Contact Stress Design Parameters for Titanium Bearings

In response to NASA 2015 SBIR Topic H4.02, Air-Lock proposes to define the maximum allowable contact stress for Titanium bearings. The modulus of Titanium is lower than legacy spacesuit bearing materials (Stainless Steel). Due to this, Titanium bearings are more susceptible to deflection under man and plug load scenarios. Bearing deflection causes a limited number of balls to absorb the full load and results in higher, localized, contact stresses. Localized contact stress is believed to be the main contributor to the bearing race degradation observed during NASA's 2014 oxygen compatibility testing. In Phase 1, we will correlate analytical contact stress data with sample bearing test data. This correlation will characterize bearing wear and degradation relative to ball contact stress. Multiple test iterations will be performed to clearly identify the contact stress that degrades a titanium race. We will also determine if there are commercial surface treatments (coatings) that may enhance Titanium wear resistance. At the conclusion of Phase 1, we shall have identified the maximum allowable bearing contact stress. This data point will serve as a valuable design guideline for future bearing designs and should yield reduced certification and development costs.

The Phase 1 deliverable is the definition of the maximum allowable contact pressure/stress for Titanium Bearings and what influence coatings, materials and lubricants may have on that stress. This definition and the process to arrive at the definition will help reduce development and certification cycle time associate to spacesuit and pressure suit bearings as well as disconnects that employ ball locking retention mechanisms. These savings can reduce risk and cost by making it feasible for bearings to go into the Preliminary Design Review process at a very high TRL. Relative to present and future NASA applications, we believe the EMU Program, advanced EVA spacesuits (Z-Series) and the Orion Ascent Entry Pressure Suits can benefit from this work.

Air-Lock's core business focuses on providing life support hardware to enhance human performance in hazardous environments. Along with servicing the space industry, Air-Lock provides this life support hardware to the aerospace, military and fire fighter industries. Similar to our spacesuit products, weight reduction and low profiles are design drivers for aerospace, military and fire fighter life support hardware. A key staple of core products for those industries are quick disconnects (QDs) that utilize bearing ball locking mechanisms. Understanding the role ball contact stresses play relative to component wear and degradation can be implemented across these QD product lines; yielding lighter weight, improved wear resistant assemblies.

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