作者 Menzel, Brian C
書名 Cyclic damage initiation and growth in bulk metallic glass
國際標準書號 9780542984167
book jacket
說明 100 p
附註 Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6675
Adviser: Reinhold H. Dauskardt
Thesis (Ph.D.)--Stanford University, 2006
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
School code: 0212
DDC
Host Item Dissertation Abstracts International 67-11B
主題 Applied Mechanics
Engineering, Mechanical
Engineering, Materials Science
0346
0548
0794
Alt Author Stanford University