The objective of the book is to present the practical and fundamental information for the analysis of composites. For the most part, these aspects are relatively consistent among companies (though each company has differences in their approaches). The basic principles can be considered “ingredients” and include:
- notched strength
- joint analysis
- stability analysis
- straight beams
- sandwich structures
- post-impact strength for small and large damage
- design practices
- mechanical properties
The reader can then use these ingredients to help develop specific methods (the “recipe”) for higher-level structures such as:
- actual skin-stringer configurations
- fuselage frames and shear ties
A “cook book” strategy is to provide both the “ingredients” and also the “recipe”. While this can sometimes be effective for metals, this strategy may not be effective for composites for the following reasons:
- Validated Analysis Method. There are multiple solutions to develop a validated analysis method. This is because the method is a function of: analysis, test data, and design practice. See Section 2.4 of the book (also in the book sample). For metals, the analysis may often accurately capture the physical behavior. Solutions for metals are associated with more consistent analytical approaches and require less testing. However, “pure” analytical solutions for composites do not exist for strength prediction. Therefore, approaches tend to vary depending on the blend of analysis and testing that is used to develop the method.
- Semi-empirical Correction Factors. For higher level structures, there are usually associated correction factors. These must be determined from high level testing and fed back into the validated analysis method. This is especially true for the static analysis of composites because of the variety of failure modes/mechanisms that are not always predicted in a straightforward manner. Without knowing the values for the correction factors, presenting a “cook book” solution may be of limited value.
- Configuration. Composites have many different manufacturing methods. Therefore, there are an increased number of possible configurations. For example, structures can be mechanically fastened together or cocured. The analysis approach is different between the two configurations.
- Company/Program Strategy. What is the approach for the program? Do they want to use higher fidelity analysis solutions or do they want to use additional testing and simpler analysis solutions?
- Company Resources. Since test data is highly integral to the development of composite analysis methods, what is the available test data and testing facilities? What is the company’s history of use with composites and the specific material system?
- Conservatism. How much conservatism is allowed? This may affect the analysis method and approach.
- Subtle but important design details. For composites, the analysis approach can be sensitive to subtle, but important design details. For example, certain configurations may be more sensitive to the presence of interlaminar stresses than others. These details may warrant special treatment and can be configuration specific.
- Material System. Carbon fiber composites behave differently than glass fiber composites. Furthermore, hybrid composites (combination of fiber systems) have their own behavior. Each “recipe” must be tuned for the given material system.
- Requirements. Requirements vary depending on the type of aircraft. Small aircraft have different requirements than large aircraft. Civil transport aircraft have different requirements from military aircraft.
So as you can see, there are many variables to consider when developing a “recipe” for higher-level composite structures. Attempting to present specific “cook book” solutions has the potential to be limiting, misleading, and in conflict with each company’s strategy. In fact, even the “ingredients” for composites are different between companies, but to lesser degree than "recipes" for higher-level structures.
That said, it is still possible to discuss higher level structures in a general manner. For example, there are typical checks that often size each type of structure and each structure has unique aspects to consider. Some of these aspects are discussed in the book and a later edition may further expand upon this. However, for the reasons previously discussed, later editions are not expected to provide “cook book” solutions for higher level aircraft composite structures.