High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa, respectively 1250 MPa and elongation of about 32.7%. These materials can be used to create HEA-steel type composite structures which resist to dynamic deformation during high speed impacts. The paper presents four different composite structures made from a combination of HEA and carbon steel plates, using different joining processes. The numerical simulation of the impact behavior of the composite structures was performed by virtual methods, taking into account the mechanical properties of both materials. For analyzing each constructive variant, three virtual shootings were designed, using a 7.62 × 39 mm cal. incendiary armor-piercing bullet and different impact velocities. The best ballistic behavior was provided by the composite structures obtained by welding and brazing that have good continuity and rigidity. The other composite structures, which do not have good surface adhesion, show high fragmentation risk, because the rear plate can fragment on the axis of shooting due to the combination between the shock waves and the reflected ones. The order of materials in the composite structure has a very important role in decreasing the impact energy.

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In this paper the authors present some of the results of research on the behavior of high entropy alloys used in ballistic protection structures. Bullet impact testing methodology and results on layered Ballistic Packages that incorporate high entropy alloys (HEA) are presented. The paper details the technological processes used to improve the mechanical characteristics of Ballistic Packages. The optimization of the high entropy alloy based layered ballistic composite structures is also investigated. Testing methodology of ballistic boxes, the special heat treatment processes, the homogenization and the artificial aging of high entropy alloys, designed and applied during scientific research; represent the novelties of the article. Ballistic Packages are layered structures which include combinations of the following materials: HEA, armored steel, ceramic plates and laminated polyamide fibers arranged in a predetermined order depending on the constructive version. Ballistic Boxes behavior was investigated by ballistic experimental methods and numerical simulation methods. For the numerical simulation a FEM with an explicit numerical code was used. The numerical and test results are consistent in underling the ballistic protection effectiveness of the investigated configuration.

In our present days numerical simulation became an important tool of engineering. Numerical simulation methods allow quantitative examination of the complex processes and phenomena in the general area of physics and also provide an insight in their dynamic evolution and even can become important tools for the discovery of new phenomena. In essence, the numerical simulation transfer important aspect of physical reality in discrete forms of mathematical description recreates and solves the problems on computer and finally, highlights issues that the analyst required. This modern numerical method approach, attacks the original problems in all their details on a much larger platform with a much smaller number of assumptions and approximations, in comparison to traditional methods. Transposition of the physics problems in the virtual space, governed by the force of computers, numerical simulation - as scientific approach - is becoming increasingly interesting for many fields of research. Basically, by means of numerical simulation are addressed fields such as mechanics deformable solids, fluid mechanics, aerodynamics, biomechanics, astrophysics. Numerical simulations follow a similar procedure to all the scientific approach, which consists in going through several stages, as follows: the phenomenon, the physical model, mathematical model, discrete model, and coding, numerical solution. In the plastic deformation of metals are involved, besides the mechanical properties and some thermal properties because even if the process is applied in the initial state to a cold material, along the process changes occur because of friction between materials and tools and transformation of plastic mechanical work into heat. Basic mechanical properties of the materials are underline through characteristic diagrams of materials obtained in simple tests of traction and compression. These tests were carried out in the Polytechnic University of Bucharest, Romanian Research & Development Institute for Gas Turbines COMOTI, Institute for Calculating and Testing Aero-Astronautic Structures STRAERO, SC UPS PILOT ARM Ltd, and Asachi Technical University of Iasi. To achieve the major objectives of the numerical simulation of the technological process of cold plastic deformation, are incorporated into the physical model three types of surfaces: cylindrical, conical and profiled. The sizes of the initial geometry were established in accordance with the basic dimensions of processed products by this method. For delimiting surfaces to be machined, the addition of grip (the tail) has a reduced diameter. Geometric models provide strength and rigidity needed for safely and accurately processing technology of cold plastic deformation. Geometric models and specimens which had been subjected to tensile tests, compression and hardness were made in the Glass Factory, Chisinau, Moldova.