Frédéric Rongieras

Contemporary body armor: technical data, injuries, and limits

The introduction of firearms in the fifteenth century led to the continuous development of bulletproof personal protection. Due to recent industrial progress and the emergence of a new generation of ballistic fibers in the 1960s, the ability of individual ballistic protections to stop projectiles greatly increased. While protective equipment is able to stop increasingly powerful missiles, deformation during the impact can cause potentially lethal nonpenetrating injuries that are grouped under the generic term of behind armor blunt trauma, and the scope and consequences of these are still unclear. This review first summarizes current technical data for modern bulletproof vests, the materials used in them, and the stopping mechanisms they employ. Then it describes recent research into the specific ballistic injury patterns of soldiers wearing body armor, focusing on behind-armor blunt trauma.

Intrathoracic pressure impulse predicts pulmonary contusion volume in ballistic blunt thoracic trauma.

BACKGROUNDnBlunt thoracic trauma including behind armour blunt trauma or impact from a less lethal kinetic weapon (LLKW) projectile may cause injuries, including pulmonary contusions that can result in potentially lethal secondary complications. These lung injuries may be caused by intrathoracic pressure waves. The aim of this study was to observe dynamic changes in intrathoracic hydrostatic pressure during ballistic blunt thoracic trauma and to find correlations between these hydrostatic pressure parameters (especially the impulse parameter) and physical damages.nnnMETHODSnThirty anesthetized pigs sustained a blunt thoracic trauma. In group 1 (n = 20), pigs were protected by a National Institute of Justice class III or IV bulletproof vest and shot with 7.62 NATO bullets. In group 2 (n = 10), pigs were shot by an LLKW. Intrathoracic pressure was recorded with an intraesophageal pressure sensor and three parameters were determined: intrathoracic maximum pressure, intrathoracic maximum pressure impulse (PI(max)), and the Pd.P/dt(max), derived from Vianos viscous criterion. Relative right lower lung lobe contusion volume was also measured.nnnRESULTSnDifferent thoracic loading conditions were obtained. PI(max) best correlated with relative pulmonary contusion volume (R² = 0.64 and p < 0.0001). This result was homogenous for all experiments and was not related to the type of chest impact (LLKW-induced trauma or behind armour blunt trauma).nnnCONCLUSIONSnThe PI(max) is a good predictor of pulmonary contusion volume after ballistic blunt thoracic trauma. It is a useful criterion when the kinetic energy record or thoracic wall displacement data are unavailable, and the recording and calculation of this physical value are quite simple on animals.

Less‐Lethal Hybrid Ammunition Wounds: A Forensic Assessment Introducing Bullet‐Skin‐Bone Entity

Abstract:u2002 Agencies all around the world now use less‐lethal weapons with homogeneous missiles such as bean bag or rubber bullets. Contusions and sometimes significant morbidity have been reported. This study focuses on wounds caused by hybrid ammunition with the pathologists’ flap‐by‐flap procedure. Twenty‐four postmortem human subjects were used, and lesions caused on frontal, temporal, sternal, and left tibial regions by a 40‐mm hybrid ammunition (33u2003g weight) were evaluated on various distance range. The 50% risk of fractures occurred at 79.2u2003m/sec on the forehead, 72.9u2003m/sec on the temporal, 72.5u2003m/sec on the sternum, and 76.7u2003m/sec on the tibia. Skin lesions were not predictors of bone fracture. There was no correlation between soft and bone tissue observed lesions and impact velocity (correlated to distance range). Lesions observed with hybrid ammunition were the result of bullet‐skin‐bone entity as the interaction of the projectile on skin and bone tissues.

Strain rate influence on human cortical bone toughness: A comparative study of four paired anatomical sites

Bone fracture is a major health issue worldwide and consequently there have been extensive investigations into the fracture behavior of human cortical bone. However, the fracture properties of human cortical bone under fall-like loading conditions remains poorly documented. Further, most published research has been performed on femoral diaphyseal bone, whereas it is known that the femoral neck and the radius are the most vulnerable sites to fracture. Hence, the aim of this study is to provide information on human cortical bone fracture behavior by comparing different anatomical sites including the radius and the femoral neck acquired from 32 elderly subjects (50 - 98 y.o.). In order to investigate the intrinsic fracture behavior of human cortical bone, toughness experiments were performed at two different strain rates: standard quasi-static conditions, and a higher strain rate representative of a fall from a standing position. The tests were performed on paired femoral neck, femoral, tibial and radius diaphyseal samples. Linear elastic fracture toughness and the non-linear J-integral method were used to take into account both the elastic and non-elastic behavior of cortical bone. Under quasi-static conditions, the radius presents a significantly higher toughness than the other sites. At the higher strain rate, all sites showed a significantly lower toughness. Also, at the high strain rate, there is no significant difference in fracture properties between the four anatomical sites. These results suggest that regardless of the anatomical site (femur, femoral neck, tibia and radius), the bone has the same fracture properties under fall loading conditions. This should be considered in biomechanical models under fall-like loading conditions.

A new method to assess the deformations of internal organs of the abdomen during impact

ABSTRACT Objectives: Due to limitations of classic imaging approaches, the internal response of abdominal organs is difficult to observe during an impact. Within the context of impact biomechanics for the protection of the occupant of transports, this could be an issue for human model validation and injury prediction. Methods: In the current study, a previously developed technique (ultrafast ultrasound imaging) was used as the basis to develop a protocol to observe the internal response of abdominal organs in situ at high imaging rates. The protocol was applied to 3 postmortem human surrogates to observe the liver and the colon during impacts delivered to the abdomen. Results: The results show the sensitivity of the liver motion to the impact location. Compression of the colon was also quantified and compared to the abdominal compression. Conclusions: These results illustrate the feasibility of the approach. Further tests and comparisons with simulations are under preparation.

The flap by flap dissection in terminal ballistic applied to less lethal weapons.

Medical examiners often have to solve questions such as firing distance and bullet trajectory for lethal weapons. Knowledge in the field of terminal ballistics has increased during the last 30 years and layer by layer dissection reveals superficial wounds that can be linked with the permanent cavity. At the end of the 1990s, terminal ballistics also focused on less lethal weapons and their wounds. Here, 2 different less lethal weapons with single bullets were tested on nonembalmed and undressed cadavers (N = 26) at different ranges and speeds. We have developed a technique for dissection which we call flap by flap dissection that reveals the advantage of the bullet-skin-bone entity, the absence of wounds linking its components and range of less lethal weapons.

3D micro structural analysis of human cortical bone in paired femoral diaphysis, femoral neck and radial diaphysis

Human bone is known to adapt to its mechanical environment in a living body. Both its architecture and microstructure may differ between weight-bearing and non-weight-bearing bones. The aim of the current study was to analyze in three dimensions, the morphology of the multi-scale porosities on human cortical bone at different locations. Eight paired femoral diaphyses, femoral necks, and radial diaphyses were imaged using Synchrotron Radiation µCT with a 0.7u202fµm isotropic voxel size. The spatial resolution facilitates the investigation of the multiscale porosities of cortical bone, from the osteonal canals system down to the osteocyte lacunar system. Our results showed significant differences in the microstructural properties, regarding both osteonal canals and osteocytes lacunae, between the different anatomical locations. The radius presents significantly lower osteonal canal volume fraction and smaller osteonal canals than the femoral diaphysis or neck. Osteocytes lacunae observed in the radius are significantly different in shape than in the femur, and lacunar density is higher in the femoral neck. These results show that the radius, a non-weight-bearing bone, is significantly different in terms of its microstructure from a weight-bearing bone such as the femur. This implies that the cortical bone properties evaluated on the femoral diaphysis, the main location studied within the literature, cannot be generalized to other anatomical locations.

Relationships between human cortical bone toughness and collagen cross-links on paired anatomical locations

Human cortical bone fracture processes depend on the internal porosity network down to the lacunar length scale. Recent results show that at the collagen scale, the maturation of collagen cross-links may have a negative influence on bone mechanical behavior. While the effect of pentosidine on human cortical bone toughness has been studied, the influence of mature and immature enzymatic cross-links has only been studied in relation to strength and work of fracture. Moreover, these relationships have not been studied on different paired anatomical locations. Thus, the aim of the current study was to assess the relationships between both enzymatic and non-enzymatic collagen cross-links and human cortical bone toughness, on four human paired anatomical locations. Single Edge Notched Bending toughness tests were performed for two loading conditions: a quasi-static standard condition, and a condition representative of a fall. These tests were done with 32 paired femoral diaphyses, femoral necks and radial diaphyses (18 women, age 81u202f±u202f12u202fy.o.; 14 men, age 79u202f±u202f8u202fy.o.). Collagen enzymatic and non-enzymatic crosslinks were measured on the same bones. Maturation of collagen was defined as the ratio between immature and mature cross-links (CX). The results show that there was a significant correlation between collagen cross-link maturation and bone toughness when gathering femoral and radial diaphyses, but not when considering each anatomical location individually. These results show that the influence of collagen enzymatic and non-enzymatic cross-links is minor when considering human cortical bone crack propagation mechanisms.

An ex vivo experiment to reproduce a forward fall leading to fractured and non-fractured radii

Forward falls represent a risk of injury for the elderly. The risk is increased in elderly persons with bone diseases, such as osteoporosis. However, half of the patients with fracture were not considered at risk based on bone density measurement (current clinical technique). We assume that loading conditions are of high importance and should be considered. Real loading conditions in a fall can reach a loading speed of 2m/s on average. The current study aimed to apply more realistic loading conditions that simulate a forward fall on the radius ex vivo. Thirty radii from elderly donors (79y.o.±12y.o., 15 males, 15 females) were loaded at 2m/s using a servo-hydraulic testing machine to mimic impact that corresponds to a fall. Among the 30 radii, 14 had a fracture after the impact, leading to two groups (fractured and non-fractured). Surfacic strain fields were measured using stereovision and allow for visualization of fracture patterns. The average maximum load was 2963±1274N. These experimental data will be useful for assessing the predictive capability of fracture risk prediction methods such as finite element models.