Simulation of Fatigue Fracture of a Rubber Rail Support

Abstract

Fatigue Crack Growth Characteristics (FCGC), the relationship between the fatigue crack growth rate and the strain energy release rate, has been used successfully to predict residual strength or the fatigue service life of metallic structures. FCGC has not been used to the same extent for rubber components, even though rubber components are often employed in dynamic rather than static applications, for which fatigue mode of failure should be used as the criterion in analysis and design. This paper investigates the application of fracture mechanics and FEM in the investigation of the propagation of crack in a rubber rail support and the estimation of its fatigue service life by using FCGC of a natural rubber. The key technique used in this investigation is to determine the strain energy release rates G of the structure by using finite element method (FEM) and the virtual crack extension method. The G versus crack growth curve is then combined with FCGC to predict the number of cycles to failure. For the case of the rubber rail support, because of the high degree of non-linearity of the problem due to rubber material properties, large deformation and great discrepancy between the rigidity of steel and rubber components, the analysis is divided into two stages: first a three-dimensional model of the structure is analysed under static loading, the maximum stress thus found and the displacements measured in static testing were used to validate an equivalent two-dimensional model. Then the two-dimensional model is subjected to the virtual crack extension simulation, from which the strain energy release rate is found and combined with FCGC of rubber to determine the service life. Results compared favourably with fatigue test results indicating that FCGC and FEM modelling can be used to predict fatigue behaviour of rubber components and provide tools for improvement in their design.