The complication of crack path and its kind under mode-I loading: The case of the DCB specimen

One significant problem of the fracture mechanics with application in engineering practice is, the determination of the path propagation of the crack tip and as well much more its kind, has not yet found a definitive answer. This phenomenon appears as a complexity process that progresses simultaneously and interactively, at the different levels of the material, depended drastic from the geometry of the structure and its loading type. Underlying reasons are the competition among local symmetries that subsist and/or those which are emerged during of the move of the crack tip. Decisive role in the outcome of the competition, is played by the heterogeneous microstructure and its micromechanisms failure, which has as a result the real fluctuation of the edge of the crack. One among of the local symmetries that prevails, appears as crack path on the macrolevel. We present here the results that arose from application of the method is based on the hypothesis of maximum gradient of the strain energy density, on DCB specimen. This hypothesis is connected with the hypotheses of SED theory, and consequently acquires a good degree of strength. The present method is a global criterion, which can to determines the trajectory a crack tip and its kind, based on the following hypotheses: • The trajectory propagation of the crack tip, will be the curve above in which prevails the maximum gradient of strain energy density (dW/dV). • The stability of the crack path can be deduced from the degree of the sharpness of this curve. The present work illuminates the complication of the phenomenon of trajectory propagation of the crack tip and its kind, in DCB specimen. The results are presented in a map of the classification of the crack path stability and metastability, and is given for the first time. Α new range of phenomena which are appeared on the tested specimens, require further scrutiny. In this work, we investigated the emergent phenomena in a system of the fracture mechanics with complicated behavior, emphasizing in ways for identify of the potential underlying mechanisms that generate the complexity.