PROBLEMY MECHATRONIKI UZBROJENIE , LOTNICTWO , I NŻYNIERIA BEZPIECZEŃSTWA ISSN 2081-5891 7, 3 (25), 2016, 113-126 PROBLEMS OF M ECHATRONICS ARMAMENT , AVIATION , SAFETY ENGINEERING Numerical and Experimental Analysis of Effectors Used in Active Protection Systems Robert PANOWICZ *, Tadeusz NIEZGODA, Marcin KONARZEWSKI Military University of Technology, Department of Mechanical Engineering and Applied Computer Science, 2 Sylwestra Kaliskiego Street, 00-908 Warsaw, Poland *Corresponding author’s e-mail address: [email protected] Received by the editorial staff on 2 November 2015. The reviewed and verified version was received on 17 February 2016. DOI 10.5604/01.3001.0009.2984 Abstract. The paper presents numerical and experimental analyses of effectors used in active protection systems. In the numerical analyses, the ALE method was used with FSI. Two types of destructors were analysed. The first destructor is a rectangular directed fragmentation warhead which can be mounted on the protected object. The second one is cylindrical and is a component of an antimissile. In both types of destructors we can distinguish several main parts, such as: the case, explosive material and fragmentation liner. The fragmentation liner is built from resin with submerged metallic spheres or cylinders. The fragmentation liner forms a cloud of fragments when the explosive material, located in direct contact with the liner, explodes. In order to perform numerical analyses, three-dimensional models of the destructors were designed in the HyperMesh software. The numerical analyses were performed with the Ls-Dyna software. The results of experimental tests carried out on one of the destructors are also presented in the study. Keywords: mechanics, finite elements method, dynamics, directed fragmentation warheads This work has been compiled from the paper presented during the 20th Engineering and Science Conference ARMAMENT 2015, Jachranka, 8-11 June 2015. 114 R. Panowicz, T. Niezgoda, M. Konarzewski 1. INTRODUCTION Passive defense systems for protection against classical and tandem shaped charge warheads (e.g. HEAT) have reached their optimum performance with the current state of the art in materials technology. However, they fail to provide sufficient protection for light armoured vehicles. Only active protection systems can ensure an improved level of protection from HEAT warheads for light armoured vehicles and their crew. An active protection system comprises several subsystems, or modules (Fig. 1): – detection module, – signal processing and decision module, – countermeasure/destructor module. The detection module is tasked with detecting and tracing the threat. Microwave or optical detectors are the most common applications for the detection modules [1]. The solution contemplated herein and developed at the Military University of Technology uses dual head with optoelectronic and radar detection. The two detector types increase the probability of threat detection and minimise false positive detections. The optoelectronic sensor is a passive device, whereas the radar sensor is a noise signal active device. This solution increases the EM emission levels of the protected vehicle by minimum values only; hence the risk of an enemy detecting a vehicle protected by this system is not increased. The signal processing and decision module analyses the input from the detectors to estimate the threat level of moving objects. If the inputs meet the characteristics of HEAT warheads and indicate a threat to the active protection area, the signal processing and resolving module will trigger the countermeasures at the suitable moment. The countermeasures, widely known as effectors, include a variety of solutions designed to neutralize an incoming HEAT warhead. In most solutions, the countermeasure is effected with fragments. The fragments are intended to trigger the HEAT warhead detonator in mid-flight or to the HEAT warhead symmetry disturbance. Only the Trophy system countermeasures are based exclusively on high-energy materials [2]. The active protection system (APS) developed as contemplated herein includes two destructor types as the countermeasures. The first one is a barrel- projected destructor for neutralization of threats further from the vehicle armour system. The other one is a fragmentation destructor intended for near-armour protection. The estimated efficiency of this tandem active protection system is approx. 80%. Numerical and Experimental Analysis of Effectors Used in Active Protection…. 115 Fig. 1. Functional diagram of the active protection system The barrel-projected destructor will soon be replaced with a smart anti- missile for threat destruction. The smart anti-missile will be a fire and forget solution. This is why it contains a miniaturized and simplified active protection The paper presents a selection of results from numerical analyses and experimental testing of the destructors at a testing ground. The numerical analyses were performed by an explicit FEM (finite element method) implementation of the Ls-Dyna software [3]. The numerical models were developed with the HyperMesh and Ls-Prepost software packages [4, 5]. 2. NUMERICAL ANALYSES OF DESTRUCTORS The paper investigates two destructor types. The first destructor can be mounted on the protected object. The unit comprises the following components (Fig. 2) [6-8]: – casing, – explosive material, – fragmentation liner (resin-embedded fragments), – detonator. 116 R. Panowicz, T. Niezgoda, M. Konarzewski a) b) Fig. 2. Numerical model of the stationary destructor with a detonator seat recess: a) the whole model; 1 – fragmentation liner, 2 – casing, 3 – explosive material, 4 – cylindrical fragments; b) the fragments and the fragmentation component, comprising a number of metallic cylinders The other destructor is axially symmetrical in form and will be applied in the anti-missile solution. The components are identical to those used in the first destructor (i.e. the casing, the explosive material, the fragmentation liner, and the detonator) (Fig. 3). a) b) Fig. 3. Numerical model of the axially symmetrical destructor: a) the whole model; 1 – fragmentation liner, 2 – inner casing, 3 – explosive material, 4 – outer casing, 5 – spherical fragments; b) the fragments and the fragmentation component, compr ising a number of metallic spheres Paper [9] shows a detailed description of the system and the applied material models. The numerical analyses were performed using the ALE method ( Arbitrary Lagrangian – Eulerian ) and FSI ( FSI – Fluid-Structure Interaction ) [10-12] implemented in Ls-Dyna [3]. Numerical and Experimental Analysis of Effectors Used in Active Protection…. 117 a) b) c) d) Fig. 4. Horizontal plane dispersion of the fragments in selected time points: a) t = 0.25 ms, b) t = 0.5 ms, c) t = 0.75 ms, d) t = 1 ms Examples of the numerical analyses results for the stationary destructor are shown in Figs. 4 to 6. Figs. 4 and 5 show the dispersion of the fragments in the horizontal and vertical planes. Fig. 6 shows a velocity of the fragments. An analogous presentation of results for the axially symmetrical destructor is shown in Figs. 7 and 8. Fig. 8 shows a cloud of fragments propelled by the blast wave from the explosive detonation. 118 R. Panowicz, T. Niezgoda, M. Konarzewski a) b) c) d) Fig. 5. Vertical plane dispersion of the fragments in selected time points: a) t = 0.25 ms, b) t = 0.5 ms, c) t = 0.75 ms, d) t = 1 ms Numerical and Experimental Analysis of Effectors Used in Active Protection…. 119 Fig. 7 shows the mean fragment velocity propel by the detonation products. Note that the velocities achieved by the fragments of the anti-missile are lower by ca. 15 to 20% than those for the stationary destructor. This is due to the volume of the explosive material varying between the specific destructor heads. The effect here is the shorter time of action of the detonation products on the fragments and a lower velocity of fragments. Fig. 6. Fragments velocity for the stationary destructor Fig. 7. Fragments velocity for the axially symmetrical warhead 120 R. Panowicz, T. Niezgoda, M. Konarzewski a) b) c) Fig. 8. Dispersion of the fragments projected by the axially symmetrical warhead at t = 0.25 ms; a) front view; b) side view; c) isometric view Numerical and Experimental Analysis of Effectors Used in Active Protection…. 121 3. EXPERIMENTAL TESTING OF DESTRUCTORS The stationary destructors were subject to experimental testing. The experimental tests began with an assessment of fragment effectiveness and the damage potentially caused by the fragments to HEAT warheads (Fig. 10a) [15, 16]. Static testing of fragmentation density distribution followed (Fig. 10b). The testing consisted in evaluating what area of a HEAT warhead would suffer at least two impacts from the fragmentation and the test results were compared to the numerical analyses results. Note that the fragment dispersion is random and can be expressed with a Gaussian discrete distribution. The random nature of dispersion is largely related to the random distribution of the fragments in the fragmentation liner and the interactions between the fragments at the stage of propelling with the detonation. In the numerical model, the fragmentation distribution is determined by the initial state of the model. The test system is shown in Fig. 9. To eliminate the ground effect on the blast pressure wave propagation from the explosive detonation, the destructor was set up on an elevated fixture. The solution which met the predefined