Gaithersburg, MD – A new instrument at the National Institute of Standards and Technology (NIST) that operates like an air-powered battering ram has been pressed into service 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.
最初计划为一个项目确定材料的属性，以改善计算机程序，以预测机床如何执行特定的金属切割工作，在6月23日的演示文稿中描述了一种独一无二的仪器关于博尔德公司的热物理特性。
有时被称为科尔斯基酒吧或拆分大便压力杆，看起来很奇特的仪器可以提供数据关键，以了解钢和其他材料如何应对高压力，高温条件。“With the NIST Kolsky bar apparatus, we will measure how each of the various types of steel used in the WTC buildings’ structural components deform under high-impact conditions, akin to those caused by the aircraft that struck the towers,” explains NIST metallurgist Richard Fields. “That data will help us model the response and behavior of the steel in the towers during the two impacts.”
该仪器是1913年创新的21世纪化身，该创新旨在衡量在动态条件下材料如何应对压力。
Starting with a customary Kolsky bar, a diverse team of NIST researchers and technicians conceived several high-tech enhancements that make the resulting instrument unique.
Key among them is a controlled means to rapidly heat sample materials, at rates of up to 50,000 degrees Celsius (90,000 degrees Fahrenheit) per second.
另一个extra, a high-resolution heat-sensing microscope designed by NIST physicist Howard Yoon, measures the temperature of a 1-millimeter diameter region of the sample about every millionth of a second. And every thousandth of a second, a thermal-imaging camera records temperatures about every 5 micrometers (millionths of meter) across the surface of the sample. About 20 readings are taken over an area equivalent to the diameter of a human hair.
During a high-impact event, much of the mechanical energy is converted into heat, which can affect how materials respond to stress. For example, when a manufactured part is milled or otherwise cut from a metal bar, the temperature in some sections of the workpiece “can increase from room temperature to 1,000 degrees Celsius (1,800 degrees Fahrenheit) in a fraction of a second,” explains NIST manufacturing engineer Richard Rhorer, the project leader.
“How materials will behave under extreme conditions may not be evident from properties data gathered under normal conditions,” he adds.
The business end of this high-tech array is the Kolsky bar itself. It consists of two painstakingly machined, mounted and aligned steel bars, each measuring 1.5 meters (about 5 feet) long and 15 millimeters (0.6 inch) in diameter. Made of hardened specialty steel, the bars are arranged end to end. Disks of sample materials are sandwiched in the split between the bars.
An air gun situated just beyond the far end of the first bar propels a striker rod, which reaches speeds up to 40 meters (130 feet) per second. When the striker hits it, the bar does not move immediately. Rather, says Rhorer, the collision creates a fast-traveling disturbance called a strain wave that races down the steel bar at 5,000 meters (16,400 feet) per second-equivalent to over 11,000 miles per hour. Upon impact, this strain wave rapidly compresses the sandwiched specimen.
该样品反映了一些波的能量，其中一些波通过到另一个杆传输。安装在两个条形中心的应变仪捕获了确定压力，应变和温度如何影响样品材料行为所需的信息。
Such information can be crucial to efforts to model and simulate materials performance during high-impact events and, ultimately, to improve the design and performance of systems that must endure such extremes. Examples range from enhancing the crashworthiness of automotive materials to increasing the protective capacity of armor and from reducing tool wear during machining to withstanding impact loading during earthquakes.
