|Figure 18. Researcher Mike Kennedy fires the air gun on NIST's Kolsky Bar Tester. This device measures the mechanical behavior of steel from the World Trade Center under stresses similar to those that resulted from the aircraft impact with the buildings.
||Figure 19. NIST researcher Mike Kennedy aligns a high-speed temperature sensor on a Kolsky bar apparatus used to measure the mechanical behavior of steel. The test sample from recovered World Trade Center steel is just visible between the two bars in the center of the picture. At high rates of deformation, heat is generated. About every millionth of a second, this instrument measures changes in the average temperature across an entire sample.
||Figure 20. NIST researcher Bill Luecke checks the calibration of a contact extensometer used in the high-temperature mechanical testing system pictured here to assess (at temperatures from room temperature to well over 1,000 degrees Celsius) the strength and ductility of the steel used to build the World Trade Center.
||Figure 21. NIST researcher Steve Banovic uses an optical microscope to examine the microstructure of steel from the World Trade Center. This information will help identify the type and quality of steel used. Pieces from actual WTC beams are visible on the right.
||Figure 22. NIST researcher Richard Fields adjusts a dial gauge on one of several creep testers that will be used to evaluate the high-temperature, time-dependent mechanical behavior of the steel used to construct the World Trade Center.