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Simulating Fatigue Cracks Growth in Spiral Bevel Gears Part 10

Tham khảo tài liệu 'simulating fatigue cracks growth in spiral bevel gears part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Section 7.3.3. The goal is to predict what operating conditions would be necessary to obtain the fracture path observed in the tested pinion. For the constant torque level of 3120 in-lb approximately five hundred thousand cycles were predicted to propagate the crack through the tooth thickness. This value is the same order of magnitude as that which occurred in the tested pinion. The number of cycles to produce the tooth fractures in the test is smaller than 4.9 million. The sensitivity of the fatigue life prediction to the values chosen for the model parameters is studied in Section 7.3.1. Alban s condition number four for classic tooth-bending fatigue scenario Section 2.5 is not captured in the numerical work. The magnitude of the applied loads during the cycle was kept constant during the crack propagation analyses Figure 7.2a. This type of loading scenario is considered load control and results in the SIFs increasing continuously as the crack grows Figure 7.2b. Fatigue crack growth will occur at an increasing rate until the SIFs satisfy a fracture criterion such as K KIC. Crack growth simulations under load control will predict a shorter number of cycles to failure than observed. This is because in reality when a cracked and uncracked tooth mesh the cracked tooth will deflect a limited amount before it s adjacent tooth picks up a portion of the load Alban 1985 . The displacement of the crack faces reaches a maximum and will be roughly equal for every remaining load cycle. As a result the rate of increase in the SIFs will decrease and reach roughly a constant maximum every cycle. An idealization of this is shown schematically in Figure 7.2c. Propagating the crack under these conditions is considered displacement control. When the maximum SIF ceases to increase the fatigue crack growth rate is relatively constant and the number of cycles to failure increases. Figure 7.2 Schematic of load cycles a Load versus time b Ki versus time load control and c Ki versus time