7. (15 pts total) A manufacturing process that unintentionally introduces cracks to the surface of a part was used to produce load-bearing components. The design requires that the components be

able to withstand a stress of450 MPa. The component failed catastrophically in-service. Working at an independent lab, the part is dropped on your desk and it is up to you to determine whether the component failed due an overload in-service or due to flaws introduced during the manufacturing process. The manufacturer claims that the components were polished to remove cracks and inspected to ensure that no surface cracks were larger than 0.5 mm, so they claim the component must have failed due to operator error. It has been independently verified that a 5 cm diameter part was subjected to an in-service tensile load of 1 MN. The material from which the component is made has a fracture toughness of 75 MPa-m2 and an ultimate tensile strength of 600 MPa. Assume external cracks for which Y is 3.4. (a) (10 pts) Who is at fault for the component failure, the manufacturer or the operator? Show your work for both cases and then justify your decision. (b) (5 pts) In addition to the analysis, what features might you look for on the fracture surfaces to support your conclusions?

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