Discussion on the paper 'Analysis of the dynamic responses for a pre-cracked three-point bend specimen' by Fengchun Jiang, Aashish Rohatgi, Kenneth S. Vecchio and Justin L. Cheney

摘要

The discussed article Fengchun et al. (2004a) is dealing with quite interesting topic. However, it contains several drawbacks that could be misleading for an inexperienced reader. Theoretical part of the article presents a very simple model of the impact specimen which was proposed by the authors in their previous paper (Fengchun et al., 2004b). As it was shown in previous discussion (Rokach, 2004), accuracy of this model and its applicability for the short time-to-fracture tests is questionable. An example that demonstrates a weak accuracy of the model is presented in the final part of this article. However the most controversial section of the article under discussion seams to be the fourth one entitled 'Comparison between the vibration period of the cracked specimen and the apparent period of specimen oscillation'. In this section authors compared the period of apparent specimen oscillations r determined by the corresponding formula from the draft ASTM standard (ASTM Draft, 1981) with the natural vibration period of the cracked specimen T determined by author's specimen model. The authors assumed that r should be close to T and discovered that in fact tau~= 0.38 T. The rest of the section is devoted to a lengthy discussion about the possible reasons of such a large difference between the 'similar', as the authors supposed, parameters.