Evaluation numérique des impacts thoraciques dûs aux projectiles non-létaux

Anti-personnel Non-Lethal Weapons (NLW) are weapons that are designed to impart sufficient effect onto a person in order to deter uncivil, suspect or hazardous behaviour with a low probability of severe or fatal injury. They are used both by military and law enforcement in situations of low-intensity conflicts like riot control, access denial, peacekeeping missions i.e. situations where the use of lethal force is not appropriate nor desired. The most used of these weapons are the Kinetic Energy Non-Lethal Weapons (KENLW). The underlying principle of KENLW is to launch a projectile with a mass varying between 5 g and 140 g at initial velocity up to 160 m/s, which by a mechanical action on the target, will cause enough physical pain to incapacitate or repel the target. But their use is not without risk as in practice, the impacts of Kinetic Energy Non-Lethal (KENL) projectiles on the human thorax resulted in injuries, some of the them were severe even fatal. Therefore there is a need to develop methods of assessment. These assessment methods are essential in order to help deciders in charge of non- lethal weapon procurement with technical information so they can choose the best product (weapon or projectile) available on the market; to give relevant information to the manufacturers in either developing new weapons or projectiles that are more effective, or improving the existing ones, and finally to the end-users (military or police forces) of these weapons, information on operational distance of engagement. In practice, it has been observed that the thorax is the body region where the impacts of KNL projectiles led to more significant injuries than other parts of the body apart from the head which is never targeted at. Therefore in the present thesis, only assessment of thoracic impacts is investigated. Besides tests on PMHS (Post Mortem Human Subjects), animals or human surrogates, one powerful tool that is used nowadays to assess the thoracic impacts is the finite element method (FEM). It has many advantages like the capability of accounting for complex geometries or complex material modelling and its cost-effectiveness. It also gives insight into physical variables (stresses, strains,...) inside the material which are inaccessible by other means. It helps for a better understanding of the injury mechanism. Moreover, it helps to reduce cadavers or animal testings. In the present thesis, only FEM is considered as tool for injury risk assessment. On the one hand, a thorax finite element (FE) model, the SHTIM (Surrogate Human Thorax Impact Model) has been developed for the injury risk assessment. Number of assumptions has been made relative to the thorax geometry and the material characteristics are based on literature. The model has been validated thanks to the results of experiments carried out by professor C. Bir. A viscous injury criterion was defined as the parameter relevant for the occurrence of the thorax skeletal injury. This criterion is used in the present thesis for the prediction of the thoracic injury outcome. On the other hand, FE models of six projectiles have been developed where most of material characteristics were taken from the literature. For the 40 mm sponge grenades, a new method of characterizing the deformable nose has been developed. The projectile FE models were validated by comparing numerical results to experimental results obtained from real firing tests of the projectile against a rigid wall structure. These firing tests have been performed within the Department ABAL. Good correspondence was found. Once the thorax FE model and the projectile FE models validated, numerical simulations of the impact between the thorax and the projectile were performed. Using the viscous injury criterion, risk assessment of the thorax impacts was carried out. For each projectile, a critical velocity was determined which thanks to the retardation can be linked to a minimum firing distance, the safe distance. This is the distance below which an impact will result in a higher risk of skeletal thoracic injury. This information is very important for the end-users (military, police). Moreover comparison of the performance of different KENL projectiles was carried out. Few years ago, the Department ABAL acquired a thorax mechanical surrogate, the 3RBID (3 Rib Ballistic Impact Dummy) for the prediction of thoracic injury. It was an opportunity to compare both surrogates and to see if the SHTIM results are consistent with the 3RBID results. Good correspondence has been found especially for projectiles with larger diameter like the 40 mm sponge grenades

Simulation numérique d'impact de projectile non létal sur thorax humain

These last decades have seen the development of a new type of weapons, the non lethal weapons. Unlike the conventional weapons which may cause severe or fatal injuries and whose injury mechanisms are well documented, the non lethal weapons are designed for temporary incapacitation with reversible consequences or minor damage to the human body. They try therefore to fill the gap wherever the use of excessive forces or conventional weapons is not necessary. There are various non lethal technologies but here we will focus on non lethal kinetic energy weapons (NLKEW). The non penetrating characteristics of non lethal projectiles lead to different injury mechanisms to those related to conventional lethal projectiles. In order to better understand these effects and assess the injury severity, experiments are carried out on Post Mortem Human Surrogates (PMHS), animals and mechanical anthropomorphic systems. Nevertheless nowadays with the development of high performance computing systems, numerical simulations based on finite element method are increasingly used because of their cost-effectiveness, their predictive capabilities and their adaptability (for example the possibility of adapting the geometry to take into account various morphologies, …). Physical injury is a consequence of the interaction between the human body and the projectile. To assess the severity of injury, injury criteria are defined. The most used criterion on the assessment of the thorax injury is the maximum viscous criterion. Because of the human body complexity, reliable information on injury mechanisms and tolerance level to the impact of non lethal projectiles is limited. The major challenge in the numerical simulations is the human tissue material model as human tissue responses to impacts are various and complex. As a consequence, models which are biofidelic to the human living tissues are a key issue. To investigate and predict the human thorax response to the impact of the usual non lethal kinetic projectiles (like the FN303, the 40mm COUGAR), a finite element thorax model has been developed from thorax CT-scan images and the projectile FN303 was used. The model was validated by using results (force-time and deflection-time characteristics of the thorax) from experiments on PHMS published in the litterature. Two types of projectiles made of polyvinyl chloride cylinder with 37 mm diameter and respectively 28.5 mm and 100 mm long were used and the human tissue material models were found in open litterature

Mesures à l'impacts de projectiles non létaux 40mm

In the world of kinetic energy non-lethal weapons (KENLW), the 40mm sponge grenade is a modern projectile that is widely being used. Indeed, it presents different advantages: firstly, thanks to its 40mm diameter, it can be fired with a classic cost-effective grenade launcher. Secondly, its big diameter makes it very unlikely to penetrate the human body, even for impact energy above 100J. Thirdly, it’s a quite accurate projectile for long distance non-lethal impacts, typically between 20m and 50m. These considerations explain why many ammunition manufacturers tend to develop their own 40mm sponge grenade. The 40mm sponge grenade is usually composed of a hard plastic body, with a deformable nose made in foam rubber. The deformation of the nose allows the projectile to absorb energy at impact, making it less lethal for a given velocity than an equivalent stiff projectile. The muzzle velocity is usually between 70m/s and 110m/s, and the mass between 30g and 40g. The muzzle kinetic energy is usually between 120J and 170J. The main issue in the study of this kind of projectiles is its ability to deform at impact. On the one hand, it makes measurements of the impact phenomena more complicated than for a stiff projectile. On the other hand, most of the published studies about KENLW deal with stiff projectiles, and their conclusions may not be applicable for deformable projectiles. Another problem is the wide variety of existing sponge grenades. As the way the projectile deform during the impact can vary from manufacturer to manufacturer, we can expect that the impact phenomena and its induced lethality can also vary, even for the same level of energy. The objective of this study is to assess the impact of different sponge grenades with force sensors and a high-speed camera. The 2 main goals are the following: • Different sponge grenades are shot at different velocities on a stiff surface equipped with a force sensor. The force and deformation occurring during the impact are measured for each projectile and then compared. • A relationship between force and deformation during the impact is established, and then compared at different velocities, for different sponge grenades

Calibration dynamique des capteurs Flexiforce pour des mesures balistiques

In the field of terminal ballistics, non-invasive force measurements are sometimes needed. The cheap and thin Flexiforce sensors can be used for this purpose with low collateral effects. This paper works on the development of a method designed to dynamically calibrate the Flexiforce sensor. The objective is to find a calibration parameter that correlates the Flexiforce output signal, in terms of conductance, to the applied force. The process used to achieve this dynamic calibration is based on a drop test. The principle is to impact the sensor with the falling of a specified mass. The force signal delivered by the Flexiforce sensor is afterwards compared to the signal measured by a reference force sensor that measures the same impact. To further validate this measurement, the impact is applied on a spring, placed directly between the falling mass and the Flexiforce. The deflection of that spring is measured with a high-speed camera. Knowing the spring properties, we can determine the force produced by the spring on the two sensors, and consequently validate the reference measurement. The calibration factor seems independent of the applied force, and follows a normal distribution. Both the frequency of the impact and the contact surface have an influence on the output of the Flexiforce sensor. For that reason the calibration process should use a frequency and a contact surface similar to the considered application

Standardisation de l'évaluation de la pénétration à l'impact de projectiles non létaux

Non-lethal weapons are in use in a lot of law-enforcement and military operations. While most of them are kinetic-energy systems, their effectiveness and dangerous limits on human targets are not clearly defined. The assessment of non-lethal projectiles effects on human targets follows usually two main directions: - The evaluation of internal damage - The evaluation of skin penetration This papers focuses on the second point. The literature gives some energy density values for a 50% skin penetration probability when different parts of the human body are shot at. These values are mainly based on cadaver and animals tests conducted in USA. Some countries don’t allow these kinds of tests and it is certainly much more convenient to use a mechanical surrogate for testing purposes. In that case, a standard on which different countries can rely would be a must. Wayne State University proposed in March 2010 a draft proposal for a surrogate to be used as a basis for NATO standardization. This surrogate is based on ballistic gelatin, foam and chamois leather. This paper goal is to assess this future standard surrogate regarding: - The equivalence between cadaver and surrogate penetration results - The reproducibility of the method and its sensitivity to external parameters - The availability and feasibility of basis elements of the surrogate. Our results rely on our own tests in our laboratory, and our views are presented in the final article. We give some recommendations about this standard, based on the statistical analysis of these results and on some practical considerations about the surrogate

Meausrement de la force à l'impact d'un projectile non létal à l'aide d'un capteur Flexiforce

Force measurements are important to experimentally assess the effects of a non- lethal projectile on a human body. In addition they are also necessary to evaluate the bio-fidelity of a system regarding PMHS (post mortem human subject) data. So far, as we can see in the literature, these measurements are usually achieved with an accelerometer placed inside the projectile. By assuming this projectile is perfectly rigid, the impact force can be calculated [1, 2]. However, the limitations are obvious: on the one hand the embedded accelerometer will change the projectile properties. On the other hand the force cannot directly be deduced for the deformable projectiles usually used nowadays. Therefore, a new system to measure impact force has to be developed. In this study, we propose to use the Flexiforce sensor, which is a cheap and very thin force sensor compatible with the expected measurement range [3]. The final objective is to realise an efficient force measurement on any kinetic energy non-lethal weapon (KENLW) projectile, using this particular sensor. We can find in the literature some static calibration [3,4]. As our application is highly dynamical, we started this study with the design and application of a dynamic calibration process. Then results from rigid projectiles (comparing to a classic KENLW projectile) impacting rigid targets (comparing to human body or a biofidelic surrogate) are collected and Flexiforce and accelerometer signals are compared (“rigid-rigid impacts). Finally, force measurements of projectiles impacting deformable surfaces (comparing to the projectile ) with the Flexiforce sensor are achieved (“rigid-soft impacts”)