Meaning
Gradual loss of the resistive pressure exerted by a seal or fastener against its housing over a period of time. In mechanical assemblies, reaction force decay is a primary factor for gaskets and O-rings that must maintain a liquid tight barrier. The material essentially loses its memory and fails to push back with the same intensity it had at the moment of installation.
This process is accelerated by high temperatures and chemical exposure. It is the mechanical equivalent of stress relaxation under a constant strain.
Stress Relaxation
Physical changes at the molecular level allow the polymer chains to slide past each other and reduce internal tension. While the external dimensions of the part might stay the same, reaction force decay means the effective sealing pressure is dropping. If the force falls below the pressure of the fluid being contained, a leak will occur.
Gasket Integrity
Maintenance schedules often rely on predictive models of this decline to determine when a seal should be replaced. Manufacturers use standardized tests to measure reaction force decay over thousands of hours, allowing them to provide a demonstrated rate of performance. This data helps avoid the cost of unplanned shutdowns caused by joint failure.
Assembly Torque
Initial tightening of bolts must account for the immediate drop in tension that occurs shortly after the parts are joined. Because reaction force decay is most rapid in the first few hours, some procedures require a second torque check to ensure the connection remains secure. A consistent rate of decay allows for more accurate long term planning of hardware reliability.
