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Panel discussion on the state of the art and future direction of high-temperature composite structures
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Composites Science and Technology 50 (1994) 129-136
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P A N E L DISCUSSION ON THE STATE OF THE A R T A N D F U T U R E D I R E C T I O N OF H I G H - T E M P E R A T U R E COMPOSITE S T R U C T U R E S C. C. Chamis NASA Lewis Research Center, 21000 Brookpark Road, MS 49-8, Cleveland, Ohio 44135, USA
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S. N. Singhal Sverdrup Technology, Inc., Brook Park, Ohio 44142, USA (Received 15 February 1992; revised version received 15 June 1992; accepted 4 February 1993) Abstrad This article summarizes the discussion of a panel: 'On State of the Art and Future Directions of HighTemperature Composite Structures', A S M E Summer Annual Meeting, Columbus, Ohio, 18June 1991. The panel objective was a joint industry/academia/government perspective on: where are we, what are the inhibiting factors, and what is needed for rapid progress? Topics addressed include computational simulation versus traditional approaches, reliance on computational simulation versus testing, computational simulation of material processing and/or fabrication, design perspective, technology base, interdisciplinary, coengineering, probabilistic description of uncertainties, educating future researchers, government~industry~ academia roles, and competitive advantage considerations. Select panel conclusions are: (1) increase use of computational simulation, (2) include material and fabrication process in the simulation, (3) apply probabilistic assessments to quantify uncertainties and minimize testing throughout the design/qualification~ certification cycles, and (4) mandate closer cooperation among industry, academia and government.
technology base encompassing various aspects of the related technology. To bring together the engineers and scientists conducting relevant research, a symposium was sponsored by the ASME Applied Mechanics Division Committee on composite materials. The symposium was titled 'Mechanics of Composites at Elevated and Cryogenic Temperatures' and was held in Columbus, Ohio on 16-19 June 1991. A special segment of the symposium was a 'meet the press' style panel discussion. The panel was chaired/moderated by Christos C. Chamis (CCC) of NASA Lewis Research Center and organized by Surendra N. Singhal (SNS) of Sverdrup Technology, Inc., Cleveland, Ohio. The panel consisted of experts on topics related to the symposium theme. The panelists were: (1) I. M. Daniel (IMD) of Northwestern University on Experimental Mechanics---Education; (2) T. G. Fecke (TGF) of US Air Force on Engine Technology; (3) R. L. McKnight (RLM) of General Electric on Advanced Engine Development; (4) S. N. Singhal of Sverdrup Technology, Inc. on Support Service Staffing; (5) G. J. Simitses (GJS) of University of Cincinnati on Aerospace Design--Education; and (6) J. A. Suarez (JAS) of Grumman Aircraft on Advanced Technology Development. The specific topics addressed/discussed include: (1) Computational Simulation versus Traditional Approaches; (2) Reliance on Computational Simulation versus Testing; (3) Computational Simulation of Material Processing and/or Fabrication; (4) Design Perspective, Technology Base, Interdisciplinary, Coengineering; (5) Probabilistic Description of Uncertainties; (6) Educating Future Researchers; (7) Government/ Industry/Academia Roles; and (8) Competitive Advantage Considerations. The focus of the discussion was: (1) Where are we?; (2) What is really
Keywords: composites, computational simulation, high-temperature, testing, uncertainties INTRODUCTION Extreme temperature composites are emerging as materials with potentially high payoffs in applications such as aerospace structures. Realization of these payoffs depends on the development of an adquate Composites Science and Technology 0266-3538/93/$06.00 © 1993 US Government. 129
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inhibiting?; and (3) What do we need to do for rapid progress? The objective of the panel was a joint industry/academia/government perspective on state of the art technology barriers and crystal ball forecasts for rapid progress in the areas of extreme temperature composite mechanics. The panel discussion is summarized below by topic. The comments by the panelists on each topic are indicated by the initials of each panelist. The audience also contributed. Their comments are indicated as 'Audience'.
COMPUTATIONAL SIMULATION VERSUS TRADITIONAL APPROACH
RLM Traditional approach is state of the art. Testing has not paid off. We need to provide designers with optimization and probabilistic computational tools. We can simulate individual discipline, linear cases, displacements, frequencies etc. We need coupled effects---thermo-mechanical fatigue, quick turnaround time, coupled multidiscipline methods, easyto-use codes. TGF We can predict stresses but there are difficulties in predicting life and effect of environment (erosion/ moisture). Quantifying defects/cracks through or around fiber takes time. We need to simulate life more accurately. We need to use simulations to guide our experiments. We need to conduct short term tests to predict long life. JAS Testing is prohibitively expensive. We have relied on computational simulation for years now. One concern is how we can use it to reduce our test certification part of the development cycle. GJS It is not clear what simulation is and what it is intended to do. One cannot rely on analysis alone. Mathematical models are okay. Need quick answers. Fundamentals are still important. The integration is most important: analysis, numerics, and experiments. IMD Experiments are important. In our laboratory we do a lot of experiments (NDE) and analysis for integrity evaluation and life prediction. We need integrated computational simulation coupled with an experimental approach.
SNS Simulation can be used to model a variety of physical phenomena quickly and even help design experiments.
Audience Carl Herakovich: Computational simulation saves money. J. N. Reddy: Mechanics has to be integrated with the methodology through the computational mechanics approach. Ozden Ochoa: We need an integrated experimental and simulation approach. John Gyekenyesi: Use computational simulation for ceramics. Need to test also. Roberto Ballarini: These things are said, but not followed. Concluding remarks Computational simulation is frequently interpreted to mean analysis using the computer. Also, it is interpreted to involve data fitting. It is needed especially with new systems. Apparently a more precise definition for computational simulation is needed. The general trend (based on expressed and implied comments from the panelists) is judicious substitution of computational simulation in lieu of testing, with integration of simulation and testing. Suggestive definition of computational simulation Elemental formulation with profusive computational simulation in contrast to computer-aided solution. Where are we ? Traditional approach with reliance on testing. Realization of need for computational simulation. What is really inhibiting? Easy-to-use coupled multidisciplinary codes with quick turn-around time to be suitable for extensive use in preliminary designs (PD) to evaluate alternative concepts. What do we need to do for rapid progress ? Use of computational simulation for minimizing testing and determining key experiments/variables, followed by corresponding experiments integrated with simulation.
RELIANCE ON COMPUTATIONAL SIMULATION VERSUS TESTING RLM Project managers are constrained by time and cost. They want combinations which will help with these. Need more sophisticated personnel and more complex machinery in conjunction with computational simulation. About 60-70% of the effort is devoted to computational simulation now.
High-temperature composite structures--panel discussion TGF Designer's biggest problem is stress concentration, 95% of the time. It is difficult to simulate stress concentration. More and more simulation will be used. However, testing cannot be and should not be eliminated. It should be held to a minimum with maximum benefit. SNS Simulation must precede testing in the development of new systems and in the qualification of new materials. IMD One cannot identify/discover physical phenomena without conducting exploratory testing. Analysis without test can be misleading; reliance on analysis alone could be disastrous. Test at the structure level as well, not just coupons. Regardless of extent of analysis or prior testing, an aircraft cannot be certified without proof testing. CCC Simulate fabrication process also. JAS Testing is held to a minimum and usually in critical areas. Mostly used for full/prototype components. Spend money on testing at basic level, eliminate building blocks. GJS Analysis verification needs control testing. Testing reveals what was missed in the assumptions for the analysis. Can't model full scale. Question is how effective are these tools. Answer is global model of the whole NASP. TGF Test full size engine. It is less expensive to do it in combination with simulation. SNS How can one test without knowing what he is looking for? On the other hand, testing is needed to ascertain that the analysis results are credible. Concluding remarks Simulation versus testing is an unresolved question; it means different things to different people. In new technology development, participant will handle it according to their past successful experience. The following suggestive procedure may help: (1) Paper designs should be computationally simulated. (2) Material capabilities should be simulated with verified control experiments.
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(3) Final designs should be simulated with material models that have been calibrated. (4) Precise definitions for validation, verification, and calibration will help clarify this unresolved question. Where are we ? Some computational simulation and a lot of testing. What is really inhibiting 9. Demonstration of integrated simulation/experimental approach with minimum experimentation guided by simulation. What do we need to do for rapid progress .9 Develop tools for specific simulations of physical phenomena currently investigated via experimentation at all levels (coupons to structure) and demonstrate significant time and cost reduction with same or better confidence. COMPUTATIONAL SIMULATION OF MATERIAL PROCESSING A N D / O R FABRICATION (MP/F) TGF We definitely need this. Because now we have no way of establishing how good is good and we compensate with extensive testing. We don't know how to do it yet. Several programs are underway to track behavior from laboratory sample behavior to component retirement for cause (birth-to-death). Residual stress in manufacturing is generally 60% of the elastic stress in composites. RLM This will be very helpful. The major drawback is a credible way to do it. Efforts should be initiated. Computational simulation can give a running start to determining what materials to use. CCC Start from structural requirements, define the fabrication process, and from there we can establish the degree of quality we can afford? IMD To simulate a process we must know the material, its desired properties and identify the process variables. There are too many variables. Computational simulation will tell us which variables are important, and will help optimize the process. JAS It is done now in an ad hoc fashion. A more formal approach will be definitely very helpful.
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C,IS Some universities realized this and are instituting/ initiating concurrent or simultaneous engineering.
SNS One should be able to simulate process based on inputs from materials scientists, fabrication people and what is the service demand on the material. LeRC/Sverdrup researchers have demonstrated that it can be done by combining high-temperature composite mechanics with suitable optimizers. There is a need for simulation of fabrication process. ANSYS people indicated this too. LeRC/Sverdrup researchers are developing codes for simulating/tailoring metal matrix laminates. Audience Air Force is working on a three-year program to model fabrication of carbon composites but development is not integrated. Concluding remarks The computational simulation (MP/F) is upon us, especially with the introduction of new hightemperature composites. It is not clear, at this time, how one develops credible simulation methods that can be used early on and concurrently with preliminary design, and identifies potential candidates that can be demonstrated. The difficulty is where t o begin, who should participate and what to include. Where are we .9 Very little is being simulated and not much is being used for material processing and/or fabrication. What is really inhibiting ? Cooperative effort between simulation developers.
materials/fabrication/
What do we need to do for rapid progress ? Develop coupled material processing/fabrication/ structural analysis simulation tools and demonstrate their use in concurrent tailoring of fabrication process and identification of material desirable characteristics. Start with a system of current interest to your company.
DESIGN PERSPECTIVE, TECHNOLOGY BASE, INTERDISCIPLINARY, COENGINEERING TGF This is a major problem. Present mind-set is testing and more testing. High temperature composite structures need design for material process, and fabrication maintenance. A coengineering approach is
needed. System acquisition agencies have recognized this and are initiating corresponding programs. Data exchange is the biggest problem. We generate a lot of test data. We should create a data base from lessons learned from 25 years of testing. RLM The present technology base is that for homogeneous isotropic materials. It is not suitable for hightemperature composites. This needs to be interdisciplinary and coengineered. Coupled multidiscipline type codes are definitely needed to do the job effectively. Need to address, now, joint effort of computer personnel and scientists. Focus attention on human part.
GJS Universities teach single discipline because of the four-year time constraint. Companies should train engineers for their needs. Universities introduce students to elements of other disciplines as part of their curriculum. Knowledge in various areas is needed to integrate multidiscipline. We can't eliminate continuous human input in the analysis-designmanufacture process. SNS Available computer codes of single discipline can be integrated to handle interdisciplinary problems. The creativity part is on what parts from what code? Technology base pertaining to issues from various industries needs to be coengineered. How do we decrease number of variables in solving a major problem? IMD We expose our students to experimental procedures, theoretical and computer-aided methods. This is more so in graduate programs than in the undergraduate curriculum. JAS Some companies have been doing it. Vertically integrated teams are formed to accomplish this. Quantifications of the procedure will help. We have been doing it concurrently all along--one discipline to the next, but disjointed and not put together. Want to make it coherent. Design drives material and testing. CCC Also need to simulate remove and replace concept in the initial design.
Audknce Status of US versus Japan.
High-temperature composite structures--panel discussion G$S
We are discussing it. They (Japanese) are doing it (concurrent engineering). CCC We have to satisfy requirements such as those pertaining to environment. The Japanese don't have such requirements as yet. They just do it. JAS
Europeans are doing it (concurrent engineering) too.
Concluding remarks Technology base for high temperature composites is lacking. Most recent graduates are not exposed to this. Graduate students in select universities are. Interdisciplinary/coengineering is what is needed. Quantification will help, but it is not clear how to do it. Focused research in this area is timely. Where are we 9. Sequential design process, without coherent multidisciplinary information base. What is really inhibiting 9. Methods to coalesce excessive information and data exchange. What do we need to do for rapid progress 9. Select a smaller specific project and demonstrate reduction in total life cycle by using a concurrent engineering approach encompassing concerns/information from all conception-to-birth-to-death issues.
P R O B A B I L I S T I C D E S C R I P T I O N OF
UNCERTAINTIES TGF So far, engines haven't failed often because we have done a good job. Venturing into new materials for achieving quantum improvements in performance will require progressively more reliance on probabilistically based designs. The Air Force recognizes this and is already including it as a part of their advanced technology development programs. • RLM
We are already doing it in one form or another. The compressed development schedules and emphasis in cost reduction will increase its applications. Existing mind-sets will have to change to accept probabilistic assessment and especially risk. Incorporating it in design phase is what we want to do. We need a probabilistic design frame to impact manufacturing, design, testing, and end use of products.
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CCC Bring materials and processing uncertainties into design concept. JAS
We have been using statistical methods for a long time. The approach consists of statistically designed experiments. It is not clear how probabilistic assessment relying on computational simulation will be integrated into design process in view of the prevailing design philosophy on deterministic approaches and safety factors. We need probabilistic analysis for fatigue and fracture. IMD
The amount of data needed to establish acceptable statistical distributions may be the determining factor. For example, in high temperature composites we cannot get enough material to develop the test procedures and determine the statistical parameters. Statistical variability is much more pronounced under cyclic (fatigue) conditions than under static loading. Testing for fatigue strength is not good enough; we need probabilistic approach for describing varibility in fatigue strength. GJS
We still have difficulties with deterministic methods. Changing to probabilistic assessment may be difficult if not impossible. We will need to re-educate the educators. We have to see how much is the cost of developing and using probabilistic methods and what do we get out of it. TGF Three per cent porosity in composite components. Odds of it in one area are high. Probabilistic approach addresses it. SNS
Limited experience to date demonstrates that probabilistic assessment via computational simulation looks very promising and may even be here already.
Concluding remarks There appears to be a lack of consensus on what is probabilistic description/assessment and what is formally inferred from statistical data. Also, probability requires the specification of reliability levels with associated risk. Management is not ready to go on record on what risk they are willing to accept. Unless a concentrated effort is made to obtain a general consensus on these and other closely related matters, probabilistic assessment will remain a distant cousin to the traditional deterministic methods.
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Where are we .9 Although deterministic approach still reigns, probabilistic approach, in one form of another, is getting more and more acceptance, at least, in the analysis phase. What is really inhibiting 9. Acceptance and more so, understanding by not just technical leaders but also managers, of the probabilistic approach. What do we need to do for rapid progress ? One way to enhance the acceptance of probabilistic assessment and risk quantification is to use it in parallel with traditional methods and observe the additional information generated that helps in decision making. We need to start applying probabilistic approach for design and certification, i.e. appropriate design tools for computational probabilistic analysis need to be developed. EDUCATING FUTURE RESEARCHERS GJS What we are already doing is the best we can do. We cannot and should not educate specialists at the undergraduate level. The present time schedule does not permit this. Speciality education is adequately handled with grants at the graduate level. However, co-op programs do help in familiarizing students with industry-specific needs. For instance, we are still graduating engineers to handle isotropic and homogeneous materials, laminated structures are handled through continuing education. RLM We definitely are not getting the students we need at the bachelors level. It is not even clear whether we get them at the graduate level. Co-op programs do help. Two other approaches will help introduce undergraduates to industrial needs. One, professors spend time (sabbaticals) in specific industry. Two, have industrial prople teach application/design courses. We are training students for non-existent jobs. JAS We recognize this deficiency in our company. To compensate for it, we have set up co-op scholarship programs with nearby engineering schools. These programs include co-op assignments, school project sponsorships and scholarship awards. It has been very successful in attracting very good students and in getting them ready. While we train students we also get current engineers to do both probabilistic and deterministic assessments to rate probabilistics.
TGF The Air Force has been aware of this for a long time. To alleviate it, we have recently sponsored co-op programs in specific technical areas with several mid-west universities. SNS Our experience has been that the new people we hire need concentrated, supervised on-the-job training to become relevant and significant contributors. The concern is the time required which is only known after the fact. Universities can help by introducing courses in newly developing technology areas much sooner than they do. It may require that the universities pay more attention to the local industry's needs rather than on educating everybody for industries located everywhere. Of course, this needs to be done within limits so as not to narrow the broad national agenda. Industry engineers should be tapped to teach multidisciplinary courses in universities. IMD Undergraduate education should concentrate on fundamentals. Once a body of knowledge has been generated, courses are developed first at the graduate level and eventually find their way to the undergraduate level. Admittedly, this is a relatively slow process. We must teach students to think on their own. If we introduce new courses, what do we skip? Need projects from industries for developing new courses. CCC We expose professors to emerging technologies so they can teach students. Everything developed at advanced levels should find itself at undergraduate level relatively quick. Additionally, students should be taught fundamentals including what and why. GJS Even at Master's level, there is a lot of breadth, but hardly any depth. TGF Need to teach topics like failure analysis at the undergraduate level. Audience J. N. Reddy: Broad-based education is important. It gives students basic tools. However, it will help to have an advisory board of industrial experts to advise on courses at all levels. Whitney: We need to train people on common sense and generalities, not just specifics like finite elements. Anon. 1: If we didn't have computers and finite elements, we would still be lagging way behind in technology. Anon. 2: Even fundamentals aren't being taught right.
High-temperature composite structures--panel discussion Concluding remarks Parochial views prevail. Universities contend that they do an excellent job based on time constraints and broad education perspective. Speciality fields are adequately treated at the graduate level at the interested industry's expense. On the other hand, industry believes that universities remain aloof and unresponsive. Universities expect industry to contribute to the university's welfare as well as train future researchers at their own (industry's) expense. Considerable improvement for closer and more extensive intercommunication is sorely needed.
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GJS Government should fund joint industry/university programs. Industry should participate in co-op programs and institute faculty/senior engineers exchange programs. IMD Industry should provide universities with material and equipment with which to educate students in these rapidly developing areas, especially in experimental methods.
Where are we ? Universities are training students in basic skills. Advanced technology is handled at the industry/government level.
SNS Support service environment provides an excellent intermediary for government/industry/university interchange. All these institutions should recognize support service as such and advocate its role.
What is really inhibiting .9 Active cooperative programs to tap available industry engineering power in complementing existing curriculum. Lack of adaptation of university curriculum for rapidly advancing high technology areas.
CCC All joint consortia are initiated by government and die when government money is gone. This should not happen. Initial funding should be used to build upon future and continuing work.
What do we need to do for rapid progress ? Conduct university-department local industry workshops where first line supervisors and seasoned industry researchers participate on a regular interval basis.
Concluding remarks The government's role is rather well defined: continue to provide support and advocate joint government/ industry academia participation. The industry's role is also clear: institute co-op programs, exchange programs, encourage adjunct professorships and contribute generously to school fund-raising activities. The university's role is more clouded: tell us what you need and we will let you know what, how, when, where and who.
GOVERNMENT/INDUSTRY/ACADEMIA ROLES TGF The government role is to encourage and perhaps recommend joint industry/university participation in government research programs. The Air Force is consciously pursuing this with a measurable success.
Where are we .9 The government and industry play their role usually on an as-needed basis for the cooperative furtherment of research or for specific applications. What is really inhibiting .9 Self-sustaining joint cooperative programs regular basis, not as a matter of need.
RLM The government role should be to continue supporting advanced research. Industry brings in the universities on an as-needed basis. Industry should make a concerted effort to avail its seasoned personnel to teach application courses at the universities. Universities must keep in touch and be flexible in introducing new material to existing courses or new courses based on anticipated directions rather than wait until sufficient information has been generated.
What do we need to do for rapid progress .9 The government can enhance the collective cooperation by making it an explicit requirement in procurement contracts.
JAS Government should continue funding challenging/ risky technology areas. Industry should use its influence with universities so that they are aware of industry's needs and future directions.
RLM This is how we (industry) stay in business. We consider government's role as very important. The universities also help by providing us with our replacements.
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COMPETITIVE A D V A N T A G E CONSIDERATIONS
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JAS
This becomes somewhat diffused in the present environment of multinationals. One important consideration is our employment numbers. Governmentsponsored programs permit us to have very active research groups which assist us in producing new programs and continuing our high employment. Admittedly, our skill levels for labor staffing have changed considerably over the years in view of the use of exotic machines for more routine tasks. A government specification requiring probabilistics for review leading to certification would be very helpful. TGF Government's role is to support a very strong technology infrastructure from which we can draw for the development of advanced weapon systems to assure the preeminence of the USA in the world. GJS We at the university strive and hope to provide the talent that our industry needs to have competitive advantages in throughout-the-world markets. Specialized experimental research at universities is prohibitively expensive so we should go the route of Ohio Aerospace Institute, for example (universityindustry-government laboratories collaboration). IMD
We assist industry by conducting specialty projects of their interest. The results of these projects are controlled by suitable agreements between the company and the university. These definitely contribute directly to our industry's competitive advantage while educating future talent to staff their research laboratories. Short courses on special topics should be offered by the government/industry. SNS
Support service enhances the competitive advantage in two ways: (1) it synthesizes available knowledge into focussed technology transfer, and (2) it assists government agencies in exploratory research/development in order to identify feasible development programs with high pay-off potential that our industry can successfully pursue.
Concluding remarks Everyone is doing his part to assure our technological competitive advantage in a rapidly growing technology-conscious world. If we are not successful, it is not 'my fault'. I did my best to assure it. I am not so sure that 'you did the same'. Where are we ? Academia, with the help of industry and government, is providing the required talent to keep the competitive edge. What is really inhibiting ? Active, cooperative and multi-industry programs in all facets of high technology, especially for applications. What do we need to do for rapid progress ? Communication avenues between government/ industry/academic must be established on a broaderformal basis. This will strengthen the acceptance that we are all members of the same team and that collectively cooperation has a synergistic precipitous effect that benefits our competitive advantage far beyond what each one of us can contribute individually.
CONCLUSIONS The panel discussion on state of the art and future directions of high-temperature composite structures was successful. The panelists discussed the past, present, and future issues relevant to the hightemperature composite structures technology and stimulated dialogue with the audience on what course of action is required for future. For rapid progress, we need to (1) develop and use computational simulation in order to evaluate the system behavior and determine key variables for minimizing testing during the development cycle; (2) develop coupled materialprocessing/fabrication/structural analysis simulation tools and demonstrate their use in concurrent tailoring of the fabrication process and identification of material desirable characteristics; (3) develop the appropriate design tools for computational probabilistic analysis and start applying probabilistic approach for design and certification; and (4) establish communication avenues between industry/government/academia on a broader-formal basis.
Composites Science and Technology 50 (1994) 129-136
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P A N E L DISCUSSION ON THE STATE OF THE A R T A N D F U T U R E D I R E C T I O N OF H I G H - T E M P E R A T U R E COMPOSITE S T R U C T U R E S C. C. Chamis NASA Lewis Research Center, 21000 Brookpark Road, MS 49-8, Cleveland, Ohio 44135, USA
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S. N. Singhal Sverdrup Technology, Inc., Brook Park, Ohio 44142, USA (Received 15 February 1992; revised version received 15 June 1992; accepted 4 February 1993) Abstrad This article summarizes the discussion of a panel: 'On State of the Art and Future Directions of HighTemperature Composite Structures', A S M E Summer Annual Meeting, Columbus, Ohio, 18June 1991. The panel objective was a joint industry/academia/government perspective on: where are we, what are the inhibiting factors, and what is needed for rapid progress? Topics addressed include computational simulation versus traditional approaches, reliance on computational simulation versus testing, computational simulation of material processing and/or fabrication, design perspective, technology base, interdisciplinary, coengineering, probabilistic description of uncertainties, educating future researchers, government~industry~ academia roles, and competitive advantage considerations. Select panel conclusions are: (1) increase use of computational simulation, (2) include material and fabrication process in the simulation, (3) apply probabilistic assessments to quantify uncertainties and minimize testing throughout the design/qualification~ certification cycles, and (4) mandate closer cooperation among industry, academia and government.
technology base encompassing various aspects of the related technology. To bring together the engineers and scientists conducting relevant research, a symposium was sponsored by the ASME Applied Mechanics Division Committee on composite materials. The symposium was titled 'Mechanics of Composites at Elevated and Cryogenic Temperatures' and was held in Columbus, Ohio on 16-19 June 1991. A special segment of the symposium was a 'meet the press' style panel discussion. The panel was chaired/moderated by Christos C. Chamis (CCC) of NASA Lewis Research Center and organized by Surendra N. Singhal (SNS) of Sverdrup Technology, Inc., Cleveland, Ohio. The panel consisted of experts on topics related to the symposium theme. The panelists were: (1) I. M. Daniel (IMD) of Northwestern University on Experimental Mechanics---Education; (2) T. G. Fecke (TGF) of US Air Force on Engine Technology; (3) R. L. McKnight (RLM) of General Electric on Advanced Engine Development; (4) S. N. Singhal of Sverdrup Technology, Inc. on Support Service Staffing; (5) G. J. Simitses (GJS) of University of Cincinnati on Aerospace Design--Education; and (6) J. A. Suarez (JAS) of Grumman Aircraft on Advanced Technology Development. The specific topics addressed/discussed include: (1) Computational Simulation versus Traditional Approaches; (2) Reliance on Computational Simulation versus Testing; (3) Computational Simulation of Material Processing and/or Fabrication; (4) Design Perspective, Technology Base, Interdisciplinary, Coengineering; (5) Probabilistic Description of Uncertainties; (6) Educating Future Researchers; (7) Government/ Industry/Academia Roles; and (8) Competitive Advantage Considerations. The focus of the discussion was: (1) Where are we?; (2) What is really
Keywords: composites, computational simulation, high-temperature, testing, uncertainties INTRODUCTION Extreme temperature composites are emerging as materials with potentially high payoffs in applications such as aerospace structures. Realization of these payoffs depends on the development of an adquate Composites Science and Technology 0266-3538/93/$06.00 © 1993 US Government. 129
130
C. C. Chamis, S. N. Singhal
inhibiting?; and (3) What do we need to do for rapid progress? The objective of the panel was a joint industry/academia/government perspective on state of the art technology barriers and crystal ball forecasts for rapid progress in the areas of extreme temperature composite mechanics. The panel discussion is summarized below by topic. The comments by the panelists on each topic are indicated by the initials of each panelist. The audience also contributed. Their comments are indicated as 'Audience'.
COMPUTATIONAL SIMULATION VERSUS TRADITIONAL APPROACH
RLM Traditional approach is state of the art. Testing has not paid off. We need to provide designers with optimization and probabilistic computational tools. We can simulate individual discipline, linear cases, displacements, frequencies etc. We need coupled effects---thermo-mechanical fatigue, quick turnaround time, coupled multidiscipline methods, easyto-use codes. TGF We can predict stresses but there are difficulties in predicting life and effect of environment (erosion/ moisture). Quantifying defects/cracks through or around fiber takes time. We need to simulate life more accurately. We need to use simulations to guide our experiments. We need to conduct short term tests to predict long life. JAS Testing is prohibitively expensive. We have relied on computational simulation for years now. One concern is how we can use it to reduce our test certification part of the development cycle. GJS It is not clear what simulation is and what it is intended to do. One cannot rely on analysis alone. Mathematical models are okay. Need quick answers. Fundamentals are still important. The integration is most important: analysis, numerics, and experiments. IMD Experiments are important. In our laboratory we do a lot of experiments (NDE) and analysis for integrity evaluation and life prediction. We need integrated computational simulation coupled with an experimental approach.
SNS Simulation can be used to model a variety of physical phenomena quickly and even help design experiments.
Audience Carl Herakovich: Computational simulation saves money. J. N. Reddy: Mechanics has to be integrated with the methodology through the computational mechanics approach. Ozden Ochoa: We need an integrated experimental and simulation approach. John Gyekenyesi: Use computational simulation for ceramics. Need to test also. Roberto Ballarini: These things are said, but not followed. Concluding remarks Computational simulation is frequently interpreted to mean analysis using the computer. Also, it is interpreted to involve data fitting. It is needed especially with new systems. Apparently a more precise definition for computational simulation is needed. The general trend (based on expressed and implied comments from the panelists) is judicious substitution of computational simulation in lieu of testing, with integration of simulation and testing. Suggestive definition of computational simulation Elemental formulation with profusive computational simulation in contrast to computer-aided solution. Where are we ? Traditional approach with reliance on testing. Realization of need for computational simulation. What is really inhibiting? Easy-to-use coupled multidisciplinary codes with quick turn-around time to be suitable for extensive use in preliminary designs (PD) to evaluate alternative concepts. What do we need to do for rapid progress ? Use of computational simulation for minimizing testing and determining key experiments/variables, followed by corresponding experiments integrated with simulation.
RELIANCE ON COMPUTATIONAL SIMULATION VERSUS TESTING RLM Project managers are constrained by time and cost. They want combinations which will help with these. Need more sophisticated personnel and more complex machinery in conjunction with computational simulation. About 60-70% of the effort is devoted to computational simulation now.
High-temperature composite structures--panel discussion TGF Designer's biggest problem is stress concentration, 95% of the time. It is difficult to simulate stress concentration. More and more simulation will be used. However, testing cannot be and should not be eliminated. It should be held to a minimum with maximum benefit. SNS Simulation must precede testing in the development of new systems and in the qualification of new materials. IMD One cannot identify/discover physical phenomena without conducting exploratory testing. Analysis without test can be misleading; reliance on analysis alone could be disastrous. Test at the structure level as well, not just coupons. Regardless of extent of analysis or prior testing, an aircraft cannot be certified without proof testing. CCC Simulate fabrication process also. JAS Testing is held to a minimum and usually in critical areas. Mostly used for full/prototype components. Spend money on testing at basic level, eliminate building blocks. GJS Analysis verification needs control testing. Testing reveals what was missed in the assumptions for the analysis. Can't model full scale. Question is how effective are these tools. Answer is global model of the whole NASP. TGF Test full size engine. It is less expensive to do it in combination with simulation. SNS How can one test without knowing what he is looking for? On the other hand, testing is needed to ascertain that the analysis results are credible. Concluding remarks Simulation versus testing is an unresolved question; it means different things to different people. In new technology development, participant will handle it according to their past successful experience. The following suggestive procedure may help: (1) Paper designs should be computationally simulated. (2) Material capabilities should be simulated with verified control experiments.
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(3) Final designs should be simulated with material models that have been calibrated. (4) Precise definitions for validation, verification, and calibration will help clarify this unresolved question. Where are we ? Some computational simulation and a lot of testing. What is really inhibiting 9. Demonstration of integrated simulation/experimental approach with minimum experimentation guided by simulation. What do we need to do for rapid progress .9 Develop tools for specific simulations of physical phenomena currently investigated via experimentation at all levels (coupons to structure) and demonstrate significant time and cost reduction with same or better confidence. COMPUTATIONAL SIMULATION OF MATERIAL PROCESSING A N D / O R FABRICATION (MP/F) TGF We definitely need this. Because now we have no way of establishing how good is good and we compensate with extensive testing. We don't know how to do it yet. Several programs are underway to track behavior from laboratory sample behavior to component retirement for cause (birth-to-death). Residual stress in manufacturing is generally 60% of the elastic stress in composites. RLM This will be very helpful. The major drawback is a credible way to do it. Efforts should be initiated. Computational simulation can give a running start to determining what materials to use. CCC Start from structural requirements, define the fabrication process, and from there we can establish the degree of quality we can afford? IMD To simulate a process we must know the material, its desired properties and identify the process variables. There are too many variables. Computational simulation will tell us which variables are important, and will help optimize the process. JAS It is done now in an ad hoc fashion. A more formal approach will be definitely very helpful.
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C,IS Some universities realized this and are instituting/ initiating concurrent or simultaneous engineering.
SNS One should be able to simulate process based on inputs from materials scientists, fabrication people and what is the service demand on the material. LeRC/Sverdrup researchers have demonstrated that it can be done by combining high-temperature composite mechanics with suitable optimizers. There is a need for simulation of fabrication process. ANSYS people indicated this too. LeRC/Sverdrup researchers are developing codes for simulating/tailoring metal matrix laminates. Audience Air Force is working on a three-year program to model fabrication of carbon composites but development is not integrated. Concluding remarks The computational simulation (MP/F) is upon us, especially with the introduction of new hightemperature composites. It is not clear, at this time, how one develops credible simulation methods that can be used early on and concurrently with preliminary design, and identifies potential candidates that can be demonstrated. The difficulty is where t o begin, who should participate and what to include. Where are we .9 Very little is being simulated and not much is being used for material processing and/or fabrication. What is really inhibiting ? Cooperative effort between simulation developers.
materials/fabrication/
What do we need to do for rapid progress ? Develop coupled material processing/fabrication/ structural analysis simulation tools and demonstrate their use in concurrent tailoring of fabrication process and identification of material desirable characteristics. Start with a system of current interest to your company.
DESIGN PERSPECTIVE, TECHNOLOGY BASE, INTERDISCIPLINARY, COENGINEERING TGF This is a major problem. Present mind-set is testing and more testing. High temperature composite structures need design for material process, and fabrication maintenance. A coengineering approach is
needed. System acquisition agencies have recognized this and are initiating corresponding programs. Data exchange is the biggest problem. We generate a lot of test data. We should create a data base from lessons learned from 25 years of testing. RLM The present technology base is that for homogeneous isotropic materials. It is not suitable for hightemperature composites. This needs to be interdisciplinary and coengineered. Coupled multidiscipline type codes are definitely needed to do the job effectively. Need to address, now, joint effort of computer personnel and scientists. Focus attention on human part.
GJS Universities teach single discipline because of the four-year time constraint. Companies should train engineers for their needs. Universities introduce students to elements of other disciplines as part of their curriculum. Knowledge in various areas is needed to integrate multidiscipline. We can't eliminate continuous human input in the analysis-designmanufacture process. SNS Available computer codes of single discipline can be integrated to handle interdisciplinary problems. The creativity part is on what parts from what code? Technology base pertaining to issues from various industries needs to be coengineered. How do we decrease number of variables in solving a major problem? IMD We expose our students to experimental procedures, theoretical and computer-aided methods. This is more so in graduate programs than in the undergraduate curriculum. JAS Some companies have been doing it. Vertically integrated teams are formed to accomplish this. Quantifications of the procedure will help. We have been doing it concurrently all along--one discipline to the next, but disjointed and not put together. Want to make it coherent. Design drives material and testing. CCC Also need to simulate remove and replace concept in the initial design.
Audknce Status of US versus Japan.
High-temperature composite structures--panel discussion G$S
We are discussing it. They (Japanese) are doing it (concurrent engineering). CCC We have to satisfy requirements such as those pertaining to environment. The Japanese don't have such requirements as yet. They just do it. JAS
Europeans are doing it (concurrent engineering) too.
Concluding remarks Technology base for high temperature composites is lacking. Most recent graduates are not exposed to this. Graduate students in select universities are. Interdisciplinary/coengineering is what is needed. Quantification will help, but it is not clear how to do it. Focused research in this area is timely. Where are we 9. Sequential design process, without coherent multidisciplinary information base. What is really inhibiting 9. Methods to coalesce excessive information and data exchange. What do we need to do for rapid progress 9. Select a smaller specific project and demonstrate reduction in total life cycle by using a concurrent engineering approach encompassing concerns/information from all conception-to-birth-to-death issues.
P R O B A B I L I S T I C D E S C R I P T I O N OF
UNCERTAINTIES TGF So far, engines haven't failed often because we have done a good job. Venturing into new materials for achieving quantum improvements in performance will require progressively more reliance on probabilistically based designs. The Air Force recognizes this and is already including it as a part of their advanced technology development programs. • RLM
We are already doing it in one form or another. The compressed development schedules and emphasis in cost reduction will increase its applications. Existing mind-sets will have to change to accept probabilistic assessment and especially risk. Incorporating it in design phase is what we want to do. We need a probabilistic design frame to impact manufacturing, design, testing, and end use of products.
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CCC Bring materials and processing uncertainties into design concept. JAS
We have been using statistical methods for a long time. The approach consists of statistically designed experiments. It is not clear how probabilistic assessment relying on computational simulation will be integrated into design process in view of the prevailing design philosophy on deterministic approaches and safety factors. We need probabilistic analysis for fatigue and fracture. IMD
The amount of data needed to establish acceptable statistical distributions may be the determining factor. For example, in high temperature composites we cannot get enough material to develop the test procedures and determine the statistical parameters. Statistical variability is much more pronounced under cyclic (fatigue) conditions than under static loading. Testing for fatigue strength is not good enough; we need probabilistic approach for describing varibility in fatigue strength. GJS
We still have difficulties with deterministic methods. Changing to probabilistic assessment may be difficult if not impossible. We will need to re-educate the educators. We have to see how much is the cost of developing and using probabilistic methods and what do we get out of it. TGF Three per cent porosity in composite components. Odds of it in one area are high. Probabilistic approach addresses it. SNS
Limited experience to date demonstrates that probabilistic assessment via computational simulation looks very promising and may even be here already.
Concluding remarks There appears to be a lack of consensus on what is probabilistic description/assessment and what is formally inferred from statistical data. Also, probability requires the specification of reliability levels with associated risk. Management is not ready to go on record on what risk they are willing to accept. Unless a concentrated effort is made to obtain a general consensus on these and other closely related matters, probabilistic assessment will remain a distant cousin to the traditional deterministic methods.
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Where are we .9 Although deterministic approach still reigns, probabilistic approach, in one form of another, is getting more and more acceptance, at least, in the analysis phase. What is really inhibiting 9. Acceptance and more so, understanding by not just technical leaders but also managers, of the probabilistic approach. What do we need to do for rapid progress ? One way to enhance the acceptance of probabilistic assessment and risk quantification is to use it in parallel with traditional methods and observe the additional information generated that helps in decision making. We need to start applying probabilistic approach for design and certification, i.e. appropriate design tools for computational probabilistic analysis need to be developed. EDUCATING FUTURE RESEARCHERS GJS What we are already doing is the best we can do. We cannot and should not educate specialists at the undergraduate level. The present time schedule does not permit this. Speciality education is adequately handled with grants at the graduate level. However, co-op programs do help in familiarizing students with industry-specific needs. For instance, we are still graduating engineers to handle isotropic and homogeneous materials, laminated structures are handled through continuing education. RLM We definitely are not getting the students we need at the bachelors level. It is not even clear whether we get them at the graduate level. Co-op programs do help. Two other approaches will help introduce undergraduates to industrial needs. One, professors spend time (sabbaticals) in specific industry. Two, have industrial prople teach application/design courses. We are training students for non-existent jobs. JAS We recognize this deficiency in our company. To compensate for it, we have set up co-op scholarship programs with nearby engineering schools. These programs include co-op assignments, school project sponsorships and scholarship awards. It has been very successful in attracting very good students and in getting them ready. While we train students we also get current engineers to do both probabilistic and deterministic assessments to rate probabilistics.
TGF The Air Force has been aware of this for a long time. To alleviate it, we have recently sponsored co-op programs in specific technical areas with several mid-west universities. SNS Our experience has been that the new people we hire need concentrated, supervised on-the-job training to become relevant and significant contributors. The concern is the time required which is only known after the fact. Universities can help by introducing courses in newly developing technology areas much sooner than they do. It may require that the universities pay more attention to the local industry's needs rather than on educating everybody for industries located everywhere. Of course, this needs to be done within limits so as not to narrow the broad national agenda. Industry engineers should be tapped to teach multidisciplinary courses in universities. IMD Undergraduate education should concentrate on fundamentals. Once a body of knowledge has been generated, courses are developed first at the graduate level and eventually find their way to the undergraduate level. Admittedly, this is a relatively slow process. We must teach students to think on their own. If we introduce new courses, what do we skip? Need projects from industries for developing new courses. CCC We expose professors to emerging technologies so they can teach students. Everything developed at advanced levels should find itself at undergraduate level relatively quick. Additionally, students should be taught fundamentals including what and why. GJS Even at Master's level, there is a lot of breadth, but hardly any depth. TGF Need to teach topics like failure analysis at the undergraduate level. Audience J. N. Reddy: Broad-based education is important. It gives students basic tools. However, it will help to have an advisory board of industrial experts to advise on courses at all levels. Whitney: We need to train people on common sense and generalities, not just specifics like finite elements. Anon. 1: If we didn't have computers and finite elements, we would still be lagging way behind in technology. Anon. 2: Even fundamentals aren't being taught right.
High-temperature composite structures--panel discussion Concluding remarks Parochial views prevail. Universities contend that they do an excellent job based on time constraints and broad education perspective. Speciality fields are adequately treated at the graduate level at the interested industry's expense. On the other hand, industry believes that universities remain aloof and unresponsive. Universities expect industry to contribute to the university's welfare as well as train future researchers at their own (industry's) expense. Considerable improvement for closer and more extensive intercommunication is sorely needed.
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GJS Government should fund joint industry/university programs. Industry should participate in co-op programs and institute faculty/senior engineers exchange programs. IMD Industry should provide universities with material and equipment with which to educate students in these rapidly developing areas, especially in experimental methods.
Where are we ? Universities are training students in basic skills. Advanced technology is handled at the industry/government level.
SNS Support service environment provides an excellent intermediary for government/industry/university interchange. All these institutions should recognize support service as such and advocate its role.
What is really inhibiting .9 Active cooperative programs to tap available industry engineering power in complementing existing curriculum. Lack of adaptation of university curriculum for rapidly advancing high technology areas.
CCC All joint consortia are initiated by government and die when government money is gone. This should not happen. Initial funding should be used to build upon future and continuing work.
What do we need to do for rapid progress ? Conduct university-department local industry workshops where first line supervisors and seasoned industry researchers participate on a regular interval basis.
Concluding remarks The government's role is rather well defined: continue to provide support and advocate joint government/ industry academia participation. The industry's role is also clear: institute co-op programs, exchange programs, encourage adjunct professorships and contribute generously to school fund-raising activities. The university's role is more clouded: tell us what you need and we will let you know what, how, when, where and who.
GOVERNMENT/INDUSTRY/ACADEMIA ROLES TGF The government role is to encourage and perhaps recommend joint industry/university participation in government research programs. The Air Force is consciously pursuing this with a measurable success.
Where are we .9 The government and industry play their role usually on an as-needed basis for the cooperative furtherment of research or for specific applications. What is really inhibiting .9 Self-sustaining joint cooperative programs regular basis, not as a matter of need.
RLM The government role should be to continue supporting advanced research. Industry brings in the universities on an as-needed basis. Industry should make a concerted effort to avail its seasoned personnel to teach application courses at the universities. Universities must keep in touch and be flexible in introducing new material to existing courses or new courses based on anticipated directions rather than wait until sufficient information has been generated.
What do we need to do for rapid progress .9 The government can enhance the collective cooperation by making it an explicit requirement in procurement contracts.
JAS Government should continue funding challenging/ risky technology areas. Industry should use its influence with universities so that they are aware of industry's needs and future directions.
RLM This is how we (industry) stay in business. We consider government's role as very important. The universities also help by providing us with our replacements.
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JAS
This becomes somewhat diffused in the present environment of multinationals. One important consideration is our employment numbers. Governmentsponsored programs permit us to have very active research groups which assist us in producing new programs and continuing our high employment. Admittedly, our skill levels for labor staffing have changed considerably over the years in view of the use of exotic machines for more routine tasks. A government specification requiring probabilistics for review leading to certification would be very helpful. TGF Government's role is to support a very strong technology infrastructure from which we can draw for the development of advanced weapon systems to assure the preeminence of the USA in the world. GJS We at the university strive and hope to provide the talent that our industry needs to have competitive advantages in throughout-the-world markets. Specialized experimental research at universities is prohibitively expensive so we should go the route of Ohio Aerospace Institute, for example (universityindustry-government laboratories collaboration). IMD
We assist industry by conducting specialty projects of their interest. The results of these projects are controlled by suitable agreements between the company and the university. These definitely contribute directly to our industry's competitive advantage while educating future talent to staff their research laboratories. Short courses on special topics should be offered by the government/industry. SNS
Support service enhances the competitive advantage in two ways: (1) it synthesizes available knowledge into focussed technology transfer, and (2) it assists government agencies in exploratory research/development in order to identify feasible development programs with high pay-off potential that our industry can successfully pursue.
Concluding remarks Everyone is doing his part to assure our technological competitive advantage in a rapidly growing technology-conscious world. If we are not successful, it is not 'my fault'. I did my best to assure it. I am not so sure that 'you did the same'. Where are we ? Academia, with the help of industry and government, is providing the required talent to keep the competitive edge. What is really inhibiting ? Active, cooperative and multi-industry programs in all facets of high technology, especially for applications. What do we need to do for rapid progress ? Communication avenues between government/ industry/academic must be established on a broaderformal basis. This will strengthen the acceptance that we are all members of the same team and that collectively cooperation has a synergistic precipitous effect that benefits our competitive advantage far beyond what each one of us can contribute individually.
CONCLUSIONS The panel discussion on state of the art and future directions of high-temperature composite structures was successful. The panelists discussed the past, present, and future issues relevant to the hightemperature composite structures technology and stimulated dialogue with the audience on what course of action is required for future. For rapid progress, we need to (1) develop and use computational simulation in order to evaluate the system behavior and determine key variables for minimizing testing during the development cycle; (2) develop coupled materialprocessing/fabrication/structural analysis simulation tools and demonstrate their use in concurrent tailoring of the fabrication process and identification of material desirable characteristics; (3) develop the appropriate design tools for computational probabilistic analysis and start applying probabilistic approach for design and certification; and (4) establish communication avenues between industry/government/academia on a broader-formal basis.