A new specimen for mixed mode-I/II fracture tests: Modeling, experiments and criteria development

Details related to modeling and experimental analyses for a new type of specimen, which is proposed to be used for mixed mode-I/II fracture tests, are presented. The specimen is similar to a T-shape and requires less material compared to some other specimens existing in the literature. Specimens are made from Al 7075-T651 rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction). Stresses in the loading apparatus and distributions of mixed mode stress intensity factors (SIFs) on the specimen are determined for all load mixity cases and comparisons are made for different specimen types. To check the validity of results obtained from numerical and experimental analyses of the T-specimen, similar studies are also performed for a different type of mixed mode-I/II compact tension shear (CTS) specimen. The results show that the T-specimen along with a suitable loading apparatus can be used for mixed mode-I/II fracture tests. Critical fracture loads obtained for the specimens are compared with criteria existing in the literature for mixed mode-I/II fracture conditions. It is found that most existing criteria start deviating from the experimental measurements for highly mixed mode loading conditions. Therefore, using all data obtained from numerical and experimental analyses, first an improved empirical mixed mode-I/II fracture criterion is proposed, which is followed by application on the T-specimen experiments for validation. The improved criterion shows excellent agreement with the experimental measurements. Thus, it is concluded that T-specimen and the newly developed criteria can be used for fracture problems with mixed mode-I/II loading conditions.