Prediction Method For Interlaminar Performance Of Unidirectional Laminates Based On Fiber Bundle Composites

The interlaminar properties of fiber reinforced composites(transverse tensile strength and interlaminar shear strength)is one of the main indexes of mechanical properties of composites,the property is closely related to the interfacial bonding between fiber and matrix.The interface between fiber and matrix is often a relatively weak part of the composites,so it is important to evaluate the interlaminar properties of the composites for the engineering application.Fiber bundle composite(FBC)test is a simple and new method to evaluate the adhesion property between fiber and matrix in composite materials.Previous studies have shown that the interfacial strength of FBC specimens has a positive correlation with the interlaminar properties measured by the unidirectional laminates,but the measured values are not consistent.The difference is mainly due to the difference of the stress state near the interface between the fiber bundle and matrix in the FBC specimen and the stress state near the interface of the unidirectional laminates.This paper carried out a systematic study using transverse fiber bundle tension(TFBT)and Fiber bundle Iosipescu shear(FBIS)test,discusses the method of estimating unidirectional laminate transverse tensile and shear strength.The main work of this paper is as follows:1)The FBC specimens and the corresponding unidirectional laminates were prepared with bisphenol A matrix /T700 carbon fiber,bisphenol A matrix /TC35 carbon fiber and bisphenol F matrix /TC35 carbon fiber with different content of nano particles.Analyzed the correlation between FBC specimen strength and composite laminate specimen interlayer performance.2)A model for predicting the transverse tensile strength of unidirectional laminates based on TFBT test is presented.TFBT transverse tensile strength was significantly lower than that of the transverse tensile strength of unidirectional laminates,which may be due to the smaller surface energy density of the interface between the fiber bundle and the matrix in the TFBT specimens after tensile fracture.Based on this assumption,the relationship between the transverse tensile strength of TFBT specimens and unidirectional laminates is established by introducing the Griffith fracture strength theory.The experimental results show that the model can predict the transverse tensile strength of unidirectional laminates.3)The interfacial stress field of FBIS specimen was solved by the interface element method,and the tensile stress and shear stress at the interface of FBIS specimen were found to exist simultaneously,it may lead to the strength of the FBIS specimen is smaller than laminated specimen shear strength.The relationship between the strength of FBIS specimen and the shear strength of unidirectional laminates is established by introducing the Yamada-Sun strength theory,and the reliability of the model is verified by experiments.A model for predicting shear strength of unidirectional laminates based on FBIS test is established.Through finite element analysis,it is found that the shear stress and normal stress of the fiber bundle and matrix interface exist in the FBIS specimen,which may be the main reason for the shear strength of the FBIS specimens is lower than that of the laminates.Therefore,the relationship between the shear strength of the FBIS specimen and the unidirectional laminates is established by introducing the Yamada-Sun strength theory,and the reliability of the model is verified by experiments.