Extent of the Surface Region in Notched Middle Cracked Tension Specimens

Abstract

This article aims at evaluating the extent of the surface region in notched Middle Cracked Tension specimens. Firstly, a fully automatic fatigue crack growth technique is developed to obtain stable crack shapes. After that, the stress triaxiality along the crack front is evaluated for different notch shapes. Then, objective criteria are defined to quantify the extent of the surface region from the stress triaxiality data collected. Next, the extent of the surface region is related to the elastic stress concentration factor of the uncracked geometry by a linear relationship. Finally, empirical two-constant equations able to evaluate the extent of the surface region from the thickness, notch radius, notch depth and elastic stress concentration factor are formulated.

On the Correspondence between Two- and Three-Dimensional Elastic Solutions of Crack Problems

“…In the past many researchers have asknowleged the influence of three-dimensional stress states on failure and fatigue. Only recently, the computational and expedrimental techniques allowed an accurate analysis of the three-dimensional stress states and the incorporation of this analysis into the advanced fatigue crack growth models [16] and to the development of new experimental techniques [12].…”

“…The front of a fatigue crack propagating in a plate under cycling loading is usually curved, which is evident from numerous experimental studies conducted in the past [3,4,5,[13][14][15][16]. Under pure mode I fatigue loading the crack front tends to intersect the free plate surface at a certain angle.…”

“…A number of careful and sophisticated numerical studies (using the finite element or boundary element methods) in the past were devoted to the evaluation of fatigue crack front shapes attracting the critical angle consideration [14][15][16]. It was demonstrated that the fatigue crack front shapes can significantly affect the crack growth rates.…”

Surface Crack Growth in Offshore Metallic Pipes under Cyclic Loads: A Literature Review

“…First, the contour numbers around the surface crack might affect the calculation results. At least two contours around the crack front are suggested in order to eliminate the errors [46]. Second, a spider web pattern of the meshing shape consisting of several concentric rings around the crack front is recommended, and the minimum angular discretisation of the elements should be 30° [47].…”

Evaluation of Fatigue Crack Front Shape for a Specimen with Finite Thickness

“…This automatic iterative procedure was modified and advanced in a number of subsequent papers [4][5][6]. The crack shape evolution in this procedure is governed by the effective stress intensity factor, which takes into account the plastically-induced crack closure phenomenon.…”