This committee has contributed significantly to the field of fracture mechanics and fatigue crack growth and was combined with ASTM Committee E in to form Committee E on Fatigue and Fracture. These failures, along with fatigue problems in othcr u. Air Force planes, laid the groundwork for the requirement to use fracture mechanics concepts in the B-1 bomber development program of the s. This program included fatigue crack growth life considerations based on a preestablished detectable initial crack size. An extensive investigation [31] of the collapse showed that a cleavage fracture in an eyebar caused by the growth of a flaw to a critical size was responsible.

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Copyright by Marcel Dekker, Inc. All Rights Reserved. Copyright Marcel Dekker, Inc. ISBN: This book is printed on acid-free paper. Headquarters Marcel Dekker, Inc. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microlming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher.

Preface My primary objective in this book is to provide a simple introduction to the subject of mechanical properties of engineered materials for undergraduate and graduate students. I have been encouraged in this task by my students and many practicing engineers with a strong interest in the mechanical properties of materials and I hope that this book will satisfy their needs.

I have endeavored to cover only the topics that I consider central to the development of a basic understanding of the mechanical properties of materials. It is not intended to be a comprehensive review of all the different aspects of mechanical properties; such a task would be beyond the capabilities of any single author. Instead, this book emphasizes the fundamental concepts that must be mastered by any undergraduate or graduate engineer before he or she can effectively tackle basic industrial tasks that require an understanding of mechanical properties.

This book is intended to bridge the gap between rigorous theory and engineering practice. The book covers essential principles required to understand and interpret the mechanical properties of different types of materials i. Following a brief introduction to materials science and basic strength of materials, the fundamentals of elasticity and plasticity are presented, prior to a discussion of strengthening mechanisms including composite strengthening concepts.

A simple introduction to the subject of fracture mechanics is then presented along with fracture and toughening mechanisms and a description of the effects of fatigue and the environment. Wherever possible, the text is illustrated with worked examples and case studies that show how to apply basic principles to the solution of engineering problems.

This book has been written primarily as a text for a senior undergraduate course or rst-level graduate course on mechanical properties of materials. However, I hope that it will also be useful to practicing engineers, researchers, and others who want to develop a working understanding of the basic concepts that govern the mechanical properties of materials. To ensure a wide audience, I have assumed only a basic knowledge of algebra and calculus in the presentation of mathematical derivations.

The reader is also assumed to have a sophomore-level understanding of physics and chemistry. Prior knowledge of basic materials science and strength of materials concepts is not assumed, however.

The better-prepared reader may, therefore, skim through some of the elementary sections in which these concepts are introduced. Finally, I would like to acknowledge a number of people that have supported me over the years. I am grateful to my parents, Alfred and Anthonia, for the numerous sacrices that they made to provide me with a good education.

I am indebted to my teachers, especially John Knott, Anthony Smith, David Fenner, and Stan Earles, for stimulating my early interest in materials and mechanics. I am also thankful to my colleagues in the eld of mechanical behavior who have shared their thoughts and ideas with me over the years.

In particular, I am grateful to Frank McClintock for his critical review of the rst ve chapters, and his suggestions for the book outline. I also thank my colleagues in the mechanical behavior community for helping me to develop my basic understanding of the subject over the past 15 years.

I simply cannot imagine how this project could have been completed without her help. I am grateful to my students and colleagues at Princeton University, MIT, and The Ohio State University who have provided me with a stimulating working environment over the past few years.

In particular, I thank Lex Smits, my current department chair, and all my colleagues. My interactions with colleagues and students have certainly been vital to the development of my current understanding of the mechanical behavior of materials.

I would like to thank the Program Managers, Dr. Bruce McDonald and Dr. Murty, for providing the nancial support and encouragement that made this book possible. Appreciation is also extended to Prof. Tom Eager and Prof. The sabbatical year at MIT provided me with a stimulating environment for the development of the rst few chapters of this book. This project would certainly not have been completed by me without their vision, patience, and encouragement. Finally, I thank my wife, Morenike, for giving me the freedom and the time to write this book.

This was time that I should have spent with her and our young family. However, as always, she was supportive of my work, and I know that this book could have never been completed without her forebearance and support. Bibliography Basic Denitions of Stress and Strain 3. Bibliography Introduction to Dislocation Mechanics 6. Dislocation Strengthening Mechanisms 8. Bibliography 11 Fundamentals of Fracture Mechanics The response can be understood in terms of the basic effects of mechanical loads on defects or atomic motion.

A simple understanding of atomic and defect structure is, therefore, an essential prerequisite to the development of a fundamental understanding of the mechanical behavior of materials. A brief introduction to the structure of materials will be presented in this chapter.

The treatment is intended to serve as an introduction to those with a limited prior background in the principles of materials science. The better prepared reader may, therefore, choose to skim this chapter. This was generally accepted by philosophers and scientists without proof for centuries.

However, although the small size of the atoms was such that they could not be viewed directly with the available instruments, Avogadro in the 16th century was able to determine that one mole of an element consists of atoms.

The periCopyright Marcel Dekker, Inc. For the rst time, scientists were able to view the effects of atoms that had been postulated by the ancients. A clear picture of atomic structure soon emerged as a number of dedicated scientists studied the atomic structure of different types of materials.

First, it became apparent that, in many materials, the atoms can be grouped into unit cells or building blocks that are somewhat akin to the pieces in a Lego set. These building blocks are often called crystals.

However, there are many materials in which no clear grouping of atoms into unit cells or crystals can be identied. Atoms in such amorphous materials are apparently randomly distributed, and it is difcult to discern clear groups of atoms in such materials. Nevertheless, in amorphous and crystalline materials, mechanical behavior can only be understood if we appreciate the fact that the atoms within a solid are held together by forces that are often referred to as chemical bonds.

These will be described in the next section. Strong bonds are often described as primary bonds, and weaker bonds are generally described as secondary bonds. However, both types of bonds are important, and they often occur together in solids. It is particularly important to note that the weaker secondary bonds may control the mechanical behavior of some materials, even when much stronger primary bonds are present. A good example is the case of graphite carbon which consists of strong primary bonds and weaker secondary bonds Fig.

The relatively low strength of graphite can be attributed to the low shear stress required to induce the sliding of strongly primary bonded carbon layers over each other. Such sliding is easy because the bonds between the sliding primary bonded carbon planes are weak secondary bonds.

Since these are relatively strong bonds, primary bonds generally give rise to stiff solids. The different types of primary bonds are described in detail below. The ions may be Copyright Marcel Dekker, Inc. Adapted from Kingery et al. Reprinted with permission from John Wiley and Sons.

Note that both ions achieve more stable electronic structures complete outer shells by the donation or acceptance of electrons. Adapted from Ashby and Jones, Reprinted with permission from Pergamon Press. Also, due to their relatively high bond strengths, ionically bonded materials have high melting points since a greater level of thermal agitation is needed to shear the ions from the ionically bonded structures.

The ionic bonds are also nonsaturating and nondirectional. Such bonds are relatively difcult to break during slip processes that after control plastic behavior irreversible deformation. Ionically bonded solids are, therefore, relatively brittle since they can only undergo limited plasticity.

Examples of ionically bonded solids include sodium chloride and other alkali halides, metal oxides, and hydrated carbonates. Covalent bonds are often found between atoms with nearly complete outer shells. The atoms typically achieve a more stable electronic structure lower energy state by sharing electrons in outer shells to form structures with completely lled outer shells [ Fig.

A wider range of bond strengths is, therefore, associated with covalent bonding which may result in molecular, linear or three-dimensional structures. One-dimensional linear covalent bonds are formed by the sharing of two outer electrons one from each atom.

These result in the formation of molecular structures such as Cl2, which is shown schematically in Figs 1. Long, linear, covalently bonded chains, may form between quadrivalent carbon atoms, as in polyethylene [Figs 1.

Branches may also form by the attachment of other chains to the linear chain structures, as shown in Fig. Adapted from Shackleford, Reprinted with permission from Prentice-Hall. Due to electron sharing, covalent bonds are directional in character. Elasticity in polymers is associated with the stretching and rotation of bonds.

The chain structures may also uncurl during loading, which generally gives rise to elastic deformation. The elastic moduli also increase with increasing temperature due to changes in entropy that occur on bond stretching.

Plasticity in covalently bonded materials is associated with the sliding of chains consisting of covalently bonded atoms such as those in polymers or covalently bonded layers such as those in graphite over each other [Figs 1. Plastic deformation of three-dimensional covalently bonded structures [Figs 1.

Furthermore, chain sliding is restricted in branched structures [Fig. The theory behind metallic bonding is often described as the DrudeLorenz theory. Metallic bonds can be understood as the overall effect of multiple electrostatic attractions between positively charged metallic ions and a sea or gas of delocalized electrons electron cloud that surround the positively charged ions Fig.


0884873315 - A&p Technician Airframe Textbook by Jeppesen Sanderson

Main and Drogue parachutes deployed successfully, and the recovery harnesses all worked flawlessly. Nala1 Liftoff on mission ALS A detailed post-flight inspection revealed damage to an internal baffle for the drogue parachute deployment. A plastic container cap designed to hold the backup deployment charge apparently damaged the baffle. When the backup charge was activated, the cap shot forward with enough force to crush the baffle system. Since the drogue parachute was deployed successfully by the primary system, this damage posed no problems for the mission.


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