|
A new instrument at the National Institute of Standards and Technology (NIST) that operates like an air-powered battering ram is being used to study steel salvaged from the World Trade Center (WTC), a key element in the agency's two-year building and fire safety investigation of the Sept. 11 disaster.
Described in a presentation on June 23, 2003, during the Fifteenth Symposium on Thermophysical Properties in Boulder, Colo., the apparatus will help improve understanding of how steel responds to high-stress, high-temperature conditions. A variation on a research instrument long used in metallurgy and ballistics research (the Kolsky bar), the apparatus consists of two 1.5-meter (5-foot) hardened steel bars arranged end to end. Disks of samples to be tested are sandwiched between the bars. A projectile from an air gun propels one bar against the other at ballistic speeds, rapidly compressing the sample.
A key feature of the new NIST apparatus is the ability to rapidly heat samples at rates of up to 50,000 degrees Celsius (90,000 degrees Fahrenheit) per second. A high-resolution heat-imaging microscope maps temperatures over the surface of the sample every millionth of a second.
"We are measuring how each of the various types of steel used in the WTC buildings' structural components deforms under high-impact conditions, akin to those caused by the aircraft that struck the towers," explains NIST metallurgist Richard Fields.
The new facility also will be used to help increase knowledge of materials behavior needed to improve computer models that predict the performance of metal-cutting machine tools.
In addition, results from the research may help improve simulations of the crashworthiness of automotive materials, the protective capacity of armor, and the resistance of structural steels to earthquakes.
Click here for additional images.