Fracture Behavior Of CFRP Layered Structure Based On Boundary Effect Theory

With the advantages of high specific modulus and high specific strength,carbon fiber reinforced polymer(CFRP)is widely used in aerospace,automobile industry,construction engineering and other fields due to its inhomogeneity and anisotropy.Under low-speed load,CFRP mainly transfers load and energy by carbon fiber and resin matrix of adhesive layer.However,the resin matrix is brittle,which leads to weak bearing capacity and is prone to damage.There are four kinds of damage in CFRP,namely matrix cracking,fiber fracture,crack propagation at interface and delamination damage.Its mechanical characteristics are complex and diverse,and the damage is different and irreversible.Based on the boundary effect theory model(BEM),this paper studied the fracture properties of commercial CFRP laminates,self-made CFRP laminates and aramid fiber reinforced CFRP laminates with different edge crack damage by single notch three-point bending test.(1)In this paper,considering the random distribution of the crack tip damage zone of the materials,the boundary effect theory model used for heterogeneous materials can predict the fracture toughness K_ICand tensile strength f_tof CFRP laminates simultaneously combined with the peak load of the three-point bending specimens with edge crack.However,the CFRP with edge crack has no layer thickness structure element,the structural characteristic parameters of the material are determined according to the internal relationship of the virtual crack length.(2)The characteristics of the damage zone at the edge crack tip of the bidirectional braided CFRP laminates are complex due to the influence of the microstructure of the material.In this paper,the relative deviation of tensile strength values of commercial CFRP laminates with plain weave and twill weave is 3.50%and 6.38%respectively by comparing three-point bending test and direct tensile test,it verifies the feasibility of BEM to predict the fracture behavior of commercial CFRP laminates.The relative deviation of f_tof plain weave and twill weave is only 0.80%,it shows that different weave methods do not affect the fracture behavior of CFRP laminates.(3)According to different manufacturing process,the mechanical properties and microstructure of CFRP laminates will also be different.In this paper,the results show that the relative deviation of tensile strength compared with direct tensile test of self-made CFRP laminates is 3.54%,BEM is reasonable to predict the fracture behavior of self-made CFRP laminates,and the fracture performance of commercial CFRP laminates is better due to the material defects of manufacturing process of self-made CFRP laminates.(4)It is necessary to study the methods to improve the fracture resistance of the materials due to the defects of the self-made materials.By inserting short aramid fiber into the bonding layer of self-made CFRP laminates,the results show that the ultimate bearing capacity and fracture toughness of CFRP laminates with short aramid fiber were increased by57.09%and 30.79%respectively.The relative deviation of tensile strength was 5.91%by comparing three-point bending test and direct tensile test,which verified the practicability of BEM to predict the fracture behavior of CFRP laminates with short aramid fiber.