In this paper, a new loading device was employed to conduct a mixed-mode fracture test. Therefore, disadvantages detected in the previous mixed-mode fracture toughness test methods can be avoided. The new fixture has perfect symmetry which provides a uniform stress state, creates the pure plane strain conditions and eliminates the unwanted mode-III loading conditions. The values of non-dimensional stress intensity factors for pure mode-I, pure mode-II, and pure mode-III were obtained using 3D models of new loading device and modified Arcan method in order to compare the results and investigate the variation of fracture parameters. Furthermore, the values of correction factors for pure mode-III in various loading angles were studied for both fixtures and it was resulted that in modified Arcan device there was a larger contribution of unwanted third mode loading conditions and therefore the values of mode-I and mode-II non-dimensional stress intensity factors were affected. In the present study, in order to compare the results, the fracture toughness values of ABS (Acrylonitrile butadiene styrene) polymeric material were determined experimentally for both fixtures and a full range of mixed-mode loading conditions including pure mode-I and pure mode-II loading were created and tested. The differences in critical stress intensity factors of the fixtures were found about 7.00% and 42.65% in mode-I and mode-II loading conditions, respectively. ness for three modes of loading (I, II and III) and also under mixed-mode loading conditions. Some of these methods include: the double cantilever beam (DCB) and the end notched flexure (ENF) specimens have been employed for mode-I and mode II tests, respectively (Davidson et al. 2012, Shokrieh and Heidari 2011, Zacharopoulos 2004. A crack rail shear (CRS) specimen has been proposed to determine the mode-III (tearing) critical strain energy release rate by Becht and Jr (1988). The mixed-mode bending (MMB) test has been proposed by combining the schemes used for DCB and ENF tests, which can produce a wide range of the ratios of mode-I and mode-II components by varying the lever arm of the specimen. A modified MMB test method was used for evaluation of the interlaminar fracture toughness of AS4/PEEK composite material by Reeder (1990), Reeder and Crews (1990). Furthermore, MMB test method was recently used for investigation of crack propagation in adhesively bonded joints by Ben Salem et al. (2014). Researchers like Verma et al. (1995) and Dharmawan et al. (2006) evaluated the fracture toughness of composite materials by using DCB, ENF and MMB specimens. However, for all these test methods there are problems in that a wide range of mixed-mode ratios cannot be tested which limits their usefulness (Reeder and Crews 1990). But in order to obtain reliable results for interlaminar fracture toughness for pure mode-I, pure mode-II, and mixed-mode loading conditions, different beam type specimens would be required. It is therefore necessary to develop other test methods to eval...

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Because there is no codified standard for a mixed-mode fracture test, this study, by summing up previous works and investigating their properties, attempts to provide the requirements for standardization of mixed-mode fracture testing. Utilizing the loading device proposed in the present paper can help avoid the drawbacks of the previous methods applied for testing fracture toughness under mixed-mode conditions. The proposed fixture has a perfect symmetry that provides pure in-plane circumstances, preventing undesired third-mode loading conditions and creating a uniform stress state. The three-dimensional finite element models of the Arcan fixture and the suggested loading device were used to obtain the correction factors for the first and second modes. The results were then compared to investigate the variations of the fracture parameters. Moreover, analysis of the dimensionless stress intensity factors (SIFs) obtained for the third mode at various angles of loading led to the conclusion that the unwanted third-mode loading conditions had a considerable contribution to the Arcan device and, as a result, influenced the values achieved for the first- and second-mode dimensionless SIFs.

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