Preface to the First Edition

This book deals with the design of structures made of composite materials, also called composites. With composites, the material and the structure are designed concurrently. That is, the designer can vary structural parameters, such as geometry, and at the same time vary the material properties by changing the fiber orientation, fiber content, etc. To take advantage of the design flexibility composites offer, it is necessary to understand material selection, fabrication, material behavior, and structural analysis. This book provides the main tools used for preliminary design of composites. It covers all design aspects, including fiber and matrix selection, fabrication processes, prediction of material properties, and structural analysis of beams, plates, shells and other structures. The subject is presented in a concise form so that most of the material can be covered in a one-semester undergraduate course.

This book is intended for senior-level engineering students, and no prior knowledge of composites is required. Most textbooks on composites are designed for graduate courses; they concentrate on materials behavior, leaving structural analysis and design to be covered by other, unspecified, graduate courses. In this book, structural analysis and design concepts from earlier courses, such as strength of materials, are used to illustrate the design of composite beams, plates, and shells.

Modern analysis and design methodology have been incorporated throughout the book, rather than adding a myriad of research oriented material at the end of the book. The objective was to update the material that it is actually taught in a typical senior technical-elective course rather than adding reference material that is seldom taught. In addition, design content is included explicitly to provide the reader with practical design knowledge, thus better preparing the student for the workplace. Among the improvements, it is worth mentioning the following: A chapter on materials and a chapter on processing, which emphasize the advantages and disadvantages of various materials and processes, while explaining materials science and process-engineering topics with structural-engineering terminology. In chapter 4, proven micromechanical formulas are given for all the properties required in the design, as well as reference to the American Society of Testing Materials (ASTM) standards used for testing. In chapter 6, shear-deformable lamination theory is presented in lieu of the obsolete classical lamination theory. In chapter 7, the truncated-maximum-strain-criterion, widely accepted in the aerospace industry, is explained in detail. Chapters 8, 9, and 10 present, simple yet powerful methods for the preliminary design of composite beams, plates, stiffened panels, and shells. The material in these later chapters does not require, for the most part, any background beyond that provided by the typical engineering curricula in aerospace, civil, or mechanical engineering.

Design content is distributed throughout the book in the form of special design-oriented sections and examples. The presentation emphasizes concepts rather than mathematical derivations. The objective is to motivate students who are interested in designing useful products with composites rather than performing research. Every final equation in every section is useful in the design process. Most of the equations needed for design are programmed into the accompanying software to eliminate the need for tedious computations on part of the students. The software, entitled Computer Aided Design Environment for Composites (CADEC), is a windows application with an intuitive, web-browser-like graphical user interface, including a help system fully cross-referenced to the book. Examples are used to illustrate aspects of the design process. Suggested exercises at the end of each chapter are designed to test the understanding of the material presented.

Composites design involves synthesis of information about materials, manufacturing processes, and stress-analysis to create a useful product. An overview of the design process as well as composites terminology are introduced in chapter 1, followed by a description of materials and manufacturing processes in chapters 2 and 3.

Composites design also involves stress- and deformation-analysis to predict how the proposed structure/material combination will behave under load. Since a one-semester course could be spent on analysis alone, an effort has been made in this book to simplify the presentation of analysis methods, leaving time for design topics.

Composites design can be accomplished following one of various methodologies outlined in chapter 1 and developed throughout chapters 4 to 7. The instructor can choose from the various design options described in section 1.4 to strike a balance between simplicity and generality. Self-study readers are encouraged to read through chapters 4 to 7, with the exception of those sections marked with a star (*) which can be studied afterward. The book is thoroughly cross-referenced to allow the reader to consult related material as needed. Since the constituent materials (fiber and matrix) as well as the manufacturing process influence the design of a composite structure, the designer should understand the characteristics and limitations of various materials as well as manufacturing processes used in the fabrication of composites, which are described in chapters 2 and 3. Prediction of composite properties from fiber and matrix data is presented in chapter 4. Although composite properties could be obtained experimentally, the material in chapter 4 is still recommended as the basis for understanding how fiber-reinforced materials work. Only those formulas useful in design are presented, avoiding lengthy derivations or complex analytical techniques of limited practical use. Some of the more complex formulas are presented without derivations. Derivations are included only to enhance the conceptual understanding of the behavior of composites.

Unlike traditional materials, such as aluminum, composite properties vary with the orientation, having higher stiffness and strength along the fiber direction. Therefore, the transformations required to analyze composite structures along arbitrary directions not coinciding with the fiber direction are presented in chapter 5. Furthermore, composites are seldom used with all the fibers oriented in only one direction. Instead, laminates are created by stacking layers with fibers in various orientations to efficiently carry the loads. The analysis of such laminates is presented in chapter 6, with numerous design examples.

While stress-analysis and deformation-controlled design is covered in chapter 6, failure prediction is presented in chapter 7. Chapter 7 includes modern material, such as the truncated-maximum-strain criterion, which is widely used in the aerospace industry. Also, a powerful preliminary-design tool, called carpet plots, is presented in chapters 6 and 7 and used in examples throughout the book.

The instructor or reader can choose material from chapters 8 to 10 to tailor the course to his/her specific preferences. Chapter 8 includes a simple preliminary-design procedure (section 8.1) that summarizes and complements the beam-design examples presented throughout chapters 4 to 7. In section 8.2, a novel methodology for the analysis of thin-walled composite sections is presented, which can be used as part of an advanced course or to tailor the course for aerospace or civil engineering students.

All of the thin-walled beam equations are programmed into CADEC to eliminate the need for tedious computations or programming by the students. Chapter 9 is intended to provide reference material for preliminary-design of plates and stiffened panels. Rigorous analysis of plate problems has not been included because it requires the solution of boundary value problems stated in terms of partial differential equations, which cannot be tackled with the customary background of undergraduate students. Similarly, chapter 10 can be used to tailor a course for those interested in the particular aspects of composite shells. Again, complex analytical or numerical procedures have not been included in favor of a simple, yet powerful membrane-analysis that does not require advanced analytical or computational skills.

Introduction to Composite Materials Design contains more topics than can be taught in one semester, but instructors can tailor the course to various audiences. Flexibility is built primarily into chapters 2, 3, 8, 9, and 10. Chapters 2 and 3 can be covered in depth or just assigned for reading, depending on the emphasis given in a particular curriculum. Chapters 8, 9, and 10 begin with simple approximate methods that can be taught quickly, and they evolve into more sophisticated methods of analysis that can be taught selectively depending on the audience or be left for future reading. Video references given in chapter 1 provide an efficient introduction to the course when hands-on experience with composite manufacturing is not feasible.

An effort has been made to integrate the material in this book into the undergraduate curriculum of aerospace, civil, and mechanical engineering students. This has been done by presenting stress-analysis and structural-design in a similar fashion as covered in traditional, mandatory courses, such as mechanics of materials, strength of materials, mechanical design, etc. Integration into the existing curriculum allows the students to assimilate the course content efficiently because they are able to relate it to their previously acquired knowledge. Furthermore, design content is provided by special design-oriented sections of the textbook, as well as by design examples. Both, integration in the curriculum and design content are strongly recommended by engineering educators worldwide, as documented in engineering accreditation criteria, such as those of Accreditation Board of Engineering Technology (ABET).

The market for composites is growing steadily, including commodity type applications in the automotive, civil infrastructure, and other emerging markets. Because of the growing use of composites in such varied industries, many practicing engineers feel the need to design with these new materials. This book attempts to reach both the senior-level engineering student as well as the practicing engineer who has no prior training in composites. Practicality and design are emphasized in the book, not only in the numerous examples but also in the material's explanation. Structural design is explained using elementary concepts of strength of materials, with examples (beams, pressure vessels, etc.) that resemble those studied in introductory courses. I expect that many students, practicing engineers, and instructors will find this to be a useful text on composites.  

Ever J. Barbero, 1998