Metal forming processes play an important part in industrial manufacturing. In most cases metal forming processes are done under the conditions of multiaxial stress state. Due to this multiaxial stress state, it is important to have knowledge of stress triaxiality which is important for ductile fracture. Nowadays, analysis in digital environment is often used for planning a forming processes. Because of this, it is vital to know material parameters which are interfaced with ductile fracture in computer programs. One of the most frequently used models, which covers parameters of stress triaxiality and is implemented in Abaqus, is Johnson-Cook model. To determine stress triaxiality parameters we performed a tensile test of aluminium AW 6082 specimen. We used a digital camera to observe changes in geometry during tensile test. From the captured images we were able to calculate stress triaxiality. Based on stress triaxiality and strain at fracture we were able to determine Johnson-Cook triaxiality parameters. And these parameters allowed us to perform the simulation of the tensile test of a notched specimen and compare the results obtained with the values from the experiment.