Tuning mechanical properties of architected materials by manipulating stresses and inelastic behaviors
Abstract
Title: Tuning mechanical properties of architected materials by manipulating stresses and inelastic behaviors PI: Dr. Grace X. Gu, University of California, Berkeley ARO program manager: Dr. Daniel Cole, Mechanical Behavior of Materials Cellular structures are types of porous materials and are prevalent as building blocks in nature. Such structures with open-cell arrangements are referred to as lattice structures and are oftentimes praised for their high strength-to-weight ratio, energy absorption, and heat transfer properties. A common feature of lattice structures employed in modern engineering applications is a symmetric configuration of repeating unit cells. The main benefit of using repeating unit cells is a greatly reduced design space, making its mechanical properties more amenable to tuning to meet a specific response criterion. This feature, however, has a major drawback: when one unit cell fails, the other unit cells will successively fail under a given loading condition, causing a sudden and catastrophic failure in the structure. Recent literature has shown that the damage tolerance or toughness of lattice structures can be increased by using asymmetric and irregular unit cells created by modifying their orientation. However, such irregular lattice structures often need to sacrifice strength to achieve higher toughness. Currently, there is a knowledge gap in understanding how to manipulate the architecture and deformation behaviors of irregular lattice structures to better balance the tradeoff between strength and toughness. Additionally, methods to create irregular lattice structures often involve rotating the unit cells, which poses a challenge for joining unit cells at interfaces and can lead to a significant strength reduction due to stress concentrations. The project objective is to design and manufacture novel irregular lattice structures and discover fundamental knowledge to overcome the tradeoff between mechanical properties by manipulating stresses and inelastic behaviors. Unit cells in lattice structures typically consist of beam elements with the same shape. This study, however, considers the shapes of beam elements in each unit cell as additional degrees of freedom for the design of irregular lattice structures. The local behaviors (e.g., deformation, buckling, failure) of each beam element and its contribution to the global mechanical properties, inelastic behaviors, and failure mode of architected materials will be examined. Moreover, this work aims to elucidate new mechanisms that can trigger the brittle-ductile transition of architected materials. It is hypothesized that by tailoring the spatial distribution of the beam elementsÕ radius, additional fracture energy dissipation mechanisms can be introduced with less reduction in the strength and stiffness. The specific aims of this program are as follows: 1) Understand how to control the mechanical properties of irregular lattice structures by adjusting the shapes of the beam elements; 2) Investigate how stress distributions vary locally in irregular lattice structures and potential to manipulate areas of high and low stress concentrations. A suite of irregular lattice structures will be additively manufactured with varying spatial distribution patterns and size distribution functions. Then, their mechanical properties such as modulus, strength, and toughness will be measured in experiments. A numerical model will be created to predict stress distributions and investigate the behavior and failure sequence of beam elements. The failure sequence of beam elements can provide insight into new mechanisms to trigger the brittle-ductile transition of architected materials such as crack detouring and buckling. The proposed research integrates computational mechanics, additive manufacturing, mechanical characterization techniques to design lightweight cellular structures with tunable mechanical properties for a variety of Army applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 02, 2022
- Source ID
- W911NF2210175
Entities
People
- Grace Gu
Organizations
- Army Contracting Command
- United States Army
- University of California, Berkeley