1. Given below are the monotonic ultimate tensile strengths, Brinell hardness, and rotating bending fatigue test data for three steels, ranging from low carbon steel (Material A) to a high strength

steel (Material C). Please make two plots of this fatigue data: one on linear-linear coordinates and one on log-log coordinates. Comment on the fatigue behavior of these three steels. Why are log-log coordinates most commonly used to plot fatigue data? Material A S, 42 ks BHN - 69 Alternating Stress (ksi) 32.3 30.3 27.9 25.9 25.4 24.4 24.4 24.0 23.6 23.5 N₂ (cycles) 4.5 x 10 2.4 x 10 8.0 x 10 1.5 x 10 2.7 x 10 7.8 x 10 1.0 x 10 2.6 x 10 1.2 x 10 2.2 x 10 *Specimen did not fail. ME/MSE/AE/CEE/CHBE 7774 Homework 1 S/S, Material B S 102.6 ksi BHN - 209 Alternating Stress (ksi) 81.4 74.7 71.6 64.7 62.1 59.6 58.8 58.7 57.2 56.2 N₂ (cycles) $1000-09 S 4.4 x 10 8.5 x 10 1.4 x 10² 6.3 x 10³ 1.9 x 10 2.9 x 10⁰ 6.4 x 10 1.4 x 10 1.0 x 10 9.0 x 10 Material C S, - 180 ki BHN - 370 Alternating Stress (ksi) Se=0.55, 206 110 105 An estimate for the fatigue limit, Se, for steels is S. * 0.5 x S for S₁ ≤ 200 ksi (1379 MPa) if S, > 200 ksi, S, 100 ksi (690 MPa) The stress amplitude corresponding to a life of 1000 cycles, S₁000, is estimated to be 0.9 x Su- A line connecting this point and the fatigue limit (assuming it is reached at 10° cycles), on log- log coordinates, can be used to estimate the S-N diagram if no actual fatigue data are available, illustrated in Figure P1.1. Let's see how well that works. Please compare all of the test data together by plotting it on this estimate of the S-N curve. Comments? 100 98 95 92 90 N₂ (cycles) 2.4 x 10 3.1 x 10 4.5 x 10 8.7 x 10 1.5 x 10² 1.0 x 10 1.0 x 10 Life to Failure, N (cycles) Figure P1.1 Generalized S-N curve for wrought steels on log-log plot.