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Friction and Lubrication in Mechanical Design Episode 2 Part 13

Tham khảo tài liệu 'friction and lubrication in mechanical design episode 2 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 530 Chapter 13 Table 13.6 Hardness Data for the Test Specimens Material Hardness BHN 1020 untreated 1020 treated 170-180 4340 low hardness untreated 4340 low hardness treated 285-311 4340 high hardness untreated 4340 high hardness treated 363-375 4350 low hardness untreated 4350 low hardness treated 321-331 4350 high hardness untreated 4350 high hardness treated 375-388 Similar tests were also performed on 1020 steep specimens for comparison. The chemical composition of the 4340 and 4350 steel used in the test is given in Table 13.7. Sample results of the unidirectional bending fatigue test data for the different materials with and without the 40 thermal cycles are given in Figs 13.31-13.35. It can be seen in Fig. 13.31 that the high-hardness 4350 steel had an endurance limit of approximately 108 ksi as would be expected from the published data on the material. The 40 thermal cycles in this case caused a reduction of approximately 45 in the value of the endurance limit. Figure 13.32 shows similar results for the low-hardness 4350 steel specimens where the same thermal cycles caused a 42 reduction in the endurance limit. Similar results for the 4340 steel are given in Figs 13.33 and 13.34 where the reduction in the endurance limit is found to be approximately 20 . It is interesting to note from the fatigue data for the 1020 steel specimens that the endurance limit was reduced by only 12 to a value of 55 ksi. This value is the mean value of the endurance limits under the same condi- Table 13.7 Chemical Properties of 4340 and 4350 Steel Steel c Mn p s Si Cr Ni Mo 4340 0.38 0.77 0.014 0.026 0.27 0.78 1.59 0.23 4350 0.49 0.66 0.009 0.025 0.25 0.77 1.61 0.23 Figure 13.31 Fatigue data for 4350 steel high hardness o without thermal cycles with thermal cycles. Figure 13.32 Fatigue data for 4350 steel low hardness o without thermal cycles with thermal cycles. 531 Figure 13.33 Fatigue data for 4340 steel high hardness o without thermal cycles with thermal cycles. Figure 13.34