91 research outputs found

    Peak Stir Zone Temperatures during Friction Stir Processing

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    The stir zone (SZ) temperature cycle was measured during the friction stir processing (FSP) of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 ⁰Cto 1015 ⁰C (0.90 to 0.97 TMelt) and were not affected by preheating to 400⁰C, although the dwell time above 900 ⁰C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement

    Use of a trabecular metal implant in ankle arthrodesis after failed total ankle replacement: A short-term follow-up of 13 patients

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    Patients and methods 13 patients with a migrated or loose total ankle implant underwent arthrodesis with the use of a retrograde intramedullary nail through a trabecular metal Tibial Cone. The mean follow-up time was 1.4 (0.6-3.4) years. Results At the last examination, 7 patients were pain-free, while 5 had some residual pain but were satisfied with the procedure. 1 patient was dissatisfied and experienced pain and swelling when walking. The implant-bone interfaces showed no radiographic zones or gaps in any patient, indicating union. Interpretation The method is a new way of simplifying and overcoming some of the problems of performing arthrodesis after failed total ankle replacement

    Network centrality and organizational aspirations: A behavioral interaction in the context of international strategic alliances

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    Whereas social network analysis has been associated with organizational aspirations, little is known on how firm's structural positioning, and particularly network centrality, affects organizational aspirations to engage in international strategic alliances (ISA). This study examines the impact of network centrality on firm's internationalization behavior within the ISA domain in response to the performance-aspiration gap. We build on social and behavioral perspectives to predict that network centrality and performance-based aspirations will be associated with the number of ISA the firm engages in. Using a sample of 7760 alliance collaborations from the top 81 global pharmaceutical firms for the period of 1991-2012, we find supporting evidence for most of our arguments

    Relationship between locking-bolt torque and load pre-tension in the Ilizarov frame

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    The wire–bolt interface in an Ilizarov frame has been mechanically tested. The optimal torque to be applied to the frame locking-bolts during physiological loading has been defined. The set-up configuration was as is used clinically except a copper tube was used to simulate bone. The force–displacement curves of the Ilizarov wires are not altered by locking-bolt torque. The force in the bone model at which pre-tension is lost increases as the locking-bolts are tightened to 14 Nm torque, but decreases if torque exceeds 14 Nm. Thus, 14 Nm is the optimal locking-bolt torque in frame. The relationship between pre-tension versus load for different locking-bolt torques arises because at low and high clamping torques poor wire holding and plastic deformation respectively occur. Wire damage was seen under light and electron microscopy. Clinically, over or under-tightening locking-bolts will cause loss of pre-tension, reduction in frame stiffness and excessive movement at the fracture site, which may be associated with delayed union
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