| In this paper, the influence of shot peening with or without carburization on fatigue strength of smooth and notched specimens and some machine parts, such as gears and blades of compressor rotor, which were made from 40Cr, 35CrMo, 20CrMnTi steel and LD7 aluminum alloy, were studied. Apparent fatigue limits of un-peened notched specimens were also studied. Following experiments are included in this paper: heat treatment of specimens, shot peening, analysis of micro-structures, measurement of surface residual stress fields, measurement of surface roughness, measurement of microhardness, measurement of apparent fatigue limit, analysis of fatigue fracture surfaces and finite element calculation.According to a "micro-meso-process theory of fatigue source initiation" and a concept of 'internal/surface fatigue limit', apparent fatigue limits of shot-peened specimens and optimization of shot peening were discussed.Through a study on apparent fatigue limits of smooth shot-peened specimens, a criterion of shot peening technology optimization was proposed, and a method to calculate the apparent fatigue limits of optimized peened specimens was also proposed. The conclusions above were applied in the shot peening optimization process of aluminum alloy blades, and good effects were achieved.During analyzing fatigue limits of notched specimens, a concept of "dimension of a critical meso-yielding region" xW was proposed. In this work, xW is about 11 times of the original austenite grains. A method to predict apparent fatigue limits of notched specimen was also suggested.The apparent fatigue limit changing rules of carburized and carburized then shot peened smooth specimens and gears were analyzed, and then a calculation method of critical fatigue load of complex machine parts, such as gears, according to the fatigue limit determined with small specimens, as well as a judgment for optimization of surface hardening technology, was discussed.
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