Blast Impulse Research Articles

Theoretical Analysis of Blast Protection of Graded Metal Foam-Cored Sandwich Cylinders/Rings.

The blast resistance of a sandwich-walled cylinder/ring comprising two metal face-sheets and a graded metal foam core, subjected to internal air blast loading, is investigated. Analytical models are developed for the deformation of the sandwich cylinder with positive and negative gradient cores under internal blast loading. The deformation process is divided into three distinct phases, namely the fluid–structure interaction phase, core-crushing phase, and outer face-sheet deformation phase. Finite element modeling is performed using the Voronoi material model. The proposed analytical models are verified through finite element analysis, and reasonable agreement is observed between the analytical predictions and finite element results. The sandwich structures with high energy absorption capacity or low maximum radial deflection are satisfied for the protecting purpose of impact/blast resistance requirements. Typical deformation processes are classified and analyzed; the effects of explosive charge, face-sheet thickness, and core gradient on the structural response are also examined. The results indicate that both the deformation modes and the structural response of the cylinders are sensitive to the blast charge and core configuration. It is concluded that energy absorption capacity and maximum radial deflection are two conflicting goals for achieving high impact/blast resistance capability. An in-depth understanding of the behavior in sandwich-walled cylinders under blast impulse and the influence of the core configuration helps realize the advantages and disadvantages of using graded foam materials in sandwich structures and can provide a guideline for structural design.

Blast response of aluminum foam sandwich panel with double V-shaped face plate

Critical instruments and buildings demand enhanced blast protection under the environments of increased local conflicts and terrorist attacks. There are currently two widely researched measures for blast protection: blast energy absorption by cellular materials and energy dispersion by V-shaped plates. Although several studies have focused on these individual protection measures, their combination has rarely been reported. Therefore, in the present study, these two measures were combined. The resulting aluminum foam sandwich panel with a double V-shaped face plate, along with its anti-blast performance, was numerically analyzed. The numerical model was validated, and then the blast responses of different structural designs of the proposed sandwich panel were examined. Finally, parametric analyses of the protection performance of the double V-shaped face plated sandwich panel were conducted. The results indicated that the designed sandwich panel could not only disperse the blast impulse but also maintain the energy-absorption property of the foam core. Gaps in the sandwich panel should be avoided to prevent acceleration of the face plate. Owing to the relatively large local energy absorption, eccentric loading did not significantly affect the performance of the V-shaped face-plated sandwich panel. The stiffness of the front and back face plates of the proposed sandwich panel must be matched properly to balance the effects of energy dispersion and energy absorption for achieving the optimal protection performance. This study provides a valuable reference for designing new protective structures and enhancing blast and impact protection.

Failure and detachment path of impulsively loaded plates

Abstract The deformation and detachment path of simply-supported and fully clamped mild steel quadrangular plates subjected to impulsive blast loads are investigated numerically. A comprehensive failure model that incorporates two competing mechanisms of damage due to ductile and shear failure is employed to simulate the progression of tearing within the plate. The stress triaxiality dependent Modified Mohr-Coulomb (MMC) fracture criterion is implemented in a finite element model, and experimental tensile and shear tests were carried out to calibrate the material parameters. The direction of crack propagation along the clamped plate support and the residual length are predicted for a wide range of impulse intensity, reproducing the failure modes observed experimentally. Furthermore, the developed model highlights the different failure mechanisms that occur in simply-supported plates, similar to those of panels subjected to localised blast loadings. Parametric studies are performed to establish dimensionless failure maps and investigate the influence of plate topology and boundary conditions on the dynamic response, for both square and rectangular geometries, thus offering an effective support for the design of impulsively loaded plates for advanced engineering applications.

Dynamic response of fiber metal laminates subjected to localized high impulse blast loading

The dynamic response of glass laminate aluminum reinforced epoxy (GLARE) structures subjected to localized high impulse blast loading is studied. A new mathematical model is proposed taking the influence of strain rates on strength into account, for the woven glass fiber-reinforced polymer (GFRP) composites. To predict the dynamic response of GLARE structures, user-defined material and blast loading subroutines are developed and implemented into the commercial software ABAQUS/Explicit. The typical failure characteristics are accurately captured, such as perforation, petaling failure, extensive tearing and interfacial debonding. The simulation results of dynamic failure behavior and damage evolution characteristics agree well with experimental data. The influences of layer types and explosive equivalents on the failure behavior of GLARE structures are systematically discussed. At the same areal density, the blast resistance of the GLARE structures first increases and then decreases with an increase of the layer number. There is an optimal ratio (A3T22) for the number of material layers. Both the diameter of the perforation and the number of petals on the back panel increased with an increase in blast loading. The research in this paper provides theoretical support for the application of GLARE structures as anti-explosion structures.

Study of Mild Steel Sandwich Structure Energy Absorption Performance Subjected to Localized Impulsive Loading.

Extensive research focus had been given to sacrificial sandwich panels to mitigate the effects of blast loads. This is due to their ability to distribute the load and absorb a significant portion of the blast energy. This paper studies the behavior of sacrificial sandwich mild steel panels of axially oriented octagonal tapered tubular cores subjected to near-field impulsive blast. The deformation behavior and several assessment parameters consisting of the peak force, stroke efficiency, energy absorption and core efficiency were investigated using validated finite element analysis. The developed deformation modes were mainly influenced by the top plate and tube thickness. Tubes of a 5° taper performed unfavorably, exhibiting increased peak force and lower energy absorption. Panels of top plate thickness of 4 mm exhibited higher stroke efficiency as compared to panels of lower thickness. The top plate and tube thickness significantly affected energy absorption. An increase of 73.5% in core efficiency was observed in thick-plate panels as compared to thin-plate ones.

Impulse Loading of Plates using a Diverging Shock Tube

Impulsive blast loading studies typically require facilities with sub-millisecond decay time simulation capability. Using a conventional shock tube for such studies, however, is not viable due to a finite shock formation distance that limits the size of the shortest, functional driven tube. To overcome this, a diverging (conical) shock tube has been proposed in this work, motivations for which are grounded in simple shock tube theory. Using such a shock tube, for the first time, blast pulses having decay times of around 0.7 ms have been achieved repeatably (± 5.5%). Subsequently, blast loading experiments (equated to 30 − 40 g TNT surface explosion at 0.5 m stand-off distance) carried out on metal plates showed that this device can replicate the deflection patterns of an impulsive blast loading which could not be obtained so far using conventional shock tubes.

Design of new energetic materials based on derivatives of 1,3,5-trinitrobenzenes: A theoretical and computational prediction of detonation properties, blast impulse and combustion parameters

This paper reports the design of some of the new ionic based high energy materials derived from the anion of picric acid (2,4,6-trinitrobenzene-1-ol), styphnic acid (2,4,6-trinitrobenzene-1,3-diol) and 2,4,6-trinitrophloroglucinol (2,4,6-trinitrobenzene-1,3,5-triol) and cation derived from the key synthon molecules such as 5-trifluoromethyl-1H-tetrazole, 5-dinitromethyl-1H-tetrazole and 5-azido-1H–tetrazole-1-carbonitrile. The detonation properties of these newly proposed compounds are predicted by using software such as EXPLO-5, EXTEC and LOTUSES and Keshvarz method. Moreover, other explosive parameters such as density, gurney velocity, and oxygen balance and decomposition products of the newly designed molecules have also been predicted and reported for the first time in this manuscript. The predicted detonation parameters of some of the newly designed compounds exhibit higher velocity of detonation (VOD) and detonation pressure in comparison to other well-known benchmark explosives such as 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazinane (RDX). Further, the peak over pressure (POP) and the blast impulse parameters of the newly designed compounds are predicted by using Shock physics explicit eulerian dynamics (SPEED) software, and the same is reported for the first time in this work. The work also reports the theoretical prediction of impact and electrostatic spark sensitivity parameters for the newly designed molecules. The ballistic performance parameters of the newly designed ionic energetic materials are also predicted by incorporating them into model composite rocket propellant formulations. The predicted ballistic parameters indicate that the proposed materials may find an application in the propellant formulation as an energetic additive.

Direct Observation of Low Strain, High Rate Deformation of Cultured Brain Tissue During Primary Blast.

The Veterans Health Administration determined that over 250,000 U.S. service members were diagnosed with a traumatic brain injury (TBI) between 2008 and 2018, of which a great proportion were due to blast exposure. Although the penetrating (secondary) and inertia-driven (tertiary) phases of blast-induced TBI (bTBI) have been studied thoroughly and are known to be injurious, primary blast brain injury has been less studied. We investigated the biomechanics of primary bTBI in our previously developed in vitro shock tube model with a fluid-filled sample receiver. Using stereoscopic, high-speed cameras and digital image correlation (DIC), we mapped the deformation of organotypic hippocampal slice cultures (OHSCs) following a range of blast exposures to characterize the induced strains. As blast exposure increased, tissue strain increased, although the levels remained relatively low (maximum < 9%), with strains rates between 25 and 85s-1. Both strain magnitude and rate were highly correlated with the in-air blast impulse and in-fluid peak pressure parameters. Comparing biomechanical parameters to previously reported blast-induced electrophysiological dysfunction, a threshold for deficits in long-term potentiation (LTP) was observed for strains between 3.7 and 6.7% and strain rates between 25 and 33s-1. This is the first study to experimentally determine primary blast-induced strain and strain rates in hippocampal tissue.

Blast loading distributions on the circular sectional bridge columns

Column is the main bearing member in bridge. It is the premise for analyzing the dynamic response of the bridge under blast loading to study the distribution law of blast load acted on bridge columns. Circular sectional bridge column has been selected as the research object, and the corresponding finite element models have been built by using the LS-DYNA software. When the height of burst is less than 0.3 times of the column height, the scaled distance is 0.5−2.1 m/kg1/3 and the column diameter is 0.15−1 m, the distributions of the blast loading impulse along column height and cross-section direction are obtained through numerical simulations. The influential parameters, e.g., the explosive equivalent, height of burst, explosion distance and sectional diameter, have been considered. It is derived that, along the column height, when the contact burst and the height of burst is 0.1 times of the column height, the blast loading impulse on the column front surface approximately follows the Single linear” distribution. When the height of burst is 0.2 and 0.3 times of the column height, the blast loading impulse approximately follows the Double linear” distribution. Along the cross-section direction, the ratio of the average net blast loading impulse to the blast impulse on the column front surface is a constant. Furthermore, the resultant net blast loading impulse of bridge column has been obtained, which can put some theoretical basis for blast-resistant analysis and design of bridge columns.

Measurement of gas detonation blast loads in semiconfined geometry

The ignition and explosion of combustible vapor clouds represents a significant hazard across a range of industries. In this work, a new set of gas detonations experiments were performed to provide benchmark blast loading data for non-trivial geometry and explosion cases. The experiments were designed to represent two different accident scenarios: one where ignition of the vapor cloud occurs shortly after release and another where ignition is delayed and a fuel concentration gradient is allowed to develop. The experiments focused on hydrogen-air and methane-oxygen detonations in a semiconfined enclosure with TNT equivalencies ranging from 9 g to 1.81 kg. High-rate pressure transducers were used to record the blast loads imparted on the interior walls of a 1.8 m × 1.8 m × 1.8 m test fixture. Measurements included detonation wave velocity, peak overpressure, impulse, and positive phase duration. A comparison of the pressure and impulse measurements with several VCE models is provided. Results show that even for the most simplified experimental configuration, the simplified VCE models fail to provide predictions of the blast loading on the internal walls of the test fixture. It is shown that the confinement geometry of the experiment resulted in multiple blast wave reflections during the initial positive phase duration portion of the blast loading, and thus, significantly larger blast impulse values were measured than those predicted by analytical models. For the pressure sensors that experienced normally-reflect blast waves for the initial blast impulse, the Baker-Strehlow and TNT equivalency models still struggled to accurately capture the peak overpressure and reflected impulse. The TNO multi-energy model, however, performed better for the case of simple normally-reflected blast waves. The results presented here may be used as validation data for future model or simulation development.

Prediction of blast pressure-duration capacity of monolithic Thermally Tempered Glass panes

Most standards and documents for blast-resistant design of glazing systems are based on simplified Single Degree Of Freedom (SDOF) models and triangular blast pressure time histories with no negative phase. Previous experimental studies have clearly indicated that pressure-duration or pressure-impulse design curves generated from such SDOF models may be overconservative, especially during impulsive blast scenarios. In this study, pressure-duration capacity curves for various monolithic Thermally Tempered Glass (TTG) panes are derived using Finite Element (FE) models. Moreover, the imposed blast pressure time histories include both positive and negative phases, which are deemed to be more realistic than considering the positive phase alone. Previous blast tests have shown that TTG panes can experience significant in-plane strain before fracture and exceeding the cracking strength does not necessarily mean fracture and disintegration of the pane. Accordingly, in the present study, glass fracture is judged based on the maximum principal strain rather than the stress criterion which has been widely used in earlier studies. The accuracy of the FE modeling technique and the abovementioned fracture criterion is verified using these blast test results on TTG panes. Pressure-duration curves of predicted capacity are obtained for TTG panes with different aspect ratios (1, 1.25, 1.5, 1.75, 2), different thicknesses (8 mm, 10 mm, 12 mm, 16 mm) and different widths (600 mm, 900 mm, 1,200 mm). Similar to current available standards, four edges of the adopted panes are restrained in the out-of-plane direction, but without in-plane or rotational restraints. The obtained pressure-duration capacity curves are compared with those provided by UFC 3-340-02. This shows that UFC's pressure-duration capacity curves are overconservative in both the impulsive and quasi-static regions.

Propulsion Performance and Blast Impulse of Explosive Charges in Near-Field Explosion

The results of numerical simulation of the blast impulse of explosive charges on structural elements are presented. The numerical method was validated against available experimental data describing the blast effect in near-field explosion. Additional experiments on explosive acceleration of steel disks were performed. The effect of blasting conditions (the presence or absence of air, additional reflective surfaces) on the blast impulse was studied.

On large deformation, damage and failure of ductile plates to blast loading

This paper concerns the irreversible deformation and failure of metal plates to brief, but intense, dynamic (impulsive) load encountered in an air-blast. Hitherto, nearly all of the dynamic structural plasticity models of ‘fully-clamped’ plate only calculates its inelastic (mode I) deformation but have largely ignored damage and failure – exemplified by the partial and/or complete detachment (modes II*, II and III) of a plate from its support through material rupture – that occurs when the blast load is sufficiently intense. An analytical model that captures all three modes of the plate deformation is developed in this paper where emphasis shall be on providing the simplest formulation that contains all the essence of a material and deformation effect needed to quantify the problem. The proposed model adopts an energy density failure criterion of Shen and Jones [19] to delineate the various inelastic failure modes; employs the constitutive framework of limit analysis for simplicity; accounts for the simultaneous influence of bending, membrane stretch and transverse shear through an interaction yield criterion; and, include the effects of strain rate on the material flow stress through the Cowper–Symonds relation. Accuracy of model predictions for square mild-steel plates are assessed through comparison with results from finite element analysis, and experimental data compiled from the literature for a range of impulsive load intensities – they will be shown to be in good general agreement. Design maps delineating the different deformation régimes for different combinations of blast impulse and length versus thickness ratio are constructed for plates of equal mass.

Experimental study on the dynamic responses of foam sandwich panels with different facesheets and core gradients subjected to blast impulse

Sandwich panels with an energy-absorbing core material have exhibited great potential in lightweight structures for blast protection. In this study, the deformation/failure modes of sandwich panels against blast impulse were investigated experimentally. The blast tests were conducted on the aluminum foam-core sandwich panels with different facesheet materials, namely aluminum alloy, steel, and carbon fiber reinforced plastics (CFRP); and the cores involve uniform foam and graded foam. The deformation modes of the whole sandwich panels as well as the front facesheet, foam core, and back facesheet were analyzed systematically. It is shown that the deformation patterns are fairly sensitive to the impulse intensity, facesheet material, and foam core gradient. Based upon the measurements, the back facesheet deflection increases linearly with the impulse, apart from the petal-tearing failure of front facesheet. When considering the specific impulse and the same metallic back facesheets, the blast resistance of the sandwich specimen with CFRP front facesheet is superior to these of the metallic front facesheet specimens. Interestingly, the sandwich panels with the aluminum front and steel back facesheet perform better in blast resistance than those with the steel front and aluminum back facesheet. The blast resistance of sandwich panels with a positive gradient of core density (i.e. core density linearly decreased along the blast direction) is superior to those with a negative gradient of core density; and the performance increases with increasing density difference. Compared with the uniform core, the positively-graded foam core with a larger density difference exhibits a stronger blast resistance, while those with a smaller density difference present a weaker blast resistance. The study is expected to provide some fundamental data and design guide for a more efficient sandwich structure with lighter weight and higher capacity of blast protection.

Numerical parameter characterisation of a buried mine blast event with further emphasis on IED shapes and soil bed conditions

The modelling of a buried charge and its impact on vehicle structures is a complex simulation task since numerous structural variables, physical properties and numerical parameters have to be determined to provide accurate estimation of the structure's response. A number of variables in question are directly related to the numerical approach chosen to perform the analysis while others relate to the overall modelling process and the detail used to describe the physical processes. This paper documents the results of a comprehensive sensitivity study of the structural response of a 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. Fourteen design variables and numerical parameters were studied requiring in excess of 1000 computational hours. 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® which has implemented the DPM for blast simulations and is called iDPM. The study includes soil characteristics and charge related parameters. The depth of burial (DOB) and number of discrete particles were also considered in the study. As a natural extension of the sensitivity study the effect of an improvised explosive device (IED) made from an oil can is investigated as well as the effect of having rocks in the soil bed making it a non-homogeneous soil bed.

Numerical parameter characterisation of a buried mine blast event with further emphasis on IED shapes and soil bed conditions

The modelling of a buried charge and its impact on vehicle structures is a complex simulation task since numerous structural variables, physical properties and numerical parameters have to be determined to provide accurate estimation of the structure's response. A number of variables in question are directly related to the numerical approach chosen to perform the analysis while others relate to the overall modelling process and the detail used to describe the physical processes. This paper documents the results of a comprehensive sensitivity study of the structural response of a 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. Fourteen design variables and numerical parameters were studied requiring in excess of 1000 computational hours. 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® which has implemented the DPM for blast simulations and is called iDPM. The study includes soil characteristics and charge related parameters. The depth of burial (DOB) and number of discrete particles were also considered in the study. As a natural extension of the sensitivity study the effect of an improvised explosive device (IED) made from an oil can is investigated as well as the effect of having rocks in the soil bed making it a non-homogeneous soil bed.

A Study on the Improvement of Structural Performance by Glass Fiber‐Reinforced Polyurea (GFRPU) Reinforcement

Polyurea has a high tensile strength, elongation, and the capability to absorb the energy generated by dynamic and impulsive blast loading. Glass fibers are a reinforcement material for repairing and retrofitting the concrete members. The polyurea provides ductility, and the fibers provide improved stiffness and strength to the composite system. Glass‐fiber reinforced polyurea (GFRPU) is a composite of polyurea and fibers and is applied as a reinforcement through a simple spraying method. GFRPU coating has a simple construction, and unlike existing strengthening methods such as fiber‐reinforced polymer (FRP) or a steel plate, it prevents a debonding from the concrete surface. Seven beams of one externally nonreinforced concrete beam and six concrete beams with and without a reinforcing bar are tested using the thickness of the spray and the number of coating faces. The applicability of GFRPU was investigated through the experiments, and the test results indicate that the GFRPU strengthening method is feasible for enhancing the load‐carrying capacity and flexural ductility.

Experimental investigation of blast mitigation and particle–blast interaction during the explosive dispersal of particles and liquids

The attenuation of a blast wave from a high-explosive charge surrounded by a layer of inert material is investigated experimentally in a spherical geometry for a wide range of materials. The blast wave pressure is inferred from extracting the blast wave velocity with high-speed video as well as direct measurements with pressure transducers. The mitigant consists of either a packed bed of particles, a particle bed saturated with water, or a homogeneous liquid. The reduction in peak blast wave overpressure is primarily dependent on the mitigant to explosive mass ratio, M/C, with the mitigant material properties playing a secondary role. Relative peak pressure mitigation reduces with distance and for low values of M/C (< 10) can return to unmitigated pressure levels in the mid-to-far field. Solid particles are more effective at mitigating the blast overpressure than liquids, particularly in the near field and at low values of M/C, suggesting that the energy dissipation during compaction, deformation, and fracture of the powders plays an important role. The difference in scaled arrival time of the blast and material fronts increases with M/C and scaled distance, with solid particles giving the largest separation between the blast wave and cloud of particles. Surrounding a high-explosive charge with a layer of particles reduces the positive-phase blast impulse, whereas a liquid layer has no influence on the impulse in the far field. Taking the total impulse due to the blast wave and material impact into account implies that the damage to a nearby structure may actually be augmented for a range of distances. These results should be taken into consideration in the design of explosive mitigant systems.

Experimental Study of Blast Wave Mitigation in Open Cell Foams

In the present study, the experimental measurements have been conducted to investigate the blast wave mitigation in open cell natural rubber as well as synthetic (polyurethane) foams. The different blast strengths have been generated by exploding different quantity of explosive at 1.5 m standoff distance. The transmitted blast pressures through both foams have been recorded using a piezoelectric pressure sensor which was incorporated at the top surface of the composite plate. The modified blast wave parameters such as peak overpressure, positive phase duration, and impulse were investigated through both natural and synthetic foams at different blast pressure strengths. It was observed that the peak overpressure was significantly decreased, while positive phase duration and blast impulse were initially increased up to a certain extent, thereafter it was found to be decreased with increasing blast strengths. The results showed that a single layer of natural foam attributed 83 % peak overpressure mitigation, whereas double layer natural foam exhibited 90 % mitigation. Secondly, it was also found that natural rubber foam showed better performance in terms of impulse than that of synthetic foam.

Behaviour and Failure of Steel Columns Subjected to Blast Loads: Numerical Study and Analytical Approach

The main objective of this study is the numerical simulation of the behaviour and failure patterns of steel columns under blast loads using the dynamic finite element package ABAQUS/Explicit. A numerical model is suggested and validated against published experimental tests on full‐scale wide‐flange steel columns subjected to dynamic blast loads under constant axial compressive force. Afterwards, the validated model is used to investigate the effect of important parameters on the behaviour and failure patterns of steel columns under blast pressure through an extensive parametric study. The parameters include the blast impulse, the blast energy, the blast load, the blast duration, the column boundary condition, the column slenderness ratio, and the blast direction. The conclusions extracted from this parametric study may be used to develop a thorough understanding of the behaviour and failure of steel columns subjected to blast load which, in turn, could lead to a more accurate practical design procedure. The study also presents derivations and validations of a proposed analytical approach to calculate the critical blast impulse at which a steel column losses its global stability. Comparison between the critical impulse‐axial force curves obtained from the proposed equation and that extracted from numerical simulations indicates the validity and feasibility of the proposed equation.