A first and a second object are joined with the aid of a joining element including at least in the region of its distal and proximal ends a thermoplastic material. Two blind holes facing each other are provided in the two objects and the joining element is positioned in the blind holes such that its distal and proximal ends are in contact with the bottom faces of the blind holes and such that there is a gap between the two objects. This assembly is then positioned between a support and a sonotrode. The sonotrode and the support are forced towards each other, while the sonotrode is vibrated, thereby liquefying at least part of the material having thermoplastic properties, there, where the joining element ends are pressed against the bottom faces of the holes and allowing the liquefied material to infiltrate into pores.