@article {583, title = {Understanding rheological hysteresis in soft glassy materials}, journal = {Soft Matter}, volume = {13}, year = {2017}, month = {Mar-07-2017}, pages = {1834-1852}, abstract = {

Motivated by recent experimental studies of rheological hysteresis in soft glassy materials, we study numerically strain rate sweeps in simple yield stress fluids and viscosity bifurcating yield stress fluids. Our simulations of downward followed by upward strain rate sweeps, performed within fluidity models and the soft glassy rheology model, successfully capture the experimentally observed monotonic decrease of the area of the rheological hysteresis loop with sweep time in simple yield stress fluids, and the bell shaped dependence of hysteresis loop area on sweep time in viscosity bifurcating fluids. We provide arguments explaining these two different functional forms in terms of differing tendencies of simple and viscosity bifurcating fluids to form shear bands during the sweeps, and show that the banding behaviour captured by our simulations indeed agrees with that reported experimentally. We also discuss the difference in hysteresis behaviour between inelastic and viscoelastic fluids. Our simulations qualitatively agree with the experimental data discussed here for four different soft glassy materials.

}, issn = {1744-683X}, doi = {10.1039/C6SM02581A}, url = {http://xlink.rsc.org/?DOI=C6SM02581A}, author = {Radhakrishnan, Rangarajan and Divoux, Thibaut and Manneville, S{\'e}bastien and Fielding, Suzanne M.} } @article {74, title = {Ultrahigh interlayer friction in multiwalled boron nitride nanotubes}, journal = {Nat Mater}, volume = {13}, year = {2014}, month = {Jul-2014}, pages = {688 - 693}, abstract = {

Friction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons\–Coulomb1, 2. Here, by using a \‘Christmas cracker\’-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF\–AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing\ surfaces.

Multiwalled nanotube Christmas-cracker experimental set-up.

Frequency shift measured by the tuning fork versus the displacement of the piezoscanner during complete tensile load experiments.

}, isbn = {1476-1122}, doi = {10.1038/nmat3985}, author = {Nigues, A. and A. Siria and Vincent, P. and Poncharal, P. and Lyd{\'e}ric Bocquet} } @article {55, title = {Understanding and Controlling the Reactivity of the Calcium Silicate phases from First Principles}, journal = {Chemistry of Materials}, volume = {24}, year = {2012}, month = {Apr-10-2012}, pages = {1262{\textendash}1267}, abstract = {
Abstract Image

First principles calculations are employed to provide a fundamental understanding of the relationship between the reactivity of synthetic calcium silicate phases and their electronic structure. Our aim is to shed light on the wide range of hydration kinetics observed in different phases of calcium silicate. For example, while the dicalcium silicate (Ca2SiO4) phase slowly reacts with water, the tricalcium silicate (Ca3SiO5) shows much faster hydration kinetics. We show that the high reactivity of Ca3SiO5 is mainly related to the reactive sites around its more ionic oxygen atoms. Ca2SiO4 does not contain these types of oxygen atoms, although experiments suggest that impurities may play a role in changing the reactivity of these materials. We analyze the electronic structure of a wide range of possible substitutions in both Ca3SiO5 and Ca2SiO4 and show that while the influence of different types of impurities on structural properties is similar, their effect on reactivity is very different. Our calculations suggest that the variation of electronic structure is mainly related to the formation of new hybridized orbitals and the charge exchange between the impurity atoms and the bulk material. The charge localization upon introducing impurities is quantified to predict candidate substitutions that could increase the reactivity of Ca2SiO4, which would broaden the applicability of this lower temperature and thus less costly and energetically less demanding phase.

}, doi = {10.1021/cm203127m}, author = {Engin Durgun and Hegoi Manzano and Roland Jean-Marc Pellenq and Jeffrey C Grossman} } @article {298, title = {Use of UHPC in Bridge Structures: Material Modeling and Design}, journal = {Advances in Materials Science and Engineering}, year = {2012}, month = {Feb-11-2012}, pages = {Article Number: 319285}, abstract = {

Ultra-high-performance concrete (UHPC) is a promising new class of concrete material that is likely to make a significant contribution to addressing the challenges associated with the load capacity, durability, sustainability, economy, and environmental impact of concrete bridge infrastructures. This paper focuses on the material modeling of UHPC and design of bridge girders made of UHPC. A two-phase model used for modeling the behavior of UHPC was briefly discussed, and the model was implemented in a preliminary design case study. Based on the implemented design and the reported use of UHPC in bridge applications, the advantages, limitations, and future prospects of UHPC bridges were discussed, highlighting the need for innovative research and design to make optimum use of the favorable properties of the material in bridge structures.

}, issn = {1687-8434}, doi = {10.1155/2012/319285}, author = {Gunes, Oguz and Yesilmen, Seda and Gunes, Burcu and Franz-Josef Ulm} }