Assessment and Validation of Incremental Hole-Drilling Calculation Methods for Residual Stress Determination in Fiber-Metal Laminates

Background Fiber-metal laminates (FML) are seeing increasing application in the aerospace industry due to their potential for significant weight reduction in structural design. Residual stresses develop through the thickness of a FML resulting from the production process. Objective To assess and validate the latest calculation procedures for residual stress determination in FMLs by IHD. The two methods in focus are advancements of methods previously developed for isotropic materials. The first is based on the so-called integral method using Tikhonov regularization, similar to that of the ASTM E837 standard, and the second is based on the power series approach, similar to that proposed by Schajer in the 80's. Methods Hybrid FML samples were specifically designed to allow the use of neutron diffraction to complement analyses performed using the two IHD calculation techniques. A symmetric FML with a ply stacking configuration of glass fiber-reinforced polymer (GFRP) and steel [0/90/steel](s) was selected. The neutron diffraction analyses were performed on the steel core (which is not possible on the non-crystalline GFRP plies). Results The residual stresses determined by both IHD methods compare well and both can characterise the distribution of residual stresses through each layer of the structure, clearly identifying the discontinuities occurring at the interfaces. The error sensitivity of the power series approach is somewhat lower compared to that of the integral one. Conclusions The IHD residual stresses determined in the inner metallic layer compare well with those determined by neutron diffraction.