Internal Blast Research Articles

Design of continuously radial density-graded aluminum foam with unidirectional and bidirectional and study on blast resistance of sandwich tube

This work focuses on investigation of the internal blast resistance of metal sandwich tubes with continuously radial density-graded aluminum foam cores. Based on the 3D-Voronoi technology in polar coordinates, unidirectionally and bidirectionally continuously density-graded aluminum foam were developed for the cores of sandwich tubes in Finite Element (FE) model. And the correctness of core gradient was verified by comparing theoretical design with the actual value generated by FE model. Effects of core density distribution and core density gradient on blast resistance of sandwich tubes were explored and identified. The results indicate that, when the core density gradient is constant, the sandwich tube with negative-gradient core exhibits the smallest maximum deformation of the outer tube, while the negative-middle-low-gradient core tube shows the highest specific energy absorption ( SEA). For negative-gradient core tube, as the core density gradient increases, the maximum deformation of the outer tube decreases significantly, with only slight reduction of the structural SEA. For negative-middle-low-gradient core tube, as the core density gradient increases, the maximum deformation of the outer tube decreases, while the SEA increases.

Experimental investigation on damage development and failure mechanism of shield tunnel lining under internal blast considering stratum-structure interaction

With the expansion of international terrorism and the potential threat of attacks against civil infrastructure, the dynamic response and failure modes of underground tunnels under explosive loads have become a prominent research topic. The high cost and inherent danger associated with explosion experiments have limited current research on tunnel internal explosions, particularly in the context of scaled model tests of shield tunnels. This study presents a series of scaled model tests under 1 g-condition simulating internal blast events within a shield tunnel based on the prototype of the Shantou Bay Tunnel, considering the influences of surrounding stratum and equivalent explosive yield. Three different TNT explosive yields are considered in the model tests, namely 0.2, 0.4, and 1.0 kg. The model tests focus on the damage behavior and collapse modes of the shield tunnel lining under internal explosive loads. The model tests reveal that the shield tunnel is prone to damage at the joints of the tunnel crown and shoulder when subjected to internal explosive loads, with the upper half of the tunnel lining experiencing segment collapse, while the lower half remains largely undamaged. As the TNT equivalent increases, the damage area at the tunnel joints expands, and the number of segment failures in the upper half of the tunnel rises, transitioning from a damaged state to a collapsed state. The influence of “stratum-structure” interaction is investigated by comparing two models, one with overburden soil and the other positioned at the ground surface. The model tests reveal that the presence of soil pressure and confinement can significantly enhance the tunnel resistance to internal blast loads. Based on the observation of the model tests, five different damage modes of segment joints under internal explosion are proposed in this study.

Experimental studies of confined detonations of plasticized high explosives in inert and reactive atmospheres

When explosives detonate in a confined space, repeated boundary reflections result in complex shock interactions and the formation of a uniform quasi-static pressure (QSP). For fuel-rich explosives, mixing of partially oxidized detonation products with an oxygen-rich atmosphere results in a further energy release through rapid secondary combustion or ‘afterburn’. While empirical formulae and thermochemical modelling approaches have been developed to predict QSP, a lack of high-fidelity experimental data means questions remain around the deterministic quality of confined explosions, and the magnitude and mechanisms of afterburn reactions. This article presents experimental data for RDX- and PETN-based plastic explosives, demonstrating the high repeatability of the QSP generated in a sealed chamber using pressure transducers and high-speed infrared thermometry. Detonations in air, nitrogen and argon atmospheres are used to identify the contribution of afterburn to total QSP, to estimate the duration of afterburn reactions and to speculate on the flame temperature associated with this mechanism. Computational fluid dynamic modelling of the experiments was also able to accurately predict these effects. Understanding and quantifying explosions in complex environments are critical for the design of effective protective structures: the mechanisms described here provide a significant step towards the development of fast-running engineering models for internal blast events.

A coupled FD-SPH method for shock-structure interaction and dynamic fracture propagation modeling

Shock wave propagation and their damage to solid structures, which involve complex multiphase and multiphysics phenomena, are difficult problems to address. In this paper, a three-dimensional graphics processing unit (GPU)-accelerated finite difference-smoothed particle hydrodynamics (FD-SPH) method was developed for the prediction of strongly compressible fluid flow and strong fluid-structure interactions. The conventional mesh-based finite difference method was used to simulate shock wave propagation, while the smoothed particle hydrodynamics method was employed to predict the dynamic behavior of solid materials. In addition, the immersed boundary method (IBM) was implemented in the GPU-accelerated FD-SPH solver for the boundary treatment of the interface between solid and fluid materials. Four numerical cases, namely shock-cylinder obstacle interaction, elastic panel deformation induced by shock wave propagation, the response of stainless steel tubes under internal blast loading, and the damage of blast loading on reinforced concrete slab, were conducted for verification of the GPU-accelerated FD-SPH solver. The numerical results were compared against the available experimental data, which shows that the GPU-accelerated FD-SPH solver is capable of capturing the shock wave propagation and its damage to structures very well.

A fast calculation method for internal blast shock wave in confined structures

Internal explosions are more complicated and destructive than external explosions. It is hard to give accurate predictions of the internal blast load by existing simplified models. In the present work, a fast calculation method for the shock wave of internal blast within a confined space was developed. Firstly, the theoretical bases of this method, the reflection addition rules and the image burst theory, were introduced and validated. Then, the concept of the influence region of image burst for internal blast calculation was proposed, and the detailed calculation method for internal blast load was presented. In addition, the internal blast loads inside a typical cubic structure and a tunnel model were calculated using this developed method, respectively. Moreover, comparison studies between the calculated results and experimental data as well as numerical simulation results were conducted. It was found that the results of the fast calculation model are in good agreement with those of the blast experiment and fine numerical simulation, but the fast calculation takes only less than 2 min. Finally, the advantages and defects of the present method were discussed and further study advices were suggested to improve the accuracy.

Semi-confined blast loading: experiments and simulations of internal detonations

AbstractFar-field blast loading has been studied extensively for decades. Close-in, confined, and semi-confined detonations less so, partly because it is difficult to obtain good experimental data. The increase in computational power in recent years has made it possible to conduct studies of this kind numerically, but the results of such simulations ultimately depend on experimental validation and verification. This work thus aims at using reliable experiments to validate and verify numerical models developed to represent blast loading in general. Test rigs consisting of massive steel cylinders with pressure sensors were used to measure the pressure profiles of semi-confined detonations with different charge sizes. The experimental data set was then used to assess numerical models appropriate for simulating blast loading. In general, the numerical results were in excellent agreement with the experimental data, in both qualitative and quantitative terms. These results may in turn be used to analyse structures exposed to internal blast loads, which constitutes the next phase of this research project.

Structural Support of Aluminum Honeycomb on Cast PBX

As the operating condition for the penetrating missile has been more advanced, the survivability of main charge has been strongly required when the warhead impacts the target. Lots of efforts to desensitize explosives such as the development of insensitive molecular explosives or optimizing plastic-bonded explosives(PBX) systems has been made to enhance the survivability of main charge. However, these efforts face their limits as the weapon system require higher performance. Herein, we suggest a new strategy to secure the survivability of main charge. We applied structurally supportable aluminum honeycomb(HC) structure to cast PBX. The aluminum HC structure reinforces the mechanical strength of cast PBX and helps it to withstand external pressure without the reaction like detonation. In this study, impact resistance character, shock sensitivity and internal blast performance of PBXs reinforced with HC structure were investigated according to the application of aluminum HC structure. The newly suggested aluminum HC structure applied to cast PBX was proved to be a promising manufacturing method available for high-tech weapon systems.

Research on internal explosion loads in folded arch tunnels: A theoretical approach

To elucidate the loading characteristics in the folded arch tunnel subjected to internal explosion, a field blast test was conducted in a large-scale (1:5) model constructed according to the immersed tube tunnel of Hong Kong-Zhuhai-Macao Bridge. The spatial distribution and time histories of the overpressure around the detonation point were recorded in the folded arch tunnel. The test data indicate that the internal blast loads in the folded arch tunnel is mainly attributed to the shock overpressure and gas overpressure. A fine FE model was developed in the LSDYNA platform, which was validated by the loading test data. The propagation process of blast waves and detonation products along the folded arch tunnel were studied by the developed model, which also helped reveal the interaction mechanism with the tunnel structure. Three existing theoretical models in predicting the internal blast loads were compared and assessed. It is found that the existing theoretical models developed for the internal blast loads has limitations in predicting the blast load in the tunnel, which especially would introduce a large error in manifesting the gas overpressure. A new loading model that enables precisely predicting the internal blast loads in the folded arch tunnel was proposed, which offers valuable insights for the blast-resistant design and disaster mitigation measures for the tunnel structure.

Elastic-plastic response for the foam-filled sandwich circular tube under internal blast loading

The dynamic response and the blast resistance of an aluminum foam-filled sandwich circular tube under internal blast loading was investigated theoretically. The deformation of the structure is decoupled into three phases corresponding to blast loading interacting with the internal tube, foam core crushing and external tube deformation. During the process, the theoretical model includes both the circumferential membrane forces and the axial moment components and considers an elastic-plastic strengthening model for internal/external tubes. The proposed model is tested against the experimental results for the mid-point deflection of the external/internal tubes. The influence of the physical and geometrical parameters of the structure on their deformation is investigated. It is shown that the dimensionless mid-point deflection of the external tube decreases as the tangent modulus of the internal/external tube increases, while the tangent modulus of the internal tube has a larger effect on the mid-point deflection of the external tube. The minimum mass of a sandwich circular tube can be found when the deformation of the external tube is specified. The research results can provide theoretical basis for lightweight structure design.

Numerical Investigation on Anti-Explosion Performance of Non-Metallic Annular Protective Structures.

Explosive shock wave protection is an important issue that urgently needs to be solved in the current military and public security safety fields. Non-metallic protective structures have the characteristics of being lightweight and having low secondary damage, making them an important research object in the field of equivalent protection. In this paper, the numerical simulation was performed to investigate the dynamic mechanical response of non-metallic annular protective structures under the internal blast, which were made by the continuous winding of PE fibers. The impact of various charges, the number of fiber layers, and polyurethane foam on the damage to protective structures was analyzed. The numerical results showed that 120 PE fiber layers could protect 50 g TNT equivalent explosives. However, solely increasing the thickness of fiber layers cannot effectively enhance the protection efficiency. By adding polyurethane foam in the inner layer, the stress acting on the fiber could be effectively reduced. A 30 mm thick polyurethane layer can reduce the equivalent stress of the fiber layer by 41.6%. This paper can provide some reference for the numerical simulations of non-metallic explosion protection structures.

Numerical Simulation of Explosive Storage Underground Structure Subjected to Blast

In this study, finite element (FE) analysis of underground structure is carried out, which is subjected to the internal blast loading and the structure is surrounded with soil media. Three different methods to analyze the effect of blast loading on structure, i.e. ConWep, smooth particle hydrodynamics (SPH), and couple Eulerian-Lagrangian (CEL) are used for the simulation of blast loading using ABAQUS/ExplicitⓇ. Concrete damage plasticity (CDP), Mohr–Coulomb, Johnson–Cook (JC) plasticity model, Jones–Wilkins–Lee (JWL) equation of state and ideal gas are utilized for defining behavior of concrete, soil, steel, explosive and air, respectively. FE analysis is performed to compare the behavior of structure under different blast modelling methods. The effect of different explosive weights is considered to see the impact of the blast load on the structure. For parametric analysis, three explosive weights, 3[Formula: see text]kg, 5[Formula: see text]kg, and 10[Formula: see text]kg of TNT (trinitro toluene), and three concrete grades, M30, M35, and M40 are considered to see the stability of the structure. The effect of varied explosive weights and varied concrete grades is compared in terms of stress, pressure, and displacement at critical locations of the structure. The outcome of this shows that the change in explosive weight and concrete grade considerably affects the stability of the structure. As the explosive weight increases, damage to the structure increases, and with the increase in the concrete grade, the blast load resistance capacity of the structure increases. It is observed that buried part of the structure is more resistant to blast load compared to the structure visible above ground.

Dynamic stability of concrete structures with varying sections to underwater contact explosion: A case study of gravity dams

Concrete structures with varying sections are widely used in the fields of ocean engineering, hydraulic engineering and civil engineering. And the damage mechanism of variable-section structures to underwater contact explosion, which involves localized damage by explosion impact and instability by overall structural vibration, is very complex. The gravity dam is taken as an example, the coupled analysis model for gravity dams under underwater contact blast is established, a prototype test on the dynamic response of a gravity dam under underwater explosion is conducted to verify the reliability of the fluid-solid interaction method, and the reliability of the concrete dynamic damage model adopted in this paper is validated by a small-scale field test on the internal blast damage of a gravity dam. The damage mechanism of gravity dams subjected to underwater contact explosion is analyzed. A stability analysis method for gravity dams to underwater contact explosion is proposed, which allows simultaneous consideration of the dam stability in the blast-induced vibration phase and the static phase after damage. The dynamic stability performance of gravity dams to underwater contact explosion is analyzed. And a stability assessment criterion that could be used to assess the safety level of dams at various stages is presented.

Damage Assessment of Multi-Box Structures Subjected to Internal Blast Loadings

In this study, a rapid algorithm is proposed to efficiently predict the damage of target structures subjected to internal explosions. Firstly, a data-driven approach was used to obtain the quasi-static peak pressure of the blast-loaded chamber based on a large amount of experimental data. The variation of the gas mass in each chamber was obtained using a pressure relief algorithm. The SDOF method was used to calculate the deformation of the wall plates to further calculate the change in volume and open area of the chamber. The change in pressure was calculated using the ideal gas equation of state. The proposed algorithm was then used to calculate the pressure change and wall deformation in each box. The results were compared with existing experimental data and found to be in good agreement. Finally, the results of the proposed algorithm are visualized, and the effects of different influencing factors such as explosion equivalent, cavity size, and wall thickness on the failure characteristics of multi-box structures were studied.

Evaluation of blast mitigation performance of cylindrical explosion containment vessels based on water containers

Using liquid materials with specific geometries can enhance the explosion-proof properties of confined structures. This approach is promising because bulk water has multiple blast mitigation mechanisms and adds almost no extra mass. In this study, a method of using water-filled containers to reduce both the peak and permanent deformation of cylindrical explosion containment vessels (CECVs) is investigated through experiments and numerical simulations. Several explosion experiments were performed to evaluate the blast mitigation of the empty containers and the bulk water with multiple thicknesses and heights in terms of dynamic deformation and afterburning suppression. The experimental results indicated that the bulk water with a larger thickness and a smaller height had better protective performance, which provided up to an 80.1% reduction in permanent deformation compared with no mitigant. Numerical models were established using LS-DYNA and verified by the deformation-time history curves measured in the experiments. The energy conversion process during the explosion was analyzed through the numerical simulations, and the results showed that water absorbed most of the detonation energy that should have been transferred to the steel shell, proving that momentum extraction of water was a significant mitigation mechanism for the internal blast in CECVs. Another significant mitigation mechanism was the shadowing effect of water, which changed the spatial distribution of the blast loading acting on the steel shell, especially for water containers with larger thickness and smaller height.

Dynamic stability analysis of metro tunnel in layered weathered sandstone

In this study a coupled-eulerian–lagrangian (CEL) approach has been applied to assess the internal blast loading conditions, for the tunnel built in three layers of sandstone rock. The three weathered stages of sandstone have been considered in this study i.e., slightly, medium and also highly weathered sandstone in three different layers. The sandstone rock weathering increases as we move towards the ground surface from deep subsurface. The elastoplastic finite element model with varied overburden depth with dimensions of 60 m (L × B × H) each to incorporate different parametric cases. An explosive is assumed at the center of the tunnel, with the capacity of hundred kg of trinitrotoluene (TNT), the explosive is assumed to be hanging in the air inside the tunnel opening with equal distance from all sides. The TNT sphere and air that is inside the rock tunnel has been modelled through CEL technique to simulate actual in-situ condition. Through Mohr-Coulomb, Concrete Damage Plasticity, and Johnson-Cook constructive material model the elastoplastic behaviour of different materials like rock, steel bars and concrete has been simulated respectively. The cage of steel bars has been embedded through interaction constraint in concrete liner to produce reinforced concrete liner. In the initial stages of simulation with 5 m of overburden depth the tunnel has been placed in the upper layer of sandstone. For further analysis, the position of the tunnel has been changed for overburden depth of fifteen, twenty-five and thirty-five meter. In accordance with the result of the simulation, for rock in terms of acceleration, velocity, and dis-placement, the depth of the overburden and the displacement of the crown are inversely related. No damage in terms of compression is seen in this simulation, but in all instances, a small damage owing to tensile failure has been noted.

Dynamic performance and damage assessment of a shallow buried tunnel under internal explosion

The tunnel entrance is usually made of arch members buried at shallow depths. These contribute to the greater performance of the tunnel under static or seismic loading. If an explosion occurs in the shallow buried tunnel, the tunnel arch at the entrance might be destroyed by the intense blast loading, thereby causing the collapse of the tunnel entrance or the surrounding ground. Hence, it is extremely important to investigate the dynamic behavior of a shallow buried tunnel arch under the conditions of an internal explosion and to evaluate its damage after the blast. In this paper, four scaled tunnel arch structures were fabricated and tested for their anti-blast performance under internal explosion. The following laboratory static load test was conducted on the undamaged and blast-damaged specimens to obtain their maximum and residual bearing capacities, respectively. The field blast test results showed that the tunnel arch experienced local punching failure under the internal contact explosion, and the dimensions of the failure zone increased as the explosive equivalent increased. In addition, for the same explosive equivalent, the residual bearing capacity of the specimen after the contact explosion at the arch crown was the lowest among other blast-damaged specimens, indicating that the damage on the arch crown significantly deteriorated the bearing capacity and stiffness of the tunnel arch. The finite element (FE) model of the shallow buried tunnel arch under the internal explosion was developed by adopting the arbitrary Lagrangian–Eulerian (ALE) algorithm in LS-DYNA and validated on the actual measurements from the field blast test. It is shown that the results from the FE model and field blast test measurements compared well in terms of damage pattern, crater diameter, acceleration and reflected overpressure readings. The full restart method in LS-DYNA was further employed to calculate the bearing capacity of the specimens. Finally, the damage levels of the blast-damaged specimens were assessed by taking the residual bearing capacity of the tunnel arch as an indicator. The damage assessment charts for the shallow buried tunnel arch under the conditions of an internal explosion were further established. From the chart, the blast resistance of the shallow buried tunnel arch can be quickly assessed under different internal blast loading conditions. This research is of direct significance for the design of the shallow buried structures with increased blast resistance.

Blast resistance of RC tubular structure under internal ANFO explosion

The degree of structural damage is significantly more severe when a blast occurs inside than outside of a structure. However, existing designs for RC structures such as reinforced concrete containment vessels (RCCV) do not include design features to protect the structure for internal blast. Therefore, the internal blast resistance capacity of RC structures is evaluated by performing internal blast tests on RC tubular structures. The main objective of the study was to observe and document the basic structural behavior data obtained from internal detonation tests. ANFO explosive charge weights of 15.88, 20.41, 22.68 and 24.95 kg were selected for a charge detonating at a cross section center of the mid-span of the specimen, giving a standoff distance to the inner wall surface of 1000 mm. The data acquisitions include blast pressure, deflection, strain, and crack pattern. When the explosive charge weight increased from 15.88 to 24.95 kg, the peak incident pressure and time duration increased from 0.1718 to 0.3394 MPa and from 5.856 to 5.981 ms, respectively. Then, the test data were used to predict the internal charge weight required to fail a real scale RCCV using simple assumptions and the test data. The results of the study are discussed in detail in the paper.

Experimental and numerical investigation on the dynamic response and damage of large-scale multi-box structure under internal blast loading

Internal blast is different from external or air blast for the reason of internal blast load is much more complicated and more destructive to target structures. The present work presents a large-scale experiment on multiple steel box structure under confined blast loading. A multi-box structure specimen with a dimension of 7.5 m × 2.9 m × 2.2 m was designed and field blast test with 1.782 kg TNT detonated inside this model was carried out. The damage features and dynamic response of the specimen were analyzed. The plates near the explosive suffer from strong impact and result in some fragments with high velocity which are destructive to other structural members. Meanwhile, the dynamic response processes were recorded by using the high-speed photography system. The response process of the whole model can be divided into two different stages, namely, localized damage response stage and integral vibration stage. In addition, numerical model considering both double-sided and single-sided fillet welding of this large-scale experiment were built, the dynamic response and the propagation of internal blast wave were analyzed. The numerical studies show that, to achieve a good consistency with the experiment, the failure strain for double-sided and single-sided fillet welding should be set to 0.1 and 0.08 respectively for such large-scale structure under explosive load. Finally, several suggestions for the design of multi-box structure are put forward based on the experimental and numerical investigations.

Analysis on the Vulnerability of a Tunnel Entrance under Internal Explosion.

Tunnels play an essential role in the transportation network. Tunnel entrances are usually buried at a shallow depth. In the event of an internal explosion, the blast pressure will cause severe damage or even collapse of the tunnel entrance, paralyzing the traffic system. Therefore, an accurate assessment of the damage level of tunnel entrances under internal blast loading can provide effective assistance for the anti-blast design of tunnels, post-disaster emergency response, and economic damage assessment. In this paper, four tunnel entrance specimens were designed and fabricated with a scale ratio of 1/5.5, and a series of field blast tests were carried out to examine the damage pattern of the tunnel entrances under internal explosion. Subsequently, static loading tests were conducted to obtain the maximum bearing capacity of the intact specimen and residual bearing capacities of the post-blast specimens. After that, an explicit non-linear analysis was carried out and a numerical finite element (FE) model of the tunnel entrance under internal blast loading was established by adopting the arbitrary Lagrangian-Eulerian (ALE) method and validated based on the data obtained from the field blast and static loading tests. A probabilistic vulnerability analysis of a typical tunnel entrance subjected to stochastic internal explosions (assuming various charge weights and detonation points) was then carried out with the validated FE model. For the purpose of damage assessment, the residual bearing capacity of the tunnel entrance was taken as the damage criterion. The vulnerability curves corresponding to various damage levels were further developed based on the stochastic data from the probabilistic vulnerability analysis. When the charge weight was 200 kg, the tunnel entrance exhibited slight or moderate damage, while the tunnel entrance suffered severe or even complete damage as the charge weight increased to 1000 kg. However, the tunnel entrance's probability of complete damage was less than 10% when the TNT charge weight did not exceed 1000 kg.

Dynamic response and energy absorption performance of aluminum foam-filled sandwich circular tubes under internal blast loading

The dynamic response and energy absorption properties of an aluminum foam-filled sandwich circular tube under internal blast loading is investigated by experimental, theoretical, and numerical simulations. A series of blast experiments were performed using spherical emulsion explosives of different masses. Three axially deformed regions are obtained for the internal and external tubes: a region with large plastic deformation, a rigid section moving around the plastic hinge, and an undistorted boundary region. Explosive mass, the internal and external tube wall thickness have a significant influence on the final deformation of a foam-filled sandwich circular tube. A theoretical explicit calculation method including the circumferential plastic membrane forces and the axial moment components has been developed to predict the internal blast response of a foam-filled sandwich circular tube. The FE model, based on a 3D Voronoi algorithm for the foam core, was developed to investigate the deformation mechanism of a foam-filled sandwich circular tube. Both numerical and experimental results are consistent with the theoretical predictions. In addition, the impact of the explosive mass, the diameter and the wall thickness of the internal and external tubes, and the axial arrangement of the core on the dynamic response and energy absorption properties are investigated. It is found that the sandwich circular tube with negative gradient core has the best anti-blasting performance among the sandwich circular tubes with gradient arrangement.