Air Blast Loading Research Articles

Implementation of an empirical tool for fast prediction of bomb airblast loading

As terrorist attacks continue all over the world and, therefore, the alarming rate of countries governments as well as the awareness of people about danger is significantly increasing, in recent years high explosive airblast effects assessment and protection have become a fundamental concern for structural designers. In this article, the implementation of an original predictive tool based on the literature empirical data to develop analyses of blast loading consequent to a bomb explosion is described. The in-house developed model enables the fast calculation of the distribution of the main blast wave parameters around and over three-dimensional complex geometries virtually reproducing potential attractive targets for terrorists. Considering these capabilities, the use of the proposed novel methodology is desirable in the preparatory and retrofit design in view of evaluating blast-induced adverse consequences and, accordingly, to identify and effectively set up the most appropriate protective strategies and countermeasures.

The effects of foam filling on the dynamic response of metallic corrugated core sandwich panel under air blast loading – Experimental investigations

This research aims to elucidate the effects of foam filling on the dynamic response of metallic corrugated core sandwich panels by conducting air blast testing. The panels were designed to investigate the influences of specific parameters, like the foam filler density, the core configuration and the filling material, on the blast performance from the aspects of permanent deformation, failure modes and associated mechanisms. Experimental results demonstrate that foam filling is an effective way to improve blast resistance of sandwich panels. The benefits from foam filler for the reduction of the levels of the failure damage and plastic deformation of panels would be improved with the increase of foam density. Comparisons of panels with different core configurations verify that the foam-filled sandwich panel performed the best under low intensity blast loading. The superiority of foam-filled sandwich panel over the foam core sandwich panel would be swallowed up with the increase of blast loading intensity. The panels filled with PVC foams displayed a superior blast resistance over the ones filled with aluminum foams of almost same density. Moreover, the difference in blast resistance would increase with the decrease of blast intensity.

Blast resilience of composite sandwich panels with hybrid glass-fibre and carbon-fibre skins

The development of composite materials through hybridisation is receiving a lot of interest; due to the multiple benefits, this may bring to many industries. These benefits include decreased brittle behaviour, which is an inherent weakness for composite materials, and the enhancement of mechanical properties due to the hybrid effect, such as tensile and flexural strength. The effect of implementing hybrid composites as skins on composite sandwich panels is not well understood under high strain rate loading, including blast loading. This paper investigates the blast resilience of two types of hybrid composite sandwich panel against a full-scale explosive charge. Two hybrid composite sandwich panels were mounted at a 15 m stand-off distance from a 100 kg nitromethane charge. The samples were designed to reveal whether the fabric layup order of the skins influences blast response. Deflection of the sandwich panels was recorded using high-speed 3D digital image correlation (DIC) during the blast. It was concluded that the combination of glass-fibre reinforced polymer (GFRP) and carbon-fibre reinforced polymer (CFRP) layers in hybrid laminate skins of sandwich panels decreases the normalised deflection compared to both GFRP and CFRP panels by up to 41 and 23%, respectively. The position of the glass-fibre and carbon-fibre layers does not appear to affect the sandwich panel deflection and strain. A finite element model has successfully been developed to predict the elastic response of a hybrid panel under air blast loading. The difference between the maximum central displacement of the experimental data and numerical simulation was ca. 5% for the hybrid panel evaluated.

Non-destructive Imaging and Residual Strength of Composite Materials After Exposure to Blast Loading

An experimental study has been conducted to evaluate the compressive residual strength of glass fiber/epoxy laminates after exposure to air blast loading. Controlled blast loading experiments were conducted using a shock tube facility which induced damage on the panels. The resulting damage in the material was quantified using non-destructive imaging technologies, specifically Terahertz (THz) and Flash Infrared Thermography (FIRT). Residual compressive strength was subsequently measured using subpanels cut from the main panel, per ASTM D7137. Furthermore, an empirical relationship has been developed to predict the residual compressive strength of the composite laminates as a function of a combined damage parameter based on individual damage mechanisms. The results show that THz and FIRT imaging can be used to quantify internal damage in a composite laminate after shock loading. Additionally, residual strength experiments show that increased shock damage causes a corresponding reduction in remaining compressive strength. The residual strength of the composite panel follows a linear trend as a function of a combined damage parameter.

Behaviour and analysis of concrete-filled rectangular hollow sections subject to blast loading

Concrete-filled Rectangular Hollow Sections have been tested under large-scale, far-field, air-blast loading for the first time. The concrete-filled, cold-formed steel tubes performed well under the blast loads, with a significant reduction in the global and local displacements compared to unfilled RHS members. The heavily instrumented tests provided a large quantity of response data that was used for the validation of numerical models. Numerical models of the concrete-filled steel tubes were first developed using explicit finite element methodologies. A parametric study was conducted with the validated finite element model to further characterize the response of the concrete-filled steel tubes under air-blast loading. The influence of several key variables on the response of the tubular members was determined and preliminary design guidance is provided. Finally, the test and finite element results were used to develop an idealized single-degree-of-freedom numerical model that is well-suited to future use in design problems.

Analysis and parametric optimization of a novel sandwich panel with double-V auxetic structure core under air blast loading

Blast shock wave is a big threat to the military vehicle and may cause vehicle damages and passenger casualties. It is a big issue to balance the protective performance and lightweight property of military vehicle. In these days, many types of sandwich panels with different cores were applied as protective plates in military vehicles. In view of the excellent energy absorption capability of auxetic structure, applying auxetic structure as sandwich panel core for blast protection purpose is a promising field. However, existing in-plane configuration of two-dimensional auxetic honeycomb core always represent anisotropic behaviour. In this paper, a novel sandwich panel with three-dimensional double-V Auxetic (DVA) structure core, which can produce isotropic mechanical behavior, was proposed for air blast protection purpose. Its primary structural parameters and their relations were discussed, and a parametric numerical model was established. In order to reduce both the dynamic response under air blast loading and mass, the design variables and objective function of the DVA core optimization problem were confirmed, then parametric optimization was conducted based on Latin Hypercube Sampling (LHD) method, Gaussian process metamodel (GPM) and multi-objective particle swarm optimization algorithm (MOPSO). Finally, it is proved that the applied optimization process is efficient and can obtain accurate optimum points. The proposed DAV core sandwich panel performed much better both in lightweight and protection than solid plate and has an apparent merit in lightweight aspect compared with square honeycomb core sandwich panel.

Dynamic failure analysis of concrete dams under air blast using coupled Euler-Lagrange finite element method

In this study, the air blast response of the concrete dams including dam-reservoir interaction and acoustic cavitation in the reservoir is investigated. The finite element (FE) developed code are used to build three-dimensional (3D) finite element models of concrete dams. A fully coupled Euler-Lagrange formulation has been adopted herein. A previous developed model including the strain rate effects is employed to model the concrete material behavior subjected to blast loading. In addition, a one-fluid cavitating model is employed for the simulation of acoustic cavitation in the fluid domain. A parametric study is conducted to evaluate the effects of the air blast loading on the response of concrete dam systems. Hence, the analyses are performed for different heights of dam and different values of the charge distance from the charge center. Numerical results revealed that 1) concrete arch dams are more vulnerable to air blast loading than concrete gravity dams; 2) reservoir has mitigation effect on the response of concrete dams; 3) acoustic cavitation intensify crest displacement of concrete dams.

Analysis of dynamical response of air blast loaded safety device

Equipment of many oil and gas processing plants in the Russian Federation is considerably worn-out. This causes the decrease of reliability and durability of equipment and rises the accident rate. An air explosion is the one of the most dangerous cases for plants in oil and gas industry, usually caused by uncontrolled emission and inflammation of oil products. Air explosion can lead to significant danger for life and health of plant staff, so it necessitates safety device usage. A new type of a safety device is designed. Numerical simulation is necessary to analyse design parameters and performance of the safety device, subjected to air blast loading. Coupled fluid-structure interaction analysis is performed to determine strength of the protective device and its performance. The coupled Euler-Lagrange method, allowable in Abaqus by SIMULIA, is selected as the most appropriate analysis tool to study blast wave interaction with the safety device. Absorption factors of blast wave are evaluated for the safety device. This factors allow one to assess efficiency of the safety device, and its main structural component – dampener. Usage of CEL allowed one to model fast and accurately the dampener behaviour, and to develop the parametric model to determine safety device sizes.

Nonlinear Transient Response of Functionally Graded Material Sandwich Doubly Curved Shallow Shell Using New Displacement Field

In this paper, the nonlinear transient dynamic response of functionally graded material (FGM) sandwich doubly curved shell with homogenous isotropic material core and functionally graded face sheet is analyzed using a new displacement field on the basis of Reddy’s third-order shear theory for the first time. The equivalent material properties for the FGM face sheet are assumed to obey the rule of simple power law function in the thickness direction. Based on Reddy’s theory of higher shear deformation, a new displacement field is developed by introducing the secant function into transverse displacement. Four coupled nonlinear differential equations are obtained by applying Hamilton’s principle and Galerkin method. It is assumed that the FGM sandwich doubly curved shell is subjected to step loading, air-blast loading, triangular loading, and sinusoidal loading, respectively. On the basis of double-precision variable-coefficient ordinary differential equation solver, a new program code in FORTRAN software is developed to solve the nonlinear transient dynamics of the system. The influences of core thickness, volume fraction, core-to-face sheet thickness ratio, width-to-thickness ratio and blast type on the transient response of the shell are discussed in detail through numerical simulation.

The response of mild steel and armour steel plates to localised air-blast loading-comparison of numerical modelling techniques

This paper presents a comparative study of numerical, experimental and empirical techniques on the effect of localised air blast loads on mild steel and armour steel plates. The blast load effects on monolithic plates have been accounted for by using different approaches provided in the Finite Element hydrocode ABAQUS 6.13, namely an Eulerian Lagrangian and a Coupled Eulerian Lagrangian model. In the first model, the air and the explosive were modelled using multi-material Eulerian grids while the plate was modelled using a rigid Lagrangian mesh, while in the second model the rigid target was replaced with deformable plate.The transient deformation of the plate, strain localisation, pressure distribution on the plate have been investigated in the FE models, which have been validated against small scale experimental data for a limited range of charge sizes for both the mild steel and armoured steel. Despite the lower deflection of armour steel compared to mild steel plates, both plates were shown to undergo rupture upon similar charge mass and stand-off. For this purpose, a non-dimensional analysis was carried out with consideration of stand-off distance and slenderness ratio to predict the rupture impulse.

Experimental and numerical investigation of v-shape plates subjected to blast loadings

This paper presents the experimental and numerical investigation of angled shape metal plates response when subjected to an air blast loading. V shaped plates were fabricated at angles of 90o, 120o and 150o respectively. The charge weight of 1 kg (PE4) was used to create a spherical blast wave at several standoff configurations. The experimental results were then compared with the numerical simulation model computed using LSDYNA3D.

Experimental and numerical investigation on blast wave propagation in soil structure

This paper presents a study on blast wave propagation in a soil structure when subjected to a surface air blast loading. The experimental work utilized the use of plastic explosive of 1 kg weight (PE4) in order to create a spherical blast wave at a fixed standoff distance. The experimental results were then compared with the numerical simulation model computed using LSDYNA3D. Although the computed simulation and experimental results showed large difference in terms of values, but both results provide a similar trend in terms of blast peak overpressure.

Laboratory scale investigation of stress wave propagation and vibrational characteristics in sand when subjected to air-blast loading

The main objective of this study is to develop a new approach for evaluating the effects of air-blast on protective barrier made of sand. The air-blast loading is simulated experimentally laboratory using the shock tube test facility. The stress wave propagation in medium dense and dense sand medium are investigated under simulated air-blast loading. Synchronised pressure and accelerometer measurement system is used to capture peak stress wave pressure and peak particle velocity (PPV). The blast wave impact generates a stress wave in the medium leading to the compaction of the soil skeleton, which has led to stress enhancement (4–5 times of peak overpressure) in top most sand layer, following which the high-pressure gas behind the shock front permeates through the sample. The intensity of stress waves and gas permeation rate gradually decrease with depth. Further, from the result of the simulated air-blast experiments, an empirical equation has been developed with a power law index of 1.88 and 1.36 for medium dense and dense sand respectively, to predict PPV against scaled blast distance. Visualisation of the sand deformation was possible with the help of a high-speed camera; displacement trajectories and strain contours are obtained through digital image correlation (DIC) analyses.

Hybrid composite sandwich panels under blast and impact loading

Naval vessels may undergo high strain rate loading, including impact, wave slamming and blast loading. Predicting the behaviour of composite sandwich structures to such loading is complicated, hence representative experiments are required. Two panels with hybrid carbon-and glass-fibre skins were fabricated and subjected to full-scale air blast loading. The panels were 1.7 × 1.5 m in size and were subjected to a 100 kg nitromethane charge at a stand-off distance of 15 m. 3D Digital Image Correlation (DIC) was implemented behind each of the panels to record the full-field out-of-plane displacement of the panels. In addition, the panels were instrumented with foil strain gauges on the front skins to record the response of the panel side in contact with the blast. The results revealed that the combination of glass-and carbon-fibre improves the blast resilience when compared to previous blast testing on panels with exclusively glass-fibre or carbon-fibre skins. However, the order in which the glass-and carbon-fibre layers were arranged did not have a significant effect on the overall panel performance. In addition, panels with the same hybrid skins were subjected to high velocity impact testing. An aluminium projectile with 25 mm diameter was fired at small scale panels (160 × 160 mm) using a laboratory gas gun at a velocity of 78 ms−1. 3D DIC was again used to record the out-of-plane displacement of these panels. In contrast to the blast experiment, the impact results showed that the order in which glass-and carbon-fibres were arranged did affect both the out-of-plane displacement and damage to the panels. The least damage occurred when glass-fibre layers were placed on the outermost layers impacted by the projectile.

Numerical study of steel sandwich plates with RPF and VR cores materials under free air blast loads

One of the most important design criteria in military tunnels and armoured doors is to resist the blast loads with minimum structural weight. This can be achieved by using steel sandwich panels. In this paper, the nonlinear behaviour of steel sandwich panels, with different core materials: (1) Hollow (no core material); (2) Rigid Polyurethane Foam (RPF); and (3) Vulcanized Rubber (VR) under free air blast loads, was investigated using detailed 3D nonlinear finite element models in Ansys Autodyn. The accuracy of the finite element model proposed was verified using available experimental test data of a similar steel sandwich panel tested. The results show the developed finite element model can be reliably used to simulate the nonlinear behaviour of the steel sandwich panels under free air blast loads. The verified finite element model was used to examine the different parameters of the steel sandwich panel with different core materials. The result shows that the sandwich panel with RPF core material is more efficient than the VR sandwich panel followed by the Hollow sandwich panels. The average maximum displacement of RPF sandwich panel under different ranges of TNT charge (1 kg to 10 kg at a standoff distance of 1 m) is 49% and 53% less than the VR and Hollow sandwich panels, respectively. Detailed empirical design equations were provided to quantify the maximum deformation of the steel sandwich panels with different core materials and core thickness under a different range of blast loads. The developed equations can be used as a guide for engineer to design steel sandwich panels with RPF and VR core material under a different range of free air blast loads.

Experimental study on counterintuitive behavior of thin aluminium plates under free airblast loading

An experimental investigation of the counterintuitive behaviour in thin aluminium plates under fullfield test is presented in the paper. Special focus is placed on structural response and permanent deflection of the panels after the complex response. Thus, a series of tests with the plates varied in two kinds of thickness were conducted, where impulsive loading was generated by detonating the explosives at various standoff distances. As loaded impulsively, the vibration response was observed and the final configuration of each plate was measured and recreated. It is shown that all plates subjected to free air blast loading in such conditions exhibited plastic permanent deformation combined with distinct counterintuitive behaviour, as the plates deformed to the opposite direction of the incident wave. In addition, the characteristics of the permanent deflection can be divided into 2 typical deformation shapes, and the occurrences of which were correlated to the dimensionless parameter proposed in previous studies, confirmed to be an approximate indicator to describe the influence of loading conditions herein.

Response of Armour Steel Plates to localised Air Blast Load – A Dimensional Analysis

We report on the results of dimensional analyses on the dynamic plastic response of square armour steel plates due to detonation of proximal cylindrical charges and ensued air blast loading. By assuming a generic function for the blast load, which is multiplicative comprising its spatial and temporal parts, a set of 14 dimensionless parameters, representative of the load and plate deformation, were identified and recast in the form of dimensionless functions of stand-off to charge diameter ratio. Parametric studies were performed using commercial code ABAQUS’s module of Finite Element hydrocode using MMALE and MMAE techniques, and combined with regression analyses to quantify the dimensional parameters and the expressions for dimensionless functions. A few numerical studies with various FE mesh types were also performed to validate the transient deflections against the small-scale experiments. For pulse loading due to proximal charges of small orders of stand-off/charge diameter ratio, the magnitude of the transverse deflection increased abruptly with incremental decrease in stand-off, in contradistinction to the plate deformations at higher stand-offs where variations in displacement are smooth. This confirmed the existence of a stand-off at which a transition in behaviour takes place. For stand-off values less than charge diameter, a dimensionless energy absorbing effectiveness factor was considered to investigate the prediction of rupture in the plate corresponding to different charge masses. This factor is measured as a baseline parameter to predict, using solely numerical means, the blast loads which ensue rupture on full-scale prototypes.

The influence of interfacial bonding on the response of lightweight aluminium and glass fibre metal laminate panels subjected to air-blast loading

This paper examines the effects of glass fibre configuration and epoxy resin type on the response of glass fibre epoxy-based fibre metal laminate panels. These lightweight materials are excellent candidates for use in transportation applications, where mass is a major factor in design and materials selection. Interfacial bond strength was characterised through single leg bend testing and revealed varying failure characteristics for different epoxy configurations and surface treatments. A combination of bead blasting and silane treatment provided the best surface treatment for the aluminium, while SE84 epoxy resin gave superior adhesion properties compared to Prime 20ULV. Blast tests were performed to investigate the effect of bond strength on panel response under localised and more uniformly distributed air-blast loading conditions. Dimensionless analysis and failure mode identification were used to show that both fibre configuration and bond strength played a role in blast response but the bond strength (and particularly resin type) was more prominent.

Influence of elevated strain rate on the mechanical properties of hollow structural sections

As protective design engineering becomes more prevalent, cold-formed steel hollow structural sections are often desired design components. As such, it is necessary to understand the behavior of hollow structural sections subject to air-blast loading, including the material response under elevated strain rates. Dynamic tensile tests have hence been performed on subsize tensile coupons taken from the flats and corners of cold-formed rectangular hollow section members. Dynamic yield stresses were obtained at strain rates from 0.1 to 18 s−1, which encompasses and exceeds the range recorded during far-field blast arena testing. The dynamic increase factor was calculated for each data point and synthesized with previous cold-formed rectangular hollow section tests at even higher strain rates (100–1000 s−1). The data set was used to determine Cowper–Symonds and Johnson–Cook parameters. The resulting material models can now be used to determine the strength increase of cold-formed rectangular hollow sections subject to a wide range of impulsive, elevated strain rate loads.

Deformation-Induced Stability of Earthen Embankment Dams Subjected to Explosive Airblast Loading

Deformation-Induced Stability of Earthen Embankment Dams Subjected to Explosive Airblast Loading