Keywords: fatigue of rubber components, finite element simulation, finite element modelling, natural rubber, fatigue failure, service life, crack propagation, fracture mechanics.

Rubber components are usually designed based on static load analysis even though they are often subjected to dynamic load. Their main functions are to absorb shock and vibration and are thus prone to fatigue failure. Natural rubber components have intrinsic micro-cracks regardless of the best quality control in the process of vulcanisation and manufacturing. A steel rail fastener support with natural rubber insert is designed to reduce vibration and noise in urban railway is such an example. It is desirable to be able to estimate the service life of such a component, where failure is considered when macro-cracks appear on the surface of the rubber insert. It is essential to be able to predict where intrinsic micro-cracks become a sharp crack and then start to propagate, the crack propagation then depends on the direction and rate of propagation. In this paper the approach of fracture mechanics and fatigue crack growth characteristics (FCGC), the relationship between the fatigue crack growth rate and the strain energy release rate G, are used. FCGC has been used successfully to predict residual strength or the fatigue service life of metallic structures, but has not been used to the same extent for rubber components. This paper investigates the application of fracture mechanics and finite element method (FEM) in the study of propagation of crack in the 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 FEM and the virtual crack extension method. The G versus crack growth curve is then combined with the FCGC to predict the number of cycles to failure. For the case of the rubber rail support, 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 require the analysis to be 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 this two-dimensional model is subjected to an iterative process of 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. The procedure adopted reduces the enormous amount of computing required had the simulation been carried out with the three-dimensional model. The fatigue service life found by FEM simulation compared favourably with fatigue test results confirming that FCGC and FEM modelling can be used to predict fatigue behaviour of rubber components and provide tools for improvement in their design.

1

K.B. Broberg, "Cracks and Fractures", Academic Press, San Diego, CA, USA, 1999.

2

H.L. Ewalds and R.J.H. Wanhill, "Fracture mechanics", Edward Arnold, London, UK, 1991.

3

S. Stevenson, J.R. Hawkes, J.A. Harris and P. Hansen, "Fatigue Life of Elastomeric Engineering Components under Biaxial Loading using Finite Element Analysis", SAE Conf. Proc.P, 331, 29-48, 1998.

4

J. Wang, "Feasibility study for deducing fatigue crack growth characteristic of natural rubber from standard fatigue test data", M. Eng. Thesis, Victoria University of Technology, Melbourne, Australia, 2000.

5

J. Wang and D. Tran, "Fatigue fracture characteristics of natural rubber components", in Computational Techniques for Materials, Composites and Composite Structures, B.H.V. Topping, (Editor), Civil-Comp Press, Edinburgh, UK, 165-171, 2000. doi:10.4203/ccp.67.3.2

6

A.N. Gent (Editor), "Engineering with Rubber. How to Design Rubber Components", Hanser Publishers, Munich, 1992.

7

A.A. Griffith, "The phenomena of rupture and flow in solids", Phil. Trans. Roy. Soc., A221, 163-168, 1920.

8

J.R. Rice, "A path independent integral and the approximate analysis of strain concentration by notches and cracks", Journal of Applied Mechanics, 35, 379-386, 1968.

9

R.S. Rivlin and A.G. Thomas, "Rupture of Rubber Part: Characteristic Energy for Tearing", Jnl. Polym. Sci., 10, 251-318, 1952.

10

ISO 6943, "Rubber, vulcanized - Determination of tension fatigue", International Standard, 1984.

11

D. Tran, "Finite element simulation of post elastic strain energy release rate for ductile thin wall structure", Proceedings of the Eighth International Conference on Civil & Structural Engineering Computing, B.H.V. Topping (Editor), Civil-Comp Press, Stirling, UK, 2001. doi:10.4203/ccp.73.69

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £125 +P&P)