|
|
|
Book Review: Fracture Resitance of Aluminum Alloys
12-27-02
Publisher: The Aluminum Association / ASM International
Aluminum alloys are used in a variety of fracture-critical applications such as commercial and military aircraft as well as other high performance structures as a result of an excellent combination of light weight, strength, and fracture resistance. The recent publication of Fracture Resistance of Aluminum Alloys: Notch Toughness, Tear Resistance, and Fracture Toughness by J. Gilbert Kaufman provides designers and materials developers alike with an indispensable resource for those cases where performance in the presence of a notch, flaw, or crack is important. Much more than simply a compilation of engineering data (and it has plenty of that), this book benefits greatly from the insights of its author, whose name is synonymous with the development of fracture testing methods and properties for aluminum alloys through the years.
This book is the next (but hopefully not the last) in the continuing efforts made by Gil Kaufman to provide reference information for aluminum alloys in a highly accessible and readable form. It follows two other publications he has authored, entitled Properties of Aluminum Alloys: Tensile, Creep, and Fatigue Data at High and Low Temperatures in 1999 and Introduction to Aluminum Alloys and Tempers in 2000, both of which have proven to be excellent resources for the working engineer involved with aluminum alloys. Again, this book is a product of a publishing collaboration between the Aluminum Association and ASM International. The bulk of the data summarized in the book was provided by Alcoa, Inc. based on decades of work at the Alcoa Laboratories, much of which the author directed or was involved in. In fact, the book is really the first significant attempt to pull together information on this topic since the 1960 publication by Alcoa of a booklet entitled "Fracture Characteristics of Aluminum Alloys". Obviously much has transpired in terms of testing methods as well as materials development since that time, and so this book was certainly needed.
Certainly the core of the book is the extensive amount of tabular data on fracture resistance properties of aluminum alloys. Perhaps Kaufman says it best in the Preface, noting "the book is unique in the degree to which it presents individual test results for many individual lots of a wide range of aluminum alloys, tempers, and products, rather than simply broad summaries of data; it is also unique for the breadth of types of fracture parameters presented." Separate sections address the key fracture resistance parameters used for aluminum alloys in depth, dealing with notch toughness and notch sensitivity (Chapter 5), tear resistance (Chapter 6), and fracture toughness (Chapter 7), as well as the effect of high and low temperature on fracture resistance (Chapter 9). It includes data on wrought and cast aluminum alloy products as well as welded structures from these alloys. So on one level, this book is a valuable reference work for locating fracture resistance information for specific alloy/temper/product form combinations.
But this book also provides something more than a database of properties. It captures the insights of an expert in the field, and presents them in a direct and unbiased way. Woven into the chapters is an assessment of the relative value of various fracture resistance methods for aluminum alloys. For example, it is noted that while notched impact testing is useful for steels exhibiting ductile-to-brittle transition as a function of temperature, this test method is not so useful for aluminum alloys that do not undergo such a transition. Similarly, the difficulties in using measures derived from tensile tests, such as area under the stress-strain curve, as fracture resistance measures are illustrated. It is also notes that the linear elastic fracture mechanics methodology that governs fracture toughness testing, assuming the extension of a crack under elastic conditions, is not applicable to the broad range of aluminum alloys due to their toughness and hence the need for crack-resistance curve testing and analysis methods. The broader applicability of tear resistance as a measure of fracture resistance for the wide range of aluminum alloys is noted. These comments, plus the historical context into which they are placed, provide helpful interpretative background.
Another useful element of this book is the presentation of key interrelationships between fracture properties. The Summary in Chapter 12 captures in concise form the major trends described in greater detail in earlier chapters. These trends are presented as summaries of subsets of the data in graphical form for clarity and improved understanding, supported by the author's commentary. Coupled with a discussion of the metallurgical considerations in fracture resistance, this enables the reader to gain a better knowledge of systematic variations in properties as a function of factors such as alloy composition, product form, and processing method. It also provides a historical snapshot of the development of more fracture resistant alloys that has been critical to their application in advanced structural applications. While not the focus of the book, there is also a chapter discussing subcritical crack growth processes, specifically fatigue, creep, and stress-corrosion cracking, and their relationship to fracture toughness. These additions benefit those involved in alloy selection as well as alloy design by adding knowledge to the numbers.
Rounding out the book are other useful reference elements, specifically:
- A listing of relevant ASTM standards that govern fracture resistance testing in general and for aluminum alloys in particular
- A chapter devoted to defining terminology related to fracture behavior
- An extensive reference list of key publications
- Both subject and alloy indexes, the latter being especially helpful for locating specific data for alloys of interest
- An appendix containing the specimen drawings for various fracture resistance tests
This new and very valuable contribution to the aluminum materials information
collection can be obtained from the Aluminum Association Bookstore online at www.aluminum.org
or from ASM International at www.asminternational.org.
Article provided courtesy of The Aluminum Association - www.aluminum.org
|
|
|
