On-line prognosis of fatigue cracking via a regularized particle filter and guided wave monitoring

•A novel state equation of multiple crack growth is proposed.•Multiple cracks are on-line monitored with the guided wave based SHM.•The regularized particle filter is used to deal with the particle impoverishment.•Initiation of a new crack is correctly identified by fusing SHM measurements. Simultaneous presence of multiple fatigue cracks in the same structural element is a critical problem affecting system safety. However, initiation and growth of these cracks is affected by various uncertainties from sources like material properties, machining quality and load conditions. Moreover, interactions among simultaneous cracks may introduce additional uncertainties, making the prognosis problem of multiple cracks more challenging. To deal with these uncertainties, this paper proposes an on-line prognostic method for multiple cracks taking advantages of the regularized particle filter and guided wave based structural health monitoring (SHM). A novel dynamic state equation of multiple cracks is proposed on the basis of the NASGRO model, which is an advanced model governing the crack growth rate from the threshold region up to the unstable crack growth region. In this state equation, a monotonic coefficient with exponentially distributed increments is proposed for each crack to determine if it starts to grow. The guided wave based SHM technique is employed to on-line collect measurements of actual crack states, which are sequentially input into the regularized particle filter framework to evaluate posterior estimations of crack states and model parameters. Based on these estimations, crack growth prognosis of each crack is performed. The fatigue test of the structure with hole-edge cracks is carried out to validate the proposed method. The result shows the effectiveness of the proposed method for identifying crack initiation and performing long-term prognosis of multiple cracks.