2015 07 07

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Master of Science in Mechanical Engineering Politecnico di Milano Course of Machine Design 2 (Prof. S. Beretta, Prof.ssa L. Vergani) Written test – 07.07.2015 Name: Surname: Polimi-ID: Do not write here 1 2 3 TOTAL Exercise 1. Consider a thin rotating disk with external radius equal to Re. Requests: 1) Consider that the disk has variable rotational speed from 0 to n (rpm). Perform the fatigue assessment (in the most stressed point) neglecting the inertia effect (i.e. consider stress state only at 0 and n state). 2) Determine the strain value s obtained from 2 rosettes placed in the centre and at the border (by considering the stress exactly at the border) . Consider 0°-45°-90° type, with 0° aligned along the radial direction. 3) Determine the maximum axial strain value. 4) Perform the static assessment considering also an external pressure pe acting on the border of the rotating disk. Data Re=500mm Radius of the disk n=4'000 rpm Rotational speed pe= -50 MPa Material of the disk: Fe510 Rm=510 MPa Rsn=360 MPa U=7860 kg/m3 volumic mass Exercise 2. Data z=2 m v=1m M=15kNm HE180B h=180mm b=180mm a=8.5mm / e=14 mm / r=15 mm Ix=3831cm4 Material of the beam/welding: Fe510 A HE180B beam is over constrained. Requests: 1) Plot diagrams of the internal forces; 2) Design and assess a proper welding joint at the clamp. Exercise 3. Let us consider a component, made of Al alloy, subjected to a cyclic stress with Smin=100 MPa and S max=200 MPa. The component, with a thickness of 30 mm, can be treated as simply subjected to axial loading. A defect with a depth a i=2mm (to be treated as a semicircular crack) has been detected on the component. Fracture toughness of the material is 30 MPa√m. Coefficients of Paris law are: m=3.70, C=1.42e-11 [m/cycle]. These parameters are given for the…