Monday, Dec. 7, 1998
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Holiday Drive ends Wednesday The Laboratory's 1998 Holiday Drive to collect nonperishable food items and toys for the less fortunate in Northern New Mexico continues Labwide through Wednesday. For more information, see the Dec. 2 Daily Newsbulletin. |
Detecting material damage by nonlinear acoustical measurements
Researchers at the Laboratory are measuring nonlinear properties of materials to demonstrate a difference between damaged and undamaged concrete.
The research, reported Sunday in a poster session at the fall meeting of the American Geophysical Union in San Francisco, may have broad application for the detection of damage in many materials.
Paul Johnson of (EES-4) Geoengineering said the Laboratory planned three poster sessions at the AGU meeting related to research in the general area of nonlinear elastic wave spectroscopy (NEWS).
"To our knowledge, there is no other method as sensitive in characterizing damage in materials," Johnson said. "We anticipate that in five to 10 years, application of nonlinear wave spectroscopy could have enormous economic impact."
He said the potential uses of nonlinear techniques to reveal defects in materials include inspections of aging aircraft, quality control for assembly line applications, monitoring containment walls of nuclear reactors and applications to the national infrastructure such as examining bridge pillars and other structures.
Nonlinear materials research includes a technique called nonlinear resonant ultrasound spectroscopy (NRUS), which is being used by graduate student Loren Byers, also of EES-4, to measure the difference in the response to an acoustic wave by damaged and undamaged concrete core samples.
"This is the first work to our knowledge that shows the difference between damaged and undamaged concrete using nonlinear methods," Johnson said.
In his research using NRUS, Byers imparts energy to a concrete sample through a speaker-like device that sends a sound wave through the sample. The speaker is set up to input tones over a range from below to above the sample's resonant frequency. This is called a tonal or frequency sweep. At each tone in the range, he measures the volume and frequency of the wave at the other end of the sample. This procedure is used at progressively increasing volume levels.
In a sample that is undamaged, the volume output is directly related to the volume input, and therefore the resonant frequency remains the same as the applied volume is increased. In a sample that is damaged, the resonant frequency shifts as the applied volume increases, and the amount of the shift can be measured precisely.
Byers makes an analogy to playing a piano. "For a sample of undamaged material, it's comparable to hitting a key harder and making the sound louder," he said. "In a nonlinear sample, when you hit the key harder, the response is not only louder, it's a different note."
Moreover, he said, the frequency shift is greater in samples that are more damaged, even with microscopic cracks. So, for example, in a piece of plastic that contains no cracks, there will be no change in resonant frequency as the wave volume is increased. In a sample with a small crack, the resonant frequency will shift readily with amplitude.
Concrete is always slightly damaged in the curing process due to pressures from chemical reactions that build up inside and crack the sample. In a fresh concrete core, the resonant frequency shift is measurable, but becomes considerably larger for the damaged sample, with the same volume input.
"This change makes it very obvious what is damaged and what is fresh concrete," Byers said. "Nonlinearity is extremely sensitive to damage."
Evidence of damage is not only provided by the amount of the frequency shift, but by other manifestations of nonlinearity. For example, Byers also tests samples in a "conditioning and recovery" mode in which a loud-volume tonal sweep is followed by several soft-volume tonal sweeps. In damaged materials it takes some period of time for the sample to return to its original resonant frequency. Further, more damaged samples take longer to return to the original resonant frequency.
"Traditionally, nonlinear properties have been ignored in favor of studying the linear properties of the material to detect damage or flaws," he said. "Nonlinearity is a new frontier in damage diagnostics."
For the immediate future, Byers said, "we would like to test more core samples so we will have a large set of data in order to study variations in concrete types and damage intensities. We're working toward a correlation between the size of the frequency shift and the amount of damage in a sample, and toward making the technique available to applications indoors and outdoors."
Another technique of elastic wave spectroscopy is nonlinear wave modulation spectroscopy, which involves applying two single-frequency waves to a sample simultaneously and measuring for nonlinear modulation effects that indicate damage.
The Laboratory is collaborating on research in this area with Russian scientists from the Institute of Applied Physics in Nizhny Novgorod, who were instrumental in developing methods to study nonlinear modulation effects for the study of damage. Other Laboratory collaborations in nonlinear diagnostics are under way with the Catholic University of Belgium in Leuven and the University of Massachusetts at Amherst.
The results stem from research supported by the Office of Basic Energy Sciences of the Department of Energy.
Other poster sessions from the Lab at the AGU meeting involving elastic wave spectroscopy present a global view of nonlinear response in materials and present more information about the slow-time dynamic response in other materials, including rocks.
--John A. Webster
Laboratory Director John Browne will hold a town-hall meeting from 8:10 to 9:30 a.m. Tuesday in the Administration Building Auditorium. A proposed new Employee Complaint Resolution Policy recently was made available for employee comment. Based on input received, significant changes were made to the draft policy. During the town-hall meeting, Browne will present the revised policy, answer questions and listen to thoughts or comments. The final draft will be made available electronically immediately following the meeting. Employees then will have until Jan. 8, 1999, to provide final comments. The meeting is open to L- and Q-cleared badgeholders; an escort will be required for all other badgeholders. |
Detour planned Tuesday near Camino La Tierra intersection
Laboratory employees who live in Santa Fe and points south and use U.S. 84-285 to get to and from Los Alamos may encounter a detour on Tuesday near the Camino La Tierra intersection.
The state Highway and Transportation Department is installing a lighting system to better illuminate a concrete barrier wall separating north and southbound traffic.
While the Lighted Guidance Tube system is being installed, both north- and southbound vehicles on US 84-285 will be detoured onto new lanes south of the Camino La Tierra intersection, said Miguel Gabaldon, traffic engineer for the State Highway and Transportation Department in Santa Fe.
The work should be completed in one day, weather permitting, and there will be signs and detours in place directing motorists through the construction area.
The work is part of the planned construction of the so-called Santa Fe Relief Route, a 14-mile road looping around the city's north and west side and connecting U.S. 84-285 with Interstate 25.
The new lighting system will help motorists see the concrete barrier wall for the full 1,800 feet of the detour, Gabaldon said. The Lighted Guidance Tube glows amber at night and replaces the reflectors normally used on top of the barrier.
"This lighting is a big improvement over the reflectors," said Gabaldon. "It should really help motorists negotiate the detour."
The posted speed limit through the detour will be 35 miles per hour.
--Steve Sandoval
Aramark Corp. is serving a traditional New Mexican holiday meal Thursday in the Otowi Cafeteria at Technical Area 3 and the cafeterias at TA-55 and the Los Alamos Neutron Science Center (LANSCE) at TA-53. "A Taste of New Mexico" includes Christmas enchiladas, tamales, rice, beans, posole, sopapilla and natillas. The meal cost $7.25. Beverages must be purchased separately. Employees and subcontract personnel may wish to eat lunch early or plan lunch schedules to avoid long lines. Employees who don't want to partake of the traditional holiday meal, can purchase prime rib, green beans almondine, roasted rosemary new potatoes and a dessert item for the same price only at the World's Fare serving station in the Otowi Cafeteria. The salad and baked potato bar and pre-packaged sandwiches also will be available, but Grille Works, the Deli bar and pizza station will be closed. Vegetarian meals also will be available at the Allegro pasta station. The Otowi Cafeteria is open for lunch from 11 a.m. to 1:45 p.m. Aramark Corp. runs the cafeteria system for the Lab. For more information, go to http://www.lanl.gov/services/CafeteriaMenu/holiday.htm online. Or call 7-3591. --Steve Sandoval |
Representatives from BlueCross BlueShield New Mexico will be at the Laboratory from 9 a.m. to 3 p.m. Wednesday to meet with employees to discuss claims or issues. The BlueCross BlueShield representatives will be in the Benefits Office on the second floor of the Otowi Building, said Deborah Lee of Compensation and Benefits (HR-1). Employees are asked to make an appointment at least a day ahead of time, said Lee. They should call the Benefits Office at 7-1806 or write to benefits@lanl.gov by electronic mail to schedule an appointment time. Lee said BlueCross BlueShield representatives are scheduled to be at HR-1 every other Wednesday to meet with employees. --Steve Sandoval |
Energy Secretary Bill Richardson recently announced his intention to name Rich Glick, a top aide to former U.S. Sen. Dale Bumpers, to serve as his principal adviser on electricity and energy efficiency. For more information, see a DOE news release. |
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