Ultimate Bearing Capacity And Influence Factors Of Hat-stringer-stiffened Sandwich Composite Panel

Stiffened panels are the basic structural form to be widely applied in the composite hulls.However,they have more complex failure modes under in-plane compression,because of the anisotropy of composite materials and the particular structure.At present,the research of composite stiffened panels has been mainly about the field of aviation,and the investigation of composite stiffened panels for ship is rarely reported.Therefore,the ultimate bearing capacity and influence factor of hat-stringer-stiffened sandwich composite panel in the hull under the external uniform load and in-plane compression were analyzed to provide guidance and promotion for the structural design of composite ship.Firstly,the non-linear finite element method in the paper was introduced.Based on comparison with the experimental results of other literatures,the progressive failure of the hat-stringer-stiffened sandwich composite panel was analyzed and the ultimate load,failure mode and mechanism were deeply discussed according to Hashin criterion and the state variable of continuum damage mechanics.On the basis of the overall analysis,the local failure area of stiffened panel was refined in the sub-model technique of finite element,and the failure behavior of each layer of composite skin was further studied in the Shokrieh-Hashin criterion and stiffness degradation.The results showed that the ultimate load of stiffened panels is 316.8kN.The failure mode was the first-order buckling failure of the panel,and finally the panel was crushed and broken in the middle.The fiber compression failure of the panels contributed to the overall failure of stiffened panel directly.The failure law of each layer was the similar.The fiber compression failure of the panels extended from the outer layer to the inner and the expansion rate decreased gradually.Secondly,the influence of core material configuration and property,stiffener width,stiffener height and skin thickness on ultimate bearing capacity was discussed.It was found that the plate core had more influences than the stiffener core material.When the stiffened panel had no plate core or the performance of core material was weak,the multi-order buckling occurred on the plate and the ultimate load decreased obviously.According to the influence results of the cross-section parameters on the ultimate load,the empirical formula for estimating the ultimate load by section size was established based on Buckingham's ?-theorem.Compared with the results of finite element analysis,the empirical formula was proved to be accurate and reliable,and could be applied to estimate the ultimate load in engineering practice.Finally,the residual ultimate bearing capacity of stiffened plates with defect or damage was researched by finite element method to discuss the influence of debonding defect and impact damage on ultimate bearing capacity.According to cohesive element,the influences of skin-to-core debonding and plate-to-stiffener debonding on ultimate bearing capacity were studied.The results showed that the debond had little influence on ultimate load,but was still the weakness of structural bearing capacity,which changed the local failure mode of stiffened panel.Based on the open equivalent method,the impact damage is simplified to a circular hole to discuss the influence on ultimate bearing capacity.It was concluded that impact damage not only decreased the ultimate load,but also become the initial location of the failure of stiffened panel.Then the influences of damage location,damage size and damage depth on the ultimate bearing capacity were further discussed and the effect of damage parameters on ultimate bearing capacity was obtained.