An S-n curve for an aluminium alloy is shown below. The curve shows the mean lifetime of specimens loaded with a fully alternating cyclic stress. The lifetimes for specimens vary, but a scatter factor of 3 encompasses all of the available test data (i.e. the lower bound lifetime for design is 1/3 of the mean lifetime). Cyclic stress amplitude S (MPa) 350 300 250 200 150 100 50 0 1.0E+04 1.0E+05 1.0E+06 1.0E+07 Number of cycles to failure N 1.0E+08 A part must be designed to survive 800,000 cycles. What magnitude of alternating stress (in MPa) should not be exceeded for the component? Answer: 130 The correct answer is: 105