Design work Vs Stress analysis 4

[floattuber]

I'm a mechanical engineer trying to change careers from semi conductor to aerospace and have come to a fork in the road. In the past (starting from college) if I wanted a part made I would do the design work, stress analysis and most times fabricate the part. Working for a smallish company I thought designing and stress analysis goes hand in hand. Afterall, how can anybody design something if they don't know whether it can take the stresses?

After talking with an aerospace friend, I have learned that there is a difference between designers and stress analyzers. In college I enjoyed both designing parts and the stress analysis involved.

My question is, can you guys elaborate on these two job descriptions? I'm still a bit confused about what a designer does.

For example, I have it in my mind that a designer who wants to join two parts with a bracket takes the predefined connection points and basically fills in the area between them with a bracket of his design. The designer then sends off the bracket design to the stress guy who does a more thorough analysis.

Is this right?

 

[GregLocock]

If you want to do the whole design process from go to woe then I suggest the aerospace is probably not the ideal industry for you.

You know what a stress analyst does.

A design engineer ensures that the part achieves its many other functions, and complies with the paperwork, and (often) controls the release of the part into the system. He'd do the FMEA, and oversee the testing.

Once in a while he might write an equation. Usually a budget!



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ctopher]

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Chris
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[SWComposites]

In a typical aerospace company, except some small companies where one person wears both the design and analyst hats, in the structural engineering field:

a designer is responsible for the form, fit and function of the part. They define and document the design requirements for the part. They select the material and fabrication process (with input from materials and manufacturing engineers), define the shape, interfaces, joints, finishes, etc. They may do some initial sizing calculations. They create the CAD models/drawings and release them into the drawing system. They prepare bill of materials, manage drawing revisions and usually deal with manufacturing issues and problems (sometimes there is a separate liaison group for this). They are responsible for the weight and cost of the part.

a stress analyst is responsible for analyzing the part/structure to ensure adequate strength, stiffness, durability, fatigue life, etc. They also determine internal loads in the structure. They plan material property, development and certification test programs, coordinate the testing with the test labs, analyze the test results and correlate the test results to analytical predictions. They often have to tell the designer what materials to use, what ply layups to use in a composite part, how to design the joints, where to put the load paths, etc. (much to the designer's annoyance).

lastly, the designer usually gets the credit when the part meets weight and cost goals, but the stress analyst gets the blame when the part is over weight. Designers are paid to be unconservative and to push the envelope; analysts are paid to be conservative and to ensure that there are no structural failures. Makes for lots of "interesting" conflicts.

Cheers,

Steve

 

[Heckler]

Steve - a great answer gets you a star

I remember my days as a design engineer in aerospace as a fondly.

An analyst in aerospace could mean you deal with static, dynamic, or thermal stresses and don't forget mass properties. As an analyst it's all about mitigating risk.





Best Regards,

Heckler
Sr. Mechanical Engineer
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[EngJW]

Designers are exposed to a much broader field and generally the stress analysis they would do is restricted to basic tension and bending equations, for example equations found in Roark, and in some cases they may do some basic fea.

The type of stress analysis done in industries like aerospace is much more complex and a design engineer would probably not have the advanced training and experience required. Of course, the stress analyst would only have a limited knowledge of design.

 

[floattuber]

It sounds like stress analysts need more formal training in math and theory of stress analysis (FEA). I only have a bachelors in ME, would that be a hindrance, do aerospace companies usually prefer advanced degrees for this type of job? Or do they hire bachelors and then give them the training required?

 

[Twoballcane]

<<I only have a bachelors in ME, would that be a hindrance, do aerospace companies usually prefer advanced degrees for this type of job? Or do they hire bachelors and then give them the training required?>>

That is a catch 22 question. How do you get a job in Structural Analysis with out the training, but in order for you to get the training you have to get a job as a Structural Analysis? Since you have your bachelors in ME, in essence you have the theoretical back ground. Now you just have to get the “training”. The training is a combination of experience and theoretical knowledge.

I am not a Structural Analysis per say. I really do heat transfer and shock/vib analysis (military equipment), but due to forces and loads created from these environments, my structural analysis experience are at these level. In the company that I started right after college, there where essential two groups. One was design and the other was analysis. I started in design, but wanted to get into analysis. Typically these two groups worked in tandem. The designer will come up with a design and then go to the analysis person for concurrence. If there was something wrong, the analysis person would make a recommendation (based on his analysis) to the designer. This back and forth would take place until both were satisfied.

Well I started in design and wanted to get into analysis. I had the theoretical back ground, but not the experience and theoretical knowledge in that specific field. When I was discussing work with the analysis guys, I’ve noticed that there were two or three books (the theoretical knowledge) that they kept referring to when they did there analysis. I bought those books and started to do my own analysis on my own work (the experience). So when I went to see the analysis guys about my work I already had the analysis done and they would correct me here and there (more experience of the tricks of the trade) to get my analysis as realistic as possible. After a program or two, a spot opened up in an analysis group in another company. Since I had some experience and theoretical knowledge under my belt, I got the job.

I guess the moral of my long winded story (sorry about that) is that you can always work in what you want to do in the future into the job you are currently doing now, so you can get around the catch 22 situation. You just have to be creative.

Good luck!
Go Mechanical Engineering
Twoballcane

 

[Heckler]

floattuber - most of the analysis guys/gals at the Big L had advanced degrees not to say you could work your way into that type of work. IMO the Big L was a little myopic in their recruiting practices.

 

[prost]

Worked at McDonnell Douglas 15 years back; even then, they hired plenty of BS in mechanical, civil, or aero, but as part of your career progression in aero/propulsion, you were expected to be working on a Masters degree (preferrably technical Masters, not MBA. Wonder where they thought the future leaders of their technology company were going to grow? Trees perhaps?)

 

[SWComposites]

floattuber - many stress analysts start out with BS degrees. Most of what is needed for practcal aerospace stress analysis is learned on the job (either working with a experienced engineer or thru in-house training classes). Very few universities teach practical stress analysis (most of the theoretical stuff you will never need or use). Similarily, practical FE analysis is typically learned on the job via training and working under an experienced engineer. Universities do a good job of teaching FEA theory, but a very poor job of teaching practical, useful FE analysis and how to properly idealize a structure, construct the model and interpret the results. There are many ways to get a wrong FE result, and many ways to incorrectly interpret a valid FE result. Stress analysis a lot more than FEA - you have to understand load paths, boundary conditions, material properties, and material and structural failure modes, etc. People these days forget that lots of aircraft were sucessfully designed without any FE analysis.

If stress analysis interests you, then go for it. There are lots of companies looking for stress analysts right now.

 

[Heckler]

Twoballcane - What are the titles of the two or three books? I have Roarks Formulas for Stress & Strain and have found that very useful thus far in my career.

 

[floattuber]

Thank you all for the first hand insight.

SWcomposites, that's what I was hoping to hear!

Even though I like to design and excelled at it during college, I think ideally I'd like to go for stress analysis.

 

[Twoballcane]

Heckler,

The three books where Vibration Analysis for Electronic Equipment and Cooling Techniques for Electronic Equipment both by Dave S. Steinberg published by John Wiley & Sons, inc and Roark’s Formulas for Stress and Strain (which you have). Other books that I found helpful are Vibration Spectrum Analysis by Steve Goldman published by Industrial Press and Electronic Packaging and Interconnection Handbook by Charles A. Harper published by McGraw Hill.

Since I do heat transfer and shock/vib analysis/test on electronic military equipment, the Steinberg approach has served me well.

Go Mechanical Engineering
Twoballcane

 

[wes616]

If you are talking about aerospace, you can't forget, BRUHN & I also like the FLABEL book.

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...

 

[GregLocock]

Bruhn, Roark, Blevins, for answers to calibrate your models

Timoshenko, Thomson, Kreyszig for methods

Shigley, for all the really important stuff



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[HVACctrl]

In my experience, the term "designer" is not used to mean "design engineer". Drafters and CAD operators are sometimes called designers.

In the HVAC world, these designers sometimes work out certain calculations on duct sizing, friction loss, etc... but it is altimately checked and approved by an engineer.

My guess is that in your original scenario, perhaps there are specialists in stress analysis (who are likely engineers). When parts are designed, the design engineer must colaborate with the stress guy to develop a worthy design.

In a co-op job I had years ago, there was a setup something like this. We had an engineer who was an expert at stress analysis. Everyone brought their designs through him to insure they were on the right track. However, this guy wasn't the "official" stress analyser. He had the same responsibilities as the other engineers as well- he was just good at the stres thing.

Ed

 

[johnsmith2]

In small company,
designers and stress analyzers are the same person to work on.

In large company, designers work on CAD while stress guy work on CAE, such as finite element analysis, abaqus, or ansys.

 

[bradpa77]

My first job here was entitled "Compressor Design Engineer". I was very excited before I started because I assumed that meant that I would be involved in the 'design' of compressors the whole way through. I thought I'd be involved in the fluid mechanics, thermodynamics, stress analysis, heat transfer analysis, rotordynamics, and pro/e design of the parts.

It turned out that I was simply the pro/e designer and that was it. All of that other stuff was done by other people and more than just one. There is a stress analysis guy, an application engineer who does the thermo, a aero engineer who does the fluid mechanics, etc. Needless to say, I was very disappointed with my job after finally realizing what the company structure was like. Everything is very specialized here. Everyone has a VERY specific duty. That kind of comes with the territory of working in a 'bigger' company. I just recently switched over to be being a stress analyst (after ALOT of complaining). I personally like it a lot better than just working on pro/e but I still wish I could get involved in more aspects of the design.

So I've been on both the design and stress analyst sides of the fence and this is my interpretation of the differences:

The designer lays out the product in a CAD system and makes sure that everything 'fits' together. The stress analyst will then take the designers work and make sure it can withstand the loads it will be subjected to. If the design is not satisfactory, the stress analyst will return to the designer and ask him to change things. Once the design has been changed, it is analyzed again. This is repeated until both the designer and stress analysts are satisfied with the product. Then the designer will go on and create final production drawings and release the parts for manufacture.

At least that's how it works here.

Hope that helps.

 

[GregLocock]

Cheer up, I once had to speak to the design engineer for headlights, trucks, left hand side.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.