Preform Structure Simulation And Elastic Properties Prediction Of Three Dimensional Braided Carbon/Carbon Composite

Three dimensional braided Carbon/Carbon (3D braided C/C) composite has aseries of outstanding physical and mechanics properties, such as excellenthigh-temperature trait, superior delaminating resistance, energy absorption capability,through-thickness reinforcement, high damage tolerance. These excellentperformances come from its integrated nature of preform and the properties ofbinding materials. However, two major drawbacks limit its developmeht andapplication. Firstly, chemical vapor infiltration (CVI) process which is used toproduce these composites is highly inefficient and leads to high product cost.Secondly, it should use the integrity specimen in order to guarantee the continuity ofthe fiber, which may take much cost and time. In this paper, considering the jam,space orientation and cross-section deformation of the fiber bundle, the structure andporosity of the preform with different braiding parameters is simulated usingcomputer simulation technology. The model for predicted elastic properties of the 3Dbraided C/C composite is developed.The main contents were summarized as follows:1) The moving regulation of fiber bundles in preform studied, and its spaceorientation and cross-section deformation were analyzed.2) The fiber bundle unit model with elliptical cross-section was put forward. Inthis model, the fiber is line inside the preform and helix at surface. Then, therelationship among the number of rows and columns, braiding angle, fiber volumefraction and packing factor were setup.3) Using Visual C++ and SolidWorks API, A software was developed byemploying the fiber bundle unit model on which the integral geometric descriptionsof 3D braided preform with different parameters could be automatically generated.The pore's shape and distribution among the fiber bundles in the preform wereexpressed clearly. The effect rule of the braiding parameters on the shape, surface area and volume of the pores in the preform was analyzed.4) The flexural properties of 3D braided C/C composites (uncut and cut edges)with different parameters were experimentally studied. The experimental resultsshow that the flexural modulus and strength decrease monotonically with increasingof the braided angle, whereas the flexural modulus and strength increasemonotonically with increasing of the fiber volume fraction. For composites whichcut edges, the damage behaviors are similar to those with uncut edges, however,there are 4.2% and 10.7% increase in the flexural modulus in specimens with oneedge cut and two edge cut separately, nevertheless, the flexural stress of specimenwith one edge cut is 12.4% lower than these of specimens with uncut edges, and theflexural stress value of specimen with two edge cut is 28% inferior to the specimenswith uncut edges.5) A mechanical model considering the integrity, bending and cross-sectionalvariation of every fiber bundle with the different braided parameters is established.Young's modulus, Poisson's ratio and shear modulus of the integral 3D braidedcomposites with different parameters were predicted.