Papers by Keyword: Cracking Morphology

Abstract: Surface and depth morphology evodslutions of short crack propagation of 1Cr18Ni9Ti weld metal are investigated. In accordance with the previous effective short fatigue crack (ESFC) criterion, attention is paid on the formation zone of the dominant ESFC (DESFC), which resulted finally in the specimen failure, in micro-structural short crack (MSC) regime and then, the tip zone(s) ahead of the DESFC in physical short crack (PSC) regime. Results show that in MSC regime the surface ESFCs were imitated from the distributed randomly delta ferrite bounds separated from austenite matrix. The initiated ESFCs on surface propagated perpendicularly to loading axle. But in depth direction, the initiated ESFCs grew first similarly to the surface behaviour but lately, tended to be perpendicularly to the formation direction of the material columnar grain structure. When sizes of some longer ESFCs reached around the material maximum barrier size, coalescence occurred to form a true DESFC. In PSC regime the surface DESFC grew almost perpendicularly to loading axle. But in depth direction, it grew first perpendicularly to the formation direction of the columnar grain structure and then, tended to having 45 degree angle to the loading axle. Obviously, the evolutions were strongly affected by interactions between the load and the microstructures, especially, the columnar grain structure.

Abstract: Cracking behavior in low cycle fatigue regime depends on the level and the multiaxiality of the applied stress and also on the microstructure. Such a complex cracking behavior affects failure life significantly. More realistic assessments of failure life and integrity require a new appropriate procedure to analyze the crack growth process in multiaxial fatigue. A model of the fatigue process has been proposed to describe the cracking behavior in biaxial stress state. There is, however, no adequate model to present features of material microstructure. In this work, simulations of crack initiation and propagation based on a previous model were carried out in microstructure modeled by using Voronoi-polygon. In a crack initiation analysis, slip-band crack was modeled for the slip system given randomly in each grain composing the modeled microstructure. In modeling crack growth, a competition model between the coalescence growth and the propagation as a single crack was applied. Simulated cracking morphology and failure life were compared with experimental results observed in biaxial fatigue using circumferentially notched specimens of a pure copper, and the applicability of the proposed model was discussed.