Examining the application of the Hartman-Schijve equation to the analysis of cyclic fatigue fracture of polymer-matrix composites

Use of fiber-reinforced polymer-matrix (FRP) composites in structural design requires material data, in particular on their cyclic fatigue delamination behavior under various modes of loading, e.g., tensile opening (Mode I) or in-plane shear (Mode II) and the associated threshold values. There are no standard test methods for characterizing delamination propagation yet, except one procedure defining the determination of fatigue delamination onset. Data analysis and interpretation is often based on the expertise obtained from cyclic fatigue testing of metals and alloys and remains empirical. In the present contribution, the applicability of the modified Hartman-Schijve equation (originally developed for metals and alloys) to the characterization of fatigue delamination behavior of FRP under cyclic mode I loading will be discussed. The main focus is on interpreting information on the fatigue threshold and its scatter in FRP composites.