Exam 2024 06 21 WT2 solutions

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1 Master of Science in Aeronautical Engineering Politecnico di Milano Course of Machine Design (Prof. M. Giglio) Written test 2 – 21.06.2023 Name: Surname: Polimi-ID: Do not write here TOTAL Instructions For each of the following 8 questions, select the right answer among those provided, by adding the symbol “x” as appropriate in the yellow-colored cells. Correct answers correspond to “+1”, wrong and no answers to “- 0.5”. Question # Text Yes 1 In FEM, a structure can be modeled as a plane problem only if: • Forces act in the out-of-plane directions • Forces act in the in-plane directions X • The thickness of the structure is constant, independently from the direction of the external loads • The dimensions of the structure are of the same order of magnitude (height, thickness, width) Question # Text Yes 2 The mean stress produces on the fatigue limit of the material the following effect: • A reduction of the fatigue limit in stress amplitude, both for positive and negative mean stresses • An increase of the fatigue limit in stress amplitude, both for positive and negative mean stresses • A reduction of the fatigue limit in stress amplitude, only for positive mean stresses X • An increase of the fatigue limit in stress amplitude, only for positive mean stresses Question # Text Yes 3 In a fatigue assessment, the notch sensitivity q: • Is generally higher for low strength respect to high strength materials • Increases with the absolute dimension of the component • Is generally higher for high strength respect to low strength materials X • Has no relationship with the strength of the materials 2 Question # Text Yes 4 For crack propagation condition, the effect of the overload could be considered by: • The use of Walker law to insert the effect of R ratio • Increasing the…