Durability of rubber components under multiaxial cyclic stresses

Abstract

An accurate understanding of the fatigue behaviour of structural components through their working life, is a key factor for a light-weight and optimal design. Fatigue life has to take into consideration a series of parameters spacing from material properties, to working condition to the nature of the cyclic loads. This work consist in the development of a technique able to determine fatigue life of rubber components as well as the location and direction of the cracks.

An hyper-elastic, third-order, five-parameter, phenomenological material model has been selected and multiple components have been simulated under variable cyclic multi-axial loading.Several fatigue indicators and damage accumulation models have been taken into account. Eventually Cauchy rotated stresses have been chosen as fatigue indicator, coupled with Palgrem-Miner damage accumulation rule calculated in different spacial directions using critical-plane method. The Cauchy rotated stresses have been selected in order to be able to implement Haigh diagram data from existing literature. Furthermore the use of this tensor enables the determination of the location and orientation of critical planes referred to the un-deformed configuration. A custom equivalent stress method has been implemented in order to take into account mean stress sensitivity deriving from phenomena like strain induced crystallization.

The developed method has been tested against literature as well as experimental data in order the evaluate its quality. Correct calculation of the co-rotated Cauchy tensor has been verified against a uni-axially loaded specimen subjected to a rotation in the reference system. A diabolo specimen has been simulated under torsional loading in order to verify the correct location and orientation of cracks. Correct interpolation of multi-axial stress states deriving from multiple external loads have been verified against results from a FEM solver. Lastly a component from literature has been tested using different load signals, and the data from fatigue life, crack location and crack orientation have been gathered.

The procedure proved to be successful in the prediction of the location and orientation of cracks referred to the un-deformed configuration. Furthermore a precise fatigue life estimation of components under different load signals has been achieved. The procedure is highly customizable depending on fatigue and material properties of the specimen analysed. This procedure has proven to be a successful predictor tool for fatigue life estimation of multi-axially, cyclic loaded rubber components.