Featured Research

from universities, journals, and other organizations

Scientists Study Cracks In Brittle Materials

Date:
November 24, 2008
Source:
Naval Research Laboratory
Summary:
The Naval Research Laboratory is part of an international team of scientists that is learning more about how cracks form in brittle materials. The team used both computer modeling and experimentation to investigate how cracks grow at low speeds in silicon. This information has potential applications in the development of a variety of materials ranging from armor to machine parts.

The Naval Research Laboratory (NRL) is part of an international team of scientists that is learning more about how cracks form in brittle materials. The team used both computer modeling and experimentation to investigate how cracks grow at low speeds in silicon. This information has potential applications in the development of a variety of materials ranging from armor to machine parts. The research team published their findings in the October 30th edition of Nature.

Using the computer simulations, the scientists began by studying the motion of atoms that takes place when cracks occur in brittle materials. The instabilities that occur when the crack grows at high speeds are well-known, and scientists have already made significant advances in understanding the origin of these kinds of cracks. However, instabilities had not been observed and studied in cracks that grow at low speeds.

Until recently, scientists studied cracks primarily by continuum mechanics techniques, but now advances in computer power have made it possible to simulate materials by describing the motion of each atom, rather than making the approximation that matter is continuous. While most simulations of cracks ignore the quantum-mechanical nature of the bonds between the atoms, the research team overcame this limitation using a technique called "Learn-on-the-fly" (LOTF). This method allowed them to use a quantum-mechanical description of bonding near the tip of the crack, where it is needed, coupled to a large (on the atomic scale) region described with a faster but non-quantum-mechanical method. This combined description was essential for correctly predicting the motion of the crack tip.

The simulations showed that even in a brittle material like silicon, rearrangements of atoms usually associated with ductile materials like metals can occur, but they remain trapped near the crack tip. The team developed a model that showed how these rearrangements at the crack tip could lead to macroscopic changes in the path of the crack, leaving behind ridges on the crack surface.

The research team also carried out single-crystal fracture experiments in which this instability was observed for the first time at a range of low speeds. They conducted experimental studies of the cracks at low speeds using a novel technique for applying very small but steady and well-controlled tensile loads. The surfaces left behind by the crack showed ridge-shaped features, very similar to those seen in the computer models. In a different crack orientation, experiments and simulations showed qualitatively different behavior.

In experiment, the crack was never able to propagate in a straight line – it was immediately deflected in different directions. The simulations showed that the structure of the crack tip caused this deflection. At extremely low speeds the crack grew by breaking bonds directly ahead of it in an orderly manner. Very soon, however, the crack sped up and began to break bonds on different crystal planes, causing it to diverge from its initial direction. For both of these instabilities, the simulation results and experimental observations indicate that more is happening at crack tips in brittle materials than previously suspected.

Preliminary results indicate that these processes also occur in other materials, such as diamond and silicon carbide. "We discovered that even in apparently simple brittle materials, complicated things can happen at the crack tip, and these atomic scale features can have macroscopic implications," explains NRL's Dr. Noam Bernstein. "We hope that we can take advantage of this complexity to affect the way cracks grow, to design tougher and more robust materials."

The team includes researchers from Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, UK; Université de Lyon, France; Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa, Israel; Center for Computational Materials Science, NRL; Institut für Zuverlässigkeit von Bauteilen und Systemen, Universität Karlsruhe, Germany; Fraunhofer-Institut für Werkstoffmechanik, Germany; Engineering Laboratory, University of Cambridge; King's College London, Department of Physics, London; INFM-DEMOCRITOS National Simulation Center and Center of Excellence for Nanostructured Materials, University of Trieste, Italy.


Story Source:

The above story is based on materials provided by Naval Research Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

Naval Research Laboratory. "Scientists Study Cracks In Brittle Materials." ScienceDaily. ScienceDaily, 24 November 2008. <www.sciencedaily.com/releases/2008/11/081120144242.htm>.
Naval Research Laboratory. (2008, November 24). Scientists Study Cracks In Brittle Materials. ScienceDaily. Retrieved July 26, 2014 from www.sciencedaily.com/releases/2008/11/081120144242.htm
Naval Research Laboratory. "Scientists Study Cracks In Brittle Materials." ScienceDaily. www.sciencedaily.com/releases/2008/11/081120144242.htm (accessed July 26, 2014).

Share This




More Matter & Energy News

Saturday, July 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) — Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) — TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) — Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) — When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins