Explosive Blast Loading Research Articles

Reprint of: Experimental investigation and simplified modeling of response of steel plates subjected to close-in blast loading from spherical liquid explosive charges

Detonations of nitromethane spherical charges have been carried out to study close-in blast loading of steel plates and the effectiveness of several protective solutions. Three types of bare steel plates, namely mild steel, high-strength steel, and stainless steel were subjected to explosive blast loading. Steel plates of the same type with polyurea coating and composite covers were also subjected to localized blast loading. During an explosive field trial, the blast pressures and displacements of steel plates were measured. Additionally, loading of steel plates by the impinging detonation products was captured by high-speed video recordings. This experimental program has produced results which can be used to calibrate numerical models and to refine the simplified models for predicting blast loads and response of structural elements due to close-in detonations. The effectiveness of polyurea coating for enhancing blast protection of steel plated structures is discussed. The engineering-level model for predicting the blast impact impulse of the detonation gases from the charges in close proximity from the target is introduced and validated using the experimental results obtained during the course of the explosive trials.

Properties and Behavior of Geopolymer Concrete Subjected to Explosive Air Blast Loading: A Review

The severe damage to civilian buildings, public area, jet aircraft impact and defense target under explosive blast loading can cause a huge property loss. Most of researcher discusses the topics on design the concrete material model to sustain againts the explosive detonation. The implementation of modern reinforcement steels and fibres in ordinary Portland cement (OPC) concrete matrix can reduce the extreme loading effects. However, most researchers have proved that geopolymer concrete (GPC) has better mechanical properties towards high performance concrete, compared to OPC. GPC has the high early compressive strength and high ability to resist the thermal energy from explosive detonation. In addition, OPC production is less environmental friendly than geopolymer cement. Geopolymer used can lead to environmental protection besides being improved in mechanical properties. Thus, this paper highlighted on an experimental, numerical and the analytical studies cause of the explosive detonation impact to concrete structures.

Experimental investigation and simplified modeling of response of steel plates subjected to close-in blast loading from spherical liquid explosive charges

Detonations of nitromethane spherical charges have been carried out to study close-in blast loading of steel plates and the effectiveness of several protective solutions. Three types of bare steel plates, namely mild steel, high-strength steel, and stainless steel were subjected to explosive blast loading. Steel plates of the same type with polyurea coating and composite covers were also subjected to localized blast loading. During an explosive field trial, the blast pressures and displacements of steel plates were measured. Additionally, loading of steel plates by the impinging detonation products was captured by high-speed video recordings. This experimental program has produced results which can be used to calibrate numerical models and to refine the simplified models for predicting blast loads and response of structural elements due to close-in detonations. The effectiveness of polyurea coating for enhancing blast protection of steel plated structures is discussed. The engineering-level model for predicting the blast impact impulse of the detonation gases from the charges in close proximity from the target is introduced and validated using the experimental results obtained during the course of the explosive trials.

Risk-based blast-load modelling: Techniques, models and benefits

There are many deterministic blast-load methods currently in use, such as (1) those for the ready calculation of explosive pressure, impulse and duration; (2) the derivation of explosive safety distances; or (3) the determination of safety hazards (and other consequences) following an explosive’s detonation. In this article, we argue that deterministic blast-loading methods do not fully account for society’s usual acceptance (or rejection) of the risks associated with damage, safety and/or injury as a result of an explosive blast-load. This article details the state of the art of probabilistic blast-load modelling that supports a quantitative calculation of risk, with respect to damage, safety and injury. The probabilistic models draw data from the literature and from our own field trials. The article details the benefits that flow from this form of blast-load characterisation and concludes with a discussion on how probabilistic methods be used to derive cost–benefit advice with respect to any proposed risk mitigation solution.

Physical mechanisms for near-field blast mitigation with fluid containers: Effect of container geometry

The use of external fluid containers for reducing the deformation of steel targets subjected to near-field explosive blast loading was investigated through experimental testing and numerical simulation. The fluid containers were placed between the explosive charge and steel target to mitigate both the transient and permanent deformation of the target. The effect of fluid container geometry on blast mitigation was evaluated by varying both the height and width of the containers while maintaining a constant volume of fluid, as well as by varying the height and width independently. The best performing container geometry provided a 65% reduction in the dynamic deformation to a reference steel target, which is more than twice the reduction provided by a steel applique panel of equivalent areal density. The blast mitigation effectiveness of the fluid containers was dependent on their geometry; for the same container volume, variations in container geometry were found to affect the peak dynamic deformation of the steel target by up to 100%. Numerical simulation of the blast experiments was performed using ANSYS® AUTODYN® and validated through comparison with temporally-resolved deformation signals. The validated numerical model was used to identify the physical mechanisms responsible for blast mitigation. The time-scale of the loading was computed to be too short for container break-up, proving that momentum extraction and water evaporation were not significant mitigation mechanisms. Whilst the loading time-scale was also too short for water cavitation to be a major mitigation mechanism, the development and collapse of cavitation bubbles were predicted to affect the loading on the steel targets. The major mitigation mechanisms were analysed to be shadowing of the detonation products and the generation of rarefaction waves, both of which are influenced by the container geometry. Whilst the fluid itself does not act as an energy absorber, the sound speed of the fluid is important due to the shock-impedance mismatch between the air and the water container and the subsequent pressure wave transmission at sonic speed through the fluid.

Experimental and numerical study on the dynamic response of RC slabs under blast loading

Abstract Anti-blast performance and damage characteristics of reinforced concrete slab with different reinforcement ratios were analyzed in the present study through both blast experiments and numerical simulations. Three sets of slabs with different reinforcement ratios under 0.13 kg and 0.19 kg TNT explosive blast loading were conducted. The experimental and numerical results show that different damage features are observed in the different tests. On the one hand, the increase of explosive charge is shown to gradually change the damage degree of RC slab. The crack diameter and spallation area of larger mass explosive test is greater than that of small mass explosive test. On the other hand, with an increasing reinforcement ratio, the damage degree, deflection and the spall radius all decrease. The results indicate that the reinforcement ratio has great influence on the survivability of RC slabs when subjected to blast loading. Ten additional simulations with different reinforcement ratios and TNT masses were conducted. The results show the deflection thickness ratio of RC slab is inversely proportional to the scale distance and the reinforcement ratio. Based on the experimental and numerical results, an empirical expression on deflection thickness ratio was obtained which considered both the scale distance and the reinforcement ratio.

The effect of explosive blast loading on human neuroblastoma cells

Diagnosis of mild to moderate traumatic brain injury is challenging because brain tissue damage progresses slowly and is not readily detectable by conventional imaging techniques. We have developed a novel in vitro model to study primary blast loading on dissociated neurons using nitroamine explosives such as those used on the battlefield. Human neuroblastoma cells were exposed to single and triple 50-psi explosive blasts and single 100-psi blasts. Changes in membrane permeability and oxidative stress showed a significant increase for the single and triple 100-psi blast conditions compared with single 50-psi blast and controls.

Reconstruction of improvised explosive device blast loading to personnel in the open

Significant advances in reconstructing attacks by improvised explosive devices (IEDs) and other blast events are reported. A high-fidelity three-dimensional computational fluid dynamics tool, called Second-order Hydrodynamic Automatic Mesh Refinement Code, was used for the analysis. Computer-aided design models for subjects or vehicles in the scene accurately represent geometries of objects in the blast field. A wide range of scenario types and blast exposure levels were reconstructed including free field blast, enclosed space of vehicle cabin, IED attack on a vehicle, buried charges, recoilless rifle operation, rocket-propelled grenade attack and missile attack with single subject or multiple subject exposure to pressure levels from \(\sim \)27.6 kPa (\(\sim \)4 psi) to greater than 690 kPa (\(>\)100 psi). To create a full 3D pressure time-resolved reconstruction of a blast event for injury and blast exposure analysis, a combination of intelligence data and Blast Gauge data can be used to reconstruct an actual in-theatre blast event. The methodology to reconstruct an event and the “lessons learned” from multiple reconstructions in open space are presented. The analysis uses records of blast pressure at discrete points, and the output is a spatial and temporal blast load distribution for all personnel involved.

The Dynamic Behaviour of the Floor of a Surrogate Vehicle Under Explosive Blast Loading

<p class="1Body">Improvised Explosive Devices have been the signature weapon in the recent conflicts in Iraq and Afghanistan. High-rate axial forces exerted by the vehicle floor to the lower limbs of occupants have been the cause of severe injuries. In order to gain a greater understanding of the mechanisms of these injuries so that countermeasures can be developed, one is required to know how the vehicle floor behaves; therefore, the purpose of this study was to characterise the behaviour of a vehicle floor surrogate to a range of explosive loads. Explosive loads between 1 and 6 kg TNT were detonated beneath a vehicle floor surrogate resulting in peak floor velocities between 5.8 and 80.5 m/s reached in a time between 0.10 and 3.13 ms. The data can now be used to (a) test numerical models of blast and its interaction with structures for validity, and (b) ensure that the velocity profiles replicated in a laboratory environment to understand human tolerance to injury are relevant to the blast process. These will ensure that preventive measures are developed based on realistic physical and numerical models of injury.</p>

The Dynamic Behaviour of the Floor of a Surrogate Vehicle Under Explosive Blast Loading

<p class="1Body">Improvised Explosive Devices have been the signature weapon in the recent conflicts in Iraq and Afghanistan. High-rate axial forces exerted by the vehicle floor to the lower limbs of occupants have been the cause of severe injuries. In order to gain a greater understanding of the mechanisms of these injuries so that countermeasures can be developed, one is required to know how the vehicle floor behaves; therefore, the purpose of this study was to characterise the behaviour of a vehicle floor surrogate to a range of explosive loads. Explosive loads between 1 and 6 kg TNT were detonated beneath a vehicle floor surrogate resulting in peak floor velocities between 5.8 and 80.5 m/s reached in a time between 0.10 and 3.13 ms. The data can now be used to (a) test numerical models of blast and its interaction with structures for validity, and (b) ensure that the velocity profiles replicated in a laboratory environment to understand human tolerance to injury are relevant to the blast process. These will ensure that preventive measures are developed based on realistic physical and numerical models of injury.</p>

In vitro studies of primary explosive blast loading on neurons.

In a military setting, traumatic brain injury (TBI) is frequently caused by blast waves that can trigger a series of neuronal biochemical changes. Although many animal models have been used to study the effects of primary blast waves, elucidating the mechanisms of damage in a whole-animal model is extremely complex. In vitro models of primary blast, which allow for the deconvolution of mechanisms, are relatively scarce. It is largely unknown how structural damage at the cellular level impacts the functional activity at variable time scales after the TBI event. A novel in vitro system was developed to probe the effects of explosive blast (ranging from ∼25 to 40 psi) on dissociated neurons. PC12 neurons were cultured on laminin-coated substrates, submerged underwater, and subjected to single and multiple blasts in a controlled environment. Changes in cell membrane permeability, viability, and cell morphology were evaluated. Significant increases in axonal beading were observed in the injured cells. In addition, although cell death was minimal after a single insult, cell viability decreased significantly following repeated blast exposure.

Spatial reliability analysis of explosive blast load damage to reinforced concrete columns

Columns are the key load-bearing elements in frame structures and exterior columns are probably the most vulnerable structural components to terrorist attack. In this paper, a spatial reliability analysis is conducted to predict the damage for reinforced concrete (RC) columns subject to explosive blast loading. The spatial variability of material and dimensional properties of RC columns are modelled by stationary and non-stationary random fields. The variability of blast loading is also taken into consideration. Monte Carlo simulation and numerical methods are used to derive Blast Reliability Curves for RC columns under explosive loading for a number of terrorism threat scenarios, based on a high–fidelity physics-based computer programme LS-DYNA to estimate design and residual axial load-carrying capacity of RC columns. It was found that spatial variability has a significant effect on structural reliabilities and the spatial model will lead to more accurate predictions of damage and safety risks.

Reliability-Based Design Load Factors for Explosive Blast Loading

AbstractReliability-based design allows the decision maker to select the level of reliability for a specific blast loading scenario and key to this is an understanding of airblast uncertainty. Hence, explosive field trials have been conducted in Australia that measured the variability of free-field blast loading caused by military standard plastic explosives. The results have revealed a high level of variability of peak incident pressure, impulse, and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The accuracy of predictive blast load models (model error) was also assessed. A probabilistic blast load computer model is revised to capture these observed variabilities. The effect of a 20% mass-increase safety factor typically applied to explosive mass on the probability of exceeding a design blast load is assessed. Reliability-based load factors are calculated where the nominal load is multiplied by the load factor to ensure that the actual load is e...

Appropriate Coupling Solvers for the Numerical Simulation of Rolled Homogeneous Armor Plate Response Subjected to Blast Loading

Rolled homogeneous armor (RHA) plate subjected to blast loading is a complex problem involving the nonlinear fluid-structure interaction. The numerical techniques using the spatial discretization scheme that has been provided as a solver in the AUTODYN computer code will be used in this study in order to predict the RHA response subjected to explosive (TNT) blast loading. The final deflection will be used as a reference in order to identify the suitable solver for both materials RHA and TNT; then the plastic deformation will be chosen in the simulation process. Instead of using the same solver for RHA and TNT domains, the optimization of solver can be achieved if it is only used in an appropriate domain, or in other words, a different domain will be using different solver. The solvers, which were available in AUTODYN, were used in the analysis of impact and explosion or fluid-structure interaction. Therefore, in this paper, we will determine the suitable solver for both materials (TNT and RHA plate), and the appropriate interaction coupling solver will be obtained. Defining TNT and RHA plates using the Arbitrary Lagrangian Eulerian solver has found the best coupling solver for this case study when compared with existing experimental data. This coupling solver will be used for future analysis in simulating blast-loading phenomena.

Modelling and Dynamic Response of Steel Reticulated Shell under Blast Loading

Explicit finite element programme LS-DYNA was used to simulate a long-span steel reticulated shell under blast loading to investigate the structural dynamic responses in this paper. The elaborate finite element model of the Kiewitt-8 single-layer reticulated shell with span of 40 m subjected to central blast loading was established and all the process from the detonation of the explosive charge to the demolition, including the propagation of the blast wave and its interaction with structure was reproduced. The peak overpressure from the numerical analysis was compared with empirical formulas to verify the credibility and applicability of numerical simulation for blast loading. The dynamic responses of the structure under blast loading with different TNT equivalent weights of explosive and rise-span ratios were obtained. In addition, the response types of Kiewitt-8 single-layer reticulated shell subjected to central explosive blast loading were defined.

Modelling and Dynamic Response of Steel Reticulated Shell under Blast Loading

Explicit finite element programme LS-DYNA was used to simulate a long-span steel reticulated shell under blast loading to investigate the structural dynamic responses in this paper. The elaborate finite element model of the Kiewitt-8 single- layer reticulated shell with span of 40 m subjected to central blast loading was established and all the process from the detonation of the explosive charge to the demolition, including the propagation of the blast wave and its interaction with structure was reproduced. The peak overpressure from the numerical analysis was compared with empirical formulas to verify the credibility and applicability of numerical simulation for blast loading. The dynamic responses of the structure under blast loading with different TNT equivalent weights of explosive and rise-span ratios were obtained. In addition, the response types of Kiewitt-8 single-layer reticulated shell subjected to central explosive blast loading were defined.

Example Validation of Numerical Modeling of Blast Loading

This paper reports a follow-up feasibility study on different approaches for numerical modeling of blast loads, implemented recently in a few commercial programs based on finite element method and explicit time integration. Four approaches have been considered including: explicit blast wave representation using fluid-structure interaction (FSI) with 2D and 3D multi-material arbitrary Lagrangian-Eulerian (ALE) formulations, direct application of empirical explosive blast loads on structures, and the most recent, combined method, in which direct empirical loading is applied to a reduced ALE domain. Each of these approaches has its own strengths and weaknesses, although the last one seems to be the most universal. Based on the published experimental data, a benchmark problem was selected, which considers a pressure loading exerted by explosion of near field hemispherical charges on a rigid steel plate. The comparison is done in terms of pressure peaks (overpressure) and time histories of reflected pressure, and reflected specific impulses.

Blast Load Variability and Accuracy of Blast Load Prediction Models

A statistical analysis of explosive blast loading field (test) data has revealed a high level of variability of peak reflected pressure, impulse and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The model error (accuracy) of a widely used predictive blast load model is also assessed. A probabilistic model of blast loading is then developed that considers variability and/or uncertainty of explosive mass, net equivalent quantity of an explosive in terms of TNT mass, stand-off distance, air temperature, air pressure, inherent variability and model error. Two widely used explosives are considered: Tritonal (military) and ANFO (terrorism). This type of statistical and probabilistic analysis is essential for structural reliability analysis of structures subject to explosive blast loading where load variability is an important contributor to damage and safety risks. It was found that the TM5–1300 design values for peak reflected pressure and time of positive phase duration adequately represent median values of the probability distribution of blast loads. The TM5–1300 design values for peak reflected impulse were 40% higher than median values with probabilities of exceedance of only 4% to 23%. This over-estimation of actual blast loads on a structure may lead to conservative design outcomes.

A coupling of empirical explosive blast loads to ALE air domains in LS-DYNA®

A coupling method recently implemented in LS-DYNA® allows empirical explosive blast loads to be applied to air domains treated with the multi-material arbitrary Lagrangian-Eulerian (ALE) formulation. Previously, when simulating structures subjected to blast loads, two methods of analysis were available: a purely Lagrangian approach or one involving the ALE and Lagrangian formulations coupled with a fluid-structure interaction (FSI) algorithm. In the former, air blast pressure is computed with empirical equations and directly applied to Lagrangian elements of the structure. In the latter approach, the explosive as well as the air are explicitly modeled and the blast wave propagating through the ALE air domain impinges on the Lagrangian structure through FSI. Since the purely Lagrangian approach avoids modeling the air between the explosive and structure, a significant computational cost savings can be realized – especially so when large standoff distances are considered. The shortcoming of the empirical blast equations is their inability to account for focusing or shadowing of the blast waves due to their interaction with structures which may intervene between the explosive and primary structure of interest. The new method presented here obviates modeling the explosive and air leading up the structure. Instead, only the air immediately surrounding the Lagrangian structures need be modeled with ALE, while effects of the far-field blast are applied to the outer face of that ALE air domain with the empirical blast equations; thus, focusing and shadowing effects can be accommodated yet computational costs are kept to a minimum. Comparison of the efficiency and accuracy of this new method with other approaches shows that the ability of LS-DYNA® to model a variety of new blast scenarios has been greatly extended.

Model validation and parametric study on the blast response of unreinforced brick masonry walls

Numerical simulations are carried out to estimate the response and damage of unreinforced brick masonry walls subjected to explosive blast loading based on the transient dynamic finite element program LS-DYNA. A previously developed dynamic plastic damage model was used for brick and mortar. A new model for strain rate effects of bricks and mortar is included in the numerical analysis. The results obtained from the numerical models are compared with field test data and good agreement can be found. Parametric studies are conducted to evaluate the effect of material strength, boundary conditions, and thickness of the wall on the blast response of unreinforced brick masonry walls. It was found that boundary conditions and wall thickness significantly affect the blast response, while the effect of material strength is relatively small.