دانلود رایگان مقاله آنالیز اطلاعات آماری و مدل سازی قابلیت اطمینان تیغه هلیکوپتر

Abstract

The concept of reliability has been attracting attentions in mechanical engineering following the developments of the aerospace industries. Limited failure data and statistical analyses of helicopter components reliability exist in the technical literature. For filling this gap, a nonparametric analysis is conducted on the performance of the 338 blades of some Iranian helicopters, which were in service between 1974 and 2012. These blades have 41 different failure modes. In this paper, statistical reliability analysis is conducted based on two strategies: In strategy I, general failure is defined as scrapping or retirement of the blade. In strategy II, the blade is assumed to be subjected to different modes of failure and the cumulative mode-specific functions are derived for each failure modes using Nelson–Aalen estimator. The Kaplan–Meier estimator is used for calculating the nonparametric reliability functions. Confidence intervals are derived for the reliability results and parametric fits are conducted using the maximum likelihood estimation. An important result from parametric analysis is that the blade reliability has a 3-parameter Weibull distribution and so the blades exhibit an increasing failure rate. Finally, considering the mode-specific hazard functions, the failure mode 1, i.e., excessive vibration is observed to have major contribution to the blade failures.

5. Conclusion

Limited failure data and statistical analyses of helicopter components reliability exist in the technical literature and few statistical studies were made to model the reliability of these parts. This issue motivates the development of the present statistical analysis of helicopter blade reliability. In this work, this gap is filled by conducting a nonparametric statistical analysis of helicopter blade reliability. It is demonstrated that the 3-parameter Weibull distribution is a good fit for helicopter blade reliability. The Weibull parameters are calculated using the maximum likelihood estimation technique. One important result from the parametric analysis is that the blade reliability function versus life has 3-parameter Weibull distribution. Regarding the Kaplan plots in both strategies, they show that in the first strategy the reliability of the blade decreases to 91.71% after 2504 flight hours. Nevertheless, in the second strategy the reliability of the blade decreases to 84.31% after 418 flight hours. Further, the blades exhibit an increasing failure rate or wear-out. In other words, their failure probability of occurrence increases over time and with regarding the bathtub hazard rate curve their expected average life in wear-out period of life can be much smaller than their mean life in the period of their useful life. This finding has important implications for the helicopter industry and should prompt serious consideration for wear-out procedures. Finally, considering the cumulative modespecific hazard functions it was observed that the failure mode 1, i.e., the “excessive vibration” is the major reason for the blade failure. After “excessive vibration” the failure mode 3, i.e., “the chipped” is the second major reason for failure of the blades. The slopes of the cumulative mode-specific functions provide rough estimates of the hazard functions λj(t).