Analysis Of Composites Bolted Joints And Study Of Secondary Bending Effect

Polymer matrix composite materials are gradually extensive in the application of the aviation realm because of the high strength-to-weight, high stiffness-to-weight and good designable characteristic. The problem in composites structure connection is unavoidable, bolt connection is commonly used in the composites structure because it can deliver larger load and is more reliable than other connection styles. For stress distribution, it is much more complex than metal material joints on account of the brittleness and anisotropy of composite materials. Damages in composite materials joints often cause structural failure, and strength prediction and failure analysis of composites structure have been the main concerns for designers. In this paper, using the finite element analysis software ANSYS as the technology platform to study strength and failure problems of composites connection in various fields to reduce testing costs and ensure the reliability of connection design, has a certain engineering value.This paper considers the relationship between the various failure modes of composite materials from the perspective of damage mechanism, as well as different degradation rates of material stiffness under the damage caused by tensile and compression stress in the progressive damage model. At first, in order to verify the accuracy of the model, the paper will predict strength of notched composite laminates and then execute failure analysis, then study impact of various parameters on the failure load and failure mode of laminates, and the calculated value will be compared with the experimental value. On this basis, using the cumulative damage model established, this paper analyses parameters of single bolted joints including overlap, tightening torque, gap and overlap style on connection strength and the impact of failure. In the stress analysis, three-dimensional finite element model of complete bolted joints is established, considering various contact and friction behavior of the bolted joints to improve stress analysis accuracy. The composites joints often have lateral displacement and bolts become tilted due to the additional moment caused by eccentric load while the single shear lap joints are applied in connection, which is called secondary bending effects. Failure analysis showed that the secondary bending makes the contact pressure of the screw hole become uniform along the direction of thickness, bolt-screw extrude areas change, affecting the connection strength and failure mode of the joints. Therefore, while designing single-lap joints, the amount of secondary bending must be considered, this thesis will establish the finite element model that can accurately simulate the bending properties of joints to study the impact of various parameters on the amount of secondary bending. Analysis showed that increasing the length of overlap region, the thickness of plate and the tightening torque can reduce the amount of secondary bending, while clearance make the secondary bending effect more seriously to some extent and affect axial tensile stiffness of the joints.