Frederik CogheRoyal Military Academy · Weapon Systems & Ballistics
Frederik Coghe
PhD
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71
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Introduction
Education
September 2008 - November 2013
October 2003 - June 2005
August 1995 - December 2000
Publications
Publications (71)
Cage armour systems have been in use since the 1960s and are still being used extensively on many armoured vehicles up to this day to offer protection against mainly a number of RPG-7 shaped charge warheads. Nevertheless, many misunderstandings still exist up to this day as well as regarding their working principle as regarding their actual efficie...
This article concerns part of the forensic analysis performed in the aftermath of the MH17 incident, when a civilian airliner was downed over the Ukraine in July, 2014. This analysis was performed in the framework of the international Joint Investigation Team (JIT) created to investigate this incident. The article describes the followed approaches...
Both in military and in law enforcement operations, the most commonly found small caliber threat is the ubiquitous Kalashnikov, also known as the AK-47 (or simply AK). For that reason, a detailed experimental and numerical study of the 7.62 x 39 M43 projectile was made. In this work, 7.62 x 39 mm mild steel core ammunition was fired against a rigid...
The field of penetration mechanics covers studies related to materials behavior under impact loading. Usually, the assessment of the ballistic resistance makes use of the V50, the bullet impact velocity with 50 percent probability of perforation of the tested target. However, the estimation of the entire curve of the perforation probability is freq...
An adapted version of the Taylor impact test was developed to study the dynamic behaviour of a specific red Weible® plastilina. Instead of accelerating Taylor test samples composed of the studied plastilina with standard methods using pyrotechnic or pneumatic launchers, the drop tower principle was considered. Cylindrical samples of ballistic plast...
Buried charges such as improvised explosive devices continue to be one of the most lethal and hidden threats service members face. On detonation, ground debris near the blast area is accelerated towards service members as secondary fragmentation, consisting of sand, gravel and rocks. In order to mitigate injury, protective equipment can be worn, ye...
Granular materials can be used as protection to stop ballistic projectiles. Nevertheless, very few studies discuss the mechanisms of kinetic energy dissipation into granulates. An experimental setup using ballistic screens was developed to evaluate the deceleration of rigid spherical projectiles penetrating CRUSHMAT® targets. The method was validat...
Studying the mechanical response of the human thorax submitted to ballistic impact is a challenging field of research. For ethical reasons, it is not possible to perform tests on the human body. Numerical simulations are therefore one of the alternatives for evaluating the mechanical response of the human thorax. In earlier research, a simplified h...
The need to develop armour systems to protect against attacks from various sources is increasingly a matter of personal, social and national security. To develop innovative armour systems it is necessary to monitor developments being made on the type, technology and performance of the threats (weapons, projectiles, explosives, etc.) Specifically, t...
This paper deals with the assessment of damages occurred to an Ultra-High Molecular Weight Polyethylene (UHMWPE) based composite during ballistic impacts with two bi-metallic projectiles of different morphologies and masses. More specifically, the evaluated composite is DYNEEMA® HB80. The conditions of impact aim at evaluating the behind armour blu...
Plastilina is often used as a ballistic witness material (BWM) behind the armour to evaluate the backface signature (BFS). Indeed, it is cheap, reusable and it keeps its deformation after being impacted. Moreover, while it aims at evaluating the performance of ballistic protections when no perforation occurs, it can be subjected to a very wide rang...
The armour technologist conducts ballistic impact testing either for evaluating armour materials and systems or for studying material’s defeating mechanism. Most standards make use of the ballistic limit velocity for ballistic assessment. This is the bullet impact velocity that leads to the protection perforation in 50 per cent of the cases. Variou...
In the field of Behind Armour Blunt Trauma (BABT), knowledge of the cavity morphology and transient pressure is important data for understanding this dynamic process. Blocks of ballistic gelatine are very often used to simulate human tissues in the case of impact studies. In this paper, the non-penetrating ballistic response of gelatine blocks shie...
This work deals with modeling the interactions between projectile, protection and plastilina backing during a non-perforating ballistic impact. For its mechanical behavior, ballistic plastilina was considered as a fluid. A capillary rheometry analysis over a wide range of shear rates was performed to obtain its dynamic viscosity. The mechanical res...
Ballistic plastilina is very often used as witness material when testing ballistic protections. Before ballistic impact testing, it must be calibrated following precise requirements. Thus, plastilina necessitates an adapted conditioning procedure, influenced by its composition and texture. According to the NIJ standard, the calibration consists of...
Currently, ballistic helmets are mostly designed to stop fragments from diverse explosive devices. Nowadays, new requirements have emerged for helmets, such as stopping direct impacts from revolver and pistol threats. The probability of these types of impacts on helmet systems is increasing due to the changes in warfare and military operations. Alt...
The objectives of the current study are to develop a multiscale numerical modelling method to predict the plastic deformation of Ti-6Al-4V sheets under blast loading, validate the method with experiments and characterise, at room temperature, the impulsive mechanical behaviour of the alloy. The numerical modelling technique relates the microstructu...
The standardized ballistic testing methodologies for Personal Protective Equipment that are currently used, incorporate the use of common mass production projectiles. The discrepancies in their attributes, material composition, geometry, assembly, production tolerances, introduce extra variability in their responses, for the stochastic physical phe...
The ballistic resistance assessment is an active research field that deals with the estimation of the perforation probability of a given protection/bullet combination. The modelling challenge is to increase
accuracy and precision of estimates based on a small sample of hidden penetration processes (limitation of experimental measurement tools due t...
The ballistic performance of materials subjected to projectile impact loading is analyzed based on the determination of the ballistic limit velocity (BLV) or the depth of penetration (DoP). The ballistic assessment of thick plates is generally based on the use of the DoP parameter. Experimental observation reveals the randomness of the DoP of a giv...
For many years, ballistic performance evaluation of protection structures makes use of the estimation of the ballistic limit velocity V50, the projectile impact velocity at which there is a 50 percent probability of perforation of the assessed structure. In recent years, enhancements to risk assessment required the estimation of the entire curve of...
Currently, military helmets have greatly reduced the risk of penetrating injuries and saved the lives of many soldiers. However, the risk of a non-penetrating impact has increased and can lead to serious injuries. Behind-helmet blunt trauma is an injury to the human body that results from the back face deformation of the head protection armour syst...
In the past few years, military helmets have greatly reduced the risk of penetrating injuries and saved the lives of many soldiers. However, the risk of a non-penetrating impact has increased and can lead to serious injuries. Behind-helmet blunt trauma (BHBT) is an injury to the human body that results from the back face deformation (BFD) of the he...
The integrity of buildings and the safety of their occupants can be catastrophically affected by the action of contact or near-field explosions. Numerical simulation studies should be carried out in order to better understand the response of reinforced concrete (RC) structures to such dynamic impulsive actions. When concrete structural elements are...
![Fig. 3. Comparison of the evolution of the temporary cavity from [4]...](profile/Lionel-Gilson-2/publication/298908126/figure/fig2/AS:905226840182791@1592834305663/Comparison-of-the-evolution-of-the-temporary-cavity-from-4-left-and-the-two-selected_Q320.jpg)
Among the different material surrogates used to study the effect of small calibre projectiles on the human body, ballistic gelatine is one of the most commonly used because of its specific material properties. For many applications, numerical simulations of this material could give an important added value to understand the different phenomena obse...
In this paper, a multiscale numerical method is presented with the aim to model the response of a Ti6Al4V sheet under explosive forming. The numerical modelling focuses on the accurate definition of the plastic deformation of the Ti6Al4V specimens based on the texture of the material. The viscoplastic self-consistent polycrystal model code (VPSC) i...
General description of impact damage mechanisms
The ballistic helmet shells used today are made of a single layer (typically composite material) offering good protection against fragments but only limited protection against small calibre projectiles. However, nowadays, due to changes in the type of warfare and the desired higher standard of protection, an improvement of the ballistic protection...
The goal of this study is to apply an elastic viscoplastic self-consistent crystal plasticity model to predict the texture evolution in a Ti-6Al-4V alloy which has a (mainly) hexagonal crystal structure. The model under consideration is an extension of the viscoplastic self-consistent model proposed by Lebensohn and Tome [1993] which has been adapt...
Numerical simulations of the impact of a 90 mm HEP/HESH-round against an 80 mm thick plate of rolled homogeneous armor (RHA) are compared with experimental data. The 2D axis-symmetrical simulations were performed in AUTODYN. Analysis of the results showed that the deformation of the projectile upon impact could be characterized by simplified linear...
Whereas the introduction of a bullet simulating projectile (BSP) to eliminate the use of commercial ammunition during the ballistic evaluation of personal armour systems may seem promising from an organisational point of view, all possible interest stands or falls with the feasibility on comparing and scaling the relevant effects of the commercial...
Currently, ballistic helmet shells are made of a single layer (typically composite material) offering good protection against fragments but only limited protection against small calibre projectiles. However, nowadays, due to changes in the type of warfare and the desired higher standard of protection, an improvement of the ballistic protection offe...
The work presented in this paper concerns a project on the optimization of protections subjected to explosions (IED’s threat). Explosions generate two types of threats for a protective structure: blast and impact of fragments. Perforating and non-perforating impact tests were performed in our laboratory with steel spherical projectiles impacting a...
This paper summarizes the ballistic considerations of a general project concerning the protection against the threats associated with improvised explosive devices (IEDs). IEDs generate two kinds of threats: blast and fragments. One possible protection com- bines a ballistic textile (Kevlar®) to stop the fragments and a crushable material (Crush- ma...
Dyneema HB26 and HB80 are two types of composite materials that can be used in personal armour systems such as vests and helmets to protect against a wide range of ballistics threats. A numerical model is developed and presented for the impact of a small calibre projectile on Dyneema HB26 and HB80 composite panels. This work focuses on determining...
This paper presents a study carried out with the commonly used
experimental techniques of ballistic pressure measurement. The
comparison criteria were the peak chamber pressure and its standard
deviation inside specific weapon/ammunition system configurations. It is
impossible to determine exactly how precise either crusher, direct or
conformal tra...
In the present work, dynamic tests have been performed on a new
ballistic steel alloy by means of split Hopkinson pressure bars (SHPB).
The impact behavior was investigated for strain rates ranging from 1000
to 2500 s-1, and temperatures in the range from - 196 to
300∘C. A robotized sample device was developed for
transferring the sample from the h...
The experimental characterisation of the dynamic (blast) behaviour of micro-agglomerated cork is presented. A 4-cable ballistic pendulum system was used to measure the transmitted impulse to a target subjected to a shock-wave originated from the detonation of an explosive. The displacement of the pendulum and the transmitted impulse were measured a...
Whereas deformation twinning is known to be an important deformation mechanism for hexagonal materials like magnesium and pure titanium, so far almost no literature exists on the twinning behaviour of the Ti–6Al–4V alloy. In this work it was shown that the activation of twinning as a deformation mechanism could have a pronounced effect on the mecha...
An accurate isotropic and kinematic hardening model and description of the strain rate dependent material behaviour is necessary for simulation of fast forming processes. Consequently, the material model parameter identification requires experiments where large strains, high strain rates and strain path changes can be attained. Usually, quasi-stati...
Quasi-static tensile tests and high strain rate split Hopkinson bar tensile experiments were used to mechanically characterize a commercially available Ti6Al4V alloy. The material was tested along different directions as to assess the influence of the initial crystallographic texture on the mechanical behaviour. In order to circumvent the problem o...
The goal of this study is to assess whether the MULTISITE and the Viscoplastic Self Consistent (VPSC) models can predict the mechanical behaviour and the texture evolution of plastically deformed hexagonal metals. Two types of Ti6Al4V,a sheet and a bar,are considered in the application. Plastic anisotropy of this type of titanium alloy is known to...
In the present work, dynamic tests have been performed on high hardness steel, aluminium and titanium alloy specimens by means of a split Hopkinson pressure bar (SHPB). The impact behavior was investigated for strain rates ranging from 1000 to 2500 s-1, and temperatures in the range from -150 ̊C to room temperature. Simulations of the temperature e...
The twinning behavior of a commercial Ti-6Al-4V alloy is studied using a combined experimental and numerical approach. An extensive microstructural investigation was performed to identify and quantify the active twin systems. The mechanical behavior as a function of initial texture and strain rate was then modeled using a visco-plastic self-consist...
Twin formation during uniaxial compression of high-purity α-Ti at room temperature is investigated for both quasi-static and dynamic conditions using electron backscatter diffraction techniques. The initial texture is favorable for 10 1 ¯ 2 twinning, yet it is observed that secondary and ternary twins occur for both strain rates, showing a higher p...
The detonation of an explosive charge has two major effects, blast wave generation and fragmentation. New technologies of energy dissipation, based on granular materials, seem to have good shock attenuation capabilities. Plastic deformation, brittle fracture and comminution are different mechanisms of dissipation which can take place in granular me...
![Physical properties of NL20 cork compound [5].](profile/Filipe-Teixeira-Dias/publication/237099505/figure/tbl1/AS:921835864616960@1596794205353/Physical-properties-of-NL20-cork-compound-5_Q320.jpg)
The integration of a high-hardness steel armor plate inside the bodywork of a vehicle may result in a decrease in the overall ballistic resistance. This phenomenon is referred to as the bodywork effect. The effect was examined for a 5.56 X45 mm North Atlantic Treaty Organization (NATO) Ball projectile. Previously reported experimental work has conf...
To study the high strain rate shear behaviour of Ti–6Al–4V, hat-shaped specimens have been used in a compression split Hopkinson bar set-up. With this technique, highly concentrated shear strains are obtained which eventually cause strain localization and adiabatic shear bands (ASB). Because of the complex stress distribution in the specimen, inter...
a b s t r a c t Ti6Al4V sheet material is subjected to simple shear deformation with strain ratio's of 10%, 30% and 50%. Optical microscopy, transmission electron microscopy and electron backscatter diffraction techniques are applied to study the presence and morphology of deformation twins. Only the 1 0 1 2 type of twins seems to be present with a...
The linear friction welding (LFW) behavior of Ti-6Al-4V, a commercial alpha + beta titanium alloy, was investigated using oscillation frequencies ranging from 30-70 Hz and axial pressures from 50-110 MPa. LFW samples were examined using electron backscattered diffraction (EBSD) to relate the texture to the welding parameters and to the estimated st...
This article is a first attempt to determine the influence of the initial texture and strain rate on the dynamic anisotropic behaviour of a material with a (mainly) hexagonal crystal structure. For this research a commercial Ti6Al4V alloy was used, composed mainly of a hexagonal α-phase. By quasi-static (servo-hydraulical) and dynamic (SHPB) compre...
In the present work, dynamic tests have been performed on AA5083 and Ti6Al4V alloy specimens by means of a split Hopkinson pressure bar (SHPB). The impact behavior was investigated for strain rates ranging from 1000 to 1800 s−1, and temperatures in the range from 100 to 300°C. A robotized sample device was developed for transferring the sample from...
Add-on armour kits composed of high-hardness steel plates are often used to improve the protection of light personnel carriers and logistic vehicles against the ballistic impact of small caliber ammunition, such as the 5,56×45 mm and the 7,62×51 mm NATO Ball projectiles. The protective kits are integrated inside the existing vehicle bodywork. There...
This work shows some first results of a study aiming to determine the deformation mechanisms of a commercially available titanium alloy Ti6A14V as a function of initial texture and strain rate. In particular this work will deal with the strain hardening behaviour of the material. Cylindrical specimens were fabricated from a textured extruded bar in...
Deformation twinning is an important and necessary mechanism to accommodate deformations in materials with a hexagonal close
packed (hcp) crystal structure, i.e. commercial pure titanium. Ti6Al4V is a dual phase alloy of which the major phase (+−
90%) is the hcp alpha-phase. The occurrence of deformation twins in this type of material is not well d...
This paper presents the results of an experimental study on the mechanical behaviour of a commercial titanium alloy Ti6Al4V. One of the aims was to characterize the influence of adiabatic shear banding during compression at room temperature and at different strain rates. Cylindrical specimens were fabricated from an extruded bar in the mill anneale...
Metals and alloys deformed at high strain rates, which are occurring during impact or metal forming situations can suffer from premature failure due to the introduction of so called adiabatic shear bands (ASB). Very high strains occur in these narrow bands of localized deformation. In case of Ti6Al4V these bands are a known mechanism of failure [1,...
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Projects (6)
This project aims at proposing new methodologies for studying the influence of temperature and ageing processes on the dynamic mechanical response of composite materials, in order to get a better knowledge of the material response of the different constituents of the ballistic protections. Therefore, the immediate profit of this study will be the performance assessment and optimization of personal armours used in the field for mitigating ballistic threats.