Exam 2024 01 24 WT2 solutions

Page 1

1 Master of Science in Aeronautical Engineering Politecnico di Milano Course of Machine Design (Prof. M. Giglio) Written test 2 – 24.01.2023 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 A crack with length is found at the center of an infinite thin plate subjected to a cyclic loading, with the plate material characterized by a fracture toughness KIC • The shape factor for the current case can be 1.2 with central crack • The crack will propagate regardless of the intensity of the load • The fracture toughness KIC depends on the crack length • Failure can be predicted by computing the critical crack length based on KIC X Question # Text Yes 2 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 3 The Sines criterion • cannot be used for the local approach • cannot be used for the global approach • can be used for both the local and the global approach X • is used for conducting static assessments 2 Question # Text Yes 4 About the fatigue crack propagation, indicate which of the following sentences is NOT CORRECT: • Stress Intensity Factor changes under a variable load with the same law • Paris law can describe the fatigue crack growth process considering the threshold and stable propagation zones X • The…