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i 6‘ FIBER FRACTURE Elsevier Science Internet Homepage - http://www.elsevier.com Consult the Elsevier homepage for full catalogue information on all books, journals and electronic products and services. Elsevier Titles of Related Interest CARPINTERI Minimum Reinforcement in Concrete Members. ISBN: 0-08-043022-8 FUENTES ETAL Fracture Mechanics: Applications and Challenges. ISBN: 0-08-043699-4 JONES Failure Analysis Case Studies 11. ISBN: 0-08-043959-4 MACHAETAL Multiaxial Fatigue and Fracture. ISBN: 0-08-043336-7 MARQUIS & SOLIN Fatigue Design of Components. MARQUIS & SOLIN Fatigue Design and Reliability. ISBN: 0-08-043329-4 MOORE ETAL. Fracture Mechanics Testing Methods for Polymers, Adhesives and Composites. ISBN: 0-08-043689-7 MURAKAMI Metal Fatique Effects of Small Defects and Nonmetallic Inclusions ISBN: 0-08-044064-9 ISBN: 0-08-04331U-Y RAVICHANDRAN ET AL. Small Fatigue Cracks: Mechanics, Mechanisms & Applications. ISBN: 0-08-04301 1-2 &MY & PETIT Temperature-Fatigue Interaction. 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Elices and J. Llorca. EURESCO Conference on High Performance Fibers: Eumonference on Fiber Includes bibliographical references and index. ISBN 0-08-044104-1 (hbk. : alk. paper) psm. Fracture held in Cala Viiias (Mallorca, Spain) during the fall of 2000. 1. Fibers-Congresses. 2. Fracture mechanics-Congresses. I. Elices, Manuel. 11. Llorca, J. (Javier) 111. Title. TA4 1 8.9F5 E87 2002 620.1‘l26 dc21 2002029479 British Library Cataloguing in Publication Data A catalogue record from the British Library has been applied for. ISBN: 0-08-044104-1 63 The paper used in this publication meets the requirements of ANSINSO 239.48-1992 (Permanence of Paper). Printed in The Netherlands. ACKNOWLEDGEMENTS This book was conceived during the EURESCO Conference on High Performance Fibers: Euroconference on Fiber Fracture held in Cala Viiias (Mallorca, Spain) during the fall of 2000 under the sponsorship of the European Science Foundation and of the European Union, (through contract HPCF-CT-1999-00126) as well as of the Spanish Ministry of Science and Technology (through grant MAT- 1999-1 822-E). The Editors would like to acknowledge the support and encouragement of these institutions as well as of others that made possible the Conference and the publication of this book. Particularly we wish to acknowledge the financial support provided by the United States Air Force Office for Scientific Research, NASA Glenn Research Center, and Dupont de Nemours Inc. In addition, the Polytechnic University of Madrid and the University of the Balear Islands contributed actively to the organisation of the Conference and helped with grants for young Spanish researchers. This book could not have published without the generous co-operation of the distinguished scientists who, besides imparting their keynote lectures at the Conference, agreed to write and polish the manuscripts. The untiring help of Rosa Morera and JosC Miguel Martinez in the edition of the book is also gratefully acknowledged. Our heart felt thanks to all of them. MANUEL ELICES and JAVIER LLORCA Madrid, October 2001 PREFACE Fibers stand among the stiffest and strongest materials either present in nature or manufactured by man. They are used in structural components, embedded in a matrix which maintains the fibers oriented in the optimum direction, distributes the concentrated loads, protects the fibers against wear and chemical attack from the environment, and provides the transverse stiffness to avoid buckling in compression. These new composite materials are rapidly taking over from the traditional structural materials (metallic alloys and polymers) in many industrial components, and accordingly, a new industry devoted to the manufacture of high performance fibers has emerged. The world wide production of high performance fibers was in excess of 2 millions tons in the year 2000, and it’s growing rapidly as new potential uses are envisaged every day. These novel applications often require further improvements in fiber properties and research in this field is very active. As a result, numerous books and conference proceedings are available on different aspects of fiber processing, properties, or applications but none is focused on the fructure behaviour of fibers. Man-made high performance fibers derive their outstanding properties from the strong ionic, covalent or metallic bonds which sustain the load. As the ductility of these links is very limited, fibers are brittle, their ultimate strength being controlled by their fracture behaviour, and further improvements in fiber properties can bc obtaincd through a deeper knowledge of the physical mechanisms involved in fiber fracture. In addition, it has long been known that the excellent combination of strength and ductility exhibited by many natural fibers comes from damage tolerance imparted by their hierarchical structure. However, contact among the researchers working on the mechanical behaviour of natural and synthetic fibers has been very limited so far, and this book also tries to cover this gap by presenting the mechanisms and models of fiber fracture currently available for both kinds of fibers. It is expected that this effort will lead to cross fertilization between the two fields, opening new frontiers to academic research and more competitive products for industry Finally, a note on the text. Differences in spelling are commonplace in English books written by scholars from different countries, and they normally pass unnoticed. This is not the case, however, in this book where they appear in the very title. Fiber (the american way) and fibre (the traditional British form) are both used freely throughout the book and, although aesthetic considerations would recommend the choice of one or the other, we have decided to keep the original spelling used by each author. [...]... Eutectic Fibers A Sayir and S.C Farmer V vii 3 27 57 75 89 I07 Glass Fibers Strength of Glass Fibers P.K Gupta 127 Carbon Fibers Fracture of Carbon Fibers J.G Lavim 157 Metallic Fibers Strength and Fracture of Metallic Filaments H.U Kiinzi 183 Fracture of Superfine Metallic Wires K Yoshida 24 1 xii CONTENTS Polymeric Fibers Fracture of Highly Oriented, Chain-ExtendedPolymer Fibres J WS.Hearle Fracture. .. is hard to imagine that fracture may be triggered by defects of human size CONTENTS Acknowledgements Preface Introduction Fiber Fracture: An Overview K.K Chawla Models of Fibre Fracture M Elices and J Llorca Forms of Fibre Fracture J.W.9 Hearle Ceramic Fibers Fracture Processes in Fine Silicon Carbide Fibres A.R Bunsell Fracture F’rocesses in Oxide Ceramic Fibres M.-H Berger Fracture Characteristicsof... overview of fiber failure M Elices and J Llorca review available models of fiber fracture and J.WX Hearle surveys the diverse forms of fiber fracture exhibited in SEM studies The second block is devoted to ceramic fibers, relevant to high temperature metal and ceramic composites A.R Bunsell deals with S i c fibers Several generations of these fibers have been produced and the changes in the fracture. .. undulations on the fiber surface of a single crystal alumina fiber, Saphikon fiber Fig 14 A typical fracture surface of alumina single crystal fiber showing cleavage planes 21 FIBER FRACTURE: AN OVERVIEW t Fig 15 (a) The rough surface of a polycrystalline alumina fiber SEM (b) The grain structure of an alumina fiber TEM Rough surface of such brittle fibers makes them break at very low strain and it makes... Saphikon fibers show undulations on the fiber surface, see Fig 13 Typically fracture surface of such single crystal fibers show cleavage planes, see Fig 14 These fibers typically have microvoids formed during fiber growth from the melt One important feature of ceramic fibers is the surface texture Their surface roughness scales with grain size Fig 15a shows the rough surface of an alumina fiber while... individual fibers whether in a fabric or in a composite to last a reasonable time Fracture in fibers, as in bulk materials, initiates at some flaw(s), internal or on the surface In general, because of the high surface to volume ratio of fibers, the incidence of a surface flaw leading to fracture is greater in fibers than in bulk materials Fractography, the study of the fracture surface, of fibers can... any polymeric fiber is the degree of molecular chain orientation along the fiber axis In order to get high strength and stiflness in organic fibers, one must obtain oriented molecular chains with full extension An important result of this chain alignment along the fiber axis is the marked anisotropy in the characteristics of a polymeric fiber Rigid-rod polymeric fibers such as aramid fibers show very... buckle on compression, forming kink bands at thinner surface of the fiber A crack initiates on the tensile side and propagates across the fiber (Johnson, FIBER FRACTURE: AN OVERVIEW 13 1990) In contrast, high-modulus mesophase pitch-based carbon fibers deform by a shear mechanism leading to kink bands at 45" to the fiber axis METALLIC FIBERS Metallic filaments represent a fairly mature technology Steel... fracture stress and the mirror radius of ceramic and glass fibers FIBER FRACTURE: AN OVERVIEW 19 derived ceramic fibers The following mirror constants were obtained from the slope of their respective lines in Fig 1 2 1.6 MPa m-'j2 for E-glass fiber and 2.2 MPa m-1/2 for optical glass and CA fibers The mirror constant for the fused-silica optical fiber is in good agreement with the Ai value of 2.22 MPa... Carbon; Ceramic; Fibers; Metal; Polyethylene; Polymer; Optical; Steel; Tungsten FIBER FRACTURE: AN OVERVIEW 5 INTRODUCTION Fracture of a fiber is generally an undesirable occurrence For example, during processing of continuous fibers, frequent breakage of filaments is highly undesirable from a productivity point of view When this happens in the case of spinning of a polymer, ceramic or a glass fiber, the . Glass Fibers Strength of Glass Fibers P.K. Gupta Carbon Fibers Fracture of Carbon Fibers J. G. Lavim Metallic Fibers Strength and Fracture. overview of fiber failure. M. Elices and J. Llorca review available models of fiber fracture and J.WX Hearle surveys the diverse forms of fiber fracture