Session: 12-03-03: General: Mechanics of Solids, Structures and Fluids

Paper Number: 141374

141374 - Computatinoal Modeling of Reinforced Annular Seals 

Seals are typically made of elastomers. When sealing conditions are severe, such as at high temperature or under high differential pressures, the elastomers can extrude through the gaps they are supposed to seal. In these scenarios, reinforcements are provided to prevent extrusion. For retrievable seals, i.e., seals which need to be removed after their temporary sealing function, garter springs reinforced elastomers are an effective solution. The garter spring reinforced seals are constructed by molding a coil spring into the seals. When the seals are set (i.e. deployed), the garter springs serve as extrusion preventors. When the seals are unset, the garter springs help the seals to recover to their original configurations, allowing easy retrieval of the seals. Modeling of garter spring reinforced seals is challenging, both geometrically through CAD software and numerically through finite element analysis, due to the complex topology of the elastomer encapsulated springs. Another challenge associated with the modeling is that there is progressive debonding between the elastomer and the garter springs.

For efficient analysis and optimization of reinforced seals, a homogenized nonlinear transversely isotropic elastic model is developed to represent the elastomer encapsulated garter spring. The axial modulus of the encapsulated spring is represented by a strain dependent elastic modulus, which is calibrated through physical uniaxial tensile tests on an elastomer encapsulated spring. The tangent modulus of the measured uniaxial tensile stress strain curve is the axial modulus. The moduli in the transverse directions are calculated through a unit cell approach. This new material model can now be implemented into a commercial finite element software which supports user defined material models, such as Abaqus.

With this encapsulated garter spring material model, the complex three-dimensional garter spring reinforced seal analysis is converted into an axisymmetric analysis. Through this axisymmetric finite element model, the deployment of the reinforced seals is simulated, and the deformation in the seal body is predicted.  The load – stroke curve of a seal setting process can be predicted and validated against the physical test measurement. This curve relates the setting load to the axial contraction of the seal system. This relationship is of particular interest because it reveals characteristics of the setting process, such as the equivalent axial stiffness of the seal system. The deployment of the reinforced seals is physically observed using not only a transparent outer pipe for an annular seal as well as cut slots on an outer metallic pipe. The new transversely isotropic elastic model was verified and validated through physical tests of various designs of the garter spring reinforced seals. The model has been extensively and effectively applied for evaluating designs and for optimizing the garter spring reinforced seal designs.

Presenting Author: Allan Zhong Halliburton

Presenting Author Biography: Allan Zhong is a Halliburton Distinguished Scientist with expertise in engineering mechanics and computational modeling. He has more than 25 years of industry experience. He was granted 22 US patents and has published over 80 technical papers. Prior to Halliburton, Allan worked at Goodyear Tire and Rubber Company, where he developed an industry leading fracture mechanics-based truck tire durability model. He is a fellow of ASME (American Society of Mechanical Engineers), and a member of SPE (Society of Petroleum Engineers). Allan holds a Ph.D. in applied mechanics from California Institute of Technology.

Authors:

Allan Zhong Halliburton
Zhong Zhou Halliburton