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DETECTINGMATERIAL DAMAGE

USING NONLINEAR WAVE SPECTROSCOPY TO INSPECT

CONCRETE COULD EXPAND TO INCLUDE AGING

AIRCRAFT AND NUCLEAR REACTORS

S cientists are measuring nonlinear properties of materials to demonstrate a difference between damaged and

undamaged concrete. The research may have broadapplications for detecting damage in many materials andcould have enormous economic impact.

“To our knowledge, there is noother method as sensitive incharacterizing damage inmaterials,” said Los Alamosresearcher Paul Johnson.

The potential uses of nonlineartechniques to reveal defects inmaterials include inspections ofaging aircraft, quality controlfor assembly line applications,monitoring containment walls ofnuclear reactors and applications

ÈA typica l set of

resonancecurves of

bereasandstone

in a i r showingthe shift in the

resonantfrequency as

the volume isincreased.

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EDITORMeredith Coonley

(505) 665-3982 • E-Mail: suki@lanl.gov

CONTRIBUTING EDITORJohn A. Webster

CONTRIBUTING PHOTOGRAPHERSJohn Flower • LeRoy N. Sanchez

CONTRIBUTING WRITERSTodd Hanson • Ternel N. Martinez

PRINTING COORDINATORG.D. Archuleta

LOS ALAMOS NATIONAL LABORATORY

PUBLIC AFFAIRS OFFICE, MS C177

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to the national infrastructure such as examining bridge pillars andother structures.

Nonlinear materials research includes a technique called nonlinearresonant ultrasound spectroscopy, which is being used by graduatestudent Loren Byers to measure the difference in the response to anacoustic wave by damaged and undamaged concrete core samples.

“This is the first work to our knowledge that shows the differencebetween damaged and undamaged concrete using nonlinear methods,”Johnson said.

In his research using NRUS, Byers imparts energy to a concrete samplethrough a speaker-like device that sends a sound wave through thesample. The speaker is set up to input tones over a range from below toabove the sample’s resonant frequency.

This is called a tonal or frequency sweep. At each tone in the range, hemeasures the volume and frequency of the wave at the other end of thesample. This procedure is used at progressively increasing volume levels.

In a sample that is undamaged, the volume output is directly related tothe volume input, and therefore the resonant frequency remains thesame as the applied volume is increased. In a sample that is damaged,the resonant frequency shifts as the applied volume increases, and theamount of the shift can be measured precisely.

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Byers likens it 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, theresponse is not only louder, it’s a different note.”

Moreover, the frequency shift is greater in samples that are moredamaged, even with microscopic cracks. So, in a piece of plastic thatcontains no cracks, there will be no change in resonant frequency as thewave volume is increased. In a sample with a small crack, the resonantfrequency will shift readily with amplitude.

Concrete is always slightly damaged in the curing process due topressures from chemical reactions that build up inside and crack thesample. In a fresh concrete core, the resonant frequency shift is measur-able, but becomes considerably larger for the damaged sample, with thesame volume input.

This change makes it very obvious what is damaged and what is freshconcrete, because nonlinearity is extremely sensitive to damage.

Evidence of damage is not only provided by the amount of the frequencyshift, but by other manifestations of nonlinearity. For example, Byers alsotests samples in a “conditioning and recovery” mode in which a loud-volume tonal sweep is followed by several soft-volume tonal sweeps.

ÓGraduatestudent LorenByers checksdata fromtest ing samplesfor damage.

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In damaged materials it takes some period of time for the sample toreturn to its original resonant frequency. Further, more damagedsamples take longer to return to the original resonant frequency.

“Traditionally, nonlinear properties have been ignored in favor ofstudying 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, the researchers would like to test more coresamples so they will have a large set of data to study variations inconcrete types and damage intensities. They’re working toward a corre-lation between the size of the frequency shift and the amount of damagein a sample, and toward making the technique available to applicationsindoors and outdoors.

Another technique of elastic wave spectroscopy is nonlinear wavemodulation spectroscopy, which involves applying two single-frequencywaves to a sample simultaneously and measuring for nonlinear modula-tion effects that indicate damage.

Los Alamos is collaborating on research in this area with Russian scien-tists from the Institute of Applied Physics in Nizhny Novgorod, whowere instrumental in developing methods to study nonlinear modula-tion effects for the study of damage.

Other Laboratory collaborations in nonlinear diagnostics are under waywith the Catholic University of Belgium in Leuven and the University ofMassachusetts at Amherst.

The results stem from research supported by the Department of Energy’sOffice of Basic Energy Sciences.

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HIGH-TEMPERATURESUPERCONDUCTING

TRANSFORMERSLOS ALAMOS TO PROVIDE ELECTRICAL

CHARACTERIZATION FOR NOVEL ENERGY PROJECT

A s partners in a project that could improve the way electrical energy is delivered in America, Los Alamos

scientists will be providing special electrical characterizationof components used in the first high-temperaturesuperconducting transformer installed in a U.S. electricutility network.The Laboratory is teaming up with ABB, American SuperconductorCorp., and Air Products and Chemicals Inc. to support the development,manufacture, installation and field testing of the HTS transformers.

Los Alamos will characterize certain wires and coils of various sizes usedin the transformers to measure their superconducting properties as theyrelate to fluctuations of temperature and magnetic fields. Lab researchersalso will provide cryogenic engineering support for the project.

“Los Alamos was designated 10 years ago as one of three Department ofEnergy national technology centers for the development and applicationof high-temperature superconductors,” said Dean Peterson, leader of theLaboratory’s Superconductivity Technology Center. “The expertise andfacilities we have to offer to development of a HTS electrical transformerwas recognized by ABB to be unique.”

The HTS transformers being tested will offer a number of improvementsover conventional power transformers including higher electricalefficiency, smaller size and weight, which increases existing substationcapacity and reduces the size of future substations, and a novel liquidnitrogen design that will greatly reduce the potential for transformer fires.

The development and manufacture of the transformer is under theauspices of the DOE’s Superconductivity Partnership Initiative.

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LOS ALAMOS RECEIVESDOE GRANTS

T he Department of Energy has awarded grants totaling about $3.6 million to six innovative Los Alamos

projects in advanced biological research and environ-mental cleanup. The four biological research grants will build on the wealth ofinformation from the Human Genome Project and other research activitiesto solve complex biological problems. This information will be valuablein a variety of areas, such as health, industry, environment and agriculture.

The two environmental cleanup research projects are targeted at someof the most difficult legacy problems facing the country — the millionsof gallons of high-level radioactive waste stored in tank farms and thethousands of contaminated buildings that must be cleaned up andclosed or torn down.

BIOLOGICAL RESEARCH

♦ A project aimed at reducing the time it takes to determine the structureof a protein from years to months, or even weeks, is designed to increasethe rate of structural determination through techniques in X-ray crystal-lography and nuclear magnetic resonance. Cutting the time would be asignificant advance since there are some 60,000 proteins in the humangenome. It is a follow-on to the Human Genome Project to decode thegenetic material of a human being.

♦ Research to improve the ability of the atomic force microscope toprovide structural information about biological molecules willultimately allow researchers to obtain three-dimensional images ofproteins and protein DNA complexes rapidly with high resolution.Atomic force microscopy generates images by “feeling” the surface

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♦ Another grant will be used to produce biological samples for structural studies.Researchers will grow bacteria that produce specific proteins, which are “labeled”with stable isotopes that don’t occur naturally, making them useful for study withneutron scattering and nuclear magnetic resonance techniques. This researchholds the promise of significantly reducing the cost of producing labeled samplesfor research.

features of a sample. The resolution of the microscope can allow thevisualization of materials at the atomic level.

ENVIRONMENTAL CLEANUP

♦ A project focusing on actinide aluminate speciation in alkalineradioactive waste addresses high-level waste. Highly alkaline radioactivewaste tanks contain a number of transuranic species, the exact forms ofwhich currently are unknown. Studies have shown that the solubility oftransuranic ions increases in the presence of aluminate ions underalkaline solution conditions. Researchers want to better understand themolecular nature of the soluble species to predict solubility and sorptionbehavior in tanks, determine whether revised chemical separations areneeded for waste treatment and design separation processes.

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♦ A grant for microbial genome research is for using DNA sequencing techniquesto identify and study soil bacteria. This project will provide a survey of bacterialspecies that may include ecologically important organisms, then use their DNA“signatures” to separate them from the environment for further study. These novelbacteria may have potential uses in such areas as environmental cleanup, productionof antibiotics and chemical manufacturing.

♦ A second environmental cleanup project involves using environmentallybenign supercritical carbon dioxide to develop a system for selectively removingmetals from contaminated surfaces while also reducing the amount of transuranicwaste and secondary waste streams generated. Currently, any solid object such asa contaminated glove must be disposed of entirely as radioactive waste.Researchers hope to use new polymers that form micelles — loosely bound aggre-gates of several molecules that form ultramicroscopic particles — in supercriticalCO2 to remove contaminants from the surfaces of such materials. The micelleswould interact with contaminated surfaces and dissolve the radioactive materialinto the micelle core, decontaminating the object and concentrating the radioac-tive materials for recovery or final disposal.

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ELECTRIC VEHICLESFROM PIPE DREAM TO PRACTICALITY

The electric-vehicle scenario has always been attractive —autos, trucks and buses that are efficient, nonpolluting

and free from dependence on imported petroleum — butit has faced major technical and economic obstacles. Inrecent years, however, the poss-ibility of putting significant numbersof electric vehicles on the roadappears to be more likely, thanksto advances at Los Alamos andelsewhere in the development of fuelcells for transportation.Fuel cells are battery-like devices thatconvert chemical energy to electricalenergy. For nearly 20 years, they have beenthe focus of a vigorous research program atLos Alamos that has included a number ofsuccessful industrial partnerships.

They were invented in 1839 by Sir WilliamGrove of Great Britain, but they did notattract serious practical interest until the 1960s, when NASA selected themto power electrical systems aboard the Gemini and Apollo spacecraft.

Fuel cells operate like batteries, but they do not run down or requirerecharging and will produce electricity as long as fuel is supplied. Infuel-cell systems built so far for vehicles, the actual fuel is hydrogen,which can come from a variety of sources, including gaseous hydrogenand hydrogen generated on board from gasoline, methane, methanol,ethanol or natural gas.

The cells consist of two electrodes separated by an electrolyte. Hydrogengas from the fuel reacts at one electrode, called the anode, producingprotons and electrons.

The protons move through the electrolyte to the other electrode, thecathode, while the electrons flow through an external circuit with amotor or other electrical device to the cathode, where they combine with

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ÕTommyRockward, agraduateresearchass istant , runsa test at a fuelce l l test ingstat ion. He iscol lect ing datato helpdetermine theeffects ofimpur it ies inthe fuel streamon fuel-ce l lperformance.

the protons and oxygen from the air to form water vapor, the onlyemission. Catalysts are used at both electrodes to boost the reaction rates.

Much of the research at Los Alamos has focused on polymer electrolytemembrane, or PEM, fuel cells, which appear to be the most promising ofvarious types of fuel cells for motor vehicles. They are highly efficient,stable and reliable. They can be packaged effectively into a smallvolume, and they operate at relatively low temperatures.

The success of fuel cells in the U.S. space program led industry to lookat their commercial potential, but technical problems and high costskept them from being economically competitive with other technologiesuntil recently. Now, integrated fuel-cell systems appear attractive forworldwide power needs.

There were three main technical obstacles to building practical PEMfuel cells: the cost of the platinum as a catalyst for the electro-chemical reactions; effective control of the amount of water in the thinmembrane used as the electrolyte; and the intrusion of carbonmonoxide, a “catalyst poison” that seriously degrades the efficiency ofthe electrolyte and is always found in hydrogen derived from methane,gasoline or alcohol.

Beginning in the mid-1980s, Los Alamos researchers began to developways to reduce the amount of platinum needed as the catalyst through anumber of technical innovations. The earlier estimate of about $30,000worth of platinum needed for a vehicle has been lowered to about $200per vehicle.

Los Alamos helped solve the water-management problems byconducting some basic experiments in understanding the processes bywhich water moved in the electrolyte. Researchers found that thinnermembranes of 50 to 100 microns worked much better than the earliermembranes of 175 microns thick.

The third big problem, carbon monoxide contamination, was solved atLos Alamos by developing a way to bleed small amounts of air into thefuel stream, which removed the impurity, and by improving upstreamfuel-processing technology to reduce the amount of carbon monoxidethat enters the fuel cell.

In addition to working on the fuel cell itself, Los Alamos researchers areinvolved in developing technologies to process the fuel, manage thebuildup and dispersion of heat, control the air supply and other systemsrequired by electrically powered vehicles.

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The Los Alamos research team has worked on such systems involvinghydrogen and methanol as fuels. Recently, it has made significantprogress with fuel-cell-processing technology, demonstrating the feasi-bility of using gasoline as a fuel. The purpose is to use the existing fuelsinfrastructure in ways that are environmentally sound.

The work earned the team, along with its collaborators at Arthur D. Little,Plug Power LLC, Argonne National Laboratory and GM, the 1998PNGV Award for technical accomplishment.

While using gasoline as fuel appears to conflict with an expected benefitof electric vehicles — reducing dependence on fossil fuels — the work isimportant in developing the necessary steps for a transition from currentpractices to a sustainable-energy future.

The fuel-processing system presents a difficult engineering problem, butthe Los Alamos’ expertise in catalysis, heats transfer and controlengineering offers real hope for continuing technological advances. Thechallenge is to combine design and improved catalysis to achieve therequired goals in performance, size and cost.

The team continues to work to improve the preferential oxidizer, theprimary device for carbon monoxide control. It also is learning moreabout processes that tend to limit the lifetime of catalysts and investi-gating a number of related fields such as heat management and alternatefuel-processing concepts.

Other current lines of fuel-cell research at Los Alamos include developingan infrastructure to deliver gaseous hydrogen to consumers, developinga system with methanol as the fuel rather than hydrogen and manufac-turing components with stable, low-cost materials such as stainless steelor composites.

Los Alamos also is involved in research into applications of fuel-celltechnology in areas other than transportation, including electricitygenerated by the utility sector and power generation for individual homes.

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INDUSTRY COLLABORATIONS

FUEL RESEARCH

Collaborations with industry have been an important partof the Lab’s work in fuel cells for many years. The approxi-mately 20 industrial partners have included General MotorsCorp. and Ford Motor Co., as well as chemical firms andautomotive suppliers.

The Laboratory and GM formed a major engineeringpartnership in 1988 and worked for nearly eight years todevelop a polymer electrolyte membrane, or PEM, fuel celland improve fuel-processing systems.

The partnership at Los Alamos resulted in a prototypicalfuel-cell system and pioneered manufacturing technologyfor U.S. industry. It also contributed to advanced componentand system diagnostics and the development of models andsystem controls.

The GM partnership was one of the longest-lived tech-transferprojects involving the Lab. Its results included a 1992 reportstressing that fuel-cell-powered vehicles were a cost-effectivetechnology that could work, leading to worldwide interest inthe approach.

Today, hundreds of companies around the world are workingon fuel-cell technology. Demonstration fuel-cell-powered busesare in operation in Chicago, while tests are being conductedacross Europe and in Japan on automobiles that use fuel cells.The total worldwide investment in fuel-cell research and devel-opment has been estimated between $1.5 billion and $2 billion.

The U.S. government’s Partnership for a New Generation ofVehicles has announced that fuel-cell development would beone of its key focus areas. The partnership is a collaboration ofthe private and public sectors created five years ago tostrengthen U.S. competitiveness by developing advanced trans-portation technologies.

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A MONTHLY PUBLICATION OF THEPUBLIC AFFAIRS OFFICE OF

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IN THIS ISSUE:

DETECTING

MATERIAL DAMAGEP A G E 1

HIGH-TEMPERATURE

SUPERCONDUCTING

TRANSFORMERSP A G E 5

DOE GRANTSP A G E 6

ELECTRIC VEHICLESP A G E 8

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BRIEFLY …

JUDITH MOURANT OF THE BIOSCIENCE AND BIOTECHNOLOGY GROUP HAS WON THEBIOPHYSICAL SOCIETY’S MARGARET OAKLEY DAYHOFF AWARD. The society’s main purpose is toencourage the development and dissemination of knowledge in biophysics; its worldwide membership isabout 6,000. The award is given to a woman who has demonstrated achievement and promise while notyet achieving a position of high recognition in her field. In this context, achievement means that the candi-date has published articles that contribute substantially to science; promise means that the candidate hasdemonstrated “leadership in ideas, organization or other ways manifest for her colleagues within the scien-tific community.” Mourant won an R&D 100 Award in 1994 for her role in the Optical Biopsy System, anoninvasive fiber-optic and spectroscopy system being developed to diagnose cancer. The system currentlyis licensed to a company in Florida for clinical applications. She and a colleague also currently are devel-oping the same technology to diagnose other forms of cancer, such as colon and breast cancer. Mourantalso holds a patent for developing a method for welding small bones together with a laser. To date,Mourant has had 21 articles published in various scientific journals.

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LALP-99-1-3Dateline: Los Alamos is available

on the World Wide Web:http://lib-www.lanl.gov/pubs/dateline.htm