Blast Protection Research Articles

Experimental response of high strength steels to localised blast loading

Modern high-strength and armour grade steels have developed continually increasing strength and fracture toughness, but there have been limited experimental investigations into their response to localised blast response. In this work, the response of four modern steels to localised blast loading is experimentally investigated. The deformation and rupture threshold is comprehensively characterised and a detailed fractographic investigation is conducted into the initiation and progression of rupture failure modes. It was found that for the current experimental setup, higher strength steels can outperform more ductile steels, and that steel with a tailored microstructure had a higher rupture threshold than three modern armour steels. All steels studied herein initiate rupture via ductile shear fracture, as opposed to tensile tearing which is common in lower-strength steels. Results showed that the deformation resistance cannot be predicted precisely using only yield strength, and only by considering strain hardening can the deflection response be more accurately predicted. A new non-dimensional impulse correction parameter was also developed that captures the effect of charge stand-off on the target plate deformation and rupture performance. The results demonstrate the suitability of high-strength steels for blast applications, and have application to the design and analysis of safer armour systems for blast protection.

Introduction to State Estimation of High-Rate System Dynamics.

Engineering systems experiencing high-rate dynamic events, including airbags, debris detection, and active blast protection systems, could benefit from real-time observability for enhanced performance. However, the task of high-rate state estimation is challenging, in particular for real-time applications where the rate of the observer’s convergence needs to be in the microsecond range. This paper identifies the challenges of state estimation of high-rate systems and discusses the fundamental characteristics of high-rate systems. A survey of applications and methods for estimators that have the potential to produce accurate estimations for a complex system experiencing highly dynamic events is presented. It is argued that adaptive observers are important to this research. In particular, adaptive data-driven observers are advantageous due to their adaptability and lack of dependence on the system model.

Experimental Investigation of Polyurea‐Coated Steel Plates at Underwater Explosive Loading

To improve the survivability of ship structures at underwater explosion, thin steel plates coated with polyurea were used to investigate the blast protection effect. During the experimental tests of bare steel plates at different standoff, an appropriate distance was selected as the reference standoff to perform the tests of coated plates. Experimental tests of different coating locations (front versus back) and coating thickness were carried out to study the influencing factors of blast resistance for metal substrate plates. Compared with the bare steel plates, the polyurea coating was found to reduce the deformation of the test plates at blast tests in both cases of the front and back surface locations of the polyurea layer. An increase in the coating thickness also mitigates substantially the deformation of plates. In addition, the properties of the material and the substrate‐coating bond strength may also affect the protective effect of the polyurea coating.

Resilience-based design of urban centres: application to blast risk assessment

Current standards for the blast protection of buildings are primarily focused on the response of single components and do not provide adequate tools to quantify the overall performance of complex structural systems. Methodologies that can translate structural damage into information actionable by policy-makers are greatly needed to support the risk management process. The best efforts produced to date towards a comprehensive analysis of the built environment under blast threats can be classified under the umbrella of probabilistic risk assessment, which can provide the public with projections of casualties and economic loss. However, additional metrics are needed in order to capture the post-blast resilience of target facilities. The current study addresses the need of a unified risk and resilience framework, wherein new design criteria – the functionality loss index and the resilience indicator – are proposed as instrumental to the assessment of a building’s post-blast functionality and resilience in an integrated fashion.

Host-Induced Gene Silencing of Rice Blast Fungus Magnaporthe oryzae Pathogenicity Genes Mediated by the Brome Mosaic Virus.

Magnaporthe oryzae is a devastating plant pathogen, which has a detrimental impact on rice production worldwide. Despite its agronomical importance, some newly-emerging pathotypes often overcome race-specific disease resistance rapidly. It is thus desirable to develop a novel strategy for the long-lasting resistance of rice plants to ever-changing fungal pathogens. Brome mosaic virus (BMV)-induced RNA interference (RNAi) has emerged as a useful tool to study host-resistance genes for rice blast protection. Planta-generated silencing of targeted genes inside biotrophic pathogens can be achieved by expression of M. oryzae-derived gene fragments in the BMV-mediated gene silencing system, a technique termed host-induced gene silencing (HIGS). In this study, the effectiveness of BMV-mediated HIGS in M. oryzae was examined by targeting three predicted pathogenicity genes, MoABC1, MoMAC1 and MoPMK1. Systemic generation of fungal gene-specific small interfering RNA (siRNA) molecules induced by inoculation of BMV viral vectors inhibited disease development and reduced the transcription of targeted fungal genes after subsequent M. oryzae inoculation. Combined introduction of fungal gene sequences in sense and antisense orientation mediated by the BMV silencing vectors significantly enhanced the efficiency of this host-generated trans-specific RNAi, implying that these fungal genes played crucial roles in pathogenicity. Collectively, our results indicated that BMV-HIGS system was a great strategy for protecting host plants against the invasion of pathogenic fungi.

Practical Aspect of Methods Used for Blast Protection

The presented paper is focused on the practical aspects of retrofit technique used for blast protection of buildings. It presents the summary of various retrofit techniques.

Recommendations for a New Generation of Standards for Testing Numerical Assessment of Blast-Loaded Glass Windows

The determination of the blast protection level of civil engineering buildings components against explosive effects represents a design topic of crucial importance, in current practice. However, some key aspects of blast resistant structures design have been only marginally considered in the last decade, and currently still require appropriate regulations. This is especially true in the case of glass windows and facades, where the intrinsic material brittleness is the major influencing parameter for blast-resistant assemblies. While blast assessment of buildings and systems is usually achieved by means of experimental investigations, as well as Finite-Element numerical simulations, general regulations and guidelines are currently missing. In this regard, the European Reference Network for Critical Infrastructure Protection - Task Group (ERNCIP-TG) “Resistance of Structures to Explosion Effects” attempts to develop guidelines and recommendations aimed to harmonise test procedures in experimental testing of glass windows under blast, as well as standardized approaches for their vulnerability assessment via Finite Element numerical modelling. In this paper, major ERNCIP-TG outcomes and next challenges are briefly summarized.

Temperature effects on laminated glass at high rate

The load bearing capacity of a laminated glass pane changes with temperature. In blast protection, laminated glass panes with a Polyvinyl Butyral (PVB) interlayer are usually employed. The post-crack response of the laminated pane is determined by the interlayer material response and its bond to the glass plies. An experimental study has been performed to determine the effects of temperature on the post cracked response of laminated glass at a test rate of 1 m/s for PVB thicknesses of 0.76 mm, 1.52 mm and 2.28 mm. Tensile tests were carried out on single cracked and randomly cracked samples in a temperature range of 0 °C–60 °C. Photoelasticity observation and high speed video recording were used to capture the delamination in the single cracked tests. Competing mechanisms of PVB compliance and the adhesion between the glass and PVB, were revealed. The adhesion showed an increase at lower temperatures, but the compliance of the PVB interlayer was reduced. Based on the interlayer thickness range tested, the post-crack response of laminated glass is shown to be thickness dependent.

Impact and close-in blast response of auxetic honeycomb-cored sandwich panels: Experimental tests and numerical simulations

Protecting building, critical infrastructure and military vehicles from Improvised Explosive Devices (IEDs) has become a critical task. This study aims to examine the performance of a new protective system utilizing auxetic honeycomb-cored sandwich panels for mitigation of shock loads from close-in and contact detonations of high explosives. Both field blast tests and drop weight tests were performed using the proposed sandwiches asa shield for concrete panels in combination with conventional steel protective plates. The combined shield was found to be effective in protecting reinforced concrete structures against severe impact and close-in blast loadings. The honeycomb core with re-entrant hexagonal cells shows evident auxetic characteristics which contribute substantially to outstanding force mitigation and blast-resistance performances of such sandwich panels. Numerical simulations showed good agreement with the experimental results. The proposed auxetic panels were found to perform better than conventional honeycomb panels of the same size, areal density and material. Both were found to boost the energy absorption of the monolithic steel plate by a factor of 2.5 by changing its deformation pattern under close-in blast loading. In addition, a combination of the steel plate and an auxetic sandwich panel has aerial specific energy absorption (ASEA) higher than either of them, showing great potential for the development of lightweight blast protection of civil, mining, military, nuclear infrastructure and vehicles.

Development of a New Fence Type Blast Wall for Blast Protection: Numerical Analysis

Blast wall is considered to be an effective passive measure for blast protection since it can effectively reduce the blast loads and protect the building structures and people behind it. However, the current practice in blast wall design mainly depends on the structural strength and ductility to resist blast loads. These designs often lead to huge solid walls which are not only expensive, but also unsuitable for construction in urban areas, as they are not aesthetically appealing. Moreover, failure of solid blast wall may generate a significant amount of debris, which imposes great threats to people and structures behind the wall. In this paper, a new fence type blast wall, instead of the solid wall, is proposed to resist the blast loads based on the concept of wave interference. The proposed fence wall uses structural columns placed at strategic locations as wave stoppers to generate wave reflection, diffraction and interaction between the reflected and diffracted waves from different columns to result in self-cancellation of wave energy, thus leads to substantial reduction in blast wall size in design. Numerical simulations are carried out to investigate the effectiveness of the fence wall layout with different column geometries, column spacing, column dimensions, and fence layers on blast loads reduction. Based on the results, an effective design of the fence type blast wall is proposed, which can reduce the pressure and impulse of the blast loads behind the wall upto 70%.

Efficacy of visor and helmet for blast protection assessed using a computational head model

Head injury resulting from blast exposure has been identified as a challenge that may be addressed, in part, through improved protective systems. Existing detailed head models validated for blast loading were applied to investigate the influence of helmet visor configuration, liner properties, and shell material stiffness. Response metrics including head acceleration and intracranial pressures (ICPs) generated in brain tissue during primary blast exposure were used to assess and compare helmet configurations. The addition of a visor was found to reduce peak head acceleration and positive ICPs. However, negative ICPs associated with a potential for injury were increased when a visor and a foam liner were present. In general, the foam liner material was found to be more significant in affecting the negative ICP response than positive ICP or acceleration. Shell stiffness was found to have relatively small effects on either metric. A strap suspension system, modeled as an air gap between the head and helmet, was more effective in reducing response metrics compared to a foam liner. In cases with a foam liner, lower-density foam offered a greater reduction of negative ICPs. The models demonstrated the “underwash” effect in cases where no foam liner was present; however, the reflected pressures generated between the helmet and head did not translate to significant ICPs in adjacent tissue, when compared to peak ICPs from initial blast wave interaction. This study demonstrated that the efficacy of head protection can be expressed in terms of load transmission pathways when assessed with a detailed computational model.

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.

Blast Protection of Infrastructure with Fluid Filled Cellular Polymer Foam

Full field blast experiments were performed to assess the potential of fluid filled polymer foam for blast mitigation. The experiments involve air blast loading of clamped mild steel plates covered with fluid filed polymer foam for blast protection. The deformation profiles and maximum deflections of plates are compared with and without foam protection. The experimental results indicate a reduction in the plate deflection up to 50% with foam protection.

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.

Diversity and Distribution of Rice Blast (Pyricularia oryzae Cavara) Races in Bangladesh

The pathogenicity of 331 blast isolates (Pyricularia oryzae Cavara) collected from different regions and ecosystems for rice cultivation in Bangladesh was evaluated by compatibility on 23 differential varieties (DV), each harboring a single blast resistance gene, and susceptible 'Lijiangxintuanheigu' (LTH). A wide variation in virulence was found among the isolates, and 267 races were classified using a new designation system. Virulence of blast isolates against DV carrying the resistance genes Pia, Pib, Pit, Pik-s, Piz-t, Pi12(t), Pi19(t), and Pi20(t), as well as avirulence against those carrying Pish, Pi9, Pita-2, and Pita, was distributed widely in Bangladesh. Cluster analysis of the compatibility data on the DV initially classified the isolates into groups I and II. The virulence spectra of the two groups differed mainly according to the reactions of the DV to Pii, Pi3, Pi5(t), Pik-m, Pi1, Pik-h, Pik, Pik-p, and Pi7(t). Group I isolates were distributed mainly in rainfed lowlands, whereas group II isolates were found mainly in irrigated lowlands; however, there were no critical differences in geographic distribution of the blast isolates. In total, 26 isolates, which could be used to identify the 23 resistance genes of the DV on the basis of their reaction patterns, were selected as a set of standard differential blast isolates. To our knowledge, this is the first clear demonstration of the diversity and differentiation of blast races in Bangladesh. This information will be used to develop a durable blast protection system in that country.

Numerical strategies for damage assessment of reinforced concrete block walls subjected to blast risk

Computational tools and numerical strategies for the determination of the response of masonry walls under blast overpressure often rely on oversimplifying and conservative assumptions, which, although justifiable for design purposes, are not as warranted when fragility analysis and risk assessment are the objectives. In addition, due to the composite nature of reinforced masonry construction, the evaluation of multivariate fragility functions may likely require significant computational effort, owing to the multiplicity of variables describing the constituent materials and their associated uncertainty. The problem is further compounded by the effects of the high strain rates typically induced by blast loading, which make the understanding of masonry behaviour even more challenging; although efforts are being made in order to account for strain rate effects at the macro-scale, no well established models are available for reinforced masonry walls. Therefore, in order to perform accurate yet expedient fragility analyses that can effectively capture rate dependent phenomena, a dynamic model based on single-degree-of-freedom (SDOF) approach is developed. The SDOF model accounts for the nonlinear stress–strain behaviour obtained from standard prism tests and integrates strain rate dependent formulations provided in the open literature. The model predictions are corroborated using data—including pressure and displacement histories—from field testing of six scaled concrete block walls subjected to the detonation of live explosives. Within the scope of the current study, the proposed model is found to be a reasonable trade-off between computational efficiency and numerical accuracy and is an improvement upon a basic SDOF approach, which is typically based on the fixed dynamic increase factors recommended by modern design standards and technical manuals for blast protection. The results presented in this study are expected to contribute to the ongoing development of a comprehensive framework for the probabilistic risk assessment of structures subjected to explosive loading.

Large scale mechanical metamaterials as seismic shields

Earthquakes represent one of the most catastrophic natural events affecting mankind. At present, a universally accepted risk mitigation strategy for seismic events remains to be proposed. Most approaches are based on vibration isolation of structures rather than on the remote shielding of incoming waves. In this work, we propose a novel approach to the problem and discuss the feasibility of a passive isolation strategy for seismic waves based on large-scale mechanical metamaterials, including for the first time numerical analysis of both surface and guided waves, soil dissipation effects, and adopting a full 3D simulations. The study focuses on realistic structures that can be effective in frequency ranges of interest for seismic waves, and optimal design criteria are provided, exploring different metamaterial configurations, combining phononic crystals and locally resonant structures and different ranges of mechanical properties. Dispersion analysis and full-scale 3D transient wave transmission simulations are carried out on finite size systems to assess the seismic wave amplitude attenuation in realistic conditions. Results reveal that both surface and bulk seismic waves can be considerably attenuated, making this strategy viable for the protection of civil structures against seismic risk. The proposed remote shielding approach could open up new perspectives in the field of seismology and in related areas of low-frequency vibration damping or blast protection.

Experimental and computational investigations of the potential improvement in helmet blast-protection through the use of a polyurea-based external coating

Purpose – The design of the Advanced Combat Helmet (ACH) currently in use was optimized by its designers in order to attain maximum protection against ballistic impacts (fragments, shrapnel, etc.) and hard-surface/head collisions. Since traumatic brain injury experienced by a significant fraction of the soldiers returning from the recent conflicts is associated with their exposure to blast, the ACH should be redesigned in order to provide the necessary level of protection against blast loads. The paper aims to discuss this issue. Design/methodology/approach – In the present work, an augmentation of the ACH for improved blast protection is considered. This augmentation includes the use of a polyurea (a nano-segregated elastomeric copolymer) based ACH external coating. To demonstrate the efficacy of this approach, blast experiments are carried out on instrumented head-mannequins (without protection, protected using a standard ACH, and protected using an ACH augmented by a polyurea explosive-resistant coating (ERC)). These experimental efforts are complemented with the appropriate combined Eulerian/Lagrangian transient non-linear dynamics computational fluid/solid interaction finite-element analysis. Findings – The results obtained clearly demonstrated that the use of an ERC on an ACH affects (generally in a beneficial way) head-mannequin dynamic loading and kinematic response as quantified by the intracranial pressure, impulse, acceleration and jolt. Originality/value – To the authors’ knowledge, the present work is the first reported combined experimental/computational study of the blast-protection efficacy and the mild traumatic brain-injury mitigation potential of polyurea when used as an external coating on a helmet.

RETRACTED: Potential improvement in helmet blast-protection via the use of a polyurea external coating: Combined experimental/computational analyses

The Advanced Combat Helmet (ACH) currently in use is designed for maximum protection against ballistic impacts and hard-surface collisions. It has been well-established now that the ACH provides relatively little protection against blast, and that a significant fraction of the soldiers returning from the recent conflicts suffer from traumatic brain injury (TBI). In the present work, an augmentation of the ACH, which involves the use of a polyurea (a nano-segregated elastomeric copolymer)-based external coating for improved blast protection is considered. To test the utility of this approach, blast experiments are carried out on instrumented head-mannequins. Three configurations of the head-mannequins are investigated: (i) unprotected; (ii) protected using a standard ACH; and (iii) protected using an augmented ACH. To provide additional insight into the problem of blast-wave interaction with a head-mannequin, a series of complementary combined Eulerian/Lagrangian transient non-linear dynamics computational...

Blast Protection of Unreinforced Masonry Walls: A State-of-the-Art Review

The recent rise of terrorist attacks has reinforced the need for mitigation of damage caused by blast loading on unreinforced masonry walls. The primary goal of the techniques is to prevent the loss of life while simultaneously preserving the integrity of the structure. This paper presents a compilation of recently available literature on blast protection of unreinforced masonry walls. It seeks to present the state of the art in this field, including mitigation techniques considered as well as testing methods selected. Fiber reinforced polymers and polyurea are the two dominant retrofitting techniques being assessed in the field. Other techniques include but are not limited to polyurethane, steel sheets, and aluminum foam. Since there is no widely implemented standard for blast loading test procedures, direct comparisons between the efficiencies of the mitigation techniques proposed are not always feasible. Although fragmentation is an indicator of the efficiency of retrofits, it is currently measured by subjective observation of postblast debris.