Book Review: Crashworthiness of Composite Thin-Walled Structural Components
One of the aspects of structural engineering that has always appealed to me is destructive testing. There's just something about breaking stuff that I find exciting, especially when it's done on purpose. The first laboratory project I worked on was a study of the compressive strength of filament wound tubes.
Although our tubes made a satisfyingly loud bang upon failure, the group working on the MTS machine next to us had an even cooler project: They were building scale-model glider fuselages and crushing them well past the initial failure point to determine their behavior during a crash.
I'm sure that group would have been interested in the book I'm reviewing this week. Crashworthiness of Composite Thin-Walled Structural Components looks at the energy absorption properties of typical composite structures, with an eye towards improving vehicle safety.
After a brief introduction, the authors give a hurried overview of vehicle crashworthiness as related to composites. This is not a complete overview of the field, and it helps to have some knowledge of general crashworthiness topics. Not having worked in the field, I found some of the discussion confusing. However, the remainder of the book focuses on failure analysis and thus requires less knowledge of crashworthiness in particular.
Chapters 2 through 4 are primarily literature reviews. Chapter 2 covers vehicle crashworthiness, and some of the citations are to general references or textbooks. If you want to learn more about the field before starting on composites in particular, these might be a good starting point. Chapter 3 covers general composite topics (failure modes, analysis, etc.) and should be familiar to most readers.
Chapter 4 is a review of energy absorption literature; as such, it provides much of the background for the book. Coverage is thorough, but on first reading I thought it lacked sufficient detail. In the later chapters, though, many of the concepts are covered in more detail.
Overall, the book lists 116 references, with maybe half of them written by one or more of the authors. Many of the references are fairly current, but a few are oddly outdated. For example, a citation about a lack of data for carbon/PEEK composites is dated 1991. I suspect the data may have become more readily available over the last several years.
The heart of the book is contained in Chapters 5 through 9, which describe a series of experiments on tubular components. Each of these chapters covers specimen manufacture, experimental setup, data acquisition, qualitative analysis (examination of photomicrographs), and quantitative analysis (theoretical modelling and data reduction). Each chapter covers a different specimen geometry (see the contents below for descriptions).
The experimental results are interesting whether you want to learn the theory or you just want to get a feel for how the parts fail. The photomicrographs are not as clear as they could be--they look like copies of pictures--but the textual descriptions are very detailed.
The compressive specimens are all placed directly against the platens, and the authors determine that a significant portion of the energy absorbed is through friction between the platen and the specimen. This may make it difficult to extrapolate to more general conditions, but it also shows the challenges in designing a component for maximum energy absorption.
In most cases, the compressive specimens split somewhere between the plies (like a delamination), and "fronds" of material peel to both the inside and outside of the specimen. A debris wedge, consisting of pulverised material, forms between the fronds. Friction between this wedge and the fronds is the other major source of energy absorption (roughly equal to the energy absorbed by platen friction).
I was hoping the book would end with a discussion of how to apply the results to an automotive structure, but that is really outside the scope of topics. Chapter 9, titled "Automotive Sections," applies the methodology of the previous four chapters to an hourglass shaped specimen which might be typical of an automotive beam.
The final chapter gets off to an odd start with a table of physical defects resulting from manufacturing processes. This is a very nice summary of such defects, but I don't see how it fits in with the rest of the book. Most of this chapter, though, contains a concise and clear summary of the failure modes observed in the experiments.
In general, Crashworthiness is a fairly technical book. It should be of interest to those conducting basic research in composite crash behavior, or to those looking for a starting point for more advanced research. It will be of less value, though, as a starting point for the design of complex structures.
Finally, I have to point out that the grammar, punctuation, and even spelling in this book are below average. It's not bad enough to make the book unreadable, and lengthy portions are fairly decent, but it's definitely annoying. I don't think it's the fault of the authors (English is probably not their first language), and this book may not be a big enough seller for the publisher to be concerned. As an engineer with a minor in technical writing, however, I tend to hold engineering communications to a high standard.
Details: Crashworthiness of Composite Thin-Walled
Structural Components, by
A.G. Mamalis, D.E. Manolakos, G.A. Demosthenous, and M.B. Ioannidis,
published by Technomic Publishing, 1998, ISBN
1-56676-635-4.
1. Introduction; 2. Vehicle Crashworthiness; 3. Failure Mechanisms of
Composites; 4. Energy Absorption Capability of Thin-Walled Composite
Structural Components; 5. Circular Tubes; 6. Square / Rectangular
Tubes; 7. Circular Frusta; 8. Square Frusta; 9. Automotive Sections;
10. Classification of Macro- and Microfailure Modes and Quantitative
Data