An experimental study of the thermomechanical response of elastomers undergoing scission and crosslinking at high temperatures.

摘要

Elastomeric materials are in wide use in critical engineering applications, and recent spectacular failures of rubber components in the shuttle Challenger and automotive tires underscore the importance of understanding their behavior under severe operating conditions. Dramatic property changes, such as loss of elastic stiffness and permanent set can occur in elastomers at elevated temperatures. Most constitutive theories for nonlinear thermo-elasticity do not take into account these phenomena or account for the underlying microstructural changes. Therefore, reliable predictive tools for durability are not available to the design engineer of elastomeric components. Consequently, this work aims to fill that need.; Based on the initial work of Tobolsky in the 1940's and inspired by an understanding of the underlying physical and chemical processes, a multi-network constitutive model is used to capture the thermo-mechanical behavior and degradation of rubbers at high temperatures. Custom-built facilities are developed for uniaxial and multi-axial experiments of rubber at high temperature. An extensive experimental program is performed on commercial grade filled rubber, especially natural rubber, provided by an automotive bushing supplier, Tenneco Automotive Corp. It is shown that monotonic stress relaxation measurements and intermittent loading experiments can be used to calibrate the constitutive model, which can then be used to predict the response for more complex deformation and temperature histories. Good agreement is shown between such simulations and experiments.; A membrane inflation facility is designed, built and used to perform the first studies of rubber degradation under nonuniform deformation and multi-axial stress states at high temperature. The inflating medium is glycerine, which does not chemically interact with rubber. The temperature and inflation volume history of the glycerine are controlled and the inflation pressure is measured. Photogrammetry methods are used with ink targets printed on the membrane to determine the deformed profile and the biaxial stretch field of the membrane. Pressure relaxation experiments, performed at constant volumes of inflation suggest that the local degradation of the elastomer depends on the biaxial stretch state.; This work develops experimentally-based simulation tools that should prove valuable for predicting rubber property changes and potential failure of elastomeric components at elevated temperatures.