Mechanical Performance Analysis of 3D Printed Hierarchical Honeycomb Structures in Aerospace Applications
Özet
Businesses have made significant progress in production methods by investing in technology in order to reduce costs and increase efficiency. These progresses are especially notable with additive manufacturing, which has a wide range of applications. Additive manufacturing increases production efficiency by offering a more effective way compared to traditional methods in the production of complex shaped parts. In addition, this technology leads to the creation of new business models, supply chain changes and the transformation of product development processes. The aviation industry has made great progress in recent years as a pioneer of additive manufacturing technology and there has been a rapid increase in the number of aircrafts. With increasing demands, manufacturers need to produce more efficient, safe and eco-friendly aircrafts. Engineers must meet a number of requirements when designing lightweight and durable aircraft components. However, current traditional production methods lead to high costs and design complexity in the production process, limiting the functionality of the components. For this reason, a comprehensive research and development study is being carried out on new production and design techniques. In line with this goal, it is expected that existing structural techniques and material technologies will be re-evaluated with modern technology and higher performance structures will be obtained in the future. The adaptation of AM technology to direct part production will change this process in a positive way. Sandwich panels play an important role in the aerospace industry due to their high bending stiffness/weight ratio and usually include honeycomb core structures. Honeycomb structures are widely used in modern aircraft design due to their lightness and strength; however, they have limitations such as limited strength and not being suitable for surfaces with complex curvatures. Cores are formed by processing a block structure into the desired form, which increases the waste rate in the production process and leads to various uncertainties. To overcome these challenges, innovations are needed in the production methods and pattern designs of core structures. Natural structures exhibit a complex and hierarchical organization from nanometer to macroscopic scales, facilitating the design of more advanced and functional materials. This approach allows the development of lighter, stronger and more functional structures by overcoming the limitations of traditional materials. Hierarchical structures are created by methodically incorporating small geometries at certain levels, and literature shows that these structures have higher specific strength and modulus values than traditional honeycomb structures. The combination of additive manufacturing technology with hierarchical honeycomb structures makes it possible to achieve desired features in aircraft sandwich designs through customization at affordable costs. The current study will provide a new look at the potential of AM technology to overcome the limitations in honeycomb production and its integration in aerospace structural applications. In the first part of the thesis, the mechanical properties of the test specimens produced with 3D printers will be determined experimentally and verified with simulation models. Determination of basic material properties is critical for the accurate characterization of hierarchical honeycomb structures. The building orientation has a great impact on the anisotropic properties, surface quality and cost of 3D printed parts. In the study, the effect of build orientation on mechanical performance was investigated while keeping all other process parameters constant. Tensile tests were performed on the produced PLA specimens and the results were analyzed by comparing with static structural simulations. In the current study, a faster and more effective finite element analysis approach is proposed to evaluate the mechanical performance of components produced with additive manufacturing. The time-consuming nature of the algorithms was emphasized in the study, but the simulation process was simplified with realistic assumptions. FE modeling accurately simulated the mechanical behavior of FDM components and high accuracy rates were achieved. In the second part of the thesis, the mechanical behaviors of hierarchical honeycomb core structures at different levels integrated into the armrest plate selected from an aircraft cockpit were investigated. It was determined that the most critical load case of the armrest occurred with the force applied to the middle part of the plate by the pilot while sitting or standing. Similar load cases were created by looking at the standards of human capabilities. A mechanical three-point bending test was used to determine the strength of the plate under these loads. PLA material data verified by tensile tests and a simplified simulation model developed for additive manufacturing were applied to new models by determining similar boundary conditions. After the parametric plate designs for honeycomb structures, a linear analytical solution was developed and compared with the results of FE models under a three- point bending test. As a result, this study presented a method that successfully simulated and analytically verified the mechanical properties of the produced hierarchical honeycomb structures and also showed the promising potential of these structures for aerospace components.
