Effect of Thermal Cycles on Flexural Behavior of Al/Al Honeycomb Sandwich Structures

The main attractiveness of honeycomb sandwich structures lies in their high stiffness/weight and strength/weight ratios, which makes them suitable for primary structural aerospace parts such as aileron, elevator and rudder where weight reduction is a primary concern. Honeycomb cores, including nomex and aluminum honeycombs, have been used in the aerospace industry where bending, buckling, impact resistance and fire retardation are required, for example in some primary structural applications like wings and stabilizers. During flight time period, structural parts of an aircraft can be subject to thousands of such thermal cycles. Due to these environmental effects, damages can be occurred, especially at the interface region of core/face sheet. From literature surveys on evaluation of honeycomb sandwich structure flexural properties, it is not easy to find an article about sandwich behaviors under the effects thermal cycling. The information probably exists, as it is used on aircrafts that are submitted to a rigorous certification process to guarantee that they operate under safe conditions. However, this information may be restricted by confidentiality because of military or commercial concerns. In this study, AA3005-H19 aluminum alloy core/AA5754-H22 aluminum alloy face sheet (Al/Al) honeycomb sandwich structures are subjected to thermal cycles (0, 50, 150 and 300 cycles) in a full function environmental test chamber at temperature ranges-30^oC to +40^oC for 120 minutes. This paper deals with the determination of flexural properties such as ultimate core shear stress, facing stress, flexural stiffness, transverse shear rigidity and core shear modulus of various thermal cycled Al/Al honeycomb sandwich structures. Three-point bending tests are performed and flexural properties are calculated according to ASTM C393/C393M-16 and ASTM D7250/D7250M-16. After three-point bending tests, damage mechanisms which are occurring in the honeycomb sandwich structures are detected by digital camera images.