Meaning
Gradual reduction of internal forces within a material held at a constant strain results in a slow change in the clamping load or shape of a component. Over time, structural stress relaxation can lead to the loosening of bolted joints in plastic or soft metal enclosures even without external vibration. The process is a function of material properties and the thermal environment along with the initial magnitude of the stress.
Creep Distinction
While creep involves a change in dimension under constant load, this phenomenon involves a change in load under constant dimension.
Thermal Acceleration
Higher temperatures increase the rate at which the internal atomic structure reorganizes to relieve the applied pressure. In systems operating near their thermal limit, structural stress relaxation occurs much faster than in room temperature environments. The initial torque specification for the assembly must account for this predicted drop in tension.
Stability Consequence
Failure to mitigate the loss of internal stress results in an interface that can no longer resist shear loads. Regular maintenance checks use ultrasonic testing to measure the remaining tension in critical fasteners without disassembling the unit. Designing with materials that have high resistance to structural stress relaxation ensures the long term integrity of the system.
