The strength characteristics of aluminum honeycomb sandwich panels

doi:10.1016/S0263-8231(99)00026-9

Thin-Walled Structures

Volume 35, Issue 3, November 1999, Pages 205-231

https://doi.org/10.1016/S0263-8231(99)00026-9 Get rights and content

Abstract

Aluminum sandwich construction has been recognized as a promising concept for structural design of lightweight transportation systems such as aircraft, high-speed trains and fast ships. The aim of the present study is to investigate the strength characteristics of aluminum sandwich panels with aluminum honeycomb core theoretically and experimentally. A series of strength tests are carried out on aluminum honeycomb-cored sandwich panel specimen in three point bending, axial compression and lateral crushing loads. Simplified theories are applied to analyze bending deformation, buckling/ultimate strength and crushing strength of honeycomb sandwich panels subject to the corresponding load component. The structural failure characteristics of aluminum sandwich panels are discussed. The test data developed are documented.

Introduction

For design and construction of lightweight transportation systems such as satellites, aircraft, high-speed trains and fast ferries, structural weight saving is one of the major considerations. To meet this requirement, sandwich construction is frequently used instead of increasing material thickness. This type of construction consists of thin two facing layers separated by a core material. Potential materials for sandwich facings are aluminum alloys, high tensile steels, titanium and composites depending on the specific mission requirement. Several types of core shapes and core material have been applied to the construction of sandwich structures. Among them, the honeycomb core that consists of very thin foils in the form of hexagonal cells perpendicular to the facings is the most popular.

A sandwich construction provides excellent structural efficiency, i.e., with high ratio of strength to weight. Other advantages offered by sandwich construction are elimination of welding, superior insulating qualities and design versatility. Even if the concept of sandwich construction is not very new, it has primarily been adopted for non-strength part of structures in the last decade. This is because there are a variety of problem areas to be overcome when the sandwich construction is applied to design of dynamically loaded structures. To enhance the attractiveness of sandwich construction, it is thus essential to better understand the local strength characteristics of individual sandwich panel/beam members.

The aim of the present study is to investigate the strength characteristics of honeycomb-cored sandwich panels made of aluminum alloy material among others. Noteworthy theoretical and experimental studies on linear elastic and nonlinear behavior of aluminum sandwich panels have been previously carried out by other investigators.

Kelsey et al. [1] derived simple theoretical expressions of the shear modulus of honeycomb sandwich cores. Witherell [2] performed an extensive theoretical study for structural design of an air cushion vehicle hull structure using aluminum honeycomb sandwich panels. Okuto et al. [3] showed the validity of the so-called equivalent plate thickness method in which a honeycomb sandwich panel subjected to in-plane loads is approximately replaced by a single skin panel with equivalent plate thickness. Elasto-plastic bending behavior of sandwich panels was studied by Kobayashi et al. [4]. An experimental study was undertaken by Yeh and Wu [5] to investigate the buckling strength characteristics of aluminum honeycomb sandwich panels in axial compression. The characteristics of the energy absorption capacity of bare honeycomb cores under lateral crushing loads have been studied by Kunimo et al. [6], [7] both theoretically and experimentally.

While existing previous investigations including the ones cited above are quite useful, there still remain some problem areas to be overcome if one is to enhance the attractiveness of the sandwich construction method, while several other potential problems have been or are being solved. Primary among the concerns are some known obstacles to using sandwich construction for strength members in dynamically loaded structures. Sandwich laminates are not isotropic. The facing skin on the laterally loaded side of the sandwich panel may buckle due to bending. The buckling and collapse strength characteristics of sandwich panels are not yet fully understood. Debonding or delamination between the center core and outer facing plates is also a likely concern. Sandwich panels can also be suspect in resisting impact loads. Some of the impact energy dissipation characteristics of honeycomb cores remain unclear. Fatigue is a crucial problem to be solved in order to more effectively incorporate sandwich panels into the design and construction of large weight critical structures.

Since physical phenomena defining the structural failures of aluminum honeycomb-cored sandwich panels are quite complex, more experimental studies are needed to clarify their strength characteristics. In the present study, we wish to make new contributions to some of the problems, e.g., related to buckling, collapse and crushing behavior of aluminum honeycomb sandwich panels. For that purpose, a series of strength tests, namely three point bending tests, buckling/collapse tests and lateral crushing tests are carried out on an aluminum honeycomb-cored sandwich panel specimen. A theoretical study is also undertaken to analyze the elasto-plastic bending behavior, buckling/ultimate strength and crushing strength of sandwich panels subject to the corresponding load component. The test data developed are documented.

Section snippets

Characteristics of aluminum honeycomb sandwich construction

The conventional single skin structure, see Fig. 1(a), which is of single plates reinforced with main frames and stiffeners normally necessitates a fair amount of welding, and has a considerable length of weld seams. Further, the lighter but thinner plates employed tend to increase weld distortions that may in some cases require more fabrication work to rectify. More weld seams also mean a greater number of fatigue initiation locations as well. Meanwhile, an aluminum honeycomb sandwich

Strength tests of aluminum honeycomb sandwich panels

Theoretically, a variety of possible failure modes for aluminum honeycomb sandwich panels can be considered when they are used as strength members in the dynamically loaded structure. They include elasto-plastic large deflection due to bending, buckling/collapse in axial compression, folding of honeycomb cores under lateral impact pressure and debonding between the center core and facing plates.

To investigate the structural failure characteristics mentioned above, three types of experiments,

Theoretical analysis of the test sandwich panels

Quick strength estimation methods are required in the preliminary structural design stage. For this purpose, the present study attempts to predict the strength of aluminum honeycomb sandwich panels using simplified approaches.

Concluding remarks

A sandwich construction, which consists of two thin facing layers separated by a thick core, offers various advantages for design of weight critical structures. Depending on the specific mission requirements of the structures, aluminum alloys, high tensile steels, titanium or composites are used as the material of facing skins. Several core shapes and materials may be utilized in the construction of the sandwich. Among them, it has been known that the aluminum honeycomb core has excellent

Acknowledgements

The present study was undertaken under financial support from the Research Institute of Marine Systems Engineering of the Seoul National University, Seoul, Korea who is thanked for this support. The views expressed in this paper are those of the authors and not necessarily those of the institutions the authors are affiliated with.

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The strength characteristics of aluminum honeycomb sandwich panels

Abstract

Introduction

Section snippets

Characteristics of aluminum honeycomb sandwich construction

Strength tests of aluminum honeycomb sandwich panels

Theoretical analysis of the test sandwich panels

Concluding remarks

Acknowledgements

J. Theor. Appl. Fract. Mechan.

Int. J. Impact Engng.

Int. J. Impact Engng.

Int. J. Impact Engg.

The shear modulus of foil honeycomb cores

Aircraft Engng.

The analysis and design of honeycomb welded structures

J. Light Met. Welding

Elasto-plastic bending deformation of welded honeycomb sandwich panel

J. Japan. Soc. Mech. Engrs.