Postbuckling response of unitized stiffened textile composite panels: Experiments

Abstract

Abstract An experimental investigation of the compressive response of unitized stiffened textile composite panels that are manufactured using two-dimensional triaxially braided composites loaded in axial compression well into the postbuckling regime is presented. The stiffened panels are unitized because the constituent material was a textile laminate with an alternative method to form the stiffener geometry to a near net shape one-piece stiffened panel structure, thus removing the mechanism of stiffener debonding (separation) that is seen in traditional stiffened panels. Textile laminae that form the skin section of each panel were used, without discontinuity of material, to form the stiffener. Eight stiffened panels were manufactured using two different triaxially braided composite textiles. All eight manufactured stiffened panels withstood significant loading in the postbuckling regime prior to collapse, and nonlinear geometric and material effects were observed. Stiffener separation was not observed. Textile architecture-dependent matrix cracking was observed with local matrix cracks strongly aligned to the constituent triaxially braided composite textile. Tow buckling was observed as the primary failure mechanism for all panels. A macro crack traversed the width of each test specimen during structural failure within the gage section. Excellent repeatability and consistency were observed for all stiffened panels. The experimental results were the motivation for developing a computational multiscale framework where a mesoscale triaxially braided composite architecture-based model is used for the material. Details of the computational multiscaling framework and results compared to the experimental study are given in Kosztowny and Waas (2021), which is part two of this two-part paper.