This study deals with the structural integrity of a co-axial octocopter cargo drone. Most unstable states in progress of various flight missions of the cargo drone are considered to be derived from take-off and landing operations. In order to evaluate the structural integrity of these states, three-dimensional FE (finite element) simulation using whole frame assembled with structural members and components is performed, and then the effective stress level and deflection degree are investigated. Also, topology optimization is adopted to improve the locally concentrated stress and large deflection around front and rear sections of the motor-support side member. From topology optimization, it is ensured that the shape and location of plate support have to be modified for improving the stress level and the deflection degree. Based on the optimized and modified feature, FE simulation is re-performed. Consequently, it is confirmed that the effective stress and the deflection are reduced to about 26.67% and 19.15% around the side member, respectively.

In this study, the structural integrity of an engine-generator support structure of hybrid drone is verified through finite element (FE) analysis and experimental investigation. From preliminary experiments, critical failures in four columns of the support structure were observed. Due to the repeated cyclic loads induced by the engine-generator operation, the results of the FE simulation pointed out that fatigue failure is the main cause. To improve the structural integrity, the geometric shape and the material of the structural members are modified and changed, and the safety factor is also reviewed using static structural analysis. The possibility of critical resonance is evaluated through FEM-associated modal analysis and a series of vibration tests. As result, it is confirmed that the re-designed support structure was structurally improved with enough safety margin through FE analysis and experimental investigation, and fatigue life by comparing the predicted value and S-N curve of the material used to the support structure was improved.

The worsening environmental pollution has increased the interest in developing eco-friendly technologies. The purpose of this study is to develop an aero-heat exchanger to reduce the emission of environmental pollutants. The operating conditions of an aircraft are extremely harsh, leading to challenges with the determination of appropriate materials and structures that can withstand the severe conditions. In addition, since the tubes brazed to the tube-sheet are structurally fragile, it is essential to assess the structural integrity of tubes. In this study, the overall structural integrity of the tubular heat exchanger under development was evaluated. An appraisal of the junctions between tubes and tube-sheet, which are the most critical parts, was conducted. A finite element (FE) analysis was employed for the assessment of structural integrity. FE analysis was used to evaluate the brazed joint of tubes using a model in which specific tubes were designed to withstand the high temperature of the tube-sheet. The evaluation was carried out compared with the fatigue strength of Inconel 625, the material constituting the heat exchanger.