Time – frequency dynamic characteristics 2D in the quality assessment of welded joints

The authors of the article have been looking for a new parameters and dynamic characteristics, which can be applied to non-destructive testing of welded joints. All characteristics have been based on recorded data generated during the vibration tests of welded joints with and without failures. The article deals with the methods of assessing welding joints using 2D: time – frequency dynamic characteristics. A calculation procedure used for analysing simultaneous changes of the response modules, registered by acceleration sensors was presented. Vibrations amplitudes were transformed to a function of time and frequency (simultaneously) and presented over 2D time – frequency characteristics. The analyses of the characteristics were performed for a plate without any welded joint, for a plate with non-defected welded joint and for a plate with a welded joint defected by an edge bonding. Having analysed registered 2D time – frequency dynamic characteristics it can be noticed that presenting the responses analysed simultaneously over the time and frequency allows evaluating if examined system maintains non-linearity and, at the same time, it allows to indirectly assess the quality of the welded joint. The proposed measure parameters of the quality of a welded joint can be defined as a dispersion of colours on the obtained characteristics. The faults (and the vibration nonlinearity) of the welded joints is bigger if the dispersion is greater.