THERMAL STRESS MODEL FOR POLYMER SENSORS

The problems of thermal stress in a new theoretical model are discussed to help gain an understanding of the piezoresistivity in polymer composites. A new polymer matrix composite is a smart material with sensor properties and good sliding behavior for the diagnosis of plain bearings. Composites consist of a polyesterimide matrix with electrical conductor powders and lubricating additives. The theoretical model and numerical simulation of such composites, designed for the understanding of the electrical (sensor) properties, involves combined thermal, mechanical, and electrical interactions between the filler particles. Electrical conductivity of the composite is due either to the thermal stress or to the external mechanical stress, leading to a positive or negative temperature coefficient of resistivity. By comparing theoretical calculations with experimental measurements, it has been shown that the model for the piezoresistant effect can predict the composite resistance with reasonable accuracy.