Not to disparage anybody's quality of training in aircraft structural analysis, nevertheless I have noticed a recent trend I thought this group could help explain. Just perusing the many ads for "stress analysts" or some similar description, I have noticed that lately in addition to asking for experience with "FEA" that "hand stress analysis" experience is also requested. It might be that my training is substantially different from that of others, so I don't know--don't all FEA stress analysts know how to do hand analysis? It would seem almost obvious to me that you would need to be able to do hand stress analysis before moving on to FEA, and that hand stress analysis is still a routine part of any finite element analysis of a structure. What am I missing?
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Hand Stress Analysis 7
- Thread starter prost
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1
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Haven't you heard?
FEA packages, and automatic mesh generators are so good these days that there is simply no need for any engineering skill or judgment when performing stress analysis anymore.
Dump in the model and click a few buttons. Lots of pretty plots come out. If there are lots of red areas, tell the desinger to add more metal in those areas.
Repeat until no more red areas.
Why would you need hand calcs?
FEA packages, and automatic mesh generators are so good these days that there is simply no need for any engineering skill or judgment when performing stress analysis anymore.
Dump in the model and click a few buttons. Lots of pretty plots come out. If there are lots of red areas, tell the desinger to add more metal in those areas.
Repeat until no more red areas.
Why would you need hand calcs?
SouthernManCT
Aerospace
Well, you have it upon the great mystery of modern stress analysis, you can have 10 years of FEM experience and make the model do wonderful things, but you can't draw a simple free body or analyze a lug/clevis.
It is sad, but it is found quite often in reviewing a stinking lot of resumes that a significant number of young to middle level engineeres equate stress analysis wih building pretty FEM's.
I talk about the old school method of using a global loads FEM and then using classical hand analysis techniques to produce margins of safery based on Allowable load not some material stress level and people look at me like I am crazy.
But some things have driven the industry to this and I blame the schools in conjunction with some of the non-aerospace industries. Suspension Arms manufacured from castings with 1-4 loadcases are one thing, but a full airframe with over 1500 load cases are not FEM stress friendly. It is easy to blow a TET10 mesh on a solid model from CATIA, put a few loads on it and you have stress contours ripe for the viewgraphs.
The schools are spitting out computer wiz's who cannot free body a simple beam and cannot explain to you why you need 6 rigid body modes for a model, but boy are they fast.
Sorry, your comments touched a nerve.
It is sad, but it is found quite often in reviewing a stinking lot of resumes that a significant number of young to middle level engineeres equate stress analysis wih building pretty FEM's.
I talk about the old school method of using a global loads FEM and then using classical hand analysis techniques to produce margins of safery based on Allowable load not some material stress level and people look at me like I am crazy.
But some things have driven the industry to this and I blame the schools in conjunction with some of the non-aerospace industries. Suspension Arms manufacured from castings with 1-4 loadcases are one thing, but a full airframe with over 1500 load cases are not FEM stress friendly. It is easy to blow a TET10 mesh on a solid model from CATIA, put a few loads on it and you have stress contours ripe for the viewgraphs.
The schools are spitting out computer wiz's who cannot free body a simple beam and cannot explain to you why you need 6 rigid body modes for a model, but boy are they fast.
Sorry, your comments touched a nerve.
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SouthernManCT
You are right on the money. It seems that very little emphasis or training has been placed on the difference and applicability of "loads" FEM versus "stress" FEM. I do realize there are applications such as engine design which inherently needs to rely on detail FEM due to the complexity of the components involved. However, it seems that the current general trend is to build all FEM as detailed stress models utilizing plates and solids. Alot of this can be blamed on the false thinking that just because its easy to port a solid Catia model to FEM it should be just as easy to let the computer to the stress analysis.
This current trend seems to be a dangerous one for our industry as it not only tends to focus the engineer more on the task of building a detailed model rather than understanding the global applied loads and internal load paths but it also tends to skew managements perception of what it takes to perform the job. For example, in the past 15 years, it has become almost common place to use young engineers to build detailed FEM of cabinets and racks for aircraft interiors. In all of the DER reviews I have made of such models to date, I have yet to find a single one without some major mistake in load path or constraint which resulted in having to redesign it. I dont think this is entirely the engineers fault but the task of building a detailed FEM requires alot of concentration on building it leaving less time to understand load path due to the ever present pressing delivery schedule. Second, detailed stress FEM of cabinets or racks or similar structure IMHO is a complete waste of time and money and does not provide proper training for young engineers. The best way to FEM these types of structure as well as many others including full airframes are as coarse grid loads FEMs using bars, rods, shears, etc. and then perform the stress analysis using classical methods backed by test based allowables. The big rub is that it can take several weeks to build a detailed stress FEM and then many more to debug it and one is still not assured of the results. On the other hand, a coarse grid loads FEM can be built quickly and detailed stress analysis can be completed in a much shorter time. Obvisouly this all depends on the complexity of the problem and the experience level of the engineer. Unfortunately management is losing sight of this and is relying more and more on the detail stress FEM route.
Anyways, it seems that the awareness, concept and proper application of loads versus stress FEM is quickly disappearing. Just try to talk to some of the FEM sales folks and ask them if they provide GPF Balance Output or Element Oriented Forces? They will look at you as if you were crazy or from another planet and why in the world would you ever want that? Just let the model give you the stress and be done with it.
Oh well,
You are right on the money. It seems that very little emphasis or training has been placed on the difference and applicability of "loads" FEM versus "stress" FEM. I do realize there are applications such as engine design which inherently needs to rely on detail FEM due to the complexity of the components involved. However, it seems that the current general trend is to build all FEM as detailed stress models utilizing plates and solids. Alot of this can be blamed on the false thinking that just because its easy to port a solid Catia model to FEM it should be just as easy to let the computer to the stress analysis.
This current trend seems to be a dangerous one for our industry as it not only tends to focus the engineer more on the task of building a detailed model rather than understanding the global applied loads and internal load paths but it also tends to skew managements perception of what it takes to perform the job. For example, in the past 15 years, it has become almost common place to use young engineers to build detailed FEM of cabinets and racks for aircraft interiors. In all of the DER reviews I have made of such models to date, I have yet to find a single one without some major mistake in load path or constraint which resulted in having to redesign it. I dont think this is entirely the engineers fault but the task of building a detailed FEM requires alot of concentration on building it leaving less time to understand load path due to the ever present pressing delivery schedule. Second, detailed stress FEM of cabinets or racks or similar structure IMHO is a complete waste of time and money and does not provide proper training for young engineers. The best way to FEM these types of structure as well as many others including full airframes are as coarse grid loads FEMs using bars, rods, shears, etc. and then perform the stress analysis using classical methods backed by test based allowables. The big rub is that it can take several weeks to build a detailed stress FEM and then many more to debug it and one is still not assured of the results. On the other hand, a coarse grid loads FEM can be built quickly and detailed stress analysis can be completed in a much shorter time. Obvisouly this all depends on the complexity of the problem and the experience level of the engineer. Unfortunately management is losing sight of this and is relying more and more on the detail stress FEM route.
Anyways, it seems that the awareness, concept and proper application of loads versus stress FEM is quickly disappearing. Just try to talk to some of the FEM sales folks and ask them if they provide GPF Balance Output or Element Oriented Forces? They will look at you as if you were crazy or from another planet and why in the world would you ever want that? Just let the model give you the stress and be done with it.
Oh well,
Gernally I've found that those with engineering qualifications have very low analytical skills and hence the prolification of CAD packages that with a single click can give you a picture of stresses. This need to produce without thinking or knowledge satisfies the requirements and abilities of the labout market, but also of a management who naively think that quality comes cheap.
corus
corus
GregLocock
Automotive
So, my little pile of geniusses, can you formulate a hand calculation that describes the forces and deflections between two leafs, of a leafspring, of arbitrary curvature, when brought together?
You get to choose /some/ parameters.
I don't want to sound like a smarty, but, ultimately t sees to me, a piecewise (ie FE) solution is the only option other than interminable trial and error.
However, I agree with the general thrust here, kids of today, yada yada.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
You get to choose /some/ parameters.
I don't want to sound like a smarty, but, ultimately t sees to me, a piecewise (ie FE) solution is the only option other than interminable trial and error.
However, I agree with the general thrust here, kids of today, yada yada.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
GregLocock
Automotive
Oh yes, 100%.
I'd put all the salesmen (and their bosses) of the integrated FEA/CAD products on a long plank and ask them to walk.
But, to be fair, I haven't seen these things used on a serious design. It'll happen, no doubt. It probably has happened. I'm waiting for the lawsuit, then at a guess this stupid fashion will dissappear.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
I'd put all the salesmen (and their bosses) of the integrated FEA/CAD products on a long plank and ask them to walk.
But, to be fair, I haven't seen these things used on a serious design. It'll happen, no doubt. It probably has happened. I'm waiting for the lawsuit, then at a guess this stupid fashion will dissappear.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
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- #9
I seemed to have touched a few nerves. One wonders, corus and others, how someone could manage to slog through all the engineering classwork needed to obtain a BS or MS and still have poor analytical skills.
Maybe your problem with these people is that their analytical skills aren't good enough? It would be hard for me to imagine a situation in which someone with an engineering degree could have poor analytical abilities, ('poor' relative to the general population of college grads that is).
Sounds like a university problem and a corporation training problem. Even with all the fancy gizmos and whizbang toys engineers now have, early engineering careers still have to be apprenticeships, don't you think?
Stil, I don't think anyone gave me any insight as to the apparent recent appearance of this phenomenom. Maybe it's something like 'feature creep'--a process so gradual that no one notices the subtle changes in which structural engineers (probably the same in other disciplines) have become so tied down to their FEM and CAD tools that someone has neglected to train them to do 'back of the envelope' type analyses. It is interesting to me that corporate engineering departments appear to have noticed that the engineers they are interviewing and hiring have large enough deficiencies in fundamental capabilities such as hand stress analysis capability that they go out of their way to specify 'hand stress analysis' as a fundamental job requirement; while oh dopey, ignorant me, I naturally assume any struct. engineer I talk to could already do 'hand stress analysis.' Showing my ignorance again, I suppose.
Maybe your problem with these people is that their analytical skills aren't good enough? It would be hard for me to imagine a situation in which someone with an engineering degree could have poor analytical abilities, ('poor' relative to the general population of college grads that is).
Sounds like a university problem and a corporation training problem. Even with all the fancy gizmos and whizbang toys engineers now have, early engineering careers still have to be apprenticeships, don't you think?
Stil, I don't think anyone gave me any insight as to the apparent recent appearance of this phenomenom. Maybe it's something like 'feature creep'--a process so gradual that no one notices the subtle changes in which structural engineers (probably the same in other disciplines) have become so tied down to their FEM and CAD tools that someone has neglected to train them to do 'back of the envelope' type analyses. It is interesting to me that corporate engineering departments appear to have noticed that the engineers they are interviewing and hiring have large enough deficiencies in fundamental capabilities such as hand stress analysis capability that they go out of their way to specify 'hand stress analysis' as a fundamental job requirement; while oh dopey, ignorant me, I naturally assume any struct. engineer I talk to could already do 'hand stress analysis.' Showing my ignorance again, I suppose.
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- #10
Please keep in mind that I am was not necessarily assigning all blame to the individual engineers (I try to keep my curmudgeonliness behavior in check!). While some responsibility to train engineers properly rests on the shoulders of individual engineers, we all have a responsibility to mentor engineers, especialy early in their careers. In particular, though, some universities appear to be doing a very poor job of training engineers, and corporations don't appear to be willing or able to pick up the slack. Somebody has to train engineers early in their careers, and it's incredibly pathetic that it has to be us (to paraphrase Jerry Garcia).
In the area of personal responsibility, it is apparent to me that most engineers go to work, put in their time (which can be a 10 hour day of course), go home, and never pick up a book or read a journal article, or attend a professional meeting (most aren't even bothering to join prof. societies, much less go to meetings), etc. Personally I consider this to be insufficient dedication to the learning of and mastering of a craft such as engineering. But that's another thread for another day.
In the area of personal responsibility, it is apparent to me that most engineers go to work, put in their time (which can be a 10 hour day of course), go home, and never pick up a book or read a journal article, or attend a professional meeting (most aren't even bothering to join prof. societies, much less go to meetings), etc. Personally I consider this to be insufficient dedication to the learning of and mastering of a craft such as engineering. But that's another thread for another day.
Prost, I have to disagree with you here. We are in "business" not academa, so it is not incumbent on senior engineers to teach junior engineers; it is the responsibility of the junior engineer to learn from the senior engineer, by working hard, asking questions, looking over the shoulder and trying to understand the backwork that has been looked over by the more senior engineer.
At one time, there may have been an apprenticeship(sp), but those days have gone the way of the slide rule and drafting board.
Plus my company just recently laid off all of the junior engineers. Because it was costing too much time for the sr.'s in mentor time, and the jr's were not efficient enough.
Most engineers I know are poor teachers. The ones that teach (professors) are generally poor practisioners(sp). And now, thanks to computers, many graduate from uni thinking that they know much more than they do. And business furthers this phenomonon by giving a new employee more responsibility than they deserve... and then it's sink or swim...
Wes C.
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SWComposites
Aerospace
Its not just the yong engineers. I've recently seen a bunch of middle age contract stress analysts who got fired because they were basically incompetent - couldn't draw a proper free body, couldn't figure out loads and boundary conditions to put on a FEM, didn't understand material properties and allowables, and in one flagrant case claimed 10000 hours of experience with Patran/Nastran yet had no idea how to even create a mesh much less a proper model.
Now here's a little treasure hunt contest:
Who can find the most "aircraft stress analysis" courses in university curriculums? Are there any these days? FEM courses do not count. Please post links to the courses that you find.
Steve
Now here's a little treasure hunt contest:
Who can find the most "aircraft stress analysis" courses in university curriculums? Are there any these days? FEM courses do not count. Please post links to the courses that you find.
Steve
I never took a course in "aircraft stress". I took all the structural dymanics, machine design, mechanics and vib courses I could, but as I got toward my sr year all my really good classes would get cancelled for lack of enrollment....
And I never took an FEA course, because it was always filled....
go figure...
AND!!! why do we always stop with the Free body Diagram, when we all know it's not reall complete without the (there are several names for it) "mass-acceleration diagram".
Wes C.
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And I never took an FEA course, because it was always filled....
go figure...
AND!!! why do we always stop with the Free body Diagram, when we all know it's not reall complete without the (there are several names for it) "mass-acceleration diagram".
Wes C.
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- #16
I think that is a cop-out. Part of the "business" of your engineering career is mentoring young engineers, passing on your "wisdom" so to speak so that these engineers can develop throughout their careers. My experience most young or inexperienced engineers do not know the way, and only senior engineers know the direction to take (apprenticeships may not be formal, but they still are occurring; at least that is what I experienced early in my career, and continue to experience).
I cannot believe that you or anyone else thinks that university training could ever be adequate to cover all contingencies--that is, all the twists and turns an engineering career over the spectrum of all engineering careers.
IMO, you do not have any business being an engineer if you are not willing to pass on the knowledge and experience of "lessons learned" you have picked up through your career. You yourself have been the beneficiary of the experience of thousands perhaps millions of engineers, from Mesopotamia to today, and personally I would consider myself immoral for not being willing to pass that experience on to inexperienced engineers.
I cannot believe that you or anyone else thinks that university training could ever be adequate to cover all contingencies--that is, all the twists and turns an engineering career over the spectrum of all engineering careers.
IMO, you do not have any business being an engineer if you are not willing to pass on the knowledge and experience of "lessons learned" you have picked up through your career. You yourself have been the beneficiary of the experience of thousands perhaps millions of engineers, from Mesopotamia to today, and personally I would consider myself immoral for not being willing to pass that experience on to inexperienced engineers.
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- #17
The inventory of structural engineering classes at the 2 universities with which I am affiliated in some way:
University of Arizona, Aerospace Engineering BS
Statics
Mechanical Behavior of Engineering materials
Engineering Component Design (looks like failure analysis)
Materials Selection (could have used that one myself!)
Composite materials
University of Southern California, Aerospace Engineering BS
Statics
Strength of Materials
Aerospace Structures
Stress Analysis
Theory of Structures II
(design and FEA classes not included). I have no idea whether any of those classes are filled or empty. Each school also has quite a few structures classes at graduate level.
University of Arizona, Aerospace Engineering BS
Statics
Mechanical Behavior of Engineering materials
Engineering Component Design (looks like failure analysis)
Materials Selection (could have used that one myself!)
Composite materials
University of Southern California, Aerospace Engineering BS
Statics
Strength of Materials
Aerospace Structures
Stress Analysis
Theory of Structures II
(design and FEA classes not included). I have no idea whether any of those classes are filled or empty. Each school also has quite a few structures classes at graduate level.
Prost,
I appologize for the scarcasm in my statement not being more clear. I wholehartedly agree with you that when you graduate, "noone knows nuthin!" and it is our responsibility to pass down what we have learned from the previous generation.
Unfortunately I am a bit disgruntled after the "layoff" here at my company, where they just eliminated all of the recent graduates (from '06 and '05) based on some idiot consultants efficiency-productivity metrics.
Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.
I appologize for the scarcasm in my statement not being more clear. I wholehartedly agree with you that when you graduate, "noone knows nuthin!" and it is our responsibility to pass down what we have learned from the previous generation.
Unfortunately I am a bit disgruntled after the "layoff" here at my company, where they just eliminated all of the recent graduates (from '06 and '05) based on some idiot consultants efficiency-productivity metrics.
Wes C.
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No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.
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- #19
wes616:
One wonders where the consultant or management thinks 'fully trained engineers' come from? Trees? Oh, I know, India, Ukraine, or China.
I personally didn't take offense, and missed the sarcasm completely--zoomed by me like a North American X-15.
One wonders where the consultant or management thinks 'fully trained engineers' come from? Trees? Oh, I know, India, Ukraine, or China.
I personally didn't take offense, and missed the sarcasm completely--zoomed by me like a North American X-15.
Although I agree with most of what has been said I think the problem is a bit more wide ranging in that the responsability for "quality" engineering IMHO lies with not only the individual engineer but with the universities and the industry. First off, just look at what has changed over the years. At one time, the management of large engineering companies were actually run by engineers. Professors at top universities were actually engineers from industry who not only excelled at engineering but also had an aptitude for teaching.
Unfortunately these days, companies are no longer run by engineers and the concept of providing training is solely focused on required lectures for avoiding lawsuits such as harassment training, dealing with diversity, export/import and whole bunch of others which may be needed but have nothing to do with the daily company business. In the old days, training was one of the major benefits which big companies used to bring in the best and brightest. Now days, they figure engineers should be happy just getting offered a job.
Universities of today only provide the basis for building an engineering career but not the tools to actual perform the task. The engineer himself must have enough self motivation to seek out the necessary training to excell at their job. I do think however that for the amount of money universities collect in tuition that they should be held liable for the quality and level of education they provide. As a test, try asking several professors in aircraft structures what MMPDS is or describe the difference between jo-bolts, hitigues, taperloks, etc. Far and few in between unfortunately.
I think that eventually this issue will come to a head, maybe sooner than later, and the industry will have to face the problem of fixing this. If leaders at major corporations would get together with both universities and professional organizations, a basic curricula which includes both theoretical and practical phases could be established. Such as the apprenticeship programs of long ago.
Unfortunately, I am not so sure this issue will get resolved until things come to a critical point. Industry is primarily reactive not proactive these days.
Unfortunately these days, companies are no longer run by engineers and the concept of providing training is solely focused on required lectures for avoiding lawsuits such as harassment training, dealing with diversity, export/import and whole bunch of others which may be needed but have nothing to do with the daily company business. In the old days, training was one of the major benefits which big companies used to bring in the best and brightest. Now days, they figure engineers should be happy just getting offered a job.
Universities of today only provide the basis for building an engineering career but not the tools to actual perform the task. The engineer himself must have enough self motivation to seek out the necessary training to excell at their job. I do think however that for the amount of money universities collect in tuition that they should be held liable for the quality and level of education they provide. As a test, try asking several professors in aircraft structures what MMPDS is or describe the difference between jo-bolts, hitigues, taperloks, etc. Far and few in between unfortunately.
I think that eventually this issue will come to a head, maybe sooner than later, and the industry will have to face the problem of fixing this. If leaders at major corporations would get together with both universities and professional organizations, a basic curricula which includes both theoretical and practical phases could be established. Such as the apprenticeship programs of long ago.
Unfortunately, I am not so sure this issue will get resolved until things come to a critical point. Industry is primarily reactive not proactive these days.
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