Permeabil ity of the 4-step 3D braided preform

Permeability of the three- dimensional braiding preform was measured by radial flow techniques. Thepermeability values were calculated by an iterative approach of the modified inlet radii. These iterations are conveniently performed based on a procedure with Visual C + + . The orientation of the principal permeability tensor wasobtained according to the following steps. Firstly , the flow f ront was ext racted via an image processing algorithm ofselecting a threshold. Secondly , the flow f ront ellipse was fitted by using the nonlinear least squares curve fittingalgorithm in Matlab. The orientation between ellipse major and braiding axes was calculated in Matlab. The result sshow that braided parameters influence the permeability. The principal permeability decreases with increasing thefiber volume fraction when the braiding angle is constant , and it also decreases with increasing the braiding anglewhen the fiber volume f raction is constant . However , the orientation of the principal permeability does not vary withthe braiding angle , and it keep s on coinciding with their braiding direction.