4 A steamy problem For winter vacation, you decide to ditch the family Christmas

Question

4 A steamy problem For winter vacation, you decide to ditch the family Christmas/Holidays gathering and spend some quiet time alone at a hot springs resort instead. As you soak in the steamy outdoor pool all by yourself and snowflakes float down and merge into the water's margin, two voices interrupt your meditation, and you decide to listen because why not? It's not like you have anything better to do Two resort staff were talking shop aout the hot water pump. The pump shaft on one of the units broke recently much to the surprise of the technicians, since the failure occurred several years earlier tharn expected lifetime of the component. The shaft is the force transmitter of the pump the motor applies a force onto the shaft, which turns the rotor blades that creates a pressure difference that pumps the water. Your prior knowledge tells you that the shaft will be under cyclic loading as it is driven by the motor. upler Shaft Earlier in the year, the technicians conducted inspection and maintenance on the pump and found no problems with the shaft at all. During that inspection, they also replaced one of the couplers used to secure the shaft to the rotor of the pump. Because of the high humidity in the pump shack, both the pump shaft and the coupler were originally stainless steel (Grade 430) to avoid rusting issues. During that inspection, the owner decided to replace the stainless steel coupler with a more expensive titanium one since business was on fire and she had cash to burn. One of the staff laments that he had a gut feeling that the titanium coupler is somehow related to the failure, but cannot find a logical reason because the titanium coupler is stronger and more corrosion resistant than the stainless steel one. Plus, the coupler looked perfectly fine even though the shaft failed. Upon hearing this, you leap out of the water then immediately jump back in when you realize that wasn't the best situation for posing. "I know why your pump shaft failed", you mumble to yourself as the staff members try their best to process what had just happened Question 4 (1 pt.): Explain why you think the pump shaft failed prematurely. Please make sure to explain clearly: what role did the titanium coupler play in this?

Explanation / Answer

The failure of the shaft happened prematurely due to two reasons.

(a) There is a mismatch of thermal properties between coupler and shaft material in the case of titanium coupler. It was not in the previous case when SS coupler was fitted with SS shaft. The mechanical work causing heat in the parts lead to a difference in thermal expansion and the coupler failed.

(b) The variation in strength and endurance limit of the two materials (titanium and SS) is also one of the reason rising the cumulative endurance limits to higher values.

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