Rereach On Mechanical Properties Of Sandwich Composite Superstructure

As a new functional/structural material,the wide application of composite material in superstructure is a necessary measure to realize lightweight of ships.Therefore,the stress-strain response law of composite superstructure under longitudinal bending,the interaction mechanism between main hull and superstructure,and the degree of superstructure participating in longitudinal bending are very important research topics in ship and ocean engineering.In this paper,the mechanical response of sandwich composite superstructure is studied under different working conditions,and the influence of different factors on the total longitudinal bending behavior of the superstructure is explored.The double beam theory formula is revised.The main achievements of this paper are as follows:（1）The reliability of the numerical simulation method is verified by ship test of integrated sandwich composite superstructure.Taking a passenger ship with sandwich composite superstructure as the research object,the stress response of the finite element model of the passenger ship under different working conditions is discussed,and the mechanical response characteristics and stress-strain distribution of the superstructure under total longitudinal bending are revealed.The results show that:Under the action of longitudinal bending,the middle part of the superstructure participates in the longitudinal bending to a greater extent,which is consistent with the bending deformation of the main hull.The longitudinal stress of the hull deck presents a parabolic distribution along the width of the ship.The longitudinal stress of the main deck reaches the maximum at the middle part of the ship,and then decreases with the increasing distance from the middle part of the ship,showing the phenomenon of"negative shear lag".The longitudinal stress distribution of each deck of superstructure is opposite along the ship width direction,which is"positive shear lag"phenomenon.（2）In order to solve the mechanical response of a passenger ship model with sandwich composite superstructure participating in total longitudinal bending,the influences of superstructure length,number of layers and construction materials on the stress distribution of the superstructure under total longitudinal bending of the ship are discussed,and the effectiveness of each model superstructure is evaluated.The results show that:The shear stress distribution curves of the lower edge of superstructure side wall are rotationally symmetric in the midship section,while the vertical stress distribution curves are mirror symmetric.In addition,when the length of superstructure is shortened and the number of floors is increased,the degree of superstructure participating in total longitudinal bending decreases.When the superstructure length accounts for more than 60%of the length of the ship,it can be approximated that the superstructure has participated in the total longitudinal bending.When the length of the superstructure is equal to the length of the superstructure,according to the validity definition,the validity of the steel superstructure can be considered as 100%,while the validity of the sandwich composite superstructure is only 18.43%,indicating that the material has a significant impact on the validity of the superstructure.（3）In view of the inaccuracy of the double beam theory for the calculation results of the longitudinal bending stress of the short superstructure,the double beam theory was proposed by curve fitting the numerical simulation results of the longitudinal bending stress of the upper edge of the main hull of the superstructure hull model with different lengths.The correction formula of,that is,a stress correction term Kσ₀ is added on the basis of the original theoretical formula,and the form of the dimensionless constant K is an exponential function form.By comparing the theoretical calculation value and the numerical simulation value,it is found that:using the original double beam theoretical formula,when the superstructure is a sandwich composite material,the relative error between the theoretical calculation value and the numerical simulation value is at most-16.8%.The maximum relative error is-72.7%.However,the revised theoretical formula in this paper is used for calculation,and the obtained results are more consistent with the numerical simulation results.The relative error of the overall calculation is less than 2%,which greatly improves the calculation accuracy.