Abstract: According to the rotor system with crack fault caused by transverse open crack， the dynamic model of crack rotor system was established using the crack compliance coefficient matrix that is derived from the stress intensity factors and strain energy density function based on the Paris theory. Since the stiffness matrix of rotor system with transverse crack fault will have corresponding changes， the surplus dynamics equation of cracked rotor system can be deduced by comparing the dynamics equations of the fault-free rotor system with that of the crack rotor system based on the flexibility coefficient matrix. Moreover， the information of open crack’s location and depth can be extracted from the vibration signal by analyzing stress condition at both ends of the shaft segment where crack exists and combining with the surplus dynamics equation. The results show that the open crack information extraction method used in this paper only needs to collect the vibration signal of three nodes at two different speeds to make diagnostic analysis. This method is simple and feasible， which may provide certain theoretical basis for the open crack fault diagnosis of the rotor system， cantilever beam and truss structure.

Key words: open crack, flexibility coefficient, crack location, crack depth, Paris theory