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Mechanical Failure (mechanical + failure)
Selected AbstractsImplantable Cardioverter-Defibrillator Malfunction due to Mechanical Failure of the Header ConnectionJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2004R. ANDREW PICKETT III M.D. Four cases of ICD system malfunction occurring within the Medtronic Marquis family over a limited time frame are reported. These cases shared a common element of defective connections between the header post and the right ventricular pace/sense terminal pin that required intervention and reconnection. Inappropriate shocks occurred in two cases. The circumstances of these cases provide important information about the potential difficulties with these devices and highlight the deficiencies of the current system in tracking and analyzing device-related problems. [source] Detachment Lithography of Photosensitive Polymers: A Route to Fabricating Three-Dimensional StructuresADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Junghoon Yeom Abstract A technique to create arrays of micrometer-sized patterns of photosensitive polymers on the surface of elastomeric stamps and to transfer these patterns to planar and nonplanar substrates is presented. The photosensitive polymers are initially patterned through detachment lithography (DL), which utilizes the difference in adhesion forces to induce the mechanical failure in the film along the edges of the protruded parts of the mold. A polydimethylsiloxane (PDMS) stamp with a kinetically and thermally adjustable adhesion and conformal contact can transfer the detached patterns to etched or curved substrates, as well as planar ones. These printed patterns remain photochemically active for further modification via photolithography, and/or can serve as resists for subsequent etching or deposition, such that photolithography can be used on highly nonconformal and nonplanar surfaces. Various 3D structures fabricated using the process have potential applications in MEMS (micro-electromechanical systems) sensors/actuators, optical devices, and microfluidics. [source] Current use of the artificial urinary sphincter and its long-term durability: A nationwide survey in JapanINTERNATIONAL JOURNAL OF UROLOGY, Issue 1 2009Yoichi Arai Objectives: Although the artificial urinary sphincter (AUS) is one of the most effective surgical treatments for severe urinary incontinence, little is known about its use in Japan. A nationwide survey was done to determine contemporary trends in AUS use and its long-term durability. Methods: Data on AUS units sold in Japan were provided directly by Takai Hospital Supply Co., Ltd., Tokyo, Japan, and a survey form was sent to all 44 institutes where AUS implantation had been carried out. The survey included various demographic and preoperative variables, surgical variables, and postoperative outcomes. Results: Between 1994 and 2007, a total of 100 AUS devices had been provided in Japan. Of the 44 institutes, 24 responded to the survey, and a total of 64 patients were enrolled in the study. Post-urological surgery incontinence accounted for 81.3% of the indications. During the mean follow-up of 50 months, mechanical failure occurred in four (6.2%), and the device was removed in 13 (20.3%) due to infection (14.0%), erosion (4.7%), or urination difficulty (1.5%). Of the 58 patients evaluated, 91.4% reported social continence. Five- and 10-year failure-free rates were 74.8% and 70.1%, respectively. On multivariate analysis, operative time was an independent predictor of treatment failure (P = 0.0334). Conclusions: Considering recent trends in prostate surgery, the AUS may be significantly underused in Japan. Although excellent long-term durability has been achieved, a learning effect appears to be evident. The Japanese urological community needs to provide appropriate patients with this treatment option. [source] Computational assessment of the effect of polyethylene wear rate, mantle thickness, and porosity on the mechanical failure of the acetabular cement mantleJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2010Oliver J. Coultrup Abstract Clinical studies have revealed that aseptic loosening is the dominant cause of failure in total hip arthroplasty, particularly for the acetabular component. For a cemented polyethylene cup, failure is generally accompanied by the formation of fibrous tissue at the cement,bone interface. A variety of reasons for the formation of this tissue have been suggested, including osteolysis and mechanical overload at the cement,bone interface. In this study, a computational cement damage accumulation method was used to investigate the effect of polyethylene cup penetration, cement mantle thickness, and cement porosity on the number of cycles required to achieve mechanical fatigue failure of the cement mantle. Cup penetration was found to increase cement mantle stresses, resulting in a reduction in cement mantle fatigue life of 9% to 11% for a high cup penetration rate. The effect of using a thin (2 mm) over a thick (4 mm) cement mantle also reduced cement mantle fatigue life between 9% and 11%, and greatly raised cancellous bone stresses. Cement porosity was found to have very little effect on cement mantle fatigue life. Failure modes and cement stresses involved suggest that only extreme combinations of a thin cement mantle and high cup penetration may lead to mechanical failure of the cement mantle, thereby allowing wear debris access to the cement,bone interface. A thin cement mantle may also lead to the mechanical overload of the cement,bone interface. In this manner, the authors suggest that the mechanical factors may contribute to the failure mode of cemented polyethylene cups. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:565,570, 2010 [source] Healing of subfailure ligament injury: comparison between immature and mature ligaments in a rat modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2002Paolo P. Provenzano This study evaluated biomechanical properties of healing ligament following subfailure (grade II) injury by comparing young and mature animals in a rat lateral collateral ligament (LCL) model. One randomly selected LCL was stretched in situ using a custom designed device in eighteen young (21 days) and eighteen skeletally mature (8 months) male rats. Animals were euthanized at 0, 7, and 14 days post-surgery, and ligament ultimate stress, strain at failure and laxity were determined (n = 6 pairs per group). At time 0 after introduction of stretch injury, ligament laxity was present in both groups. The mature rats had 54 ± 9% strength of the control while the immature rats had 58 ± 11% of the strength of the control, representing a consistent and significant injury. The immature and mature ligaments showed similar patterns of cellular damage post-injury and had similar modes of mechanical failure. Ligament laxity decreased in each group as healing time increased, however ligament laxity did not completely recover in either group after 2 weeks of healing. After 7 and 14 days of healing, the mature rats, respectively, had only 63 ± 14% and 80 ± 8% strengths of the controls while the immature rats had 94 ± 6% and 94 ± 10%. Hence, mechanical data showed that immature animals recovered their strength after a grade II sprain at a faster rate than mature animals. However, ligament laxity was still present in both groups two weeks after the injury and was not completely removed by growth in the immature group. These findings are clinically relevant since joint laxity after injury is common, and these results may explain the presence of continued instability in a joint injured at a young age. Hence, this study, with a new injury model, showed differences in ligament healing associated with maturity and quantified the clinically observed persistance of ligament laxity. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] SIMULTANEOUS INSTRUMENTAL MEASUREMENT OF FIRMNESS AND JUICINESS OF APPLE TISSUE DISCSJOURNAL OF TEXTURE STUDIES, Issue 3 2003F. ROGER HARKER Discs of apple tissue were compressed to 75% of their original height. Throughout compression, the force-distance curve was collected and the electrical impedance of the discs was measured at two frequencies of alternating current,1 kHz and 1 MHz. Electrical impedance was separated into its resistive and reactive components, and at these particular frequencies changes in resistance predominated. Measurements at 1 kHz indicate the resistance of extracellular regions of the discs (ruptured cells as well as those regions external to the plasma membrane), while measurements at 1 MHz indicate the resistance of the entire disc (combined intracellular and extracellular regions). Juice was released from the discs as a result of damage to cells and the extrusion of cellular fluid into intercellular air spaces. This resulted in a decline in electrical resistance at 1 kHz, but little change to the resistance at 1 MHz. Changes in juice release as determined by electrical measurement were related to the mechanical properties of the discs. Generally, the release of juice occurred after the inflection point on the force-distance curves, but much earlier than mechanical failure (indicated by maximum force). The extent of tissue damage was determined from the relative decrease in resistance at 1 kHz, and was found to vary among apple cultivars and in response to fruit ripening. [source] The role that bond coat depletion of aluminum has on the lifetime of APS-TBC under oxidizing conditionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008D. Renusch Abstract Bond coat oxidation as well as bond coat depletion of Al are still believed to be a major degradation mechanism with respect to the lifetime of thermal barrier coating (TBC) systems. In this study the top coat lifetime is described as being limited by both bond coat depletion of Al and mechanical failure of the top coat. The empirical results are introduced by considering three spallation cases, namely, Al depletion failure, thermal fatigue failure, and thermal aging failure. Al depletion failure occurs when the Al content within the bond coat reaches a critical value. In this paper bond coat depletion of Al is modeled by considering the diffusion of Al into both the thermally grown oxide (TGO) and substrate. The diffusion model results are compared to Al concentration profiles measured with an electron beam microprobe. These measured results are from oxidized air plasma sprayed TBC systems (APS-TBC) with vacuum plasma sprayed (VPS) bond coats for exposures up to 5000 h in the temperature range of 950,1100,°C. This paper focuses on the Al depletion failure and how it relates to top coat spallation. [source] Field study on superheater tubes in the loop seal of a wood fired CFB plantMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2004A. Nafari Abstract Two full scale superheaters were exposed in the loop seal of a 30 MW wood-fired CFB plant in Nässjö, Sweden, for one firing season each. Some austenitic steel tubes from the first tube bundle were reinstalled in the second superheater. The superheater tubes were made from one ferritic steel, X10 (Fe8.8Cr) and three austenitic steels; Esshete 1250 (Fe15Cr9Ni6Mn), 347H (Fe17Cr11Ni) and AC66 (Fe27Cr32Ni). Commercial coatings mainly on iron, nickel and carbide base were deposited on some of the X10 and 347H tubes. The material wastage kinetics was non-linear showing that pure corrosion and not erosion-corrosion is the major degradation mechanism in the loop seal. It is however clear that the environment is not very aggressive and the corrosion attack on the uncoated tubes is very small. The largest oxide thickness was only about 150 ,m recorded on the X10 alloy. The austenitic steels mainly suffered from internal corrosion and grain boundary corrosion, the extent and distribution of which strongly depended on the alloy composition. Generally, it was more pronounced in the regions with the thinnest deposit layers. Eight out of 17 coating qualities tested were unaffected by the exposure. Corrosion was only recorded on the lowest alloyed iron based coatings. The only coatings which could not resist the conditions in the loop seal were the carbide containing Metco 3006 and Metco 3007, where severe oxidation and delamination took place. Also the thermally sprayed Inconel 625 coating delaminated, but this was rather due to a mechanical failure resulting from thermal expansion. [source] Incident investigation: Process to identify root causes of mechanical failures,PROCESS SAFETY PROGRESS, Issue 1 2006A. M. (Art) Dowell III P.E. This paper describes an actual incident investigation into unexpected premature failure of sealed diaphragm pressure transmitters in a chemical process. Some nontypical investigation tools from the CCPS Guidelines for Investigating Chemical Process Incidents (2nd edition) were used. A typical failure allowed a release of a corrosive process fluid with potential injury to personnel. The failures also required a shutdown of the process with loss of production. The cause of the problem was elusive; pressure transmitters from the same manufacturer had no problems in a similar process unit, although component designs differed between the two units. The investigation included confirmation of materials of construction, photographic and visual analyses of failed components, simulation of assembly of the pressure transmitter in the process and measurement of torque values, and brainstorming of possible failure mechanisms. Several hypotheses were tested using a fact,hypothesis matrix to determine most likely cause scenarios. Similarly, a matrix was used to illustrate which scenarios could be prevented by which corrective actions. The investigation included a root cause analysis tree to confirm cause scenarios. The paper discusses the incident investigation process, including diversity of skills on the investigation team, and how each of the tools was used. The paper also discusses the communication of the findings to operations. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] | ||||||||||||||||