Underwater Explosion Test Research Articles

Experimental and numerical investigation on normal strength and high strength RC arches subjected to underwater explosions

As a common structure in engineering, reinforced concrete (RC) arch may be subjected to explosion load in its life cycle. However, there are few studies on the blast resistance of RC arch against underwater explosion. A normal strength reinforced concrete (NSRC) arch and a high strength reinforced concrete (HSRC) arch were designed, and two sets of underwater explosion tests were carried out. Multi-media coupling models of the two RC arches subjected to underwater explosions were established based on the Arbitrary-Lagrangian-Eulerian (ALE) algorithm. The propagation characteristics of shock wave, the acceleration response and damage evolution of the arches were experimentally and numerically investigated. The reliability of the numerical method was verified by comparing the numerical results with the test results. Employing the verified numerical method, the effects of standoff distance and explosive weight on the dynamic response and damage distribution of the NSRC and HSRC arches were further studied. Based on extensive numerical simulations, the prediction formulas for the peak displacement of the given NSRC and HSRC arches due to specific underwater explosions were proposed. The results show that the arch vault and both sides of hance are the most vulnerable to failure when suffering the explosions centrally above the arch. The blast resistance of the HSRC arch is much stronger than that of NSRC arch. The failure modes of RC arches can be summarized as: arch vault cracking, global bending failure, combination of global bending failure and local damage, combination of global bending failure and penetration failure.

Energetic Coordination Compounds: Investigation of Aliphatic Ligands and Development of Prototype Detonators.

In this work, energetic coordination compounds (ECCs) of transition metals (Fe, Ni, Cu, Zn) containing aliphatic amines as ligands were synthesized: ethylenediamine; 1,3-diaminopropane; tris(2-aminoethyl)amine; tris(3-aminopropyl)amine. The compounds were investigated in terms of ignition/explosion temperature, friction and impact sensitivity. For selected compounds, structural characterisation was presented (IR-ATR spectroscopy, Raman spectroscopy) and their morphology was determined (SEM, powder XRD). They were also investigated by differential scanning calorimetry (DSC). In order to assess the potential application of selected ECCs in detonators, underwater explosion tests were carried out, determining energetic performance. The results achieved for detonators containing ECCs were compared with those for reference detonators (containing pentaerythritol tetranitrate, PETN), indicating their potential use as a "green" alternative to nitric acid esters.

Blast resistance performance and failure modes of prestressed thin-walled aqueducts subjected to underwater contact explosion

To solve the problem of regional water resource shortage, water diversion projects have been built around the world. As an essential lifeline project, the prestressed aqueduct is commonly used in cross-regional water transfer and diversion projects. However, the prestressed aqueduct is inclined to damage and collapse under explosion loading due to its thin structure. The main purpose of this paper is to investigate the nonlinear dynamic performance and failure modes of the large prestressed U-shaped thin shell aqueduct to underwater contact explosion. The prestress application approach is validated by theoretical calculations. The reliability of the analysis method of underwater contact explosion for reinforced concrete structures is verified by the underwater contact explosion test. Damage cracking process and nonlinear dynamic response characteristics of prestressed aqueducts to the underwater contact explosion with different explosive weights are performed. Blast resistance performances of prestressed aqueducts are discussed in terms of the crack length, residual displacement, and prestressing force loss. The influence of prestress level on the damage modes of the prestressed aqueduct under the blast loading is discussed. The results indicate that thin-walled U-shaped structures are extremely vulnerable to localized damage from underwater contact explosions. The blast-resistance performance of the U-shaped thin shell aqueduct can be significantly improved by applying prestress.

Dynamic behaviors of concrete gravity dam against combined blast wave and bubble pulsation of underwater explosion

Underwater explosion process mainly includes the preceding blast wave and the succeeding bubble pulsation, while the effect of bubble pulsation on hydraulic structures is always neglected. This paper aims to numerically study the dynamic behaviors of prototype concrete gravity dam against underwater explosion, considering the combined effects of blast wave and bubble pulsation. Firstly, a finite element analysis (FEA) approach for predicting the underwater explosion loadings, as well as the damage evolution and dynamic responses of dam against underwater explosions was proposed, in which the hydrostatic pressure of reservoir and the dead load of dam were considered. Based on Cole's formula and the existing underwater explosion tests, the reliability of FEA approach, including the mesh sizes, material models and the corresponding parameters, as well as the mapping, Fluid-Structure Interaction and contact algorithms, was comprehensively validated. Secondly, to realize the simulation of the prototype gravity dam impeded by the validated small Lagrange mesh size, a mesh transition strategy was proposed based on the equivalence of dam damage modes and total eroded element mass. Finally, the dynamic behaviors of a typical 120 m-height concrete gravity dam against underwater explosion, i.e., 1 t of TNT equivalence detonated at a depth of 35 m and standoff distances of 4–16 m, were examined. The dimensionless distance λR, i.e., the ratio of the standoff distance to the maximum bubble radius, was introduced to quantitatively evaluate the underwater explosion loadings and dynamic behaviors of the dam. It indicates that, the blast wave firstly leads to the local compressive damage on the upstream surface, as well as the tensile damage on the downstream folded slope and dam heel. The succeeding free vibration and bubble pulsation will further aggravate the damage degree, resulting in the cracking of dam neck and heel. Especially for the scenarios when λR ≤ 1.22, the overall sliding of dam is highly prone to occur.

Dynamic behaviors of RC caisson subjected to underwater explosions

Due to the vulnerability of wharves against accidental attacks, the reinforced concrete (RC) caisson quay wall, as a widely adopted wharf form, is faced with the potential threat of underwater explosions. The present work aims to study the dynamic responses and damage modes of caisson against underwater explosions through the underwater explosion test and numerical simulations. Firstly, four shots of underwater explosion test were conducted, including two cases for different focuses, i.e., two shots of the free field underwater explosion with a charge weight of 0.2 and 1 kg respectively, and another two shots of a 1/5 reduced scale caisson specimen subjected to the underwater explosion with a charge weight of 0.2 and 1 kg successively. The underwater explosion overpressure-time histories and periods of bubble pulsation, as well as the deflection-time histories and damage modes of caisson specimen were experimentally obtained. Then, the refined finite element (FE) models were established, including the 1D model for explosion loading and the 3D model for predicting the dynamic behaviors of caisson with adopting the Coupled-Eulerian-Lagrangian algorithms and remapping technology, which were validated by comparing with the test data. Finally, the influences of explosion conditions, such as explosion standoff, depth of burst, and charge weight on the dynamic behaviors of caisson specimens were numerically discussed. It derives that, the existing calculation formulas of overpressure and period of bubble obtained from the spherical charge are also applicable to the group charge; the reflection coefficient of hydraulic RC structure is around 1.7; the bubble pulsation induced by the underwater explosion could further deteriorate the damage level of RC caisson when the blast wave has already led to an inelastic structural response. The present work could provide beneficial references for the blast-resistance evaluation and design of hydraulic RC structures against underwater explosions.

Dynamic response and vulnerability analysis of pier under near-field underwater explosion

Marine reinforced concrete constructions (suspended tunnels, undersea pipelines, and cross-sea bridges) are inherently at risk from underwater explosions due to the rising incidence of worldwide terrorism. Sea-crossing bridges are as an important land-sea connection channel, whose anti-explosion performance cannot be ignored. In this paper, the dynamic response and damage mechanism of piers of sea-crossing bridge under underwater explosion loads are studied by the arbitrary Lagrangian-Eulerian (ALE) method. Firstly, the correctness of the explosive load and reinforced concrete material models is verified by the Zamyshlyaev formula and underwater explosion test, respectively. Secondly, the finite element (FE) model of a pier under an underwater explosion load is established. Taking the residual vertical bearing capacity of the pier as the performance index, the damage evaluation method and four damage levels of the pier under explosion load are put forward. The study of different parameters such as explosive weight, explosion location, explosion height, and explosion distance shows that the damage to the pier is the most serious when the detonation point is directly below the projection of the pier cap. The residual bearing capacity of the pier falls exponentially as explosive weight increases. Different detonation heights have significant effects on the damage to the pier. Additionally, it is found using the explosion vulnerability analysis approach that the pier is very susceptible to collapse when the explosive weight is 350 kg.

Temperature and pressure propagation characteristics in multi-media interfaces of PVDF pressure sensor near underwater explosion source

In this paper, based on the self-made PVDF pressure sensor, the underwater explosion test of the emulsion explosive was performed to verify the measurement accuracy of the self-made PVDF pressure sensor and the feasibility of the pressure measurement near the explosive source. Then the single column emulsion explosive and gram-grade Al/PTFE underwater explosion experiment and numerical simulation were carried out, and the error between the experimental and numerical simulation results is small (The difference between the pressure peaks obtained from the emulsion explosive experiment and numerical simulation is about 25.07 MPa and the pressure decay trend is close; the peak difference in lane 1 obtained by Al/PTFE experiment and simulation is about 23 MPa, the second peak difference is about 0.8 MPa, the pressure decay trend after the second peak is close, and the shock wave arrival moment in experiment lags the numerical simulation by about 30μs), which verifies the reliability of the simulation model. Meanwhile, the numerical simulation of explosion at a depth of 10m below sea level was performed, the evolutionary law of the sensor and water pressure at 1–10 times the charge diameter is expounded, the variable rule of temperature during sensor response period is analyzed. The numerical simulation results show that the time-history curve of pressure includes two stages: bubble microjet and shock wave propagation, which the bubble microjet pressure can reach 10 GPa, and the sensor structure and shock wave pressure test will not be affected within the response period. The time history curves of shock wave pressure in experiments are basically the same by comparing with the simulation results of underwater pressure at the same position, and impact temperature rise will affect the measurement accuracy of PVDF film, but the lasting time of heat conduction in the PVDF sensor is longer than the response period of impact pressure, therefore the influence of heat conduction on the test accuracy can be ignored.

Damage boundary spectrum of pelvis-lumbar spine of seated human under vertical wide-band shock environment

The assessment methods of personnel damage under real shock environments are still an issue. In this paper, a damage boundary for vibration-impact injury in a wide range of frequency domain based on pseudo-velocity shock spectrum (PVSRS) is first proposed with numerical simulation. A high-fidelity three-dimensional finite element (FE) model of pelvis-lumbar spine (P-LS) that the vulnerable organs of seated human under vertical impact conditions, was developed and validated. The random and complex impact loads in real environments were simplified to a series of sinusoidal accelerations with a single frequency and within one period, next loading those equivalent loads on P-LS FE model in vertical direction for batch computing. The results indicated that there is a certain critical failure load that can cause initial damage to P-LS for a specific single frequency. The injury patterns of P-LS show significant frequency sensitivity. The P-LS damage boundary can be obtained from the envelope curve of critical failure loads in PVSRS, which is a V-shaped curve and the frequency corresponding to the trough (18 Hz) is the first natural frequency of the coupled P-LS structures. The asymptote lines of damage boundary are highly consistent with that of theoretical results. The damage boundaries after classifying and standardizing, which rationality in wideband is verified by underwater explosion test data, show more comprehensive and advanced potentials for engineering application.

Investigation on bubble load characteristics of near-field underwater explosion

The wall pressure generated by near-field underwater explosion bubble involves significant nonlinear problems. This has been the focus and difficulty of the research on the anti-explosion design of battleships. To quantify the load characteristics of bubble pulsation and water jet pressure, underwater explosion tests were conducted beneath a clamped square plate subjected to 2.5g TNT at different distances (R = 10, 15, 20, 22.5, and 25 cm). Results showed that as the stand-off distance increased to the maximum radius of the bubble, there was a peak value of the impulse for bubble pulsation and water jet. A finite element model was then established and benchmarked. The benchmarked model was used to further explore the load characteristics of the bubble pulsation and water jet, considering the effect of the stand-off distance, plate dimension, horizontal distribution, and explosive equivalent. It was found that: a) as the plate dimension increased, the pressure of the shock wave to the plate was basically unchanged, while the period and impulse of the bubble pulsation and water jet decreased; b) the impact of the water jet pressure was concentrated within 6.72 times the radius of the explosive. Finally, an empirical formula was proposed to predict the impulse of the bubble pulsation and water jet. This research is able to provide guidance to investigate the blast resistance of ships.

Multi-peak phenomenon of large-scale hull structural damage under near-field underwater explosion

The underwater explosion (UNDEX) may cause more serious damage to the hull structure under certain detonation conditions. In this study, through a near-filed UNDEX test with a full-scale barge in a natural environment, a detailed simulation of the entire UNDEX process applying the S-ALE method is conducted and validated. Several near-field UNDEX simulations of the barge with different detonation distances are then conducted to study the response characteristics and damage results. The double-peak phenomenon of ship bottom deformation and the single-peak phenomenon of residual strength under different detonation distances, which is referred to as the multi-peak phenomenon, are identified based on the results of local deformation and residual strength, and their mechanisms are further analyzed and clarified.

Underwater explosion resistance of air-backed plate with steel and polyurea: Effect of polyurea spraying position

Improving hull-structure resistance against underwater explosion (UNDEX) is an important problem for designers. It has been proved that polyurea coating on steel can reduce the deformation of a plate subjected to UNDEX. In this study, the effect of the polyurea position was explored by performing a series of UNDEX tests on air-backed plates. They had polyurea sprayed on the front side (PS type), back side (SP type), and both sides (PSP type). The deformation result was obtained using three-dimensional (3D) scanning technology, and the bubble movement was observed by a high-speed camera. The experimental results proved that the polyurea spraying position had no significant effect on the formation and movement of bubble or water jet. More importantly, the PS-type plate exhibited the best explosion resistance when standoff distance was less than 3Rexplosive (radius of charge), whereas the SP-type plate did so when standoff distance exceeded Rbubble (maximum bubble radius). Numerical models for these UNDEX tests were established and verified by experimental results. The numerical results demonstrated that the PS-type plate could reflect part of the energy back into the water by compression, thus reducing the energy absorbed by steel. The SP-type plate could disperse impact stress in the steel, but the protective effect was poor within close standoff distance. This was attributed to spallation under reflected tensile wave.

Damage mechanisms of full-scale ship under near-field underwater explosion

The near-field underwater explosion produced by the torpedo and other weapons was one of the most critical threats to naval ships. However, most underwater explosion tests were scale models, which would bring dissimilarities between the gravity and strain rate. We carried out a near-field underwater explosion test on a full-scale ship and recorded the dynamic response processes to make up for this shortcoming. The ship damage was mainly embodied in the loss of overall strength and damage of local structures. The Coupled Eulerian–Lagrangian (CEL) method was used to establish the model of the near-field underwater explosion, and the effectiveness of the calculation method was validated. Based on the analysis results, the near-field underwater explosion could be divided into three stages: shock wave and after flow, bubble pulsation, and water jet. The overall strength of the ship was lost under the combined action of these three stages. The “negative pressure” caused by bubble pulsation was the key to the sagging deformation of the ship. This study would guide the production of underwater weapons and ship protection design.

Study on explosion reaction mechanism and energy release characteristics of HMX-based explosives containing B-Al

To explore the application of the micro-sized B-Al (boron-aluminum) compound powder in enhanced blast explosive(EBX) and thermobaric explosive(TBX), three HMX-based explosives containing B-Al (PF-1, PF-2 and PF-3)were designed and prepared. The ignition and combustion characteristics of various samples (micro- and nano-sized B, B-Al compound powders without and with HMX) under different pressures and atmospheres were studied by a laser ignition and combustion experimental system, and the flame evolution images and emission spectral characteristic parameters of the ignition and combustion process were obtained. The structures of detonation reaction zone of ideal and non-ideal explosives were studied by PDV (photonic doppler velocimeter), and the characteristic parameters and explosion reaction mechanism of wave profile were obtained. The energy output characteristics of explosives containing B-Al were evaluated by air blast and underwater explosion test. The results show that nano-sized B has better ignition and combustion characteristics than micro-sized B; the ignition and combustion property of B-Al compound powder with HMX is obviously superior to that of B-Al compound powder. PBX-1 is an ideal explosive, and the reaction zone width is 44ns, whilePF-1 and PF-3 are typical non-ideal explosives, the reaction zone widths are 112ns and 102ns, respectively. In the air blast and underwater explosion test, under the detonation of HMX, the combustion of micro-Al can promote the afterburning effect of micro-B, which releases a great amount of combustion heat, then generates expansible products with higher temperature and pressure, and finally increases the duration of fireball and total energy in underwater explosion.

Experimental investigation of steel fiber reinforced concrete slabs subjected to underwater contact explosions

Fiber reinforced concrete has gained significant attention due to its higher ductility and flexural behavior, making it a promising material for resisting extreme loads such as those caused by blast and impact. In this study, we present experimental results from static tests conducted on steel fiber reinforced concrete with different content of hooked end steel fibers and concrete strength. Underwater contact explosion tests were performed for 6 pieces of 50 cm × 50 cm x 6 cm steel fiber reinforced concrete slabs. The damage patterns observed in the slabs were analyzed, and shock pressure data was measured and compared with empirical formula calculations. Test results demonstrate that the addition of steel fiber effectively enhances the compressive and tensile strength of concrete while also significantly improving its anti-explosion capacity. In contrast, the plain concrete slab (control group) displayed an overall state of failure during underwater contact explosions. Steel fiber reinforced concrete slabs primarily experienced bending failure and “Y" crack damage, accompanied by local collapse failure on the back surface. Overall, these findings suggest that steel fiber reinforced concrete holds great promise as a superior material for resisting extreme loads, particularly in marine environments.

Study on damage effect of caisson wharves subjected to underwater explosion

This study aimed at investigating the destructive effect of explosion shock waves on caisson wharves in shallow water. First, underwater explosion tests were conducted on caisson wharves, full-size finite-element models of caisson wharf-water-explosive were established, and the accuracy of the models was verified by comparison. The destruction pattern and damage characteristics of the caisson wharf structure were then studied, and the effects of different explosion depths and different explosive quantities on the dynamic response of caisson wharves were analyzed. The results show that the destruction pattern of shock waves on the caisson wharf is manifested as plastic damage at the joint of the reinforced concrete (RC) box wall, shear destruction at the lower edge of the explosion loading wall, and integral displacement of the superstructure. When the scaled distance remains unchanged and the explosion depth and explosive quantity increase, the bottom reflection effect strengthens, turning the bending damage on the explosion loading wall into shear damage. By strengthening the performance of the RC box wall joints, explosion loading wall, and superstructure joints, and taking measures to reduce the reflection effect, the anti-explosion capacity of caisson wharves can be effectively improved.

Research on the dynamic response of pressurized cylindrical shell structures subjected to a near-field underwater explosion

To study the dynamic response of a pressurized thin-walled circular tube structure subjected to a near-field underwater explosion, deformation and damage tests of a pressurized cylindrical tube shell with different internal pressures and wall thicknesses with the effects of an underwater explosion from 2 g of explosives at different stand-off distances were carried out in a water tank. LS-DYNA finite element software was used to carry out relevant numerical simulations to explore the anti-explosion mechanism of a pressurized cylindrical shell structure affected by factors including the initial internal pressure, the thickness of the cylindrical shell, and the stand-off distance. The simulation inputs are high-speed photography images and the damage results of the cylindrical shell. The simulation results highlight the bubble pulsation, action process deformation, and energy change of the cylindrical shell. The results indicate that an increase in the initial pressure of the cylindrical shell can effectively improve its anti-explosion ability, while the different stand-off distances of r = 12 cm and r = 9 cm correspond to the same initial internal pressure. Increasing the initial internal pressure also causes the deflection difference of the cylindrical shell to decrease. The modeling results also indicate that an increase in the wall thickness may weaken the anti-explosion ability of the cylindrical shell, which has an initial internal pressure of Pr = 0.7 MPa. After an underwater explosion, the maximum displacement difference of a cylindrical shell with thicknesses of h = 1 mm and h = 1.5 mm is less than the maximum rebound distance difference. With this decrease in the distance, the proportion of the high-pressure cylindrical shell subjected to a shock wave increases while the proportion of bubble pulsation decreases. Specifically, the maximum proportions of bubble pulsation are 30% and 92% at the stand-off distances of 3 and 12 cm, respectively.

Experimental Study on Emulsion Explosive Blasting under Different Under-Water Pressure

This paper aims to study the effects of different water depths on the properties of emulsion explosives by use of an emulsion explosive underwater explosion test system for different hydrostatic pressure under the condition of 0.2% sodium nitrite sensitized emulsion explosive blasting model experiments. The results showed that the experiment designed by simulation of underwater explosion test equipment can be used in the explosive performance test sample in the compression state explosion. It can better simulate the explosive environment under different depth conditions. After blasting, the fractal dimension of concrete fragments decreases first and then rises with the increase of water pressure, and reaches an inflection point between 0.3 mpa and 0. 5mpa, which proves that water depth has a certain effect on the performance of explosives, and the effect is not linear distribution. This experimental study could provide a certain basis for subsequent research on underwater explosive characteristics of emulsion explosives.

Effect of Perlite Content on Performance of Emulsion Explosive in Under-Water Environment

Emulsion explosive has been widely used in underwater blasting construction. To study the effect of perlite content on the performance of emulsion explosives under deep water conditions, the performance of emulsion explosives with different applied pressures and different perlite contents was studied by using the self-built underwater explosion test system. The results show that, with the increase of pressure in the water, the energy of emulsion explosive with different content of perlite as sensitizer has a decreasing trend, which is consistent with the actual situation, and when the perlite content is 4%, the sensitized bubble is adiabatically compressed, and the hot spot fully explodes, and its detonation performance is the best.

Influence of water level on RC caisson subjected to underwater explosions

With the increasing significance of marine safety issues, the studies on the underwater blast-resistant performance of wharves, e.g., reinforced concrete (RC) caissons, has become an urgent demand. At present, the influence of water level on caisson subjected to underwater explosions was studied experimentally and numerically, e.g., underwater explosion loading characteristics and dynamic behaviors of caisson. Firstly, four shots of underwater explosion test were carried out both in free field and on a partially submerged caisson specimen, and the overpressure- and deflection-time histories, as well as the structural damage pattern were recorded. Then, the underwater explosion loading characteristics including the preceding blast wave and the succeeding bubble oscillations, the cut-off effect of the water surface, as well as the dynamic behaviors of caisson are comprehensively discussed. Furthermore, both the 1D and 3D finite element (FE) models were established, and by adopting Coupled Eulerian-Lagrangian method and remapping technology, the reliability of the FE models and analysis approach were validated by comparing with the test results. Finally, the influence of water level on the dynamic behaviors of caisson against underwater explosions were numerically examined. It derives that, the empirical formula derived based on spherical charge for underwater explosion peak overpressure is applicable to group charge, while the formula for impulse provides higher prediction on group charge; bubble oscillation has great influence on the impulse of underwater explosions; the unsubmerged part of hydraulic structures suffers slighter damage during underwater explosions than submerged part; the upper part of caisson is more sensitive to the change of water level; the partially submerged caisson shows better blast-resistant performance than fully submerged caisson. The present work could provide helpful reference for the studies on the underwater explosion loadings, as well as the blast-resistant assessment and design of hydraulic structures.

Experimental verification of different analytical approaches for estimating underwater explosives

The clearance of underwater ordnance is one of the most complex tasks entrusted to appropriately trained and equipped soldiers. State-of-the-art knowledge in this area is rarely published and is most often possessed by a narrow group of navy specialists. The aim of this paper was to find a link between the existing mathematical models for the peak pressure of underwater explosion with measurements of small charge detonations for long ranges to the observation point in real life scenarios. We have shown the results of the research in which the underwater explosion tests were presented for different TNT equivalents and standoff distances and thus distance ratios. The curves of pressure versus time of ignition were reported. The measurements were confronted with empirical formulas. The comparison showed large, but expected, differences, since the empirical formulas are advised for smaller distance ratios. Based on the conclusions from the study, the new methodology to identify the loading from underwater explosions based on a database collected was postulated. By creating a survey methodology for ships crew for recording explosion parameters, a large number of events can be registered without a strict setup of the test area. The database obtained can be used by military commanders to identify the explosive hazard in the Baltic Sea region.