S3E7
Episode 7 (February 28, 2021)
Abhinendra Singh
University of Chicago
Manav Manav
California Institute of Technology
Xingsheng Sun
California Institute of Technology
Shear thickening in dense suspension: a master-curve and "roll" of friction
Abstract of Talk 1
The mechanism of shear thickening in dense suspensions has been linked to a stress-controlled transition from unconstrained lubricated (“frictionless”) to constrained unlubricated (“frictional”) rheology. However, it is unclear how these constraints are affected by particle surface chemistry. We show that simulations incorporating reasonable values of sliding friction with a small amount of rolling friction can collapse experimental data covering orders of magnitude in particle size and different particle-fluid chemistries simply by scaling the onset stress for shear thickening. Still, there are notable exceptions where enhanced hydrogen bonding between particles decreases the jamming volume fraction in a manner analogous to sticky or rough particles, which can only be modeled using higher rolling and/or sliding friction coefficients. These observations thus connect the stress-activated formation of hydrogen bonds at the particle surface to rolling and sliding constraints and macroscopic shear thickening behavior.
Biosketch of Speaker 1
Dr. Singh is a joint Postdoctoral Scholar at the University of Chicago between James Franck Institute and Pritzker School of Molecular Engineering. He obtained his Ph.D. at the University of Twente in The Netherlands, where he was co-advised by Professor Stefan Luding and Dr. Vanessa
Magnanimo investigating the flow behavior of the dense granular material. He moved to the Levich Institute in the City College of New York after finishing his Ph.D., where he developed the constitutive model for dense frictional suspensions as a part of post-doctoral research co-supervised by Professors Jeff Morris and Morton Denn. Dr. Singh was awarded the 2020 Journal of Rheology Publication Award for his work entitled ‘A constitutive model for simple shear of dense frictional suspensions.’ JOR 62, 457 (2018). Dr. Singh also recently won the Best Presentation by a Young Scientist award at the virtual Physics of Dense Suspension symposium.
Molecular dynamics simulation study of the shock response of polyurea
Abstract of Talk 2
Polyurea is a thermoplastic elastomer with excellent chemical and mechanical resistance. Its shear resistance of ∼500 MPa at high strain rates (10^5-10^6 s-1) and pressures (∼9 GPa) matches that of high strength steels. It is a promising material for shock resistance applications such as in blast resistant body armor and headgear, retrofitting strategic installations to protect against blast among others. However, molecular-scale and mesoscopic mechanisms governing shock response are not well understood. The phase-segregated microstructure of polyurea makes it challenging to study its response using molecular dynamics (MD) simulation. In our recent work, we leverage the microstructure to develop MD models of the different phases within polyurea independently and investigate the molecular-scale mechanisms mitigating shock energy. A multiscale simulation approach yields shock Hugoniot of polyurea which is in close agreement with the experiment. In the talk, I will present the simulation approach and discuss the results from our investigation.
Biosketch of Speaker 2
Manav is currently a postdoctoral scholar research associate in Professor Michael Ortiz’s lab in aerospace engineering at Caltech. He obtained his PhD and MASc degrees in mechanical engineering from the University of British Columbia, Vancouver in 2019 and 2014 respectively. His research interests are in the mechanics of soft, polymeric, and nanostructured materials.
Diffusive Molecular Dynamics and Its Application to Hydrogen Diffusion in Palladium Nanoparticles
Abstract of Talk 3
Diffusive Molecular Dynamics (DMD) is a class of recently developed computational methods for the simulation of long-term mass transport and heat transfer with a full atomic fidelity. This talk focuses on the development and application of a DMD computational model for the long-term, three-dimensional, deformation-diffusion coupled analysis of solute mass transport in nanomaterials. First, a DMD model is developed for simulating interstitial solute diffusion in nanomaterials. This model couples a discrete kinetic law for the evolution of mass transport process with a non-equilibrium thermodynamics model that governs lattice deformation and supplies the requisite driving forces for kinetics. Then, the developed DMD model is employed to investigate the long-term hydrogen diffusion in palladium nanoparticles. Several significant findings will be shown, including the propagation of an atomistically sharp phase boundary, the dynamics of solute-induced lattice deformation and stacking faults, and the effect of lattice crystallinity on absorption rate. The two-way interaction between phase boundary propagation and stacking fault dynamics will be discussed in detail.
Biosketch of Speaker 3
Dr. Xingsheng Sun is a Postdoctoral Scholar in Aerospace at California Institute of Technology (Caltech). He holds a Ph.D. degree in Aerospace Engineering from Virginia Polytechnic Institute and State University (Virginia Tech). He received his B.S. degree in Mechanical Engineering from Dalian University of Technology in 2011, and his M.S. degree in Mechanical Engineering from Hunan University in 2014. His research background includes computational solid mechanics, uncertainty quantification, and high-performance computing. He is interested in long-term atomistic modelling and simulation, multi-length-scale uncertainty quantification, mechanics of materials in extreme conditions, and application-driven materials by design.
Guest Host: Jingjie Yeo
Prof. Jingjie Yeo is an assistant professor at Cornell University, and his research group performs interdisciplinary, computational studies of material and biological phenomena to develop dynamically-responsive, living materials and design synthetic biological platforms for engineering and medical applications. He is also a co-instructor in Station1, a social nonprofit organization dedicated to building the foundations of the university of the future through educational opportunity and socially-directed frontier STEM education, research, and internships. He did his postdoctoral studies at both Tufts University and Massachusetts Institute of Technology. Prior, he was a research scientist in the Institute of High Performance Computing, Singapore. He received his Ph.D. and his B.Eng. degrees from Nanyang Technological University Singapore.