23,663 research outputs found
Recommended from our members
Unraveling the Role of Interfaces on the Spall Failure of Cu/Ta Multilayered Systems.
Molecular dynamics (MD) simulations are carried out to investigate the effects of the type and spacing of FCC/BCC interfaces on the deformation and spall behavior. The simulations are carried out using model Cu/Ta multilayers with six different types of interfaces. The results suggest that interface type can significantly affect the structure and intensity of the incoming shock wave, change the activated slip systems, alter dislocation slip and twinning behavior, affect where and how voids are nucleated during spallation and the resulting spall strength. Moreover, the above aspects are significantly affected by the interface spacing. A transition from homogeneous to heterogeneous dislocation nucleation occurs as the interface spacing is decreased to 6 nm. Depending on interface type and spacing, damage (voids) nucleation and spall failure is observed to occur not only at the Cu/Ta interfaces, but also in the weaker Cu layer interior, or even in the stronger Ta layer interior, although different mechanisms underlie each of these three distinct failure modes. These findings point to the fact that, depending on the combination of interface type and spacing, interfaces can lead to both strengthening and weakening of the Cu/Ta multilayered microstructures
Graph Dynamical Networks for Unsupervised Learning of Atomic Scale Dynamics in Materials
Understanding the dynamical processes that govern the performance of
functional materials is essential for the design of next generation materials
to tackle global energy and environmental challenges. Many of these processes
involve the dynamics of individual atoms or small molecules in condensed
phases, e.g. lithium ions in electrolytes, water molecules in membranes, molten
atoms at interfaces, etc., which are difficult to understand due to the
complexity of local environments. In this work, we develop graph dynamical
networks, an unsupervised learning approach for understanding atomic scale
dynamics in arbitrary phases and environments from molecular dynamics
simulations. We show that important dynamical information can be learned for
various multi-component amorphous material systems, which is difficult to
obtain otherwise. With the large amounts of molecular dynamics data generated
everyday in nearly every aspect of materials design, this approach provides a
broadly useful, automated tool to understand atomic scale dynamics in material
systems.Comment: 25 + 7 pages, 5 + 3 figure
A New Phenomenon: Sub-Tg, Solid-State, Plasticity-Induced Bonding in Polymers
Polymer self-adhesion due to the interdiffusion of macromolecules has been an
active area of research for several decades [70, 43, 62, 42, 72, 73, 41]. Here,
we report a new phenomenon of sub-Tg, solid-state, plasticity-induced bonding;
where amorphous polymeric films were bonded together in a period of time on the
order of a second in the solid-state at ambient temperatures nearly 60 K below
their glass transition temperature (Tg) by subjecting them to active plastic
deformation. Despite the glassy regime, the bulk plastic deformation triggered
the requisite molecular mobility of the polymer chains, causing
interpenetration across the interfaces held in contact. Quantitative levels of
adhesion and the morphologies of the fractured interfaces validated the sub-Tg,
plasticity-induced, molecular mobilization causing bonding. No-bonding outcomes
(i) during the compression of films in a near hydrostatic setting (which
inhibited plastic flow) and (ii) between an 'elastic' and a 'plastic' film
further established the explicit role of plastic deformation in this newly
reported sub-Tg solid-state bonding
Recommended from our members
A Comprehensive Study of Hydrolyzed Polyacrylamide as a Binder for Silicon Anodes.
Silicon anodes have a high theoretical capacity for lithium storage, but current composite electrode formulations are not sufficiently stable under long-term electrochemical cycling. The choice of polymeric binder has been shown to impact stability and capacity of silicon anodes for electrochemical energy storage. While several promising polymeric binders have been identified, there is a knowledge gap in how various physicochemical properties-including adhesion, mechanical integrity, and ion diffusion-impact electrochemical stability and performance. In this work, we comprehensively investigate the physical properties and performance of a molecular-weight series (3-20 × 106 g/mol) of partially hydrolyzed polyacrylamide (HPAM) in silicon anodes. We quantify the mechanical strength, electrolyte uptake, adhesion to silicon, copper, and carbon, as well as electrochemical performance and stability and find that HPAM satisfies many of the properties generally believed to be favorable, including good adhesion, high strength, and electrochemical stability. HPAM does not show any electrolyte uptake regardless of any molecular weight studied, and thin films of mid- and high-molecular-weight HPAM on silicon surfaces suppress lithiation of silicon. The resulting composite electrodes exhibit an electrochemical storage capacity greater than 3000 mAh/g initially and 1639 mAh/g after 100 cycles. We attribute capacity fade to failure of mechanical properties of the binder or an excess of the solid electrolyte interphase layer being formed at the Si surface. While the highest-molecular-weight sample was expected to perform the best given its stronger adhesion and bulk mechanical properties, we found that HPAM of moderate molecular weight performed the best. We attribute this to a trade-off in mechanical strength and uniformity of the resulting electrode. This work demonstrates promising performance of a low-cost polymer as a binder for Si anodes and provides insight into the physical and chemical properties that influence binder performance
- …