure ◽  
Design Criterion ◽  
Specific Strength ◽  
The Core ◽  
Aerospace Applications ◽  
The Face ◽  
Aluminum Honeycomb ◽  
Strength And Stiffness

A honeycomb composite structure is usually composed of a lightweight hexagonal core sandwiched between two thin face sheets that are adhesively joined. Both the core and the face sheets can be combinations of many types of materials depending on the application. In this article, an overview of the design and manufacturing process of aluminum honeycomb composite structures particularly for aerospace application is presented. Aluminum honeycomb composite structures are lightweight constructions with high specific strength and stiffness that are applied mainly in the aerospace industry. An aluminum honeycomb panel is typically made up of the secondary structural components and interiors of an aircraft such as the wing skin, trailing edge, control surface, flooring, partitions, aircraft galleys, and overhead bins, to name a few. Other applications are in the spacecraft, helicopter, missile, and satellite. Owing to its honeycomb design peculiar to the hexagonal beehives, it can reach more than 30 times higher in stiffness and 10 times higher in flexural strength compared to its solid counterpart of the same weight. The mechanical properties of the honeycomb composite structure hinge on the materials of the core and face sheets, the core geometries, and the thickness of the face sheets. Designed for superior flexural and shear loading, the selection of the optimal honeycomb design will depend on the application requirements. The principal design criterion of a sandwich structure in aerospace applications is weight saving, and there is a trade-off between performance and cost. In terms of manufacturing of the honeycomb composite sandwich structure, the two main processes are the expansion process commonly used for low-density cores and the corrugation process for higher density cores.

scholarly journals Alzheimer’s Disease Progressively Reduces Visual Functional Network Connectivity

2021 ◽  
pp. 1-14
Author(s):  
Jie Huang ◽  
Paul Beach ◽  
Andrea Bozoki ◽  
David C. Zhu
Keyword(s):  
Visual Cortex ◽  
Lower Order ◽  
Resting State ◽  
Visual Processing ◽  
Network Connectivity ◽  
Higher Order ◽  
Functional Network ◽  
Functional Networks ◽  
The Face ◽  
Processing Network

Background: Postmortem studies of brains with Alzheimer’s disease (AD) not only find amyloid-beta (Aβ) and neurofibrillary tangles (NFT) in the visual cortex, but also reveal temporally sequential changes in AD pathology from higher-order association areas to lower-order areas and then primary visual area (V1) with disease progression. Objective: This study investigated the effect of AD severity on visual functional network. Methods: Eight severe AD (SAD) patients, 11 mild/moderate AD (MAD), and 26 healthy senior (HS) controls undertook a resting-state fMRI (rs-fMRI) and a task fMRI of viewing face photos. A resting-state visual functional connectivity (FC) network and a face-evoked visual-processing network were identified for each group. Results: For the HS, the identified group-mean face-evoked visual-processing network in the ventral pathway started from V1 and ended within the fusiform gyrus. In contrast, the resting-state visual FC network was mainly confined within the visual cortex. AD disrupted these two functional networks in a similar severity dependent manner: the more severe the cognitive impairment, the greater reduction in network connectivity. For the face-evoked visual-processing network, MAD disrupted and reduced activation mainly in the higher-order visual association areas, with SAD further disrupting and reducing activation in the lower-order areas. Conclusion: These findings provide a functional corollary to the canonical view of the temporally sequential advancement of AD pathology through visual cortical areas. The association of the disruption of functional networks, especially the face-evoked visual-processing network, with AD severity suggests a potential predictor or biomarker of AD progression.

Material Selection for CFRP-Aluminium-Foam-Sandwiches Manufactured by a PUR Spraying Process

2017 ◽  
Vol 742 ◽  
pp. 317-324
Author(s):  
Peter Rupp ◽  
Peter Elsner ◽  
Kay André Weidenmann
Keyword(s):  
Manufacturing Process ◽  
Sandwich Structures ◽  
Bending Stiffness ◽  
Effective Density ◽  
Sandwich Composites ◽  
Open Cell ◽  
The Core ◽  
Bending Modulus ◽  
The Face ◽  
Spraying Process

Sandwich structures are ideal for planar parts which require a high bending stiffness ata low weight. Usually, sandwich structures are manufactured using a joining step, connecting theface sheets with the core. The PUR spraying process allows to include the infiltration of the facesheet fibres, the curing of the matrix and the joining of the face sheets to the core within one processstep. Furthermore, this manufacturing process allows for the use of open cell core structures withoutinfiltrating the core, which enables a comparison of different material configurations, assembled bythe same manufacturing process. The selection of these materials, with the aim of the lowest possiblemass of the sandwich composite at a constant bending stiffness, is displayed systematically within thiswork.It could be shown that the bending modulus calculated from the component properties matched theexperimentally achieved values well, with only few exceptions. The optimum of the bending modulus,the face sheet thickness and the resulting effective density could be calculated and also matched theexperimental values well. The mass-specific bending stiffness of the sandwich composites with corestructures of open cell aluminium foams was higher than with closed cell aluminium foams, but wasexceeded by sandwich composites with Nomex honeycomb cores.

Devolution processes and the theory of historical development by S. Sanderson

2021 ◽  
pp. 72-77
Author(s):  
A.V. Verkhoturov ◽  
◽  
A.A. Obukhov
Keyword(s):  
Historical Development ◽  
World System ◽  
Human Society ◽  
Evolutionary Trend ◽  
The Core ◽  
The World ◽  
The Face ◽  
American Historian ◽  
Immanuel Wallerstein ◽  
Main Ideas

Analyzed is one of the most comprehensive modern approaches to the problem of the existence of evolution of human society as such and of specific human communities, i.e. “General Theory of Historical Development” by American historian and sociologist Stephen Sanderson. While agreeing, in general, with its main ideas, we believe that it is important to note that the issue of existence of individual communities demonstrating devolution (regression to an earlier historical state), stagnation or degeneration at certain historical stages is practically ignored in the framework of the theory under consideration. This creates its vulnerability in the face of specific empirical data, indicating a deviation from the evolutionary trend. We believe that overcoming this theoretical difficulty is possible in the process of comprehending the theory of S. Sanderson in the context of ideas of the world-system approach of Immanuel Wallerstein. We want to show that examples of devolution, stagnation and degeneration of societies do not deny general progressive evolutionary tendencies, characteristic for the world-system as a whole, but only indicate the transition of a particular society to a lower level within the world-system (from the core to the semi-periphery, or from the semi-periphery to the periphery).

scholarly journals Public Space as a Venue for Peacebuilding in Lebanon? The Role of Civic Movements in Reclaiming Public Space in Beirut and Tripoli

2021 ◽  
pp. 25-46
Author(s):  
Aseel Naamani ◽  
Ruth Simpson
Keyword(s):  
Public Space ◽  
Public Life ◽  
Public Spaces ◽  
Urban Spaces ◽  
Building Relationships ◽  
The Core ◽  
The Face ◽  
History Of ◽  
Post War

The issue of public spaces is increasingly at the core of civic movements and discourse of reform in Lebanon, coming to the fore most recently in the mass protests of October 2019. Yet, these most recent movements build on years of activism and contestation, seeking to reclaim rights to access and engage with public spaces in the face of encroachments, mainly by the private sector. Urban spaces, including the country’s two biggest cities – Beirut and Tripoli – have been largely privatised and the preserve of an elite few, and post-war development has been marred with criticism of corruption and exclusivity. This article explores the history of public spaces in Beirut and Tripoli and the successive civic movements, which have sought to realise rights to public space. The article argues that reclaiming public space is central to reform and re-building relationships across divides after years of conflict. First, the article describes the evolution of Lebanon’s two main urban centres. Second, it moves to discuss the role of the consociational system in the partition and regulation of public space. Then it describes the various civic movements related to public space and examines the opportunities created by the October 2019 movement. Penultimately it interrogates the limits imposed by COVID-19 and recent crises. Lastly, it explores how placemaking and public space can contribute to peacebuilding and concludes that public spaces are essential to citizen relationships and inclusive participation in public life and affairs.

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