On the effects of surface finish and geometry on strain-life curves: a. Plot strain-life curves for steels SAE 1045 and SAE 4142(450 HB). Use log-log coordinates and cover lives from

1to 10ʻcycles. The plotted curves are for polished machined surfaces. Now, consider and plot the effect of unpolished surface finish on the strain-life curves and comment on the effect of surface finish on the strain-life curves. b. A rotating shaft has been made of SAE 4142 (670 HB) and it has two different diameters: d = 150 mm and d,= 175 mm.The surface has been machined with a fillet of radius r =10%mm. Adjust the constants for the stain-life curve so that it is appropriate for making life estimate for this shaft. Then-plot both the original and modified curves for log-log-coordinates from 1 10 cycles and comment on how they differ.