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Exercise 2.  Describe the effect of a different load ratio on C and m parameters by means of Walker equation.  Specify for which load ratio (R) the Walker equation converges on the Paris’s law.  Plot the crack growth rate vs stress intensity factor range curves for increasing R. Master of Science in Mechanical Engineering Politecnico di Milano Course of Machine Design 2 (Prof. S. Beretta, Prof. M. Giglio, Prof.ssa L. Vergani) Written test – 08.09.2016 Name: Surname: Polimi-ID: Do not write here 1 2 3 4 TOTAL Exercise 1. Figure 1 shows the runway beam of a bridge crane. The beam has a length of 4L and a HE cross-section. A load (P) moves along the beam from A to E. 1) Calculate bending moment diagrams as a function of P-load position (only consider positions A-B-C-D-E) 2) Select the smallest HE profile which guarantees a maximum transversal displacement of 25 mm in B (considering load P). 3) Focussing on section B, schematise the stress cycle in the most loaded point as a function of load position (only consider positions A-B-C-D-E) 4) Consider the load spectrum within one day can be schematised as in Table 1. Each cycle consists of a force moving from A to E. How many working days can the structure be operative? Figure 1 – Scheme of the runway beam. Table 1 – Typical load spectrum for one day Load Cycle # 2P (overload) 20 P 300 0.4 P 680 P = 50000 N Maximum load on the runway beam L = 3 m semi-span between supports Material: steel (E = 206000MPa; UTS = 450 MPa; YS = 350 MPa; A = 1280MPa; b = - 0.166; ms = 0.7) Master of Science in Mechanical Engineering Politecnico di Milano Course of Machine Design 2 (Prof. S. Beretta, Prof. M. Giglio, Prof.ssa L. Vergani) Written test – 08.09.2016 Name: Surname: Polimi-ID: Exercise 3. It is required to design the fatigue test for…