Fatigue Damage-Block-Package Method

The new S-N curve is the full line of Fig. 8.48 whereas the dotted line represents the S-N curve under fully reversed condition R — —1). It can be seen how the two lines merge at 10 cycles since mean stress is losing its effect in low cycle fatigue. The slope Hb of the line is equal to —1/0.129 = —7.75. Since there will be stress amplitudes below the fatigue limit that can have an effect because of the 

The Haibach line is shown in Fig. 8.56. Table 8.1 list the corresponding life cycles Ni below the fatigue limit and the ratios hi/Ni. Equation (8.43) yields the number m of allowable blocks 

The gear, then, can withstand about 187,000 km. Note that the first package of cycles alone can be tolerated by the gear for 188,000 cycles which actually means the remaining three packages reduce the life of just 1000 km. The gear fife is determined by the amplitude of the first package. 

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