Fatigue in the Core of Aluminium Honeycomb Panels: Lifetime Prediction compared to Fatigue Tests

in International Journal of Damage Mechanics (2014), 23 no.5

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway ... [more ▼]

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway-cars and vehicles. The sandwich panels consist of two thin and stiff aluminium face sheets , which are bonded to a thick and lightweight aluminium honeycomb core. These structures are subjected to dynamic loading. However, in literature, there are hardly any fatigue properties of the honeycomb core described. The fatigue properties of the core are investigated using the finite element method and experiments. Depending on the load application, the honeycomb core fails either through core indentation or shear failure. For a fatigue prediction, both failure modes have to be investigated. Additionally the physical behavior of the honeycomb core is depending on the orientation of the core. Hence, fatigue tests were conducted in three directions of the core: the stiffest direction, the most compliant direction and the direction with the highest stresses. A three-point bending test setup was built to study the fatigue properties of the honeycomb core. Several fatigue tests were carried out with a load ratio of R=0.1 (maximum load 10 times bigger than minimum load) and the fatigue diagrams being illustrated. Additionally, Food-Cart Roller Tests (wheels of a cart rolling in a circle on a floor panel) were done to dynamically test the panels in every angle. The sandwich structures were modeled with the ANSYS finite element software. The simulations, which were used to determine the stress amplitudes in the specimens, are described in the following pages. In addition, buckling analyses were used to examine core indentation failure. Based on these simulations, failure predictions can be made. The fatigue life of the examined specimens is successfully approximated in this manuscript, with the lifetime analysis being based on the FKM-guideline (error less than 14% in load amplitude). [less ▲]

Shear Stresses in Honeycomb Sandwich Plates: Analytical Solution, Finite Elemente Method and Experimental Verification

in Journal of Sandwich Structures & Materials (2012), 14(4), 449-468

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of ... [more ▼]

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of aluminium. Compared to normal plates, sandwich panels have a very high stiffness and simultaneously a low weight. The core of these structures is mainly subjected to shear stresses. The shear stresses depend strongly on the angle of the load application. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. When doing finite element simulations of honeycomb cores, often the core is homogenized in order to reduce the calculation time. In this article, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. The equations are validated by finite element simulations and partially by tests. Three-point bending tests and additionally some Food Cart Roller Tests were conducted in order to test the panels in different angles. [less ▲]

Fatigue in Aluminium Honeycomb-core Plates

in Benchmark: The International Magazine for Engineering Designers & Analysts (2011), (January), 26-32

Honeycomb composite lightweight structures made of aluminium or aramid fibres are used in airplanes, railway carriages and automobiles. These structures are subjected to dynamic loading but hardly any ... [more ▼]

Honeycomb composite lightweight structures made of aluminium or aramid fibres are used in airplanes, railway carriages and automobiles. These structures are subjected to dynamic loading but hardly any fatigue properties of the honeycomb core exist in current literature. Hence here a theoretical and experimental approach is presented. [less ▲]