Research On Plastic Damage Of Typical Structures Of Vessels Subjected To Underwater Explosion

In modern naval warfare,because of the rapid development of weapons’ guidance technology and damage power,the threat of the vitality of submarines and ships subjected to underwater weapons is growing in the process of performing tasks.However,because of the complexity of the load and structure forms,researchers at home and abroad still haven’t a clear understanding of the damage mechanism of the typical structures of vessels subjected to impact load,which severely restricted the advance of the anti-impact ability of modern vessels.In this paper,based on the investigation of a large number of related paper at home and abroad,the status of the research on damage problem of the vessels has been summarized,and the deficiency of the current method has been discovered at the same time.Then on the basis of it,this paper has began to do a research on the calculation method of the plastic damage of these respective typical structure forms of submarines and ships subjected to underwater explosion and the corresponding mechanic characteristics.Meanwhile model tests have been designed to validate these methods and characteristics.For anti-impact problem of submarine structures,only the shock wave has been considered in traditional calculation methods of large plastic deflection of stiffened cylindrical shells usually,and the influence of the water depth at which submarines work practically has also been ignored.In this paper,firstly,for the problem of the overall impact damage of submarines,the whole sag mechanics model of cabin has been established using the rigid plastic theory of long shells.Then a theoretical calculation method of large plastic deflection of the stiffened cylindrical shell under the second load because of the bubble pulsation,considering the initial damage from shock wave and the influence of hydrostatic pressure on the basis of the principle of conservation of momentum,and the movement regularity of plastic hinges were obtained.Secondly,for the prolem of the local damage of submarine structures,the shell between two ribs has been selected as a research object to establish a rigid-plastic slat beam model with solid ends simplified by the ribs.Then the whole process of plastic dynamic responses of shells subjected to shock wave and bubble pulsation was obtained by solving a dimensionless shell motion equation eventually,considering the different load on single-layer and double-layer cylindrical shells because of the load transmission.To reflect the damage characteristics of real submarine structures objectively and explore the difference of damage mechanisms of single-layer and double-layer cylindrical shells subjected to underwater explosion,tests about the shrinkage ratio model of single-layer and double-layer stiffened cylindrical shells were designed and implemented in this paper,in which the damage modes of cylindrical shells in near-field underwater explosion have been obtained,and the correctness of the proposed calculation methods of overall and local damage of submarine cylindrical shells has been proved.So these methods can be applied in real submarine structures well,and have a certain value of engineering application.Then rules of plastic damage of single-layer and double-layer cylindrical shells with change of the charge stand-off distance,the charge size,water depth through these methods have been analyzed,which is that the sensitivity of the overall and local plastic damage to the working parameters of a single-layer cylindrical shell is higher than that of a double cylindrical shell.And these rules can be used as a design reference of submarine structures.For ships,grillage is their typical structure form,and it was simplified as a simple structure like a beam or a plate to analyze the deflection ignoring the interaction force between structures of the beam system in traditional methods usually.And another method is using the energy method to get the deflection in the end,but the movement process cannot be obtained.For these reasons,two common kinds of grillages like a cross member grillage and a multiple cross members grillage were selected as a research object.Firstly,for the plastic deformation mode,the deflection calculation method of the grillage considering the coupling deflection in the association was obtained using rigid-plastic cross beam mechanical model with the theorem of momentum,and the calculation method of plastic region was obtained through the plastic hinge’s movement law.Then a crevasse’s diameter calculation method was obtained using the above calculation method of plastic region,and the principle of conservation of energy was used in another one,which makes up the blank of the calculation methods of estimating the size of the crevasse considering the influence of the charge stand-off distance in near-field contact underwater explosion.Because the bottom structures of large ships have this kind of special structure high web,the double bottom scaled test model and the cabin test model of real ships were designed and carried out in this paper.Then through the analysis of test results,the damage modes of the double bottom in near-field and contact underwater explosion were summarized,and the Q235 and 945 steel’s fracture strain in the tensile failure mode were obtained,which provides reference data for the theoretical and numerical study of the ship’s impact resistance,and the correctness of the deflection and crevasse calculation methods has been verified through these tests.Meanwhile it shows that the methods can accurately forecast the plastic damage degree of the ships’ local structure.and they have good engineering applicability.Then the algorithms were obtained through these methods to provide reference data for structural design.The plastic degree of the grillage decreases with the increase of the section modulus and the yield limit,and the growth rate of the grillage with the change of displacement decreases with the increase of the space of ribs and the longitudinal girder.Within the range of high-strength steel,improving the material yield limit has little effects on its damage degree,when the displacement is more than 4000t.