Due to the changes in the external environment and the changes of internal mechanisms, some components of high-reliability products may have multi-stage failure processes under long-term operation. Some components of the degradation mechanism will show the phenomenon of multi-stage degradation, that is, a mutation occurs in a degraded trajectory at some time. This mutation is not caused by external shocks but due to the qualitative change caused by the degradation of natural degradation to a certain extent. Such as the expansion of the crack, this natural mutation point is called the change point, change point presents different degeneration characteristics. For example, the crack growth. This natural mutation point is called a change point, showing different degeneration characteristics after the change point. The traditional approach is to ignore the mutation point. Considered the mutation point is sick data, as an error directly discarded. However, this traditional approach obviously ignores the information of mutation point. The change point is not easy to be observed through the process of degradation. We can deduce it through statistical inference. In this paper, we determine the interval where the change point exists by using Schwarz information criterion (SIC) and then determine the change point estimate based on the minimum residual square sum criterion. The current study only considers that external impact has a certain impact on the degradation process, but does not take into account the abrupt change that is not caused by the external force when the natural degradation degenerates to a certain extent. In this paper, we consider the influence of natural degradation mutation on the degradation process and describe the degradation process more accurately. At present, the research on the reliability models based on system performance degradation mainly focus on the competing failure between natural degradation failure and impact failure, do not consider the effects of the impact time interval on the degradation process. A time interval in the degradation process is considered which called T. when the interval between the two shocks is greater than the time interval T, the damage caused by the impact is non-cumulative. When the interval between the two impacts is less than the time interval T, the damage caused by the impact is cumulative. The situation that the damage caused by the impact is non-cumulative when the interval between the two shocks is greater than the time interval T is called impact damage recovery. The natural degradation mutation and impact damage recovery in the degradation process is considered to improve the existing competitive failure models of natural degradation failure and impact failure.
