Research On Strength Test And Evaluation Method Of Hull Sandwich Composite Compartment

The overall longitudinal strength of a large hull is very important for the normal operation of the ship.The most accurate method to obtain the overall longitudinal strength of the hull is the real-scale test,but for large structures such as hulls or cabins,the larger size makes the real-scale test cost Huge and demanding test.Nowadays,composite materials are widely used in hull structures.In order to ensure the reliability of composite material structure design and reduce the test risk,building block test verification methods are generally adopted internationally.However,when this method is applied to large-scale structures,the number of tests and test costs will be unbearable.At present,composite material manufacturers have established a rich and complete material system,and the basic material properties have been studied clearly.There is no need to start the structure from the lower level according to the building block method.Complete building block test verification.Therefore,the test assessment method of the hull composite compartment is of great significance to the design and application of the composite hull.This test assessment method selects a suitable local model,studies the loads and constraints imposed on the local model,so that the local model can reflect the stress distribution of the large model of the tank section.Through the evaluation of the strength test of the local model,the purpose of studying the failure mode of the cabin and evaluating the strength of the cabin is achieved.In this paper,based on the two-dimensional Hashin failure criterion,the finite element method is used to study the ultimate bending moment in the sag and mid-arch conditions of the sandwich composite cabin model,and the bending moment-rotation curve of the reference point of the end face of the cabin is drawn.The ultimate bending moment,failure area distribution,failure mode and cabin strength evaluation method of the cabin under sagging and arching conditions lay the foundation for the selection of local models.Introduce the stress difference value K to analyze the four-point bending test of the cabin section.Since the influence of the bearing and load on the stress in the vicinity of the four-point bending test cannot be ignored,the range of influence of the bearing or load on the stress distribution is determined by the stress difference value K,and the transition section and the test section of the cabin model are determined according to this range To determine the size of the local model.In the test section,select four different half-width observation stress distributions along the length of the ship.According to the selection of local models mentioned above,select several local models,and determine the final local model by comparing the local model with the stress distribution of the large model of the cabin section.Based on the assumption of flat section,the axial displacement at any height of the cabin section is derived under the conditions of sagging and arching,and then the axial displacement of the local model and the cabin axis are derived through the geometric relationship between the local model and the cabin model To the relationship of displacement,determine the calculation method of the loading displacement applied by the local model.Based on the derivation of the previous loading displacement theory,combined with the actual experimental axial displacement loading method,the method of applying the load fixed at one end and the other end was determined,and the actual applied loading displacement was calculated.Finally,by comparing the geometric relationship between the cabin model and the local model and the finite element stress results,combined with the boundary constraints of the local model in the cabin model,the local model boundary constraint method is determined.Through the above research,this paper finally proposes the strength test assessment method for the hull sandwich composite cabin.It mainly includes the selection range of the test local model,the calculation method of the local model load under the sagging and arch conditions,the method of applying the model load and the constraint method.The local model selected by this method can reflect the stress distribution and failure mode of the large cabin model.Through the test evaluation of the local model,the purpose of studying the failure mode of the sandwich composite hull cabin and evaluating the strength of the cabin is to reduce the cabin The difficulty and cost of the strength test provide a reference for the design of the sandwich composite hull cabin structure.