Research & Application Of Defect-prefabricated 2.5D Woven Composites

2.5D woven composite has become one of the most popular materials within many high-tech fields due to its excellent integrity and designability.Although the research achievements of 2.5D woven composites have been abundant,they still need to be developed into a broader application prospect.Based on the design principle of composite missile launching box cover and the idea of prefabricated defects of 2.5D woven composite structure,the design of integrated woven box cover with weak areas is one of the new fields of 2.5D woven materials application.This paper focuses on the study of mechanical properties of defect-prefabricated 2.5D woven composites and their preliminary application on launch box covers,which has certain academic value and engineering significance for deepening the understanding of woven structure characteristics containing defects.Firstly,resin transfer molding(RTM)process was used to prepare tensile test pieces forming of defect-free,warp yarn removing,weft and warp yarn cutting defect-prefabricated 2.5D composite boards.By performing quasi static tensile test on each form of defect-prefabricated composite specimens,the tensile modulus and strength were obtained.The influence trends of different defect forms on the warp and weft mechanical properties of 2.5D woven materials were thus compared.Then,the model of representative volume cell from defect-free 2.5D twill woven composite was established based on weaving technology and microstructure of yarn and weaving parameters.According to the practical operation,several local models of materials with different preset defect structures were established by geometric processing of defect-free unit cell’s warp and weft yarns.The unit cell model of defect-free 2.5D woven composite material was then meshed,the warp and weft tensile modulus and Poisson’s ratio were calculated by finite element analysis combined with periodic boundary conditions.The UMAT subroutine of progressive damage during tensile process was written by Fortran language to reduce the stiffness of yarn fiber bundle and resin matrix elements during tensile process.By simulating the tensile failure process of materials,the warp and weft tensile strength is calculated and compared with the experimental results,the accuracy of the finite element model and the rationality of the calculation method are proved.Afterwards,according to the experimental results,it is practical to exclude the warp drawn type preset defective material.The defect local models of 2.5D woven composites with weft and warp cutting type preset defects with different number of cutting layers were subjected to tensile finite element stimulation in their loading directions,and the tensile modulus and strength results were obtained.Compared with the experimental results,the negative influence law of yarn cutting defect form on the mechanical properties of the loading direction of the material was verified,and the reasonable yarn defect form suitable for the weak area of the missile cover was determined.Finally,according to the mechanical performance experiment and the simulation result of 2.5D woven composites with prefabricated weft and warp yarn cutting defects,the structure of the weak area of the square woven composite missile cover was designed.In addition,finite element simulation analysis was carried out to verify the rationality of the yarn defect pattern setting in the weak area of the cover under typical working conditions,and the improvement assumption of the weak zone structure was put forward.