Determination of Paris parameters from S−N curve in the simulation of fatigue in Nomex honeycomb sandwich structures

Abstract

Determination of S-N and Paris parameters form the two primary approaches as far as fatigue testing is concerned. With many economic factors and complexities involved in experimentation, these approaches are not related to each other and require implementation of separate test standards for both of them. In this work, an attempt is made on the interconvertibility of these experimental parameters and a numerical technique based on virtual crack closure technique (VCCT) is proposed for the evaluation of Paris parameters from S-N curve, corresponding to four-point bending end notched flexural (4ENF) sandwich specimen made up of Nomex® aramid honeycomb core with glass fibre reinforced composite (GFRP) facesheets. VCCT was effectively utilised for the estimation of strain energy release rates (SERR), in both 2D plane stress/strain and 3D conditions, which were compared with each other, and the resultant was incorporated with the S-N data for the determination of parameters of the Paris curve. These determined parameters were employed for the simulation of fatigue delamination growth by using “Direct Cyclic” step and compared with the results obtained from literature. The comparison revealed a good agreement between the two, thereby validating the proposed technique.