Numerical characterisation of uncured elastomers by a neural network based approach

•Model-free neural network approach captures large strain inelasicity.•Inelastic model-free approach represented by recurrent neural network.•Adaptive recurrent neural network represents different kinds of inelasticity (viscous, plastic and visco-plastic).•Novel combination of neural network based material formulation and micro-sphere framework.•Application of novel model-free approach to describe uncured rubber material.•Different strategies to identify the parameters of the neural network.•Performance demonstrated by numerical characterisation of uncured rubber.•Analysis of a rubber forming process. This research paper contributes to the model-free characterisation of elastic and inelastic materials. The introduced material description is based on neural networks for the constitutive stress-strain-relationship and is an alternative to a classical constitutive material description. This approach is an efficient method to represent the material behaviour numerically. The performance of the novel model-free formulation is exemplary shown for uncured natural rubber. One major advantage of the presented approach is the capability to use it for the representation of a wide range of materials. The novel model-free characterisation consists of a neural network that is coupled to the so-called micro-sphere approach. This formulation was developed for the characterisation of rubber like materials and takes the micro-structure of the material into account. As a benefit of this coupling, the neural networks, representing the stress-stretch-dependency, have to be exploited analysed only in onedimensional direction. In the first instance, the derivation is introduced for an Artificial Neural Network to yield a pure elastic description. Subsequently, the model-free approach is expanded in order to represent inelastic material behaviour as well. This extended formulation is obtained via a Recurrent Neural Network. Finally, uncured natural rubber material is described by the derived numerical approach. The model-free characterisation is validated by the finite element simulation of material tests. A complex forming of a rubber block into a mould is basis for a final validation of the model-free description.