GATE MT 2022 Q36

High cycle fatigue data for an alloy at various alternating stresses, 𝜎_a (see figure) is given below.

A specimen of this alloy is subjected to multiple stress cycles sequentially in the following order: (i) first 5000 cycles at σa = 400 MPa followed by (ii) 25000 cycles at σa = 300 MPa and finally (iii) at σa = 500 MPa. Assuming that Miner’s law is obeyed, the number of cycles to failure at the final applied stress of

500 MPa is                     .