Influence of Non‐Uniform Swelling Behavior on the Mechanical Properties of <scp>HNBR</scp>

ABSTRACT Hydrogenated Nitrile Butadiene Rubber (HNBR) is widely used in sealing applications, particularly in environments exposed to aggressive media and high temperature and pressure (HTHP). It is prone to swelling, which affects its mechanical properties. In this study, swelling experiments were conducted on HNBR samples with two different hardness levels under HTHP conditions. The swelling gradient field was coupled with the mechanical response. Finite element simulations were performed to analyze non‐uniform swelling, revealing the swelling behavior and mechanical properties of HNBR under these conditions. The results show that the rubber softens with increasing swelling duration. After 24 h, the average swelling degrees of the specimens with Shore A hardness 85 (85HA) and 90 (90HA) reached 78.59% and 74.91%, respectively, accompanied by non‐uniform swelling and uneven stress distribution, with higher stress at the center and lower stress at the edges. After 168 h, both specimens were nearly fully swollen, with average swelling degrees of 99.79% and 99.51%, and the stress distribution became uniform. Under the same swelling duration, the 90HA specimen showed superior resistance to swelling. The simulation results agreed well with the experimental data, confirming the model's capability to capture rubber swelling and mechanical behavior under non‐uniform conditions.