Ebook: Critical Energy Infrastructure Protection

This book presents edited contributions from the NATO Advanced Training Course (ATC) entitled “Critical Energy Infrastructure Protection: Innovative Structures and Materials for Blast and Ballistic Protection”, held as a virtual event from 22 to 25 March 2021. This ATC was organized by the Ecole Militaire Polytechnique-Algeria and the Military University of Technology-Poland. The principal aim of the course was to gather specialists from those NATO member countries, represented by France, Belgium and Poland, and NATO partner countries, represented by Algeria and Tunisia, interested in the protection of critical infrastructure against terrorist attacks, and to share research and practical experience in this field. The meeting provided a forum for participants and speakers to disseminate their recent work on the protection of critical infrastructure, with a special focus on advanced materials and structures, modeling and numerical simulation, behavior of materials at a high strain rate and high temperature, and blast mitigation techniques. We also believe that this ATC served to promote the exchange of ideas, as well as international cooperation among scientists and engineers from this important field. We are particularly indebted to the head of the Ecole Militaire Polytechnique (EMP) for hosting fifty (50) Algerian participants/speakers at the EMP for the duration of the ATC event. Furthermore, we are indebted to the organizers for the success of the virtual meeting of participants and speakers from these two parts of NATO. We offer our sincere gratitude to all the speakers for their excellent lectures, and we are also deeply indebted to all those who answered our call for the papers included in this book. We acknowledge the excellent and active participation of the trainees and their invaluable critical discussions. In conclusion, this ATC contributed added value to NATO’s role in the protection of critical infrastructure and the Alliance’s Strategic Objective of Partnership. The book will be of interest to all those whose work involves protecting critical infrastructure from the threat of terrorist attacks.

Finally, on behalf of the co-directors of the ATC and all the authors, we would like to express deep gratitude to the NATO Emerging Security Challenges Division for the moral, professional, and financial support which enabled the organization of this event.

Leopold Kruszka

Faculty of Civil Engineering and Geodesy, Military University of Technology, Poland

Djalel Eddine Tria

Laboratoire Dynamique des Systèmes Mécaniques, Ecole Militaire Polytechnique, Algeria

The subject of this paper is a broadly understood critical infrastructure (CI) that performs a key role in the functioning of the state and the life of its citizens. Critical infrastructure can be destroyed or damaged, and its functioning can be disrupted both as a result of natural events and as a result of human activity. Hence, the lives and property of citizens may be at risk. Concomitantly, such events harm the economic development of the state. Therefore, the protection of critical infrastructure is one of the priorities facing the states. The aim of this paper is to present selected issues concerning risks and vulnerabilities within the protection of critical infrastructure.

The modern concept of resilience relies on adequate metrics of the objective and utility functions, pertinent evaluation of the damages and utility drops, multi-hazards modeling, adaptive options and recovery functions. The paper presents some key topics for the theoretical resilience in industrial and urban contexts. Three case studies are investigated:

- The case of industrial tanks: fragments generated by explosions, their trajectory and impact on surrounding facilities, risk and domino effects.

- The case of industrial tanks: effect of tsunamis and fragility curves development.

- A construction site: risk analysis, optimal layouts, guided crowd evacuation, and digital twins.

Critical infrastructure covering different interdependent sectors (energy, transportation, health, telecommunications, etc.) has the important role of ensuring the daily vital logistics for a comfortable and safe life of a country’s citizens. In recent times, this infrastructure is increasingly subject to various natural and man-made risks. One of the most widespread anthropogenic hazards is the phenomenon of explosions, either due to technological accidents or terrorist attacks, which effects are the most destructive to the infrastructure. Given the extreme importance of its role in the normal functioning of a country, the protection of critical infrastructure is a strategic issue.

In order to minimize the vulnerability of infrastructure to these risks, one of the important measures is to take into account its security beginning at the design phase. Indeed, it has been proven that taking this measure into account ab-initio often allows improving the security of the buildings or facilities that make up this infrastructure at a lower cost. However, the optimal design of structures likely to be subjected to blast loads requires an understanding of their responses as well as the dynamic behavior of their constituent materials.

This article is a state-of-the-art report on the responses of structures and their constituent materials to blast loads. Experimental techniques for obtaining very high strain rates, of the order of those generated by blast loads, are briefly described. The results of recent tests obtained with these techniques on ordinary and special concretes as well as on reinforced concrete structural elements are presented. Recent constitutive models of these materials and structures subjected to blast loads as well as numerical methods simulating the tests conducted are also reviewed.

Shock Physics that deals with material behavior at a very high strain rate (in the order of material propagation speed) reveals more and more its importance in engineering applications (automotive, defense, aeronautic, space, energy, etc.), geophysics (earth’s behavior, asteroid impacts) or astrophysics (planets and stars behavior). Nowadays, this term is used more often when classical high-speed dynamics reach their physical limits. After a short introduction to shock physics, an application to lightweight armor is used to illustrate the importance of coupling tuned experiments with simulations for dynamic material studies: In fact, lightweight armors of soldiers are in constant evolution to optimize protection efficiency. In this area, more and more complex simulations are investigated with compound structures including polymeric foam, composite, metal, and ceramic. Even if numerical capabilities are in perpetual evolution, there is a constant need of improving the knowledge of individual material response in the strain, strain rate regime closed to the threat. Collecting parameters for Equation Of State (EOS), strength and/or rupture models to fit material models is thus mandatory to ensure reliable numerical investigations. Since 2015, THIOT INGENIERIE Shock Physics Laboratory has been selected by the French Ministry Of Defense (MOD) Land Systems to perform materials characterization in three main families of ballistic materials. Parallel to those tasks, in-house simulations done by the dynamic material department have shown a very good agreement with validation tests based on the dynamic material characterizations. A coupled approach between laboratory experiments and numerical simulations has shown its relevance with ceramic, [1], an Ultra High Molecular Weight Polyethylene composite (UHMWPE) [2] and a polymeric foam [3]. For all those materials, the BBA methodology has been used to calibrate EOS, strength, and damage models by conducting a step-by-step procedure with a dual approach, mixing together experimental tests and numerical works simultaneously.

Among several blast mitigation methods, the use of lightweight layers, in particular sacrificial cladding, are investigated. The latter consists of a crushable core sandwiched between a front plate and the structure. This paper presents an optimal sacrificial cladding design required to protect a given structural element against a free-air blast loading. The structure property, the fluid-structure interaction and the blast loading are taken into account.

The aim of the paper is to show a type of the round-Robin test on the example of experiments at a high strain rate using various split Hopkinson pressure bar test stands located at different locations in Warsaw – a scientific-technical center and a university. The results of the conducted experiments in the form of a circumferential stress and radial stress were shown for each analyzed SHPB test stand, using an identical research specimen. A comparison was made, and the obtained results were compared on the graphs of the stress-strain curve for various SHPB test stands and on the strain rate – strain graphs for the selected SHPB test stand.

Due to their high specific mechanical properties, composite materials are used in a large number of structures in different fields and domains in replacement of conventional materials. With the increasing threat of accidental and intentional explosions, the risk for such structures to face blast waves cannot be neglected. Thus, it is a necessity to study the response of composite structures to this transient loading. Moreover, it is paramount to study the dynamic behavior of composite materials. However, the experimental identification of the dynamic mechanical properties of composite materials presents several difficulties, which make it an active research topic. This work deals with this subject. It discusses the use of high-speed imaging and numerical simulation for the identification of the high strain rate tensile and shear strength model parameters for fiber reinforced laminates.

This study aims to investigate experimentally and numerically the ballistic trauma absorption of different armor ceramics with aramid composite reinforcement. The studied ceramic materials include homogeneous alumina oxide, with different Al2O3 contents, alumina-mullite and reaction-bonded boron carbide (RBBC) ceramics where their composition, structure, and main mechanical properties are examined and analyzed. Likewise, the penetration behavior of a 7.62x39 mm Mild Steel Cored (MSC) bullet from an AK round and 7.62x51 Full Metal Jacket (FMJ) bullets was studied, since the selected armors are often subjected to such particular threats in personal body armor systems. Three dimensional FE models of the bullets and armor plates were developed to study the penetration behavior of the bullets, the fracture pattern of ceramics and to predict the Back Face Deformation (BFD) of the considered armors. It was found that the studied armors have been proved to have very acceptable protection levels due to the measured ballistic trauma, which was in accordance with standard NIJ-0101.06. Also, despite the total erosion of the 7.62x51 mm FMJ bullet during the penetration process, it has the highest recorded ballistic trauma. Blunting and mushrooming of the 7.62x39 mm MSC bullets leads to decreasing of its intrusion in the armor plates. The combination of the constitutive relations and the FE algorithms has successfully matched details of impact tests for the bullets and the armor plates that lead to the explanation of the dispersion of the BFD measures for each impact situation. The propagation of radial and circumferential cracks, fracture conoid formation has been well predicted for alumina ceramics. The highest BFD values were shown in the RBBC ceramics with the absence of residual fracture conoid after the impact.

One of today’s state-of-the-art techniques for strengthening of reinforced concrete structural elements is the use of Carbon Fiber Reinforced Polymer (CFRP) composite strips as Externally Bonded Reinforcement (EBR). This is justified for quasi-static loads by the high strength, light weight, and excellent durability characteristics of CFRP EBR in combination with their ease of application. This paper deals with the performance of the technique for blast loads. This paper investigates the usefulness of CFRP EBR to improve the flexural resistance capacity of reinforced concrete hollow core slabs (RCHCS) under blast loads. In order to achieve this objective, three simply supported RCHCS with a compression layer were subjected to an explosion test. The obtained experimental results of the RCHCS without and with EBR are presented and discussed with the aim of evaluating the influence of EBR on the blast response of the RCHCS. A numerical analysis is also carried out using the finite element software LS-DYNA to complement the experimental results.