Key Engineering Materials Vols. 326-328

Abstract: In this study, for EPDM rubber conventionally used as a radiator hose material the aging behaviors of the skin part under the electro-chemical stresses were nondestructively evaluated. On account of the penetration of coolant liquid into the skin part the weight of rubber specimens degraded by ECD test increased, whereas their failure strain and IRHD hardness decreased largely. The penetration of coolant liquid seemed to induce some changes in inner structure and micro hardness distribution of the rubbers. Consequently, EPDM rubbers degraded by ECD could be characterized nondestructively by micro-hardness and chemical structure analysis methods.

Abstract: The reliability, that is long-term quality, requires a different approaching from short-term quality which is used before. As the electronic components are to be easily normalized on the reliability evaluation, many reliability prediction methodologies are used. In this study, integrated reference model of reliability prediction is serviced for existing PRISM and Bellcore which is related on reliability prediction about electronic components, and will service reliability data based on PoF (Physics of Failure) from domestic research center. The constructed frame of reliability evaluation system, which can predict and evaluate reliability of electronic components and MEMS, is designed by using online service of the reliability data accumulated on web. To evaluate proposed system, the reliability evaluation of PCB (Printed Circuits Boards), which is used in NC controller of machine tools, is introduced according to PRISM, the representative reference model of reliability prediction about electronic components based on MIL-HDBK-217F.

Abstract: Back-propagation network (BPN) has the advantage of simulating a nonlinear system that is difficult to describe by a physical model. This study introduces a back-propagation network methodology to estimate the accelerated life reliability. The environmental stresses and failure times are chosen as the input variables. An optimum prediction system is acquired by adjusting the number of neurons in the hidden layer and the output layer of neural networks. For a numerical example, the developed BPN architecture is applied to real accelerated life testing data of the STNLCD modules which are distributed as a Weibull distribution. By the research result, we can have the conclusion that the BPN methodology is practical to make the reliability inference with the advantages of self-learning ability even without mathematics models.

Abstract: The methods of reliability assessment of technical system at the base stages of life cycle, such as conceptual design, detail design, test, and service are described. The developed by authors new methods of taking into account the mutual correlation between failure of separated components of system at reliability evaluation are proposed. The practical examples of employment of described methods confirm the rationality of their practical use.

Abstract: For the fatigue design of a large scaled welded structure, the readily accessibility of various engineering tools is required for the static, fatigue, dynamic analysis and parametric study. In this paper, a multi-agent system is suggested for the development of distributed, open and intelligent design system. The developed design system is applied to assess cumulative fatigue damage on the welded bogie frame of railway vehicles. The engineering tools for fatigue durability analysis are chosen as I-DEAS, ANSYS and BFAP, in which iterative analysis is performed automatically caused by geometrical changes of transom support bracket attached in the bogie frame. The prototype of design system is implemented successfully for the assessment of cumulative fatigue damages of the welded bogie frame.

Abstract: Oilless bearings, which are made with metal powders and then impregnated by oils, are widely used in rotating components. The friction coefficients and the oil loss rates of two types of oil-impregnated sintered-metal bearings (porous bearings, oilless bearings, or oilless metals) with varying loads were measured. One is the Cu-based bearing and the other is Fe-based bearing. The frictional forces of the bearings were measured using the journal bearing tester. By measuring the change of weight before and after sliding tests, the oil losses of oilless bearings were surveyed. Also, PV curves, which could be used to predict the life of the oilless bearing, were plotted. By observing the roundness, the cylindericity and the images of scanning electron microscopy of bearings before and after sliding tests, the tribological characteristics of the bearings were evaluated. It was found that Fe-based bearing show lower friction, more oil flow, less wear and longer life than Cu-based bearing.

Abstract: The fatigue analysis and lifetime evaluation are very important in design procedure to assure the safety and reliability of the rubber components. The interest of the fatigue life of rubber components such as the engine mount is increasing according to the extension of warranty period of the automotive components. In this study, the fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue tests. Finite element analysis of 3D dumbbell specimen of natural rubber was performed based on a hyper-elastic material model determined from the tension, compression and shear tests. The Green-Lagrange strain at the critical location determined from the finite element analysis was used for evaluating the fatigue damage parameter of the natural rubber. Fatigue tests were performed using the 3D dumbbell specimens with different levels of maximum strain and various load. The basic mechanical properties test and the fatigue test of rubber specimens under the normal and elevated temperature were conducted. Fatigue life curves can be effectively represented by a following single function using the maximum Green-Lagrange strain. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the engine mount agreed fairly with the experimental fatigue lives a factor of two.

Abstract: The inverse problem to identify the load is normally based on the measurement of frequency response transfer functions. In this paper, the dynamic response due to external load of vehicle structure is described with inverse problem in terms of strain from experimental and analytical response. The function of the practical dynamic load is a combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit load and with measured strain by strain gage under driving load, respectively. The regularization technique is adopted to alleviate the ill-posedness of the inverse problems. To examine the proposed method, the external load applying on bus frame is identified. The load of bus is identified by the combination of the analytical and experimental method with analyzed strains. In order to get analytical strains, a quasi-static finite element analysis under unit load is performed. Road simulation test is conducted to get measured strains with strain gages. The sparseness and the noise in the measurements should be considered properly in the load identification. In this study, the regularization method is adopted to alleviate the ill-posedness of the inverse problems. This procedure can be used to get the transferred load to use an input data of fatigue analysis for a substructure of which the experimental response is difficult to get directly.

Abstract: In this paper, the failure probability is estimated by using the FORM (first order reliability method), the SORM (second order reliability method) and the Monte Carlo simulation to evaluate the reliability of the corroded pipeline. It is found that the FORM technique is more effective in estimating the failure probability than the SORM technique for B31G and MB31G models with three different corrosion models. Furthermore, it is noted that the difference between the results of the FORM, the SORM and the Monte Carlo simulation decreases with the increase of the exposure time.

Abstract: An important characteristic of a steam power plant is its ability to maintain reliability and safety of the plant against frequent start-ups and load changes. Transient regimes arising during start-ups, shut-downs and load changes give rise to unsteady temperature distribution with time in steam turbine rotor(HP/IP), which results in non-uniform strain and stress distribution. The rapid increase of temperature and rotational speed during starts-ups, especially, makes conditions more severe and causes main components’ damage and reduction of life span for steam turbine. Thus accurate knowledge of thermal and centrifugal stresses are required for the integrity and lifetime assessment for the turbine rotor. So far, only elastic calculations are currently performed for simplicity. However, it is well known that the materials of steam turbine rotor deform inelastically at high temperature. Existing models proposed to describe the viscoplastic(rate-dependent) behavior are rather elaborate and difficult to incorporate with computer simulations in the case of complex structures. In this paper, the life assessment for steam turbine rotor was established by combining the inelastic behavior and the finite element method. The inelastic analysis was particularly focused on viscoplastic behavior that is simple enough to be used effectively in computer simulation and matches the essential features of the time-dependent inelastic behavior of materials reasonably well for cyclic loading under non-isothermal conditions. Using this study, life consumption of steam turbine rotor can be obtained.