A steel component is subjected to a reversed cyclic loading of 100 cycles/day over a period of time in which ±160 N/mm^2 is applied for 200 cycles, ±140 N/mm^2 is applied for 200 cycles and ±100 N/mm^2 is applied for 600 cycles. If the fatigue life of the material of the component at each of these

Question

A steel component is subjected to a reversed cyclic loading of 100 cycles/day over a period of time in which ±160 N/mm² is applied for 200 cycles, ±140 N/mm² is applied for 200 cycles and ±100 N/mm² is applied for 600 cycles. If the fatigue life of the material of the component at each of these stress levels is [latex] 10^{4}, 10^{5} ext { and } 2 imes 10^{5} [/latex] cycles respectively, estimate the life of the component using Miner’s law.

Accepted Answer

Suppose that the component fails after P sequences of the three stages. Then, from Eq. (8.5)

[latex] \frac{n_{1}}{N_{1}}+\frac{n_{2}}{N_{2}}+\cdots+\frac{n_{r}}{N_{r}}=1 [/latex] (8.5)

[latex] P\left[\left(200 / 10^{4} ight)+\left(200 / 10^{5} ight)+\left(600 / 2 imes 10^{5} ight) ight]=1 [/latex]

which gives

P = 40

The total number of cycles is 1000 so that at the rate of 100 cycles per day the total number of days to fracture is 40×1000/100=400 days.

Question 8.7: A steel component is subjected to a reversed cyclic loading ...

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