Simulation And Experiment Researches On Cold Expansion Process Of CFRP

Carbon Fiber Reinforced Plastic (CFRP for short) has gained widespread popularity in the areasof Aeronautics and Astronautics due to its outstanding characteristics, such as high strength, highstiffness, low density and excellent fatigue property. Mechanical joints are the main method applied inthe assembly and fastening of CFRP structures. However, as the stress concentration places and weaklinks in the CFRP structures, holes for installing fasteners not only destroy the integrity but alsoreduce the anti-fatigue performance of CFRP structures, which will directly affect the durabilitydesign of airplanes. Therefore, taking reasonable measures to enhance the structural reliability of theholes is the key way to improve their anti-fatigue performance and enhance the fatigue lives ofassembly and fastening structures. In this paper, based on the methods of enhancing fatigue life inmetal structures and combining the joints characteristics of CFRP structures, a cold expansion methodwith sleeves for CFRP holes is proposed and the effect of the new method is studied by experimentsand finite element simulations.The main contents are summarized as follows:(1) The cold expansion method for CFRP makes sleeves expanded by mandrels and assembled inthe holes to enhance fatigue lives of assembly and fastening structures. In order to confirm thefeasibility of the method, based on cold expansion process in metal materials, an experimentalplatform for cold expansion process in CFRP structures is built and a series of experiments areconducted to study the changes of extrusion force, extrusion quality and fatigue lives.(2) The finite element analysis model of cold expansion method for CFRP structures, containingmandrels, sleeves and CFRP specimens, is established. Based on the progressive damage models forCFRP material and through user subroutines to design calculation process for cold expansion work,numerical simulations and the correctness verification work for the model are conducted.(3) The results of numerical simulations with different process parameters are studied, includingdisplacement variations of elements around holes, changes of extrusion force, stress distributions anddamage distributions under different interference values. Besides, these results can propose someguidance for cold expansion process with sleeves for CFRP holes.