Finite Element Analysis For Ballistic Impact Of 3-D Braided Composites

High strength fiber reinforced composites have been widely used in ballistic protection because of their high performance-weight ratio and high impact damage tolerance. The reinforcing phase of composites can significantly influence the penetration resistance of composite materials at the same composite system(fiber, matrix and fiber volume fraction).Laminated composites are the most common composite materials in ballistic protection. The damage of laminated composites under ballistic impact includes fiber breakage, matrix crack and interlaminar fracture or delamination. The interlaminar fracture is the most distinct damage mode for laminated composites. Compared to the laminated composites, the three-dimensional braided composites have the higher inter-laminated shear strength and fracture toughness which leads to the higher impact damage tolerance. Because of the complexity of the microstructure, the research and the application of such kind of composites in person armor protection field is still in the primary state. It is very important to investigate the penetration process and the damage mechanism of this kind of the composites under the ballistic impact for optimization of bullet-proof composites.This paper is to clarify the damage pattern and model of 3-D braid composites by ballistic perforation of two different thickness 3-D braided composites. Based on observing on microstructure of 3-D braided composites, two finite element model were constructed. The 'fiber inclination model' for the description of 3-D braided structural reinforced composites is employed to decompose the 3-D composites at quasi-microstructure hierarchy based on the real composites structure. From this decomposition scheme, the 3-D braided composites equivalent to four inclined laminae and the crossover of the four laminae is neglected. Then the lamina model considering the microstructure and having the same fiber volume content with the 3-D braided composite is established. This is regarded as refined quasi-microstructure model. Another is real microstructure model. According to its geometry structure, 3-D braided composites were decomposed of different groups, and every group has different configuration. Then the whole structure of 3-D braided composites were constructed, And the actual microstructure model of 4-step 3-D rectangular braided composite materials which has the same fiber volume fraction with the braided composite specimen was described and established in the preprocessor of FEM. The projectile is regarded as rigid because of non-distortion in penetration. And the maximum strain criteria and mechanical properties of fibers, matrix at high strain rates were adopted in FEM calculation. The finite element method (FEM) code with explicit algorithm is used to simulate the ballistic penetration of the rigid projectile into the target. The residual velocity of the projectile and the deformation of target are obtained. The comparison between the numerical results and the experimental results proves that the two models are valid and reasonable. In addition, the damage pattern and the damage mechanism of the composite is also discussed.The main conclusions are as follows: (1) Damage modes of 3-D braided composites under ballistic impact: major failure mechanisms are shear and compression failure in the impact side of the target while extensive tension failure in the distal side;(2)the refined quasi-microstructure is established based on the real structure of 3-D braided composite. The structure of the calculation model is equivalent to the real structure of composite. (3)The comparison between the residual velocity of the projectile, the deformation of the lamina target according to the model calculation and the experimental results proves that the decomposition scheme of the 3-D composite at the microstructure hierarchy is valid and reasonable.(4) Simulation results for microstructure model of 3-D braided composite is closer to experimental results especially ballistic impact damage pattern because of the model is based on the actual microstructure of 3-D braided composites. And some middle results which can not attained from experimental can be gotten, for example discrepancy of energy absorption between fibers and resin and force-time curve during penetration etc.(5) velocity vs. time and acceleration vs. time history of projectile, the deformation of fibers and resin was used to analyze the whole process of penetration .The damage pattern and the damage mechanism of the composite is also discussed with two different model.(6)From the comparison between the model based on the homogeneous continuum assumption of 3-D braided composite and the models based on the real structure of 3-D braided composites, it proves that this paper models are more reasonable and accurate, and they also can be applied to numerical simulation for the ballistic perforation process of other 3-D reinforced composites.