Research On Strength Of Composite Sandwich T-joints Under Bending Load

Due to its excellent properties such as light weight,high strength and low magnetism,composite material has been widely used in ship design and construction.As the typical joint form in ship structure,T-joints are usually used in the connection between hull and bulkhead to transfer the load and keep the watertight integrity of the hull.However,the researches for composite sandwich T-joints are not mature in domestic and foreign countries.Therefore,the strength of composite sandwich T-joints under bending load has been studied in this paper,which has important significance for the design of composite ship structure.Firstly,the Shokrieh-Hashin failure criterion is selected according to the characteristics of composite sandwich structure,and the corresponding stiffness degradation model is selected.Then,progressive failure analysis of composite sandwich TA-joint under bending load is conducted using the numerical simulation method with Abaqus to predict the failure load and failure mode of TA-joint,and the predicted results are compared with the test results to verify the reliability and accuracy of this method.Then,the numerical simulation method is used to predict the failure load and failure mode of different composite sandwich T-joints under bending load.Different types of T-joints in accordance with the ultimate load value from large to small can be arranged as: TC,TA,TB,TD,and TE.As for the finial failure mode,TB-joint is similar to TA,which is mainly adhesive layer debonding and panel matrix failure;TC-joint is mainly fiber matrix shear failure and delamination failure of panel;TD and TE are mainly panel delamination failure.Finally,TC-joint is selected to be further studied as it has the largest ultimate load value in five kinds of T-joints.Single variable method is used to investigate the affecting factors of strength of TC-joint under bending load,and the selected four variables are the bottom angle of triangle foam,length of the lap panel,length of the right-angle side of triangle foam,and thickness of the foam core.It can be concluded that the bottom angle of triangle foam has the greatest influence on the ultimate load of TC-joint.As the bottom angle of triangle foam increases,the ultimate load valueincreases first and then decreases,and the largest ultimate load exists when the angle is 45°;As the length of the lap panel increases,the ultimate load value slowly increases,and almost no change;With the increase of right-angle side length of triangle foam,the ultimate load value increases first and then decreases;The ultimate load value increases with the increase of the thickness of the foam core,but the increasing value is smaller and smaller.As for the final failure mode,failure of the composite panel is the mainly failure mode among all the four series models.In the series models of bottom angle of triangle foam,as the bottom angle of triangle foam increases,the final failure position is transferred from the corner of apex angle of triangle transition zone to the corner of bottom angle.Moreover,the final failure positions of the other three series models occur at the corner of bottom angle.