Oral History Transcript — Dr. Robert Green
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Robert Green; August 25, 2000
ABSTRACT: Among the topics discussed are Robert Green's career in teaching and research and his work in nondestructive evaluation.
Bass:So youíre here to do the oral history for ASA, and so could you tell me, what is your present address?
Green:I am a professor in the engineering school at Johns Hopkins University in Baltimore, Maryland.
Bass:Can you tell your present telephone number?
Green:Area code 410-516-6115.
Bass:So how long have you been at Johns Hopkins?
Green:Iíve been there forty years.
Bass:Will you tell me a little bit about what you do at Johns Hopkins currently?
Green:Sure. Iím a professor at the engineering school and I have a chaired position in the school in general, but my current department is Material Science and Engineering where I do the teaching. I also for the last fifteen years have run a Center for Nondestructive Evaluation at Johns Hopkins, and so I have sort of two hats. One is the director of that center and one is a full professor in the engineering school. My specialty in research is nondestructive evaluation, meaning testing things to learn about their properties or to look for defects without changing the material or the object which you are inspecting.
Bass:In terms of the school, you teach and you run the center as well?
Green:Correct. Thatís right.
Bass:What kind of courses do you teach?
Green:This semester Iím teaching a class in X-ray diffraction. Itís a little broader than just for nondestructive evaluation but it involves looking at the orientation of materials like single crystals and also looking for defects in them and you can also use X-rays like X-ray spectroscopy for determining the chemical composition of materials. So this is a class for either undergraduates or graduate students sort of at an intermediate level. Next semester Iím scheduled to teach a class in nondestructive evaluation, again at the same level where I cover all of the techniques I know about that people use to study materials and structures and get information from that without harming the structure.
Bass:So you do powder methods as well in X-ray and all the different single crystal methods?
Green:Thatís right. Right. I donít do really extremely complicated crystallography like for organic molecules and things like that. We have a Biophysics Department, Biochemistry Department where there are X-ray guys that do that, and also at the medical school who look into organic materials, but I do inorganic materials. Since Iím in engineering school, thatís the ones that you use for making engineering objects and structures.
Bass:So most of your students are engineering students? Or do you have physics students?
Green:Most of them are engineering students. In our department we have obviously students who are interested in materials, but a lot of the biomedical engineering students also double major at Hopkins. I think they are correct in that they may not get jobs that they would like exactly in the biomedical field, so they learn some other aspect of engineering — or perhaps physics and chemistry — to be a little more sure of getting jobs in maybe a broader field. Hopkins is dominated by medicine, as you may guess, and so I might just mention that the center that I run is really divided into three groups. They interact with obviously an engineering school where I am, but also we have an Applied Physics Lab at Hopkins which is pretty much funded by the U.S. Navy, something like the lab here in Mississippi. Also I work with the radiologists at the medical school, because they use X-rays and ultrasonic techniques on people and we use them on non-people generally. So itís three groups that interact with three different parts. In different parts of Maryland, the APL, the Applied Physics Lab, is halfway between Baltimore and Washington. It used to be in a very rural area, although now with the population increasing in the area itís not so rural anymore. The medical school is in the middle of the city, and we are somewhat north. We are in the city limits but we are north of the business area of the city on a nice campus — smaller, but similar to this one.
Bass:The Center for Nondestructive Testing that you run uses almost any technique available to do nondestructive testing?
Green:Anything we can think of. We watch and see what other people are doing, for whatever purpose, and well I can give you an example. For example we have been doing some work for NASA and they contacted us recently and asked us to do something else. And for a long time people have been worried about the structure of airplanes and aerospace structures, — the mechanical structures — and since a lot of space shuttles are getting older and older and older. Most of them are getting older and older and older. They are now concerned about the electrical wiring. And I know one of their scientists down there who is going to head up that project is a man that uses infrared cameras to look for heat. So I feel relatively certain he is going to put current through the wires and see where the hot spots are.
We could do that too, but Iím looking for something different to do. Perhaps unfortunately, I have bad teeth so I go to the dentist a lot. The dentist is a friend of mine and among the techniques he uses is X-ray radiography on peopleís teeth. And so we were talking and he showed me some new developments in that. They now, instead of just having little packets of film that they expose and then go and do the chemical development and fixing it and then cleaning and washing, they now have systems that are digital systems with some luminescent powder inside, sort of a solid-state device but still somewhat flexible, that they can put in and have a wire coming directly out to a computer and record the image directly on a computer rather than as it goes through a film processing.
So Iíve been contacting companies, which he also provided me, who manufacture those because I want to try using this thing to scan on the wire and record the data. And unlike what he uses and which most medical doctors use (they use continuous X-ray sources), but because of the desire to see impacts of different things, there are flash X-ray systems just like there are flashbulbs — not the same thing, a different process — but itís still the same idea. And this means you go to set up something, push a button, get it away, move the thing around a little bit and do it again. So thatís my intention of doing it. We are just starting on that project. Next week I go down to NASA Langley in Hampton, Virginia where they are and talk to them about that.
But sometimes the people call me. We do quite a bit of work for industry also, and so it just depends. I guess the biggest project weíve had recently is turbine blades and hollow section of jet engines both for flight vehicles and also for electric power generating and turbine engines. The hotter they can run the combustion chamber, the more efficient the engine is, and historically to my knowledge every piece of metal that is used in any structural application is a fine grain polycrystal — meaning if you etched it acid or perhaps a base you can see the indigo grains in it. It looks like a bunch of grains of sand that you collected together. And the reason is that all metals, in general, have defects in them on an atomic scale, caused by dislocations that cause them to deform plastically at lower stress levels than they would if they didnít have the defect. An analogy I use sometime, although I donít think women wear these stocks anymore, is a run in a womanís stocking or something like that. But anyway, any kind of thing like that, that would propagate because of a defect in it.
And they make the metals, the fine grain polycrystals, because a dislocation moving along one crystal plane and one crystal will hit a boundary and wonít necessarily line up with a plane in a next crystal. So the grain boundaries are all like fences to keep the dislocation from propagating. But as you run a polycrystalline blade, itís like a blade that you see in a cooling fan in your house or something. The faster they can spin it, the more efficient it is. And if it starts spinning so fast, and itís hot at the same time, it slides along the grain boundaries. Itís called creek, grain boundary creek, and the blades get longer. And as they get too long they hit the side and there goes the engine. So after many years the aerospace industry has developed this. They now use single crystal blades which are one grain and they impede the dislocation motion by alloying additions, putting other elements into the blade — of which is confidential, but each company has its own recipe for this. And therefore they can run at high temperatures because thereís no grain boundaries because theyíre discrete. But they need a technique to make sure itís a good crystal. And so for a number of years we developed real time X-ray diffraction techniques. We donít use film; we use actually a night vision imaging tube like you see sometimes on television either with the police or military, sort of a green looking scene that you normally see because [inaudible phrase] the central spectral sensitivity of the human eye. But anyway, you can put a phosphorus green or fluorescent screen on the front of this and convert X-rays to invisible light and use all the features of the night vision tube.
So with the assistance of RCA back in the sixties who made these things, I worked for a year and I started making silicon X-ray diffractions with that. So we used that for a number of industrial companies, both the manufacturer of these blades and also the user of the blades, people who buy them and check them out. I showed them how to check them out to show that they are really good and not have a few stray grains somewhere or something like that. So weíve been doing a lot of work with that.
Bass:So this technique scans the blade?
Bass:And evokes that different — itís looking for dislocations.
Green:Yeah. What weíd do is we diffract the continuous spectrum of X-rays that are generated by a standard X-ray machine. This is a continuous source of electrons hitting the metal target, and it has a spectrum of a large number of wavelengths, essentially white radiation. It has some spectrum to it, but essentially white. And we diffracted it off a highly perfect silicon crystal. Silicon crystals because the advances in microelectronics industry have no dislocations in them. And so theyíre much more perfect than any metal crystal Iíve ever seen, including these blades. And most people who do such a thing are looking for very high special resolution, so they cut the silicon crystal so that if you have a larger beam coming in it makes that beam narrow. In other words it focuses the X-rays.
Green:But we want to look at large areas so we could have a crystal so it expands a beam, so that when the X-ray hits the silicon crystal it not only becomes monochromatic; it gets longer, and itís one wavelength. And so then we scan the blade with that, and usually we pick the most energetic characteristic. Or — some of the spectra is more or less continuous, but some of it is discrete line spectra, and thatís usually the most intense, so we pick the copper [inaudible word] for example, which is the copper target, and use that so then we can scan. So weíre really looking at one live spot. One of these spots, you know, may get a little bit larger.
Bass:So you use copper tubes or tungsten tubes, or you just pick that characteristic [inaudible phrase]?
Green:You match the tube up with the material you investigate, altogether [correct word?] linked up, because certain things image better with one wavelength or another. The tungstens, the crystals that we are looking at are made from sometimes titanium, sometimes tungsten, something like that, and so the copper seems to work well with that. They also make a lot of them in nickel alloys. But I donít know, they donít tell me exact composition of them.
Bass:Yeah. Everythingís proprietary.
Green:Yeah. Well, I never ask the company that wants me to do something for them anymore than I need to know. Then I donít give away any company secrets and I donít have to worry about it. But we do sign confidentiality agreements, but weíre careful because most of the real work is done by graduate students and graduate students want to get a thesis, so they canít work on things they canít publish papers on. So if we donít know it we donít give away any secrets and the graduate students can work on it. And sometimes truthfully, even though I may sign a confidentiality agreement, I just donít tell the students either any more than they need to know to do their project so they can publish. Sometimes even basic research papers or applied research papers.
Bass:And thatís a problem with doing work for industry or military at a university.
Green:Thatís right. Thatís right.
Bass:You have grad students who need to get a dissertation or a thesis or they need to publish papers and you canít do that because —
Green:And so do young faculty, because they want to get promoted also, so itís a problem. At the present time we canít do classified research on campus. We used to, and somehow because of the Vietnamese War there were protests and things, so now itís forbidden. But itís not forbidden at the Applied Physics Lab. I suspect itís forbidden at the medical school, but I donít know why they would do it down there anyway.
Bass:So the Applied Physics Lab is very similar to NCP, I guess.
Green:In a sense.
Bass:Itís Navy funded or —
Green:I think they work pretty much on undersea problems.
Bass:But your center for nondestructive testing is under the umbrella of Johns Hopkins? Itís a center within the university?
Green:I have a separate — I donít have the same thing you do except a big building, but Iím in a separate location in one of the engineering school buildings. Okay?
Bass:So do you use any acoustic techniques, interesting acoustic techniques in your work?
Green:Yes. Historically the standard technique that most people use at an industry is whatís called the ultrasonic C-scan. It just means thereís three ways of looking at something, called A, B and C. [There is nothing] special in that. But normally if you want to look at something, just a piece of metal, slab of metal or something, [there are] two ways of looking at it. One way, as in one way most often used in industry, and we put it in a tank of water and then we have at least one or more transistors. If we are sort of looking at the surface quality — or we can look [at a] rather thin piece, too, this way — we use whatís called a pulse echo, just like radar, I mean or sonar. And it comes in sonar, Iím pretty sure. And so you send it a pulse of sound and wait for it [to] come back, and in the meantime you switch on the piece of electric transducerís receiver, and then you do a raster scan, x-y scan of the piece and pretty much see the thickness by the wave speed, and also look at the defects because youíll get a signal back in time if you select a signal with a defect in the middle or somewhere. So you can discriminate by the time the back reflection echo from the echos prior to the back reflection.
Sometimes for large structures they donít use a tank; they use a water squirter where in front of the transducer there is a nozzle that is set up. So water passes around the transducer in a laminar flow, and you get like a water waveguide with bubbles eliminated if you do it correctly, and use that. So then you need some grating or something underneath to take the water away, which you donít need to have [in] a big tank. Now we have a big tank because we are in a [inaudible word] lab facility with this one and we can squirt water over everything in there, so we do it that way.
The other thing they do, when they canít put it in a tank, canít squirt water at it, you put oil or grease on an object and hand scan the object and look for defects in pieces like that, that are not successful coming into a lab and being put in a tank or have water squirting at it. The thing that we do more — a lot of — which they donít usually use that much in practice is, most of the people — [phone ringing] — maybe you ought to answer that.
Bass:The secretary will answer it.
Green:Most of the people who work in the field and do this are not researchers, they are more technician-like people, and they only use the velocity — even in the tank of water — they only use the velocity measurements. They donít look at the absorption attenuation of the sound. And so many researchers are now — more and more of the people in the field are also using the other half of the information they can get, is the attenuation of the material. I mean sometimes he may have some changes in the material that is too small to give you a reflection back, so Iíll use an analogy of imaging a shark or whale versus a school fish or something. So this scattered a sound [inaudible word] so if it was small defects the attenuation gives you a better indication of defects inside them just waiting for reflection.
Bass:Calibration of the equipment becomes more crucial then, I guess, than in pulse.
Green:Thatís right, thatís right.
I think — The same thing happened with X-rays. I remember taking a course and the first thing weíd do is index patterns, right? But nowadays through using the actual amplitudes of these X-ray peaks they get structure factors or —
Green:Thatís right. The other thing to redo is like they do computer assisted tomography with X-rays. We did that also with ultrasound. So if you make a scan in the right direction and you put the data into the computer program properly then you can do three-dimensional imaging with ultrasound. Itís different and perhaps not such high resolution as the X-ray, but itís doable and, in general, itís much safer, particularly on people.
Bass:It probably makes it a lot easier to take it out in a working environment too, because [with] X-rays you usually have a lot of safety concerns and that kind of thing.
Green:There are two projects we just started. When someone breaks a bone — we work with the medical guys, I mean mostly — when somebody breaks a bone completely in two and they want to put it back together, they put a metal tube in there called a stint. And in that stint there are two threaded holes, one on each side of the break. And so now they put it in the medullary canal of the bone where the bone marrow is and shove the two pieces together. And then they can see the holes where they want to put screws which will hold it in place so they can screw down through the bone into the stint on both sides of the break. And I only learned a few months ago that the medical doctors do this in X-ray machine in real time; put their hands in the X-ray beam. Itís not the best thing to do.
So one of my colleagues who — I have two associates sort of. One is my expert in ultrasonics and one is my expert in X-rays. Sometimes itís good to keep people separate [inaudible phrase] reason. But anyway, so the guy thatís the ultrasonics guy, he worked with the medical doctors and showed them itís really easy to image their holes with ultrasound so they donít have to put their hands in X-ray beams. And best we know this ultrasound we are using is really nondestructive and shouldnít hurt them if they get a little bit of sound somewhere off in their hands. So I think that he and the medical doctor are trying to get a patent on this. Iím surprised they didnít do it before, but you never know. The other one we are working on is guns.
Green:Unfortunately in Baltimore, like many big cities, there is crime and crime with guns, and the criminals usually scrape the serial numbers off the guns. Or maybe the person who sells them to them already has scraped them off. And in my opinion, most criminals are pretty lazy people or else they wouldnít be criminals and so they [donít scrape] them off too well. And [the serial] numbers, if not most of them, are put on by stamping the numbers in. So if they donít do it too well, the metal underneath where the stamping was is still deformed. And so weíve been showing in certain cases we can use acoustic microscope high resolution acoustic imaging to the see the deformation of the metal underneath and recover the serial numbers. We are also suggesting ways they might do better in this, but I donít want to talk about it because if they do I donít want the criminals to know how to do it. But after we get over this Iíll tell it to you. I mean this [inaudible phrase].
Bass:To remove the serial number.
Green:Well, to put the serial number in a different way which might not be visible on the surface but might be read acoustically.
Bass:Okay. So that would be a good thing for the companies to do.
Bass:Right. Donít even [tell] them where the serial number is.
Green:And I suggest that you do something like that and then you put a serial number on somewhere else so they can scrape it off and it makes them comfortable. So sometimes we make suggestions on things like that. But we do — I would say nowadays probably ultrasound is used more than X-ray by people in nondestructive testing, because itís harmless, the apparatus is cheaper, it is very portable, small, instruments you can carry around now and do stuff with, so historically it probably wasnít true but it is now. X-rays are around longer than ultrasound as far as engineering applications are concerned. I donít think it came into being until sonar was developed and it was a spinoff of sonar. Thatís my opinion.
Bass:So maybe weíll talk a little bit about your relationship with the Acoustical Society of America.
Green:Okay. All right.
Bass:Do you remember what year you joined ASA?
Green:No, but I know I was a graduate student at Brown University when I did it, and I was there at first about 1953 to Ď59 — so somewhere in the late fifties is when I joined. Robert Bruce Lindsay, who everyone at the Society knows was my chairman of the department at the time, was [my] Masterís thesis advisor. And I think all the graduate students joined the Acoustical Society — or at least all of them that were doing anything with sound anyway. And so Iím pretty sure I might have been just a student member then, but thatís when I did it. And I did it because that was the sort of thing for us to do in that department. We were encouraged to do it, the professors were all active — or most of the professors — were active members in the Acoustical Society. So the students were also encouraged to do that, and we did.
Bass:So was there a particular ASA committee that you were a member of, or you had been Technical Committee Chairman or anything?
Green:No, I havenít done that much. When I firstĖ Because once I did my Masterís degree — you may not be interested in this, but Lindsay suggested I use ultrasound [inaudible phrase] elastic moduli [correct word?] values [correct word?]. People had done something like that optically [inaudible word(s)] transparent looking at the change in light shining through when it vibrates. It would be sort of an optical resonance experiment.
Green:And he thought that would be a good project. I actually was scheduled to work on some low temperature physics using acoustics, which a visitor from England was setting up a lab. And so, other than carrying liquid nitrogen and helium around, he wanted me to have a little project where I could get my Masterís. So I started trying to grow ice crystals. And I wonít go into great detail. It wasnít very easy to get them with an air entrainment in them, and I wonít go into that now but eventually [inaudible phrase] I succeeded. And I was well into my Masterís when a hurricane came in [inaudible word(s)] and the power went out and my thesis melted. So Lindsay suggested since I did it once, I could do it faster the second time. And so I did. So I finished that and did that, and then the question comes, what do I do for my Ph.D? And by this time, because it took me three years to [complete] my Masterís, they had some other students working with the low temperature guy. And so that position wasnít available.
A guy interested in metals came from Germany and asked, ďDoes anybody know anything about crystals or crystalline materials?Ē And I assume Lindsay told him, ďGreen is working with ice crystals for three years. He should know something about it.Ē And so I went over and started working — They had a metals research lab where different faculty were working on different projects. And so I shifted into being a metals man. And there I was doing X-ray diffraction [inaudible word] as well as studying some of the mechanical properties and some of the technical properties of these materials and growing some metal crystals and things like that. So I got off more into being a materials man than acoustical man and I use X-ray diffraction an awful lot.
And when I, while I was finishing my Ph.D. he went back to Germany. His professor died and he went to try to get the job. He didnít get it, but he got another job over there. And I had worked in an [inaudible word] Naval shipyard as an undergraduate when I was at William & Mary, because Iím from [inaudible phrase] where the [inaudible phrase] Naval ships [inaudible word] is in Virginia, and I worked on nondestructive testing. It just seems crazy how your life turns sometimes. But in any case, that was not a place where a person with a Ph.D. could work, but they had a branch of what was then called David Taylor Model Basin, Underwater Explosive Research Lab, that was centered there in that naval establishment, and I got a job there working on underwater sound. And the two chiefs of the lab were German scientists that had come over after the war, and Iíd applied for — Lindsay had put me up or suggested I apply for a Fulbright Grant to go to Germany. And I thought at the time that Germany had the best scientists, although later on [I] learned they were all in the United States or in Russia, but nevertheless, at that time anyway. It all came together, and I thought about working in a lab. It was my hometown, too, where there were two German scientists, but I forgot [got] the fellowship. They let me go, and [I] did.
And while I was in Germany, they moved to Carderock, where they are currently located, and the [missing word], which is [inaudible word] by Washington... while I was in the shipyard, and then I got the Fulbright to go to Germany to work with [inaudible word] never came back, and I did that. And while I was in Germany, the group at the [inaudible word] naval shipyard moved to Carderock. And so that meant I had to move somewhere. In the meantime, I received a letter from Johns Hopkins asking me if I wanted to apply for [an] assistant professor position in their mechanical engineering department. And I told them, ĒNo, I was a physicist, I didnít want to be an engineer, I didnít like engineers,Ē and they wrote back, ďWonderful. Thatís the kind of guy we are looking for.Ē And then I got a letter from a professor of metallurgy there who was also from Virginia on the other side of [inaudible word] swamp from me and a very nice, sensible letter, and since I figured I had to move anyway, and I kind of like university life after been doing it a good while, so I took the job, and so Iíve been there ever since now.
Iíve been in different departments over the forty years, but in any case itís always been in engineering because thatís where I kind of — I think Iím an applied physicist, but they donít have an applied physics department on campus so Iíve been in the mechanics department and civil engineering and materials department, so it always related to something like that, and thatís where I still am, and I do pretty much what I told you, testing materials — both destructively and nondestructively.
But with ASA I have gone to meetings on somewhat of a sporadic fashion. Iíve been active in the American Society for Metals and more recently the American Society [for?] Nondestructive Testing. I do — I am a fellow of ASA as well as the other two societies I just named, and so I like the Acoustical Society of America and I go to meetings when I can, but I guess if I had to say my main interest [it] would be in physical acoustics as far as the group that I prefer. And so I go to meetings more or less in a random fashion.
Bass:What other professional organizations do you belong to?
Green:Well, like I said, I belong to the American Society for Metals, I belong to [the] Metals, Minerals and Ceramic Society, [inaudible phrase] well, the American Society for Nondestructive Testing obviously. Iíve gone through the offices there and Iím currently chairman of the board of directors for them. American Physical Society, Iím a member of that. So.
Bass:Okay. Letís talk a little bit about past history, your early years and pre-college years.
Green:Okay, yeah. Okay.
Bass:When and where were you born?
Green:I was born in Allegheny County, Virginia on a farm in 1932 during the Depression and lived there until I was around three or four years old when my father got a job in [inaudible word] Naval shipyard. He was a machinist. And so I spent my years from three or four until I went away to college there, and continued returning there until I finally went to Baltimore to Johns Hopkins. When I, you know, it was my home base with my parents.
My mother was a dietician first in elementary school in the neighborhood where I lived and she later became dietician for the junior high school, and she stayed in that position pretty much until she retired.
Bass:Do you have brothers and sisters?
Green:I have one brother who was a pharmacist. Heís younger than me, but heís deceased now so at the moment I donít have any brothers and sisters. But I married a young woman from my hometown and we had two daughters and now have two granddaughters.
Bass:Two daughters and two granddaughters. All girls.
Green:All girls. Itís not so bad. They take good care of the old man, so.
Bass:I have one daughter.
Green:Well, I have a son-in-law who is a nice guy, so at least I got a man around somewhere.
Bass:Certain things you just need men to talk about.
Bass:So, as a youngster did you ever think youíd grow up to be a nondestructive engineer?
Green:No, but I knew I wanted to be a scientist. I used to do what I guess young guys who want to do that [do], play with chemistry sets and makes things and stuff like that, and I had a very good chemistry teacher in high school so when I went to undergraduate school [inaudible phrase] I started off in chemistry. And I didnít have a very good physics teacher in high school. They had the track coach doing that, so it could have been good but it wasnít as good, as fascinating as she was. But then when I got to college and took sophomore physics I liked that better than I did [in high school], so from then on I became a physics major completely through my education.
Bass:Looking back, was there any person during the high school years that influenced you on your future, a strong influence?
Green:Well yeah, there were a couple of people. There was one woman who went to the same church I did in Portsmouth, and so I saw her a lot, and she [inaudible word] English teacher, which had nothing much to do with that part, but she would talk to me a lot and I would see her in church and weíd talk about different things and so I did very well in high school. I was valedictorian and I also was president of the student body. And so that helped me, I think, to get into college. I know that when I went to William & Mary, the assistant principal took me up there. I didnít come from a rich family, and so I got some very nice scholarships to go to school there. And so he helped me, too. I think it was mainly because of a couple of the teachers, like my home room teacher, and this woman who was a teacher but knew my family from the church activities and so forth, so somebody put in good words for me on that.
And at that time, William & Mary only had undergraduates, and you werenít allowed to have cars or anything, and there wasnít any Busch Gardens. So you were pretty isolated there. And so you either participated in — and itís smaller than your school, but itís still a bit like here, isolated — and so my opinion is you participate in school activities or you donít participate. So I think thatís — I like that. I think it was good for me, anyway, so that part was good.
But there has always been some teacher somewhere that — I mean for example ([Iím] telling on myself), but the physics department at William & Mary in those days only had three professors — the chairman, the guy who did most of the teaching, and the guy who did the labs. And the chairman and I didnít get along well. I have always had difficulty with authority, sometimes, so the chairman, he had one to Brown University [inaudible phrase] in physics, and I wonder if it was a subliminal thing that I went there, but I really got the best fellowship there, when I applied for a number of schools. But in any case, at one occasion he told me that, when I suggested I might want to go to graduate school in physics, he said, ďOf all the people that Iíve ever taught, you are the least likely to be able to go to graduate school in physics.Ē Well, I donít know whether he was using reverse psychology or not. And when I got my Ph.D. in physics I went back to tell him off, but he died, so I will never know the answer to this case, [that was] a thing that did help me a lot though.
It seems interesting what helps you in your life. The second guy who did most of the teaching lived on campus. They had some housing for faculty like you do here. And he always said — a real nice guy, and he always said, ďIf you see my light on, you can knock on the door and get help.Ē There was only seven physics majors when I was there — the maximum that they ever had. And so, you know, other people took physics classes, but as far as a major — and so I used to, when I had trouble Iíd knock on his door and heíd help me, as well as during the daytime, you know, when you saw him. So I go to Brown, that graduate school, and Lindsay is head of the department, and most of them [inaudible phrase]. And he just finished writing his theoretical physics book and so he taught theoretical physics to all the new graduate students.
Now Iím in school there with guys from Harvard, Yale and all the prep schools in New England, and one day a group of them come to see me. They said, ďGreen, we know we are smarter than you, but you are getting better grades than we are.Ē And they said, ďHow come?Ē I said, ďOh, Lindsay helps me.Ē They said, ďWhat?Ē I said, ďYeah,Ē I said, ď[I] go up to the office, I say I need some help on problem six, the secretary says ĎJust a minuteí, goes in his office, comes back, says ĎCome back at 3 oíclockí, I come back at 3 oíclock.Ē They [inaudible phrase] all of [inaudible word]. See, I was stupid. I didnít know better. Because Iíd been at the other place and the guy helped me, right? And later on, Lindsay thought it was funny. So I really had good relations with him, okay? Later on I invited him down to Hopkins, as you would guess I might, and had him give special lectures and things like that. And then, somewhat strange as it may seem, his grandson went to Hopkins in the history of science and had written a fairly thick article. Maybe itís printed in the book now, about his grandfather — and so we had nice conversations about it. And so itís interesting. Yeah, I think different people have helped me. Obviously the professor who did the teaching mostly at William & Mary and then Lindsayís influence at least. And he then moved up to be head dean of the graduate school, but he still would stop by the physics department and talk to people and so forth, and I used to go over and talk to him some, soÖ He also used to take graduate students, he and his wife, to dinner at their house, you know a small group at a time. And so he was a very personable guy and was a nice guy, a very nice guy. Fortunately he finally got [inaudible phrase]. Maybe not too many of them, but you can find some.
Bass:Some people you are compatible with, other people —
Green:Can make an influence on your life, yes. I mean maybe you donít know until you think back on it so much, but itís true.
Bass:I think nowadays thereís probably a better chance of that happening because a lot of schools will invite students in to talk to research scientists or to professors there before they actually decide to go, and so you know, itís hard to tell with maybe meeting someone for a day or two, but you still have a better chance of compatibility.
Green:Although Iíll tell you something. If I had seen where they put me at Johns Hopkins before I came, I wouldnít have gone there.
Bass:You would not have gone.
Green:Because of the war, the town what I went to as a Postdoc in Germany had been completely demolished by Americans, Iím sorry to say, which is also an interesting experience I wonít go into here. But they had rebuilt it into a very new facility. It was like some of these — like this building here, almost. So I was in the plushest facility I had ever been in in my life, okay? When I came to Hopkins I was in the worst building that Iíve ever been to in my life. And Iím still in the same building, by the way. Itís been renovated some, but anyway I just —
Bass:I hear the acoustics people here used to be over in a really small building over on campus but then I guess they lucked out and we got this new building.
Green:Yeah. So itís nice.
Bass:Itís nice to have a nice building, but you know if you have the equipment and you have a lot of good people around thatís —
Green:Yeah, thatís what you really [inaudible word]. Well, the guy that wrote me, the Virginian, native Virginian, he became my mentor so I should mention heís the one that helped me mostly as a [inaudible word] person. Heís retired now. Heís eighty-five or something, but heís one of the — heís also an outstanding teacher. Probably as far as Hopkins goes, heís the best teacher Iíve ever seen. Most people would agree with that. So also he could teach young faculty things too. Heíd help you with your courses if you didnít quite know a subject or something like that, so he was a most valuable influence to me in my professional career at Johns Hopkins, this guy. Now his son-in-law works for me.
Bass:And heís a professor there or just —?
Green:Heís a research professor.
Green:He sort of helps run the lab and stuff like that. But he works for me. He works for me under the department, but most of all his work with me, the research work. So he and his father-in-law live in the same town, which is a suburb of Baltimore.
Bass:I think weíve covered your undergraduate and Masters and [inaudible word]. Maybe you could tell me what your doctorate thesis was about at the time.
Green:Yeah. Itís —
Bass:The Masters was on the ice crystals.
Green:[inaudible phrase] ice. The doctorate was on the re-crystallization of aluminum. You can change the makeup of the grain structure. Aluminum [inaudible phrase] but crystal, so you canít change that. But you can change grain size, the orientation of the grains, I mean, for example, if you have relatively round grains, a sheet, if you roll it they become elongated. And so then it has Ė they call this texture, the texture of cloth [correct word?], okay? And you can also see it by etching it, but you can also scan it with an X-ray and do a little better than just looking at it, as far as getting some numbers on it. So at that time they didnít know a whole lot about it. I mean, they knew they could do it, but it didnít, [they] hadnít pursued it extremely scientifically. So they werenít sure about why this occurred in the way it did.
And so with the help of a technician, we grew I think the longest metal crystal ever grown. We grew aluminum crystals thirty feet long in the bell tower at Brown. The biggest obstacle was getting permission to cut holes in the floors of the bell tower, but we finally got some, and we grew long aluminum wire crystals. And then we cut them into symmetrical pieces and they formed in different amounts, and then with a special technique of heating them — the tip about heating the whole thing [inaudible phrase] water into a flame. We re-crystallized part of the thing. So now you got a new crystal on one end and thereís [inaudible word] crystal on the other. And then by putting it in a furnace and taking [inaudible word] periodically and etching it, you could see where the grain probably moved and measured the grain growth. Because one reason [inaudible word] was the rate that the grains grew in different directions. A possibility, right? And so it was a very tedious, repetitive process. [inaudible phrase] later on in Johns Hopkins I did it in a furnace with a real time X-ray, so I didnít take it and etch it. Because etching grooves the grain boundary, and that can influence the measurements. But I didnít say anything about that when I did my Ph.D.
Bass:So you were doing real time X-ray [inaudible word].
Green:[inaudible phrase]. I did the same way of getting strain free grain on a strain crystal. And, but Ponge [spelling?; first name?] is the one that helped me do it. Actually we took two sheets of aluminum foil on both sides and had two heating coils, like next to where we dropped the crystal in, and used the line source of X-rays with a metal grid every millimeter across, so when you looked at the — if you took the grid out and looked at the diffraction pattern now from this wire you got lines.
Green:Different lengths at different angles where the spots [correct word?] are going to be. And when you put the grid in, there are no lines or dash lines all of them, and so when the dash change — when you lose a dash or gain a dash the crystal grew one millimeter.
Green:Okay? So then we had a [inaudible phrase] papers on that technique. I didnít do a thorough thing, just showed the technique could be done. But so I continued doing that, just that part, when I went to Hopkins. But thatís what it was, so we tried to — then we showed that the different crystals — [the] relation between one grain and another weíd grow [would grow? Weíd grown?] at different rates. So at least thatís possible. It might be other things influencing it too. But I might just mention that later on at Hopkins I could grow aluminum crystals of infinite length.
Green:By a different techniques, but thatís another story, okay?
Bass:These are single [inaudible phrase]?
Green:Wire. I grew them from wires, yes, single crystal wires.
Bass:How big is like [inaudible phrase] size [inaudible word]?
Green:Well, like a millimeter or something like that.
Bass:So you just, itís kind of like a continuous growing. You just have I guess a wire. Itís polycrystalline aluminum?
Green:In the salts [correct word?], yes.
Bass:And then you just, it just —
Green:You melt it. Well, the one at Brown, we did it by re-crystallization. We grew it by this process. But at Hopkins I was setting up something like that and I melted it. And I didnít have a real tall thing, so I had a spool of wire coming off of some stuff to sort of straighten it before it got out. It was sort of high [inaudible word] but not too high. And sometimes — and then I didnít want it to hit the floor or something, so other people came in and [inaudible word] that lab and would shake it, and thatís not too good. So I had it going into a plexi-glass tube of glycerin so it would kind of be protected. Sometimes if they would shake it, it would break at the end where it was being heated. [inaudible word] get too close to the side of a furnace and melt or something. But anyway, what happened was that on some occasions, I melted it instead, and was just heating it. Usually re-crystallizations temperatures are between the melting temperature and half [correct word?] the melting temperature — not the melting temperature. All right? And so what happened was that I took an X-ray of them, anyway, and I saw they were good crystals even if they melted. And I didnít quite understand it, but now I know. The answer is that aluminum has a very tenacious continuous oxide film on it if exposed to air, and itís strong. So it had that glycerin thing there and a [inaudible word] of aluminum wires hanging out — it would pull the oxide film tight even if it was molten.
Green:And so you had crucibles for, automatic crucibles for — holding aluminum in. So thatís, so then we started doing it that way then, without having to strain or anything, just put the wire up there and set the furnace right so you hit a narrow zone of heating. And the glycerin helped glue it up so it would stay together over a couple meters, and then when it was coming near the bottom, I always took a pair of little pliers and pulled it, and it broke in the zone [correct word?]. And for reasons I donít know, it kept on growing the same orientation crystals. So it must — it canít hardly be the [that] liquid has a memory, but it was a mushy [correct word?] or something, you know?
Green:I donít know the answer to that one. I mean, I never investigated that to the extent, but, but if I — if the furnace burned out or something changed and I rebuilt it, I could grow crystals again but [in] a different orientation. But I donít know why that was either. But something was changing, obviously, in the system that causes that.
Bass:One place where actual oxidation has a good use to —
Green:Yeah, yeah, and yeah.
Bass:I was wondering, you know, when you heat these things up that re-crystallize, you know, youíd like to put this in an inert atmosphere. If youíre pulling it outside the furnace, then you definitely have oxygen there which [inaudible word] causes —
Green:We did some of this in inert gases and things, but sometimes we didnít. I mean, you know you kind of learn by doing stuff and all.
So you donít do too much in the way of crystal growing, nowadays. Itís —
Green:No, I havenít done that in a good while, no. Most of the time nowadays I look at material that other people send me, like the turbine blade manufacturers, for example. And more recently we got into composites, because a lot more composites are being used in a structural application like aircrafts, and so forth, and so a lot of the recent projects of that — I donít know if you heard my lecture on air couple, [correct phase], but we got into that, really. I didnít talk about it, but the Smithsonian contacted us about helping them inspect some of their art objects before they go on exhibit and make sure they are not damaged by whomever they loan them to. If they are really broken, they see it, but it may be damage not obvious just to the human eye. And they use X-ray radiography routinely, [or] did then. What they didnít do is the ultrasound. And X-rays — every technique will show something that the other one donít. Okay? So the other technique most often used by the people in X-rays is ultrasound. Even the medical guys now do it. And so — but these valuable paintings, they wanted to look at wooden paintings, paintings on wooden substrates like religious ones from Europe and so forth. And [inaudible phrase] let you put them in a tank of water and squirt water at them, okay? [inaudible phrase] grease on them, right? So I started checking around, because people were doing a couple ultrasound, but not a lot. And a family guy that was in the Bureau of Standards, but in Boulder, Colorado, where they had a small NDA group, a real nice guy — and so I talked to him and he would come in periodically to Gaithersburg, Maryland, where the main Bureau of Standards now called NIST (change their name) is, and they prevailed upon him to come over and work with my student. And she was a very good looking young woman so it didnít take much trouble to get him to come over, but nevertheless he did.
She was Canadian and she had worked on totem poles of wood in Canada, so she was really able to work with wooden objects. And so with his help and her hard work, we developed a scan system, ultrasonic scan system, which showed things that the X-rays didnít do and vice versa. So thatís how we got started. And there are a few papers on that at different places, some of them not technical meetings, like I would usually go to, but that gets to be kind of fun too, seeing something different and what other people were doing.
And then the Forest Products lab at Madison, Wisconsin asked us could we grade lumber? So we can scan lumber, you scan two-by-fours and stuff, but I couldnít analyze the data because if it was like this table, I could do it, because everything is in a straight line, but some things are grain and not — if it was just nice, uniform grain [inaudible phrase] I could do it. But when itís getting grain wiggling like this, the sound waves are going every which way, so you get images, but I never could interpret them. And I didnít get enough money to try. I mean, it isnít worth it, right? So then about that time, a company that makes tree-products — itís sheets of — look like sheets of paper, but itís black and itís got fibers in it, and then itís got this sticky epoxy. And if they do — if they wanted to make something like this, they would take sheets of this stuff, cut it up and stick it down, make a stack of it. And it may change the properties by which way they turn the stacks because [inaudible phrase] fibers are going. And then they put it in an autoclave, pressure and temperature. Cure it. [inaudible phrase] the stuff out of it and make it. So they had no process control, [inaudible phrase] company in Idaho. Utah. Utah. The other ones did it, but thatís where we went, and [inaudible phrase] was very easy with an air couple [inaudible word] to scan back and forth across the thing, it was so thin, and then we were getting more and more to composites, so I knew they had a composite center at the University of Delaware, which is one hour north of us. So I went up there and was talking to them, and we got some contracts together to do process control on some of their stuff, so we got pretty much into it. [inaudible word] plates and [inaudible word].
Bass:So itís full cycle system exactly, except you are using air as the coupling medium rather than —?
Green:Thatís right. The coupling efficiency is lousy, but itís not zero, and right now more and more people are working on this. I mean, the piezoelectric things have been used so long and all that no one bothered with thinking of anything else. And a few guys — this guy, [who] had worked with some people in California, had been doing it a long time. And I forgot what. Itís probably — they werenít thinking of a nondestructive inspection I think. I think itís just sensing [inaudible phrase]; I mean, you know, some other reasons. I donít know what it was, and but now itís catching on pretty much. When I went over to mechanical engineering the other day they already knew about it. They were getting ready to buy a system, right? From the people in Pennsylvania, right? So theyíre really being advertised pretty heavily. Not a whole lot, but itís coming around pretty much, and so the competition [inaudible word] to make them more and more efficient. We get them from a guy up in Canada. He was an ex-graduate student. Iíve forgotten his name, and heís the one that [inaudible phrase] and he builds them by hand, I guess, and we buy them from him. I know a professor at Stanford [who] is in the business. Now he was a microelectronics guy. So they are using some micro machining techniques now, which is better controlled than the kind at a machine shop at a university. And what he is doing is taking a silicon wafer and etching it away so you get sort of a thin cylindrical cup, like, like if you cut off that coffee cup at the bottom, and then they put it in a furnace, and nitra [correct word?] is part of it, and build up a nitra bridge like. So now they got the electroconducting silicon at the bottom, and then they got this bridge, like, and then they put a, say, aluminum membrane across it and put some more silicon oxide on it, nitride on it, or something like this, so that to make a long story short they build a membrane-like thing that can vibrate. It was like a loudspeaker or something. And see, that seems to work pretty well, and so it was variations on that.
Bass:Okay. Other terms of academic — Did you teach classes while you were going through grad school or —?
Green:Yeah, we were TAís. If you want to hear an interesting — does this get censored sometime? [inaudible phrase] you guys?
Bass:What is this?
Green:I can tell you my first teaching experience [inaudible phrase].
Bass:Sure. Go ahead.
Green:I wonít tell you what — Iíll be careful what I say. Unfortunately, well we had a class for nine physics majors, you know like physics for housewives or something. And not knowing, not being in the know, I got the first lab on Monday. There were two each day, because a lot of students had to take this course. And the first experiment was — also that the other TAs came to watch me, because [most] of them didnít have any experience either, as well, so I had a big audience for this. And the [inaudible word] idea of the course was to show some principle as simply as possible. And then get the best piece of equipment you had and do it with that, too. So, this one was to measure the acceleration due to gravity. And the physics building, at that time, was an old building that had a spiral staircase in it. So the idea was to put students at various levels and go up into the attic with a red rubber ball and a metronome. And when they all got ready on different levels you started the metronome ticking. You dropped the ball and each groupís got to tell what tick of the metronome it came to them.
I donít usually say ďyou allĒ that much. I probably never say it, now. I mean [inaudible word] more than anybody. Even one of the Bostonian does, right? But anyway, I was nervous and so I yelled down, ďAre you already in the basement?Ē and everybody laughed, all the Yankees laughed, and ďAre you already on the first floor?Ē and all giggling, laughing, see. So I finally got all of them ready, and I said, ďOkay. Throw it over.Ē And I swear to God, this guy threw the metronome. The other guy says, ďWhat do I do with the ball [inaudible phrase]?Ē I figured Iím out of school anyway. So anyway, from them on — they are not in the same building anymore — but sometimes I would go back and they would be doing that experiment, and they would let the metronome tick over the PA system all day. Which drives people crazy. They donít give anybody the metronome anymore.
But the sequel to it was this: second semester Iím a wise guy by now. I got the last laugh on Friday. And [inaudible phrase] things good, but it was particularly good because Brown had a separate school named Pembroke. Itís all part of Brown, now. And the young women in the class, like the young men in the class, on Monday didnít look too good. Theyíd been out on the weekend having a good time. Friday they were getting ready to go out. They were all dressed in high heels and looked really nice, so it was a more pleasant class. But at that time, my problem came that there was a fifty year old ex-Air Force officer who decided to come back to college, and I was only twenty-five. So hereís a guy twice my age and [inaudible word] and extremely enthusiastic. And I never had tried to teach somebody older than me before or in a class, so it made me nervous, but he was a nice guy, didnít do anything.
By this time these guys have had a year of this, and now they are physics experts. So they get to their project. And his project is to build a radio. And they are, like probably the same way now, I donít know. He made a list all the stuff he wanted. I went into the stockroom man, and he didnít have anything the guy wanted, but he says, ďTake two of these resistors and together, you know, hereís a capacitor, hereís something else, use this instead,Ē So now we finally get all this stuff assembled, and the other students too. And they had a good rule. The good rule is they couldnít plug anything at the 110 AC until I OKíd it. So heís got this pile of junk on this table — different size wiring, different kind of things none of us would have asked for. And he says, ďWould you check this out?Ē And I said, ďYeah, itís fine. Go ahead and plug it in.Ē When we were plugging it in, one of the young girls went by, caught her high heel in the cord, and it flew all off on the floor and music came out of it. He said, ďThatís what I like about physics.Ē I said, ďYeah, me too. I had a gander.Ē So I hit it on a high note. So sometimes itís good to be lucky. Itís better to be lucky I guess, right, or unlucky sometimes and lucky other times.
Bass:Now weíll go on to I guess, other training. Were you ever in the military?
Green:No, I never was. I worked for the military ten years total in my life by taking sabbaticals or something. The last time, I worked for the Pentagon, the Defensive [inaudible word] Research Project, which is a big research of the Pentagon. Because, see I had started working at the underwater explosives lab, and then I took a sabbatical and worked at Aberdeen proving ground near me. They use a weapon called a shape charge jet, and they didnít know whether the jet was liquid or solid, and so I showed them how to modify a pulse X-ray machine. They had [inaudible phrase] in the tubes because thatís easy. Thatís [inaudible phrase] metal made by Westinghouse has a coefficient thing [inaudible phrase] expansion is glass. And so they sealed everything with that, with its pretty high absorber for X-rays, and Iíve got to have low-energy X-rays for diffraction. They match up with the [inaudible word] and the crystals and the material. Diffraction tubes all had beryllium windows for a long time, so it wasnít a great achievement to suggest they get a tube made with beryllium windows. But they did. And so in any case, I worked for them and with that modified tube and a lot of help from those guys — took a diffraction pattern of the shape george jet when it went off.
And then a friend of mine from Brown [inaudible phrase] graduate student became chief of the polymer section of the National Bureau of Standards. And Iíd gone down to give a lecture on real time X-ray to see if they could use it for polymers and so forth, and he asked me what I was doing, and I told him, well, I had never been overseas except for Germany. Iíd never been the other way to the Orient anywhere, and I written a guy about going to Japan I knew at Tokyo University. In fact, I knew them because when I first did real time X-ray, I did it working for RCA on leave of absence, and they didnít want to patent it. They [inaudible word] selling color picture tubes, so they werenít interested in trivia. And so I published papers with my first graduate student and two Japanese came over and took a lot of pictures and all, and they started making [inaudible word] in Japan, so [inaudible phrase] so they were really friendly with me. So I wrote to them about coming over and he passed it to a guy in Nogoria, and I thought it was their polite way of saying no. But the guy in Nogoria is a friend of the current emperor. But I then backed off. I backed off because I thought they were — I took their thing to do that that they werenít going to do that.
And then I thought another good place to go would be Israel, because we had some visitors sometimes from the [inaudible phrase]. And I signed up to do that when the Yom Kippur War started. And Iím not Jewish, but some people think I am, so I was afraid to go over there. I didnít know it was going to be only three days. But anyway, so, I didnít go. And in the meantime I was down at the polymers division talking to Ebie [E.B.?], who is fairly active in the acoustical side too. And I guess all of us from Brown. He was president of the Washington chapter, which I used to go to some. But anyway, Ebie asked me what I was doing and I told him my sad story. He said, ďWhy donít you come here?Ē And he said, ďWeíll pay you. Come here. Come here for six months.Ē And I said, ďWell, I donít know.Ē I said, ďYou know, I got — other places were going to pay me.Ē He said, ďWhatís your salary?Ē I told him and he said, ďNo problem, no problem.Ē Makes you feel good, right? So he gave me a six monthsí appointment and I went five months. Now Iíd worked eleven months, six with this army project and five here, and my wife liked to travel, so we decided to go around the world. So I spent a lot of money and make a two and a half monthsí trip starting in the East to the Middle East, ended up in Europe and the [inaudible word] and so forth. But I had a month left over. So he said, ďWhy donít you come down one day a week?Ē So I did that for ten years. They have wonderful equipment there, and I put several graduate students in a car every Friday and drop them off at their different labs and picked them up again. So I did that a lot.
And then the tenth year of that I was asked to come to DARPA and run their NDE. They started the NDE program and they asked me to come and run it. And I did that for just about a year. I really was there a year, but I wasnít on the books the whole year. It took me a while to get clearance and all this kind of crap. But I didnít like it as much. Iím not anti-military, but Iíd been a professor I donít know, ten or fifteen years by then, and Iíd been pretty independent, like most professors. So I didnít like to take orders, even as a civilian. And so —
So this was all on sabbatical leave while you were at the —?
Yeah. Yeah, thatís right. The one day a week wasnít. I was just going down one day a week.
Green:But the rest of it was sabbatical. And so thatís the last time that I worked officially for the government. Somebody said, you know, you have certain retirement, and so I went and drew out my retirement. It wasnít that much money, but I took it all out because I needed the money. I may do it again sometime. But I consult for them some, but I donít do, you know, full time stuff. I probably wonít ever do that again. But it was interesting. Different problems. So the question started as ďWas I in the military?Ē, and the answer is ďNo, but Iím not anti-military.Ē
Bass:Yeah. And youíve done some work for [inaudible phrase].
Green:It just happened that when I was going through school, if you took certain exams or something, you didnít go. I would have gone in the Korean War. And, but they gave me exams to take, and it was technical exams, so I would guess that the scientist guys [inaudible phrase] scientist guys would do well on our thing, because I donít know any of my buddies in my class that went in. Not that they were trying to avoid it, but they didnít have to. Didnít have to, thatís all. Almost all my relatives went.
Bass:[inaudible word] some of these other questions, like did you ever attend a technical, business or trade school, I guess probably not, since you went the university road all the way.
Green:No, no, I never did that.
Bass:And correspondence courses, I guess that would be —
Green:No, I never did that either.
Bass:[inaudible phrase] unless you went to do a course off [inaudible word] some company or something or —
Green:Well, I did do this. I did take a couple different courses in — I took sculpture as an undergraduate and I took charcoal painting as a graduate student. The Rhode Island School of Design is right next to Brown, and I lived right across the street from the School of Design. So as a graduate student — also there was more women in that School of Design than there were in the physics department.
Bass:The other question was, were you married at the time?
Green:No, I wasnít. Also I played the role — one of my good friends — he is very active in the Acoustical Society, a guy named Giddy Madonni. I donít know if you know Madonni. He is a theoretician and heís down at what was [inaudible phrase] his whole career, I think. Now they call it Naval Surface Warfare Center in Carderock, but and since heís in Washington heís been my friend all this time, but while in graduate school he was still Israeli. And when the Yom Kippur War, maybe itís Three Day War, I donít know, some war they had over there. I think it was around the time of the exodus and so forth. I donít know what it was, right, but anyway; you know theyíre always fighting in the Middle East. So they were going to take away his visa, but he was married to an English woman, so he went back to London. But he had a beard, so all of his buddies grew beards, and we had a group picture taken and sent it to him for Christmas. And since I had the beard anyway, then I became a good guy for the art group. There was a coffee house down the hill.
Bass:You fit in?
Green:Yes. But when I was getting ready to leave, I knew [inaudible phrase] very well, see he had a beard like mine, and he kept asking me what I did and I wouldnít tell him, see. So I finally told him. I said, ďYouíre probably not going to believe this,Ē I said, ďbut Iím a physics major up here at Brown University. Iím getting my Ph.D. now and Iím leaving.Ē And he said, ďYou probably donít believe it either,Ē he said, ďbut Iím a graduate of Bryant Business College down the street.Ē He was playing the same kind of game.
Bass:Everybody thinks theyíre fitting into the art world and [inaudible phrase].
Green:Thatís right — a bunch of phonies with beards in there. But it was fun. Iím not an artist by any sense, but I enjoyed doing something like that on the side. But thatís about the only kind of thing I guess of the different courses I ever took.
Bass:I think weíve covered most of your career in terms of [inaudible word] you went through your education and then [inaudible phrase] back to —
Green:Yeah. Well, on this paper youíve got a few other things like, ďDid you ever do any protests or things?Ē I donít think so. I mean, I protested a lot of things, but never was it a group effort, you know what I mean? Just, you know, objecting to something that goes on in some organization that you belong to, or at the school, or something like this. I was in a fraternity as an undergraduate. It was an athletic fraternity, but I never got to play Varsity. I did run track. Because most of the guys — veterans — were coming back, then to school, and some of the guys were a lot older than us guys that were making all the first teams and so forth. Also, we sort of say that at William & Mary they had an athletic scandal. They were bringing in people that really were not supposed to be playing, even under assumed names and stuff. You wonder if they do it here or not. I donít know. But you donít know, I mean, but they donít do it anymore, at least not — but they had All-Americans and all kinds of stuff there. Itís a much smaller school than this, so you knew something must be going on, but in any caseÖ I did play, I belonged to a fraternity, and I played, you know, in inter-fraternity games, and so forth. I played a lot of baseball. It was always softball when I was growing up, so I did that a long time. Even in Brown we used to play the other graduate schools, both basketball and softball.
Bass:So weíll continue the ASA oral history, and what weíre going to do is weíll review your professional career.
Green:Okay. After I graduated with my Ph.D. the first place I worked was in the Underwater Explosions Division of the Norfolk Naval Shipyard in Portsmouth, Virginia. After six months there, I was notified I received the Fulbright postdoctoral fellowship to go to Germany, and I did that in the fall and stayed there a year. While I was in Germany, the group that I was working with at the Naval Shipyard moved to Carderock, Maryland and therefore I was — had the possibility of going there. In the meantime, I received an offer to enter the Engineering School faculty at Johns Hopkins and I did join the Mechanics Department. Iíve been in one department or another at Johns Hopkins for forty years and am currently director of a Center for Nondestructive Evaluation, a chaired professor in the Engineering School with my active appointment being in the current Material Science and Engineering Department.
Green:Well, while at Hopkins — I might mention that while at Hopkins, I spent sabbaticals at Aberdeen Proving Ground, at the National Bureau of Standards — now named National Institute of Standards and Technology — spent time at our Applied Physics Lab where I also hold an appointment as principal research scientist and worked approximately a year at DARPA, the Defense Advance Research Projects Agency.
Bass:So weíll go on now. Publications. Have you published a book or write a book?
Green:I wrote one small book, but I have edited — I run an international conference every two years out of my center, and we just had the tenth one in Japan. Sometimes, Iím the sole editor of these publications. Sometimes Iím not. Usually, if itís in a foreign country itís co-edited with me, perhaps another guy at Hopkins, and usually one or two people from the country where we do it. I have about 270 publications in refereed journals, and most of them deal with either measuring material properties by some destructive or nondestructive technique or something similar to that.
Bass:So what was the title of your book that you wrote? Do you remember?
Green:Ultrasonic Measurement of Mechanical Properties.
Bass:Now weíll talk a little bit about your family. Youíre married?
Green:Yes. Iíve been married for thirty-eight years to the same woman. Her name is Sidney Truitt Green. She now is assistance to a dean at Johns Hopkins — the dean that advises undergraduate students. I met her in my hometown of Portsmouth, Virginia. She lived one block from where I used to live. And my best friend through elementary school and high school, a boy, lived in that house until he graduated, and then her family moved in. We got married at a Methodist church in that same neighborhood, and as I said itís roughly — weíve been married thirty-eight years, and I dated her about a year or two before, maybe forty years ago, something like that. Two children — two girls. The oldest one has her Ph.D., which she got with me. She got a Bachelors at Johns Hopkins, a Masters at Brown and a Ph.D. at Hopkins. The youngest one got a Bachelorís degree at Hopkins, went halfway through law school and decided she didnít like law. She currently works at the Johns Hopkins Hospital in an office capacity.
Bass:So you have two grandchildren.
Green:Two grandchildren. One is close to a year old, the newest one, and the oldest one is close to three years old.
Bass:Well, itís going to be a while before they do their bachelorís degree.
Green:Well, I think so. You never know these days.
Thatís right. At the age of seven —
Green:Well down here it also lists entertainment, so I guess my favorite is books. Mainly mystery books.
I find I can relax and lose myself in reading pretty easily, so I do that a lot to relax. Probably unfortunately, the second is TV programs. But I just — sometimes I listen to them, sometimes I donít, but itís like some noise [in the] background. It might be, for some reason. And I like sports a lot. I donít go to movies much anymore, and I donít dislike music but Iím not a singer by any stretch of the imagination, so I guess books and TV programs and then sports. I used to be more [inaudible word] in sports, professional sports, but Hopkins is not noted for its sports. They play — the homecoming is in lacrosse season, not football season, and they [inaudible word] D or C or something as far as the teams they play in most other sports.
Bass:What about Brown University?
Green:Yeah, they play in an ivy league [inaudible phrase] play guys like Harvard, Princeton.
Bass:In terms of art? I guess you inspect art.
Green:Yeah. I took sculpture as an undergraduate and I took charcoal drawing as a graduate student for the fun of it, so — I donít do any. Iím not a real artist. In fact my wife threw out all of my art, all of my sculpture. No appreciation for the [inaudible word].
Bass:No appreciation for the finer things in life.
Green:Thatís right, thatís right.
Do you have a favorite quote? This is always —
Green:No, I donít, but despite the fact — well, Baltimore is south of the Mason-Dixon line, but I still consider myself a Southerner. I like the South, I like Robert E. Lee. Iím named after him. In fact, my fatherís real name was Robert E. Lee Green. He was born on his birthday. But Iím a junior, and my father never used the Lee part, so in those days they didnít have birth certificates, or he didnít have one, and so — In fact, all of my other relatives [inaudible phrase] these people have an ďeĒ on the end of their Green. He didnít. He thought that was too fancy, so my father changed his name, and since Iím a junior, so Iím just Robert Edward Green, not Robert Edward Lee Green, Jr.
Bass:Do you have any particular hobbies?
Green:I guess not. Now I used to play a lot of sports. I donít do much now I guess as far as that goes. We go to some — my wife likes baseball very much. Her father loved baseball, and Baltimore does have a new ballpark with a fairly decent team, so we go to quite a number of baseball games. I donít go to anymore football games anymore, but the old stadium was one mile from Hopkins where they played both baseball and football and I could walk to the games very easily, and so I went to most of the games when they were there. But now they moved further downtown and I just havenít bothered. They are very expensive now compared to the old days too.
Bass:More money floating around. People like to spend it on tickets.
Green:Well itís extremely expensive now.
Bass:Well, the teams are, you know, the cost of having a team is probably expensive as well.
Bass:Whatís in your future plans?
Green:Probably keep [inaudible phrase] administration for a while, but theĖ Itís very difficult for me to say. I donít think Iíll ever stop doing some scientific or engineering work, but I might cut back on the level of it. Iím just guessing that I would probably end up — I kind of like to work at certain things around the house, and so probably, you know, odds and ends, but maybe consult one or two days a week, something like that, with one of the government or industrial people in the Baltimore or Washington area.
Bass:Your grandchildren are going to keep you busy too [inaudible phrase].
Green:Yeah, thatís right. I enjoy playing with them now. Well, the oldest one is running all around. The youngest one is just starting to walk so —
Bass:Mineís fifteen months and sheís everywhere, so. So is there, I guess, anything else that you would like to add?
Green:No, nothing I can think of.
Green:Iím relatively content. I mean — Iíve had some, well, I will say this. Iíve had some outstanding students, in my opinion. Iíve been very blessed with the quality of the students I have had, and most of them have done very well in their individual professions. A large number of them are professors at other schools and those who arenít have done very well in industry. To the best of my knowledge only one has his own company, and his wife is my student also, so they both are doing very well making more money than any of the rest of the students Iíve had.
Bass:So how many? Do you have a number of how many Ph.D. students you graduated and masters students?
Green:Iím guessing forty or fifty, something like that. I usually have about three or four a year.
Bass:Thatís a good group of students. You have a good following.
Green:Well, whatís happened — it changes over the years. You know, now I have a lot of them that are doing other things in the Baltimore-Washington area. I mean, I have one in Lawrence Livermore National Lab doing her thesis, one at the Nuclear Regulatory Commission, one at Federal Highway, [inaudible phrase] at the Smithsonian. So, some of these are a little more mature, a little older than the average graduate student. And then I still have a couple who are relatively new. Iím taking a new student this fall, and I took one last fall, but Iím not going to take too many more because it usually takes five or six years if they are going for the Ph.D., and there is some possibility of a colleague who could pick them up, but there are not as many colleagues in the field I work now, that could pick them up.
Bass:And students usually decide to go with a particular advisor in order to get their degree under that advisor.
Green:I think the ones ďin the knowĒ do. I mean, some people go where they get the most financial support if they donít have the money to go someplace else, or go to a school nearby or something like that, but I think if they can that they do. And also, if youíve been in the business a long time like myself, some people get to know you and know if you are interested in this, go to that school or that other school. But itís kind of like your center here. Someone was in striking distance or [inaudible phrase] wanted to do acoustics or something, they would come here, see. You know, acoustics in a broad sense, I think rather than go somewhere else. So, there are only two centers of nondestructive evaluation in the whole country. Thereís not five in the whole world. Now thatís getting bad. I think itís good. In fact, thereís only two in the United States. I say we are the number one and number two. Of course, I think weíre number one and the other guy thinks heís number one, but in any case, and you can say, well, it canít be an important discipline because thereís only two centers. So thatís what my enemies say.
The problem is, itís a cross-discipline —
Yeah, thatís right.
Bass:It is the problem of setting up something like nondestructive evaluation. You have people from, you know, different fields interacting.
Bass:Itís hard to do inside a University environment.
Green:Yeah. Well, thatís [inaudible word] the center, not the department. I mean, I couldnít really do it as a department. Thereís no way I can do it really.
Bass:But even putting it together as a center, I think it makes it difficult because you have — I mean you have to bring people together from different departments and that can be sometimes difficult to do.
Bass:You know people sometimes see things differently from say a mechanical engineering viewpoint and from a physics viewpoint. Trying to get all these people interested into one center.
But you can... I mean, some of them will do it. I mean, it depends on what the subject is. Well, sometimes too, you just go find the guy. I mean, when I first started doing optics stuff, I wasnít doing optics and I thought an optical thing might be good to try, and I went over to electrical engineering where they were doing a lot of optics and talked a guy into doing it. And then later on he [inaudible word] write many research proposals. A real smart guy, just kind of a shy guy, and so once we got rolling, we both wrote proposals and I sold them and he was better off and he got tenure because of it. It was about my age, but he didnít have tenure. And since he started going this he had enough publications and didnít raise much money, so they kind of went together. Because [inaudible word] many graduate students and couldnít support them except as TAs. So itís kind of mutually beneficial. But you kind of keep your eyes open and do stuff like this.
Bass:Well, weíd like to thank you for doing this ASA oral history for the Acoustical Society of America and I hope you have a safe trip back home.
Green:Well, thank you very much.