Research On The Strength Test Evaluation Method Of Typical Joints Of Hull Sandwich Composites

L-joints and T-joints of sandwich composites are the common local structures in the composite hull structure.Most of the components of the hull structure are connected by these typical joints,and the strength of these joints directly affects the strength of the entire ship structure.The hull structure strength test can be divided into: prototype test and model test.The prototype test can accurately reflect the strength of the actual structure,but its structure size is generally larger and the test cost is higher.The model test can reduce the test cost to some extent,but it can not accurately reflect the strength of the actual structure.In this paper,combining the advantages of prototype test and model test,a method for evaluating the strength test of L-joints and T-joints of sandwich composites is proposed.Without considering the scale ratio,the minimum size of specimens that can effectively reflect the true stress of L-joints and T-joints is studied.The method of constraint and load application for L-joints and T-joints is also explored.Firstly,the TA-joints finite element model of sandwich composite is established by ABAQUS software.Based on the characteristics of orthogonal braided fibers,the Shokrieh-Hashin criterion is modified as the failure criterion of orthogonal braided composite panel.The progressive failure analysis method is used to calculate the strength of composite panel,and the cohesive force model is used to simulate the adhesive layer between the panel and the core.The ultimate load and failure mode of composite TA-joints under bending load are predicted,and the applicability of the simulation method is verified by comparing the model results with the experimental results.Then,based on the numerical simulation method,an experimental evaluation study on the L-joints of sandwich composite is conducted.The calculation results of the strength of the superstructure indicate that the dangerous area of the superstructure is located in the arc transition zone of the L-joints.The arc transition zone is selected as the test zone of the L-joints,and the initial model of the L-joints is selected according to the characteristics of the superstructure.According to the actual stress of L-joints,the method of applying the constraint and load of L-joints is determined,so that the stress distribution in the arc transition zone of L-joints is similar to that in the superstructure,and the test tool is designed according to the selected constraint and load.Then,the minimum size of the specimen with L-joints meeting the test requirements is explored,so that the test using the small-size model can effectively reflect the actual stress of the structure in the L-joints test area.The study shows that the minimum length of the L-joints sandwich board is 600 mm and the minimum width is 300 mm under the condition that the thickness of the L-joints sandwich board remains unchanged.Finally,an experimental evaluation study of the sandwich composite T-joints is carried out.The results of the strength calculation of the composite superstructure indicate that the danger area of the superstructure is located in the trapezoidal transition zone of the T-joints.The trapezoidal transition zone is selected as the test zone of the T-joints,and the initial model of the T-joints is selected according to the characteristics of the superstructure.According to the actual stress of T-joints,the method of applying the constraint and load of T-joints is determined,so that the stress distribution in the trapezoidal transition zone of T-joints is similar to that in the superstructure,and the test tool is designed according to the designed constraint and load.Then,the minimum size of the specimen with T-joints meeting the test requirements is explored,so that the test using the small-size model can effectively reflect the actual stress of the structure in the T-joints test area.The results show that the minimum length of the bottom plate of T-joint is 450 mm on the premise of the constant thickness of the sandwich plate.