Mechanical modelling of self-diagnostic polymers

The safety level in advanced load bearing applications can be enhanced if the material would be able to detect the in-service deformation, allowing a real time evaluation of the reliability state of the components. Polymeric materials can be used to get such a functionality through the insertion of so-called mechanophore units, whose main property is to chemically respond to mechanical stimuli. In the present paper, a micromechanical approach is developed to model the response of polymers containing reporting units, whose activation is triggered by the deformation of the underneath network or by a chemical stimulus. The model, through an Arrhenius-like equilibrium reaction law, provides a quantitative evaluation of the fraction of stress-activated molecules. Moreover, if the mechanophore activation involves also a change in their geometrical conformation, it influences the network deformation and the corresponding mechanical effects must be also accounted for. The formulated micromechanical model is presented and implemented in a FE code in order to simulate structural elements made of a self-diagnostic material. In particular, we consider the fluorescence-based strain detection of pre-cracked elements made of polymers with supramolecular complexes cross-linked to the polymer’s chains; the fluorescence intensity is assumed to be proportional to the volume fraction of the activated units, thus enabling to quantify the associated material’s strain value.