C. Kassapoglou – Design and Analysis of Composite Structures. Aerospace Structures

Автор: C. Kassapoglou
Название книги: Design and Analysis of Composite Structures. Aerospace Structures
Формат: PDF
Жанр: Архитектура
Качество: Изначально компьютерное, E-book

This book is a compilation of analysis and design methods for structural components made of
advanced composites. The term ‘advanced composites’ is used here somewhat loosely and
refers to materials consisting of a high-performance fiber (graphite, glass, Kevlar
, etc)
embedded in a polymeric matrix (epoxy, bismaleimide, PEEK etc). The material in this book is
the product of lecture notes used in graduate-level classes in Advanced Composites Design and
Optimization courses taught at the Delft University of Technology.
The book is aimed at fourth year undergraduate or graduate level students and starting
engineering professionals in the composites industry. The reader is expected to be familiar with
classical laminated-plate theory (CLPT) and first ply failure criteria. Also, some awareness of
energy methods, and Rayleigh–Ritz approaches will make following some of the solution
methods easier. In addition, basic applied mathematics knowledge such as Fourier series,
simple solutions of partial differential equations, and calculus of variations are subjects that the
reader should have some familiarity with.
A series of attractive properties of composites such as high stiffness and strength-to-weight
ratios, reduced sensitivity to cyclic loads, improved corrosion resistance, and, above all, the
ability to tailor the configuration (geometry and stacking sequence) to specific loading
conditions for optimum performance has made them a prime candidate material for use in
aerospace applications. In addition, the advent of automated fabrication methods such as
advanced fiber/tow placement, automated tape laying, filament winding, etc. has made it
possible to produce complex components at costs competitive with if not lower than metallic
counterparts. This increase in the use of composites has brought to the forefront the need for
reliable analysis and design methods that can assist engineers in implementing composites in
aerospace structures. This book is a small contribution towards fulfilling that need.
The objective is to provide methodology and analysis approaches that can be used in
preliminary design. The emphasis is on methods that do not use finite elements or other
computationally expensive approaches in order to allow the rapid generation of alternative
designs that can be traded against each other. This will provide insight in how different design
variables and parameters of a problem affect the result.
The approach to preliminary design and analysis may differ according to the application and
the persons involved. It combines a series of attributes such as experience, intuition, inspiration
and thorough knowledge of the basics. Of these, intuition and inspiration cannot be captured in
the pages of a book or itemized in a series of steps. For the first attribute, experience, an attempt
can be made to collect previous best practices which can serve as guidelines for future work.
Only the last attribute, knowledge of the basics, can be formulated in such a way that the reader
can learn and understand them and then apply them to his/her own applications. And doing that
is neither easy nor guaranteed to be exhaustive. The wide variety of applications and the
peculiarities that each may require in the approach, preclude any complete and in-depth
presentation of the material. It is only hoped that the material presented here will serve as a
starting point for most types of design and analysis problems.
Given these difficulties, the material covered in this book is an attempt to showrepresentative
types of composite structure and some of the approaches that may be used in determining the
geometry and stacking sequences that meet applied loads without failure. It should be
emphasized that not all methods presented here are equally accurate nor do they have the
same range of applicability. Every effort has been made to present, along with each approach,
its limitations. There are many more methods than the ones presented here and they vary in
accuracy and range of applicability. Additional references are given where some of these
methods can be found.
These methods cannot replace thorough finite element analyses which, when properly set
up, will be more accurate than most of the methods presented here. Unfortunately, the
complexity of some of the problems and the current (and foreseeable) computational
efficiency in implementing finite element solutions precludes their extensive use during
preliminary design or, even, early phases of the detailed design. There is not enough time to
trade hundreds or thousands of designs in an optimization effort to determine the ‘best’
design if the analysismethod is based on detailed finite elements. On the other hand, once the
design configuration has been finalized or a couple of configurations have been downselected
using simpler, more efficient approaches, detailed finite elements can and should be
used to provide accurate predictions for the performance, point to areas where revisions of
the design are necessary, and, eventually, provide supporting analysis for the certification
effort of a product.
Some highlights of composite applications from the 1950s to today are given in Chapter 1
with emphasis on nonmilitary applications. Recurring and nonrecurring cost issues that may
affect design decisions are presented in Chapter 2 for specific fabrication processes. Chapter 3
provides a review of CLPT and Chapter 4 summarizes strength failure criteria for composite
plates; these two chapters are meant as a quick refresher of some of the basic concepts and
equations that will be used in subsequent chapters.
Chapter 5 presents the governing equations for anisotropic plates. It includes the von
Karman large-deflection equations that are used later to generate simple solutions for postbuckled
composite plates under compression. These are followed by a presentation of the
types of composite parts found in aerospace structures and the design philosophy typically
used to come up with a geometric shape. Design requirements and desired attributes are also
discussed. This sets the stage for quantitative requirements that address uncertainties during
the design and during service of a fielded structure. Uncertainties in applied loads, and
variations in usage from one user to another are briefly discussed.A more detailed discussion
about uncertainties in material performance (material scatter) leads to the introduction of
statistically meaningful (A- and B-basis) design values or allowables. Finally, sensitivity to
damage and environmental conditions is discussed and the use of knockdown factors for
preliminary design is introduced.
Chapter 6 contains a discussion of buckling of composite plates. Plates are introduced
first and beams follow (Chapter 8) because failure modes of beams such as crippling can
be introduced more easily as special cases of plate buckling and post-buckling. Buckling
under compression is discussed first, followed by buckling under shear. Combined load
cases are treated next and a table including different boundary conditions and load cases
is provided.
Post-buckling under compression and shear is treated in Chapter 7. For applied compression,
an approximate solution to the governing (von Karman) equations for large deflections of plates
is presented. For applied shear, an approach that is a modification of the standard approach for
metals undergoing diagonal tension is presented. A brief section follows suggesting how postbuckling
under combined compression and shear could be treated.
Design and analysis of composite beams (stiffeners, stringers, panel breakers, etc.) are
treated in Chapter 8. Calculation of equivalent membrane and bending stiffnesses for crosssections
consisting of members with different layups are presented first. These can be used with
standard beam design equations and some examples are given. Buckling of beams and beams
on elastic foundations is discussed next. This does not differentiate between metals and
composites. The standard equations for metals can be used with appropriate (re)definition of
terms such as membrane and bending stiffness. The effect of different end-conditions is also
discussed. Crippling, or collapse after very-short-wavelength buckling, is discussed in detail
deriving design equations from plate buckling presented earlier and from semi-empirical
approaches. Finally, conditions for inter-rivet buckling are presented.
The two constituents, plates and beams are brought together in Chapter 9 where stiffened
panels are discussed. The concept of smeared stiffness is introduced and its applicability
discussed briefly. Then, special design conditions such as the panel breaker condition and
failure modes such as skin–stiffener separation are analyzed in detail, concluding with design
guidelines for stiffened panels derived from the previous analyses.
Sandwich structure is treated in Chapter 10. Aspects of sandwich modeling, in particular the
effect of transverse shear on buckling, are treated first.Various failure modes such as wrinkling,
crimping, and intracellular buckling are then discussed with particular emphasis on wrinkling
with and without waviness. Interaction equations are introduced for analyzing sandwich
structure under combined loading. A brief discussion on attachments including ramp-downs
and associated design guidelines close this chapter.
The final chapter, Chapter 11, summarizes design guidelines and rules presented throughout
the previous chapters. It also includes some additional rules, presented for the first time in this
book, that have been found to be useful in designing composite structures.
To facilitate material coverage and in order to avoid having to read some chapters that
may be considered of lesser interest or not directly related to the reader’s needs, certain
concepts and equations are presented in more than one place. This is minimized to avoid
repetition and is done in such a way that reader does not have to interrupt reading a certain
chapter and go back to find the original concept or equation on which the current derivation
is based.
Specific problems are worked out in detail as examples of applications throughout the book
Representative exercises are given at the end of each chapter. These require the determination
of geometry and/or stacking sequence for a specific structure not to fail under certain applied
loads. Many of them are created in such a way that more than one answer is acceptable
reflecting real-life situations. Depending on the assumptions made and design rules enforced,
different but still acceptable designs can be created. Even though low weight is the primary
objective of most of the exercises, situations where other issues are important and end up
driving the design are also given. For academic applications, experience has shown that
students benefit the most if they work out some of these exercises in teams so design ideas and
concepts can be discussed and an approach to a solution formulated.
It is recognized that analysis of composite structures is very much in a state of flux and new
and better methods are being developed (for example failure theories with and without
damage). The present edition includes what are felt to be the most useful approaches at this
point in time. As better approaches mature in the future, it will be modified accordingly.

The field of aerospace is wide ranging and covers a variety of products, disciplines and
domains, not merely in engineering but in many related supporting activities. These combine to
enable the aerospace industry to produce exciting and technologically challenging products. A
wealth of knowledge is contained by practitioners and professionals in the aerospace fields that
is of benefit to other practitioners in the industry, and to those entering the industry from
University.
The Aerospace Series aims to be a practical and topical series of books aimed at engineering
professionals, operators, users and allied professions such as commercial and legal executives
in the aerospace industry. The range of topics is intended to be wide ranging, covering design
and development, manufacture, operation and support of aircraft as well as topics such as
infrastructure operations, and developments in research and technology. The intention is to
provide a source of relevant information that will be of interest and benefit to all those people
working in aerospace.
The use of composite materials for aerospace structures has increased dramatically in the last
three decades. The attractive strength-to-weight ratios, improved fatigue and corrosion
resistance, and ability to tailor the geometry and fibre orientations, combined with recent
advances in fabrication, have made composites a very attractive option for aerospace
applications from both a technical and financial viewpoint. This has been tempered by
problems associated with damage tolerance and detection, damage repair, environmental
degradation and assembly joints. The anisotropic nature of composites also dramatically
increases the number of variables that need to be considered in the design of any aerospace
structure.
This book, Design and Analysis of Composite Structures: With Application to Aerospace
Structures, provides a methodology of various analysis approaches that can be used for the
preliminary design of aerospace structures without having to resort to finite elements.
Representative types of composite structure are described, along with techniques to define
the geometry and lay-up stacking sequence required to withstand the applied loads. The value
of such a set of tools is to enable rapid initial trade-off preliminary design studies to be made,
before using a detailed Finite Element analysis on the finalized design configurations