Charpy impact test modelling and local approach to fracture

Abstract

This study aims at the establishment of a non-empirical relationship between the Charpy V-notch energy CVN and the fracture toughness K Ic on the lower shelf of fracture toughness and on the onset of the ductile-to-brittle transition of a low alloy structural steel. The methodology employed is based on the ‘local approach’. Brittle cleavage fracture is modelled in terms of the Beremin model [1], whereas the ductile crack advance preceding cleavage in the transition region is accounted for with the Gurson-Tvergaard-Needleman (GTN) model [2,3,4] . Temperature and rate dependence of the material flow stress were determined from tensile and compressive tests. Numerous fracture tests on CT and Charpy V-notch specimens provided the large data set necessary for statistical evaluation. Finite element analysis was empoyed for modeling. Special consideration was taken in order to handle the dynamic effects in the Charpy impact test. On the lowe shelf, the fracture toughness could be predicted from the Charpy impact test results. In the transition region the parameters of the Beremin model were found to deviate from those established on the lower shelf. Detailed fractographic investigations showed that the fractographic and microstructural features of regions of cleavage fracture initiation change with temperature.