Previously we explained creep under constant load. Within the mechanical system of gaskets, there exists another common corresponding phenomenon: stress relaxation. The two phenomena differ significantly in operating conditions and deformation mechanisms. We will use the relatable analogy of a porter carrying loads to clearly distinguish them, helping you accurately grasp the essence of stress relaxation and its impact on sealing assemblies.
Let us adjust the constraint conditions: instead of allowing the porter to sink freely, he must keep his shoulder height fixed at 1.35 meters, corresponding to the mechanical state of constant strain.
To hold this fixed posture, the porter will find the load unbearable over extended time and must reduce the weight of the carrying pole. The original total load of 60 kilograms (split evenly front and back) is cut by 5 kilograms on each side, bringing the total down to 50 kilograms, allowing the porter to easily maintain the set shoulder height. Throughout this process, the overall dimensional form remains unchanged, while only the borne load decreases — this is stress relaxation.
We can derive relevant ratios for stress relaxation via professional calculation methods. Given an initial load of 60 kg and a residual load of 50 kg after adjustment, the degree of stress relaxation can be quantified by comparing the two values. Translating this to flanged gasket assemblies: once equipment assembly is complete, the gasket thickness is locked in place, meaning strain stays constant. As service time elapses, the internal compressive stress borne by the gasket gradually diminishes, accompanied by a loss of bolt tightening force — this is the typical stress relaxation behavior of gaskets.
Stress relaxation is a normal mechanical evolution during sealing component operation. Mastering its variation rules enables rational control of bolt preload and extends the service life of sealing assemblies.
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