Microgrid Plastic Strain Analysis of a Representative F-111C Fuel Flow Vent Hole 13 Coupon

摘要

This report presents results for the application and associated improvement of an AED microgridding procedure for the determination of highly localized strains. The procedure has been applied to determine plastic strains at the critical location for a plate with a reworked FFVH13 geometry, subjected to F-111C CPLT loading. By using multiple measurements over an increased gauge length of 150 micrometers, highly accurate strains, ranging in accuracy between 57 and 135 micro strain were determined. This accuracy level is approximately an order of magnitude better than the prior microgridding approach. For the critical region, detailed non-linear strain hysteresis responses were obtained, and the measured peak and residual strains of -2.16024% strain and -0.79349% strain respectively agreed well with prior finite element predictions. The measured residual compressive strains at the critical location indicate that there is a significant residual tensile stress, which is consistent with the known occurrence of fatigue cracking in the fleet. This investigation has also provided valuable strain data for use in validating advanced FE based constitutive models, which are currently used and under development in AED for obtaining airframe structural integrity assessments.