S5E15

Abstract

Understanding the fracture toughness of glasses is a fundamental problem of prime theoretical and practical importance. Here, in this talk, I will talk about our theoretical study of fracture toughness dependence on the loading rate, the age (history) of the glass, and the notch radius. Reduced-dimensionality analysis suggests that the notch fracture toughness results from a competition between the initial, age- and history-dependent plastic relaxation time scale and an effective loading time scale and predicts the brittle-to-ductile transition. These predictions are verified using 2D computations and previous experimental observations, providing a unified picture of the notch fracture toughness of glasses. The theory highlights the importance of time-scale competition and far-from-steady-state elasto-viscoplastic dynamics for understanding toughness. I will discuss possible implications for applications.

Introduction of speaker

Manish is a postdoc at Texas A&M University, working on developing a thermodynamic consistent discrete framework to model inelastic deformations mechanisms that can be applied to various contexts such as amorphous (STZ) plasticity, twinning, phase transformation, solute interactions, and geophysics. Before this, he contributed to developing a fracture model that predicts the brittle-to-ductile transition in the notch toughness of amorphous materials. He did his Ph.D. in crack propagation in heterogeneous materials from Sorbonne University, France, a master’s in engineering Mechanics from IIT Delhi, and a bachelor’s in mechanical engineering from Nirma University, India.

Abstract

Intelligent microscopic structures that combine complementary metal oxide semiconductor (CMOS) circuits with nano actuators could fine-control the microscale environment and show vast potential from biomedical applications and microfluidic manipulations. Here, inspired by the microorganisms, we make the first CMOS circuits, and nano actuators integrated microscopic structures and demonstrate their ability to do microfluidic manipulation based on cilia pumping. We first develop voltage-actuated actuators that can generate bending in microscales. And by designing the actuator geometry, we observe non-reciprocal trajectories that can drive surface flows at tens of microns per second at actuation voltages of 1 volt. We then show that a cilia unit cell can create a range of elemental flow geometries locally. Combining these unit cells, we create an active cilia metasurface that can generate and switch between any desired surface flow pattern. Then, we integrate the cilia with a light-powered CMOS clock circuit to demonstrate wireless operation. We propose that more advanced circuit functions could be combined to make smarter structures, such as tuning the flow directions based on programming. This work paves the way for intelligent microscopic structures that can sense the local environment, make decisions, and communicate with the external world.

Introduction of speaker

Wei Wang got a bachelor’s degree in Engineering Mechanics (Qian Lingxi program) at the Dalian University of Technology in 2015. He went to Tsinghua University and earned a master’s degree in Mechanics in 2018. He studied the mechanics of origami structures at Tsinghua University. He entered Cornell University in 2018 and is now a Ph.D. candidate in Mechanical Engineering. His current research is to build intelligent microscopic structures, including developing nano actuators for artificial cilia and micro-origami devices, combining CMOS circuits with nano actuators, and designing microscopic robots. He has more than ten publications, including one selected as the cover of Nature.