Wiesław Barnat

EXPERIMENTAL INVESTIGATION OF SELECTED EXPLOSION PARAMETERS FOR NUMERICAL MODEL VALIDATION

The aim of presented work is examination of blast wave, especially incident and reflected wave pressure. Due to many difficulties and complexity of phenomenon a complete study for different charges should be done. In presented paper two cylindrical TNT charges were used, weighting respectively 100 g and 200 g. Pressure wave was examined using original test stand designed and developed on Department of Mechanics and Applied Computer Science. A test steel test plate with 5 mm thickness was equipped with pressure gauge to measure reflected wave. Additionally, the plate was placed on four special electroresistance strain gauges. To measure force Vishay EA-06-120-060LZ strain gauges were used. For amplification of the dynamometers with strain gauges, MS1001 INFEL bridge was used. The system was used to validate the results from reflected wave pressure gauge. Shock wave pressures was measured using a special sensor model 137A21 amd M350B21 made by PCB Piezotronics At specific distance there was also incident wave pressure gauge. In order to fully examine the dynamic response of the plate an accelerometer was used. As a result, pressure versus time and acceleration versus time plots were obtained. The results will be used to validate numerical model of blast wave impact on a plate.

Numerical and experimental research on the impact of the Twaron T750 fabric layer number on the stab resistance of a body armour package

Faculty of Mechanical Engineering, Department of Mechanics and Applied Computer Science, Military University of Technology, Kaliskiego 2, 00-908 Warsaw, Poland E-mail: dsokolowski@wat.edu.pl, wbarnat@wat.edu.pl Abstract The aim of the paper was to research how the depth of penetration in dependence on the fabric layer number used in the ballistic package is changed. During the research, the following methodology was adopted: the object of study was Twaron T750 fabric, specially dedicated for use in bulletproof vests. Then a numerical model consisting of 35 layers of fabric was established, from which the following parameters were selected for registration: depth of the knife’s penetration, displacement, velocity and acceleration. Then experimental studies were carried out which reflected the numerical model. In the next step a numerical model was validated and variants for the number of layers included in the package were created. The computing environment was commercial software LS-Dyna. Experimental studies were recorded using a super-high-speed camera PhantomV12. The studies were conducted on the basis of the NIJ Standard -0115.00 norm.

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.

EXPERIMENTAL INVESTIGATION OF DEFLECTOR'S ANGLE INFLUENCE ON ENERGY ABSORPTION

Numerical simulations without preliminary validation and model verification are vulnerable to errors. Best results are obtained when full experimental research is provided. Such tests are expensive and may be dangerous. Due to cost control and personnel safety, studies are often done in scale. Scale can affect both construction dimensions and applied load. In this paper four different vehicle’s bottoms are examined: flat bottom and 3 types of deflectors. The paper presents four different vehicle’s bottom shapes in order to examine deflector angle influence on energy absorption. The test included 4 cases: flat bottom broken-shaped deflector and deflectors with different apex angles 124° and 144°. For all cases the distance between explosive and panel was approximately 400 mm. The charge used was 100 g TNT. Flat bottom and deflectors were made of St3 steel with 2 mm thickness. For the purpose of the research a special test stand to examine effects of detonation wave was used. The force measurement system was designed in Department of Mechanics and Applied Computer Science. As a result, force versus time plots were obtained. The use of any deflector decreases maximum force affecting vehicle’s hull.

Numerical and Experimental Examination of Ballistic System Subjected to IED Explosion

This article presents results of experimental validation of complex phenomenon of blast wave and fragment impact on protective panel. Protective panel was made of HTK900K steel and Dyneema HB50 polyethylene. Standard level 1 IED surrogate was used. Test was conducted with regards to NATO STANAG 4569 and NATO AEP 55 standardizations. Computational analysis was performed using LS-DYNA code using explicit time integration scheme. Properties of steel, polyethylene and glue were obtained during laboratory tests. Steel was modeled using simplified Johnson-Cook model whereas polyethylene was modeled as composite material. Both blast wave and fragment impact was implemented in simulation. Good agreement between experimental and numerical data was obtained.

Determination of Dynamic Characteristics of Welded Joints Made of Steel S460NL

Examination of the behavior of materials under very high speed plastic deformation are widely used during the designing process of dynamically loaded steel structures. Steel is widely used as a basic material for designing engineering structures. Characteristics of steel obtained under static experiments are different from those obtained during static tests.

The study of stab resistance of dry aramid fabrics

Abstract The paper presents the issue of a knife proof ballistic package. This issue was emphasized since most of modern vests are designed to match the threat posed to them only by firearms. There was observed negligence of protection against melee attacks. There is, thus, a need to develop a research methodology in this matter, because it is a valid and necessary problem in a modern developed society. The aim of this study was to perform a numerical model which simulated the phenomenon of penetration of a ballistic package by an engineering blade. Specification of an engineering blade was taken from standard NIJ Standard-0115.00. Commercial software LSDYNA was used to carry out the analysis.

Experimental Investigation of IED Interrogation Arm During Normal Operation and Mine Flail Structure Subjected to Blast Loading

The paper presents experimental static tests of IED interrogation arm for Shiba special vehicle. The test was performed by Military University of Technology and Military Institute of Engineer Technology. A number of strain gauges and camera markers were placed on the arm to allow recording strains and movements of specific construction points. The arm’s motion was recorded using high speed camera. The equipment used were Vishay EA 06 120LZ 120 strain gauges with ESAM Traveler bridge. The sampling rate was 1000 Hz. The test was to pick up maximum design weight, move it to maximum overhang and then drop it on the ground. During the test, signal from gauges and video capture was recorded. The data was then processed using TEMA 3D software to obtain markers displacements and angular changes of both arm parts. Afterwards, the test was repeated for different weight. The analysis showed, that maximum stresses in examined construction parts did not exceed yield stress of material. As well as that, in-depth motion analysis of the arm was conducted. Further works are twofold. Firstly, there will be tests concerning arm under dynamic load occurring during normal maintenance During this test only strains in specific construction parts will be recorded. Secondly, numerical model of an arm will be developed and validated using data obtained during both tests. This will help visualize stress distribution in each arm’s part

Dynamic Analysis of Column Stand for Aircraft Multi-barrel Machine Gun with Consideration of Bearing Clearance

To build a machine gun on a helicopter board or on a vehicle, a sufficiently rigid and strong stand is required [2]. The construction of a column stand ensures changing a shot direction in the vertical plane and rotation in the horizontal plate. In a bearing of the column, a clearance can occur. It can cause a change in accuracy of a trajectory angle of the bullet. The paper presents a dynamic analysis of a machine gun taking into account clearance in the bearing. The target of the analysis is to find an impact of clearance on the trajectory angle of the bullet.

Analysis of IED sidebar explosion influence on hull of light fighting vehicle

This paper shows preliminary numerical analysis of impact of IED sidebar blast on the hull of the light fighting vehicle in order to meet the current standards. Numerical analysis was carried out using a 3-dimensional shell FE model of the vehicle. The problem of the modelling method and computer simulations required several specific features for applied material models, e.g. physical state, plasticity, crispness, hardness. All necessary material properties were taken from the available literature or they were based on the experimental tests carried out in the Department of Mechanics and Applied Computer Science at the Military University of Technology. The STANAG 4569 is a legal basis that regulates the level of ballistic protection for such vehicles. Companies producing that kind of armoured vehicles for army, constantly look for the best and the newest energy consuming materials to ensure appropriate protection of the vehicle and the crew inside it against the effect of IED blast. The connection between a detonation wave and a formed shrapnel shell after detonation of the IED is created depending on the mass and kind of the charge. It is caused by impulsive load on a side bar or the bottom of a light vehicle. Both, safety of people and equipment endurance, is compatible with main rules that are common in Polish Army and it will be common rule in future. It is the fact that motivates the research centres and the arms industry to develop a product using advance computation method to construct new energy absorbing construction which will increase safety of the crew in the armed vehicle.