Damage Tolerance Analysis of Dissimilar Butt-Joints Obtained by Stationary Shoulder Friction Stir Welding

Monday, May 11, 2015: 4:00 PM
Room 202C (Long Beach Convention and Entertainment Center)
Mr. Alessandro Barbini , Helmholtz-Zentrum Geesthacht GmbH, Institute of Materials Science, Materials Mechanics, Geesthacht, Germany
Dr. Jorge F. dos Santos , Helmholtz-Zentrum Geesthacht GmbH, Institute of Materials Science, Materials Mechanics, Geesthacht, Germany
Prof. Norbert Huber , Helmholtz-Zentrum Geesthacht GmbH, Institute of Materials Science, Materials Mechanics, Geesthacht, Germany
The application of integral structures in primary aeronautical components is attractive under the point of view of weight saving and material optimisation. On the other hand a deep study is required in order to satisfy damage tolerance criterion and the security regulations. In the present study the possibility of creating integral structures composed by dissimilar AA 2024 and AA 7050 aluminium alloys, through the use of an evolution of the standard Friction Stir Welding process, has been analysed under the point of view of the crack resistance behaviour.

Specimens MT(200) have been obtained by Stationary Shoulder Friction Stir Welding with three different welding speeds and positioning the AA 2024 in the advancing side of the weld, being this one the best configuration in the case of butt-joints. The machined cracks have been inserted in three different areas of the weld, AS, RS and nugget in order to analyse the different material behaviour generated after the process. In addition a Digital Image Correlation system has been used to identify the strain field in front of the crack tip.

During the experiments a strong phenomenon of crack path deviation has been noticed, with the crack tilting, in all the different cases analysed, in the direction of the AS and tending to enter in the AA 2024 base material. It was possible to define an area in which the crack resistance curve would lay and evaluate the better behaviour in term of toughness in the case of the joints obtained with the higher welding speed. Thanks to the DIC system it was possible to define the level of strain in front of the crack for different level of load and estimates the dimension of the plastic zone. Through simple analytical models a first approximation of the stress intensity factor was also obtained.

See more of: Welding and Joining II
See more of: Welding and Joining