Density Evolution of the Surface Short Fatigue Cracks of 1Cr18Ni9Ni Pipe—Weld Metal

The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1 Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints,respectively.The local viewpoint ,which is in accordance with a so-called “effectively short fatigue crack criterion“,paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips.The overall viewpoint focused on the whole test piece of specimen.The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages.The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location.The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed.Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given.In contrast ,the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations.Therefore,the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint.

Density Evolution of the Surface Short Fatigue Cracks of 1Cr18Ni9Ti Pipe-Weld Metal

The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is in accordance with a so-called ``effectively short fatigue crack criterion", paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The overall viewpoint focused on the whole test piece of specimen. The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages. The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location. The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed. Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given. In contrast, the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations. Therefore, the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint.