March 5, 2010 Physicists unlock the mysteries of crack formation
(PhysOrg.com) -- In research published in the March 4 issue of the journal Nature, Northeastern University physicists have pioneered the development of large-scale computer simulations to assess how cracks form and proliferate in materials ranging from steel and glass to nanostructures and human bones.
For years, scientists have tried to understand the propagation of cracks and how they affect the materials in which they form, said Alain Karma, distinguished physics professor and lead investigator on the project.
“We now better understand what path cracks follow as they propagate in a stressed material,” said Karma, director of Northeastern’s Center for Interdisciplinary Research on Complex Systems . “This knowledge will allow us to develop new materials — for advanced aircraft turbine blades, micro-electronic circuits and artificial bone — that better withstand destruction caused by cracks.”
Karma and the research team started out by examining the combined effects of two types of stress on crack propagation: shearing and tension. Shearing occurs naturally when material is twisted out of shape while tension occurs when material is pulled out of shape. The combination of shearing and tension causes crack instability. The mechanism for how this instability develops and spreads, however, remained elusive until Karma utilized the power of a computer.
Large-scale computer simulations yielded the surprising result that shearing and tension cause cracks to take the shape of a helix. Based on the simulation results, Karma and his team developed a theoretical equation to predict how the helix would rotate, expand and multiply in different materials.
“The fundamental question we are answering is how these cracks grow inside materials, said Karma. “Now that we have that information, we can develop new materials to withstand cracks, as well as more effectively reduce the damage of cracks once they form.”
The research could yield innovations in the production of lighter automobile and aircraft parts that reduce energy consumption, and composite artificial bones that will not fracture when inside the body. The results also have implications for understanding the evolution of geologic faults and fractures in the earth’s crust.
- wong chee tat :)
Tuesday, March 16, 2010
HDB launches 2 BTO projects in March
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SINGAPORE: The Housing and Development Board (HDB) has launched two new Build-To-Order (BTO) projects - Fernvale Ridge in Sengkang and Sembawang RiverLodge in Sembawang.
Close to 830 flats will be offered in total, most of which are four-room units. HDB said 95 per cent of the flats will be set aside for first-timers.
Flats in Fernvale Ridge range in price from S$128,000 for a three-room unit to S$352,000 for a five-room flat.
At Sembawang RiverLodge, three-room units start from S$128,000. Four-room units cost between S$212,000 and S$268,000 each. Sembawang RiverLodge will also have 126 two-room flats.
HDB said they will not be offered for sale at this time, but will be set aside to meet the housing needs of lower-income families at a later date.
Next month, HDB will launch another 1,200 BTO flats in Punggol. These launches are part of its plan to offer at least 12,000 new BTO flats this year, or more if there is demand.
- CNA/sc
- wong chee tat :)
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