Microstructural response of aluminum honeycomb to combined out-of-plane loading

This paper deals with the experimental investigation on the microstructural response of aluminum honeycomb under combined normal and shear out-of-plane loading. The enhanced Arcan apparatus (EAA) was used to apply a controlled biaxial displacement field to the boundaries of a flat butterfly-shaped honeycomb specimen. The specimen thickness corresponded to the width of a single honeycomb cell. Two reaction force components related to all the stresses acting on the specimen were directly measured during the experiments: a vertical force measured by a load cell of a standard universal testing machine and a normal force measured by an additional EAA-integrated load cell. Flat specimens were extracted from honeycomb blocks of 1.8% relative density compared to the solid cell wall material (aluminum 5056 H39). Observations on the behavior of the honeycomb microstructure during biaxial testing were made and discussed in detail. Two sources of macroscopic inelasticity of a honeycomb microstructure were identified and defined, namely: plastic collapse of the hexagonal honeycomb microstructure over a wide range of combined loading and conventional yield of the cell wall material at loading states dominated by tensile stresses. According to these mechanisms, a macroscopic yield envelope was found to be described by two different intersecting yield functions. (C) 2002 Elsevier Science Ltd. All rights reserved.