New method for predicting lifetime of seals from compression-stress relaxation experiments

Abstract

Interpretation of compression stress-relaxation (CSR) experiments for elastomers in air is complicated by (1) the presence of both physical and chemical relaxation and (2) anomalous diffusion-limited oxidation (DLO) effects. For a butyl material, we first use shear relaxation data to indicate that physical relaxation effects are negligible during typical high temperature CSR experiments. We then show that experiments on standard CSR samples (-15 mm diameter when compressed) lead to complex non-Arrhenius behavior. By combining reaction kinetics based on the historic basic autoxidation scheme with a diffusion equation appropriate to diskshaped samples, we derive a theoretical DLO model appropriate to CSR experiments. Using oxygen consumption and permeation rate measurements, the theory shows that important DLO effects are responsible for the observed non-Arrhenius behavior. To minimize DLO effects, we introduce a new CSR methodology based on the use of numerous small disk samples strained in parallel. Results from these parallel, minidisk experiments lead to Arrhenius behavior with an activation energy consistent with values commonly observed for elastomers, allowing more confident extrapolated predictions. In addition, excellent correlation is noted between the CSR force decay and the oxygen consumption rate, consistent with the expectation that oxidative scission processes dominate the CSR results.

An Experimental Facility to Measure the Chemorheological Response of Inflated Elastomeric Membranes at High Temperature

“…Since then, many researchers [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] have studied elastomers undergoing scission and cross-linking effects. A recent time-dependent constitutive model for elastomers that includes scission and additional cross-linking effects can be found in Wineman et al [23].…”