Fatigue stiffness loss and life prediction technique development of a real rubber automotive component by means of Finite Element Analysis
The main aim of the study has been to investigate the potential of providing a complete rubber fatigue behaviour predictions. The work explores the nucleation and growth of cracks, but including stiffness loss and damage evolution. It has been performed in two filled rubbers, one natural rubber and one blend of StyreneButadiene (SBR) with polibutadiene (BR). Such techniques involve various topics to be analyzed: material mono tonic and cyclic deformation behaviours, knowledge of stress/strain histories, the fatigue life and failure plane associated with the nucleation of cracks and their subsequent growth, fatigue damage quantification parameters, cycling control type, influence of density and size of cracks. Material characterization is designed to be economically and feasible in time limits. An industrialization of procedures has been carried out in our facilities for a complete material characterization, with high automation on test executions and data processing. Fatigue life prediction methods are studied by means of computer aided analytical techniques. Fatigue crack nucleation and growth life prediction approaches are studied. The equivalence criteria selected for life predictions, the cracking energy density, is adequate for multiaxial and variable amplitude loadings. Similarly, critical plane approach is used for identifying the failure plane. Although in the scope of the project there are only uniaxial and fully relaxing strain conditions. The major research potential is directed to develop stiffness loss and damage evolution prediction capacity. A damage function is defined to contemplate the effect of stiffness loss and crack size on the strain energy density. The parameter that quantifies the damage is the normalized stiffness. In rubber fatigue the strain energy density may depend not only on the instantaneous strain or stress, but also on damage state of material. The stiffness loss approach relates the differentiated particular damage developments of different loading modes (strain, stress or energy) in a function. Additionally, the damage function can be fitted by a constitutive model for stiffness loss computations, and using this model additionally the influence of size of the crack and its density are considered. The approaches are implemented in Endurica CL solver for rubber fatigue analysis. The characterization and prediction capabilities are settled at Leartiker facilities, and operative for giving a reasonable fatigue damage and stiffness loss predictions.
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