...and STILL the answer key is wrong. From the Wikipedia:
"In materials science, the strength of a material refers to the material's ability to withstand an applied stress without failure. Yield strength refers to the point on the engineering stress-strain curve (as opposed to true stress-strain curve) beyond which the material begins deformation that cannot be reversed upon removal of the loading. Ultimate strength refers to the point on the engineering stress-strain curve corresponding to the maximum stress."
The last edition of this book was in 2005. What exactly in the above definition of this subject matter has changed in the last four years? Are our bridges in danger of breaking into pieces and floating into space? Or perhaps the authors have lost a great deal in the stock market and picking the pockets of students who had a great supply of affordable used fourth editions was the solution to the authors' problems?
I used this book in one of its much earlier incarnations (early 90's) for a class, and it was wonderfully written. The prose was clear, the examples to the point, and the illustrations were entirely adequate. However, that was the second or so edition, and the answer key was still wrong back then. I compared the fourth edition of this book to my stepson's fifth edition, and I have to say, what is the point? The sections have been rearranged as have the questions, and it appears some of the errors in previous editions are gone, but new ones have popped up, in some cases to problems that have been in this book for years but have just been put in a different place in the book.
If this book was about the underlying subject of material science aimed at seniors or graduate students, well that subject changes quickly. However, this is a book aimed at college sophomores, and the underlying calculations have not changed. I really loved studying this subject with my second edition. Since that edition was sufficient in 1992, I don't know why three more editions with no more room for improvement with the exception of the answer key which has still not been fixed is necessary for anything but the publisher's bottom line.