Thermo-mechanical coupling and strain energy-driven fatigue crack initiation in reciprocating rubber seals

Under reciprocating sliding conditions, rubber O-rings are susceptible to fatigue cracking governed by the complex interplay of multiaxial shear loads, pre-compression, and thermal fluctuations. Previous studies largely address macroscopic failure, lacking insights into the dynamic spatial evolution of crack initiation points under coupled thermo-mechanical fields. In this study, a comprehensive numerical framework is developed to predict the fatigue life and locate crack initiation in rubber O-rings using a Strain Energy Density (SED) approach. A two-dimensional axisymmetric finite element model was established using an isotropic nearly-incompressible elastic constitutive relation. The evolution of the equivalent elastic strain and strain energy fields was tracked across a broad thermal operational envelope and various compression ratios. Rather than a monotonic degradation, our simulations reveal a non-linear competing mechanism between thermal softening and geometry-induced strain concentration. Notably, at a critical compression ratio of 15.4%, raising the temperature to 75°C optimally relaxes local stress concentrations, increasing the predicted fatigue life by 24.9%. However, under excessive compression (21.1%) combined with high temperatures, the primary failure mechanism transitions from contact-surface wear to severe deformation interference at the groove root, irrecoverably locking the crack initiation site and halving the structural life. This purely numerical study establishes a theoretical map for identifying micro-crack initiation hotspots in complex dynamic seals, providing a mechanics-based design guideline pending future experimental validation.