Fremont, CA, United States
Fremont, CA, United States

Time filter

Source Type

Pelton A.R.,Nitinol Devices & Components | Fino-Decker J.,Nitinol Devices & Components | Vien L.,Nitinol Devices & Components | Bonsignore C.,Nitinol Devices & Components | And 3 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2013

The rotary bending fatigue properties of medical-grade Nitinol wires were investigated under conditions of 0.5-10% strain amplitudes to a maximum of 107 cycles. The results from this study provide insight into the behavior of Nitinol under fully reversed (εmin/εmax=-1) fatigue conditions for three compositions, two surface conditions and three test temperatures. For pseudoelastic conditions there are four distinct regions of the strain-cycle curves that are related to phases (austenite, stress-induced martensite, and R-Phase) and their respective strain accommodation mechanisms. In contrast, there are only two regions for the strain-cycle curves for thermal martensite. It was further observed that the strain amplitude to achieve 107-cycles increases with both decreasing test temperature and increasing transformation temperature. Fatigue behavior was not, however, strongly influenced by wire surface condition. SEM of the fracture surfaces showed that the fatigue fracture area increased with decreasing strain amplitude. Finite element analysis was used to illustrate strain distributions across the wire as well as to calculate the tension-compression contributions to the rotary bending curves. The results from this investigation are discussed with respect to mechanisms of strain accommodation under cyclic tensile and compressive conditions. © 2013 Elsevier Ltd.


Runciman A.,University of California at Berkeley | Runciman A.,Lawrence Berkeley National Laboratory | Xu D.,University of California at Berkeley | Xu D.,Lawrence Berkeley National Laboratory | And 3 more authors.
Biomaterials | Year: 2011

Medical devices, particularly endovascular stents, manufactured from superelastic Nitinol, a near-equiatomic alloy of Ni and Ti, are subjected to complex mixed-mode loading conditions in vivo, including axial tension and compression, radial compression, pulsatile, bending and torsion. Fatigue lifetime prediction methodologies for Nitinol, however, are invariably based on uniaxial loading and thus fall short of accurately predicting the safe lifetime of stents under the complex multiaxial loading conditions experienced physiologically. While there is a considerable body of research documented on the cyclic fatigue of Nitinol in uniaxial tension or bending, there remains an almost total lack of comprehensive fatigue lifetime data for other loading conditions, such as torsion and tension/torsion. In this work, thin-walled Nitinol tubes were cycled in torsion at various mean and alternating strains to investigate the fatigue life behavior of Nitinol and results compared to equivalent fatigue data collected under uniaxial tensile/bending loads. Using these strain-life results for various loading modes and an equivalent referential (Lagrangian) strain approach, a strategy for normalizing these data is presented. Based on this strategy, a fatigue lifetime prediction model for the multiaxial loading of Nitinol is presented utilizing a modified Coffin-Manson approach where the number of cycles to failure is related to the equivalent alternating transformation strain. © 2011.


Saffari P.,Nitinol Devices & Components | Senthilnathan K.,Nitinol Devices & Components | Duerig T.,Nitinol Devices & Components
ASM International - International Conference on Shape Memory and Superelastic Technologies, SMST 2015 | Year: 2015

Finite Element Analysis requires a UMAT to describe the stress-strain relationship for Nitinol. This, in turn, determines how each element interacts with its neighboring elements. Typical UMAT inputs for superelastic Nitinol include the elastic moduli of martensite and austenite, loading and unloading plateau stresses and strains, and Poisson's ratio, plus a single material data point for the compressive side of the stress as shown in Figure 1. Lifetime prediction in Nitinol is generally based on mean and cyclic strain calculations. While it is often assumed that strain calculations are primarily geometric and largely independent of the UMAT inputs, that is not the case-far-field behavior is displacement controlled, but near-field calculations are force controlled (stress-based) and thus dependent upon the UMAT inputs. The current paper will present several case studies highlighting the sensitivity of FEA strain calculations to various UMAT inputs, showing a particularly powerful influence on stress hysteresis. Copyright © 2015 ASM International® All rights reserved.


Sengupta A.,University of California at Berkeley | Papadopoulos P.,University of California at Berkeley | Kueck A.,Nitinol Devices & Components | Pelton A.R.,Nitinol Devices & Components
Computational Mechanics | Year: 2011

Fully coupled thermomechanical models for Nitinol at the grain level are developed in this work to capture the inter-dependence between deformation and temperature under non-isothermal conditions. The martensite transformation equations are solved using a novel algorithm which imposes all relevant constraints on the volume fractions. The numerical implementation of the resulting models within the finite element method is effected by the monolithic solution of the momentum and energy equations. Validation of the models is achieved by means of thin-tube experiments at different strain rates. © 2011 Springer-Verlag.


Kuo W.T.,Stanford University | Deso S.E.,Stanford University | Robertson S.W.,Nitinol Devices & Components
Journal of Vascular and Interventional Radiology | Year: 2013

A 48-year-old man presented with symptomatic inferior vena cava (IVC) occlusion from a chronically thrombosed and embedded Vena Tech LGM filter resulting in exercise intolerance from diminished cardiac preload and postthrombotic syndrome from chronic venous insufficiency. The patient was treated using a new PRIME technique - Piecemeal Removal by Intentional MEchanical fracture - to achieve successful filter retrieval 16 years after implantation. Removal of the obstructing filter permitted endovascular IVC recanalization with restoration of venous outflow and alleviation of venous obstructive symptoms. Cardiac preload was restored, allowing the patient to resume long-distance running, and he successfully completed a half-marathon 3 months after treatment. © 2013 SIR.


Kuo W.T.,Stanford University | Robertson S.W.,Nitinol Devices & Components | Odegaard J.I.,Stanford University | Hofmann L.V.,Stanford University
Journal of Vascular and Interventional Radiology | Year: 2013

Purpose: To evaluate clinical outcomes, characterize adherent tissue, and analyze inferior vena cava (IVC) filter fractures in patients undergoing complex retrieval for management of filter-related complications. To elucidate mechanisms of filter fracture by radiographic and electron microscopic (EM) evaluation. Materials and Methods: Over 2.5 years, 50 consecutive patients with fractured and/or penetrating filter components were prospectively enrolled into a single-center study. There were 19 men and 31 women (mean age, 42 y; range, 15-73 y). All patients underwent complex filter retrieval after failure of standard methods, and retrieval indications along with resultant clinical outcomes were evaluated. Specimens with adherent tissue underwent histologic analysis, and all fractured components were studied with EM. Results: Retrieval was successful in all 50 cases (mean implantation, 815 d; range, 20-2,599 d) among the following filters: G2X (n = 23),G2 (n = 9), Eclipse (n = 3), Recovery (n = 4), ALN (n = 1), Celect (n = 7), OptEase (n = 2), and Simon Nitinol (n = 1). Mean indwell time in fractured filters (n = 31) was 1,082 days, versus 408 days in nonfractured filters (n = 19; P =.00169). Neointimal hyperplasia/fibrosis was seen in 46 of 48 specimens with adherent tissue (96%). Among 61 fractured components from conical filters, 35 had extravascular penetration whereas 26 remained intravascular (11 free-floating in IVC, 15 embolized centrally), and EM revealed fracture modes of high-cycle fatigue (n = 53), overload (n = 6), and indeterminate (n = 2). Following retrieval, previously prescribed lifelong anticoagulation was discontinued in 30 of 31 patients (97%). Filter-related symptoms from IVC occlusion, component embolization, and penetration-induced abdominal pain, duodenal injury, and/or small-bowel volvulus were alleviated in all 26 cases (100%). There were no long-term complications at a mean follow-up of 371 days (range, 67-878 d). Conclusions: The risk of filter fracture increases after 408 days (ie,>1 y) of implantation and is associated with symptomatic extravascular penetration and/or intravascular embolization. Complex methods can be used to safely remove these devices, alleviate filter-related morbidity, and allow cessation of anticoagulation. © 2013 SIR.


Ndc

Trademark
Nitinol Devices & Components | Date: 2012-10-30

Nitinol alloys; nitinol alloy materials, namely, sheets, tubes, wires, ingots, and bar stock made from nitinol alloys; nitinol alloys for industrial and consumer applications. Nitinol alloys for medical applications; nitinol alloy materials, namely, sheets, tubes, and wires for medical device implant and medical instrument applications; medical guidewires made of nitinol alloys. Manufacturing and fabrication services of medical components and materials made of nitinol alloys for others; custom manufacturing of medical devices, medical instruments, implantable medical devices and components made of nitinol alloys; processing of medical components made of nitinol alloys. Testing, design, and development of medical components made of nitinol alloys.


Ndc

Trademark
Nitinol Devices & Components | Date: 2012-10-30

Nitinol alloys; nitinol alloy materials, namely, sheets, tubes, wires, ingots, and bar stock made from nitinol alloys; nitinol alloys for industrial and consumer applications. Nitinol alloys for medical applications; nitinol alloy materials, namely, sheets, tubes, and wires for medical device implant and medical instrument applications; medical guidewires made of nitinol alloys. Manufacturing and fabrication services of medical components and materials made of nitinol alloys for others; custom manufacturing of medical devices, medical instruments, implantable medical devices and components made of nitinol alloys; processing of medical components made of nitinol alloys. Testing, design, and development of medical components made of nitinol alloys.


Trademark
Nitinol Devices & Components | Date: 2012-11-30

Nitinol alloys; nitinol alloy materials, namely, sheets, tubes, wires, ingots, and bar stock made from nitinol alloys; nitinol alloys for industrial and consumer applications.


Loading Nitinol Devices & Components collaborators
Loading Nitinol Devices & Components collaborators