Modeling and interpretation of fatigue failure initiation in rubber related to pneumatic tires
Abstract
This dissertation is concerned with the multiaxial fatigue behavior of rubber related to pneumatic tires. The results provide the methodologies to predict the fatigue life in the states of complex stresses and for arbitrary geometries by utilizing experimental data from simple stress states on simple geometries. Most practical applications are under multiaxial and nonrelaxing conditions, but most of the data on fatigue life of rubber obtained from laboratories are for uniaxial and relaxing conditions. When the data are not available for actual loading conditions, the fatigue life can be evaluated from experimental data for uniaxial fatigue loading by an empirical relationship. The methodologies of predicting the crack initiation life were developed for filled SBR by the use of strain-fatigue life curves. They combine a modified Goodman relationship and the various fatigue failure theories, and were developed for linear and nonlinear models of the stress-strain relationship. The multiaxial fatigue failure approach using the total strain energy was found to give the most practical agreement with experimental data. The statistical behavior of fatigue life was investigated experimentally, and lognormal and Weibull distribution approximations were found to be acceptable from an engineering viewpoint. The lognormal distribution was, however, recommended to save experimental time. The test can be terminated after only half the number of specimens fail when a number of specimens are tested simultaneously. The statistical strain-fatigue life curves were approximated by a family of straight lines in log-log coordinates. Therefore, the data for fatigue life distribution can be extrapolated to lower strain levels and the cumulative density function can be formulated in simple forms. Also, a method of predicting the reliability of rubber components at an expected fatigue life was presented. Besides the mechanical factor affecting the fatigue failure of rubber, two other factors, temperature and environmental aging, were considered to adjust the fatigue life predicted for mechanical deformations to real operating conditions. A method of predicting fatigue life for arbitrary periodic loading was proposed, which deals with the experimental data generated by harmonic and constant amplitude loading on uniaxial strips.
Degree
Ph.D.
Advisors
Soedel, Purdue University.
Subject Area
Mechanical engineering|Materials science
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