Prediction and Validation of Continuous Fiber Stiffened Plates Manufactured With Continuous Fiber Fabrication

Abstract

The purpose of this thesis was to develop an analytical method for predicting the structural properties of continuous fiber stiffened plates, which was then validated both experimentally and via finite element analysis. The MarkForged Mark Two 3D printer enables parts to be printed with continuous carbon fibers embedded within them. A manufacturing process was developed for printing stiffened grids with our without skins, with continuous fiber reinforcement on the top and bottom of the stiffening ribs, which allows bending stiffness can be maximized. An orthotropic grid was printed using Continues Filament Fabrication (CFF), an additive manufacturing process that embeds reinforcing fibers into plastic parts manufactured with Fused Filament Modeling (FFM). The stiffness of this orthotropic grid was then analyzed with laminate plate mechanics. To accomplish this, the results of research conducted by Chen and Tsai was utilized to obtain the stiffness matrices of a grid stiffened plate. Chen-Tsai provided the formulation for the stiffness matrices, allowing the material properties of the carbon fiber and nylon, along with the moment of inertia of the ribs, to be used to calculate the matrices. The stiffness matrices allowed the calculation of bending stiffness, and in turn allowed the deflection to be calculated for a given load. Subsequently, the analytical deflection prediction was validated via experimental and Finite Element Method analysis. The cantilevered beam experiment provided a result that was very close to the analytical prediction. However the FEM analysis showed significant deviation from the other methods and there was a 50% difference between FEM results and analytical results.