Investigation of notch effects on load-bearing capacity of AA7075-AA7075 friction-stir welded joints under mixed mode I/II loading

In this research, mixed mode I/II fracture of AA7075-AA7075 friction-stir welded (FSWed) joints weakened by V-notches is studied. This study consists of two parts: experimental and theoretical. In the experimental part, the load-bearing capacity (LBC) of rectangular specimens made of welded AA7075-T6 aluminum alloy containing a central V-shaped notch under mixed mode I/II loading is measured. Due to the elastic-plastic behavior of the specimens and noticeable deformations at the notch neighborhood, prediction of fracture of the specimens under test using nonlinear fracture mechanics criteria is complex and time consuming. As a result, in the theoretical part, using the Equivalent Material Concept (EMC) in combination with two brittle fracture models (mean stress, MS, criterion and maximum tangential stress, MTS, criterion), the LBC of the samples tested is estimated. By comparing the experimental results with the theoretical ones, it is clear that both theoretical criteria used in combination with EMC are well able to predict the LBC of the notched specimens. Also, based on the fracture tests performed and the analysis of the samples in a commercial finite element software, it is observed that the size of the plastic zone in the vicinity of notch increases with increasing the share of mode II, i.e. from pure mode I to pure mode II. Observed is also that the enlargement of the plastic zone increases the LBC of the samples.