High temperature strain heterogeneities tracking within hole-specimens of fv566 turbine steel via digital image correlation

Abstract

This paper presents experimental and numerical investigations to study spatial-temporal distributions of strain heterogeneities within a FV566 turbine rotor steel subjected to high temperature conditions. Strain field were determined during monotonic tensile tests performed on flat specimens containing a circular hole to give rise to heterogeneous strain fields. A home-made digital image correlation system with an image restoration module was developed and employed to record and analyse the deformation process till the macroscopic fracture of the investigated specimens. Noticeable in-plane strain concentration zones and effects of the sample design were highlighted and deeply examined. Experimental results combined with finite element analyses based on a classical Johnson-Cook model indicated that the hole shape was the important factor affecting the strength and the spatio-temporal distribution of the strain fields. Microstructural investigations were also conducted to characterize and assess the microscale damage features of the FV566 steel. The ruptured area for all the investigated temperature tests revealed ductile rupture behaviour. Changes on grain boundaries and misorientation near strain localized regions were also investigated. It was found that the propagation of cracks surrounding the hole in FV566 specimens was mainly affected by the nucleation and propagation of strain localization zones.