Reliability analysis of static sealed joints.

Leaking, friction and wear of seals are concerns for machine designers and users everywhere. Although perfect sealing may be the general aim, in practice, considering apparently identical seals in the same application, some may seal while some may not. This is due, at least in part, to surface-related random phenomena. Therefore, the importance of considering the reliability of sealed joints cannot be overemphasized. Up to now, there is no paper in the published literature about the reliability analysis of static sealed joints. All of these facts provide the motivation for the current research work. A computer simulation model for the leakage analysis of static sealed joints has been developed based on the percolation theory. The features of the leakage simulation model can be concluded as follows: (1) It reveals the effect of random properties of rough surfaces on the sealing performance and makes it possible to apply the statistical concepts in discussing the sealing reliability of static sealed joints; (2) It provides much simpler and more economic tool for the statistical analysis of leakage by computer simulation than by experiments; (3) It makes it possible to describe the leakage phenomenon more accurately using the leakage path model instead of the clearance between surface centre-lines; (4) It eliminates the need for individual asperity model of rough surfaces, because the actual digitized surface is used directly. The relationship between the leakage probability and the applied load, which is of great general interest to the designers of static sealed joints, has been predicted by the leakage simulation model. The simulated results show that for a given leakage probability, the required load will increase as the value of RMS o height a increases or the value of correlation length decreases. It is confirmed that a certain value of contact ratio can be used as the criterion for identifying the reliability of static sealed joints with a certain confidence level. The contact ratio criterion provides a simple, inexpensive and useful tool to evaluate the effects of rough surfaces, material properties and applied load on the sealing reliability of static sealed joints. However, in order to be of practical use, experimental work is required to evaluate its validity