Rice University models reveal nanoindentation can benefit crystals in concrete
Rice University scientists have determined that no matter how large or small a piece of tobermorite is, it will respond to loading forces in precisely the same way. But poking it with a sharp point will change its strength.
Indented tobermorite, a natural analog to the calcium-silicate-hydrate mix in cement, responds differently than bulk tobermorite, depending on the size of the indentation and the force. Layers that bond through indentation remain that way after the force is removed, according to Rice University engineers.
Credit: Lei Ren/Rice University
Tobermorite is a naturally occurring crystalline analog to the calcium-silicate-hydrate (C-S-H) that makes up cement, which in turn binds concrete, the world's most-used material. A form of tobermorite used by ancient Romans is believed to be a key to the legendary strength of their undersea concrete structures.
The finely layered material will deform in different ways depending on how standard forces -- shear, compression and tension -- are applied, but the deformation will be consistent among sample sizes, according to Rice materials scientist Rouzbeh Shahsavari. He conducted the research, which appears in Nature's open-access Scientific Reports, with lead author and graduate student Lei Tao.
For their latest survey, Shahsavari and Tao built molecular dynamics models of the material. Their simulations revealed three key molecular mechanisms at work in tobermorite that are also likely responsible for the strength of C-S-H and other layered materials. One is a mechanism of displacement in which atoms under stress move collectively as they try to stay in equilibrium. Another is a diffusive mechanism in which atoms move more chaotically. They found that the material maintains its structural integrity best under shear, and less so under compressive and then tensile loading.
More interesting to the researchers was the third mechanism, by which bonds between the layers were formed when pressing a nanoindenter into the material. A nanoindenter is a device (simulated in this case) used to test the hardness of very small volumes of materials. The high stress at the point of indentation prompted local phase transformations in which the crystalline structure of the material deformed and created strong bonds between the layers, a phenomenon not observed under standard forces. The strength of the bond depended on both the amount of force and, unlike the macroscale stressors, the size of the tip.
"There is significant stress right below the small tip of the nanoindenter," Shahsavari said. "That connects the neighboring layers. Once you remove the tip, the structure does not go back to the original configuration. That's important: These transformations are irreversible.
"Besides providing fundamental understanding on key deformation mechanisms, this work uncovers the true mechanical response of the system under small localized (versus conventional) loads, such as nanoindentation," he said. "If changing the tip size (and thus the internal topology) is going to alter the mechanics -- for example, make the material stronger -- then one might use this feature to better design the system for particular localized loads."
Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering.
The National Science Foundation (NSF) supported the research. Computing resources were supplied by the National Institutes of Health and an IBM Shared University Research award in partnership with CISCO, Qlogic and Adaptive Computing and Rice's NSF-supported DAVinCI supercomputer administered by Rice's Center for Research Computing; the resources were procured in partnership with Rice's Ken Kennedy Institute for Information Technology.
Editor's note: A link to a high-resolution image for download appears at the end of this release.
Read the open-access paper at https:/
This news release can be found online at http://news.
Follow Rice News and Media Relations via Twitter @RiceUNews
Rice probes ways to turn cement's weakness to strength: http://news.
Multiscale Materials Laboratory home page: http://rouzbeh.
George R. Brown School of Engineering: http://engineering.
Rice Department of Civil and Environmental Engineering: http://www.
Rice Department of Materials Science and NanoEngineering: https:/
Images for download:
Indented tobermorite, a natural analog to the calcium-silicate-hydrate mix in cement, responds differently than bulk tobermorite, depending on the size of the indentation and the force. Layers that bond through indentation remain that way after the force is removed, according to Rice University engineers. (Illustration by Lei Ren/Rice University)
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,879 undergraduates and 2,861 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for happiest students and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.
David Ruth | EurekAlert!
Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern
20.07.2018 | Princeton University
Relax, just break it
20.07.2018 | DOE/Argonne National Laboratory
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences