Titanium Fan Disc Structural Life Prediction/Correlation Program

A Structural Life Prediction/Correlation (SLP/C) program developed advanced methods of analyzing cumulative fatigue damage to more accurately predict the LCF life of a fan disk for correlation to the experimentally determined life for an accelerated duty cycle. The critical location (bolt holes) of the fan disk was determined using detailed elastic finite element analyses. Special “calibrated models” of the bolt holes were designed and tested to determine the fatigue notch factor. A materials program characterized a specific heat of disk material (Ti-6Al-4V) used in the program. The fan disk life was predicted based on materials, calibrated model and fan rotor test data for an accelerated cycle developed from a representative trainer mission. Two fan rotors were subjected to the accelerated duty cycle until crack initiation was detected, using eddy current techniques. Additional testing was conducted to determine the initial stages of crack propagation. Results indicate excellent correlation between predicted and experimental crack initiation lives, whereas crack growth lives were overpredicted.