Question

A large spacecraft is on a long mission of exploration. Part of the craft rotates so that the crew can experience artificial gravity. During the mission, it is found that a non-serviceable structural member connected with the rotating section has been unexpectedly subjected to high cycle fatigue, with one cycle of elastic deformation and zero mean stress for every revolution. Back on Earth, the mission control centre has an identical member tested under accelerated high cycle fatigue conditions with zero mean stress. They find that the member fails with a stress range, Δσ, of 300 MPa after 105 cycles and with a stress range of 200 MPa after 107 cycles. Assuming that the fatigue behaviour can be represented by: Δσ (Nf a) = C Where a and C are material constants, calculate the number of cycles to failure, Nf, for the structural member in the spacecraft, if it is being subjected to a stress range of 120 MPa

Answer 1