Advanced Materials Research Vols. 44-46

Abstract: Testability is a new and important technology as reliability and maintainability. A lot of literature has discussed the optimal problems of testability in recent years. In Chiu’s paper, a new kind of precedence constraints, parallel-chain precedence constraints, was presented, which is a common constraint in many products and systems. He discussed the optimal inspection strategies to determine the states (good/failed) of some typical reliability systems with parallel-chain precedence constraints. But in reality we encounter more problems with fault-testing models, and how to locate all the failed components with minimal cost is our interest. Suppose that a coherent system has n independent components, each of which has a known prior probability of fault. The true state of each component can be obtained by inspecting it with some cost. This paper discusses the optimal inspection strategies of the coherent system with parallel-chain precedence constraints when the system fails, which can minimize the total expected inspection cost. If the system is known to have failed, there are two situations: one is that the number of the failed components in the system is unknown, which is a common phenomenon; another is that the number of the failed components is known. In addition, the coherent systems concerned in this paper are all typical reliability systems, such as series, parallel, parallel-series, series-parallel and k -out-of- n systems, and all of them are subject to parallel-chain precedence constraints.

Abstract: Reliability of products has long been considered as an important quality characteristic. Traditional methods of product reliability assessment are based on lifetime data. With products being much more reliable and the growing need for developing new products within shorter period and at lower cost, we can hardly get enough lifetime data in many cases. Performance degradation data can also be used for reliability assessment. Recently, they are found to be useful in some cases where they are easier to collect. But when performance degradation data are also limited and some lifetime data are available, it is preferred to utilize both information sources. This paper deals with the problem of reliability assessment combining both performance degradation data and lifetime data. It is assumed that two samples from the same product are tested differently. Degradation data are collected from one sample and lifetime data from the other. First, the performance degradation model is established, using either statistical methods or methods from physics of failure. Then lifetime of the product, which is defined as the first time when the performance crosses the known failure threshold, is calculated. The MLE method is used for parameter estimation where the maximum likelihood function is multiplication of the one from degradation data and the one from lifetime data. To illustrate the proposed method, an example of the metallized film capacitor, which is used in inertial confinement fusion (ICF) facility, is given. We model the performance degradation data of metallized film capacitor with Wiener process with drift. The failure of the capacitor is defined as the first time when its capacitance drops below a threshold. The lifetime distribution is deduced and the parameters are estimated from the joint maximum likelihood function. A comparison is conducted between the assessment results of degradation data only and those of combination of degradation data and lifetime data. In conclusion we propose that both degradation information and lifetime information should be used when neither of them is sufficient enough for reliability assessment. Some directions for future work are also discussed.

Abstract: Blade which transfers thermal energy of steam into power, is a basic component in steam turbine. The reliability of blade is heavily influenced by the operating environment. The rotating blade experiences large inertial load and the wake of nozzle flow impose large variations of aerodynamic load on blade, in addition, the last stage blade is also affected by corrosion, so accidents of blade happen from time to time. Preventing blade failure has become one of the major objectives of turbine design and in-service maintenance. It is said that the reason for most of blade failure is fatigue fracture. In this study, a synthetical numerical model has been developed to evaluate service life of blade. At first, a numerical model to analyze the excitation force, dynamic frequency and dynamic stress of steam turbine blade has been developed, based on the results of dynamic stress analysis, a model to evaluate the service life of turbine blade has been developed. Many factors such as manufacturing technology of blade and erosion operating environment are considered to get more accurate results for service life of blade. At last, a last stage blade group of a large power steam turbine is analyzed in detail. It is shown clearly that the numerical model can give some rational quantitative results, and it is suitable for its engineering application to the improvement of the blade reliability.

Abstract: It is very important to forecast the fatigue crack development upon welded girder of bridge crane during use. When it happens, it will have a lot of clout with performance of enterprises. For security purpose in use, ANFIS model is built to predict the length of the fatigue crack extension about welded girder of bridge crane. Membership function is adjusted according to inputs and outputs of fuzzy reasoning, and appropriate fuzzy regulation numbers are chosen. The model which is closest to the real development of fatigue crack is built with the help of the If-Then rules. According to the result from the fatigue experiment of the welded girder of bridge crane, ANFIS model, ANN model and Three Order Spline Interpolation model are respectively built. After analysis and verification, it is obvious that ANFIS model is more accurate and feasible.

Abstract: The ability of executing assigned function of repairable system under certain condition is quite different from that of single unit due to redundant configuration. It is well understood that proper management strategy can greatly prolong the mean time to failure (MTTF) of repairable system. By introducing operating cycle or partial test interval, repair time and maintenance efficiency, the MTTF of classic 1oo1, 1oo2 and 2oo3 redundant systems is studied in this paper. It is found that periodical maintenance can dramatically improve the availability of repairable system, while the efficiency of maintenance has great influence on the MTTF of repairable system.

Abstract: By virtual reality technology and ergonomics theory, a basic method of ergonomic analysis on virtual maintenance of civil airplane is herein presented based on DELMIA modeling tool. The method is characterized by two steps: (1) establish the appraisal indexes of ergonomics on virtual maintenance of civil airplane; (2) give a quite complete ergonomic analysis and confirmation system flow chart. By defining maintenance cases and simulating the virtual maintenance process under the DELMIA platform, it is possible to accomplish the ergonomic analysis and evaluation with respect to the ergonomics indexes. The strengths of this method are in its ability to provide the available data and experience for further ergonomic design research and in its broadly applicable 3-D digital human model well suited for computer simulation. Furthermore, because the ergonomic analysis problem in maintainability design is indeed a simulation and confirmation process, the use of simulation techniques and confirmation techniques in this work lends itself to maintainability concurrent design of civil airplane. The ergonomic analysis method is demonstrated using vision analysis as an example.

Abstract: Causes are analyzed to the three shelling failures of railway 353130B type of roller bearings on China 70t grade of freight cars with K5 type of tilting bogie. These bearings are all failed in service lives less than two years, which is quit less than the overhaul inspection interval of 800, 000 km mileage of vehicles and the design life of 2, 000, 000 km mileage. The failures are all originated from the position at the outer ring inboard side nearly to the seal seat. Metallurgical observations reveal that the material chemical composition and microstructures are all in the reasonable range except for the hardness values. This implies that the manufacturing techniques may not match the requirements to lead to the reduction of fatigue strength. Elastic-plastic finite element (EPFE) analysis reveals that the position at the outer ring inboard side nearly to the seal seat is subjected to the maximum equivalent stress amplitude, which well match the situations of failures. In addition, a comparison is made to the bearing on the same axle weight freight cars But K6 type of bogie. Results reveal the maximum stress amplitude for K5 type of bogie is larger than that for K6 type of bogie. This means the bearings failures are relative to the local structures. Therefore, both the manufacturing techniques and the bogie structures should be advanced to improve the bearing service lives.

Abstract: Globalization has been around for a couple of centuries but never like today. Even not far just a decade ago, companies setting up a branch office overseas was a subsidiary for management team to operate. Today, there are ODM/OEM, Build-to-Order, B2B, or other kinds of business relationships, but less and less of headquarter-subsidiary relationship. The evolving of the new business relationships in today’s globalization creates a huge potential quality risk which actually exists behind the whole value chain: (1) product quality from design to manufacture, and (2) quality cost due to defective products, reputation loss, recall, delinquency, etc. The Quality System used to commit quality that serves enterprise now under pressure to reapply to a cross-the-boundary value chain environment. This paper is a case study that demonstrates a methodology solving the previously addressed quality issues by installing a Qualify System into a piecewise organization in a supply chain. In this case the quality factor has been nearly eliminated since 2000 with millions of wafers supplying from supply network by adapting this methodology: a Quality System Vee Model.

Abstract: As a high-performance flexibility coupling, nonlinear grid coupling has been used widely in many fields, such as aerospace, aviation, metallurgy for instance compressor system and so on. Over a long period of fatigue operation, its structure parameters will change a lot. The system is apt to go chaos, which results in the whole system instability. According to reliability theory and adaptive control theory, an adaptive control model of nonlinear grid coupling is built in this paper, and a novel parametric adaptive algorithm is presented. In addition, combining with an instance some numerical simulation analyses are performed. The reliability of chaotic system of nonlinear grid coupling is calculated, and some comparisons with the reliability that in normal state are provided. Calculation and analysis results show that the parametric adaptive control method possesses strong capability of stability in control, and the working state can be adjusted to normal timely. Consequently, the reliability of controlled system increases remarkably compared with the reliability of chaotic system. The method opens up a new way for reliability design of mechanical system, and provides a way to monitor the security of the whole system dynamically.

Abstract: As for load-sharing parallel system like multi-engine system and wire cable, dependence-failure must occur due to load redistributing, so the component life distributions changed. After the analysis of the disadvantage of failure probability equivalent principle and the transformation of equivalent working time of different life distribution based on damage equivalent principle, the parallel system reliability model applying full probability formula is established. The established reliability model provides a new method for reliability analysis of load-sharing parallel system whose component life follows any distribution.