QUANTITATIVE ANALYSIS OF APPARENT FATIGUE LIMITS OF NOTCHED SPECIMENS
缺口件表象疲劳极限的定量化分析

In this work, the apparent fatigue limits of notched specimens were analyzed quantitatively from a comprehensive point. Three-point bending fatigue limits of smooth specimens and three kinds of notched specimens of quenched and then high temperature tempered 35CrMo steel are determined. The stress distributions of notched specimens are calculated by finite element analysis software ANSYS. The experimental results are analyzed with the "micro-meso-process theory of fatigue source generation": though the generation of fatigue source appears in individual weak grains as a result of dislocation movements, it must satisfy certain deformation harmonization condition as well as probability condition, therefore a "meso-yielding region" containing quite a few grains must be formed. According to above analyses, the apparent fatigue limit of specimens is the maximum stress (expressed as nominal stress) required to create a critical meso-yielding region on the dangerous section of specimen when it is bearing alternating loads. The analyses also show that when take the critical dimension of the meso-yielding region, xW,as 11 grains, the compositive error between calculated apparent fatigue limits of notched specimens and their measured values reaches the least. Under this condition, the errors of calculated ones are all under 5%, so xW can be considered as a characteristic parameter of material. The study above also elucidates the physical essence of concentration factor of fatigue stress kw. In engineering practice, apparent fatigue limits of notched specimens can be predicted according to fatigue limits of material (W), xW and the stress distributions on the notch section.