Metal Fatigue Part 11

Tham khảo tài liệu 'metal fatigue part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 284 Chapter 15 Inclusion w area à o Specimen ỌT Quenched and tempered Specimen VAI Annealed in a vacuum at 300C for 111 after QT Specimen VA2 Annealed in a vacuum at 300C for 2h after QT A Specimen VQ Quenched in a vacuum and tempered area Inclusion size area Inclusion size the size of the dark area ODA Figure The importance of the Optically Dark Area ODA in ultralong life fatigue failure. For symbols and see caption of Fig. or . a Relationship between ODA size and cycles to failure. Open symbols show ODAs in Specimen QT. The symbols and show ODAs in Specimen VAI and Specimen VA2 respectively. The symbol shows ODAs in Specimen VQ. The ODAs in Specimens VAI and VA2 are smaller than those for Specimen QT. The ODAs in Specimen VQ are much smaller than in other specimens. The symbols and in Fig. show the ODAs in Specimens VAI and VA2 respectively. The symbol A shows the ODAs in Specimen VQ. The ODAs in Specimens VAI and VA2 are smaller than those for Specimen QT. The ODAs in Specimen VQ are much smaller than in other specimens. Thus we may conclude that the hydrogen trapped by an inclusion crucially influences the formation of an ODA the particular fracture morphology around the inclusions at fracture origins. Although the mechanism of the interaction of hydrogen and stress is still not clear a possible mechanism may be 19-28 that hydrogen enhances the mobility of screw and edge dislocations and reduces internal friction. In this context we may regard the influence of hydrogen on superlong fatigue as an internal environmental factor contained within a material. Examples of fish eyes that were formed at origins other than inclusions may support this hypothesis. Murakami et al. 29 conducted rotating bending fatigue tests on a bearing steel produced by a special melting method the same material as presented in Chapter 7 page 148 . In this particular case no ODAs were observed adjacent to fracture origins except for very rare examples in which .

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