the effect of pre-stressing on the static indentation load ... young’s modulus of elasticity, gpa...

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  • Christopher DellaCorteGlenn Research Center, Cleveland, Ohio

    Lewis E. Moore III and Joshua S. CliftonMarshall Space Flight Center, Huntsville, Alabama

    The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60NiTi


    January 2013 2018-05-15T20:01:18+00:00Z

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  • Christopher DellaCorteGlenn Research Center, Cleveland, Ohio

    Lewis E. Moore III and Joshua S. CliftonMarshall Space Flight Center, Huntsville, Alabama

    The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60NiTi


    January 2013

    National Aeronautics andSpace Administration

    Glenn Research Center Cleveland, Ohio 44135

    Prepared for theInternational Joint Tribology Conferencecosponsored by the American Society of Mechanical Engineers (ASME) and the Society of Tribologists and Lubrication Engineers (STLE)Denver, Colorado, October 710, 2012

  • Acknowledgments

    The authors wish to acknowledge NASAs Subsonic Rotary Wing Project and the NASA Engineering and Safety Center for their continuing support of this work. The authors also acknowledge the technical contributions made to this work by NASA Glenn Research Centers Richard A. Manco II, Walter Wozniak, Fransua Thomas and Joy Buehler. Without their efforts in machining, heat-treating and metallographic polishing preparation of the raised land indent plates this work would have been impossible. Lastly, the importance of doing such detailed characterization of the static load capacity of 60NiTi and the specific methodology used were inspired by the continuing interest and support of Mr. A. R. Leveille who has been a pioneer in this field. The author is deeply indebted to his supportive and guiding interest.

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  • NASA/TM2013-216479 1

    The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60NiTi

    Christopher DellaCorte

    National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135

    Lewis E. Moore III and Joshua S. Clifton

    National Aeronautics and Space Administration Marshall Space Flight Center Huntsville, Alabama 35812

    Abstract Superelastic nickel-titanium alloys, such as 60NiTi (60Ni-40Ti by wt.%), are under development for

    use in mechanical components like rolling element bearings and gears. Compared to traditional bearing steels, these intermetallic alloys, when properly heat-treated, are hard but exhibit much lower elastic modulus (~100 GPa) and a much broader elastic deformation range (~3 percent or more). These material characteristics lead to high indentation static load capacity, which is important for certain applications especially space mechanisms. To ensure the maximum degree of elastic behavior, superelastic materials must be pre-stressed, a process referred to as training in shape memory effect (SME) terminology, at loads and stresses beyond expected use conditions. In this paper, static indentation load capacity tests are employed to assess the effects of pre-stressing on elastic response behavior of 60NiTi. The static load capacity is measured by pressing 12.7 mm diameter ceramic Si3N4 balls into highly polished, hardened 60NiTi flat plates that have previously been exposed to varying levels of pre-stress (up to 2.7 GPa) to determine the load that results in shallow but measurable (0.6 m, 25 in. deep) permanent dents. Hertz stress calculations are used to estimate contact stress. Without exposure to pre-stress, the 60NiTi surface can withstand an approximately 3400 kN load before significant denting (>0.4 m deep) occurs. When pre-stressed to 2.7 GPa, a static load of 4900 kN is required to achieve a comparable dent, a 30 percent increase. These results suggest that stressing contact surfaces prior to use enhances the static indentation load capacity of the superelastic 60NiTi. This approach may be adaptable to the engineering and manufacture of highly resilient mechanical components such as rolling element bearings.


    HRC Rockwell C hardness E Youngs modulus of elasticity, GPa stress, GPa y yield stress, GPa , deflection, elongation strain Poissons ratio W load, Kgf F force, N D indenter diameter, mm dp dent depth, m dp/D dent depth ratio

  • NASA/TM2013-216479 2

    Introduction The nickel-rich, binary nickel-titanium alloy 60NiTi is among several intermetallic, superelastic

    alloys currently under consideration as candidate materials for use in mechanical components (Ref. 1). Materials such as 60NiTi (60Ni-40Ti by wt%) exhibit an unusual combination of physical properties that impact the design and performance of mechanical components especially rolling element bearings (Ref. 2). Namely, 60NiTi can be hardened to high levels (Rockwell C 58-62), has a relatively low apparent elastic modulus (E~100 GPa) and exhibits a very large elastic deformation range (typically >3 percent). The combination of these three physical characteristics impart extraordinarily high resiliency that translates to high static indentation load capacity, an important attribute for a bearing material. Additionally, because the composition contains no iron, such alloys are immune to atmospheric rusting behavior observed even for the stainless steel 440C. Table I gives the approximate properties of 60NiTi along with the shape memory alloy 55NiTi and selected conventional bearing materials.

    TABLE I.NOMINAL PROPERTIES FOR CONVENTIONAL BEARING ALLOYS AND 55NiTi AND 60NiTi Property 60NiTi 55NiTi 440C Si3N4 M-50 Density 6.7 g/cc 6.5 g/cc 7.7 g/cc 3.2 g/cc 8.0 g/cc Hardness 56-62 HRC 35-40 HRC 58-62 HRC 1300-1500 Hv 60-65 HRC Thermal conductivity W/m-K 18 19 24 33 ~36

    Thermal expansion ~12.4106/C ~10106/C 10106/C 2.6106 ~11106/C Magnetic Non Non Magnetic Non Magnetic Corrosion resistance Excellent Excellent Marginal Excellent Poor

    Tensile/flexural strength ~1000 MPa ~900 MPa 1900 MPa 600-1200 MPa (bend strength) 2500 MPa

    Youngs Modulus ~95 GPa ~100 GPa 200 GPa 310 GPa 210 GPa Poissons ratio ~0.34 ~0.34 0.3 0.27 0.30 Fracture toughness TBD TBD 22 MPa/m 5-7 MPa/m 20-23 MPa/m Maximum use temp ~500 C ~300 C ~400 C ~1100 C ~400 C Electrical resistivity ~80106 -cm ~80106 -cm ~36106 -cm Insulator ~60106 -cm

    TBD: to be determined

    The high static indentation load capacity was first verified experimentally in an earlier study by the

    authors (Ref. 2). The primary impetus for that work was derived from data obtained from rather conventional compressive strength tests conducted as part of a more general


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