The problem of assessment of initial point of crack development in impact bending test

The problem of assessment of the initial point of a crack in in static tests is already recognizable and simple to determine. On the basis of this point the force Fp and energy Ep necessary to initialize fracture, thus due to these parameters it is possible to determine parameters of crack resistance. In case of dynamic loads, especially during the impact bending test of material samples, this problem is much more difficult and at the present level of science it is still current matter. In the article, in compliance with own research, the comparison of different methods of initial point determination in bend-test was performed, which is: compliance change of the sample, strain gauge tests (tensometric), mathematical processing of registered actions F(t), method of maximum force Fmax with the most accurate method (pattern method): crack alteration, for tested steels 18G2A and St3S and aluminium alloy Ak12, in order to demonstrate essential differences in assessment of initial point of crack in impact bending test.