Prognostic modelling of crack growth in a tensioned steel band

The general problem of identifying the condition of a structure or machine, and in particular its vibration signature, as a means to optimise maintena nce costs and reliability is currently of great interest. This work present s a method for predicting the state of damage in the future for prognostic maintenance, rather than just identifying the current state of damage for d iagnostic maintenance. Prognostics carries great economic importance becaus e it allows the assessment of the likelihood of failure as a function of fu ture time in terms of past and current conditions. We present an experiment al example using the modal response of a notched, tensioned, steel band und ergoing broadband vibration excitation to propagate cracks across the notch ed area until failure. The natural modes of the band are monitored during f atigue and the modal frequency shifts are used as a prognostic observable. A Kalman filter is then used track these modal frequency shifts and predict the likelihood and time when the amount of frequency shift is indicative o f imminent failure. As a practical approach for prognostics of the band fai lure, we examine whether the modal frequencies are converging towards a sta ble state (such as during the break-in period), or diverging away from a st able state. A new probability density function for the remaining useful lif e is derived from the kinematic model. This method of using the kinematic s tate of a damage observable for failure prognostics can be extended to any dynamical system with observable features which correlate with damage or fa tigue state. (C) 2000 Academic Press.