Advanced Materials Research Vols. 118-120

Abstract: This paper presents the working principle of a remote data acquisition system based on SCM(single chip microcomputer) and analyzes the system's failure modes. It establishes the system simulation model by using fault tree analysis, and it uses Monte Carlo method to carry on reliability simulation. The total failure rate, MTBF, importance of each component and the system reliability distribution histogram are obtained. Based on the result mentioned above, we can find an effective way to improve system reliability.

Abstract: Multiple site damage (MSD) is the occurrence of small fatigue cracks at several sites within aging aircraft structures. Focusing on this typical structure, an analytical method for calculating the stress intensity factor (SIF) of an infinite plate containing multiple holes was introduced in this paper. The properties of complex variable functions are used to evaluate the stress function. The approximate superposition method is applied to solve SIF problems on multiple holes. Some numerical examples of radial cracks appearing at the boundary of two circular holes are examined by this method. By comparing the analytical and finite analysis results it was realized that the analytical results are accurate and reliable. This modified analytical method is easier to apply than traditional analytical method and can provide SIF solutions for an infinite plate containing multiple holes.

Abstract: The thesis designed a robot which can crawl along the mast or the rope, introduced this robot’s composition and his function, and carried on the kinematics modeling, analysis and simulation design to the robot. The crawling robot can carry the detector set to inspect the mast or the rope.

Abstract: Fatigue crack growth was simulated by using a newly developed unified model on the fatigue initiation and crack growth based on an incremental multiaxial fatigue criterion. The cyclic elastic-plastic stress-strain field was analyzed using the general-purpose finite element software (ABAQUS) with the implementation of a robust cyclic plasticity theory. The fatigue crack growth rates with respect to three different stress ratios were selected as the benchmark to check the unified model. The predicted results agreed with the experimental data very well. The insensitivity of the crack growth rate to the stress ratio is due to the fast mean stress relaxation.

Abstract: The research on multiaxial fatigue life prediction methods is reviewed in the present paper from two aspects of experiment and theory. It is pointed out that the reasonable methods of the critical plane determining, multiaxial cycle counting and multiaxial fatigue damage parameter fixing are necessary if the fatigue life prediction models established under the multiaxial constant amplitude loading were applied to the life prediction of the complex multiaxial load. The shortcomings of existing researches are discussed. In the aspect of experiment, it is devoid of the multiaxial fatigue test that the loading components acted with different frequencies, and in the aspect of theory, the additional hardening effect of the multiaxial out-of-frequency loading is not considered. Both in the theoretical research and practical engineering applications, the problem of the out-of-frequency multiaxial loading is a pressing issue.

Abstract: Small fatigue crack behaviors in a nickel-based directionally solidified superalloy DZ4 were studied by in situ scanning electron microscopy. The crack initiation and propagation manners were identified under different temperatures, i.e. 25oC, 350oC, 700oC. Crack growth showed to be associated with the configuration and relative direction of carbide. The anomalous short crack growth was pronounced at 25oC, 350oC and not evident at 700oC, which was analyzed by in situ examining the effect of microstructure.

Abstract: In this study, a contacting model was investigated for interference fit shaft–hub system (rotor system) on rotational speed 30000 r/min by finite element method (FEM) which gives more complete and accurate results than the traditional method. 2-d and 3-d FEM contacting models were established first; then the stress distribution and contact state of rotor system which containing four interference fit couples were analyzed with the contacting FEM model system while the rotor system rotates on 30,000r/min. Finally, an optimal design of shrink range of the rotor system above was debated.

Abstract: Based on the reliability theory, the probability perturbation technique, the reliability sensitivity technique and robust design were employed to discuss the reliability-based robust optimization problem of structure system with multiple failure modes. By means of the probability network evaluation technique (PNET), the representative failure modes of structure system were defined. Then, the reliability and the reliability sensitivity of the system were obtained. By integrating the reliability sensitivity into the reliability-based optimization design model, the robust reliability design of structure system was discussed. According to the numerical results, the method proposed is validated to be practical and effective.

Abstract: For high reliability and long-life equipments, regular test on their performance is an effective approach to keep a fine status during the whole life. Because the number of failures increases with the duration of service, it is very important to use a rational testing strategy with unequal testing period instead of equal testing period. If testing period is not suitable, failure cannot be timely found and repaired, early failure or accident may occur. Reliability detection strategy of exponential distribution products is studied. And for every testing period, on the basis of the assumption that products should be tested when the rate of reliability deterioration reaches a certain value, an equal reliability degradation model on testing period is discussed. Furthermore, according to the idea that environment and personnel factors can lead to characteristic deterioration of products, a mathematical model of testing period incorporating reliability, failure rate, cost and testing efficiency is proposed. As the objective function of minimum cost and constraint functions of reliability and testing interval, an optimization model of unequal testing period is put forward. The optimization model is much better than traditional equal testing interval model in maintenance reliability lifetime, for it conforms to the reality that testing period must be shorten when the reliability degrades.

Abstract: This paper deals with modeling the operational reliability of a bus fleet. The operational reliability is represented by the rate of occurrence of minor failures. A power-law failure point process model with the cumulative numbers of type-II and type-III preventive maintenance (PM) as covariates is fitted to a set of real-world data. We evaluate the effect of these two types of PM on minor failures of buses using the fitted model. This provides a method to quantitatively evaluate the effectiveness of a kind of PM actions.