As part of the junior professorship ‘Joining and material modification by power ultrasonics’, the joining of multi-materials and material modification using power ultrasonics are investigated in a fundamental and application-orientated manner. The mechanical behaviour of ultrasonically welded composites under load is characterised experimentally and simulatively in combination with digital twins. On the subject of material modification, phenomena observed during and after stimulation by power ultrasonics, such as particularly pronounced plastic deformation or microstructural changes, are investigated.