Validation of improved methods for predicting long-term elastomeric seal lifetimes from compression stress-relaxation and oxygen consumption techniques.

Abstract Conventional high-temperature compression stress–relaxation (CSR) experiments (e.g., using a Shawbury–Wallace relaxometer) measure the force periodically at room temperature. In this paper, we first describe modifications that allow the force measurements to be made isothermally and show that such measurements lead to more accurate estimates of sealing force decay. We then use conventional Arrhenius analysis and linear extrapolation of the high-temperature (80–110 °C) CSR results for two commercial butyl o-ring materials (Butyl-A and Butyl-B) to show that Butyl-B is predicted to have approximately three times longer lifetime at room temperature (23 °C). To test the linear extrapolation assumed by the Arrhenius approach, we conducted ultrasensitive oxygen consumption measurements from 110 °C to room temperature for the two butyl materials. The results indicated that linear extrapolation of the high temperature CSR results for Butyl-A was reasonable whereas a significant curvature to a lower activation energy was observed for Butyl-B below 80 °C. Using the oxygen consumption results to extrapolate the CSR results from 80 °C to 23 °C resulted in the conclusion that Butyl-B would actually degrade much faster than Butyl-A at 23 °C, the opposite of the earlier conclusion based solely on extrapolation of the high-temperature CSR results. Since samples of both materials that had aged in the field for ∼20 years at 23 °C were available, it was possible to check the predictions using compression set measurements made on the field materials. The comparisons were in accord with the extrapolated predictions made using the ultrasensitive oxygen consumption measurements, underscoring the power of this extrapolation approach.

[1]  Mohammed Tahir,et al.  Appraisal of the current standards for stress relaxation measurements in compression for rubbers , 1986 .

[2]  G. J. Van Amerongen.  Influence of structure of elastomers on their permeability to gases , 1950 .

[3]  K. Gillen,et al.  Quantitative model for the time development of diffusion-limited oxidation profiles , 1997 .

[4]  K. Gillen,et al.  Thermal Degradation Studies of A Polyurethane Propellant Binder , 1999 .

[5]  M. Keenan,et al.  New method for predicting lifetime of seals from compression-stress relaxation experiments , 1998 .

[6]  A. Birley,et al.  Stress-relaxation measurements on rubbers in Compression Equipment and methodology , 1986 .

[7]  P. Pincus,et al.  A theoretical basis for viscoelastic relaxation of elastomers in the long-time limit , 1983 .

[8]  A. Birley,et al.  A new concept for stress relaxation measurements of rubbers in compression , 1983 .

[9]  R. Chasset,et al.  Viscoelastic Relaxation of Rubber Vulcanizates Between the Glass Transition and Equilibrium , 1966 .

[10]  Kenneth T. Gillen,et al.  An ultrasensitive technique for testing the Arrhenius extrapolation assumption for thermally aged elastomers , 1995 .

[11]  Arthur Victor Tobolsky.  Properties and Structure of Polymers. , 1960 .

[12]  Kenneth T. Gillen,et al.  Extrapolation of Accelerated Aging Data - Arrhenius or Erroneous? , 1997 .

[13]  K. Murakami,et al.  Chemorheology of polymers , 1979 .

[14]  Aurelio Savadori,et al.  Impact testing of plastics: présent knowledge , 1985 .

[15]  A. Cunliffe,et al.  Photo-oxidation of thick polymer samples—Part II: The influence of oxygen diffusion on the natural and artificial weathering of polyolefins , 1982 .

[16]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[17]  Kenneth T. Gillen,et al.  Time development of diffusion-limited oxidation profiles in a radiation environment , 1997 .

[18]  J. Ferry.  Viscoelastic properties of polymers , 1961 .

[19]  G. Skirrow,et al.  Transport and equilibrium phenomena in gas–elastomer systems. I. Kinetic phenomena , 1948 .

[20]  A. A. Collyer,et al.  Irradiation effects on polymers , 1991 .

[21]  Michael R. Keenan,et al.  Methods for Predicting More Confident Lifetimes of Seals in Air Environments , 2000 .

[22]  D. K. Ottesen,et al.  Correlation of Chemical and Mechanical Property Changes During Oxidative Degradation of Neoprene , 2000 .

[23]  K. Gillen,et al.  The wear-out approach for predicting the remaining lifetime of materials , 2000 .

[24]  K. Gillen,et al.  Rigorous experimental confirmation of a theoretical model for diffusion-limited oxidation , 1992 .

[25]  E. A. Salazar,et al.  Physical and chemical stress relaxation of elastomers , 1975 .