Blast Impulse Research Articles

Dynamic response of UHMWPE/polyurea composite plates under combined blast and ballistic impact

Combined load caused by blast impulse and fragmentation impact poses a synergetic damage threat to the protective structure. To improve the blast and ballistic impact resistance of Ultra-high molecular weight polyethylene (UHMWPE), polyurea coated Ultra-high molecular weight polyethylene structure was proposed, and the composite structures with different coating thickness and coating position were prepared. Composite projectiles formed by combining foam projectiles and steel projectiles were launched by light gas gun to simulate the combined load of explosion impact and fragmentation. Comparative experimental studies were carried out. The experimental results show that the polyurea layer has good elastic properties, preventing the excessive deformation of the PE layer. The polyurea coating position and the time interval of the combined load show significant influence on the impact resistance of the composite structure. When the load was relatively low, PE plate with polyurea coating on booth face has both the advantages of PE plate with coating on the front and back face, but when the load increased, the impact resistance potential of polyurea layer was not fully developed. With the increase of the combined load, structures with polyurea coating on the back face has a good resistance of combined impact.

Cumulative Blast Impulse Is Predictive for Changes in Chronic Neurobehavioral Symptoms Following Low Level Blast Exposure during Military Training.

Cumulative low-level blast exposure during military training may be a significant occupational hazard, increasing the risk of poor long-term outcomes in brain function. US Public Law 116-92 section717 mandates that US Department of Defense agencies document the blast exposure of each Service member to help inform later disability and health care decisions. However, which empirical measures of training blast exposure, such as the number of incidents, peak overpressure, or impulse, best inform changes in the neurobehavioral symptoms reflecting brain health have not been established. This study was approved by the US Army Special Operations Command, the University of North Carolina at Chapel Hill, and the VA Puget Sound Health Care System. Using methods easily deployable across different organizational structures, this study sought to identify and measure candidate risk factors related to career occupational blast exposure predictive of changes in neurobehavioral symptom burden. Blast dosimetry-symptom relationships were first evaluated in mice and then tested in a military training environment. In mice, the righting time neurobehavioral response was measured after exposure to a repetitive low-level blast paradigm modeled after Special Operations training. In the military training environment, 23 trainees enrolled in a 6-week explosive breaching training course, 13 instructors, and 10 Service member controls without blast exposure participated in the study (46 total). All participants provided weekly Neurobehavioral Symptom Inventory (NSI) surveys. Peak blast overpressure, impulse, total number of blasts, Time in Low-Level Blast Occupation, and Time in Service were analyzed by Bayesian analysis of regression modeling to determine their probability of influence on the post-training symptoms reported by participants. We tested the hypothesis that cumulative measures of low-level blast exposure were predictive of changes in neurobehavioral symptoms. In mice, repetitive blast resulted in reduced righting times correlated with cumulative blast impulse. In Service members, peak blast overpressure, impulse, total number of blasts, Time in Low-Level Blast Occupation, and Time in Service all showed strong evidence of influence on NSI scores after blast exposure. However, only models including baseline NSI scores and cumulative blast impulse provided significant predictive value following validation. These results indicate that measures of cumulative blast impulse may have utility in predicting changes in NSI scores. Such paired dosimetry-symptom measures are expected to be an important tool in safely guiding Service members' occupational exposure and optimizing force readiness and lethality.

Managing occupational impulsive noise from explosive depth hardening operations

The assessment and identification of measures to eliminate or reduce risks from occupational exposure to impulsive noise for the protection of hearing of employees in industry is an important yet comparatively neglected technical area. The aim of this work is to examine the current best practice to assess auditory hazards associated with impulsive blast noise generated by an infrastructure test process at a UK-based test site. A summary of the literature is presented on the measurement methodologies, hearing conservation and relevant guidance for the selection of hearing protection within the context of near-field impulsive noise. The current UK best practice recommends the adapted HML method from Defence Standard 0027:2015, using a C-peak measurement of exposure to compare with the national regulations. On-site measurements of personnel exposure were made at the DNV Spadeadam Testing and Research Site (STaR), of an industrial process known as Explosive Depth Hardening. Analyses of the trials data show that the C-peak personnel exposures resulted in acceptable levels below the 140 dBCpk limit within the national regulations when using the prescribed hearing protection, according to the adapted HML method. Waveforms recorded of repeated charge sizes were uncorrelated and additional signal artefacts were present. It is concluded that the adapted HML assessment is unclear on how excessive low-frequency content and multiple pressure peaks are accounted for in the assessment of hearing protector performance. The implication of this work is that further research is required to improve current best practice to quantify the uncertainties introduced by the additional characteristics found within real impulsive noise exposures.

Study on the blast impulse characters of high explosive charge with reactive metal casing

Study on the blast impulse characters of high explosive charge with reactive metal casing

Performance-based blast-resistant design of RC bridge piers under vehicular bombs

Bridge piers are the critical components to support the superstructures and the blast resistance of piers has attracted extensive attention considering the ever growing deliberate and accidental explosion attacks on bridge structures. However, most of the existing studies focus on the blast-induced dynamic response of a single pier without considering the bridge redundancy, even less the actual traffic performance of the entire bridge. This paper aims to propose a performance-based blast-resistant design approach of RC bridge piers under explosions of vehicular bombs. Firstly, the distribution model of blast impulse on bridge piers is proposed with considering both the ground reflections and diffractions of piers based on the validated finite element analysis (FEA) approach. Then, the fiber beam element-based model and the above blast impulse distribution model were validated based on the dynamic monotonic loading test and the explosion test on RC frame column. Furthermore, the simplified fiber element beam-based prototype RC bridge was established and the parametric studies were performed. Finally, the response surface methodology was adopted and the performance-based blast-resistant design procedure for three design basis threats specified in FEMA, i.e., cargo van bomb, small moving van bomb, moving van bomb, was proposed with utilizing the relative vertical displacement of the mid-bent as the performance index. It derives that, (i) the proposed distribution model of blast impulse is applicable to explosions at scaled distances of 0.5–2.1 m/kg1/3; (ii) the fiber beam element-based model can well describe the global response of the blast-exploded columns/piers; (iii) the proposed performance-based blast-resistant design approach can provide an efficient tool for bridge engineers.

Rigid-plastic membrane response of thin plates under impulsive blast loads using the extended Hamilton principle

The response of plates subjected to blast loads is of considerable scientific interest. The loading imparted to a structure following a close-in detonation of a high explosive is typically high in magnitude, near-impulsive, spatially non-uniform, with localised variability and a high dependence on factors such as charge shape, position, and composition. The resulting structural response may induce large displacements in materials whose properties may not be fully characterised. In order to properly account for the effects of such intrinsic and extrinsic uncertainties, modelling approaches must balance the competing demands of accuracy and low computational demand. This article applies the extended Hamilton’s principle to rigid-plastic thin plates subjected to impulsive blast loads to derive the governing equation of motion without a prior assumption of the initial specific impulse distribution. Closed-form solutions to predict the plastic response are derived for rectangular and circular plates. The analytical models for uniform specific impulses are found to be in good agreement with high-fidelity numerical simulations performed using LS-DYNA and experimental data available in the literature.

Comparative study of the explosive blast resistance of metal and composite materials used in defence platforms

Naval ships, military aircraft and land defence platforms are mostly constructed using steel, aluminium alloy, carbon fibre composite and/or glass fibre composite materials. Defence platforms are at risk from shock wave loads generated by explosive events, and therefore it is imperative that the construction materials are resistant to blast-induced deformation and damage. A comparative assessment is presented into the dynamic deformation and damage of metals and composites representative of naval construction materials when subjected to explosive air blasts. Flat plates of equal thickness (4 mm) or plates of similar areal density (in the range 6.2–9.2 kg/m2) made of the four materials were subjected to explosive blasts. Experimental blast testing and finite element (FE) modelling revealed that when the plate thickness was the same (4 mm) then the steel experienced less deformation (by ∼50–60%) and plasticity than the aluminium alloy due to its higher mechanical properties. The steel and aluminium plates were more resistance to blast-induced deformation (by up to ∼260–320% and ∼130–145% respectively) than the composite materials of the same thickness (4 mm). However, when the materials are compared on similar areal density, which is critical for lightweight design, the blast performance of the composite materials was similar to aluminium alloy and superior to steel. Deformation of the steel was up to 50% higher than the other construction materials, with the percentage increase rising with blast impulse.

A Study on the Bending of Laminated Glass Under Blast Loading

BackgroundThe bending behaviour of laminated glass plays an important role in determining its overall response to blast loading. It is costly and difficult to characterise the bending behaviour by carrying out full-scale blast tests, therefore an alternative method is required.ObjectiveThe objective of this study is to understand the response of laminated glass under high-rate bending in the laboratory at rates representative of blast loading.MethodsIn this paper a novel testing method is presented in which laminated glass strips of 700 mm long by 60 mm wide are tested up to speeds of 10 m/s in the laboratory. The laminated glass is accelerated to speeds comparable to blast loading and then brought to rest at its edges to mimic impulsive blast loading conditions. Different interlayer thickness, impact speeds, and boundary conditions were explored. Additionally, modelling methods were used to study the flexural rigidity of post-cracked laminated glass.ResultsFrom the experiments it was found that the interlayer thickness plays a key role in determining whether the dominant failure mechanism is de-bonding of interlayer from the glass or interlayer tearing. In addition, it was found that by allowing the frame to bend under loading, the laminated glass can carry greater loads without failure. Finally, an iterative method was used to quantify the flexural rigidity of post-cracked laminated glass depending on the speed of travel. This is a novel finding as it is usually assumed that laminated glass behaves like a membrane in the post-cracked phase of the response.ConclusionIn modelling and design of laminated glass structures under blast loading, post-crack flexural rigidity must be taken into account. Additionally, having novel frame designs to add further load bearing capacity to the framing members, plays a key role in reducing the load intensity on the laminated glass structure.

Response of thin walled transversely stiffened clamped circular plates under uniform impulsive loads

Paper presents numerical models based on detailed characterization of various uncoupled damage models in a finite element analysis (FEA) setup to assess large deformations and observed ductile fracture failure modes of fully clamped circular plates as well as transversely stiffened circular plates in cross stiffened configurations under uniform impulsive loads. The numerical schemes have been based on a detailed definition of the constitutive properties based on inverse FEA simulations of the uniaxial tension test for the calibration of material and failure parameters. Experiments have been conducted using two types of freshly prepared mild steel uniaxial tension test specimens covering the envisaged range of stress tri-axialities to establish the steel plate material and fracture characteristics necessary for the calibration of the presented phenomenological damage models. Published results based on extensive experimental works by various authors on response of thin walled clamped circular plates under transversely applied uniform air blast loads, manifesting in large plastic deformations, thinning and tearing under various ductile fracture modes, have been used in the performance assessment of presented numerical models and procedure, which incorporate different damage models including temperature effects due to plastic dissipation. Based on evaluated performance of the discussed failure models within the FEA setup, a hybrid damage model with a tri-axiality based two part ductile fracture locus has been proposed, which shows very good correlation with the published experimental results, presented in terms of non-dimensional parameters over a wide range of impulsive loading. The validated numerical setup using the proposed hybrid damage model has also been used to predict the effect of transverse cross stiffened configurations of flat bar stiffeners on large deformations and ductile fracture of clamped circular plates under transverse uniform impulsive blast loads, along with some key insights in the evolution of plastic zones and damage progression.

Prediction of Initial and Striking Velocity of Primary Fragments from Cased Spherical Explosive inside Steel Cubical Structure

Usually, energy generated from an explosive’s detonation is transferred partly in the form of the blast impulse and some in the form of the kinetic energy of casing fragments. When detonation occurs in an explosive casing, it breaks the casing into fragments of different weights with varying velocities. The extent of destruction by these energized fragments depends upon the initial velocity they gain after an explosion. The momentum gained by the fragments decides the capability to perforate a barrier or propagate an explosion. A three-dimensional non-linear FEA method is used to model a box-shaped steel structure. This box-shaped structure is subjected to an internal cased explosion for estimating the initial and striking velocities of primary fragments. The effect of varying charge weight and the effect of the sacrificial wall on the initial and striking velocity of fragments via numerical simulations are also carried out. The initial and striking velocity values obtained through simulation are compared with the design guidelines of the code-based approach, and a good agreement is reported.

Experimental study on damage magnification effect of lightweight auxetic honeycomb protective panels under close-in blast loads

Sandwich panels/sacrificial cladding systems composed of an auxetic core sandwiched between two faceplates can be considered an effective protective measure for reinforced concrete structures from blast loads. In this study, the effectiveness of re-entrant honeycomb core sandwich (RHS) protective panel systems, which exhibit a negative Poisson’s ratio, to protect one-way simply supported reinforced concrete (RC) slabs subjected to a close-range detonation from high explosive charges was experimentally evaluated. Three large-scale field blast trials were carried out, namely an RC slab without protection as the reference test and two RC slabs with RHS protective systems under similar blast loading conditions. The RC slabs with RHS protective systems experienced catastrophic failure, unlike the unprotected reference slab that experienced only localised concrete damage. LS-DYNA numerical models were validated and agreed well with the experimental results. It was demonstrated that the transferred blast impulse to the main structure can be magnified by a factor of 1.6 by using an RHS protective system compared to an unprotected structure. Furthermore, the effect of the mass of the protective system was numerically studied. The numerical results showed that the blast protection level of the main structure is governed by the inertial resistance of the protective system rather than through energy absorption of the auxetic honeycomb core structure.

Revealing the Effect of Skull Deformation on Intracranial Pressure Variation During the Direct Interaction Between Blast Wave and Surrogate Head.

Intracranial pressure (ICP) during the interaction between blast wave and the head is a crucial evaluation criterion for blast-induced traumatic brain injury (bTBI). ICP variation is mainly induced by the blast wave transmission and skull deformation. However, how the skull deformation influences the ICP remains unclear, which is meaningful for mitigating bTBI. In this study, both experimental and numerical models are developed to elucidate the effect of skull deformation on ICP variation. Firstly, we performed the shock tube experiment of the high-fidelity surrogate head to measure the ICP, the blast overpressure, and the skull surface strain of specific positions. The results show that the ICP profiles of all measured points show oscillations with positive and negative change, and the variation is consistent with the skull surface strain. Further numerical analysis reveals that when the blast wave reaches the measured point, the peak overpressure transmits directly through the skull to the brain, forming the local positive ICP peak, and the impulse induces the local inward deformation of the skull. As the peak overpressure passes through, the blast impulse impacts the nearby skull supported by the soft and incompressible brain tissue and extrudes the skull outward in the initial position. The inward and outward skull deformation leads to the oscillation of ICP. These numerical analyses agree with experimental results, which explain the appearance of negative and positive ICP peaks and the synchronization of negative ICP with surface strain. The study has implications for medical injury diagnosis and protective equipment design.

Application of transfer learning for the prediction of blast impulse

Transfer learning offers the potential to increase the utility of obtained data and improve predictive model performance in a new domain, particularly useful in an environment where data is expensive to obtain such as in a blast engineering context. A successful application in this respect will improve existing surrogate modelling approaches to allow for holistic and efficient strategies to protect people and structures subjected to the effects of an explosion. This paper presents a novel application of transfer learning for the prediction of peak specific impulse where we demonstrate that previous knowledge learned when modelling spherical charges can be transferred to provide a performance benefit when modelling cylindrical charges. To evaluate the influence of transfer learning, two artificial neural network architectures were stress tested for three levels of random data removal: the first model (NN) did not implement transfer learning whilst the second model (TNN) did by including a bolt-on network to a previously published NN model trained on the spherical dataset. It is shown the TNN consistently outperforms the NN, with this out-performance increasing as the proportion of data removed increases and showing statistically significant results for the low and high threshold with less variability in all cases. This paper indicates transfer learning applications can be used successfully with considerable benefit with respect to surrogate modelling in a blast engineering context.

Investigation of effect of perforations in honeycomb sandwich structure for enhanced blast load mitigation

Sandwich structure is one of the blasts protecting and energy absorbing materials with different types of light weight cores. This article aimed at investigating blast response of hexagonal honeycomb sandwich structure having perforations along the cell height of core over conventional honeycomb cores. The study discussed the mechanics of deformation behavior of perforated sandwich structure to improve the energy absorption characteristics of the bare honeycomb core sandwich structure. Detailed numerical analysis is conducted to accurately produce the deformation process with finite element analysis using explicit software LS-DYNA®. Blast load resulting from 1 kg TNT on the sandwich structure is applied using Conventional Weapons Effects Program (ConWep) function available in LS-DYNA. Several different parameters consisting of varying sizes of perforation by changing d/l ratio, shape, number of perforations and different facesheet and backsheet thicknesses, and different scaled distances are investigated in detail. The results indicated that both size and shape and number of perforations have significant influence on reduction of blast impulse. The variation of facesheet and backsheet thicknesses without changing the overall thickness of the structure also has evident effect in blast resistance capability of perforated honeycomb sandwich structure. The blast mitigation and energy absorption capacity of honeycomb core sandwich structure can be improved with the provision of perforations and optimizing the arrangement of holes. The perforated honeycomb core is further investigated based on analytical formulation developed using single degree of freedom (SDOF) system analysis approach. Optimization study is done further to get the best configuration based on different design variable limits.

Paper tube-guided blast response of sandwich panels with auxetic re-entrant and regular hexagonal honeycomb cores – An experimental study

Auxetic honeycomb structures have drawn increasing attention for impact/blast protection purposes owing to their superior indentation resistance and energy absorption capability. However, few comparative study on the blast performance among sandwich structures with different auxetic and non-auxetic cores has been performed to date. In this paper, the dynamic behaviors of metallic sandwich panels with auxetic re-entrant and regular hexagonal honeycomb cores (i.e. RHSPs and HHSPs) under the paper tube-guided explosions were investigated by a series of blast tests. The failure modes and underlying mechanisms of the target panels with different core relative densities under different impulse levels were classified and analyzed in detail. The panel blast resistance was evaluated by means of the back-face maximum permanent deflections, introducing the testing results of double arrowhead honeycomb sandwich panels (DAHSPs) in a separate paper. It indicates that the introduction of the paper tube achieved the concentration of shock energy, thus aggravating the panel central damage levels remarkably. For the RHSPs with NPR effect, the predominated failure modes of front faces transitioned essentially from the complete petal-like tearing to a local inner dome as the blast impulse decreased. The ones for the back faces ranged from partial tearing to pure global bending deformation, while the core failure modes tuned from central crushing and peripheral buckling to global compression deformation with central shrinkage and boundary adduction. Relative to the RHSPs, the equivalent HHSPs with a higher compressive strength were less insensitive to the blast intensity. Within the scope of present study, the DAHSPs could experience lower back face deflections than those of RHSPs regardless of core relative density. The auxetic honeycomb sandwich panels not always exhibited better over the non-auxetic HHSPs, which depended greatly on the blast impulse and core density level. This comparative research provides a useful reference for the auxetic sandwich honeycomb core design in protection applications.

Experimental study of the bond interaction between CFRP and concrete under blast loading

Specific to blast loading, bond shear tests between carbon fiber reinforced polymer (CFRP) strips and concrete have not yet been reported in literature, to the best knowledge of the authors. Given the high potential of strengthening concrete with CFRP to increase blast resistance, it is necessary to better understand the dynamic interaction between concrete and CFRP under blast impulse. This article presents a new experimental setup developed in order to study blast driven bond interaction between CFRP and concrete. An evaluation of the bond at the interface between the CFRP strip and the concrete is conducted in order to identify the parameters that affect the bond strength under blast loading. Several retrofitted specimens with different bond strength are tested. An explosive driven shock tube (EDST) set-up is used to generate the blast loading. Piezo resistive strain gauges and digital image correlation (DIC) measurement are used to record the debonding process and the evolution of the strain along the bonded area. As such, the bond behaviour is studied for three different bond lengths and the effect of interaction of the blast wave within the concrete is highlighted. The experimental tests demonstrate that under blast loading, the debonding between the CFRP strip and the concrete occurs due to a combined effect: interface stresses caused by the induced force in the CFRP and additional stresses resulting from the propagation of the blast induced stress wave within the concrete.

Parameter characterization of a buried mine blast event with further emphasis on sympathetic detonation and layered soil bed conditions

The presented work documents the results of a comprehensive sensitivity study of the structural response of a military vehicle subjected to the impulse from a buried charge using the discrete particle method (DPM) to model the soil and high explosive (HE) coupled to a finite-element solver for the structure. Eighteen different process and numerical parameters were studied. Each of the numerical results was compared with a base model to see the influence of the considered parameter. The structure in the base model was the TARDEC Generic Vehicle Hull and the response parameter was chosen to be the total blast impulse (TBI) on the structure. The non-linear transient dynamic explicit finite-element solver used for the analysis was the IMPETUS Afea Solver®. The study includes soil characteristics and charge related parameters, such as size, type, geometry, and location. The depth of burial (DOB) and number of discrete particles were also considered in the study. Further, different numerical parameters were included. The results provide a good understanding of process and numerical parameters when modeling buried charges with a coupled finite-element model (FEM) and DPM approach. As a natural extension of the sensitivity study the effect of a layered soil bed is investigated, the topsoil either being dry or wet soil. Further, it is illustrated how to model a sympathetic detonation where the detonation of one improvised explosive device (IED) generates a pressure that results in the detonation of a second IED.

Novel high performance energetic materials of fluorine-containing 2,6-dinitro-4-(trifluoromethyl)phenol derivatives with substituted azoles

Azoles such as tetrazole, triazole, pyrazole, and imidazole are considered to be core nitrogen rich structures. 2,6-Dinitro-4-(trifluoromethyl)phenol was treated with imidazole, 3-nitropyrazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, 3,5-diamino-1,2,4-triazole, 5-aminotetrazole, and 5-nitrotriazolone to synthesize acid-base salts using a proton transfer mechanism. The spectroscopic characterization of the synthesized compounds 1–7 was carried out by IR, 1H NMR, 13C NMR, and 19F NMR spectroscopies. Single crystal X-ray diffraction studies of compounds 1 and 3 showed that they possess densities of 1.675 and 1.670 g/cm3, respectively. The detonation properties of all the synthesized compounds were studied using computational software such as the LOTUSES, EXPLO 5, and EXTEC codes. The blast peak over pressure and blast impulse were determined for each compound. The thermal behaviour of the synthesized compounds was analyzed using TGA/DSC thermogram, and each compound was found to exhibit acceptable thermal stability. The performance of the synthesized compounds were found to be high and fit into the category of high-energy-density materials (HEDMs).

Experimental and numerical study of square sandwich panels with layered-gradient foam cores to air-blast loading

The blast response of clamped sandwich panels with layered-gradient aluminium foam cores was studied experimentally and numerically. The effective blast impulse acting on specimens in ballistic pendulum tests was first calibrated, and the influences of blast impulse and core-layer arrangement on the deformation modes and shock resistance were revealed. Then, the corresponding numerical simulations were conducted. The finite element model was validated via the displacement–time curves of the ballistic pendulum system and the deformation profile and deflection response of sandwich specimens. The blast pressure, deformation process, energy absorption, strain evolution, and distribution of blast-loaded sandwich panels are discussed. The experimental and numerical results show that all the layered-gradient core sandwich panels have a weaker blast resistance capability than the ungraded sandwich panels because of the reduction in structural integrity of the specimens. For a given effective impulse, the specific energy absorption value of the positive gradient sandwich panels is the largest, followed by that of the ungraded sandwich panels, whereas that of the negative gradient sandwich panels is the lowest.

Failure of Glass Fibre-Reinforced Polypropylene Metal Laminate Subjected to Close-Range Explosion.

The present study investigates the effects of close-range blast loading of fibre metal laminates (FMLs) fabricated from woven glass polypropylene and aluminium alloy 2024-T3. The polypropylene layers and anodized aluminium are stacked in 3/2 layering configuration to investigate the impact energy absorbed through deformation and damage. In order to study the blast responses of FMLs, a 4-cable instrumented pendulum blast set-up is used. Effects of blast impulse and stand-off distance were examined. Investigation of the cross-section of FMLs are presented and damages such as fibre fracture, debonding, and global deformation are examined. Increasing stand-off distance from 4 to 14 mm resulted in a change of damage mode from highly localized perforation to global deformation.