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Nowadays, the mitigation of damage to a ship caused by the underwater explosion attracts more and more attention from the modern ship designers. In this study, two kinds of scale tests were conducted to investigate the effects of polyurea coatings on the blast resistance of hulls subjected to underwater explosion. Firstly, small-scale model tests with different polyurea coatings were carried out. Results indicate that polyurea has a better blast resistance performance when coated on the front face, which can effectively reduce the maximum deflection of the steel plate by more than 20% and reduce the deformation energy by 35.7%–45.4%. Next, a full-scale ship (approximately 50 m × 9 m) under loadings produced by the detonation of 33 kg of spherical TNT charges was tested, where a part of the ship was coated with polyurea on the front face (8 mm + 24 mm) and not on the contrast area. Damage characteristics on the bottom were statistically analyzed based on a 3D scanning technology, indicating that polyurea contributes to enhancing the blast protection of the ship. However, damage results of this test were different from those of the small-scale tests. Moreover, the deformation area of the bottom with polyurea was greatly increased by 40.1% to disperse explosion energy, a conclusion that cannot be drown from the small-scale tests.

The time-sequenced damage behavior of the reactive projectile impacting double-layer plates is discussed. The analytical model considering the combined effect of kinetic and chemical energy is developed to reveal the damage mechanism. The influences of impact velocity and reactive projectile chemical characteristics on the damage effect are decoupled analyzed based on this model. These analyses indicate that the high energy releasing efficiency and fast reaction propagation velocity of the reactive projectile are conducive to enhancing the damage effect. The experiments with various reactive projectiles impact velocity increasing from 702 to 1385 m/s were conducted to verify this model. The experimental results presented that, the damage hole radius of the rear-plate increases with the increase of impact velocity. At the impact velocity of 1350 m/s, the radius of damage hole formed by PTFE/Al/Bi2O3, PTFE/Al/MoO3, PTFE/Al/Fe2O3 projectile on the rear-plate become smaller in sequence. These results are consistent with the analytical model prediction, demonstrating that this model can predict the damage effect quantitatively. This work is of constructive significance to the application of reactive projectiles. [ABSTRACT FROM AUTHOR]

In this paper, the penetration mechanism of reactive jet with non-uniform density distribution is studied. The simulations show that the density deficit occurs in the whole reactive jet, and the density increases from the jet tip to tail. The density of jet tip is approximately 1.5 g/cm3, which is lower than that of the reactive liner materials. The X-ray experiments show similar results with the simulations. The density decreasing effect of jet tip has a significant influence on the penetration behavior when the reactive jet impacts steel plate. According to the simulation results, this paper assumes that the density gradient in the jet section has linear distribution. Then, the deflagration pressure generated by each jet element at the bottom of crater is introduced into the Bernoulli equation. Based on the virtual origin model and Szendrei-Held equation, the analytical models for penetration depth and radial cratering of reactive jet with the density reduction are obtained. Moreover, to further prove the validity of analytical models, the penetration experiments of the reactive liner shaped charge against steel plate under different standoffs are carried out. There is a convergence between the analytical crater profiles and experimental results when reactive jets penetrate steel plates under different standoffs, especially at standoff of 1.5 and 2.0 charge diameters. [ABSTRACT FROM AUTHOR]

In this paper, the reaction characteristic and its application in shaped charge warhead of a novel reactive material, which introduced copper (Cu) and plumbum (Pb) into traditional polytetrafluoroethylene/aluminum (PTFE/Al), are studied. The thermal analysis and chemical reaction behavior of the PTFE/Al/Cu/Pb mixture are investigated by Differential Scanning Calorimetry (DSC), Thermo-gravimetry (TG), and Xray Diffraction (XRD) techniques. Then, the shaped charge liners with PTFE/Al/Cu/Pb reactive materials are fabricated, and the X-ray experiments show that they could form reactive jets with excellent performance under the detonation effects of the shaped charge. Based on that, the penetration experiments of shaped charge with PTFE/Al/Cu/Pb reactive liner against steel plates are carried out, and the results demonstrate that the PTFE/Al/Cu/Pb reactive jets could produce a deeper penetration depth compared to the traditional PTFE/Al reactive jets. Meanwhile, the PTFE/Al/Cu/Pb reactive jets also show significant inner-blast effects, leading to dramatically cracking or fragmentation behavior of the penetrated steel plates. This new PTFE/Al/Cu/Pb reactive liner shaped charge presents enhanced penetration behavior for steel targets that incorporates the penetration capability of a high-density and ductility jet, and the chemical energy release of PTFE-matrix reactive materials. [ABSTRACT FROM AUTHOR]

Force chains based mesoscale simulation is conducted to investigate the response behavior of aluminumpolytetrafluoroethylene (Al-PTFE) granular composites under a low-velocity impact. A two-dimensional model followed the randomly normal distribution of real Al particles size is developed. The dynamic compressive process of Al-PTFE composites with varied Al mass fraction is simulated and validated against the experiments. The results indicate that, force chains behavior governed by the number and the size of agglomerated Al particles, significantly affects the impact response of the material. The failure mode of the material evolves from shear failure of matrix to debonding failure of particles with increasing density. A high crack area of the material is critical mechanism to arouse the initiation reaction. The damage maintained by force chains during large plastic strain builds up more local stresses concentration to enhance a possible reaction performance. In addition, simulation is performed with identical mass fraction but various Al size distribution to explore the effects of size centralization and dispersion on the mechanical properties of materials. It is found that smaller sized Al particle of composites are more preferred than its bulky material in ultimate strength. Increasing dispersed degree is facilitated to create stable force chains in samples with comparable particle number. The simulation studies provide further insights into the plastic deformation, failure mechanism, and possible energy release capacity for Al-PTFE composites, which is helpful for further design and application of reactive materials. [ABSTRACT FROM AUTHOR]

In this research, the effect of the sintering and cooling process on geometry distortion and mechanical properties of PTFE/Al reactive material is investigated. Six particularly selected sintering temperatures, three different cooling modes (annealing cooling, normalizing cooling and rapid cooling), three different initial cooling temperatures, as well as six different final cooling temperatures were designed to compare the effects of sintering temperature, cooling rate, initial cooling temperature and final cooling temperature on the properties of reactive materials. Geometry distortion was quantitatively analyzed by a statistic on the dimensional changes of the specimens and microscopic morphology. A mechanical response properties transition from brittle to ductile was found and analyzed. By combining the thermodynamic properties of PTFE and unsteady heat conduction theory, mechanisms of cooling induced morphology change, temperature induced distortion and strength decrease were obtained. The results showed that the cooling rate has the most significant effect on the morphology transformation, while initial cooling temperature has more significant effect on the dimensional distortion than final cooling temperature. As to the mechanical properties transition from brittle to plastic, a more prominent effect of initial cooling temperature than cooling rate and final temperature was revealed. [ABSTRACT FROM AUTHOR]

Enhanced damage to the full-filled fuel tank, impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile (RMP) with a density of 7.8 g/cm3, is investigated experimentally and theoretically. The fuel tank is a rectangular structure, welded by six pieces of 2024 aluminum plate with a thickness of 6 mm, and filled with RP-3 aviation kerosene. Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s, and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed. However, the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene. Based on the experimental results, the radial pressure field is considered to be the main reason for the shear failure of weld. For mechanism considerations, the chemical energy released by the RMP enhances the hydrodynamic ram (HRAM) effect and provides additional ignition sources inside the fuel tank, thereby enhancing both rupture and ignition effects. Moreover, to further understand the enhanced ignition effect of RMP, the reactive debris temperature inside the kerosene is analyzed theoretically. The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene, resulting in the enhanced ignition of the kerosene.

Chain damage is a new phenomenon that occurs when a reactive jet impacts and penetrates multi-spaced plates. The reactive jet produces mechanical perforations on the spaced plates by its kinetic energy (KE), and then results in unusual chain rupturing effects and excessive structural damage on the spaced plates by its deflagration reaction. In the present study, the chain damage behavior is initially demonstrated by experiments. The reactive liners, composed of 26 wt%Al and 74 wt% PTFE, are fabricated through a pressing and sintering process. Three reactive liner thicknesses of 0.08 CD, 0.10 CD and 0.12 CD (charge diameter) are chosen to carry out the chain damage experiments. The results show a chain rupturing phenomenon caused by reactive jet. The constant reaction delay time and the different penetration velocities of reactive jets from liners with different thicknesses result in the variation of the deflagration position, which consequently determines the number of ruptured plates behind the armor. Then, the finite-element code AUTODYN-3D has been used to simulate the kinetic energy only-induced rupturing effects on plates, based on the mechanism of behind armor debris (BAD). The significant discrepancies between simulations and experiments indicate that one enhanced damage mechanism, the behind armor blast (BAB), has acted on the ruptured plates. Finally, a theoretical model is used to consider the BAB-induced enhancement, and the analysis shows that the rupturing area on aluminum plates depends strongly upon the KE only-induced pre-perforations, the mass of reactive materials, and the thickness of plates.