Abstract:The final deformation of a metal structure under impulsive load occurring in the direction opposite to that of loading， which is a phenomenon known as counter-intuitive behavior. It was found that the flexible polyurea-protected concrete target plate on the back blast surface also experienced counter-intuitive behavior under 75 g TNT blast load. To investigate the counter-intuitive behavior of the flexible polyurea-protected concrete target plate on the back blast surface under blast load， a finite element model of the back blast surface of the flexible polyurea-protected concrete target plate subjected to blast load was developed using the ANSYS/LS-DYNA finite element software. The finite element model was utilized to analyze the dynamic response regularity of the flexible polyurea sheltered concrete target plate on the back blast surface， and to study the occurrence mechanism of the target plate's counter-intuitive behavior from the perspective of energy. Taking the center point displacement and deflection of the concrete target plate as indexes， the influence of the amount of explosive charge and coating thickness of polyurea on the counter-intuitive behavior of the target plate was analyzed parametrically. The results demonstrate that the counter-intuitive behavior of target plate is attributed to strain energy release from the polyurea coating， energy dissipation from concrete damage， and mutual transformation of energy between both materials. Furthermore， it is found that explosive charge mass is the dominant factor affecting counter-intuitive behavior. The concrete target plate is unable to undergo counter-intuitive behavior when either the charge mass was too small or too large. Within a range of coating thicknesses from 2 mm to 8 mm， an initial increase followed by subsequent decline in bending degree was observed for the target plate exhibiting counter-intuitive behavior.

Abstract:The study and application of explosion containment vessels （ECVs） subjected to internal blast loading is a multidisciplinary and interdisciplinary issue encompassing energetic materials， explosion and impact dynamics， and vibration mechanics. The investigation on the internal blast effects and dynamic mechanical behavior of ECVs is an important foundation for enhancing the explosion-resistant performance of equipments， and the mechanisms of strain growth and anti-intuitive phenomenon are important scientific issues. The relevant research progress and key scientific findings are reviewed from five aspects： the internal blast loading characteristics and effects within ECVs， the dynamic response mechanisms of metal ECVs， the complex working conditions of ECVs， the blast effects of thermobaric explosives and fragmentation warheads， as well as composite ECVs. The analysis demonstrates that establishing an effective mechanical analysis model and fully revealing the dynamic response mechanisms of structures can effectively guide blast damage assessment and protective structures’ analysis and design under complex working conditions. Considering the challenges and opportunities posed by high destructive explosives and high-performance protective materials， this study proposes the fundamental directions and emerging trends in the study of blast damage and safety protection.

Abstract:To enhance the modeling and computational efficiency of numerical simulations for penetration resistance in ultra-high molecular weight polyethylene fiber （UHMWPE） laminates， an equivalent mechanical model of UHMWPE laminates was established based on the theory of three-dimensional equivalent elastic constants， and a three-dimensional equivalent rapid simulation method suitable for predicting the penetration resistance of fiber composite laminates was developed. As verified by the UHMWPE laminates" penetration test data， the equivalent method can accurately simulate and predict the staged penetration characteristics of laminates by taking into account the influence of the fiber lay-up on the mechanical properties of the laminates， and the average errors for the ballistic performance of 9.1-60.0 mm laminates are less than 10%. The method bypasses the need for detailed modeling of fiber bundles and matrices， as required in mesoscopic scale numerical simulations， and eliminates the necessity of specifying individual fiber/resin ply orientations and inserting numerous bonding elements， as in quasi-mesoscopic scale simulations.

Abstract:In order to characterize the enclosed space blast loads of reactive damage element warheads， comparative enclosed space blast tests of reactive damage element warheads， inert warheads and bare charges were carried out. Combining the high-speed data acquisition system and three-dimensional scanning technology， the blast pressure， temperature and deformation response of the loaded structure in cabin and the energy release characteristics of the reactive materials for different types of warheads were analyzed. The results show that the reactive damage element warhead substantially increases the quasi-static pressure， the peak temperature and the residual deformation of the loaded structure in the cabin. Compared to inert warheads and bare charges， the blast pressure， temperature and structural residual deformation are improved by maxima of 79.7%， 93.6% and 62.1%. In addition， the energy release rate and energy release amount of the reactive material show a positive correlation with the detonation energy， and the energy release amount of the reactive material shows a convergence phenomenon with the increase of the blast energy. Based on the load characteristics of reactive damage element warheads and the blast response law of sheet metal， it was found that the continuous energy release phenomenon of reactive materials leads to large increases in the quasi-static pressure of the cabin and the impulse applied to the structure within 1 ms， which together affect the residual deformation of the structure.

Abstract:The condensation and accumulation of Nitroglycerin （NG）-containing volatiles on various solid surfaces during the propellant rolling process， which pose safety hazards， were investigated using molecular dynamics simulation methods. The study was conducted by constructing a hybrid system model consisting of NG volatiles and solid surfaces， examining the effects of solid surface material， surface roughness， and NG content on molecular dynamics characteristic parameters such as radial distribution function， mean square displacement， diffusion coefficient， and relative density distribution of NG volatiles in the hybrid system. The findings demonstrate that as the mass fraction of NG increases， the size of volatile condensate clusters on the solid surface progressively diminishes. Conversely， the condensation ratio of volatiles exhibits a trend of initial increase followed by a decrease， with the maximum condensation ratio occurring at 70 % NG， corresponding to a diffusion coefficient of 0.0364. The diffusion coefficient for the condensation of volatiles containing NG on a silica （SiO₂） surface is 2.1228， which is substantially greater than that on surfaces composed of copper （Cu）， calcium oxide （CaO）， and ferrum （Fe）. However， the uniformity of the SiO₂ surface condensate cluster is poor. The introduction of surface roughness factors has opposite effects on the condensation amount of volatiles on the SiO₂ and Fe surfaces. When the SiO₂ surface goes from smooth to roughness of 0.4 nm， the diffusion coefficient increases from 2.1228 to 10.7156， and the condensation amount of volatiles on the surface increases； however， when the Fe surface goes from smooth to roughness of 0.4 nm， the diffusion coefficient decreases from 17.5673 to 1.8462， and the condensation amount of the surface volatiles decreases.

Abstract:To study the characteristics of after-effect parameters of shaped charge jet penetrating finite thickness steel target， the experiments on small shaped charge jet formation and penetration on finite thickness plate with after-effect target were carried out. The numerical simulation on the process of shaped charge jet penetrating finite thickness target plate was carried out by ANSYS/LS-DYNA finite software. The influence of target plate thickness， standoff and after-effect material density on the after-effect parameters of shaped charge jet penetration was analyzed， including the residual jet tip diameter d， tip velocity v and after-effect initiation ability v²d. The results show that with the increase of target thickness， the after-effect initiation ability v²d shows a linear attenuation trend， and around 16% of the initial initiation parameter is lost for every 20 mm increase in thickness. In the range of standoff that the jet keeps continuous， with the increase of standoff， the after-effect initiation ability v²d first increases and then decreases， and its stagnation point appears at the standoff of 8 times the shaped charge diameter. In the range of common explosive density， with the increase of after-effect material density ρ， the attenuation rate of after-effect initiation ability v²d first decreases and then increases. At the same time， there is a stagnation point in the v²d-ρ curve. The peak value of v²d is distributed between ρ=1.6-1.8 g·cm^-3， and the stagnation point position moves to the right with the increase of penetration time.

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