Early warning method for fatigue damage state of tie rod in diameter expanding machine based on oil pressure of power cylinder

A method for early warning of fatigue damage in a tie rod of a diameter expanding machine based on oil pressure of a power cylinder, the diameter expanding machine comprising the tie rod and the power cylinder, the power cylinder comprising a piston, and the method comprising:

• (1) installing an oil pressure sensor on the power cylinder;
• connecting the oil pressure sensor with a microcomputer;
• and collecting oil pressure data of the power cylinder in real time;
• (2) inputting a minimum cross-sectional area of the tie rod, and an effective action area of the piston during expansion and return processes into an early warning system of the microcomputer;
• (3) based on a linear cumulative damage theory, building a function model associated with a health state evaluation indicator of the tie rod;
• (4) based on a material fatigue test of the tie rod and data analysis, calculating a fatigue strength S0.95 of the tie rod at a 95% confidence level;
• and calculating a constant term in a linear equation to construct a stress-number of cycles (S-N) fatigue curve equation for the tie rod at a 95% confidence level;
• (5) based on the oil pressure data of the power cylinder at a current diameter-expanding operation, calculating a damage factor for the tie rod during the current diameter-expanding operation;
• calculating a cumulative damage factor for the tie rod;
• constructing a health indicator model for the tie rod based on the power cylinder's oil pressure;
• and calculating a current health indicator for the tie rod;
• and
• (6) determining, by the early warning system, whether the current health indicator of the tie rod obtained in step (5) is not greater than 60.5:
• if so, raising an alarm to an operator;
• otherwise, maintaining normal operation of the diameter expanding machine.