Answer Happy

Introduction You are working for a large consortium that mines diamonds. The company uses a large underwater dredging system to suck rubble from the sea floor to find and extract diamonds. This large dredging system utilizes a swivel that is connected to a hoist cable at one end and an underwater drill head at the other (Figure 1). The swivel facilitates rotation of the cable with respect to the drill head. The swivel shank has a shrunk fitted stainless steel sleeve (Figure 2a) to accommodate slip seals, which would prevent the entry of sea water into the greased bearings of the swivel interior. The inner shank of the swivel collapsed catastrophically (Figure 2b). It is suspected that fatigue had initiated at the stress concentration caused by the shrink fit stainless steel sleeve on the shank. However, the ultimate failure has ignited a massive debate. One argument pointing towards a design failure. The system was designed to be loaded in tension; however, it was suspected that the dredging system could, on occasion, lie on the seabed (Figure 3). The mass distribution (i.e., loading) of the drill head could be assumed to be wn = 15 kN/m for the lowest 2 m and w2 = 2.5 kN/m for the upper 8 m. The other argument points towards manufacturing failure. The design specified that the swivel material be mild steel (0.11% carbon), but upon testing, it was found to be 0.49 % carbon steel (Figure 5). You have been tasked with settling the debate. Conduct a swivel fracture mechanic analysis and comment on the nature of the fracture. The shank fracture surface is as shown in Figure 4. The fracture toughness of the actual shaft mas measured as K c = 77 + 8 MPa/m. Assume that the temperature of the seawater is 10 °C Assignment You need to compile a short report of a maximum of two pages (excluding calculations). Please use the report template provided - there is no need for a cover page, table of contents, etc. The report should be submitted via Vula electronically in PDF format (no other format will be accepted). This report should include the following sections, as outlined below. A: Introduction. Write a short introduction. Clearly state the purpose of the report. [3] B: Failure analysis. Conduct a failure analysis. Show all the calculations and assumptions made. [32] C: Recommendations. Provide a summary of the cause of failure. Discuss a possible redesign. [5] Total marks [40]
Dredging system Swivel Figure 1. Underwater drilling and dredging system. tensile force rotation Fig 4.1 Swivel Tower bearing top section of swivel screwed into lower canister of swivel top bearing stainless steel shrink fit sleeve fracture thrust bearing lower bearing stainless steel shrink fit sleeve Tower eye section rotation tensile force (a) (b) Figure 2. (a) Swivel layout. (b) Section aa, swivel fracture with shrink fit.