Research On The Residual Thermal Stress Of Carbon Fiber/Vinyl Ester Composites

Carbon fiber reinforced polymer(CFRP)is a promising alternative material in the field of automotive lightweight because of its advantages over traditional materials such as light weight,high strength and good design ability.Sheet molding compounds(SMC)are intermediate for formed composites which are prepared by impregnating short fibers with resin matrix modified with other additives.Sheet molding compounds are widely used in automobile manufacturing because of the good repeatability,low cost and smooth surface of the products.Bisphenol A type vinyl ester is a polymer material synthesized by addition reaction of methacrylic acid and bisphenol A epoxy resin.With the feature of rapid curing and low shrinkage,bisphenol A vinyl ester is more and more popular in the producing of sheet molding compounds,and carbon fiber/ vinyl ester(CF/VE)composites prepared by SMC method is an effective way to lightweight and batch production of automotive parts and components.However,the residual thermal stress caused by the mismatching of the thermal properties between fibers and the matrix will lead to many negative outcomes such as reduction of compressive strength,fatigue strength,and interfacial bond strength.Besides,fiber buckling and even warping of integral structure are also possible to exist when the residual thermal stress is excessively high.Herein,a systematic study is performed to demonstrate the effects of fiber volume fraction on thermal residual stress applying finite element simulation and Raman spectroscopy,and the warping of composites caused by thermal residual stress is researched.This work provides good theoretical reference for the application of CF/VE composites on the automotive lightweight.Firstly,three-dimensional cell model of randomly distributed short carbon fiber is generated through secondary development of ABAQUS finite element software using Python language,and the finite element calculation on the residual thermal stress of CF/VE composites is achieved through thermal-structural coupling analysis assisted with meshing and boundary condition settings.The effects of fiber volume fraction on thermal residual stress of CF/VE composites are researched and the results show that the volume fraction has a great influence on residual thermal stress,and the residual thermal stress tends to decrease in fiber-intensive areas.Secondly,Raman spectroscopy is applied to determine the value of residual thermal stress because of the sensitivity of carbon fiber structure affected by Raman spectroscopy.According to the testing results,there is a linear relationship between the strain of carbon fiber and Raman spectral characteristic peak frequency shift,and the coefficient is-14.6.The effect of fiber volume fraction on the residual thermal stress of CF/VE composites is studied.When the fiber volume fraction is increased from 20% to 40%,the residual thermal stress is decreased by.It can be inferred that the higher fiber volume fraction leads to relatively less resin to each fiber,and the influence of the shrinkage deformation of the resin on the fiber becomes smaller,resulting in a lower stress value.