The influences of torsion stiffness of harmonic gear drive considering crack were studied by use of fracture splits mechanics, the material mechanics and the system dynamics theories. The analytic calculation formulas of flexibility and stiffness coefficient on each member considering crack were deduced, the calculation methods of torsion stiffness were given and example enumerated. This method is simple and applicable to engineering calculation.

The fractal interpolation method based on affine transformation is a kind of method of fractal interpolation function by iterative function system (IFS). Through the derivation, the fractal interpolation function model was introduced. And a GM(1,1) model was established to predict oil and gas pipeline corrosion. Prediction accuracy and case analysis show that the result accords with the ideal. It indicates that when the original data is missing, grey prediction can still be used; it has certain practical value to take corresponding measures to provide reliable basis for preventing corrosion.