中文摘要：

在介绍期望序和NBUE类分布的定义后,首先证明了年龄更换策略和成批更换策略的更换间隔依期望序分别大于正常更新过程的更换间隔的充要条件是基分布属于NBUE类.随后,还考察了参数不同的年龄更换策略之间和成批更换策略之间的更换间隔.

英文摘要：

After some basic definitions being introduced,the replacement intervals under the age replacement policy and under the block replacement policy were proved to be larger respectively,in the sense of expectation order,than that of ordinary renewal process if and only if the underlying distribution belongs to NBUE class.The stochastic comparisons of the replacement intervals between the age replacement policies and between the block replacement policies with different parameters were made as well in this paper.