NASA EPSCoR: R3 ARMD RFA-006: Multiscale Modeling of Heterogeneous Architected Materials under Impact

1. Goals, Objectives and Expected Significance of the Proposed Research 1.1 Research goal, specific objectives, and expected significance As NASA strives to advance technology for delivering science and technology payloads to the Moon, with the aim of enhancing human lunar lander capabilities, the challenge lies in reducing material weight while preserving energy absorption capacity. Analogous goals in NASA Aeronautics pertain to aircraft survivability and impact resistance for fan case and fuselage materials and structures. Heterogeneous architected materials (HAMs), proposed as potential solutions for energy absorption, exhibit recoverable deformation and ultra-lightweight structures [1-8]. To conduct nonlinear large strain analysis at the unit cell scale, the finite element method based direct numerical simulation (DNS) offers a viable approach for predicting dynamic responses and failure mechanisms. However, the DNS approach, resolving all microstructural features, becomes computationally prohibitive for large-scale simulations. Introducing a promising alternative paradigm, multiscale computational modeling facilitates achieving predictive capability at the structural scale. Despite attempts to extend the homogenization approach to nonlinear material behavior, particularly in truss-based metamaterials [9, 10], these methods fall short in addressing coupled complex phenomena, such as plasticity and failure. Currently, there is a lack of an efficient computational method capable of accurately capturing dominant deformation mechanisms for architected materials. The overarching goal of this NASA R3 project is to overcome this challenge by developing a heterogeneous multiscale method capable of spanning two scales in nonlinear dynamic analysis, especially where the standard homogenization approach becomes inadequate. The specific objectives of the proposed project are threefold: (1) to create a geometric library comprising building blocks and joints, facilitating the combinational design of heterogeneous architected materials, (2) to develop a heterogeneous multiscale method capable of spanning two scales in nonlinear dynamic analysis, and (3) to validate the computational model through dynamic mechanical testing on 3D printed heterogeneous samples. The expected significance of this research lies in its potential to revolutionize lightweight material design, modeling, and characterization in aerospace applications by addressing the demanding performance requirements for future applications, where traditional material systems often struggle to meet weight competitiveness standards. Our proposed project aims to develop impact- resistant architected metamaterials specifically tailored for aerospace applications. Successful implementation of this research could lead to the development of a groundbreaking material design and evaluation approach, thereby significantly improving the mobility, reliability, maintainability, and survivability of space and aircraft structures. Furthermore, our findings could significantly advance our understanding of damage mechanisms of metamaterials under extreme loading conditions, thus paving the way for future research in advanced structural materials. 1.2 Technical approach and methodology 1.2.1 Heterogeneous architected metamaterial design We aim to develop and implement a 3D metamaterial library comprising diverse geometric building blocks and joints. This entails two key requirements: (1) establishing a geometric model library capable of accommodating various basic geometries, and (2) incorporating joining or ligament elements to connect discrete building blocks, such as pins, springs, and short beams. To create lattice-based building blocks with distinct mechanical properties, we first choose two lattice structures with differing stiffness characteristics. For example, the stretch-dominated octet lattice exhibits high stiffness and strength, but experiences catastrophic collapse with marked fluctuations in the stress-strain curve. In contrast, bending-dominated lattices like auxetic lattices demonstrate a stable and long post-yield plateau in the compressive stress-strain curve, though their lower plateau force limits energy absorption capacity. Leveraging their distinct yet complementary mechanical behaviors, we will opt for octet and auxetic lattices as the building 3