The Sterophotogrammetrical reconstruction of crack topography in Cr-Al-Mo nitrided steel and determination of condition at the crack front of sub-surface iniateted crack

Abstract

This article deals with problem of determination of condition at the crack front of specimens with nitrided surface layer. The determination of the conditions at the crack front is realized using the HRR theory of the stress field. The COD obtained by fractographic analysis were used as input values for the calculations This method for determining the conditions was applied to samples with fatigue crack, loaded by the Push-pull mode and further by torsion, bending and their combination. The fractographic analysis used 3D reconstruction of the fracture surface realized by stereophotogrammetry. In order to verify the effectiveness and applicability of the method, measurements performed on samples without a surface layer were also included in the analysis. Experimental work has shown that the described method can determine the conditions at the crack front, however, the method is much more suitable for samples without a surface layer than for nitrided samples. This is probably due to the fact that it is easier to measure COD values in this case.