This book presents basic structural deformation and stress analysis as applied to optical systems. It provides the tools for first-order analyses required in the design concept phase before handling the intricate details of a full-up design. While finite element analysis is paramount to a successful design, the purpose of this text is not to use finite element analysis to validate the hand analysis, but rather to use hand analysis to validate the finite element models. The hand analysis forces a discipline that is paramount in the understanding of structural behavior. Presuming that the reader has a working knowledge in the strength of materials, the text applies engineering principles to opto-structural analysis.
Texts on structural and mechanical analysis are numerous, and indeed, this entire text is based on the pioneering works of others in the field. This book, therefore, draws on those texts and presumes a working knowledge of the strength of materials [see J. W. Pepi, Strength Properties of Glass and Ceramics, SPIE Press (2014)]. With that foundation, we apply those engineering principles to opto-structural analysis. In the precision world of optics, we are often concerned with displacements and deformations of very small values, from fractions of a wavelength of light to the micron and nanometer (millionths of an inch) order. Furthermore, optical systems designed for flight are often required to be of very light weight. While the analytical techniques in any case are the same as on the macro-level, careful analysis is required when moving the decimal point so far to the left.
In preparing to write this book, some thought went into the title. Before selecting the term “opto-structural analysis,” an alternative term “optomechanical analysis” was considered for the title. However, several excellent texts under that latter title are available. It is certainly not the intent to replace those worthy sources but rather to supplement them. To this end, the title contains the term “opto-structural,” perhaps because the author is a structural engineer, but more so, to point out the “static” nature of the topic. If structural analysis is defined as applying to things that don’t move once they are deformed, mechanical analysis as applying to things that move (such as mechanisms), and dynamic analysis as applying to things that move slightly, the title selection becomes more clear (although these latter topics are discussed in the book).
This book is written with the intent to understand basic structural deformation and stress analysis as applied to optical systems. It provides the tools for first-order analyses required in the design concept phase before entering into the intricate details of a full-up design. Ever-increasing computer technology has allowed former tedious and unwieldy problems to be solved in a fraction of the time by using finite element analysis. Unfortunately, reliance on such fast methods without hand analysis backup can lead to unsuspected errors. Thus, first-order calculations are an excellent way to complement the current state of the industry that relies more on computational design techniques. These calculations accelerate the design process by allowing an understanding of the critical governing parameters and allowing accelerated design trades and sensitivity studies to be performed that decrease schedule and cost. The insights gained from these techniques can then be used to guide the development of appropriate finite element models, including model fidelity, and details focusing on the critical and most sensitive design parameters. These models, in turn, are more efficient and provide the optostructural engineer a comprehensive and insightful design approach. This approach can then inform the roadmap for risk reduction and environmental testing.
While finite element analysis is paramount to a successful design, the purpose of this text is not to use finite element analysis to validate the hand analysis but rather to use hand analysis to validate the finite element models. The hand analysis forces a discipline that aids tremendously in the understanding of structural behavior. It is the intent, then, not to forget such techniques.
“Forsan et haec olim meminisse iuvabit.”1
1. From Virgil’s The Aeneid [translation: “Perhaps, someday, we will look back fondly on these things.”]
John W. Pepi