Papers by Author: L.Y. Yu

Abstract: Experimental study is performed on the probabilistic cyclic stress-strain responses of grade B cast steel, which is utilized in the manufacture of Chinese K6 type bogie. Fatigue test is carried out by an incremental strain-controlled method with 8 strain levels. Analysis of test data and observation on fatigue fracture surfaces of test specimens indicate that difference and evolution of local conditions are basic causes of the random fatigue damage behavior. So it is verified again that the random character of stress-strain responses is an intrinsic fatigue behavior of engineering materials. Taking the scattering regularity and the size of specimens into account, cyclic constitutive models of present test data with arbitrary probability and confidence are obtained. The analysis reveals that these models can reflect the random responses of material correctly.

Abstract: An efficient finite element (FE) method, multivariate quadratic regression approach, is proposed for calculating the fatigue stress spectrum of engineering structures. The calculation starts from a dynamic load history. A regression function is established as a relation from the concurrent components of structural balance force systems into the structural stress. Parameters of the relation are measured by the stress data using an elastic-plastic FE method under selected groups of balance force systems. The selected systems should cover the possible load range with a similar service condition. After passing the fit effect check, the regression equation can transfer the structural load history into the stress history at the preferred position. Application on the determination of fatigue stress spectrum for the bolster of K6 type bogie has indicated availability of the present approach. Some deficiencies have been overcome from the much time cost by transient approach and the entire elastic material relation by quasi-static approach.