Effect of initial crack length on mode I fracture toughness in PMMA using pseudo-compact tension test

  fracture toughness (KIC) is one of the most important parameters in fracture mechanics, which represents the ability of a material containing a pre-existing defect to resist tensile failure. In this paper, the crack length effect on the mode I fracture toughness of an isotropic homogeneous material was investigated. For this purpose, several disc shaped PPMA samples were loaded in pure tension by performing pseudo-compact tension (pCT) tests. Digital image correlation (DIC) method was utilized to assess and monitor the distribution of the deformation field during the tests. DIC results were also used to compare the effect of crack length on the deformation field variation in samples. Very good agreement was found between the KIC values estimated in this study and those reported in the past for the similar material; indicating that the pCT method is convenient for the assessment of KIC. The experimental results also show that the initial crack length has a tangible impact on KIC, although the magnitude of its influence is closely related to material structure and type. According to the tests results, an increase in the initial crack length leads to increase the ultimate displacement at failure point, decrease the maximum load, and the amount of absorbed energy until the moment of failure, and finally decrease the mode I fracture toughness of the material. According to the comparisson of the results, in the optimum range of sample diameter, the initial crack length is suggested between 11.5 to 15.5 mm for PMMA.