Multi-spar Composite Box Design And Its Post-buckling Analysis

Stiffened thin-wall structures made of composite materials have been proved to have a largestrength reserves in the post-buckling range. Based on the design criteria of composite structure, thisarticle fulfilled the design and post-buckling analysis of a multi-spar composite box by using thecommercial software ABAQUS. The main contents of this article are summarized as follows:1. The fundamental theory at the post-buckling stage for thin-wall composite structures isintroduced, including the basic concept and analysis method. The cohesive element used to simulatethe failure of composite interface is also discussed; the quadratic nominal stress failure criterion andthe mixed-mode strain energy release rate criterion are involved, which are utilized to predict thedamage starting and propagation of cohesive element.2. According to the multi-spar composite box design requirements, this article has finished thestructural design and buckling analysis of the multi-spar composite box under bend, twist andbend-twist load by using ABAQUS.3. The post-buckling courses of multi-spar composite boxes with three molding processes (fullyco-cured, mechanical connected up-panel and co-cured lower-panel, mechanical connected up-paneland stitch reinforced lower-panel) are analyzed in ABAQUS under bend, twist and bend-twist load.By comparing the post-buckling capability of the boxes with three different molding processes, it isverified that the stitch reinforcement technique could inhibit the failure of the skin/flange interface sothat the post-buckling loading capability of the reinforced box is improved significantly. The initialfailure mode which induces the final failure is also changed. The final failure of stitch-reinforced boxis caused by the initial damage of the composite structure in up-panel; while the final failure of thebox without stitch is induced by the initial damage of interface in lower-panel.4. The post-buckling capability of reinforced box is researched by testing under bend-twist load.The rationality of FEM results is certified by comparing with the test results. Therefore, this articleprovides an effective means to predict the post-buckling loading capability and failure mode ofmulti-spar composite box.