Mechanical characterization and modeling of polymeric materials for high pressure sealing

The choice of a proper material is probably the most critical factor in the design of seals able to withstand extremely high pressure, and knowledge of material mechanical properties is essential for the finite-element model (FEM) simulations needed to understand and optimize seal behavior. The aim of this work is the mechanical characterization of polymeric materials for ultrahigh-pressure sealing applications (600 MPa). After a short presentation of seal design and materials commonly used, the testing of four thermoplastic materials is described: PA6, H-TPU and UHMWPE reinforced with glass or ceramic microspheres to enhance wear resistance. Uniaxial tension and compression, shear and planar tension tests were performed as well as a stress relaxation test to gain information about viscoelastic effects. Experimental data are then discussed and elasto-plastic and hyperelastic constitutive models for polymeric materials reviewed, focusing on the application of these models at high pressure. The Young's modulus and yield strength are very sensitive to hydrostatic pressure for polymeric materials and a proposal for the implementation in the FEM of this effect is illustrated.