Mode I fracture toughness determination of granite samples using pseudo-compact tension method

Mode I fracture toughness (KIC) is one of the most important parameters in fracture mechanics . Several laboratory methods have been suggested to determine the mode I fracture toughness., Many of these methods are dealing with the lengthy sample preparation procedure, premature failure of samples, and difficulties in obtaining the precise value of the fracture toughness property. In this paper, recently proposed pseudo-compact tension method is used to evaluate mode I fracture toughness of a middle-grain granite benefiting the advantages of this method including; simplicity of the test, high level of test control and high accuracy of the KIC value. For this purpose, granite samples in four different diameters have been prepared and tested using the pseudo-compact tension method. In addition to recording the load and displacement data, the acoustic events during the loading process were also recorded simultaneously by an acoustic emission equipment. First, the resulted fracture toughness value for each sample have been determined, then the size effect has been evaluated and analyzed. Finally, results of the acoustic emission method, as the monitoring tool in the fracturing process of tested samples, have been analyzed. The qualitative evolution of acoustic emission parameters well illustrates the mechanical process occurring in the tested samples with well-matched coinciding with the mechanical transitions observed in samples during loading process. Experimental results show that mode I fracture toughness is positively related to the specimen size and there is a noticeable size effect in KIC value up to a certain diameter.