Development of Load Coupler Profiles of Spar Wingskin Joints with Improved Performance for Integral Structural Construction of Aircraft Wings

Abstract

Three-dimensional non-linear finite element analyses (FEA) have been carried out to evaluate the stresses in a variety of adhesively bonded laminated fiber reirforced polymeric (FRP) composite spar wingskin joint (SWJ) concepts, viz. triangular, circular, elliptical, and modified elliptical load coupler profiles. Both in-plane and out-of-plane stress variations on different surfaces of the wingskin have been evaluated. These are in good agreement with the experimental results available in the literature. Coupled stress failure criteria have been used to determine the locations of onset of delamination induced damages. The critical locations for onset of delamination induced damages in the wingskin are at the transition points where the spar changes its orientation from horizontal to inclined. Also, it is found that by varying the aspect ratios of the adhesive core (ratio of base to height) a significant effect on the joint strength could be realized. Joint strengths have been predicted through the application of Tsai—Wu failure criteria. It is recommended not to use triangular adhesive core profiles in the SWJ and never to use triangular adhesive core profiles with aspect ratio b/h ≤ 1.0. SWJ with circular or elliptical profiles of the adhesive core are preferred over triangular profiles. The SWJ with modified elliptical adhesive core profile with b/h=1.5 has been found to be the most suitable.