An enhanced spring-mass model for stiffness prediction in single-lap composite joints with considering assembly gap and gap shimming

An enhanced spring-mass stiffness model was proposed, which was based on the supposition that the transverse shear stress under preload satisfies conical and spherical envelope, to predict the stiffness of the single-lap single-bolt composite joint with considering assembly gap and gap shimming. The validation experiments were conducted for different configurations. It shows that the analytical results were all in good agreement with the experimental results. Meanwhile, experimentally validated finite element model was used as an assistant validation in consideration of convenience and cost saving. The presented analytical model was then used for parameter studies, including gap size, gap radius and shim thickness. The major conclusions are: 1) as gap size increases 0.1 mm, the shear stiffness decreases about 1.1%; 2) the shear stiffness quickly becomes zero when the gap radius exceeds the boundary of the highly stressed portion; 3) shim thickness has much greater influence on the bolt stiffness than on the shear stiffness.