Resources for learning about aircraft structural design using composites?

[WK95]

Some of you especially those who do work in aircraft structures may be familiar with Bruhn's Analysis and Design of Flight Vehicle Structures. I've heard great things about the book but was also told that it was written for metal structures.

Is anyone familiar with any books written in a similar style to Bruhn but teaches aircraft structural design with composites in a comprehensive manner? A book that relates aircraft structural design to FEA would be even better.

Some of the books I've come across including Jone's Mechanics of Composites Materials only have a chapter or so giving and introduction to the composite structural design process. From the brief look I've taken at Bruhn's book, what I like is the numerous worked out examples covering nearly every structural component of an airplane. His approach seems very practically minded unlike some books which are heavy in theory but light in practice.

 

[RPstress]

Michael Niu's books are bit more modern than Bruhn. On the other hand, a lot of what's in Bruhn is structural design and applies to any almost solid made into a structure (with inevitable differences between composites and isotropics needing to be catered for; this takes common sense and some imagination but is not impossible). I certainly wouldn't be without it (in spite of not working on a metallic structure for some years). Same applies to Roark's/Young's "Formulas for Stress and Strain" and Pilkey's "Formulas for Stress, Strain, and Structural Matrices". (And doubtless many, many others. Peery? Timoshenko? Southwell?)

If you have to choose just one of Michael Niu's books his "Airframe Stress Analysis and Sizing" is probably most useful. Like many engineers I own all three of his books and would certainly buy more if he produced them. I remember being quite excited when his first ("Airframe Structural Design") came out in 1988. We had someone who was in the States bring back a couple of dozen copies all of which were snapped up in spite of the cost.

Niu is aware of FE analysis and how it impinges on design and analysis but it's not a major issue in his books, though it is mentioned occasionally. I'm not sure what book deals comprehensively with practical aspects of FE.

 

[ESPcomposites]

Right, some of the aspects of composite analysis carry over well to metals, but some do not. At the "detail" level, composites differ quite a bit from metals. CMH-17 probably has the best collection of modern information, but it is a difficult read for someone new to composites. It is probably better as a reference book than something to learn from. On the other hand, I think "Composite Materials for Aircraft Structures" by Baker, Dutton, and Kelly is a pretty good introductory book and has a lot of practical information. I prefer both of those to Niu's book on composites, although Niu's book has some good information as well. The difficulty is separating the useful information from misleading/incorrect/out of date information. Some books are better at this than others, but analysis of composite is such a vast field that it will probably always exist to some degree.

I think one of the challenges with composites is that many of the practical methods are semi-empirical (engineering solution). Therefore, the books from academia do not tend carry over well to practical composite structure. This is because academia seeks to find the physical nature of analysis and they shy away from semi-empirical approaches, which can be fluid. Conversely, metals are relatively well suited to many classical solutions. Therefore, much of the work from academia (and the associated books) tend to carry over to practical analysis better. At the very least, this provides a better foundation for practical metal structural analysis, which is why then tend to be more developed.

Brian

http://www.espcomposites.com

 

[cpinz]

Take a look at Kassapoglou's books edited by Wiley

Cpinz

 

[Burner2k]

ESPComposites,
I am eagerly awaiting your book on Composite Design/Stress Analysis to come out. I am looking for such a resource which is aimed at practicing engineers.

One of the good thing about Flabel is inclusion of numerous examples to illustrate application of various concepts. I hope you follow similar pattern for Composite Materials.

Just wanted to post this...

Thanks for making an attempt to publish such an above book.

 

[ESPcomposites]

Flabel's book is excellent. The original goal was to try stay close to that approach.

It eventually became clear that what Flabel did with metals was not going to work as well for composites. This occurs for a variety of reasons, but mostly because of (a) the semi-empirical nature of practical composite analysis and (b) the many failure modes of composites (especially the interlaminar failure modes).

That said, the goal changed to providing: detailed explanations of what to do and pitfalls to avoid, formulas that are effective and commonly used, physical explanations of how to tie everything together, and trying to make it as organized and clear as possible. By focusing on this approach, there was no room left for examples. In addition, original attempts at providing examples muddied the waters and made it a difficult read. Composite analysis tends to be more mathematically involved than metals.

There is still an effort to provide examples. But those will either be done in another book or provided online. I think that by decoupling the reference book from the examples, it will be easier to digest the material.

Brian

http://www.espcomposites.com

 

[Burner2k]

Thanks for explaining the possible content of your book.

One more topic possibly if included will be of great help. I assume currently majority of the sizing of composite components will be done using FE. So may be a brief explanation/illustration of how to model laminate panels in FE for most commonly used FE solvers (Nastran, Ansys & Abaqus)? Also how to post process FE results. For example, one firm which is consulting on MRB Stress for composite parts uses FE results to determine interlaminar peel stresses at ply drop-offs/transition, at curvatures & right-angled parts (T-junctions etc).

 

[ESPcomposites]

While detailed FE content would be useful, it would be too overwhelming for this book. I think the FE discussion deserves a separate book. Considering there are limited offerings, I have started work on that effort. But it won't be available for some time. Also, FE is good for getting internal loads, stress concentrations, elastic stability, provide insight, etc. But most final sizing will not be done with a FEM. Detail sizing with FEM is not good at incorporating semi-empirical methods, is subject to significant user error, difficult to check (especially for certifying authority). It is also inconvenient when you want to: change the design, change parameters such as thickness/height/layup/etc., and address hundreds/thousands of load cases.

The approaches to address interlaminar failure modes are not universal. Stress based solutions can work for some problems, provided they are calibrated via test and the derivatives are not considerably different than the validated range. Curved beams are commonly addressed in this manner. For some problems, the trend is to use interlaminar fracture mechanics since you frequently need to account for possible manufacturing disbonds/defects or delamination after impact. Stress based solutions are not as good for those cases because of the sharp stress gradients (or infinite stress) that may exist (among other reasons). In either case, when interlaminar stresses dominate the structural capability, you will need a lot of testing to validate whatever method you use (or may exclusively use testing with the recognition that predictive methods are relatively undeveloped for these failure modes). You can't simply use an interlaminar strength and combine it with a FEM. Interlaminar strength design values are very much configuration dependent and contrary to what some may believe, are not true material properties. The same can be said for the fracture properties, but to a lesser degree.

Brian

http://www.espcomposites.com

 

[VN1981]

Well, I believe your book will be a valuable resource for any newcomer in to Composite Stress field as well as practicing engineers. Looking forward. Your website mentions a tentative time period of late 2016. Hopefully it will be sooner.

 

[Wynd]

In the interim period ESP, what would one recommend as a general reference starter book in to Composites? We did cover some composite material in our undergraduate degree, but I would like to expand my knowledge from this level.

 

[ESPcomposites]

Well, there are a lot of areas (materials, manufacturing, design, structural analysis, etc.). If you are interested in structural analysis, you probably want to understand the basic mechanics first. Jones and Daniel/Ishai have good books for that.

After that, things become a challenge because the academic and engineering approaches tend to diverge (though some of the academic material carries over). The most complete single resource is probably CMH-17. But that may be difficult to transition to. I think the book by Baker, Dutton, Kelly (mentioned in the 3rd post) does a good job at introducing some of the practical aspects. ASM Volume 21 also has some good information. Some other practical oriented books are by Niu and Kassopglou. After that, you have to start looking at the technical papers. Much of the really good information is found in them, but that is a time consuming task. Furthermore, you have to know which papers are the useful ones.

Note that all of this assumes you have a strong foundation of the basics. If not, you may be better served by first improving skills in mechanics of materials or other areas related to your field. Even if those books concentrate on metals, you will be better prepared to address composites when you are ready to do so. I think there is a general tendency to want to jump into more specialized areas like composites or FEA without having a strong foundation of the basics.

Brian

http://www.espcomposites.com

 

[Wynd]

Thank you very much for the detailed response.Jones and Daniel/Ishai, Sold! That looks like a winner and a great place to start.

Are you familiar with Krisham K Chawla's Composite Materials?