Benjamin Erzar

ArcelorMittal · Global R&D

With the exponential increase of computational power, numerical simulations are more and more used to model the response of concrete structures subjected to dynamic loadings such as detonation near a concrete structural element or projectile-impact. Such loadings lead to intense damage modes resulting from high strain-rate tensile loadings in the c...

During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar sampl...

Ceramic materials are commonly used to build multi-layer armour. However reliable test data is needed to identify correctly models and to be able to perform accurate numerical simulation of the dynamic response of armour systems. In this work, isentropic loading waves have been applied to alumina samples to induce spalling damage. The technique emp...

Due to their large aggregates size and their heterogeneous microstructure, concretes are difficult materials to test at high strain-rates. Direct tensile tests, spalling tests and edge-on impact experiments have been especially developed and performed on a standard concrete (max grain size of 8mm). The influence of free water on the high strain rat...

In the present work, dynamic tensile strength of concrete is experimentally investigated by means of spalling tests. Based on extensive numerical simulations, the paper presents several advances to improve the processing of spalling tests. The striker is designed to get a more uniform tensile stress field in the specimen. Three methods proposed in...

ABS is commissioning a new hot rolling line dedicated to the production of grinding balls. The process requires an adequate combination of induction heating, rolling, and quenching to achieve the desired characteristics for the final grinding balls made of high carbon steels. This study focuses specifically on the on-line quenching process. Firstly...

Numerical simulation can be a powerful tool to study the chemical heterogeneity within continuously casted steel, i.e. the macrosegregation. To do so, one must model phenomena activated in multicomponent alloy solidification at different length scales. At the microscopic scale of the solidification front, several parameters must be defined for each...

Hot rolling process is essential to obtain high-quality finished products from as-cast blooms. Numerical simulation constitutes a useful tool to better understand and to optimize such industrial process. In this work, a methodology is implemented to limit the risk of surface defects in the hot rolling of long products. The analysis is conducted in...

Hot rolling of bars issued from continuous-casting aims at refining the material structure and guaranteeing the central soundness of the metallurgical product. The rolling route must be designed to achieve the complete closure of the shrinkage porosity inherent in the continuous casting process. To predict the void evolution, many models exist that...

When a projectile hits a concrete target, several specific mechanisms are activated. Craters forms on front and rear faces of the target mainly due to shear and tensile damage. In the vicinity of the projectile nose, the concrete material is subjected to intense pressures (several hundreds of MPa), increasing its apparent ductility. Ultra-high perf...

The initiation of solid explosives under shock loading is commonly related to the formation of hot spots. These hot spots are mainly formed at the heterogeneities of the microstructure: porosities, cracks, debondings, particle edges, etc. To study the initiation of these materials, their microstructural properties have thus to be taken into account...

Ceramics are particularly well suited to build protective structures. However, the maximum tensile stress that the material can withstand is generally ten times less than their compressive strength. The knowledge of the dynamic tensile behavior of ceramics is essential to simulate their ballistic response. Spalling tests by means of plate impact te...

In previous work, impact experiments were performed at ISL on three energetic materials composed of 70 % in weight of RDX particles embedded in a wax matrix. These materials differ by the microstructural properties of the explosive particles. The experimental results reveal that the detonation thresholds, and so the sensitivity to shock, are differ...

CEA-Gramat studies the sensitivity of energetic materials to enhance their security and reliability. The conditions leading to the initiation of an explosive must be understood to control its sensitivity. According to the hot spots theory, the shock initiation of heterogeneous explosives is related to their microstructure: the shock interacts with...

Due to the wealth and diversity of their properties, advanced ceramic materials are well known for a wide range of applications, such as biomedical implants, electrical insulators, semiconductors or conductors, filters and membranes against aggressive environment. The microstructure of a ceramic plays a major role in its ballistic performance. Dept...

Ceramics are particularly interesting as protective materials due to their high compressive strength. However the maximum tensile stress withstood by these materials is usually lower by one order of magnitude. To study the dynamic strength in tension, spalling tests are commonly performed. In this work, a new spalling configuration is presented to...

Subjected to a dynamic traction, a ceramic material will eventually fail as a consequence of the triggering, propagation and coalescence of a distribution of microcracks. The DFH (Denoual-Forquin-Hild) anisotropic damage model considered in this study is based on a description of three physical phenomena activated all along the fragmentation proces...

The impact response of silicon carbide ceramics is a key issue due to the fact that they are increasingly used in lightweight armor solutions. In the present work, four silicon carbides with different microstructural properties are obtained by varying the sintering process (pressureless or spark plasma sintering in liquid or solid state). The dynam...

Cemented tungsten carbide, with its very high density and high strength, is known to be the material composing several small calibre armour piercing ammunitions. The impact of a tungsten carbide core projectile onto a high efficiency armour often leads to the fracture of the tungsten carbide core. Thus, the pertinence of material models used in num...

The dynamic response of brittle materials like ceramics is usually studied by means of flyer plate impact experiments. In this work, original tests has been carried out on several ceramics (alumina and silicon carbides) using a high pulsed power generator named GEPI. This electromagnetic device allows obtaining a ramp loading, spread over 500 ns. T...

Since a few years, the CEA Gramat has developed a "computational standard" intending at proposing a numerical simulation methodology program, tailored to guaranty the simulation of current and future weapons. In this work, two impact configurations involving specific mechanisms are simulated using the in-house code named OURANOS: the oblique impact...

To evaluate the vulnerability of ultra-high performance fibre-reinforced concrete (UHPFRC) infrastructure to rigid projectile penetration, over the last few years CEA-Gramat has led an experimental and numerical research programme in collaboration with French universities. During the penetration process, concrete is subjected to extreme conditions...

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary...

To evaluate the vulnerability of ultra-high performance fiber reinforced concrete (UHPFRC) infrastructure to rigid projectile penetration, CEA-Gramat has led since few years an experimental and numerical research program in collaboration with French universities. During the penetration process, concrete is subjected to extreme conditions of pressur...

Nowadays, the design of protective structures may imply ultra-high performance concretes. These materials present a compressive strength 5 times higher than standard concretes. However, few reliable data on the shock response of such materials are available in the literature. Thus, a characterization of an ultra-high strength concrete has been cond...

Ceramic materials are commonly used as protective materials for infantry soldiers and military vehicles. However, during impact, intense fragmentation of the ceramic material is observed. This fragmentation process has to be correctly numerically simulated if one wants to accurately model the dynamic behaviour of the ceramic material during impact....

Ceramic materials are commonly used as protective materials particularly due to their very high hardness and compressive strength. However, the microstructure of a ceramic has a great influence on its compressive strength and on its ballistic efficiency. To study the influence of microstructural parameters on the dynamic compressive behaviour of si...

Quasi-static and shock characterization of UHPC up to 6 GPa

Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et hétérogène. La modélisation mésoscopique présentée est un outil utilisé pour affiner l’échelle d’analyse et étudier l’importance de la microstructure sur la réponse mécanique, particulièrement lorsque le chargement appliqué est très rapide. Des essais d’écailla...

To better evaluate the vulnerability of reinforced concrete infrastructures to rigid projectile penetration, CEA-Gramat has conducted for a few years a research program with the help of French universities. The different phases appearing during the penetration process, like tunneling, scabbing or cratering, are respectively associated to several lo...

Thanks to their high mechanical properties and their low densities, ceramic materials are commonly used for armour systems. In this work, five spalling tests using ramp loading have been performed on an alumina ceramic. This technique allows determining more accurately the strain-rate at failure, in comparison to plate impact experiments generally...

Concrete is a material used all over the world for civil engineering but the mechanisms governing its dynamic behaviour are still not well understood. In this work, spalling tests and edge-on impact experiments have been used to determine the influence of the free-water contained in pores and micro-cracks on the dynamic strength and on the fragment...

Résumé — Le béton est un matériau difficile à modéliser à cause de sa nature à la fois fragile et hétérogène. La modélisation mésoscopique présentée est un outil utilisé pour affiner l'échelle d'analyse et étudier l'importance de la microstructure sur la réponse mécanique, particulièrement lorsque le chargement appliqué est très rapide. Des essais...

Concrete is a material widely used for constructions like bridges, nuclear power stations or bunkers. These buildings can be subjected to dynamic loadings such as industrial accidents or projectile-impacts. Consequently a good knowledge of the mechanical behaviour of concrete is a significant safety issue. This work aims to study the damage mechani...

Concrete is a material widely used in civil engineering. Thus the knowledge of its mechanical behaviour is a major safety issue to evaluate the ability of a structure to resist to an intense dynamic loading. In this study, two experimental techniques have been applied to a micro-concrete and a common concrete to assess the influence of the aggregat...

Intense damages as scabbing on front face, spalling on rear face, radial cracks are observed in concrete structures when subjected to the impact of a kinetic striker. To characterize the dynamic strength and damage of concretes under such loadings one may perform spalling tests and EOI (edge-on impact) tests. Both tests have been conducted with dry...

This book presents recent and cutting edge advances in our understanding of key aspects of the response of materials under extreme loads that take place during high velocity impact and penetration. The focus of the content is on the numerous challenges associated with characterization and modeling of complex interactions that occur during these hig...

To investigate the tensile strength of a dried mortar over a wide range of strain-rate (1e-5 s−1 – 5e3 s−1), quasi-static tests and dynamic tests have been conducted on dry specimens. The device used for the quasi-static experiments is a hydraulic press armed with ball-and-socket joints on both sides of the loading platens between which the mortar...