Papers by Keyword: Fatigue S-N Relation

Abstract: Fatigue S-N relations are investigated experimentally on the grade B cast steel for Chinese railway freight car bogie frames. Group test method was employed. Results reveal that the fatigue cracks were initiated from the material cast shrinking cavities with hot ties. Distinct fatigue striations, river-like flowers, and second cracks appeared on the fracture surface in perpendicular to the fatigue crack path. Lots of dimples in the transient fracture district indicate that present material is ductile. Considering both the scattered S-N relations and no fatigue limits under variable loads, the S-N relations are measured probabilistically in terms of continuous declined probabilistic S-N curves including super-long life regime (SLLR) of >107 cycles. Affordable novel approach, i.e. concurrent probability extrapolation method, was applied. The test S-N data in mid-long life regime (MLLR) and conventional fatigue limits are used. The curves are established by extrapolating the conventional S-N curves crossing the fatigue limits, in a concurrent probability manner, into the SLLR. Appropriate measurements have been given for the test data of the present material.

Abstract: Scale-induced effect is investigated on the fatigue properties to the grade B cast steel for China railway rolling wagon bogie frame. Three kinds of structure-like specimens with production structural surfaces and different scales were fatigued in a manner of group tests at same stressing amplitude. Their fatigue properties are compared with those of material specimens. Fracture surface observations reveal that the fatigue cracks were initiated from the material casting shrinking cavities with/or hot ties. Distinct fatigue striations, river-like flowers, and second cracks appeared in perpendicular to the fatigue crack path. Lots of dimples appeared in the transient fracture zone to indicate a ductile fracture. Slight deference was observed that more dimples are for material specimen. To consider the scattered fatigue properties, effective sectional area-fatigue life relations are established for the structure-like specimens. And then, a probabilistic model is established for the scattered effect factors on fatigue lives. An effective application is given for constructing structural probabilistic S-N relations including super-long life regime from material S-N curves.