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Tham khảo tài liệu 'simulating fatigue cracks growth in spiral bevel gears part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | the photographs of the fracture surfaces designate the tooth number the level of magnification and a length scale. Figure 6.4 Low magnification 5.3x view of tooth 11 s fracture surface on concave side. 6.3.2 Results The morphologies of teeth 5 and 11 are very similar. Lines emanating radially from the starter notch are visible at low magnifications 4.6x in Figure 6.3 and 5.3x in Figure 6.4 . These lines are indicative of fatigue crack growth. On tooth 11 some fatigue striations can be seen near the EDM notch. Region A in Figure 6.5a is the EDM notch. Figure 6.5b is a magnified view of the striated region.8 As expected the striations are roughly parallel to the edge of the EDM notch. The crack growth direction was perpendicular to the striations and as mentioned above from the bottom of the figure towards the top. In general however most of the surface near the notch was flat with no significant features or texture. This flat surface leads to the conclusion that significant rubbing took place. The rubbing polished the surface and removed all features that would have indicated the mode of fracture e.g. fatigue striations dimples etc. The rubbed surface was visible over approximately 80 of the surface when moving away from the notch toward the ridge of the fracture. Point B in Figure 6.3 is the approximate location where Figure 6.6 was taken. Figure 6.6 is an example of the typical surface appearance in the rubbed region.9 The 8 Figure B.l in Appendix B also contains magnified views of the striated region. 9 Figure B.2 in Appendix B is another picture of the typical surface appearance in the rubbed region. Point B in Figure 6.4 is the approximate location where Figure B.2 was taken. NAS A CR 2000-210062 73 polishing might have resulted from rubbing of the crack faces while the gear was in operation or rubbing against a part of the gearbox after fracturing away from the pinion. The extent and uniformity of the flat polished surfaces support the former hypothesis. .
