Three-dimensional Reconstruction Of High Performance Fiber Needle Felt And Its Composite Properties

The needled felt made of high performance fibers(carbon fiber,glass fiber,etc.),is the essential raw material of three-dimensional(3D)needle-punched composites.The needled felt has advantages of simple processing technology and high automation,which can not only improve the interlaminar performance,but also reduce production cost and shorten processing time of the 3D needle-punched composites.With the widely application of these needled felts,it becomes more and more important to study their structures and properties.In this study,the 3D models of carbon fiber needled felt had been established on the basis of structure analysis.Furthermore,the elastic properties,interlaminar shear strength and thermal conductivities of needled felt reinforced composites were investigated.The main contents include:(1)The fiber length was obtained by using the random sampling method.The beam under pure bending model was used to simulate the curved fiber in carbon fiber needled felt.The mixed Weibull distribution was applied to describe the fiber length distribution and bending radius distribution,and the fitting curves were well consonant with the observation data.The measurements of fiber orientation distribution verified that the orientation of carbon fiber in needled felt was nearly random.Based on these,a parametric representative approach for carbon fiber needled felt had been presented.(2)Based on the fiber models for straight and curved fiber,a fiber generation model was developed.A fiber-shift method was presented,which was used to find a suitable position for a new fiber and avoid the overlap of each fibers.The Python language was used to write the modeling script file,which was executed in software ABAQUS.Finally,a statistics-based 3D model for carbon fiber needled felt was built.(3)Three kinds of 3D models for carbon fiber needled felts were proposed,and they were closed model,open model and cut model.A series of analytical methods were proposed to investigate these 3D models.As the size of the cutting model increased,the average length of the fiber was increasing.The results and cut model could be used to simulate the elastic modulus of carbon fiber needled felt reinforced composites.The compression and needling process of pre-needling technique were simulated.Based on these,the moving path and morphology of the fiber and the interactions between fibers were studied.(4)The elastic properties of carbon fiber needled felt reinforced composites were analyzed by experiments and theoretical prediction,and the effect of cutting size on the tensile properties of the composites was discussed.The results showed that,within limits,the elastic properties of carbon fiber needled felt reinforced composites decreased with the increase of sample size.The equivalent fiber bundle was proposed and the embedded element technique was used to build the 3D finite element model of the composite.The predicted results of the finite element method were closer to the experimental values than that of the rule of mixtures and the inclusion theory,which verified the availability of the 3D model of carbon fiber needled felt.(5)The study of mechanical properties of three kinds of 2.5D fabric laminated composites was carried out.The results showed that,the addition of carbon fiber needled felt improved the interlaminar shear strength significantly,and the needling process further increased the interlaminar shear strength.The interlaminar failure mechanisms of the three kinds of composites were different.The in-plane properties were increased slightly by carbon fiber needled felt,but were decreased evidently by the needling process.(6)The thermal conductivities of needle-punched quartz fiber reinforced composites with different preform structures were measured by using transient hot-wire method.The thermal conductivities of composites increased with the increase of fiber volume fraction,and the thermal conductivity would also be affected by the content and orientation of the fiber in the non-woven cloth of preform.In addition,the influence of carbon fiber needled felt on thermal conductivities of 2.5D fabric laminated composites was studied.It could be concluded that,the addition of carbon fiber needled felt improved the thermal conductivity,but the needling process led to a slight decline.