Predicting the in-plane elastic constants of diamond braided composites

Abstract

An analytical model based upon repeat unit cell approach is proposed to predict the in-plane elastic constants of two dimensional diamond braided composites. A new geometrical model is developed which considers the yarn undulation and inter-yarn gap in a diamond braided fabric reinforced composite. The actual state of yarns in composites is modeled by the use of sinusoidal shape functions, which employ parameters such as braid construction, yarn geometry, inter-yarn gap and overall volume fraction to quantify the geometry of braided fabric. Stiffness is predicted by calculating the engineering constants for each subcell followed by averaging it over the repeat unit cell's volume using a combination of iso-stress and iso-strain conditions. Composites using four different fabric architectures are fabricated and tested in tensile mode to verify the model. The experimental results indicate reasonable correlation with predicted results. Parametric study is conducted over a range of structurally possible geometrical parameters to study the effects of braiding angle, yarn aspect ratio and gap on the in-plane elastic properties of the textile composite.