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Bronislav Prokhorov
Bronislav Prokhorov

Flabel Practical Stress Analysis For Design Engineers Pdf //TOP\\ Download



TTFN RE: Training New Hires tbuelna (Aerospace)25 Apr 06 18:19I don't think "Boeing" and "Tech Excellence" should be used in the same sentence. RE: Training New Hires 2 GregLocock (Automotive)25 Apr 06 20:34Yeah, all those 747s tumbling out of the sky. CheersGreg LocockPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips. RE: Training New Hires wes616 (Aerospace)26 Apr 06 09:22Being on the Design end of a/c engineering, I am always fascinated with things I can do to better my designs before sending them to stress (and I consider myself a perpetual stress newbie) . I'd be very much interested in reading a training "faq" here about being a stress eng. Wes C.------------------------------When they broke open molecules, they found they were only stuffed with atoms. But when they broke open atoms, they found them stuffed with explosions... RE: Training New Hires AminG (Aerospace)26 Apr 06 12:23I would be interested in seeing a FAQ for stress as well. I recall seeing a Boeing Stress manual - never had the chance of using it.As to getting tired of answering the same questions - now you know how your prof's felt and how your supervisors felt when you were at your first real job. RE: Training New Hires diamondjim (Mechanical)27 Apr 06 13:56I was the old guy on the block and trainedmany underlings. It was always amazing tome that many would come back with the samequestions rather than making a reference tothe source that I would give them the firsttime they asked. I was quick to copy thesources from the guy who trained me. Is that familiar? RE: Training New Hires GregLocock (Automotive)27 Apr 06 19:26That always annoys me. I carried a notebook around for the first 6 years after graduating, even now I usually have the latest one in my bag. Asking the same question twice is sheer bad manners. CheersGreg LocockPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips. RE: Training New Hires RPstress (Aerospace)28 Apr 06 10:01The Cranfield (UK) Introduction to Aircraft Stress Analysis was a two week course which did a pretty effective intro. I don't have my course notes any more (it was over twenty years ago)...if anyone still has the contents for them it might make a good framework for a training course. RE: Training New Hires planedr (Aerospace)29 Apr 06 23:36I am not an old timer, well I am, but not really. I find I am constantly training newbs out of great schools that don't really know that much. Design is great but try to fix a bad design and get it through stress, whether you are doing the stress or not.I find the only way to start is proved them my list of newbie references and dircect them to the photocopier. I also tell them which ones to read first. I then will help with questions as we go.Their reviews or my report to the supervisor will discuss whether they have read it (effort), whether they retained it, and whether they have chosen the correct field. RE: Training New Hires 14 crackman (Aerospace)30 Apr 06 14:33Well, next year will be my 20th in aerospace as a stress engineer and I can tell you without a doubt the days of training courses are all but over at any of the OEM. In addition, there just arent enough experienced people to go around at the OEM since they pushed many of them out of the industry during downturns and the rest into early retirement. It seems these days, the status quo is hire an army of new college grads and have them solid FEM every single CATIA drawing of a part there is, then write MS based on Von Mises. Never thought I would see the industry end up this way! In addition, it seems the OEMs really dont care anyways. They say they want to provide training but dont allocate the time. In fact, I think its ironic that the OEM spend an obscene amount of money to provide mandatory training for sexual harassment, export/import, diversity, etc, etc., etc. but cant spend a nickle for any substantial engineering courses. I have personally witnessed many good new engineers trown to the wolves without any training to end up quitting their jobs out of frustration and switching industries.Anyways, I run a consulting company and we too have had to hire a couple of new hires BUT we made darn sure to set up a process to train them and make the appropriate time available. It consists of basically the following:#1. Have them spend several weeks working real aircraft structures problems and getting familiar with all of the terminology, materials, and references (MMPDS, Bruhn, Aircraft Stress Manuals (BDM,SMM,etc.)). Above all, expect them to be able to perform FBD at a drop of a hat and understand all of the basic MS failure modes. This is the most fundamental of capabilities.#2. Assign them tasks on topical subjects which provide them experience in the various aspects of structures (ie design and detailed joint stress analysis are the basics, then, other tasks such as internal loads, post-buckled behaviour, stiffened panels, etc.)#3. Assign them increasingly more difficult problems with a focus on getting them proficient in every area.#4. Make the TIME to provide guidance and help.Anyway you look at it, it is a time consuming difficult task to train new stress engineers. BUT, we need to do it otherwise the whole industry will suffer. For anyone interested, I can email a pdf of a course MACAIR wrote twenty some years ago to train stress people. It is by no means exclusive but just a good sample of the type of problems to have new stress engineers work.Also, just as an aside. MACAIR around the late 1960's use to give a test to all new direct hires and shoppers (before all of the employment restrictions were imposed). The test consisted of about 10 difficult but good sound structural problems all of which had to be completed by hand without references. Those who did not pass, were walked out that day. The old stressers of yeasteryear sure left some big shoes to fill. Unfortunately, I am not sure the industry is up to it anymore these days.Good luck to all and hope this helps someone.James BurdAvenger Aircraft and Services RE: Training New Hires SWComposites (Aerospace)30 Apr 06 16:52Yeah, the thought that everything gets dumped into a 3D FEM without any real understanding of load paths, materials and structural failure modes is downright scary. But it won't change until the next "Comet" disaster occurs. Some of us were appalled when the Airbus VP stated that the fact that the A380 wing failed at 1.47 DLL proved the accuracy FE analysis!James-I hope you can retain the engineers that you spend the time to train.Steve RE: Training New Hires GregLocock (Automotive)30 Apr 06 20:53James, can you estimate how much (a) time for the new hires and (b) mentoring/supervision time is involved? CheersGreg LocockPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips. RE: Training New Hires crackman (Aerospace)30 Apr 06 23:23Unfortunately we no longer have "real" engineers running aerospace companies any more and they have NO idea as to the real value of experience and the need to have engineers trained in the fundamentals. It is all too common today to see 3D FEA of intercostals and shear clips. Can no one FB a clip anymore? I really do hope the industry learns this lesson without the need for any accidents.I too hope that the young engineers who are getting mentoring appreciate it. Hopefully they will see the value of working with someone who is truly interested in helping them into the industry.As for the time to train: a) new hires - 1 year to just understand/appreciate the basics / 5 years of good work til they reach journeyman level where they can handle most stress tasks. Other more complex areas require more training such as FDT which requires about 2 to 3 years of solid training and hands on work.b) mentoring/supervising - about 20% of a 40 hour work week.Good luck all and lets hope ours is not a dying field.James RE: Training New Hires Asanga (Mechanical)1 May 06 07:31Hello all, Very interesting and useful topic. Crackman, thank you for the tips. If its not too much trouble, may I have a copy of that PDF file on the stress course emailed to me? I am about to sign up also for the correspondance course by the Lake City Publishing group (Based on the Stress Analysis Book by Jean Claude Flabel). This would be an added guide to the course I think. Thank you again for sharing your wisdom.CheersAsanga RE: Training New Hires 3 prost (Structural)1 May 06 15:42Crackman: I'd be most grateful if you sent me a stress course PDF file too. How could I obtain it? thanks RE: Training New Hires Lcubed (Structural)1 May 06 15:51Hi all,For James Burd: What is the best way to get my email address to you? I would like a copy of the Macair document.thanks RE: Training New Hires crackman (Aerospace)1 May 06 15:56If anyone is interested, just send me your email address (you can do this by going to www.avengeraircraft.com and using the Contact Us tab and email me from there) and I will post it off to you. The file is pdf format and its 4.4MB so make sure your email can handle it.James BurdAvenger Aircraft & Services RE: Training New Hires StressMan2506 (Structural)1 May 06 16:04Hi SWComposites:Firstly, the Airbus VP who "stated that the fact that the A380 wing failed at 1.47 DLL proved the accuracy FE analysis" is not at the frontline of Airbus wing stressing. Secondly, Airbus wing stressing is not solid-element FE all the way; it is nothing like that at all. A stiffness model up of plates, shells & bars is run and the stresses arising used in a multitude of computerised manual-type calculations. Maybe more judicious use of FE would have produced a better result... RE: Training New Hires crackman (Aerospace)1 May 06 20:34Just as a note, the MACAIR stress course was developed (over 20 years ago) for the USAF Air Logistic Centers to train liasion engineers in basic airframe stress analysis. Not a bad cut at it, though there are many other very good ones around.James Burd RE: Training New Hires crackman (Aerospace)2 May 06 22:11To answer a few questions, the liasion structures course that I spoke of is just that, a collection by chapter of progressively more difficult structures examples and problems. There are several of these courses that the OEMs used to put on about 20 or 30 years ago but alas no more. Lockheed used to teach a very good series of courses included a very famous one on Thin Sheet theory.The course notes basically do not have an actual document number or title or any restrictions, it is more a compilation of course work and so has not proprietary stamps or references on it since it is all derived from textbook equations. Its the type of course companies and the government used to send engineers to in order to get trained on "real" world problems right after graduating. The information in it is basically what one would get from several structures textbooks but only in a simpler and more focused manner as applicable to aircraft liasion work.Hope this clarifies some questions.James RE: Training New Hires Sparweb (Aerospace)3 May 06 02:25Crackman,I'll also contact you for a copy of that training course. The test sounds... humbling. Steven Fahey, CET RE: Training New Hires Asanga (Mechanical)3 May 06 03:27Thank you for the notes Crackman. Even if its not as detailed as Bruhn, it gives quite an insight into the background of the engineering fundementals knowledge expected of a liaison engineer, or for that matter any engineer involved with aircraft structures. The course outline for the correspondance course that I want to take (Based on Flabel's book) follows a similar pattern to Macair's.CheersAsanga RE: Training New Hires aerodog (Aeronautics)3 May 06 21:43Crackman,I would be curious to hear your opinion on the use of CATIA/FEA vs. the old hand crank method. In particular, which is the more accurate predictor of the stress levels that get recorded during static test. RE: Training New Hires crackman (Aerospace)4 May 06 00:02aerodogDepending the type of test being performed (small component to full scale) both can make good and/or bad predictions based on how they are applied. Typically though, the most direct and best way in my own opinion for large scale tests is to use some sort of FEA BUT this means a normal industry standard (or that which used to be standard in our industry) "coarse" grid airframe model built by a well experienced stress analyst who knows load path very well following standard modelling practices. NOT, some ultra fine mesh or autogenerated model (dont even think about solid elements) with every minutia modeled as seems to be the practice these days. Another good alternate method for wing boxes and even fuselage structure (as long as you account for cutout redistributions) is to use a Unit Beam method (ie Cozzone method) which was used by most OEMS for decades. In fact, most OEMs designed and built all of the 1940s to late 1960s transports with this method in various forms. Boeing used it on the 707, 727, 737, 747 (and I have heard still does for prelim design purposes). The Boeing fuselage code was named TES057 while the wing was TES170 as I recall. From the old ultimate correlation reports I have seen they did a pretty good job for the most part in predicting the values.One thing to keep in mind is that whenever you are correlating always pick very clean areas to instrument. That is to say, I have very rarely ever seen test correlations to strain gages in stress concentration areas provide good (within 10%) correlation. For instance, if you are trying to validate a wing coarse grid FEM, place your gages on basic general spar cap, stringer, or skin locations as nearly close to the NA as possible and away from any cutouts, splices or discontinuities. The best way to correlate areas with stress concentrations is to perform very localized tests and even then it is difficult to obtain very good correlation. The main point in any aircraft FEM is to correlate internal loads not necessarily detail stresses. This is typically what regulation agencies are looking for in order to gain confidence in model results.James BurdAvenger Aircraft and Services RE: Training New Hires 2 SuperStress (Aerospace)4 May 06 15:39Crackman makes an excellent point about strain gage correlations.Stress engineers tend to want to locate strain gages for the static test right on the "hot spots": areas of very high strain and very high strain gradient. Gages in these location do a lousy job of providing data for a correlation effort.The best strain gage layout for a correlation is to put gages in areas of high strain but LOW strain gradient. This way the gages are less sensitive to mislocation.The best way to validate a FEM distribution on a wing, for instance, might be to put axial gages on every stringer and spar cap on both surfaces at a single wing station, with a good number of rosettes scattered on the skins in the bays between stringer gages.Too often the engineer is asked to do a correlation without the right tools.Another sign of untrained management... asking for FEM results that are "conservative". For a given set of externally applied loads, there is exactly one solution for any given structural system. Inasmuch as the model overpredicts the load in one location, it must necessarily be underpredicting somewhere else.Maybe the engineers need to be training the management!SuperStress RE: Training New Hires aerodog (Aeronautics)4 May 06 16:48crackman/Superstress,Thanks for the good answers to my off topic question?The basis for my question is to see if the reliance on FEA is the reason why manufacturers (especially start-up business jet mfg) miss their empty weight projections so often. This might make a good topic by itself since there is great effort being expended trying to make lighter and stronger materials, avionics are certainly lighter but everyone keeps missing empty weights.aerodogjust because a process can be automated does not mean it should. RE: Training New Hires SuperStress (Aerospace)4 May 06 17:05I think the reason manufacturers miss their empty weight projections is because they are made by the Marketing department, not Engineering.SuperStress RE: Training New Hires GregLocock (Automotive)4 May 06 18:35More cynically (or even more cynically) - in order for the project to proceed it has to offer better payload etc than the competition. Therefore, in order for everyone to keep their jobs, at the start of the program it is in EVERY team meber's interests to emphasise the superior performance. CheersGreg LocockPlease see FAQ731-376 for tips on how to make the best use of Eng-Tips. RE: Training New Hires aerodog (Aeronautics)5 May 06 07:28Greg/Super,There is inconsistency here. On one hand a lament, industry is losing the ability to do good stress work yet blaming marketing/management for not hitting empty weight targets.An outsider might assume bad stress work leads to an unsafe airplane. Bad stress also leads to a heavy airplane.Take the Eclipe airplane for instance. It sailed through static test with no failures and management is thrilled. Their press release proudly proclaimed "no detrimental permenant distortion at limit or ultimate load".Is that good stress work or extreme conservatism? If an individual sheet metal part is .063 and it could have been made from .050, then it is 25% heavier than it should be.If .050 called out where .040 would have worked out, again the part is 25% heavier.If .040 instead of .032, again a 25% weight penalty.Keep this up and you have an airframe 25% heavier than it should be and it will sail through static test. Is this good stress work?aerodogdon't just rock the boat...jump up and down on the gunnels. RE: Training New Hires prost (Structural)5 May 06 11:19Would it even be possible to design the kinds of really advanced, high performance airplanes (such as the 787 will be) without the sophisticated design and analytical tools we have now? You can cite the SR-71 as one of those really advanced airplanes that was designed and built without many of the fancy tools that we have now--I doubt the SR-71 could be built in the current budget and legal environment we have now; there'd be way too much risk for the GAO and other bean counters.The positive correlations between the test data and the analytical tools are what is allowing the 'pushing of the envelope' we are seeing now, IMO. While it may trouble me to see phrases such as "Insights from FEA" (Machine Design just had such a front cover), there is no doubt in my mind that the current tools for analyses such as CFD have enabled signficant evolution of design practices. RE: Training New Hires prost (Structural)5 May 06 11:25Trying to get back close to the original topic--Anybody out there get as disturbed as I do when some person not under your supervision (say at another company) starts asking you how to use engineering software that takes advanced knowledge and years to training to understand the results (such as FEA or fracture mechanics analysis tools) and you know from the questions tha


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