Stiffness degradation in fatigue life of composites using dielectric state variables

Composite materials are widely used in aerospace and automotive structures for decades and over the years the community has gained a better understanding of the damage and failure modes of composites under fatigue. In this article, a dielectric characterization methodology for in-situ monitoring of composites under fatigue environments is proposed. A novel method of measuring the dielectric state variables in Broadband Dielectric Spectroscopy (BbDS) using Extremely Conductive Silver Epoxy Adhesive (ECSEA) paste is presented. These dielectric state variables serve to identify the precursor of the beginning of the end of life of the composite material under fatigue loading. The reliability of using this method for in-situ monitoring to provide fatigue life estimates and to indicate the immediate need for maintenance, repair and/or replacement of the structural component is discussed.