Revealing cracks before structural components fail

RESEARCHERS ARE INVESTIGATING HOW COMMON structural components break under strain using a system that reconstructs growing cracks in common structural materials. The microtopography system, designed and built at the U.S. Department of Energy's Idaho Natio

RESEARCHERS ARE INVESTIGATING HOW COMMON structural components break under strain using a system that reconstructs growing cracks in common structural materials. The microtopography system, designed and built at the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory (INEEL), could improve building design and analysis and bolster the safety of structures ranging from aircraft to waste-storage tanks.

Until now, researchers have relied on surface measurements to see how components crack. But this only reveals part of the picture, according to INEEL research engineer Randy Lloyd, who developed the process. He says that it's not unusual for the center of a crack to grow faster than it does at the surface (called crack tunneling).

Microtopography takes information from the permanent deformation of ductile materials as cracks grow. The result is a rough surface of two halves of a broken specimen that no longer fit together. Using those microscopic differences, microtopography reconstructs a virtual version of the cracked material.

From maps of the cracked surfaces, the method reconstructs the entire fracture process in three dimensions, letting researchers peer into a virtual version of the structure to make internal measurements at any stage of the fracture process.

"It's like making the material transparent so you can look inside and measure all aspects of the crack at different stages of its growth," remarks Lloyd. The detailed rendition allows precise measurements to be made both inside and outside of the specimen and at any stage of the fracture process.

"With knowledge gained from our ductile-fracture research, we will be able to analyze existing structures with known defects to determine if continued operation is safe, making that decision with a higher degree of certainty than is now possible," Lloyd says.

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