Problem 4 (25 points) The flat plate shown is a part in a machine. The plate has a width reduction as shown in the diagram. The dimensions are: W = W2 W1 M 14 mm, w = 21 mm, t = 5 mm, and notch radius p = 0.7 mm. When the machine is switched on, the machine applies a cyclic loading to the plate: a completely reversed bending moment amplitude M = 39 Nm. The material (aircraft quality AISI 4340 steel) has ultimate strength = 1172 MPa. Based on experimental data of smooth specimens subjected to completely reversed cyclic loading (m = 0), the S-N curve of this material is described by the Basquin equation: ar = f (2N+) , where the fatigue strength coefficient = 1758 MPa, and the fatigue strength exponent b = -0.0977. (a) Determine the fatigue notch factor ky of this plate. (b) Determine the fatigue life N, of this plate. 3.0 W2 2.6 W1 M 2.2 K W/W=3 6M S = 1.5 W2t 1.8 1.1. 1.05 1.4 1.02 1.0 0 0.05 0.1 0.15 0.2 0.25 0.3 p/W Elastic Stress Concentration Factor kt Peterson material constant a for steel: log = 2.654 10-7-1.309 10- +0.01103 , mm = 10 log a (345 2070 MPa)