Coherent testing and simulation of composite blade repair

Abstract

The objective of this research program is to experimentally and computationally determine the static and fatigue response for two methods of repair to an E/Glass-Epoxy sandwich laminate. The proposed methods of repair are a scarf and overlap patch. A series of tests was carried out on square composite sandwich panels under direct tension and rectangular sandwich panels under four-point flexure. The performance of the repaired panels was compared against undamaged panels to establish a baseline comparison for the methods of repair. Computational models were constructed, which incorporated a non-linear material response subroutine, to model damage initiation and propagation and its effects on the structural integrity of a repaired panel. The material subroutine accurately predicted the mode and location of damage initiation and propagation under static and fatigue loading. It also provided excellent agreement with the global effects of damage observed during the static and fatigue tests. Both methods of repair proved to perform in an excellent manner under static and fatigue loading. Negative R ratio fatigue loading, however, was found to have a much greater effect than positive R ratio fatigue loading on the initiation and propagation of damage and the endurance of the panels. The scarf repair demonstrated a slightly higher endurance to fatigue loading than the overlap repair for both positive and negative R ratio loading. Both i-methods, however, proved to viable options for field and depot level repair. The simplicity of the overlap over the scarf patch make it a more practical option for field level repair.