loosening

Loosening is the reduction of tightness in a connection or the loosening of constraints that keep an object, structure, or material in a defined position. It can occur in physical systems, where joints, fasteners, or interfaces lose preload or clearance increases, and in materials or soils where density and friction decrease due to disturbance.

In mechanical engineering, loosening commonly refers to fastener loosening, where threaded connections gradually back off under vibration, impact, thermal cycling, or wear. Causes include insufficient torque, over- or under-tightening, improper thread engagement, corrosion, and lubrication failure. Consequences can include loss of clamping force, leakage, misalignment, and unintended motion.

Prevention and control include proper torque and tensioning, use of locking features (thread lockers, jam nuts, lock washers), preloading, adhesives, and regular maintenance and inspections. Design strategies include appropriate fit class, redundancy, and audible or visual indicators of loosening.

Loosening can also occur in soils and granular materials when disturbance, vibration, or cyclic loading reduces compaction and increases permeability, potentially affecting foundation stability and bearing capacity. In industrial and structural contexts, monitoring through vibration analysis or periodic torque checks helps manage risks associated with loosening.