Mechanical and Civil Engineering Seminar

In my presentation, I will first briefly introduce research projects in my group and focus on two studies about how we can make materials/structures that can adapt to loading conditions by changing their mechanical properties and/or repair damages.

An architected material (or metamaterial) is a class of materials that provide new properties that are not observed in natural materials and/or from a bulk material that the "material" is made of. I will present adaptive energy-absorbing "materials" with extreme energy dissipation and improved energy absorption with increasing strain rate. We utilize energy dissipation mechanisms across different length scales to maximize energy dissipation by utilizing architected liquid crystalline elastomers (LCEs). As a result, our energy-absorbing material shows about order of magnitude higher specific energy dissipation at quasistatic condition compared with the previous studies and even higher energy dissipation at faster strain rates with power-law relation, whose exponent can be tuned by controlling the mesoscale alignment of molecules using a simple strain control-based approach. The findings from our study can contribute to realizing extremely lightweight and high energy dissipating materials, which will be beneficial for various applications including aerospace, automotive, and personal protection.

Nature produces outstanding materials for structural applications such as bones and woods that can adapt to their surrounding environment. For instance, bone regulates mineral quantity proportional to the amount of stress. It becomes stronger in locations subjected to the higher mechanical loads. This leads to the formation of mechanically efficient structures for optimal biomechanical and energy-efficient performance. However, it has been a challenge for synthetic materials to change and adapt their structures and properties to address the changes of loading conditions. To address the challenge, we are inspired by the findings that bones are formed by mineralization of ions from blood onto scaffolds. I will present a material system that triggers mineral synthesis from ionic solutions on organic scaffolds upon mechanical loadings and/or damages so that it can self-adapt to mechanical loadings and regenerate upon damages. For example, we observed ~30% increase in the modulus of the material upon periodic loadings for 3 days. We also observed that the material could self-repair damages generated by removing ~5 μm thick minerals from the matrix, in 7 days. We envision that our findings can open new strategies for making synthetic materials with self-adaptable mechanical properties and self-repair capability.