Tribologisches Einsatzverhalten von PVD-Festschmierstoffsystemen im fluidfreien Wälzkontakt

For special applications, the lubrication of gearboxes with liquid lubricants is not feasible. Liquid lubricants lose their positive lubricating properties when exposed to high contact stress and temperature fluctuations, for example. In the food industry and medical technology, liquid lubricants are often not permitted due to hygiene regulations. Solid lubricants offer an approach to implement dry tooth contacts. In this report, three different solid lubricant coating systems are investigated under different operating conditions. The focus of the experi mental investigation is the application behavior in terms of friction force and wear behavior. In a direct comparison, the MoS2:Ti-TiN coating system achieves the highest load level and exhibits a station ary frictional force behavior compared to the a-C:H:Ti-TiN coating system. In the wear investigation, continuous coating wear was found in addition to coating delamination. The layer wear correlates with an increasing friction force in interval operation.

Importance analysis based on universal grey operation for an aircraft landing gear retraction system

In order to improve the reliability and performance of landing gear retraction systems, this paper presents two importance analysis methods based on universal grey operation. According to the system principle and fault mechanisms, the fault tree of the retraction system was first established. The uncertainties of the bottom events were then described using the universal grey number to obtain the universal grey representation of the system failure probability. And compared with the traditional interval operation, the results show that universal grey operation can solve the problem of interval expansion with uncertainty. Importance analyses of the bottom events were then conducted based on the probability importance and the key importance. By comparing the two important indices of the bottom events, the larger the value is, the higher the importance is. It was found that the occurrence of the bottom events “pipeline oil leakage,” “pump motor damage,” and “oil pollution” had the greatest impact on system failure probability, thus determining the key weak links affecting system failure and indicating the most effective targets for improvement.

Based-restraining interval extension improved truncation algorithm for response analysis of uncertain mechanical systems

Purpose This study aims to propose an improved affine interval truncation algorithm to restrain interval extension for interval function. Design/methodology/approach To reduce the occurrence times of related variables in interval function, the processing method of interval operation sequence is proposed. Findings The interval variable is evenly divided into several subintervals based on correlation analysis of interval variables. The interval function value is modified by the interval truncation method to restrain larger estimation of interval operation results. Originality/value Through several uncertain displacement response engineering examples, the effectiveness and applicability of the proposed algorithm are verified by comparing with interval method and optimization algorithm.

Fault Tree Interval Analysis of Complex Systems Based on Universal Grey Operation

The objective of this study is to propose a new operation method based on the universal grey number to overcome the shortcomings of typical interval operation in solving system fault trees. First, the failure probability ranges of the bottom events are described according to the conversion rules between the interval number and universal grey number. A more accurate system reliability calculation is then obtained based on the logical relationship between the AND gates and OR gates of a fault tree and universal grey number arithmetic. Then, considering an aircraft landing gear retraction system as an example, the failure probability range of the top event is obtained through universal grey operation. Next, the reliability of the aircraft landing gear retraction system is evaluated despite insufficient statistical information describing failures. The example demonstrates that the proposed method provides many advantages in resolving the system reliability problem despite poor information, yielding benefits for the function of the interval operation, and overcoming the drawback of solution interval enlargement under different orders of interval operation.

Application of Rough Set Theory in Stochastic Fatigue Analysis of Vehicle Frame

Considering the up-down deflection of vehicle frame as a random variable when a car runs unsteadily, the alternating stress cased by deflection is random. The probability density function is determined by date of the alternating stress acting on the frame. Using the concepts of upper and lower approximation in the rough set theory and confidence degree, random parameters of vehicle frame can be transferred into certain interval values. When the confidence degree took a value from 0 to 1, a series of intervals between the upper and lower approximation are determined respectively. With the algorithm of the interval operation, a method of fatigue analysis is put forward.

Removing Symptomatic Gallstones at their First Emergency Presentation

INTRODUCTION Early operations for symptomatic gallstones are gaining favour as the complication rate is thought to be lower and it reduces the overall morbidity. This study was performed to clarify how frequently early operations were being performed and what benefits resulted. PATIENTS AND METHODS Case notes of 171 patients who underwent laparoscopic cholecystectomy at Princess Alexandra Hospital Harlow were retrospectively reviewed. They were grouped according to their initial diagnosis (cholelithiasis, acute cholecystitis) and the delay to surgery (early, interval). Forty-one cases were excluded as they either had incomplete notes or the initial diagnosis was a different manifestation of gallstones such as pancreatitis. Those receiving interval operations were then grouped according to the mode of their initial presentation. A total of 130 case notes were analysed. RESULTS The delay for an interval operation was 3–6 months compared with less than 2 weeks for early operations. Of patients with acute cholecystitis, 43% had early operations but only 12% of patients with cholelithiasis. Waiting for interval operations was associated with multiple re-admissions equivalent to an average of one extra presentation to accident and emergency per patient. This was particularly marked if the initial presentation was to accident and emergency rather than out-patients (P = 0.003). Complication rates were also higher in the interval group. CONCLUSIONS Early cholecystectomy on the next available list is likely to reduce morbidity and the long-term in-patient burden so should be recommended for all patients presenting as an emergency with symptomatic gallstones.