Papers by Keyword: Loosening

Abstract: Prosthetic loosening in absence of infection (aseptic loosening) is the most common reason for revision of Total Hip Replacements (THR) Alumina and/or zirconia-based ceramic materials generally displayed high wear resistance and are considered suitable for load bearing application. To characterize the possible chronic cellular reactions to ceramic debris is then relevant in view of their long-term implantation. Low density ceramic pellets obtained by alumina and zirconia (Y-TZP) medical-grade precursors, were sintered at intermediate density and implanted in the patellar tendon of 24 NZW adult rabbits (group A). In this way the progressive release into the joint space of grains detached from surface of the pellets by the motion of the joint. Other 24 NZW rabbits (group B) received 5mg of powders injected in the articular capsule. Animals were killed at different intervals (1,3,6,12 months). Retrieved knee joints underwent X-Ray, histological and ultrastructural analysis. Peripheral organs (liver, kidney, lung, spleen, brain) were collected at same time. For, histologic analysis of tissue specimens collected in revision surgeries were fixed in 10% formalin, then decalcified ethylendiamintetracetic acid (EDTA), dehydrated and embedded in paraffin, sectioned and stained with hematoxylin-eosin. Histologic reaction was similar for the two ceramics and independent of the physical form (powders or pellets). Ceramic particulate was observed in the periprosthetic tissue membrane, the smaller inside mononuclear histiocyte-like cells in granuloma-like tissue, while the largest were in a synovial-like membrane inside a stroma poor in vessel containing mononuclear cells and rarely giant cells. No toxic nor carcinogenic effects were observed in peripheral organs retrieved at different time intervals. Although the ankyloses of the joints is a limiting factor for the duration of the test, this method may be a useful tool to evaluate the reactions to wear debris, and may result suitable also to evaluate the chronic response to metals or polymers of clinical interest.

Abstract: DEFORM is a software used for FEA (Finite Element Analysis) simulation. By using this software, I take a research on the procedure when a steel billet with defect of artificial loosening is drawn out in a simulated environment. Then I build a FEA model about the loosening and compaction of a large-sized rotor and stimulate the procedure in accordance with current craft card involving rotor forging. Finally, I get a result: the relative density of the loose area reaches up to 85% after the first drawing-out process (note: forging ratio 1.47). After simulating the procedure of chamfering on a billet which has been already drawn out, I found that chamfering had little substantial impact on the its loosening and compaction.

Abstract: Considering backlash, radial clearance of bearing and time-varying mesh stiffness, nonlinear dynamic model of gear bearing rotor system is established considering unbalance and loosening fault. Nonlinear dynamic equations are solved using Runge-Kutta method and Newton-Raphson method. Numerical simulations of the dynamic equations and the affection of the depth of crack and length of wear to the nonlinear dynamic behavior are studied. The results shows that tooth off, bilateral impact phenomenon are occurred, with increasing gear failure when unbalance occurs, and the gear system exhibits a diverse range of periodic, quasi-periodic and chaotic motion. When loosening fault occurs, the range of chaos motion is increased, and gear burnishing is also intensified.

Abstract: In our previous study, loosening-fatigue tests under small transverse vibrations had been performed to elucidate bolt behavior and loosening-fatigue mechanism in the long life region. In this study, the influences of bolt property class and the plastic region tightening on loosening-fatigue characteristics under transverse vibration have been investigated. Result shows that bolt property class has little influence on the loosening-fatigue limits under transverse vibration. Result also shows that the transverse loosening-fatigue limit of the bolt which has been tightened to within the plastic region is lower than the transverse loosening-fatigue limit of the bolt that has been tightened to within the elastic region. This result is the opposite of the result of the axial fatigue characteristics of bolted joints.

Abstract: To evaluate the mechanical deformation phenomena of dental abutment screw after tightening and loosening, five species of abutments were selected (3i-three, Avana- two) respectively by two pieces. The abutment screws were repeatedly tightened and removed 20 times with a digital controller. Field emission scanning electron microscope (FE-SEM) was used to observe changes of each part caused by repeatedly tightening and loosening experiment. As the number of tightening and loosening was increased, the wear or distortion of hexed or squared slot that contacted with the driver tip was more severely progressed. Wear or distortion of hexed slot was more severe than that of squared slot and it was more remarkable in the titanium screw than in the gold screw. All the tested screws showed that the width in the crest of their screw thread decreased gradually as the test was proceeded.