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High Speed Impact

Determination of Impact Loads for a Tracked Military Vehicle during a Crash Scenario

In this study, crash simulation for a tracked military vehicle is performed and equivalent static and dynamic design loads are determined for a subsystem using LS-DYNA® and LS-OPT®. Detailed finite element model of the track geometry, suspension system and the hull is created. In order to have an accurate vehicle suspension behavior; some verification simulations are conducted with another commercial multibody software and the suspension kinematic is optimized. Full vehicle crash simulations are performed firstly and stress results are obtained from the sub-system mounts of the vehicle. Afterwards, small scale simulation model of the sub-system is created and LS-OPT® is used to get equivalent static and dynamic acceleration loads using the stress results which are obtained from crash simulation.

Armor Steel Impacted by Projectiles with Different Nose Shapes – Numerical Modelling

The presented experimental investigation concerns 3 mm thick target plates impacted by strikers with different noses at velocity close to 300 m/s and is conducted to gain an insight into mechanisms of deformation and fracture characteristic for a high strength high hardness armour steel, [1]. Guaranteed by the producer yield strength and ultimate tensile strength of the steel are 1300 MPa and 2200 MPa, and the hardness is within 600 – 640 HB, [2]. Due to impacts, the projectiles and targets, both extracted from the armour steel, are severely deformed and fractured. Numerical simulations of the performed test are carried out using the explicit solver of the finite element software package LS-Dyna R9.0.1. The model used in the simulation implemented through the user material subroutine accounts for a yield function with a non-associated flow rule, a Swift–Voce strain hardening law and Johnson–Cook type of multipliers with the effects of strain rate and temperature. The stress-triaxiality, Lode angle parameter and strain-rate dependent Hosford–Coulomb fracture initiation model is employed to predict a steel failure, [3-4].

Simulation of Concurrent Detonation of Multiple High Explosive Charges

A 1D spherical LS-DYNA Multi-Material Arbitrary Lagrange Eulerian (MM-ALE) model was constructed to simulate the three single charge events reported in MABS 25 manuscript P-029 Stojko, et al. (2018). These three simulations were repeated using 2D axisymmetric meshes. Multiple charge simulations were made using 2D axisymmetric and 3D models of the double and triple charge experiments. As stated by Stojko et al. “The primary purpose of the experiments was to provide a database of results for the validation of numerical modeling of the effects from multiple high explosive charges.” The model results presented in this manuscript support this statement of the data representing a valuable validation database for both single and multiple charge explosions.

Blast Detonated by Impact Simulation

The purpose of this study is to present parameters required for blast detonated by impact simulation in LS-DYNA with comprehensive approach and compare with AUTODYN results. Blast detonated by impact is a widely used method for controlled blast. However, design of the problem is more likely limited to simulation results. For a proper and reliable simulation, it has to be taken care of reacted and unreacted state parameters of detonative product, mesh size and method.

Numerical Methods for the Analysis of Behind Armor Ballistic Trauma

The asymmetric character of current military conflicts causes that soldiers are often exposed to projectile impacts. Body armor (helmets, vests, etc.) protects them from the negative effects of highly dynamic loads by absorbing and dissipating kinetic energy of a projectile. However, severe local and distant injuries can occur in the human body, even in case of a non-perforating impact. A large amount of energy and momentum is converted into deep back face deformation (BFD) of the armor and dynamic acceleration of the body walls. In case of high-velocity impacts a trauma may be caused also by the stress waves generated and propagated through the tissues. Injury of the human body as a result of non-perforating projectile impact into the armor is defined as Behind Armor Blunt Trauma (BABT) [1].

Fluid-Composite Structure-Interaction in Underwater Shock Simulations

Fiber reinforced plastics (FRP) and sandwich components are widely made use of in today’s submarines owing to their advantages such as high strength-to-weight ratio and durability in marine environment over conventional submarine building materials. Fig. 1 shows a state-of-the-art conventional submarine with an upper deck consisting of mostly composite components.

Bolted Joint Connections of FRP-Components in Submarines Subjected to Underwater Shock

The application of fiber reinforced plastic (FRP) and sandwich components is an established practice at various locations in state-of-the-art submarines. Due to acoustic reasons, easy formability and low mass density at comparatively high strength values, these components bear a huge potential for buoyancy-related constructions. The shock-design and -calculation of these components as well as their connecting parts are crucially supported by Finite Element simulations using LS-DYNA. The present work shows an investigation of FRP-based bolted joint connections in today’s submarines and their connection to the pressure hull in terms of modelling and simulation. The transfer from detailed models to simulation of a full-scale shock submarine, as shown in Fig. 1, is presented and discussed.

Numerical and Experimental Investigation of SPH, SPG and FEM for High Velocity Impact Applications

During a high-velocity impact event large pressure, strain rate, and deformation occur. This is a very demanding scenario for mesh-based approaches like the FEM (Finite Element Method). In particular, for the description of fracture, special techniques like erosion or node splitting are required. For a comprehensive validation, we have designed a projectile surrogate and conducted impact experiments at different oblique angles in our laboratories. These experiments are observed with X-ray cinematography and physical properties for validation are extracted from the images. For the highly dynamic behavior during the impact, an alternative to mesh-based approaches are particle-based methods. LS-DYNA® offers two pure particle methods, SPH (Smooth Particle Hydrodynamics) and SPG (Smooth Particle Galerkin). This study compares SPH to the FEM results and the experimental data. Since the discretization requirements for the numerical approaches are different, it is not possible to compare exactly the same discretization. Instead, the number of nodes is chosen similarly. The accuracy is investigated qualitatively, using X-ray images, as well as quantitatively, using the extracted properties from the experiments.

Improvement of Satellites Shielding under High Velocity Impact using Advanced SPH Method

A huge number of debris coming from human activities is currently gravitating around Earth. Their size, their nature, their orbit and their velocity can highly vary, but they all represent an increasing risk of collision and a threat for the current and future space activity [1]. The space actors are looking for solutions in order to limit these risks and to protect the structures from impacts and generation of new debris (spacecrafts conception, limitation of the debris multiplication, waste life stage strategies…).

Random Vibration Analysis for a Gunner Platform Frame using Experimental Data

Remote controlled weapon systems have gained great importance in defense industry as they maximize crew safety with accurate shooting capabilities. On the other hand, vibration levels are of great consideration because of its effect on crew comfort and system reliability especially for tracked armored vehicles. In this study, vibrational evaluation is performed for a remote control gunner platform frame, which is mounted to the top plate of an armored tracked vehicle. Vibrational response of the gunner platform is critical for a successful completion of especially mobile missions. In order to perform random vibration fatigue evaluation, the experimental data obtained from the top plate of an armored tracked vehicle is used and random vibration analysis are performed using LS-DYNA®. Power Spectral Density (PSD) profiles provided in NATO AECTP 400 document are also included in the random vibration analysis with a degree of modification in order to make a comparison. Finally, random vibration analysis results from LS-DYNA® are compared with the results of another commercial software using similar analysis parameters.

Study on Blast and Ballistic Loading of Auxetic Composite Sandwich Panels with LS-DYNA

Response of novel structures designed for impact, blast and ballistic protection can be enhanced using composite sandwich panels, which are able to extend the energy absorption capabilities [1]. Cellular metals offer very good energy absorption to weight ratio and are consequently used as the core of such composite structures [2]. One of the most promising for this kind of application are auxetic cellular structures, which are modern metamaterials with some unique and superior mechanical properties [3]. They exhibit a negative Poisson’s ratio, i.e. they get wider when stretched and thinner when compressed, as a consequence of their internal structure deformation. The effect of negative Poisson’s ratio is useful for many different applications to enhance properties in density, stiffness, fracture toughness, energy absorption and damping [3]. In case of impact the auxetic material moves towards the impact zone and thus increases the penetration resistance. The conventional cellular materials with a positive Poisson’s ratio in contrast move away from the impact area. The benefits of using auxetic materials as core layers in sandwich panels are obviously crucial to increase the impact energy absorption capability.

Ballistic Behaviour of UHMWPE Composite Material: Experimental Characterization and Numerical Simulation

This paper presents a comprehensive mechanical study of UHMWPE (Ultra High Molecular Weight Polyethylene) composite material under dynamic loadings. The aim of the study is to provide reliable experimental data for building and validation of the composite material model under impact. Three types of dynamic characterization tests have been conducted: in-plane tension, out-of-plane compression and out-of-plane shear. Moreover, impacts of spherical projectiles impact have been performed on larger specimen. Regarding the numerical simulation, an intermediate scale multi-layered model (between meso and macro scale levels) is proposed. The material response is modelled with a 3d elasto-orthotropic law coupled with fiber damage model. The modelling choice using *MAT_ORTHOTROPIC_SIMPLIFIED_DAMAGE is governed by a balance between reliability and computational cost. Material dynamic response is unconventional [1, 2]: it shows large deformation before failure and very low shear modulus and peeling strength. Numerical simulation has been used both during the design and the analysis of tests. Mechanical properties related to elastic moduli and failure strength have been measured. The ballistic numerical model is able to reproduce the main behaviors observed in the experiment. The study has highlighted the influence of temperature and fiber slipping in the impact response of the material.

Modelling Back Face Deformation of Woven Layered Composite Targets under Oblique Impact

Body armour is the only protection a dismounted soldier has against projectiles or fragments in case of combat. Perforation is prevented in body armour as the kinetic energy of the projectile is transformed to deformation work in the armour material. This dynamic material response upon impact is especially crucial for helmets, as it acts directly on the human head. One potential threat nowadays a foot soldier faces during missions is the 7.62x39 mm projectile fired from a rifle. Helmets are not designed to withstand a direct impact of such a projectile, which is launched at an initial velocity of vi=720+/10 m/s. Under an obliquity angle of θ>65 degrees (NATO) projectile ricocheting is observed. The aim of the ongoing project is to promote the projectile ricochet off helmets to increase the likelihood of projectile deflection and the survivability of the wearer. The focus of this paper is the target back-face deformation (BFD) upon oblique high velocity impact. Experiments were conducted on projectile impact on plane aramid plates. These plates have the same material properties, such as layer number, as used for manufactured helmets – other ballistic helmet materials are covered in future research. Upon impact, the dynamic BFD of the aramid targets was measured, using digital image correlation (DIC). Additionally, the experiments were repeated to capture the projectile trajectory through the target thickness, using X-ray cinematography. The BFD and trajectory results are used for the qualitative comparison of a numerical model, defined within the LS-DYNA® explicit Lagrangian solver. Model components, the projectile and target plate are defined using fully integrated hexahedral elements. The projectile deformation is represented by *MAT_JOHNSON_COOK and its failure criterion; and the target plate is represented by *MAT_COMPOSITE_DAMAGE. The projectile and the composite target are in a symmetric contact defined by *CONTACT_ERODING_SURFACE_TO_SURFACE. The aim of this paper is an investigation on the most suitable modelling approach for a numerical validation of the BFD response obtained from the DIC measurements. This work is a first step to implementing experimentally and numerically achieved BFD data in a LS-DYNA® Finite element (FE) head model, using a head injury criteria (HIC).

Experimental and Numerical Study of Submillimeter-Sized Hypervelocity Impacts on Honeycomb Sandwich Structures

This paper deals with hypervelocity impacts of submillimer-sized debris on honeycomb sandwich panels. These debris, which are mostly present within the low Earth orbit, indeed represent a real threat for spacecrafts and satellites. In fact, for debris large enough to be tracked, pre-determined debris avoidance manoeuvre is usually conducted to prevent any damage. Submillimer-sized debris, however, are too small to be identified and therefore spatial structures must be protected against such threat. Honeycomb structural panels and whipple shields have been used as primary shielding against orbital debris impact. The protection capability is usually estimated using Ballistic Limit Equations (BLE). These data have been built from experimental tests on whipple shield protection and transposed to honeycomb sandwich panels. In the case of Whipple shield, the debris cloud generated at the impact on the bumper sheet expands until reaching the rear wall. BLE for Whipple shields only depends on materials properties, protection geometry, angle of incidence and impact velocity. For honeycomb sandwich panels, the debris cloud is partially channelled within honeycomb cells, thus limiting its radial expansion. The channelling effect is thus a function of the honeycomb cell geometry. The honeycomb BLE presented by the Centre d’Etudes de Gramat (CEG) in 2008 has been introduced in order to take into consideration such effect.

Numerical Modeling of Honeycomb Structure Subjected to Blast Loading

The main objective of this study is related to the modeling of an aluminum thin-walled honeycomb structure under blast loading. The blast test is performed by means of an explosively driven shock tube (EDST). A planar shock wave is generated by a small amount of an explosive charge detonated in front of the tube. The honeycomb core is compressed by a movement of the steel plate located at the end of the tube. In the experiment, the honeycomb deformation is recorded by a high-speed camera and the absorbed loading by the structure is measured by a force sensor fixed on the rear sample face. The simulation of the material behavior is carried out using the Lagrangian approach implemented in LS-DYNA, ver. R9.0.1. The shock pressure generated by the explosion is recalculated to define the force applied to the plate being in contact (*AUTOMATIC_SURFACE_TO_SURFACE with friction) with the honeycomb and causing its deformation. The honeycomb is meshed by shell elements with a default formulation ELFORM: BELYTSCHKO-TSAY. The front plate is assumed as a rigid body to induce a uniform deformation of the honeycomb structure modeled using *MAT_SIMPLIFIED_JOHNSON_COOK 098 with parameters published in, [1-2]. The simulations are performed for different number of unit cells to define the honeycomb, from a single cell to fifty-three cells, aiming to indicate a minimal cell number required to model properly the entire structure. A dependence of numerical results on the mesh size, unit cell dimensions, friction conditions and the strain rate has been verified. The comparison between values of the load absorbed by the sample crushed numerically and experimentally shows a good agreement providing an insight into mechanisms of blast wave absorption by honeycomb structures. Such an analysis may be further applicable in development of advanced cellular structures applied to dissipate blast energy.

High Velocity Impact Response of High Strength Aluminum using LS DYNA

Experimental and numerical studies were conducted to determine the impact response for high strength aluminum armor. A series of ballistic impact tests were carried out for the impact of a 20mm Fragment Simulating Projectile (FSP) with 25.4mm high strength aluminum armor plate at 960m/s impact velocity. This study deals with the measurement of ballistic limits of the deformable FSP against high strength aluminum armor material. The numerical models were developed using the explicit finite element code LS-DYNA®. All parts in the model are modeled with Modified Johnson-cook material model calibrated with performed tests in the company. Material properties are not shared due to confidential issues. A high-speed camera was used for calculation of projectile residual velocities and projectile output images. The numerical model was validated with live test results and a good agreement was achieved between experiments and numerical results. Parameter sensitivity analyses were performed to examine the effect of material model‘s parameters on the response.

IRIS 3 Program: Study of the Vibrations Induced by a Missile Impact on a Reinforced Concrete Structure

The IRIS program (Improving Robustness assessment of structures Impacted by a large miSsile at medium velocity) consists in an international benchmark under the hospice of OECD/NEA. After two first phases of this benchmark realized in 2010 and 2012 which aimed at assessing the ability of numerical simulations to describe the experimental structural response of the mock-up when subjected to impacts, the IRIS Program is now in its third phase. The main objectives of this phase are to assess the effect of a local damage caused by a missile impact on the induced vibrations and to assess the propagation of these vibrations to other parts of the structure, especially to pseudo-equipments which are anchored on it.