Study On Injection Molding Simulation And Mechanical Properties Of Short-cut Fiber Composites

Chopped fiber composite materials have been developed and applied because of their lightweight,high design ability,high specific strength,a nd high specific modulus,which have become the new lightweight materials for automotive lightweight projects.Injection molding is one of the main molding methods of short-cut fiber composites,which has the advantages of low cost and high efficiency.In the injection molding process,uneven distribution of fiber orientation can cause a series of problems such as uneven production shrinkage and warpage.At the same time,accurate prediction of the effective mechanical properties of composite materials lays the foundation for the design and application of composite materials.The representative volume element method(RVE)has been widely used due to its ease of implementation.Based on the above,the interface problems of fiber-reinforced composites have also been discussed.In this paper,the key issues of fiber orientation and its properties in injection molding of short-cut fiber composites are analyzed and studied.First,based on a comprehensive review of the residual stress field and inhomogeneous anisotropy thermodynamic properties formed during injection molding of fiber-reinforced polymer matrix composites,a finite element shrinkage deformation prediction model of fiber reinforced composites was established.The simulation results show that the shrin kage deformation of the injection molded parts is not uniform,which is mainly caused by the residual stress caused by the flow imbalance and solidification difference in the injection molding process.Then,considering the plastic development and fracture of the matrix,an anisotropic elastic model affected by the change of the local fiber direction was established.The uniaxial static tensile simulation experiment was conducted.The results showed that the short fiber filled polymer was compared with the pure polymer material.The material shows a great deal of plasticity before final failure,which is caused by tearing the polymer matrix with a certain degree of short fiber elongation.Secondly,the prediction of the effective properties of the short fi ber composite material considering the orientation of the injection molding fibers was carried out.A three-dimensional RVE model with a typical fiber-oriented skin-core structure was established.By applying periodic boundary conditions,the effective mechanical properties of the short-fiber-reinforced resin-based composites were obtained.Compared with the Tendon-Weng model based on the mechanical properties of unidirectional fiber-reinforced composites considering the effects of injection molding,the calculated results are consistent.On this basis,the influence of the three typical arrangement of fibers and the length-to-diameter ratio of fibers on the mechanical properties of fiber-reinforced composites is discussed.The results show that simply incre asing the length of the short fiber alone does not always improve the effective properties of the composite,and maintaining a certain fiber aspect ratio is the most effective and economical.Finally,composite materials transmit loads through the interfac e and improve interface adhesion is the key to improving the mechanical properties of carbon fiber composites.Based on this,by a sizing agent to improve the interfacial method,a chopped carbon fiber reinforced vinyl ester resin was prepared a sheet-like molding material test piece,and damage to and destruction of the interface was simulated using the model theory cohesion.Tests and simulations show that the modulus and strength of the composites are improved by the interface modification,and the inter face layer is alternately cracked when the interface is destroyed,and both the modulus and the strength are improved.