Strain sensing behavior of conductive polymer composites under corrosion fatigue

Strain sensing behavior of conductive polymer composites (CPCs) is governed by the intrinsic structure of polymers and fillers. However, corrosion fatigue is often an inevitable challenge for CPCs in applications, significantly impacting their strain sensing performance. To reveal the underlying mechanism and the main effect, a mechanistic connection is established from microscopic polymer and filler structures to macroscopic mechanical and sensing performance. Firstly, a fractional hyperelastic-damage-relaxation constitutive model is proposed in terms of polymer and conductive networks, and the governing equation for strain sensing is further derived based on the piezoresistive theory. Secondly, the change mechanism of polymer chains and conductive fillers under corrosion fatigue is explored through macro- and microscopic experiments. The results show that the physical breakage and disentanglement of molecular chains are regarded as the main changes under corrosion fatigue, which lead to damage of matrix holes and filler agglomerations observed in cross-section of CPCs. The multiscale experiments validate the rationality of the mechanical and strain sensing models. By comparing the experimental and theoretical results of stretching, the effectiveness and accuracy of the proposed models are significantly demonstrated. The degradation of strain sensing performance during uniaxial stretching is well described and predicted by the introduction of damage factors in the model. This work provides a clear understanding of the changes in strain sensing performance of functional materials such as CPCs under corrosion fatigue.