چكيده به لاتين
Studying the behavior of materials under dynamic loadings is one of the most important subjects in mechanical engineering. Also, due to the importance of fracture mechanics in the design and analysis of engineering structures, it is necessary to investigate the dynamic fracture parameters. The experimental studies on brittle and quasi-brittle cracked materials shows that the fracture toughness, which is considered as one of the inherent characteristics of the material, is dependent on the size, initial crack length and the geometry of the specimen. It has also been determined that the dynamic fracture toughness (KId) is completely different from static fracture toughness (KIC) and the loading rate has a significant effect on this parameter. Although various studies have been conducted on the size and loading rate effects on fracture toughness of rocks, the research gap for polymeric materials is quite evident. Specifically, no study has been conducted on the simultaneous effects of specimen size and loading rate on the fracture behavior of PMMA polymer so far. In this study, the effect of specimen size, loading rate, initial crack length and sample geometry have been investigated on the mode I fracture toughness of PMMA. PMMA is one of the most common brittle polymers, which, in addition to many industrial applications, is used in many fracture mechanics studies. Split Hopkinson pressure bar test (SHPB) has been used to perform dynamic tests, and also due to the expensive and complicated nature of classical methods for measuring the fracture time in dynamic fracture tests, a new optical method has been proposed, which in addition to simplicity and low cost, has relatively good accuracy. The results of this research showed that the dynamic fracture toughness of PMMA increases with the increase of loading rate and its value is significantly higher than its static value. It was also found that with increasing sample size, the static and dynamic fracture toughness of PMMA increases, and at higher loading rates, the effect of dynamic size is more severe. It was found that the dependence of loading rate on dynamic fracture toughness is greater in larger samples. Also, a relative increase in dynamic fracture toughness was observed as a result of increasing the initial crack length. However, no clear relationship between dynamic fracture toughness of PMMA and specimen geometry was observed.
