Stability analysis of stitched composite plate system with delamination under hygrothermal pressure
In this study, a very recent stitched composite structure made of fiber reinforced polymers is analyzed. This composite structure is modeled by two specially orthotropic adhesively bonded, delaminated and stitched plates under in-plane compressive and shear loads and internal hygro-thermal pressure acting on delamination surfaces of plates which are considered as identical simply supported plates. While the adhesive layer between plate layers is modeled by mechanical linear normal and shear springs, stitches are modeled by discrete bilinear normal springs for the first time in the literature. In the stitch modeling, it is assumed that they can carry only normal loads because they are very thin and also initial imperfections are included with the parameter of looseness because of the fact that the stitching yarns are slack initially. The mathematical model of the problem is solved by Rayleigh-Ritz method. After strain energies of plates, the adhesive layer and stitches and energy potentials for external loads such as compressive normal loads, shear loads and internal hygro-thermal pressure are expressed, sine series as shape functions for plate vertical deflections satisfying simply supported boundary conditions are applied. Then, minimizing them gives deflections for the given loading. The stability condition is obtained as an eigenvalue problem to give critical buckling loads and corresponding mode shapes as well. Results are presented as plots of deformed shapes of the system and tables of parametric studies showing effects of changing parameters on stitch stresses and displacements, critical buckling loads and corresponding mode shapes.