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The stiffness degradation represents one of the most interesting phenomena used for describing the fatigue behaviour of composites. In this regard, in literature, several works have been presented for modelling the fatigue life by studying the stiffness degradation. A critical aspect of modelling damage fatigue is represented by the difficulties in simulating the whole behaviour of material and then in describing the damage progression in all its stages. In addition, the validation of models requires the measurement of stiffness variations by means of experimental techniques. Above all for real components, the difficulties in defying proper models are accompanied by the difficulties in measuring stiffness degradation due to inapplicability of classic experimental techniques. In this work, the stiffness degradation of quasi-isotropic carbon-fibre-reinforced-polymer obtained by automated fiber placement, has been assessed by means of Thermoelastic Stress Analysis. The amplitude of temperature signal at the mechanical frequency (thermoelastic signal) was considered as an indicator of material degradation and compared to the data provided by an extensometer. The correlation between thermoelastic and mechanical data allowed to build a new experimental model for evaluating and predicting material stiffness degradation by just using thermoelastic data. The proposed approach seems to be very promising for stiffness degradation assessment of real and complex mechanical components subjected to actual loading conditions.

Background The stereolithographic-guided surgery system involves a sequence of diagnostic and therapeutic events, and errors can arise at different stages. In these systems, one of the potentially clinically relevant errors may be the mechanical errors caused by the bur-guide gap due to the presence of a rotational allowance of the drills in the tubes. Purpose The purpose of this retrospective clinical study is to determine if it is possible to reduce the total error by limiting the tolerance among the mechanical components and to evaluate its clinical incidence. Materials and Methods Sixty-six implants were inserted using the External Hex Safe® (Materialise Dental, Leuven, Belgium) system (Group A), and 71 implants were inserted using the same system with mechanical components modified to minimize the tolerance (Group B). Regarding only the angular deviation values, the t-test was used to determine the influence of reduced tolerance among the mechanical components on the accuracy values. Results t-Test showed that there is a statistically significant better accuracy with the modified system (Group B). Conclusions Limiting the error that originates from mechanical components, total error could be statistically significantly reduced. Mechanical error is one of the most important source of error using External Hex Safe stereolithographic surgical guide.

During the last decades, the Ti-6Al-4V titanium alloy has been widely used for several advanced applications in the aerospace, automotive and naval industry. Particularly, an improvement on the knowledge of the fatigue behaviour of mechanical components made of Ti-6Al-4V, while operating in corrosive media, would be fundamental for aircraft or offshore applications to prevent dramatic failures due to environment-assisted fatigue or notch-induced fatigue crack growth. The fatigue resistance of smooth Ti-6Al-4V components and specimens tested in air has been already extensively studied, but the effect of a very aggressive environment, such as a methanol solution, has not been evaluated enough despite its great importance in some technical applications. The purpose of this paper is to investigate the effect of a methanol solution (at different concentrations) on the axial fatigue performances of smooth flat dog-bone specimens. The collected data will be then compared to previous experimental results obtained for the same specimens tested in a NaCl solution (3.5 wt%) and under inert environments, by considering also the influence of mechanical notches.

Modelling ductile damage is one of the most important applications of continuum damage mechanics (CDM) models. Scientists have previously tried to identify the damage parameters and have calibrated the failure behaviour of different materials using CDM models. However, more comprehensive studies are still needed to investigate the capabilities of CDM models for different materials. It is possible to extend the methodology to titanium alloys that are, currently, an optimal solution for highly stressed mechanical components. Therefore Lemaitre's CDM model parameters for ti-6Al-4V titanium alloy have been identified and reported in this work. A series of experimental tests have been carried out to identify the CDM model's parameters by the method of degradation of elastic modulus. A subroutine has been written in ABAQUS to numerically simulate the behaviour of the simple specimen using Lemaitre's model. Die Modellierung duktiler Schadigung ist eine der wichtigsten Anwendungen der Kontinuums-Schadigungsmechanik (CDM). Forscher haben versucht die Schadigungsparameter verschiedener Materialien durch CDM zu identifizieren und somit die Versagensverhalten zu kalibrieren. Um die Fahigkeit von CDM in verschiedenen Materialien zu untersuchen, sind jedoch umfassende Studien erforderlich. Es ist moglich, diese Methode auch auf Titanlegierungen zu erstrecken, die sich heutzutage als eine optimale Losung fur anspruchsvolle mechanische Komponenten anbieten. Deshalb werden in dieser Arbeit auch die Lemaitre CDM-Parameter identifiziert und prasentiert. Um die CDM-Parameter (durch die Bestimmung der Abnahme des Elastizitatmodul) zu identifizieren, wurden eine Reihe von experimentellen Untersuchungen durchgefuhrt. Um das Verhalten durch ein einfaches Modell (Lemaitre) zu simulieren, wurde eine Unterprogramm in Abaqus geschrieben.

This article introduces a unique miniaturization process of a magnetically levitated axial flow blood pump from a functional prototype to a pump suitable for animal trials. Through COMSOL three-dimensional finite element analysis and experimental verification, the hybrid magnetic bearings of the pump have been miniaturized, the axial spacing between magnetic components has been reduced, and excess material in mechanical components of the pump was reduced. Experimental results show that the pump performance was virtually unchanged and the smaller size resulted in the successful acute pump implantation in calves.

Foetal echocardiographic ultrasound techniques still remain the dominating modality for diagnosing foetal atrioventricular block (AVB). Foetal electrocardiography might become a valuable tool to measure time intervals, but magnetocardiography is unlikely to get a place in clinical practice. Assuming that AVB is a gradually progressing and preventable disease, starting during a critical period in mid-gestation with a less abnormal atrioventricular conduction before progressing to a complete irreversible AVB (CAVB), echocardiographic methods to detect first-degree AVB have been developed. The time intervals obtained with these techniques are all based on the identification of mechanical or hemodynamic events as markers of atrial (A) and ventricular (V) depolarizations and will accordingly include both electrical and mechanical components. Prospective observational studies have demonstrated a transient prolongation of AV time intervals in anti-Ro/SSA antibody-exposed foetuses, but it has not succeeded to identify a degree of AV time prolongation predicting irreversible cardiac damage and progression to CAVB. Causes of sustained bradycardia include CAVB, 2:1 AVB, sinus bradycardia and blocked atrial bigeminy (BAB). Using foetal echocardiographic techniques and a systematic approach, a correct diagnosis can be made in almost every case. Sinus bradycardia and CAVB are usually easy to diagnose, but BAB has a tendency to be sustained and shows a high degree of resemblance with 2:1 AVB when diagnosed during mid-gestational. As BAB resolves without treatment and 2:1 AVB may respond to treatment with fluorinated steroids, a correct diagnosis becomes an issue of major importance to avoid unnecessary treatment of harmless and spontaneously reversing conditions.

Astronomy has experienced a great boost over the last 20 years. As a consequence, the telescopes used are getting larger and larger. In the past, radio telescopes with a reflector diameter of up to 100 m were built. Now, even optical telescopes are being planned with main mirror diameters exceeding 40 m! For all these telescopes the structural system – the steel structure – and the related mechanical components – the bearings and drives – are the “backbone” for the optical elements and play a major role in the planning, construction and related overall costs. From the structural engineer's point of view, the design and construction of a telescope structure is very different from all other applications of steel structures. The design is not dominated – as it usually is – by issues of strength and stability, but mainly by issues of deformations and dynamics. The requirements for the structural system have to be developed in close cooperation with the overall telescope system engineer, who has to integrate the needs of the astronomers, the optics engineers, control engineers, etc. From the market point of view, there are only a few large telescope projects in progress worldwide, and not many structural engineers are working in this field; so no specialized companies are available for the manufacture and erection of large telescope structures. This situation resulted in the emergence of a small group of project managers and engineers in Mainz, Germany, who were and are involved with many large telescope structures worldwide. This paper explains the specific design and construction issues by way of two current examples: the 64 m Sardinia Radio Telescope (SRT) under construction at San Basilio, Sardinia, and the 30 m Large Cherenkov Telescope (LCT) under construction at Golschau near Windhoek, Namibia.

After repeated passive stretching, tendinous tissue compliance increases in the human soleus (SOL) muscle–tendon unit. During movement, such changes would have important consequences for neural and mechanical stretch responses. This study examined the existence of such effects in response to a 75 min walking intervention. Eleven healthy subjects walked on a treadmill at 4 km h−1 with a robotic stretch device attached to the left leg. Ultrasonography was used to measure SOL fascicle lengths, and surface EMG activity was recorded in the SOL and tibialis anterior (TA) muscles. Perturbations of 6 deg were imposed at three different measurement intervals: Pre (immediately before the walking intervention), Mid (after approximately 30 min of walking) and Post (immediately after the intervention). Between the Pre–Mid and Mid–Post intervals, subjects walked for 30 min at a gradient of 3%. After the intervention, the amplitude and velocity of fascicle stretch both decreased (by 46 and 59%, respectively; P < 0.001) in response to a constant external perturbation, as did short (33%; P < 0.01) and medium (25%; P < 0.01) latency stretch reflex amplitudes. A faster perturbation elicited at the end of the protocol resulted in a recovery of fascicle stretch velocities and short latency reflex amplitudes to the pre-exercise values. These findings suggest that repeated stretching and shortening of a muscle–tendon unit can induce short-term structural changes in the tendinous tissues during human walking. The data also highlight the effect of these changes on neural feedback from muscle sensory afferents.

The walking parts are the most important mechanical components in military tanks and other vehicles having palettes. The matrix phase of carrying wheels is Cu-based aluminum alloy. In this study, the microstructure of walking parts of military tanks was investigated deeply by optically and scanning electron microscopy.

Micromachined resonant fatigue characterization structures have been used by a variety of investigators to evaluate the stress-life fatigue behaviour of thin films. This work will review the design, testing and analysis of these versatile thin-film characterization structures. Subsequent discussion will illustrate how this material characterization approach has been used to evaluate the high-cycle fatigue behaviour of silicon films commonly used in microelectromechanical systems (MEMS). This work demonstrates that properly designed resonators can be used to monitor extraordinarily low fatigue crack growth rates (i.e. ≪ 10−10 m/cycle) relevant to these minute mechanical components.

Most mechanical components used for transmission of movement are subjected to repeated impacts or cyclic stress. If these elements are well designed and the materials well chosen, their durability is linked to surface fatigue mechanisms. In order to improve the fatigue behaviour of these parts, hard coatings, such as physical vapour deposition (PVD) or plasma-assisted chemical vapour deposition (PACVD) coatings, can be appropriate. Unfortunately, such hard coatings cannot be used for elements whose replacement is more difficult than, say, cutting tools. An understanding of failure mechanisms should make it possible to optimise the fatigue behaviour of hard coatings. In order to study the surface fatigue behaviour of thin, hard PVD coatings, a special apparatus has been developed to carry out repeated impacts over a broad range of speeds. The possibility of mapping the fatigue behaviour of different coatings is illustrated through the examples of TiN and TiN/CrN multilayer coatings of different thicknesses deposited on several substrates.

Introduction Overdentures supported and retained by endosteal implants depend upon mechanical components to provide retention. Ball attachments are frequently described because of simplicity and low cost, but retentive capacity of these components may be altered by a lack of implant parallelism. Purpose The aim of this in vitro study was to investigate the retention of gold and titanium overdenture attachments when placed on ball abutments positioned off-axis. Methods and materials Four ball abutments were hand-tightened onto ITI dental implants and placed in an aluminum fixture that allowed positioning of the implants at 0 degrees, 10 degrees, 20 degrees, and 30 degrees from a vertical reference axis. Gold and titanium matrices were then coupled to the ball abutments at various angles and then subjected to pull tests at a rate of 2 mm/second; the peak loads of release (maximum dislodging forces) were recorded and subjected to statistical analyses. A balanced and randomized factorial experimental design testing procedure was implemented. Results Statistically significant differences in retention of gold matrices were noted when ball abutments were positioned at 20 degrees and 30 degrees , but not at 0 degrees and 10 degrees. Statistically significant differences were noted among the titanium matrices employed for the testing procedure, as well as for the 4 ball abutments tested. Angle was not a factor affecting retention for titanium matrices. Conclusions (1) The gold matrices employed for the testing procedures exhibited consistent values in retention compared to titanium matrices, which exhibited large variability in retention. (2) Angle had an effect upon the retention of gold matrices, but not for titanium matrices.

Der nachfolgende Beitrag prasentiert Ergebnisse praxisnaher Untersuchungen mit PVD-beschichteten Verzahnungen und Spindellagern unter dem Einsatz biologisch schnell abbaubarer und entfeinerter Schmierstoffe. Um das aus der Entfeinerung resultierende Leistungsdefizit und den Verschleisanstieg der Maschinenelemente zu kompensieren, wird im Rahmen des SFB 442 untersucht, inwieweit durch die Verwendung geeigneter Schichtsysteme fur die gleit- und walzbeanspruchten Laufflachen die tribologischen Funktionen herkommlicher, additivierter Fluide auf die PVD-Schichten ubertragen werden konnen. Das Ziel ist, ein umweltvertragliches System aus Maschinenelement und Schmierstoff zur Verfugung zu stellen, das in seiner Leistungsfahigkeit mindestens den konventionell eingesetzten Varianten entspricht. Service Behaviour of PVD-coated Gearings and Bearings Lubricated with Biodegradable Oils The following report presents the results of practical investigations with PVD coated gears and spindle bearings in combination with biodegradable lubricants. In order to compensate the performance deficit and the rising wear of the mechanical components when using non-additived oils, suitable PVD coating systems were used on the loaded surfaces. This coatings are capable of substituting the tribological functions of conventional, additivated lubricants. All investigations have been carried out in the context of the Collaborative Research Center 442 (“environmentally friendly tribosystems by suitable coatings and fluids with respect to the machine tool”). The aim is to realize an environment-friendly system consisting of the mechanical components and the corresponding lubricants, which at least provides an equal performance compared to conventional systems.

Die Betriebsfestigkeit und Zuverlassigkeit einer Konstruktion ist nur durch sorgfaltige Bemessung zu erreichen. Dabei sind die aus den Einsatzprofilen stammenden unterschiedlichen Anforderungen an die Festigkeit der Bauteile zu berucksichtigen. Um einerseits alle Einflusse aus Belastung, Werkstoff, Herstellungsprozess, ortlicher Geometrie zu erfassen und andererseits Forderungen bezuglich der Konkurrenzfahigkeit zu erfullen, muss der Konstrukteur effiziente Methoden anwenden, mit denen Betriebsfestigkeit und Zuverlassigkeit gewahrleistet werden. Heute steht im Entwicklungsprozess einer Konstruktion die Verringerung der Markteinfuhrungszeit im Vordergrund. Dies erfordert den vermehrten Einsatz numerischer Methoden (Simulation des dynamischen Systemverhaltens, der Bauteileigenschaften und der ortlichen Spannungen), um den Aufwand der experimentellen Vorgehensweise fur Optimierung und Nachweis zu reduzieren. In Zukunft werden immer mehr Konstruktionsteile von mechatronischen und sogar multifunktionalen Komponenten ersetzt. Kenntnisse des Systemverhaltens sowie der gegenseitigen Beeinflussung von elektronischer Steuerung und mechanischem Verhalten sind erforderlich, um die Zuverlassigkeit dieser Entwicklung zu bewerten. Structural Durability and Reliability of Complex and Intelligent Structures Structural durability of a product is achieved only by careful design, taking into account the different aspects of the required mission profile with regard to component strength. In order to include all effects on component strength (like material, manufacturing, local geometry, scatter) on one hand, and to meet competition requirements on the other hand, the design engineer has to apply efficient methods for guaranteeing service durability. A brief overview over these methods is presented. Today`s developments are focusing on the reduction of time-to-market periods. This fact is putting more emphasis on numerical methods (simulations of dynamic system behaviour, of component properties and local stresses) in order to reduce experimental procedures of optimizing and proof. The mechanical components of future mechanical engineering constructions are increasingly being replaced by electric and even multifunctional components. Electronics are gaining influence which is reflected by current keywords like brake or steer-by-wire technology. Knowledge of the system behaviour as well as all interactions between electronical control and mechanical behaviour are absolutely imperative to assess the reliability of such approaches.

Intravascular hemolysis was studied in a large, non-selected series of patients with aortic and mitral valvular disease or valve prostheses in order to clarify the mechanisms of the erythrocyte destruction. Hemolysis was slight in unoperated patients, even in cases with severe valvular disease. The degree of erythrocyte destruction in operated patients was mainly determined by the design and material of the prostheses, whereas it was similar in cases with aortic and mitral valves replaced. Our data suggest that the hemolysis in patients with prosthetic heart valves mainly is due to crushing of erythrocytes by the mechanical components of the prostheses, turbulent blood flow probably being a rather unimportant factor.

The total artificial heart (TAH) being developed by these authors successfully completed hydrodynamic and hemolysis studies followed by two acute implantations. Before commencing preclinical studies on any device, documentation of the reliability and durability of each component has to be done. This TAH was submitted to a 4 month destruction test under the most severe driving conditions to detect any weak mechanical components of the system. The maximum dP-dt in the left pumping chamber was chosen of more than 15,000 mm Hg/s, which is almost 6 times higher than that of the normal driving condition. The pump was submersed into a water bath that was maintained at 37 degrees C. The TAH was driven in a left master alternative (LMA) variable rate mode at 8 L/min output flow, 15 mm Hg reload, 100 mm Hg left afterload, and 25 mm Hg right afterload. The outflow, pressures, and temperature inside the TAH were monitored. Several stress concentration areas were detected. The connection between the roller nut and support plate proved to be one of the most stressed regions, and a more reliable fixing procedure was required. This portion was redesigned to offer a durable connection. No malfunctions of the actuator or controller were detected throughout the testing duration. No temperature elevation more than 1 degree C on the center piece of the TAH was demonstrated.

The application of a stabilized space-time finite element formulation to problems involving fluid-structure interactions and two-fluid interfaces is discussed. Two sample problems are presented and the method is validated by comparison with a test problem.

Hard disk drives are an indispensable element of modern computer systems and their failure often causes loss of precious data. Hard disks are encapsulated to prevent contamination; a defect of any of the encapsulated mechanical components means that no data can be accessed. Another type of hard disk effect is disk sector failure: in this case only a relatively small amount of data can be lost and the failed sector can be replaced by a spare sector. This ensures that the drive is fully functional. However, the number of spare sectors is limited: If the number of failed sectors exceeds it, the drive is written off. This paper, taking into consideration the forementioned two drive-defect types, discusses a strategy for preventive replacement of hard disk drives. Expected replacement cost is expressed analytically, and the function is then minimized, leading to the optimum age replacement strategy in terms of cost.

EG&G is a Fortune 200 company with annual sales of $2.7 billion. It designs and manufactures laboratory and field-test instruments and electronic and mechanical components for commercial customers. EG&G provides systems engineering, precision component manufacturing, and test-site operating and management services to many government agencies and laboratories. It employs 34,000 people worldwide. Recognizing the need to improve its business practices as they related to environmental excellence, EG&G initiated policies, procedures, and programs to establish itself as an environmentally responsible company. Waste reduction was designated priority number one in EGG's environmental program. Our major customers are also making waste reduction a high visibility program. For example, on August 3, 1993, the president signed Executive Order 12856 making pollution prevention at federal facilities a goal of this administration. This article describes the EG&G Waste Reduction Pays (WARP) program, developed for use by all its operating entities, and why it is a model program to implement Executive Order 12856. It also depicts how the implementation of the program at federal facilities differs, in some respects, from that at other EG&G operating units.

Der Artikel beschreibt die Modellbildung und Simulation von elektromechanischen Drucksystemen, die nach dem ballistischen Funktionsprinzip arbeiten. Fur das aus den Teilkomponenten Elektromagnetik und Mechanik bestehende Gesamtsystem werden physikalische Ersatzmodelle entwickelt und die mathematischen Beschreibungen abgeleitet. Hierbei ist es erforderlich, die transienten Vorgange der Magnetik und die elastischen Systemkomponenten der Mechanik zu berucksichtigen. Anhand einiger ausgewahlter Simulationsergebnisse, die sich aus der numerischen Losung des nichtlinearen Differentialgleichungssystems ergeben, wird die Druckkopfdynamik verdeutlicht und ein Vergleich mit Mesergebnissen dargestellt. This article deals with modelling and simulation of a electromechanical printer system, which works based on the ballistic principle. The entire system can be divided into a magnetic and mechanical subsystem. For both parts the mathematical model has been developed. To derive a realistic model the transient phenomena of the magnetic and the elastic behaviour of mechanical components have been taken into account. The differential equations can be solved during simulation. Finally some simulation results are presented in order to show the complex system behaviour. Moreover the simulation results are compared with experimental data.

The major objective of this study is to show how to carry out the process of structural and parametrical synthesis that is understood as a method intended to seek for the structure and parameters of a discrete model of the system with active suppression of vibrations. Active components are implemented as mechanical components with kinematic excitations. The other objective is to analyze how the active subsystem interacts with the overall investigated structure. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple hand-operated balloon inflation device has been developed for use in coronary and peripheral transluminal angioplasty procedures. This device is compact, portable, and easily sterilized and eliminates the need for compressed gas, pneumatic pistons, carbon dioxide cartridges, or a complex holder or mounting apparatus. This device, the Dorros-Spring pressurizer, provides for precise control of pressures which inflate the angioplasty dilatation catheters by means of an hydraulic salinecontrast system. This inflation device has been used in over 150 coronary and 100 peripheral transluminal angioplasties without the occurrence of failure of mechanical components or loss of calibration.