Research On Bolted Joint Performance Of CFRP Components Considering Shimming Assembly

Carbon Fiber Reinforced Plastic(CFRP)has become one of the preferred material for current aircraft manufacturing due to its excellent properties of light weight and high strength.Composite material consumption of the China C919 aircraft reaches 12%,while those of the American Boeing 787 aircraft and the European Airbus A350XWB aircraft are more than 50%.The proportion of advanced composite materials,such as CFRP,has become an important index to evaluate the manufacturing level of high-end equipment.There is still a gap between China's core manufacturing technology of composite and the world's advanced level.After years of hard work,our country has accumulated some basic theory and assembly technology of composite material connection.However,in the research of high-performance connection and assembly of composite components considering manufacturing deformation with complex influence factors,the relevant theoretical methods and key technologies still need to be further studied.At the same time,aeronautical CFRP components are still mainly manufactured by separate fabrication and connection assembly currently.Various errors are accumulating in the manufacturing process,which results in the assembly gap between the two components at the assembly interface and makes the connection quality difficult to guarantee.Therefore,how to achieve high performance connection and assembly of composite components with assembly gap is one of the major challenges for aeronautical composite components manufacturing in China.Aiming at the urgent need of high performance joint assembly technology of CFRP components with assembly gap for C919 aircraft manufacturing,bolted joint performance of CFRP components was studied in this paper,in which a CFRP bolted joint performance analysis model considering shimming assembly was established using analytical methods and finite clement method,and the mechanism of the effect of assembly gap on the CFRP bolted joint performance was revealed based on the bolted joint performance analysis model for carbon fiber composite components.At the same time,a new shimming technology with hybrid shim was proposed to improve bolted joint performance for CFRP component,which effectively overcomes the performance limitations of the liquid shim and the solid shim.The main achievements of this paper are as follows:(1)According to the requirement of high precision and high efficiency calculation for bolted joint performance of CFRP components with assembly gap,the CFRP bolted joint performance analysis model was established,including analytical models of the single-bolt single-shear stiffness and the multi-bolt single-shear stiffness based on the spring-mass model were established,analytical model of the three-point bending stiffness of composite joint based on the calculation method of bending deformation of sandwich structure,and finite element model for bolted joint based on the progressive damage model.Above model provide a feasible method for engineering calculation of the CFRP bolted joint performance.(2)The effects of assembly gap on the bolted joint performance of CFRP components were revealed using the bolted joint performance analysis model:it will significantly reduce the friction stiffness when assembly gap radius approaches the radius of highly shear stressed boundary;shear stiffness decreases to zero and the bolt stiffness decreases with the increase of assembly gap,when assembly gap radius exceeds the radius of highly shear stressed boundary.(3)The effects of different shim materials and shimming percentage on bolted joint performance were systematically analyzed,and a new shimming technology with glass fiber resin laminated hybrid shim was proposed to improve the bolted joint performance of CFRP components with the assembly gap.Meanwhile,technological criteria for shims selection were formed.The research results have been successfully applied to the assembly of an aeronautical composite wing-box section validator.The research results of this paper provide a feasible method to the calculation problem of the bolted joint performance of composite components with assembly gap,and promote the progress of high-performance connection and assembly technology for large aeronautical composite components in China.