高置信度的载荷与寿命消耗折算方法

Load and Life Consumption Conversion Methods with High Confidence

在载荷谱编制和单机寿命监控中常常需要进行载荷折算和寿命消耗折算,传统的未考虑置信度的折算方法,往往将载荷和寿命消耗折算小了,导致结果偏于危险,为此本文提出一种高置信度的载荷与寿命消耗折算方法。文中首先研究了载荷折算与置信度、可靠度的关系,结果表明在置信水平为γ、可靠度为R的定寿延寿中,应采用置信水平为γ、可靠度为R的P-S-N曲线进行载荷折算,而只有在方差相等的情况下,才可以采用置信水平为γ的中值S-N曲线进行载荷折算。然后建立了方差相等时中值S-N曲线斜率的单侧置信下限小样本评估方法,给出了方差未知和方差已知两种情况下的斜率置信下限计算公式。在此基础上,针对载荷谱编制,建立了其高置信度的载荷折算公式。针对单机寿命监控,在方差相等或已知的情况下提出了载荷谱当量应力水平计算公式,并采用整机试验结果对中值S-N曲线进行了修正,建立了任一应力水平下的置信水平为γ、可靠度为R的可靠寿命单侧置信下限计算公式,给出了将实际使用载荷转换为标准载荷或试验载荷谱上消耗的循环数公式,以及其置信水平为γ、可靠度为R的可靠寿命消耗百分比(即损伤)单侧置信上限公式,从而能够更加精准、更加简便地对产品进行单机寿命监控和在线寿命管理。

Load and life consumption conversion are commonly required in load spectrum compilation and individual life monitoring.The converted load and life consumption by traditional methods will be less without confidence consideration,causing dangerous results.Therefore,a high-confidence load and life consumption conversion method is proposed in this paper.Firstly,the relationship between load conversion with confidence and reliability is studied.It indicates that the P-S-N curve with the confidence level ofγand reliability of R should be applied for load conversion in the life determination and extension with the same confidence and reliability requirements,while the median S-N curve with the confidence level ofγcan only be applied for equal-variance cases.And then for cases with known and unknown equal variance,the lower confidence limit evaluation methods and formulas for the slope of the median S-N curve are established with a small sample.On this basis,the high-confidence load conversion formula for load spectrum compilation is established.Besides,for individual life monitoring with equal variance,the calculation formula for equivalent stress level of load spectrum is provided and the median S-N curve is modified by test results of whole machine.By that,the lower confidence limit of reliable life under any stress level with the confidence level ofγand reliability of R,the consumed cycles converted from actual loads to standard load or test load spectrum,and the upper confidence limit of reliable life consumption percentage(reliable damage)with the confidence level ofγand reliability of R can be all calculated to realize more accurate and easier individual life monitoring and online life management.