2022 Timoshenko Medal Acceptance Lecture: A Trip the Light Fantastic Presented at the ASME Applied Mechanics Division Banquet, Columbus, OH, November 2, 2022.
2023; ASM International; Volume: 91; Issue: 1 Linguagem: Inglês
10.1115/1.4063864
ISSN1528-9036
Autores Tópico(s)Advanced Machining and Optimization Techniques
ResumoMichael Albert SuttonMichael Albert Sutton Friends, colleagues, and family:First, I want to express my deepest appreciation to the Applied Mechanics Division of ASME for bestowing this honor, which I feel is the highest professional honor in our field and one for which I am truly humbled to receive. During my presentation, I will do my best to illustrate that, the simple fact that I am here tonight presenting the 2022 Timoshenko Medal Lecture, is one of the finest examples of the statement that America is a land of opportunity where anything is possible.I was born in 1950 in my parent's home on Main Street in the small town of Carmi, Illinois, growing up in a lower middle-class family in rural southern Illinois. My father graduated high school in 1925 at the age of 23, riding a horse to school every day while working on the family farm year-round. My mother graduated high school in the middle of the Great Depression, working in a rooming house after her father passed away suddenly at age 30, so that she could have a warm bed at night and a good meal. My father opened Sutton Shoe Store in Carmi, Illinois, circa 1936, an auspicious time to do so. However, with my mother as a successful proprietor in later years, the store stayed in business until 1976 when our small-town businesses met head-on with the world of superstores.During my early years, and with no internet, I spent most of my days outside, wandering by myself in the miles and miles of woods, lakes, streams, ponds, and rivers so common in the area. In the process, I developed an active imagination, constructing a virtual, immersive world of ballparks, forts, and battlefields. My father rented a small farm and, whenever possible, I would chase rabbits through the grasses while he tended the horses and cows and mowed the 40-acre field. I was taught to shoot at the age of eight, hunting quail, rabbits, and doves with my father, older brother, John, and my uncles Frank and Charles Kaffenberger for several years. In many ways, this was an idyllic time for a young boy, with few responsibilities in my virtual world. Even today, it brings back fond memories.Though my parents had no more than a high school education, and they were far from Berkeley and Haight Ashbury with limited understanding of the growing counter-culture movement, they were well aware of the changes in society that were occurring in the 1960s. They encouraged me to be a good student so that I could go to college. Due to the relative isolation that I had experienced in the early years, and my complete lack of social skills, I only had a few friends in high school. Considered by my classmates to be a “nerd,” I reinforced this perception by bringing a leather bag to school, transporting my books from class to class in the bag while wearing black horn-rimmed glasses; though not fashionable, they were all my parents could afford.Even though I graduated as high school valedictorian in the turbulent year of 1968, my parents could not afford to send me to college. Fortunately, I was a good golfer and, with considerable help from folks in my hometown, I received a full golf scholarship from Southern Illinois University in Carbondale (SIU-C) and completed my B.S. degree in Engineering Mechanics and Materials in 1972.After graduation, I accepted a position as an analyst with Consolidated Coal Company. Instead of assigning me desk space in an office, management decided to assign me to become a coal mine foreman in Sparta, Illinois, and told me to meet at the mine with my supervisor for training. When I arrived at the mine after purchasing work clothes and steel-toed boots, my supervisor was nowhere to be found. So, I was given a beat-up old truck and told to drive around the strip mine to get an overview of its operation. Passing massive Le Tourneau coal trucks, I entered the active mine region and could see the 20 story Bucyrus-Erie bucket stripper on the left, rising tall above the surrounding fields. Seeing all the coal trucks over on that side, I headed down an empty incline on the right until I saw the open pit area that was left after the coal had been mined. With no one around, I parked on the incline and walked down into the open pit full of boulders and detritus left by the bucket stripper. Walking into the pit, I could see the 6-foot-deep coal seam near the bottom of the 100-foot sidewall. As I continued along the open pit, I was pondering what all the colorful wires strung along the wall of the pit might be used for. After walking for several yards, I heard a horn honking loudly behind me and saw a truck bouncing along the rugged pit and heading toward me at high speed. When the driver reached me, he yelled to get in the truck. Before I was properly seated, we sped back down the pit and headed up the incline. Shortly after we passed the truck that I had parked on the incline earlier, our truck was thrown several feet in the air by a deafening blast wave, slamming me into the top of the cab. After we came to a stop, I turned to see my truck had been destroyed and the pit where I stood just a minute earlier was covered in nearly a hundred feet of overburden. When I was finally sent home later that day, after lengthy interviews and considerable yelling, I knew my future was not in coal mines but in more intellectual pursuits. Thus, I called one of my professors, Dr. Phillip K. Davis, who was Chairperson for the Engineering Mechanics and Materials Department at SIU-C, to arrange for my return to school for graduate study a few months later.After returning to school, I completed my M.S. degree in 1974 in computational fluid mechanics with Dr. Davis. I then took industrial positions at Bettis Atomic Power Laboratory in West Mifflin, PA, and Babcock and Wilcox Company in Mt. Vernon, IN, each lasting less than 2 years. Through my industrial experiences, I learned three things about myself. First, when working on any project, I wanted to know why. Second, I needed to improve my mathematical and theoretical backgrounds so that I could solve more complex problems. Third, I could not work collaboratively with folks that were unwilling to take whatever time was necessary to learn why. It was at this point that I decided industrial positions were not going to work for me and I should return to school and obtain a Ph.D.Fortunately, I received good advice from Prof. William O. Orthwein at SIU-C, Ivan Elliot, an SIU-C Board of Trustee member in my hometown, and my M.S. advisor, Prof. Phillip K. Davis. Since SIU-C did not have a Ph.D. program at that time, they suggested I consider the University of Illinois at Urbana Champaign (UIUC). After Prof. Orthwein introduced me to my future Ph.D. advisor, Prof. Charles E. Taylor, I joined the Theoretical and Applied Mechanics (TAM) Department at UIUC as a teaching assistant. Taking a phrase from Prof. Reddy's Timoshenko lecture, “this was the beginning of my journey in mechanics.”When I arrived at Talbot Laboratory which housed the TAM Department at UIUC in the fall of 1977, I met with Prof. Taylor. He immediately said that I should call him “Chuck” or not come back, which was difficult for me. I discussed with him expanding my theoretical background by taking classes in mathematics, physics, and computational methods. He immediately agreed, providing a list of outstanding educators as I began my journey in mechanics. Taking two or three classes each semester from world-class faculty such as Arthur Boresi, Marvin Stippes, Henry Langhaar, John Rudnicki, Robert McMeeking, James Phillips, George Sinclair, George Costello, Ray Langebartel (Math), Ronald Adrian and, most influentially, Donald Carlson and Robert Miller, was the equivalent of drinking from a firehose, and it was the most exciting time in my entire education. In some ways, my experience seemed to parallel those noted by Prof. Bazant in his 2009 Timoshenko Lecture, when he took multiple courses from Prof. Brdička at Charles University in Prague. For me, the knowledge gained in these years underpinned my entire research career while also preparing me to teach classes in solid mechanics, fracture mechanics, continuum mechanics, and experimental solid mechanics.Prof. Taylor's laboratory was located on the third floor of Talbot Lab. The lab was composed of three small rooms. One room was filled with many of the scattered-light photoelasticity slice specimens used in Prof. Taylor's nozzle–shell intersection studies, along with an exceedingly small dark room in one corner for developing film. In another room, a ruby laser system was being used for dynamic experiments. In the third room, an 18-inch thick concrete slab on a rubber inner-tube foundation served as an optic bench for quasi-static interferometry studies. Since a student, Michael Tafralian, was using the ruby laser for his research, I focused on the theory of laser interferometry for slope and curvature measurements in small structures before beginning optical experiments on the concrete slab. Fortunately, a new student arrived from Taiwan, Yuh-Jin (Bill) Chao, who had experience with interferometry systems. He took considerable time to show me how to construct a speckle interferometer and then demonstrated how the system could be used to obtain fringes related to specimen deformation. Since that time, Bill has remained a close friend.As I became more experienced in the laboratory, I became acutely aware of the major issue we faced: developing the exposed film and then attempting to analyze the film to extract meaningful measurements. Not only did I spend hundreds of hours developing film, which was prone to failure during chemical processing, I also spent countless hours trying to analyze the as-developed film to extract accurate point-by-point measurements, which I learned was either extremely time-consuming and tedious, or virtually impossible. Given the difficulties experimentalists faced with film-based measurement methods, the words of Prof. Biot in his 1962 Timoshenko lecture are remarkably prescient.It was during the last year of my Ph.D. work that I first learned of the potential for digital reconstruction of images to eliminate film and automate the extraction of data from images. A fellow student, Frederick Mendendall III, had worked with computers during his M.S. degree at Michigan State. Fred envisioned using video cameras to record images in digital form for computer-based post-processing and suggested this approach to Prof. Taylor. Since Prof. Taylor retired from UIUC and moved to the University of Florida during this time, the opportunity was not pursued in our laboratory. However, from conversations with Prof. Taylor, I learned that a group at the University of South Carolina was making progress on a similar idea. Thus, I was fortunate to join the South Carolina group in 1982 to see whether we could develop a much easier-to-use, simpler measurement system that could be used in a broad range of engineering problems, traits that are embodied in digital image correlation (DIC) methods.When I moved to South Carolina, I joined the on-going research effort led by Profs. William Ranson and Walter H. Peters III, having confidence that my education at Illinois prepared me for the opportunity. Working closely with Ph.D. students T.-C. Chu and Stephen McNeill for single camera imaging studies, key issues were identified in digital image acquisition, image reconstruction, software development for efficient image analysis, and extraction of measurements from comparative image analysis. The ubiquitous terminology for the vision-based measurement method, DIC, naturally arose from our optical methods backgrounds. Since reference and deformed images in laser speckle methods are “compared” through optical cross-correlation to extract encoded measurements from the images, and a variety of correlation methods are available in the digital domain, the abbreviation DIC was adopted.The most confounding difficulty in our earliest experiments was related to the digital image acquisition process. In the 1980s, video cameras obtained analog signals that were transferred to an A/D board on a computer for digitization and storage. Since we did not have a video camera, we borrowed one from the photographic group and began our experiments. When we attempted to digitally correlate the images stored on the computer, we obtained a strange set of displacement measurements with large variability and, in some cases, poor correlation values. After multiple attempts gave comparable results, we began to test each part of the process. First, the software was tested and retested with artificial image arrays, confirming that software was not the issue. We then used an oscilloscope to confirm that the analog signal from the video camera was in the correct voltage range and had the specified lag time between individual rows. Next, the A/D board was removed, tested by our electronics technician, and shown to be operating correctly, though we replaced it with a new one just to be sure. After 6 months of fruitless testing, we asked a colleague in the photographic group if he had a different camera we could try. When he came over to our laboratory, we showed him our results. As he looked at our data, his only question was “How did you handle the interlacing?” Prof. McNeill and I looked at him and, in near perfect harmony, said “What is interlacing?” Once we understood that 1980s video cameras acquired all the odd rows and then acquired all the even rows, storing them sequentially as they were scanned, we reconstructed the recorded image, line by line in the correct order, and reanalyzed the images to obtain the first set of consistent DIC displacement data while running our software on a VAX 11-780 mainframe: each 31 × 31 pixel image subset took 30 min to analyze in those early years. Suffice it to say, I will never forget the word “interlacing.”During this time, we initiated our first advanced solid mechanics applications in fracture using a single camera imaging system to measure crack tip fields and estimate stress intensity factors. During the next few years, single camera DIC measurements were obtained for a range of solid mechanics problems, including mixed-mode loading of an aluminum fracture specimen and strain measurements on high temperature alloys undergoing tensile loading at elevated temperature: the latter studies were completed in 1995. It was during this time that we addressed my personal favorite solid mechanics application. Working with my Ph.D. student, Jin Liu, we developed a long-term experimental system and performed a series of high temperature loading experiments on a C(T) fracture specimen, obtaining DIC data every few minutes for 400 h. Combining theoretical creep fracture concepts that we were learning in real time with full-field deformation measurements on two high temperature alloys, the evolution of crack tip fields and creep fracture parameters was studied in detail. It was a heady time for both of us, developing a long-term, high temperature DIC measurement system, while simultaneously studying an interesting problem. Though the published papers have received few citations over the years, I am particularly fond of the research for both the technical contribution as well as for what we learned throughout the process.Even as we continued to use single camera imaging systems in some applications, we had become aware of the major limitation in single camera imaging, out-of-plane motions induce in-plane strain errors. These observations led to the development of stereo-based imaging systems to overcome the limitation. The first proof-of-concept stereovision imaging experiments at University of South Carolina (USC) were performed by Prof. McNeill and his student, Marc Paquette, in 1988. This was followed in 1990 by Prof. Chao, his student, Dr. Luo, and me completing the development of a laboratory-scale stereovision system. The system was then used to obtain the first full-field, three-dimensional surface displacements and surface strains near a crack tip during tensile loading of a C(T) specimen.A watershed event in the development of modern StereoDIC systems was my 15-month sabbatical leave at NASA Langley, begun in 1992 to perform research in the US Aging Aircraft Program that was led by Dr. Charles E. Harris. Noting that full-field surface deformation measurement methods did not exist to help validate computational predictions for non-planar aircraft components, we began development of the first-ever, field-capable, three-dimensional surface deformation measurement system for curvilinear, full-scale aerostructures. Confirmation of the StereoDIC technology and its field capabilities for non-planar structures was demonstrated outdoors in rainy, windy conditions at Boeing in Seattle, WA in 1995, when Jeff Helm, Stephen McNeill, and I obtained measurements on both the sides and top of a Boeing 727 test article during combined tension, torsion, and internal pressure loading, completing the experiments on February 5, 1995, which was my 45th birthday. Given our unwavering belief in the measurement methodology, and the disinterest shown by both state and federal agencies that declined to pursue its development, a small business, Correlated Solutions Incorporated (CSI), was formed in 1997 to transfer DIC technology to industry, academia, and government laboratories, with the first StereoDIC system constructed and installed in the US Air Force Research Laboratory in Dayton, OH for Dr. Clare Paul and Colonel Scott Fawaz in 1998.During the first two decades of development that were discussed earlier, the broader community expressed minimal interest in the innovative DIC measurement technology, with few publications in the literature. All of this changed at the dawn of the new millennium as computer technology became more accessible and processing speeds increased, making computer-based DIC methods more attractive. As interest in DIC grew, key advances in the methodology occurred at the dawn of the new millennium. The advances included (a) demonstration of the effect of higher order shape functions, (b) development of a validated theoretical description for StereoDIC equations and, most importantly, (c) a theoretical explanation for the remarkable, milli-pixel accuracy of DIC displacement measurements. It is the latter of these developments that requires further discussion.In the mid-1990s, Prof. Chao introduced me to Prof. Hans Weber, a faculty member in Chemical Engineering at Karlsruhe University in Germany. One of his students, Hubert Schreier, was interested in pursuing a Ph.D. in the USA and agreed to join our group circa 1996. Dr. Schreier's education included an interdisciplinary background in computer science and control theory, areas that are uniquely relevant when performing research with DIC methods. Like the “interlacing” issue noted earlier, another area which had perplexed Prof. McNeill and I was the experimentally demonstrated lower bound of ±0.01 pixels on displacement measurements. To identify the source of the lower bound, we modified correlation algorithms, used synthetic images with different levels of contrast and different spatial frequencies, and tried different polynomial intensity interpolation functions, none of which were successful. One day in late 1999, Hubert knocked on my office door and said that he had something for me to see. He then showed me a plot of DIC displacement error versus the magnitude of displacement for various intensity interpolation methods. Not only were the trends interesting but also the plot for one of the interpolation methods showed a maximum error that was far less than the previous threshold of 0.01 pixels. He then proceeded to explain how he and a visiting colleague, Joachim Braasch, had used control theory and his previous studies in computer science and computer vision to develop optimal interpolation functions that would minimize DIC displacement measurement errors. Even as I write this, I have cold chills in recognition of the import of this contribution, which showed that it is possible to obtain displacement measurements with an accuracy that is 1/1000th or smaller of the image sampling frequency (one pixel), providing theoretical confirmation that the method can obtain even elastic displacements and strains with high accuracy.Since there may be future entrepreneurs that read this, I would like to share three personal thoughts regarding technology transfer and small business development. First, and foremost to me as an academician, is the inevitable conflict that arises when active faculty members start a business. Issues such as intellectual property, university commitments (teaching, research, and service), graduate student research activities, and university resources (computers, laboratories, and technical staff) should be carefully considered, professionally and openly discussed among all stakeholders, and plans cooperatively developed and implemented to maintain a healthy relationship between the academic institution and the new business. For situations where a faculty member expects to spend substantial time on business development and operational aspects, such stakeholder plans may involve requests and approvals for leave from their faculty position for a specified time. In my case, it was straightforward to maintain a good relationship with the institution since I primarily focused on academic activities while former students developed and grew the business to transfer DIC technology worldwide. Over the years, I have continued to try and provide long-term vision to the company, as appropriate, to help guide future developments.A second point that I would like to make is that successful small businesses take time to become self-sustaining, even if there is an influx of capital to expand more quickly. If an individual is planning to grow and sustain a business as a long-term enterprise, one should not expect to show a substantial return during the first few years but should show steady improvement over time as the product obtains a foothold in the market. Though CSI has been in business over 25 years, it was several years into the new millennium before CSI was self-sustaining.A final point is related to the individual's level of commitment to a concept and the resulting product. Many folks start small businesses to monetarily capitalize on a current need but have no vested interest otherwise. In such cases, the goal is to develop a concept and sell the business as soon as possible to maximize return. In situations where the product takes longer than expected to develop, the likelihood of success decreases significantly since dissemination of a product was not the long-term goal. Conversely, CSI was, and is, based on a commitment to the concept of developing and disseminating a product for which we have a vested interest that has underpinned and sustained the company for well over two decades. Given these two disparate approaches, individuals should acknowledge in the early stages which business development strategy they are going to pursue and be aware of the issues that may arise over time for each approach.Today, DIC methods are used worldwide in industry, government laboratories, and academia. In myriad cases, full-field DIC measurements are employed in model validation. In other applications, DIC measurements are part of a hybrid experimental-computational model for parameter identification. One does not have to look far to see why the method is so popular. As the first, fully digital, full-field measurement system, its power and speed improve as computer technology advances and processing speeds increase. Not only is image processing faster each year, but imaging technology also improves, with larger digital camera arrays increasing measurement data density and improved electronics increasing camera framing rates for high-speed imaging applications. Taken together, these observations regarding DIC and its continued growth in a broadening range of applications lead me to paraphrase Professor Rice when he remarked in the 1990s on the opportunities for modeling contributions. “Come on in, the water is fine!”I want to thank my colleagues, students, and family, especially my wife Elizabeth Ann Severns Sutton, who have contributed so much to my professional career; without their support this moment would not have been possible. I must reiterate that this country, America, is a place where hard work, commitment to your profession, and unwavering belief in what you are doing can make anything possible and where accomplishments that make a difference eventually will be appreciated. My unimaginable journey along this uniquely American path truly has been a “trip the light fantastic” that I can only look back on with a mixture of marvel, joy, pride, and gratitude. Thank you and all the best to you and your families.
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