Mechanical Engineering Seminars

Electrons Dynamics Control in Femtosecond Laser Micro/Nanofabrication

Wednesday, January 29, 2020 @ 4 p.m.
3110 Etcheverry Hall
Professor Lan Jiang – Changjiang Distinguished Professor; Beijing Institute of Technology

Russell Severance Springer Colloquium

Abstract: During femtosecond laser fabrication, photons are mainly absorbed by electrons, and the subsequent energy transfer from electrons to ions is of picosecond order. Hence, lattice motion is negligible within the femtosecond pulse duration, whereas femtosecond photon-electron interactions dominate the entire fabrication process. Therefore, femtosecond laser fabrication must be improved by controlling localized transient electron dynamics, which poses a challenge for measuring and controlling at the electron level during fabrication processes. Pump-probe spectroscopy presents a viable solution, which can be used to observe electron dynamics during a chemical reaction. In fact, femtosecond pulse durations are shorter than many physical/chemical characteristic times, which permits manipulating, adjusting, or interfering with electron dynamics. Hence, we proposed to control localized transient electron dynamics by temporally or spatially shaping femtosecond pulses, and further to modify localized transient materials properties, and then to adjust material phase change, and eventually to implement a novel fabrication method. This talk covers our progresses over the 11 years regarding electrons dynamics control (EDC) by shaping femtosecond laserpulses in micro/nanomanufacturing: (1) Theoretical models were developed to prove EDC feasibility and reveal its mechanisms; (2) on the basis of the theoretical predictions, many experiments are conducted to validate our EDC-based femtosecond laser fabrication method. Some examples are presented, which proves that the proposed method can significantly improve fabrication precision, quality, throughput and repeatability and effectively control micro/nanoscale structures; and (3) As examples of practical applications, our method was employed to fabricate some key structures, for which commercialized equipment has been developed and sold for broad applications in industry.

Biography: Dr. Lan Jiang, the Changjiang Distinguished Professor at the Beijing Institute of Technology, received the Second Award of National Natural Sciences (Central Government of China), Ho Leung Ho Lee Innovation Award, the First Award of Natural Sciences (Ministry of Education of China), the First Award of Innovation (Ministry of Education of China), and National Outstanding Young-Scientist Award (National Natural Science Foundation of China). Over the past twelve years, as the Principal Investigator, he has received 25 grants totaling RMB181 million (approximately $26 million including facilities). He was elected as the National Leading Researcher for S&T Innovations and the Leader of Innovation Group of Ministry of Education of China. Dr. Jiang serves as Chief Scientist of National Basic Research Program of China, Director of National Innovation Center for High-Precision Micro-Fabrication, and Dean of the School of Mechanical Engineering at the Beijing Institute of Technology. He is an ASME Fellow, OSA Fellow, and ISNM Fellow. Dr. Jiang has authored 247 journal papers and 60 patents. He has delivered 19 plenary/keynote presentations and 50 invited talks in mainstream international conferences.

Hosted by: Professor Costas Grigoropoulos, 6129 Etcheverry Hall, 510-642-2525, cgrigoro@berkeley.edu

Multiscale Measurement of Electron Dynamics in High-Speed, High-Quality, High-Aspect Ratio Femtosecond Laser Drilling

Friday, January 31, 2020 @ 4 p.m.
3110 Etcheverry Hall
Professor Lan Jiang – Changjiang Distinguished Professor; Beijing Institute of Technology

Russell Severance Springer Colloquium

Abstract: By spatially/temporally shaping femtosecond laser pulses, localized transient electron dynamics can be actively controlled during ultrafast laser-material interactions. Based on this mechanism, high-quality microholes with a diameter of 1.6 μm and an aspect ratio of 1000:1 are fabricated by a shaped single femtosecond laser pulse. It takes 42 min to fabricate 251,000 holes in a 1 cm × 1 cm area. The holes are very uniform in size and shape. A multiscale measurement system (from the femtosecond scale to microsecond scale) is proposed and developed for cross-time-scale electron dynamics during femtosecond laser drilling. It consists of a pump-probe shadowgraph imaging technique, laser-induced breakdown spectroscopy (LIBS), and an intensified charge-coupled device (ICCD) camera. We reveal the multiple time-scale fundamentals during femtosecond laser material interactions, including the femtosecond-scale propagation of a laser pulse, picosecond-scale generation/evolution of laser-induced plasma, nanosecond-scale plasma ejection/expansion, and microsecond-scale hole formation.

Hosted by: Professor Costas Grigoropoulos, 6129 Etcheverry Hall, 510-642-2525, cgrigoro@berkeley.edu

Predictive CFD Modeling for Industrial Fire and Suppression: Progress and Challenges

Monday, February 3, 2020 @ 12 p.m.
3110 Etcheverry Hall
Dr. Yi Wang – FM Global, Research Division

Berkeley Fluids Seminar

Abstract: Accidental fire is the most costly peril for commercial and industrial facilities, with the total fire loss equal to the combined losses due to all natural hazards. The technical complexity related to the highly-coupled physical and chemical processes in fire and suppression has restricted the industrial fire protection solution to be mostly dependent on full-scale testing and empirical analysis. The early CFD fire modeling work has been limited to only a small part of the practical fire problem, such as smoke transport of a pre-determined fire size. This talk will present the recent progress that enables fully-coupled fire growth and suppression simulations. The sub-models include turbulent diffusion combustion, convective and radiative heat transfer, solid fuel pyrolysis, droplet atomization and transport, surface film flow and fuel suppression, etc. It will be demonstrated that a validated CFD model has been applied to industrial fire hazard evaluation and suppression designs, either along with experiments or solely by itself as a predictive tool. On-going research tasks and future challenges, especially those related to thermal fluids, will be highlighted.

Biography: Dr. Yi Wang received his Ph.D. in 2005 in Mechanical Engineering from the University of Maryland, College Park. His research focus has been high-performance CFD modeling of fire related phenomena. He is currently the manager of the Fire Dynamics Group at FM Global, where he oversees the research activities of material flammability, fire dynamics and testing, as well as CFD fire modeling. Dr. Wang serves on the editorial boards of Fire Safety Journal, Fire Technology, Fire and Materials. He is also a committee member of the International Association of Fire Safety Science (IAFSS).

Hosted by: Professor Philip Marcus, 6121 Etcheverry Hall, 510-642-5942, pmarcus@me.berkeley.edu

Elastica Catastrophe Machine and Configurational Forces in Dynamics

Tuesday, February 4, 2020 @ 4 p.m.
3110 Etcheverry Hall
Associate Professor Francesco Dal Corso – Department of Civil, Environmental and Mechanical Engineering; University of Trento, Italy

Abstract: Nonlinear structural mechanics breaks the limits of traditional linear elastic design, to create elements working much beyond the realm of linearized kinematics, fully inside the nonlinear range, so matching the strong requirements imposed by soft robotics, flexible locomotion devices, metastructures, architected structures for vibration mitigation, and morphable structures. Within this context, the following recent results are presented:

The number of stable equilibrium configurations is disclosed for a planar stip with varying the kinematics conditions at its ends [1]. This result leads to the definition of a ‘universal snap surface’, collecting the sets of critical boundary conditions for which the system snaps;
A catastrophe machine based on a continuous flexible element has been designed and realized [2]. In contrast to the classical Zeeman’s machine, the catastrophe locus of the elastica catastrophe machine may display a number of bifurcation points different than four and the convexity measure may significantly vary;
The sudden release of a rod partially inserted into a frictionless sliding sleeve is shown to be strongly affected by the action of configurational forces [3]. During its motion, the elastic rod dances by alternatively slipping in and out from the sliding sleeve. The nonlinear dynamics eventually ends with the rod completely injected into or completely ejected from the constraint.

The presented structural systems are modelled as nonlinear elastic structures and solved analytically. Physical models have been designed, realized and tested, confirming the theoretical predictions. These results represent innovative concepts ready to be used for enhancing the efficiency of snapping devices and retractable/extensible soft actuators towards advanced technological applications.

(1) Cazzolli, A., Dal Corso, F. (2019). Snapping of elastic strips with controlled ends. International Journal of Solids and Structures, 162, 285-303. doi: http://dx.doi.org/10.1016/j.ijsolstr.2018.12.005

(2) Cazzolli, A., Misseroni, D., Dal Corso, F. (2020). Elastica catastrophe machine: theory, design and experiments. Journal of the Mechanics and Physics of Solids, in press. doi: https://doi.org/10.1016/j.jmps.2019.103735

(3) Armanini, C., Dal Corso, F., Misseroni, D., Bigoni, D. (2019). Configurational forces and nonlinear structural dynamics. Journal of the Mechanics and Physics of Solids, 130, 82-100. doi: https://doi.org/10.1016/j.jmps.2019.05.009

Biography: After earning a PhD in Materials and Structural Engineering at the University of Trento, Italy, Francesco Dal Corso had a postdoctoral fellowship at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK. Dal Corso is currently Associate Professor of Solid and Structural Mechanics at the Department of Civil, Environmental and Mechanical Engineering of the University of Trento, Italy.

Dal Corso’s research activity is devoted to the mechanical behaviour of Solid and Structures. In particular, he dealt with problems related to the localization of deformation, plasticity, large deformations, homogenization, higher-order continua, stress concentrations and singularities, contact mechanics, configurational mechanics and stability. He has co-authored more than 40 journal papers and has co-guest edited a Special Issue of the Journal of the Mechanics and Physics of Solids in 2020.

Hosted by: Professor Oliver O’Reilly, 5131 Etcheverry Hall, (510) 642-0877, oreilly@berkeley.edu

Glassomer – 3D Printing of Transparent Fused Silica Glass

Monday, February 10, 2020 @ 11 a.m.
Vogt Room, 6153 Etcheverry Hall
Dr. Frederik Kotz – Co-Founder and Chief Science Officer, Glassomer

Abstract: Fused silica glass is an important material due to its high chemical and thermal stability and its outstanding optical transparency, hardness and well known surface properties. Due to these properties fused silica glass is an interesting material for future applications in chemical synthesis or optics and photonics. However, structuring of glasses is difficult, especially when high-resolutions are needed. Structuring is usually done using wet chemical or dry etching with hazardous chemicals.

We have previously described a new technology to fabricate and structure fused silica glass. We have therefore developed nanocomposites (called Glassomer) which can be processed like a polymer e.g. by UV casting, 3D printing or high-throughput polymer replication. After the structuring process the nanocomposites are turned into fused silica glass via thermal debinding and sintering (see Figure 1). We have demonstrated that the sintered fused silica glass is chemically and physically identical to commercial fused silica glass. It shows the same high transparency in the UV, visible and infrared combined with the same mechanical strength, hardness and chemical and thermal resistance. A novel variation of the process called sacrificial template replication allows fabrication of arbitrary microchannel structures in fused silica glass. Hereby a polymeric template structure is embedded in Glassomer and leaves the inverse structure inside fused silica glass after the debinding and sintering process. Furthermore, colored glasses can be fabricated by doping the parts with alcoholic solutions of metal salts. Glassomer will enable many applications from optics and photonics and chemistry to life sciences and biotechnology.

Figure 1: The Glassomer process: Liquid nanocomposite are consisting of silica nanopowders in a photocurable binder matrix, are printed using stereolithography printers. The polymerized nanocomposites are subsequently turned into high purity fused silica glass via thermal debinding at 600 °C and sintering at 1300 °C.

Biography: Dr. Frederik Kotz studied mechanical engineering at the Karslruhe Institute of Technology (KIT) in Germany. During his PhD thesis he developed novel strategies for the fabrication of transparent glasses. His work has been published in Journals like Nature and Advanced Materials. He is Co-founder and Chief Science Officer (CSO) of Glassomer which is commercializing the technologies he developed. For his work he has been awarded among others the Innovators under 35 by MIT Technology Review Europe.

Hosted by: Assistant Professor Hayden Taylor, 6159 Etcheverry Hall, 510-642-4901, hkt@berkeley.edu