MARC 主機 00000nam  2200349   4500 
001    AAI3242595 
005    20071221131703.5 
008    071221s2006                        eng d 
020    9780542984167 
035    (UMI)AAI3242595 
040    UMI|cUMI 
100 1  Menzel, Brian C 
245 10 Cyclic damage initiation and growth in bulk metallic glass
300    100 p 
500    Source: Dissertation Abstracts International, Volume: 67-
       11, Section: B, page: 6675 
500    Adviser:  Reinhold H. Dauskardt 
502    Thesis (Ph.D.)--Stanford University, 2006 
520    A high-cycle stress-life fatigue study was conducted on a 
       Zr-based bulk metallic glass to investigate damage 
       initiation and growth mechanisms. Stress-life tests were 
       conducted using tension-tension, compression-tension and 
       compression-compression loadings. Distributed damage was 
       observed to initiate rapidly from pre-existing defects as 
       either shear bands or mixed mode surface cracks that 
       propagated at ∼49° to the maximum tensile stress 
       axis. On reaching a characteristic size, surface damage 
       abruptly changed orientation and continued to grow as mode
       I cracks. The growth rates of these "small" surface cracks
       were carefully characterized and shown to be consistent 
       with "long" crack-growth rate behavior. Fatigue life was 
       estimated from the observed initial defect sizes and 
       "small" crack-growth rate behavior. The resulting life 
       predictions were found to be consistent with measured 
       stress life data for tension-tension loading suggesting 
       that the apparent lack of a damage initiation stage may 
       account for the low endurance limit measured. Several 
       surface modification techniques were explored as possible 
       methods to reduce the number of damage initiation sites 
       and to increase the fatigue life and the endurance limit 
       of metallic glasses. A focused ion beam (FIB) was used to 
       introduce well-defined distributions of initial defects to
       systematically elucidate damage initiation and growth 
       processes in a separate set of specimens. High-resolution 
       techniques were used to characterize the effect of defect 
       size, shape and orientation on damage initiation and the 
       early stages of damage growth. Damage initiation was found
       to be a strong function of defect spacing and to 
       correspond well with region of high equivalent stress. 
       Damage growth was also observed to correspond to 
       directions of high equivalent stress which is highly 
       dependent of the spacing and orientation of defects. Rapid
       damage initiation and mode I damage growth was observed 
       for closely spaced defects while longer initiation 
       followed by initially mixed mode growth was observed for 
       more widely spaced defects 
590    School code: 0212 
590    DDC 
650  4 Applied Mechanics 
650  4 Engineering, Mechanical 
650  4 Engineering, Materials Science 
690    0346 
690    0548 
690    0794 
710 20 Stanford University 
773 0  |tDissertation Abstracts International|g67-11B 
856 40 |u