Mechanics-based design and sealing performance evaluation of bridge plug rubber cylinders with gradient porous structures

To overcome shoulder stress concentration and sealing failure in traditional bridge plug rubber cylinders, three optimized gradient-structure designs are proposed. Finite-element simulations were used to analyze the mechanical responses of uniform, central-gradient, and negative-gradient structures under different setting loads. Considering the contact stress distribution between the rubber cylinder and the casing, a new sealing performance evaluation method was established, and the sealing performance of all four types of rubber cylinders was assessed. Results show that, compared with the traditional structure, the new designs increase compression distance by 14.56–15.91% and reduce maximum equivalent stress by 10.14–15.26%. They also increase average contact stress by 8.01–16.03% and eliminate shoulder bulging. Among them, the negative-gradient structure provides optimal stress distribution and superior mechanical stability, while the central-gradient structure achieves the best sealing performance index K*, with a 26.44% improvement over the traditional design. Both designs significantly enhance sealing performance and service life.