PAPER CANCELLED: Energy Balance and Tearing During High Pressure O-ring Extrusion Into a Small Gap

Elastomeric O-ring operating pressures are in general limited by a failure mode in which o-ring material is forced through the small gap separating the high and low pressure sides of the seal. The initiation of such ‘extrusion failures’ is analyzed here via fracture mechanical principles, considering in particular the energy requirement for extending the extrusion by propagating a tear at the gap inlet. The analysis produces a closed-form model relating critical pressure to compound stiffness and strength, and to gap size. The applicability of the model is established by comparing predictions to finite element calculations of the extrusion process, to previously published results for o-ring extrusion, and to newly obtained experimental measurements for a series of typical HPHT materials. It is demonstrated that the critical extrusion pressure is controlled by the dimensionless ratio Tc/gE, where Tc is the fracture mechanical strength, g is the gap size, and E is Young’s modulus.