Elastic behavior of 3-D braided composites under compressive loading

In this study, a systematically conducted experiment has been carried out to characterize the compressive properties of 3-D braided composites. Two analytical models have also been modified and incorporated into finite element codes to predict the elastic behavior of 3-D braided composites under compressive loading.; On the experimental characterization, three different composite systems, each reinforced by carbon, S-2 glass and Kevlar fibers, respectively, were employed to study the material effect on the compressive properties. Four different braided structures were used to study the effect of fiber architecture. In addition, two compression test fixtures, namely, the shear-loaded fixture (IITRI) and the end-loaded fixture, were used. The experimental results reveal that fiber architecture plays a significant role in carbon and S-2 glass braided composites under compressive loading. Kevlar composites are not sensitive to fiber architecture. The compressive strength and modulus of braided composites are comparable with those of equivalent ({dollar}{lcub}pm{rcub}theta{dollar}/0) laminates.; In theoretical analysis, two models are used to predict the elastic behavior of 3-D braided composites under compressive loading. The Fabric Geometry Model (FGM) based on the micromechanics of composite materials and the Finite Cell Model (FCM) based on a frame-truss structural finite element method have been modified and implemented into finite element codes. In general, Fabric Geometry Model is seen to yield much better predictions than Finite Cell Model does. For carbon and S-2 glass braided composites, FGM predictions of all properties agree quite well with the experimental results for all four different braiding percentages. FCM, on the other hand, works only for composites with lower (i.e., 25% or 50%) braiding percentage. Besides, neither FGM or FCM does not account the non-linear behavior of Kevlar braided composites.