Peculiarities of the crack initiation and propagation in different specimen types

Abstract

The paper presents the results of impact tests of standard Charpy specimens, sub-sized specimens, and side-grooved specimens made of steel 45. The instrumented vertical impact testing machine is used together with the system of high-speed recording of strain and forces. Based on the impact test results and the methods of quantitative fractography, the temperature dependences of the total specific energy of strain and fracture and its components are plotted: energy of the crack initiation, energy of the ductile crack growth, energy of the brittle crack jump, and energy of the ductile rupture area. Noteworthy is that the elimination of the influence of shear lips in the determination of different characteristics (energy of the crack propagation, moment of the crack initiation) defines the use of the side-grooved specimens instead of standard Charpy specimens. The authors have determined the average velocities of the crack propagation in the typical fracture zones of the specimens of all types. The dependencies of the instantaneous velocity of the crack propagation on its length and time in standard Charpy specimens are determined using the tensile impact gauges.