Measuring Surface Roughness

Minutes

President Collins called the 2151st meeting of the Philosophical Society of Washington to order at 8:25 p.m. on October 25, 2002. The Recording Secretary read the minutes of the 2150th meeting and they were approved. The speaker for the 2151st meeting was Theodore Vorburger of the National Institute of Standards and Technology. The title of his presentation was, “Measuring Surface Roughness from Atomic Level to Highway Bumps.” Surface finish is important to the function of a range of industrial things including optics, semiconductors, mechanical parts, ship hulls and propellers, and interstate highways. There is a telling need to provide standard reference materials having properties that industry cannot supply for itself, and resolving methods divergences in surface measurements between different techniques and laboratories. Use of new standards will lead to the development of improved and new products. The speaker discussed a wide range of surface metrology applications including surface measurements at the atomic level, road roughness measurements and surface calibration for ballistics testing. Here, roughness regimes range from the roughness of highways on the order of tens of millimeters, down through ship hulls to optical surfaces with roughness on the order of tenths of a nanometer. The speaker continued to describe the use of a calibrated atomic force microscope to measure the height of a silicon single-atom step where the height of the step is about 300 picometers – or 0.3 billionths of a meter. The goal of this work is to provide independent, traceable values of atomic step height masters. This would then be the basis for calibrating other instruments for atomic level height measurements accurate to about 6%. The NIST results showed that traceable, atomic level surface height metrology is practical. NIST plans to propose this approach to different American standards committees. Moving from the atomic level, the speaker smoothly moved to discussions of an old engineering problem – road roughness. He quoted from the Old Testament's Book of Isaiah 40:3-5 written about 700 BC, “Prepare in the wilderness a road for the Lord…Fill every valley; level every mountain. The hills will become a plain and the rough country will be made smooth.” The problems caused by rough roads include accelerated wear and tear on vehicles, people and the materials transported over the roads. In addition, rough roads themselves wear out faster than smooth roads because of the impact of vehicles on the road surface valleys. Consequently, quantification of road roughness enables engineers to set practical criteria for when to resurface roads and how to evaluate irregularities of newly finished roads. Here the speaker described calibration for road roughness measuring equipment including an Inertial Road Profiling System accurate to several hundredths of an inch. It consists of a van and computer, accelerometers, optical sensors to measure the road surface height, a wheel encoder and filter software. Comparative profile results verified the profiling system as a suitable calibration device for use with measuring road surface roughness. Lastly, the speaker described NIST efforts since 1997 to develop new bullet and casing standards for use in ballistics testing. The work was initiated at the behest of the Department of Alcohol, Tobacco and Firearms – or ATF. Here the goal was to develop requirements for a standard bullet and casing to calibrate commercial ballistics testing machines and systems – by providing repeatable and reproducible information on a bullet's surface characteristics – a bullet's signature. The project started with six master bullets from ATF and FBI, each fired from a different gun. Then they established a two-dimensional virtual bullet signature standard using a stylus instrument at NIST to measure the six bullets. Next, they manufactured standard reference bullets using numerical controlled machines and successfully tested and verified the new reference bullets – and later bullet casings using both stylus instruments and a commercial Integrated Ballistics Identification System or IBIS. This computerized ballistics identification approach is being used in major US cities. For example, use of the New Orleans Police Department IBIS showed one single handgun had been used in eight separate crimes. Similarly, use of the ATF IBIS linked eight crimes here in the District to three separate guns. Anecdotally, the speaker noted that use of a similar ballistics information database with manufacturers' data for assault weapons could have provided help with the recent Sniper murders here. Mr. Vorburger then closed his presentation and kindly answered questions from the floor. President Collins thereupon thanked Mr. Vorburger for the Society, welcomed him to membership, announced the next meeting and made the usual parking announcement. He then adjourned the 2151st meeting to the Social Hour at 9:35 p.m. Attendance: 28 Temperature: 17°C Weather: Raining Links: NIST Surface Metrology Program Respectfully submitted, Bill Spargo Recording Secretary