Development of novel additive manufactured hybrid architected materials and investigation of their mechanical behavior

Topology optimization is gaining popularity because it enables designers to maximize the performance of a component or structure while minimizing the quantity of material required. Complex structures with intricate geometries can be produced on an industrial scale by employing sophisticated design software and additive manufacturing techniques. This combination of topology optimization and additive manufacturing permits the creation of completely functional components for a variety of applications. In topology optimization, the density-based method and the lattice method are two common techniques. Lattice structures, which provide lightweight characteristics, high porosity, and a high ratio of surface area to volume, have been utilized in topology optimization for a variety of applications, including implants, catalysts, and aeronautical components. Extensive research has been conducted on the mechanical properties of lattice structures, and it has been observed that mechanical behavior depends on the relative density of the lattice structure. Lattice structures’ mechanical performance can exhibit two distinct behaviors: bending-dominated behavior and stretching-dominated behavior. The relative density chosen has an effect on the mechanical properties of lattice structures. Regardless of the specific lattice structure employed, as the relative density decreases, the mechanical properties of the structure deteriorate. Using techniques such as functional gradation, hybridization, higher-order lattice structures, and the combination of existing cellular materials, researchers seek to enhance the mechanical performance of architected materials for practical applications.

In a new study published in the peer-reviewed Journal Mechanics of Materials, Dr. Nikolaos Kladovasilakis, Professor Konstantinos Tsongas and Professor Dimitrios Tzetzis from the International Hellenic University in Greece presented a novel approach to address the limitations of traditional lattice structures by developing novel hybrid architected materials with much better and enhanced mechanical strength, utilizing topology optimization methods and additive manufacturing. The selection and design of the materials were governed by particular criteria with the ultimate goal the minimization of stress concentration regions. Using the Boolean process and the structures of Schwarz Primitive, Neovius, Kelvin, Rhombic Dodecahedron, Face-Centered Cubic, and Schwarz Diamond, four novel hybrid lattices were created. The hybrid structures were designed with the software nTopology^TM and manufactured with varying relative densities.

The research team studied the impact of strut and wall thickness on the relative densities of hybrid cellular materials. The effect of various thicknesses of struts and walls on the overall relative density and subsequent mechanical response of the materials was analyzed. The analysis of mechanical behavior was performed using hyper-elastic finite element models based on real experimental data, revealing an exponential relationship between strut thickness and relative density for strut-based structures and a nearly linear relationship between wall thickness and relative density for all examined structures. The authors also investigated the anisotropy of hybrid structures using normalized elastic modulus diagrams. Calculated anisotropy measurements revealed that all four structures displayed differing degrees of anisotropic behavior. Due to their more complex geometries, Schwarz Primitive and Kelvin structures exhibited the greatest anisotropy among the examined structures. These findings have significant ramifications for applications requiring directional-dependent mechanical properties, enabling designers to optimize lattice structures for desirable results. After examining the anisotropy of each hybrid structure, quasi-static compression experiments were conducted at 10%, 20%, 30%, and 40% relative densities to assess the compressive strength and deformation behavior of the structures under different loading conditions. Compression loading revealed distinctive mechanical behavior for all four hybrid-architected materials. According to lattice structures and relative densities, rigidity and strength varied.

In a nutshell, the research team created successfully finite element models for each structure to simulate their mechanical response with high precision. Under compression loading, verification specimens were tested, and the results were compared to the data from the finite element analysis, revealing very good agreement. This demonstrated the accuracy of the finite element models developed by the authors to simulate the behavior of the hybrid-architected materials. Using experimental and finite element analysis data, the authors were able to analyze the stress distribution for low strain rate experiments. Under compression, they observed fracture occurring on the specimen’s upper surface.

To conclude, the new study focused on the development of hybrid architected materials by exploiting and improving strut and triply periodic minimal surface lattice structures, in order to achieve superior mechanical properties. These novel materials have the potential to revolutionize the design and production of components, resulting in more sustainable and efficient products.

Acknowledgement

The publication of this research highlight in Advances in Engineering is co-financed by Greece and the European Union (European Social Fund-SF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “Support for Internationalization Actions of the International Hellenic University”, (MIS 5154651).