Evaluation of crack depth and profile using DCPD method in full scale axle loaded by rotating bending

Safe life design philosophy has been used as a standard approach in railway vehicles for many years and has been incorporated in railway design standards being used by present days. However, in connection with recent rapid increase of railway vehicle speed, weight reduction of railway vehicles and particularly suspension components and wheelsets as unsprung mass started to be an important issue. A significant weight reduction is not possible without full exploitation of material properties close to their limits. At such circumstances, damage tolerance (fail safe) approach has to be considered. Knowledge about fatigue crack propagation characteristics belongs to most important and most needed material characteristics. Particularly data about fatigue crack rate in full scale components — axles and data about crack shape and crack front are one of the essential characteristics necessary for a safe and reliable application of damage tolerance principles. The paper contains results of a study aimed at exploring possibilities of use of direct current potential drop (DCPD) method for evaluation of depth and profile of cracks occurred under or near press fitted hubs in a full-scale axle during severe rotating bending loading. dcpd method was applied on section of an axle after fatigue by a specific way and potentials were measured in several circumferential areas of the axle section, when direct current passed longitudinally. Results are analysed and discussed. It was indicated that unlike previous use of the method for crack measurement of different components, even large and complicated, described in the literature, when potentials corresponded to ratio of cracked and uncracked area, in this case of approximately circumferential crack, measured potentials correspond better to relative crack depth in the relevant point of the circumference.