Progressive Failure Analysis Of Marine Composite-to-steel Joints

Composite-to-steel joints are most easily founded in the aerospace industry and are used to connect lightweight composite components to metal structures.With the increasing acceptance of composite materials as structural materials,the application of composite-to-steel joints has been extended to the field of ships,as a new method of connecting composite superstructure and steel hull.In steel ships,there is a large stress concentration at the joint between the superstructure and the deck.The application of composite materials can alleviate this phenomenon because the stiffness of steel hull and composite superstructure is different.When bending load is applied,the relatively low stiffness of composite materials reduces the stress transferred through deck and connecting structure,thus the stress concentration is reduced.In this paper,the composite steel adhesive joint is taken as the research object,combined with two methods of experiment and numerical simulation,the effects of lap length,foam chamfer,foam thickness and skin thickness on the ultimate load carrying capacity of the joint under bending load are studied,which provides a important basis for the design of composite-to-steel joint.Firstly,the progressive failure analysis method of composite materials is introduced,which mainly includes material failure criterion and stiffness degradation model.The different material failure criteria and stiffness degradation models are summarized and analyzed,their advantages and disadvantages are introduced,which would provide a theoretical basis for the establishment of progressive damage model of composite-to-steel joints.Secondly,the joints were prepared by the vacuum assisted resin infusion process.The effects of lap length,foam thickness and foam chamfer on the performance of the joint under bending load were studied.The results showed that the lap area of the steel and sandwich foam was the stress concentration area,and the failure of the adhesive joint mostly occurred in the lap area.Thirdly,in order to select the progressive damage model which is most suitable for the structure of this paper,five different progressive failure models are established.and the ability of different progressive damage models to predict the initial failure,final failure position and load-displacement curve of the joint is considered.The results show that the PDM-V containing the Hashin-like criterion and the Apalak stiffness degradation model is most suitable for the strength analysis of the composite-to-steel joint under bending load.Then the numerical analysis method is used to study the influence of geometrical dimensions on the ultimate bearing capacity of composite-to-steel joints.The difference between simulation results and experimental results is very small.Finally,in order to study the effect of skin thickness on the ultimate bearing capacity of the joint,the finite element models with skin thickness of 2 mm,3 mm and 4 mm were analyzed by the established progressive failure model.The specimen with skin thickness of 3 mm were tested by experimental method.The results are quite consistent,which further verified the validity of the model.