Robert Panowicz

Introduction to numerical analysis of directed fragmentation warheads

The aim of the paper is to presents one of the possible approaches to the numerical analysis of the behaviour of directed fragmentation war heads. These kinds of warheads consists of: metallic or composite cover, explosive material and a driven and fragmentation liner. The explosives are initiated by a booster causes driving the liner in a few milliseconds up to about 900 m/s. The liner fragments into many parts during this intensive and dynamic load. The fragments move in a cone which dimensions depend on the warheads shape and mechanical parameters of others warheads parts. All of the warheads elements are selected to meet the assumed parameters. The fragments velocity, their mass or geometric dimensions and cone angle are the most important parameters of the warheads fragments. Such a warhead, in the initial phase of the liner driving can be numerically modelled in the field of the continuum damage mechanics. Such a description is presented in other papers. This approach in a further phase of driving cause the increases of inaccuracies. Therefore, this paper proposes the use of ALE and FSI approach to describe the behaviour of the fragmentation warheads. A three-dimensional numerical model of the directed fragmentation warheads was made in the MSC Patran, and the dynamic phenomena analysis used a nonlinear finite element method implemented in the LS-Dyna program.

ANALYSIS OF SELECTED CONTACT ALGORITHMS TYPES IN TERMS OF THEIR PARAMETERS SELECTION

The analysis of many engineering problems involves not only deformation of the considered system, but occurrence of the interaction between the individual separate elements of the system as well. The occurrence of friction is the most common phenomenon occurring during this interaction. In the case of intense friction, the heat released in this process is also important. In computer methods of mechanics, the process of interaction between bodies is carried out using special algorithms. The most frequently applied are: the penalty method, the barrier method, direct elimination of constraints, the Lagrange multiplier method, the perturbed Lagrangian method, the augmented Lagrangian method, Nitsche method. Owing to its easy implementation process, an approach based on a penalty function is often applied. In this approach, the contact between the bodies can be identified with the presence of the spring between the elements of the bodies in the contact. The stiffness of the spring depends on: material bulk modulus, face area, volume or shell diagonal and a numerically selected scale factor. The article will present the results of analyses that will allow fast and easy selection of its value. In the analyses there were presented the results considering the basic types of contacts: node to surface, surface to surface and surface to surface mortar.

Numerical simulation of dynamic weld compression

The article presents some numerical results and experimental validation of Split Hopkinson pressure bar (SHPB) tests for welded S40NL steel. The goal of this research is to define material constants for modelling it in FEM. Steel was tested with Charpy impact test to determine properties of material. Next, the joint for welding was prepared. It was welded with electric arc welding method (MAG) with flux-cored wire. Hopkinson bar test is well-known experiment method used to determine material properties at high strain rates. The tests were performed in Institute of Fundamental Technological Research. Material properties for Johnson-Cook material model were obtained. Comparison between experimental results taken in quasi-static conditions and dynamic conditions proves that the behaviour of materials in those two states is quite different. Results from one type of loading condition cannot be used to create a realistic model of material when it is loaded dynamically. Numerical simulation of Hopkinson bars was performed on cylindrical model with known length and accelerated to high speed in direction of incident bar. For the purpose of the simulation, a Finite Element Code LS-DYNA was used. It allows simulation of dynamic response of SHPB system. The results show quite good agreement. The model can be used to simulate weld performance under high strain rate.

NUMERICAL ANALYSIS OF THE INFLUENCE OF THE DEFLECTOR STIFFNESS AND GEOMETRY ON ITS EFFECTIVENESS

The aim of the paper is to present the results of numerical analyses of designed classical system for measuring impact of the pressure wave originating from the detonation of explosive charge. In the paper, authors present classical ballistic pendulum in the form of the 1-meter length, HEB220, double T beam, which was suspended on the four parallel steel cables. On the front part of the pendulum, steel deflector was attached, whose aim was to disperse the energy. A few variants of used deflector were prepared, differing in the deflector geometry and thickness of the used material. In the next step, presented system was loaded with use of pressure wave, originating from detonation of 50 grams explosive charge. In order to properly describe the detonation process ConWep method was used. In this method, on the basis of preset geometric and mass parameters, together with TNT equivalent, the pressure pulse is determined. A three dimensional model of classical ballistic pendulum was prepared in MSC Patran software and numerical analyses were performed using LS-Dyna software. As the result of numerical analyses, the maximum deflection of the pendulum was determined for each case. Based on obtained results the influence of deflector geometry and stiffness on energy absorbing was identified and presented in the form of graphs.

Numerical analyses of the V-shaped deflector effectiveness

One of the most effective ways to protect mobile objects from the effects of the pressure wave originating from the detonation of a landmine or an explosive charge is to use a special design of the bottom of the protected vehicle. Such structure, called the deflector, in most cases has the shape of the V letter. Article presents the study of effectiveness of the V-shaped deflector. Authors prepared numerical model of a ballistic pendulum consisting of the 1 meter long HEB220 H-beam, suspended using four parallel steel ropes. In the front part of the beam, deflector was mounted. The test component was loaded with pressure wave coming from the detonation of an explosive charge. The article presents an analysis of the ability of the deflector to disperse and/or absorption of energy, depending on the type of the used explosive material and its mass. Studies have been done on the basis of numerical analysis performed with use of the finite element method with explicit integration over time scheme, implemented in the LS-Dyna software. For generation of the pressure wave originating from the detonation of explosive charge ConWep algorithm was used. It uses the predefined by the user geometric and mass parameters, and TNT equivalent to the generation of a pressure pulses.

INFLUENCE OF DIMENSIONAL PROPORTIONS OF CYLINDRICAL EXPLOSIVE ON RESULTING BLAST WAVE

Explosives are broadly used today in many applications, both civilian and military. Many experiments involving explosives use either ball or cylinder charges. However, there can be raised a question whether an exact shape influences the resulting blast wave, and, additionally, if the length to diameter ratio of the cylinder influences the wave. To answer the question, numerical analysis was conducted. A 3D model of the charge was constructed in LS-Prepost software and calculated with use of an explicit FEM method in LS-DYNA software. To determine the change of character of the blast wave, the dimensions of the charge change, whereas the mass and distance from the centre of the charge are constant. Several length to diameter ratios was tested, starting from 0.25, to 2, in 0.25 increments. Two explosives, HMX and TNT, were used. As expected, the resulting Blast wave was different in each case, with 100% difference in pressure values between 0.25 and 2 L to D ratios, especially along the length axis of the cylinder. The results show that the exact diameters of the charges need to be taken into consideration while determining a type of charge to be used as well as determining the goal to be achieved during a particular conducted experiment.

Analysis of the detonation initiation point position influence on the cylindrical fragmentation warhead effectiveness

The article presents results of the numerical analyses of the fragmentation warhead, which is one of the key elements of the missile used to combat anti-tank missiles. The fragmentation warhead is composed of such elements as outer casing, inner casing, explosive material and fragmentation liner. The fragmentation liner is built from steel spheres or cylinders embedded in epoxy resin. As a result of the explosive material detonation the pressure wave is generated, which affects the liner, causes its fragmentation, and drives each splinter. In order to perform numerical analyses the model of the cylindrical fragmentation warhead with a diameter of 80 millimetres and a length of 100 mm was prepared. The fragmentation liner consists of steel spheres with a diameter of 5 mm. It was assumed in simulation that the detonating material is the plastic explosive C4. The influence of the position of the explosive charge detonation initiation point of the fragmentation warhead on its effectiveness was studied. Effectiveness was evaluated by measuring the maximum speed obtained by the fragments and their spatial distribution. A threedimensional model of the studied system has been prepared using the MSC Patran software and the numerical analyses were performed using the finite element method with explicit scheme of the time integration implemented in the LS-Dyna solver. To model gas domain Arbitrary Lagrangian-Eulerian (ALE) method was used and interaction between gas and solid body was modelled with FSI coupling.

Numerical analysis of temperature influence on deformation and effort of bimetallic element

Bimetallic elements consist of at least two, connected together, material layers. The materials have different coefficients of thermal expansion. An active layer of bimetallic elements has a greater thermal expansion coefficient, whereas a passive layer has a lower one. Therefore, deformation of bimetallic elements occurs due to a change in temperature. The simplest case of bimetallic elements is a strip, which bends in the shape of an arc. As a consequence of elements deformation, stresses appear in them. An important problem is optimization of each layer of the element to achieve certain characteristics of the system. The elements should work in an elastic domain in the entire operating range. The aim of the paper is to present both numerical and analytical results for three different bimetallic elements. The following pairs of materials are considered: invar – incoloy, steel – brass and aluminium – molybdenum subjected to uniform heating. An influence of temperature and active layer dimensions of the sample on deformation and stresses of each layer was developed. It was found that the stress value is close to zero, on the boundary of each layer, for characteristic deflections of the considered bimetallic elements. The results of numerical analyses were compared with a theoretical solution presented by Timoshenko. Numerical analyses were performed using the Finite Element Method implemented in the commercial software LS-Dyna.

Experimental Studies on Protection Systems of Military Vehicles against RPG Type Missiles

The aim of this article is to present the results of experimental studies on protection systems of military vehicles against RPG type missiles. The paper presents the research methodology of rod armours and active protection system. On the basis of the presented methodology, both a rod armour and an active protection system were investigated. The effectiveness of these solutions reaches 70% in the rod armour and about 80% in the case of the active protection system.

Introduction to modelling side IED explosion influence on special military vehicle

One of the most endangering and challenging threats during recent warfare are explosions of Improvised Explosive Devices (IED) and their destructive influence on a light armoured vehicle. Providing sufficient protection is the most challenging issue which can be achieved thanks to complex studies and a proper design process. The article presents preliminary numerical analyses of side explosion near a special military vehicle with regards to newdeveloped standards. The results were used to modify the existing hull and enhance its protection capabilities against critical charge to provide better protection for personnel inside the vehicle. A numerical model was developed in LSPrePost software. All the computational analyses were carried out using an explicit LS-Dyna solver, where material properties of finite elements were described by the Johnson-Cook material model with the basic parameters specified in the standard tensile tests. Due to time consuming simulations, the Linux-based computational cluster was adopted. The setup (mass of the explosive, distance between explosive charge and vehicle, etc.) was taken from military codes. In their computational research, the authors performed also a kind of a sensitivity study changing some of parameters. Pressure, stress distribution and plastic deformations vehicle structure were analyzed.