Study On Collision Failure Criteria Of Ship Structure

Due to the influence of changeable marine environment and human factors,collision accidents are inevitable.In case of collision between ships that transporting petroleum,LPG(liquefied petroleum gas),LNG(liquefied natural gas)and chemicals,serious accidents are easy to occur.Under the huge impact load,the hull structure will often be damaged or even broken,resulting in cargo leakage,environmental pollution,casualties and other catastrophic consequences.Human factors are the main causes of ship collision,which are also difficult to eliminate.In this paper,for the aim of personnel safety,environmental protection and economic loss reduction,the dynamic response,damage deformation,energy absorption and failure mechanism of the hull structure under the impact load are studied in depth.Considering the influence of biaxial stress and strain rate,combined with the falling weight collision experiments and numerical simulation technology,the accurate collision failure evaluation method of the ship structure is established.The main research contents of this paper are as follows:(1)This paper summarizes the research status and research methods of collision damage mechanism and failure evaluation criteria of ship structures at home and abroad,expounds the contents that need to be supplemented and improved,and puts forward the research significance and main research contents of this paper.(2)Based on Swift?s plastic instability theory,a modified BWH failure criterion(m-BWH)is proposed to improve the failure evaluation accuracy of materials under high strain ratio stress.Considering the influence of biaxial stress and strain rate,combined with the Cowper-Symonds model,a dynamic BWH failure criterion is proposed.Based on the plastic stress updating algorithm,the secondary development of user material subroutine(VUMAT)for Abaqus is carried out by Fortran language,and the application of failure criterion in numerical simulation is realized.(3)The biaxial tension experiments of high strength hull steel were carried out.Six specimens with different shapes were used to study the effect of different biaxial stress states on material failure.By using the method of VUMAT subroutine,the m-BWH failure criterion and BWH failure criterion are embedded into the simulation model to carry out numerical simulation research on the biaxial tension experiments and compared with the simulation results of the constant strain failure criterion.The experiments verify that the failure criterion considering the influence of biaxial stress is more accurate in predicting the failure of materials.(4)The high-speed tensile experiments,SHPB compression bar experiments of high strength hull steel and falling weight collision experiments of stiffened panels were carried out.The dynamic BWH failure criterion is embedded in the numerical simulation model by using the method of VUMAT subroutine.The numerical simulation of falling weight collision experiments of stiffened panels is carried out,and the results are compared with the simulation results of the constant strain failure criterion.The experiments verify the accuracy of the proposed dynamic failure criterion.The effects of friction coefficient,strain rate and grid size on the fracture shape of the stiffened panels are discussed.(5)Based on the research in the previous chapters,the dynamic response,damage deformation,energy absorption,structural failure mode and failure characteristics of the side structure of a container under different initial impact speeds are studied.The results show that the overall anti-collision performance of the ship structure predicted by the dynamic BWH failure criterion is better than that predicted by the constant strain failure criterion.The influence of different impact positions on the structural failure shows that the cross structure of the side longitudinal truss and the web frame at the impact point is more likely to cause the fracture of the outer plate than where there is only side longitudinal truss or web frame structure.The influence of different friction coefficient on structural failure shows that when the initial velocity of impact is small,the increase of friction coefficient will affect the crack direction and fracture shape of the side inner plate,and reduce the tearing degree of the side upper structure.When the increase of friction coefficient has less effect on friction dissipation energy than the decrease of the friction action time and the friction work,the friction dissipation energy may decrease.