Online damage evaluation based on monitored complex cyclic loadings has become an important technique for reliability assessment, especially in high-temperature environments where creep occurs in addition to fatigue. Accuracy and rapidity of calculation are basic requirements for online damage evaluation methods. However, current creep damage evaluation methods seldom consider the fluctuation in stress, which leads to inaccuracy in life-consumption estimates. In addition, traditional cycle-counting methods are not applicable to online use. In this study, an online creep-fatigue damage evaluation method is proposed that accounts for the creep behavior that occurs under fluctuating loads. The cycle-counting method is modified from a rainflow-counting algorithm; it broadens the counting of half-cycles and adopts a new equivalent temperature in the stress-strain response calculation. The proposed method is explained in detail and demonstrated with a case study. The application of this method to a high-temperature, high-pressure pipe demonstrates its online applicability and accuracy. A time-matching algorithm is developed to display the damage evolution in real time, thus revealing the link between the incremental damage and the current load conditions, and yielding an intuitive demonstration of a given component’s state of health.

基于监视的复杂循环载荷的在线损伤评估已成为可靠性评估的重要技术，尤其是在高温下，除了疲劳外还会发生蠕变。计算的准确性和快速性是在线损伤评估方法的基本要求。然而，当前的蠕变损伤评估方法很少考虑应力的波动，这导致寿命消耗估算的准确性。此外，传统的周期计数方法不适用于在线使用。在这项研究中，提出了一种在线蠕变疲劳损伤评估方法，该方法考虑了在波动载荷下发生的蠕变行为。循环计数方法是从雨流计数算法修改而来的；它拓宽了半周期的计数范围，并在应力-应变响应计算中采用了新的等效温度。对该方法进行了详细说明，并通过案例研究进行了演示。该方法在高温高压管道上的应用证明了其在线适用性和准确性。开发了一种时间匹配算法来实时显示损伤的演变，从而揭示了增量损伤与当前载荷条件之间的联系，并直观地显示了给定组件的健康状态。