Abstract: The axial stiffness of the part that be connected will directly affect the formation of the clamping force, the maintain and recession of clamping force in the process of bolt fastening under different working conditions. As a result , a significant influence will appear on the reliability and stability of the assembly structure. On account of the material property of composite laminates itself and the limitation of the molding process method, small assembly gaps are difficult to avoid in the composite laminates bolted fastening. Liquid shim is commonly be used to compensate for the small gaps between the laminates parts in aircraft assembly. First, with the single bolt fastening of composite laminates as the object, the finite element model is built by using ABAQUS software. And two cases are considered in the process, that is, with a liquid shim to compensate for the gap and without it. Secondly, the experiment is designed: the effective contact surface dimension of the bolt fastening. The results of the model are in good agreement with the experimental data. Under different liquid shim compensation parameters, the effective contact area of the bolt fastening is studied based on the model. Research results show that with the increase of the gap′s thickness, liquid shim will significantly improve the axial stiffness of laminates relative to the forced assembly. In the thickness range of process specification, the increase of the gap′s thickness plays more obvious role in promoting the laminates axial stiffness. At the same time, the use of high elastic modulus of liquid shim is more beneficial to improve the axial stiffness of laminates. It is suggested that gap compensation process must be carried out when the thickness of gap reached 0.05 mm in aircraft assembly.

Key words: composite laminates, bolt fastening, liquid shim, gap compensation, axial stiffness