Tham khảo tài liệu 'simulating fatigue cracks growth in spiral bevel gears part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | tooth is once again reduced due to the double tooth contact. The contact area will differ for single tooth and double tooth contact. The change in area of the contact is schematically illustrated in Figures and . Figure Schematic of load progression on adjacent pinion teeth. NAS A CR 2000-210062 13 In Figure tooth 1 and 2 are two adjacent teeth of a spiral bevel pinion. The ellipses represent snap shot areas of contact between a gear and a pinion s tooth. The darkened ellipse is the area that is currently in contact with the gear at a particular instant in time. Similar to Figure the larger ellipses represent single tooth contact and the smaller are areas of double tooth contact. The first row in Figure begins with tooth 1 at the last moment of single tooth contact. After a discrete time step the load on tooth 1 has progressed up the tooth and tooth 2 has come into contact near the root as depicted in row two. In the final row or time step tooth 1 loses contact and tooth 2 advances into the stage of single tooth contact. It is seen in Figures and that the contact area between mating spiral bevel gear teeth moves in three spatial dimensions during one load cycle. Most of the previous research into numerically calculating crack trajectories in gears has been performed on spur gears with two dimensional analyses and has not incorporated the moving load discussed above. Instead a single load location on the spur gear tooth that produces the maximum stresses in the tooth root during the load cycle has been used to analyze the gear. This load position corresponds to the highest point of single tooth contact HPSTC . Contact between spur gear teeth only moves in two directions and therefore this simplification to investigate a spur gear under a fixed load at the HPSTC has proven successful Lewicki 1995 Lewicki et al. 1997a . However since the contact area between mating spiral bevel gear teeth moves in three dimensions the crack front .
