Pre-tensioning device for fastening elements and method for pre-tensioning a fastening element

The fastener's pre-stretch device, the pre-stretch unit (4,5) in the first of the fastener (2) connection, and to which is composed of a rigid member (1a, 20) and second area, a fastener can with the pre-stretch extending to the rigid member. The pre-stretch unit (4,5) comprises a shape memory of metal; if the picture with the shape memory metal of the component (4), wherein inner device used, comprising a variable time through gradually (5) and shaft.