This paper presents a novel approach for improving the resiliency, debris and shock load tolerance, and efficiency of mechanical components via the adoption of emerging hard yet superelastic construction materials. Through a series of conventional and unconventional materials tests, it has been shown that low modulus, hardened superelastic materials, such as 60NiTi, can withstand extreme loading conditions without incurring permanent surface damage. In contrast, bearing and gear materials currently in widespread use readily sustain damage at much lower load levels. The test results, when taken together, indicate that the superior performance of loaded contacts made from this hard superelastic material is directly related to its unique combination of high hardness, significantly reduced 'effective' modulus, and extremely high levels of recoverable strain (superelastic behavior). Based upon the investigations, the following specific remarks are made: (1) the use of hardened materials with a modest effective elastic modulus that exhibit superelastic behavior results in significantly enhanced load capability for contacting surfaces; (2) the extreme levels of recoverable deformation that occur when superelastic low effective modulus materials such as 60NiTi are placed under heavy contact loads result in larger Hertzian contact areas that effectively distribute the load, reduce peak and average stresses, and prevent contact damage; (3) 60NiTi appears to undergo a small amount of irrecoverable plastic deformation during initial loading. After that, it exhibits remarkably reversible, superelastic strain behavior, as evidenced by cyclic compression tests. These observations indicate that some mechanical working of the material, such as coining or forging, might be desirable prior to use; (4) when the exemplary load tolerance of 60NiTi is considered with its previously proven benign tribological behavior, a compelling case for significantly enhanced machine component performance is expected; and (5) when one considers that the 60NiTi material is the least complex superelastic alloy currently available, it is likely that through alloying and other developments, materials with greatly enhanced performance will emerge. Though much more research will be required before we can fully understand 60NiTi material and its metallurgical relatives, the results obtained thus far point to a very bright future for many applications in which extreme loading is unavoidable. Further, it is anticipated that many other materials with similar superelastic behavior will emerge to greatly expand the tools available to mechanical design engineers for problem solving and technological development.
Resilient and corrosion-proof rolling element bearings made from superelastic Ni-Ti alloys for aerospace mechanism applications
Elastische und korrosionsbeständige Wälzlager, hergestellt aus superelastischen Ni-Ti-Legierungen für Luft- und Raumfahrt-Anwendungen
2012
24 Seiten, 13 Bilder, 5 Tabellen, 15 Quellen
Conference paper
English
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