A catastrophic failure of manufacturing equipment has occurred in a specialized facility. The facility was damaged and large amounts of revenue are now being lost by the manufacturer while repairs are underway. Additionally, a Nickel superalloy casting weighing 24.3 metric tons (24,300kg) being lifted by the hoist was damaged during the failure. As an engineer on a team of independent investigators, it is your job to determine if a design, operational, manufacturing or other engineering failure took place and who is ultimately responsible if so.
a) Calculations performed by your team determine that the 3cm diameter cylindrical member on the hoist was subjected to the full weight of the casting during lifting. If the hoist is rated to normal operation up to 325MPa, was the facility operating in accordance with the design limitations? (8 Points)
b) The parts supplier for the company that makes the hoist states that a typical fracture toughness of the material is 35MPasqrt(m). Assuming that the value of Y is 1.1 , what size surface flaw must be present on the hoist member in order for fracture to occur at the design stress? (7 Points)
c) Following the investigation, you find that the rated stress on the hoist member provided by the hoist manufacturer is actually the yield strength of the member. Your team performs a redesign of the operational criteria such that the member is operated within the design stress and an added factor of safety of 3. However, as the member is loaded to this stress many times per day, the likely failure mechanism now becomes fatigue. If the member is completely unloaded in the minimum stress condition and has a mean crack length of 1.4mm, estimate the number of cycles to failure for the member. Assume power law parameters for the crack growth per cycle relationship of C=6.9**10^(-12) and n=3.0. (15 Points)
d) Assuming that the casting damaged during the failure is an average component, that 6 components per shift are lifted by the hoist, and that your company operates 3 shifts/day 5 days/week, when would you reasonably need to replace the hoist member component as part of preventative maintenance? Show your work, state at least 2 assumptions, and briefly explain your reasoning. (10 pts)
A catastrophic failure of manufacturing equipment has occurred in a specialized facility. The facility was damaged and large amounts of revenue are now being lost by the manufacturer while repairs are underway. Additionally, a Nickel superalloy casting weighing 24.3 metric tons (24,300 kg) being lifted by the hoist was damaged during the failure.As an engineer on a team of independent investigators, it is your job to determine if a design, operational, manufacturing or other engineering failure took place and who is ultimately responsible if so.
a) Calculations performed by your team determine that the 3 cm diameter cylindrical member on the hoist was subjected to the full weight of the casting during lifting. If the hoist is rated to normal operation up to 325 MPa, was the facility operating in accordance with the design limitations? (8 Points)
b) The parts supplier for the company that makes the hoist states that a typical fracture toughness of the material is 35 MPaVm.Assuming that the value of Y is 1.1,what size surface flaw must be present on the hoist member in order for fracture to occur at the design stress? (7 Points)
c) Following the investigation, you find that the rated stress on the hoist member provided by the hoist manufacturer is actually the yield strength of the member.Your team performs a redesign of the operational criteria such that the member is operated within the design stress and an added factor of safety of 3.However, as the member is loaded to this stress many times per day,the likely failure mechanism now becomes fatigue.If the member is completely unloaded in the minimum stress condition and has a mean crack length of 1.4 mm,estimate the number of cycles to failure for the member. Assume power law parameters for the crack growth per cycle relationship of C=6.9*10-12 and n=3.0. (15 Points)
d) Assuming that the casting damaged during the failure is an average component, that 6 components per shift are lifted by the hoist, and that your company operates 3 shifts/day 5 days/week, when would you reasonably need to replace the hoist member component as part of preventative maintenance? Show your work, state at least 2 assumptions, and briefly explain your reasoning.(10 pts)
