^* Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, TX 78712, U.S.A.

^** Kobe Steel, Ltd., Materials Design Section, Materials Research Laboratory, 1-5-5 Takatukadai, Nishi-ku, Hyogo, Japan

^*** Department of Mechanical Systems Engineering, College of Engineering, University of Osaka Prefecture, Sakai, Osaka 593, Japan

^**** Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, U.S.A.