Experimental & Simulation Research On The Ultimate Bearing Performance Of Typical Marine Sandwich Composite Structures

The Demands from modern navy for stealth,electromagnetic compatibility,and lightweight characteristics are increasing.Composite superstructure is an inevitable trend in the development of naval vessels.At the same time,in view of safety,lightweight and economic demands from large cruise ships,composite structures are currently the only solution.For now,the understanding of the failure mechanisms of sandwich composite structure under load is still far from perfect,and there is no unified engineering method of calculating its ultimate carrying capabilities.Firstly,a progressive damage model is constructed.Tensile failure on fiber direction is clearly divided into two stages: matrix tensile failure on fiber direction and fiber breakage.The matrix tensile failure on fiber direction has an independent criterion.Its damage initiation strength and fully damaged residual stiffness are presented.The criterion in La RC03 that governs fiber kinking failure in unidirectional composite is extended to adapt for plain-woven reinforced composite materials.A new hybrid stiffness reduction model is proposed to replace the instant or continuum damage model.Based on the modified failure criteria and damage evolution model,the application of this progressive damage model(PDM)is achieved by developing a UVMAT subroutine in commercial software Abaqus with explicit algorithm to avoid convergence problems.Subsequently,experiments and simulation research on the ultimate strength of sandwich composite L joints and T joints are carried out.Experiments are conducted on L joints of three different transitional radius under both ultimate tensile bending and compressive bending.A method to identify damage features are concluded by utilizing both test data and recorded video.Simulation using the developed VUMAT subroutine have matching results with the tests in both damage feature points and failure phenomenon.A damage and failure prediction map is concluded to estimate the failure load and the detailed damage process.Tests and simulation research on T joints are conducted.In the experimental study,two featured damage load ranges are obtained by analyzing data obtained in the ultimate strength tests and the cyclic loading tests respectively.More refined modeling strategies are used in the simulation work.Combined with the developed subroutines,the simulation results that can accurately restore the complex failure morphology and damage characteristic load of the "T-shaped" joint are obtained.Finally,a study is carried out on the progressive damage simulation model for large-sized sandwich composite ship structures.The previous PDM method is adapted to two-dimensional shell element,and a corresponding simplified modeling technique is proposed.The L joints and T joints are used as objectives to discuss the model techniques and element sizes selection.Experiment and simulation of the reinforced sandwich panel are carried out to verify the accuracy and efficiency of the method.In the end,anti-explosion performance analysis and the low-speed intrusion damage analysis are conducted on a sandwich composite superstructure.The two cases both demonstrate the advantages of the simplified simulation method in terms of the complicated yet efficient PDM analysis capabilities when facing large composite structures.