Fabrication And Mechanical Behavior Of Composite Sandwich Structure With Folded Core

Aircraft fuselage generally consist of stiffened panels with a complicated fabrication technique and strict assembly process, and thus the quality of the stiffened panels is difficult to control. Therefore, small airplanes use sandwich structures with honeycomb or foam cores in fuselage construction. Howe ver, the low impact resistance capacity and water condensation problem in the closed cell core materials, have restricted their extensive application. Recently. sandwich panels with foldcore of high specific stiffness and strength and outstanding acoustic properties, have attracted lots of attention, and are considered to be the most likely core materials used in large airplane fuselages. In the present study, we have reviewed and commented the research status of chevron foldcore sandwich structure. Two new configurations based on the origami ideology are designed: M-pattern and Olive-pattern foldcore. Subsequently, their mechanical behavior and failure modes were comprehensively analyzed and also compared with chevron folded sandwich panels.Firstly, analytical models are established to study the stiffness and strength of the composite folded core under compressive and shear load. Finite element model is established to simulate the mechanical response of the composite folded sandwich panel. In the model, cohesive element is introduced to simulate the crack initiation and propagation of the adhesive layer, and 3D solid element C3D8 is used to simulate the stress field of composite panel and folded core. The improved Hashin criteria and power exponent rule are used to characterize the damage and stiffness degeneration, while the cohesive model and B-K criteria is used to simulate the damage and evoluation of the adhesive layer.Secondly, the mechanical properties and failure mode of the composite chevron folded sandwich structure are studied theoretically, numerically and experimentally. Based on analytical models and numerical simulation, effects of the fiber layup and core geometry on the compression and shear properties of the structure are studied, The mechanical properties and failure modes of composite folded core sandwich panels in the L and W direction under shear, bending and lateral compression are characterized, and the effect of the wall thickness is discussed. Cell walled thickness are analyzed, and the failure mechanism of the structure is revealed.Thirdly, M-pattern folded core is designed to increase the shear performance of chevron folded core. M-pattern folded sandwich structures are fabricated and the compression and shear behavior of the new structures is investigated by experiment and theoretical analysis. The effect of cell walled thickness on the mechanical properties of M-pattern folded core are demonstrated. The modulus, strength and failure mode of M-pattern foldcore with three different walled thicknesses were investigated under compression and shear loads. The mechanical behaviors of this structure were tested under three-point bending and side compression, the along L and W orientation strength, limit load and energy absorptive characteristics of structure are analyzed, respectively. The influences of the adhesive area and the thickness of core wall were also included and the failure mechanism of this structure are investigated.Finally, a novel Olive-pattern foldcore were designed aiming to reduce wall wrinkling in chevron and M-pattern foldcore. The mechanical behavior and failure mechanism of Olive-pattern folded sandwich structures under compression, shear, bending were characterized by theoretical and experimental methods, and then compared with chevron and M-pattern folded sandwich structures. The effects of core wall thickness and adhesive layer on the mechanical properties and failure modes for folded sandwich structure are discussed.