The RTD partners TWI and KTU have pioneered novel finite element modelling methods for ultrasound prediction and they are using these techniques to help develop the SpotTrack device. The models make it possible to study a large set of cases relatively inexpensively and will provide a more detailed insight. The modelling results enable the visualisation of the sound field throughout the whole volume at any point in time during the test. This will result in a deeper understanding of the effects of the variables on the reliability of the results of the test and so the reasons behind the A-scan results will be fully understood.

Figure 12, shows an example of one of the finite element models being used to predict the reflections from a spherical pore in the centre of the nugget.

Figure 12,  Example of the von-Mises stress prediction from the ABAQUS finite element model of ultrasound interacting with a pore in a spot weld.
Figure 12, Example of the von-Mises stress prediction from the ABAQUS finite element model of ultrasound interacting with a pore in a spot weld.

In order to obtain increased resolution, the SpotTrack prototype will include an array probe and will make use of a multiplexer with a single pulser-receiver.  The multiplexer allows the signals to be collected without the need for expensive multiple pulser-receivers.

In order to give a simple pass or fail indication for each spot weld, an algorithm is being developed.  The algorithm will automatically identify the main reflections (from the backwall of the weld), intermediate reflections (in the case of an undersized weld or defects in the weld) and certain parameters of the reflections such as arrival time and amplitude.  Using this information, the thickness and the approximate size of the weld can be determined, and a verdict on the weld quality is then obtained.