Experimental Study On The Mechanical Properties Of Multi-layer Cross-linked 3D Three-dimensional Braided Composites

Multilayer interlock three-dimensional(3D)tubular braided composites have been widely used in propeller blades,high pressure pipelines,rocket nose cones and engine nozzles owing to prominent interlaminar shear properties,reliable damage tolerance and outstanding torsion performance.The prediction of the mechanical properties and the design of the fabric structures for the braided composites are dependent on the trajectory distribution of strands,the geometrical model of the braided structure and the basic mechanical properties of the material.In this paper,a series of researchs has been carried out in order to study the mechanical properties of multilayer interlock 3D braided composites.On one hand,mathematical models of braiding strand trajectories are derived based on the analysis for the characteristics of carrier paths,the interlacing and interlocking of braided structures,and the motion of braiding strands.The mathematical models are then developed to establish parametric expressions for multilayer interlock tubular braided structures by advanced development of UG NX 10.0.The comparison between the braided preform and the simulation model shows that the maximum errors of the braiding diameter,braiding angle,the area of singal fiber bundle and the fiber filling coefficient are 0.56%,2.67%.4.20%and 4.50%respectively.The results validate that the simulation model show a good agreement with the braided preform.On the other hand,based on the simulation model of the braided structure,12 types of carbon fiber 5-layer interlock 3D braided resin matrix composites with axial yran and 9 types of non-axial yam braided structures were designed and prepared.And tensile test and three-point bening test of the longititudinal and transverse samples were carried out.The results of the tensile test show that the tensile properties of the 5-layer interlock 3D braided composites are negatively correlated with the braiding angle of braided structures,and positively correlated with the fiber volume content.The specimen of the composites whose reinforcement structures are axial or non-axial yrans braided structures with 50%fiber volume content and 30°braiding angle has the best performance.And the tensile strength and tensile modulus are 860.68 MPa/263.44 MPa and 58.65 GPa/20.38 GPa respectively;The specimen of 45'braiding angle with non-anxial yrans shows necking phenomenon in the experirmental process,and the load-displacement curve shows the characteristics of a typical plastic material curve.The fracture morphology shows the resin cracking and fibre breakage in the necking area with no obvious fiber ectraction.The specimens of other groups have brittle material characteristics.The bending test results of the longitudinal specimens show that the bending performance of the 5-layer interlock 3D braided composites decreases with the increase of the braiding angle and increases with the increase of the fiber volume content.The specimen of the composites whose reinforcement structures are axial or non-axial yrans braided structures with 50%fiber volume content and 30°braiding angle has the best performance.And the bending strength and flexural modulus are 689.55 MPa/420.16 MPa and 51.82 GPa/20.06 GPa respectively;The force-deflection curve of the specimen with axial yrans is linear;When the braiding angle is 45°or 60°,the force-deflection curves of the specimen with non-axial yams are parabolic and show strong characteristics of the plastic material curve.The bending test results of the transverse specimens show that the bending performance of the 5-layer interlock 3Dbraided composites increase with the increase of the braiding angle and is positively correlated with the fiber volume content.The specimen of the composites whose reinforcement structures are axial or non-axial yrans braided structures with 50%fiber volume content and 75°/60°braiding angle has the best performance.And the bending strength and flexural modulus are 663.94 MPa/499.78 MPa and 48.24 GPa/29.27 GPa respectively;The force-deflection curve of the specimen with axial rans is linear;When the braiding angle is 30°or 45°,the force-deflection curves of the slpecimen with non-axial yams are parabolic and show strong characteristics of the plastic material curve.