對機械系統而言，由於失效發生之主要原因是為操作過程之損傷累積所致。因此本論文針對損傷累積過程之可靠度退化情形，發展一動態可靠度模型。由於系統操作時無法避免振動、摩擦等行為，使得系統受往復的操作應力變化負載。在這樣的情況下，有一些破壞性的能量會儲存在系統中，而此能量之累積將造成疲勞進而破壞。 由於此累積行為與操作時間有關，且由於操作時間與平均壽命之比值能描述系統之能量累積情形，因此將此比值定義為累積損傷量，並以此量發展一描述系統退化之模型。在複雜系統視應力為單峰分布負載下，當可靠度為1時，此量為0，系統完好無損；可靠度為0時，此量為1，系統已完全損壞。因此以可靠度度量累積損傷量的變化情形為最適切之方式。而此由可靠度評估損傷之方式，能使物品折舊率之研判與維修保養之策略擬定容易許多。 接著由上述模型出發，考慮二階段負載之各階段失效模式相似且與未做負載調整之失效模式相似的情形，與分段嵌合的概念，利用步階函數將各階段模型疊加成一可描述二階段負載之動態可靠度模型。當系統受L-H負載時，在可靠度為0處累積損傷量小於1；當系統受H-L負載時，在可靠度為0處累積損傷量小於1。而此模型之優點在於能以一系統特性參數p，就能反應出負載調整對系統之影響。且此模型之物理觀念清楚，能將負載調整前後之系統行為分段處理，使得容易了解負載調整之順序與現象。本文最後以累積損傷量及系統特性參數所能反應之系統行為作為結論之闡述。 For mechanical systems, the primary source that failure occurs is due to the cumulative damage which executed in the operating process. A dynamic reliability model is developed in this thesis to meet the reliability degradation on the process.Mechanical systems usually bear an oscillating load as a result of the unavoidable vibrations and friction. In this situation, some destructive energy accumulates inside the system and leads to the damage generating failure. The destructive energy accumulation is propotional to the operating time. Therefore, the ratio of operating time to the mean life of system can properly describe the destructive energy accumulation and this ratio can be defined as cumulative damage D. Based on this idea, a model for the strength decay is proposed. When the complex system bears one-peak-distribution loading, assume the system is perfect initially, i.e. the reliability is one, D should be zero. When the system is failure, i.e. the reliability is zero, D should be one. Consequently, the most appropriate parameter to scale D is reliability. Typical definition data of mechanical systems checked with this model satisfying results are conclude. The next problem is developing the two-level loading model which is considered that the failure modes in both stages are similar to the loading of nonadjustment and the concept of the part fitting. The advantage of this model is that it can represent the two-level loading completely by adding only one parameter and the physical meaning of this model is obvious enough to show the sequence and phenomenon of the system. The fitting results are also satisfied.
