Slackening
First, the slackening phase occurs in the slackening mechanism of bolted joints. During slackening—or in the slackening phase of bolted joints—the initial assembly preload is reduced by physical and mechanical processes. This reduction occurs due to settling, relaxation, and creep phenomena within the joint.
During the loosening phase, the sliding resistance is maintained, so that the bolted joint continues to transmit operational forces through a force-fit connection by clamping. Embedding begins as early as the assembly stage. The amount of embedding depends on the number of interface surfaces and the surface roughness values of the contact surfaces. Over time, relaxation reduces the preload force over a period of weeks to months.
Creep, on the other hand, leads to plastic, irreversible deformations and usually occurs over a period of months to years. The extent of these processes depends heavily on the material, the type of load, and the environmental conditions. The maintenance of slip resistance is largely determined by the elastic resilience of the bolted joint.
Overall, slackening represents a phased but technically manageable phase in the life cycle of bolted joints. Screw connections can be secured against slackening using special thread-locking elements or, more generally, using multifunctional thread-locking elements.