MEAM Seminar: “Accelerated Design of Heterogeneous Materials for Improved Failure Characteristics”

Nature provides countless examples of the use of heterogeneity to enhance the failure properties of materials. Many biological materials, such as bone, marine shells, and fish scales, are extremely resilient to fracture and failure. These often consist of regions that are highly mineralized and stiff and regions of biopolymers that are extremely soft. In practice, combining such disparate materials in synthetic systems is fraught with difficulties, such as poor interfacial adhesion. However, as we show in our work, other types of heterogeneities lead to similar enhancements to failure characteristics, including voids (inspired by bamboo) and spatial variations in fiber orientation (inspired by many materials, such as aorta). With the rise of 3D printing technology, it is possible to arbitrarily place materials with spatially-varying microstructure to mimic biological materials, ultimately with the goal of achieving comparable improvements to failure properties in synthetic materials.

In this talk, I will discuss three different types of heterogeneities that can be easily introduced to enhance failure characteristics. First, inspired by the microstructure of the Mantis shrimp club, we show how process defects that are intrinsic to extrusion-based additive approaches (voids and weak interfaces) can be spatially arranged in a helical (Bouligand) pattern to produce complex crack patterns and enhanced energy absorption. Next, we show how arrangements of voids (inspired by conch shells) can deflect cracks and enhance energy dissipation during fracture. Finally, we show how spatial variations in fiber orientation (inspired by aorta) can be produced using direct ink writing (DIW), leading to soft composites with high toughness and fatigue threshold.

Heterogeneities in materials, and the 3D printing processes used to create them, introduce a large number of parameters into the material design process, such as infill layer angle, fiber orientation, void placement, etc. Bio-inspiration provides a starting point and some basic intuition about how to design heterogeneous materials for improved failure properties, but it cannot guarantee optimal failure properties. I will therefore conclude the talk with a discussion of the use of Bayesian optimization for the acceleration of the design of architected heterogeneous materials with optimal failure properties. This will include the use of Bayesian optimization to design optimal architectures for energy dissipation using arrangements of voids inspired by conch shells. The second example uses a multi-fidelity Bayesian optimization approach to accelerate the design of heterogeneous triangular lattices with maximal energy absorption during compressive loading.