Mechanical fatigue in a magnetically levitated axial blood pump

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Title: Mechanical fatigue in a magnetically levitated axial blood pump
Author: Slevar, Amy
Abstract: This research investigated some of the mechanical fatigue associated with the use of a rotary pump as a left ventricular assist device, LVAD, for long term therapy (>20 years). In this magnetically levitated axial pump, we identified one feature most susceptible to mechanical stress and fatigue. the thin-sectioned inducer blade is made of titanium and is the first point of contact between the housing and impeller should the levitation system momentarily lose control. !e inducer blade is also long and thin and will experience both normal and bending loads when contacted by the impeller. The incidence of contact and relative speed between the pump impeller and the inducer blades were modeled for a variety of lifetime “G” force producing activities (e.g. walking, running). !e normal and shear forces resulting from the contact of the spinning impeller and the stationary inducer blades are not obvious or easily modeled, so an experimental test rig was developed to model the impeller touchdown and empirically determine the force at contact. Using the data collected from the test rig, fatigue analysis was performed to determine the pump life and mode of failure; whether the pump would fail due to cracking and fracture of the blades or have infinite life. Infinite life was defined as ~10 million cycles, which corresponds to one contact per minute for twenty years. The finite element analysis shows the inducer blade surviving all testing with a factor of safety greater than one. the result of this preliminary study shows that thin sectioned features are viable as touchdown surfaces within an LVAD intended for destination therapy.
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Date: 2007-06

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