Patent ID: 8504338

Claim:
A computer implemented measuring method of mechanical fatigue in turbo-unit shafting, comprising the steps of: 1) determine a lumped mass model and model parameters of a turbo-unit; 2) compute, using a computer, torsional mode frequency and vibration curve based on the mass model; 3) record real-time changes of terminal palstance Aw, then record changes of palstance Δω1, Δω2, Δω3 . . . , Δωn in different modes by filtering, and then compute, using the computer, terminal rotation angle of each mode Δθ k by Δθ k =Δω k *sin(ω k t )/[ω k *cos(ω k t )] where Δω k =A k ω k cos(ω k t ), Δθ k =Δω k t=A k sin(ω k t ) (k=1, 2, 3, . . . n) ω k =2πf k , A K : palstance changing amplitude of each mode; f k : mode frequency; 4) using the mode frequencies, vibration curve and equivalent spring constants of the lumped mass model of the turbo-unit, calculate, using the computer, a torque on each cross-section of the shafting in each mode by multiplying Δθ k and torque between mass blocks in each mode when excited by unit signal on each cross-section of the shafting, then calculate a torque on each cross-section of the shafting by accumulating torques on said cross-section in each mode respectively, and thus obtain a torque-time history plot; 5) find out stress cycle in the history plot for the torque on each cross-section of the shafting, and compute, using the computer, equivalent stress magnitude corresponding to each stress cycle; 6) look up Stress-Fatigue Life curve for dangerous cross-sections so as to obtain fatigue damage value caused by a single stress cycle; and 7) compute, using the computer, a cumulative fatigue value of all cross-sections of the shafting caused by a specific vibration, namely the mechanical fatigue of the turbo-unit shafting.