A. Biscarini

Internal friction spectra of the Ni40Ti50Cu10 shape memory alloy charged with hydrogen

Abstract The temperature dependence of the dynamic Young’s modulus E, the elastic energy dissipation coefficient Q−1 and the heat flow (DSC) has been studied between 90 and 370 K in an Ni40Ti50Cu10 alloy containing various amounts nH of H (nH=H/Me=0; 0.004; 0.008; 0.013 and 0.018 at.). The Young’s modulus exhibits softening when the start temperature Ms of the B2→B19 martensitic transition is approached on cooling and a much steeper modulus decrease between Ms and Mf. This steep decrease appears to be associated with stress-induced motions of twin boundaries within the B19 martensite as it is drastically reduced by H pinning of these boundaries. No internal friction (IF) peak occurs at the B2→B19 transition and the values of Q−1 are high in the B19 martensite (≅100×10−4). Two IF peaks, PH and PTWH, occur below Ms in the H-doped material; the first is likely due to stress-assisted reordering of H elastic dipoles within a hydride phase, the second to H dragging processes by twin boundaries.

Extraordinary high damping of hydrogen-doped NiTi and NiTiCu shape memory alloys

Abstract The internal friction, Q −1 , and the Young’s modulus, E , have been investigated as a function of temperature at kHz frequencies in the Ni 30 Ti 50 Cu 20 alloy containing various amounts n H ( n H =H/Me at.) of H. Several dissipation processes have been observed which are associated with stress-induced motions either of isolated H atoms, or of twin boundaries interacting with H. Values of Q −1 as high as 0.075 have been measured in the presence of H impurities over extended temperature regions at around the B2–B19 and B2–B19′ martensitic transitions. The observed damping is not a transient effect as those usually reported at low frequencies in H-free materials, thus, it does not depend on the rate of temperature change. No appreciable dependence of the damping on the frequency and strain-amplitude are observed between 0.48 and 1.5 kHz and between 1×10 −7 and 3×10 −5 , respectively. A brief review of previous results obtained with other alloy compositions and relevant comparisons is also included.

Enhanced Nitinol Properties for Biomedical Applications

In recent years, Nitinol producers and medical products have experienced an exponential growth, driven by advanced manufacturing techniques and the use of progressively less invasive medical procedures. Concurrently, new processing techniques have been developed to further enhance the valuable properties of Nitinol used in medical devices; recent patents on these techniques include changing the composition of nickel and titanium, alloying the nickel-titanium with other elements, improving melting practices, heat-treating the alloy, and mechanical processing of the alloy. For example, alloying the nickel-titanium with ternary elements may widen the superelastic temperature operating window, maximize/minimize the stress-strain hysteresis, and improve the radiopacity of a Nitinol intraluminal device comparable to that of a stainless steel device of the same strut pattern coated with a thin layer of gold. Limiting to less than 30% the final cold work step (after a full anneal, and before the shape-setting step) may improve the Nitinol fatigue lifetime of about 37%, the fatigue lifetime being a primary factor limiting the performances of Nitinol endoluminal prosthetic implants. Local selective and differential thermo-mechanical treatments have also been devised to achieve different physical properties in different portions of a Nitinol medical device in order to improve its performance under expected operating conditions.

Hydrogen diffusion and interpretation of the 200K anelastic relaxation in NiTi alloys

The internal friction, the Young’s modulus, and the heat flow have been measured as a function of temperature (20–360K) at kilohertz frequencies in a H-free and H-doped Ni50.8Ti49.2 alloy, solubilized under vacuum and rapidly furnace cooled. The chemical H-diffusion coefficient DC has been deduced from absorption experiments (323–1063K) and has been compared with the Einstein diffusion coefficient DE derived from a Snoek (or Zener)-type relaxation PH. The comparison has allowed the interpretation of the so-called 200K relaxation as a Snoek (or Zener)-type relaxation due to hydrogen.

Mechanical spectroscopy of the H-free and H-doped Ni30Ti50Cu20 shape memory alloy

Abstract The temperature dependence of the dynamic Young’s modulus E , the elastic energy dissipation coefficient Q −1 and the heat flow (DSC) has been studied between 20 and 370 K in a H-free and H-doped ( n H =H/Me=0.006 and 0.01 at.) Ni 30 Ti 50 Cu 20 alloy. The Young’s modulus exhibits softening when the start temperature M s of the B2→B19 martensitic transition is approached on cooling and a steep modulus decrease between M s and M f . This steep decrease is associated with stress-induced motions of twin boundaries within the B19 martensite. Hydrogen reduces background damping of the martensite and dramatically enhances the dissipation in the temperature region of the transformation. These observations suggest that hydrogen (a) forms fixed pinning points for twin boundaries at low temperature and (b) gives rise to an anelastic relaxation P H associated with H dipoles and to a peak P AM due to H-twin boundary interactions.

Selective contribution of each hamstring muscle to anterior cruciate ligament protection and tibiofemoral joint stability in leg-extension exercise: a simulation study.

A biomechanical model was developed to simulate the selective effect of the co-contraction force provided by each hamstring muscle on the shear and compressive tibiofemoral joint reaction forces, during open kinetic-chain knee-extension exercises. This model accounts for instantaneous values of knee flexion angle

Long-lasting effects of neck muscle vibration and contraction on self-motion perception of vestibular origin

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A neutron-spectroscopy study of the local vibrations, the interstitial sites and the solubility limit of hydrogen in niobium-molybdenum alloys

, angular velocity and acceleration, and for changes in magnitude, orientation, and application point of external resistance. The tibiofemoral shear force (TFSF) largely determines the tensile force on anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). Biceps femoris is the most effective hamstring muscle in decreasing the ACL-loading TFSF developed by quadriceps contractions for