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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
This book studies the flow of materials and the influence of strain rates on the relationship between imposed stresses and the dynamic deformations obtained. It provides applications for shaping, molecular molding, shrink-fit assembly and welding, including details of the various specific processes for implementation at high strain rates, illustrated by numerous industrial examples. Rheology, Physical and Mechanical Behavior of Materials 1 presents analyses of plasticity mechanisms at microscopic and macroscopic scales, and of the various forms of stressstrain behavior laws according to working speeds, mechanisms, athermics, viscoplasticity and formability limits at types and speeds of change. It is aimed at researchers involved in the mechanics of deformable media, as well as industrial design and manufacturing departments
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Seitenzahl: 261
Veröffentlichungsjahr: 2023
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Preface
Chapter 1: Dynamic Plasticity: Dislocations
1.1. Introduction: how to describe plasticity?
1.2. Strain speed: ( for shearing)
1.3. The microstructural mechanisms of plasticity
Chapter 2: Obstacles and Mechanisms of Crossings
2.1. Obstacles
2.2. Nature and resistance of obstacles
2.3. Example of measuring dislocation speeds
2.4. Microstructural mechanisms of the deformation rate
2.5. Mechanisms due to obstacles: hardening mechanisms
2.6. Athermal mechanism of the movement of a dislocation
2.7. Thermally activated mechanism of the movement of a dislocation
2.8. The viscous friction mechanism
Chapter 3: Dynamic Flows for Monocrystals and Polycrystals
3.1. Type of monocristal and polycrystal dynamic shear test samples (anisotropy and isotropy at high speeds)
3.2. The tensor of the shock stresses
3.3. Study of strain on a polycrystal
3.4. Dynamic flows by electromagnetic shocks, polycrystalline aluminum A5
3.5. The case of six polycrystals
3.6. The case of monocrystals
3.7. Models for CFCs
3.8. Dynamics of flows shown using an ultra-fast camera
3.9. Viscoplasticity
3.10. References for viscoplasticity
Chapter 4: Limits to Static and Dynamic Formability
4.1. Plastic instability
4.2. Forming by pressing
4.3. Damage: area between necking and fracture, the case between Forming Limit Curves (FLCs) and Fracture Forming Limit Curves (FFLCs)
4.4. Limit of the formability during necking (FLCs) and during fracture (FFLCs): influence of the strain rate
Chapter 5: Dynamic Resistance to Mechanical Shocks
5.1. Shock stresses
5.2. Resilience test
5.3. Typical loads, stress waves
5.4. Dynamic tests, Hopkinson technique, laws of behavior
Appendix A. Primary Times of Mechanisms
References
Index
Other titles from iSTE in Mechanical Engineering and Solid Mechanics
End User License Agreement
Guide
Cover
Table of Contents
Title Page
Copyright Page
Preface
Begin Reading
Appendix A. Primary Times of Mechanisms
References
Index
Other titles from iSTE in Mechanical Engineering and Solid Mechanics
End User License Agreement
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Series EditorNoël Challamel
Rheology, Physical and Mechanical Behavior of Materials 1
Physical Mechanisms of Deformation and Dynamic Behavior
Maurice Leroy
First published 2023 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK
www.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA
www.wiley.com
© ISTE Ltd 2023The rights of Maurice Leroy to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2023940623
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78630-765-1
Preface
In many circumstances, different materials are subjected to high levels of stress, which may result from the processes of forming, shock and impact problems, dynamic stresses of certain structural elements and other causes. Also, in recent years, the interest shown in plastic deformations at high speeds has developed considerably.
The researchers concentrated their efforts in laboratory studies using simple tests, within a speed range from 102 to 104 s−1 in order to fill the gap existing between the tests done on conventional hydraulic machines and those done with explosives. In addition to carrying out inexpensive tests, they were seeking to achieve easy implementation and provide as much information as possible on the behavior of the materials that were tested.
The experimental methods used for these studies vary greatly. Some of them are given in Table P.1, with the range of deformation speeds in which they are implemented.
In this book, three types of actions on materials are used (see Figure P.1): mechanical, electromagnetic and electrohydraulic stresses, 102 ≤ ≤ 104 s−1.
Table P.1.Deformation speed
Type of device
Experimental difficulties
< 10
−4
Creep
-
10
−4
to 1
Mechanical or hydraulic
-
1 to 10
2
Hydraulic or pneumatic
Resonance of the device
10
2
to 5.10
3
Hopkinson bar impact machines
Wave propagation, adiabatic heating
> 5.10
3
Impact of projectiles
Wave propagation, high pressures heating
10
3
to 10
6
Expansion of structures caused by explosives
High pressures difficult to measure
Figure P.1.Dynamic stresses – techniques used
1Dynamic Plasticity: Dislocations
1.1. Introduction: how to describe plasticity?
The microscopic description of the plastic strain of metals and alloys mainly relies on the knowledge of the mechanisms for the generation and propagation of dislocations. Though the modeling of macroscopic observations using these microscopic mechanisms has made great progress from a qualitative point of view, much remains to be done from a quantitative point of view.
Under these conditions, the use of a descriptive approach to macroscopic observations remains of great interest. These observations are made on the basis of an examination of mechanical tests in which the strain experienced by the metal as a result of the action of a given system of stresses.
It is necessary here to distinguish the mechanical properties where the time and the rates of strain play only a secondary role (plasticity in the usual sense of the term) from those where time and/or strain rates play an important role (creep, fatigue, dynamic plasticity, etc.).
The mechanical properties reflect the microscopic behavior of the material, and the strain observed at the macroscopic level is the result of local strains on a much finer scale. This microscopic aspect is fundamental for the understanding of different phenomena.
That is why the mechanical tests are often supplemented by a local physical study of the strain mechanism (observations using X-rays, optical microscopes, electronic scanning microscopes, transmission electron microscopes, etc.).
In order to better identify the fundamental mechanisms, it is essential to work on well-defined systems. This is why many studies of the plasticity have been carried out on single crystals.
However, the most commonly used materials are polycrystalline, meaning that they are made up of a more or less isotropic group of monocrystals. It should be noted that for polycrystalline materials, it is more correct to speak of quasi-isotropy than of isotropy.
If the technological material deviates significantly from an isotropic state, then it is said to have a texture. More precisely, a material has a texture if the orientation of its monocrystalline grains, which are generally very numerous, is not totally random but instead presents specific directions which are prevalent. Textures are created at the time the material solidifies, or during an anisotropic strain. They can be transformed by annealing or through phase change. They are of interest economically insofar as they make it possible to improve certain properties of the materials.
Despite the interest industry has in textured materials, we will only consider quasi-isotropic materials in this book.
The application of the experimental laws of plasticity from polycrystalline materials to the calculation of structures in plastic strain, or to the study of processes for forming, can be done by associating two tensors with the stresses and strains shown in the tests with two quantities:
the generalized stress (or equivalent stress) ;
the generalized strain (or equivalent strain) .
It can then be shown that the curve of the variations of on the basis of those of is independent of the type of mechanical test performed. The value of for a given load can thus be deduced from the results of the tensile test, which gives a very particular interest to this type of simple test.
1.1.1. Equivalence between forming processes and mechanical tests
A forming method is in itself a mechanical test. Therefore, it is equivalent to any mechanical test conducted under the conditions indicated above.
A number of simple modeling methods allow for a practical implementation of the laws of plasticity.
REMARK.– The forming processes are generally carried out in dynamic plasticity, with strain speeds from 10 to 104 s−1 (including cases such as forging, wire drawing, stamping, rolling, metal cutting with machining at high speeds, pulsed magnetic fields, explosive, etc.). These cases involve a dynamic rheology, which will be the subject of a dedicated chapter.
1.1.2. Early stages of strain
The yield strength is usually defined as the stress above which a strain does not return to zero once the material is no longer subjected to a load.
