Fragment Resistant Mechanism Research Of Safety Liquid Cabin

Warships are faced with explosion fragments ships coming from the anti-shipmissile and contact underwater explosion. With strong penetration ability, explosionfragments which are serious threat to fuel tanks and important ship equipments canusually penetrate4-6bulkheads. As one of the most efficient instrument to resistagainst the explosion fragments, the safety liquid cabin is widely used in war shipprotective structure. A combined theoretical, experimental and numericalinvestigation on fragment resistant mechanism, and the following main researcheswere accomplished.The dynamic behavior of liquid protective tank bulkhead steel was investigated.Theσ-εrelation of ship-build steel945under different strain rates (0.00033～2760s-1) has been studied with the MTS(Materials test system) and the split Hopkinsonpress bar (SHPB), JC model and CS model were compared, two improvedCowper-Symonds models and the parameters were obtained, and then theapplicability of the models was investigated. The experimental results show thatship-build steel has a remarkable strain rate effect and a nonlinear strain hardeningeffect. Dynamic constitutive CS model of ship-build steel945can describe thedynamic mechanical behaviors under high strain rate more exactly than JC model.The two improved CS models have different application field. Difference of takinginto account of strain rate was investigated by numerical simulation method.Damage characteristic of liquid protective tank bulkhead steel was investigated,and a fracture criterion taking stress triaxiality into account was proposed. Specimensunder different stress triaxiality were designed, and quasi-static tensile tests onsmooth and notched specimens, pure shear test, compression-shear tests, pure sheartests and compressive tests were carried out. A correction method of average degreeof stress triaxiality based on finite element method (fem), and fracture strain underdifferent stress triaxiality was compared. The cut-off of stress triaxiality, below whichfracture never occurs, was analysised, microscopic fracture mechanism was discussed. Parameters of two fracture criterions taking stress triaxiality into account wereobtained,and different fracture criterions were compared based on Taylor impact bar.The anti-fragments mechanisms of tank bulkhead were analyzed, a velocitytheory model of fragments penetrating tank bulkhead was provide based on adiabaticshear mechanism. The process of fragments penetrating tank bulkhead was dividedinto four stages, the critical temperature and critical strain with adiabatic shear, andthe energy loss relationship and the residue velocity formulation were given bymaterial constitutive equations. Furthermore, the temperature effects of materials andthe liquid effects on the residual velocity were discussed respectively by numericalsimulation method.The velocity decay mechanism of fragments in the cabin liquid was launched,even the velocity decay formulation was derived, and the drag coefficient wasdetermined to be the key factor that affects velocity decay. After verifying theaccuracy of the numerical simulation method, a serial analysis were launched,fragments with different length-diameter ratio, or with different impacting watervelocity were analyzed, the decay law of fragments was given and the dragcoefficient formulation in different stage was given by statistical fitting method.The fragments penetrating process has been simulated and the energy absorptionmechanism was analyzed. The theory of fragments with high speed impacting waterand producing shock wave was analyzed. Based on the slight wave potential flowtheory, combined with fragments decay kinetic energy and water increases the kineticenergy, potential energy conservation relations, a theoretical model to calculate shockwave was given from the flat-head fragments velocity decay formulation.Furthermore, a simulation of a small-scale tank was calculated, with which thevalidity of the theoretical model was verified. The process of fragments penetratingtanks was divided into four stages, the velocity decay law of fragments with orwithout liquid, and the energy absorption law with different thickness ratio offore-cabin and back-cabin, and the relation of energy transfer and conversion wereanalyzed.From the research, the results can be used to provide necessary theoreticalfoundation of fragments absorption mechanism and design principle for shipbroadside tanks, which is important to theoretical and practical value.