Based on damage mechanics and fractal theory

a damage evolution equation of welded joints is built up which it involves surface factal characteristics of fatigue fracture suface based on statistical self-similarity of surface profiler of fatigue fracture surface.Two dimensional fractal dimension and Parameters in damage evolution equations of fracture surface in Titanium alloy Ti-6.5Al-3.5Mo1.5Zr-0.3Si(TC11) is obtained according to the related experimental data.So damage evolution equations of low-cycle fatigue life under three levels loads in TC11 is established and these models are compared with damage evolution equations abased on line fractal charactertistic in fracture surface.