Roma Plastilina Research Articles

Matched-pair hybrid test paradigm for behind armor blunt trauma using an experimental animal model

BackgroundThe current behind armor blunt trauma (BABT) injury criterion uses a single penetration limit of 44 mm in Roma Plastilina clay and is not specific to thoracoabdominal regions. However, different...

Improvement of forensic medical diagnosis of projectile type injuries from automatic firearm chambered in 5.45 mm caliber through spatial 3D modeling

Spatial 3D modeling has become one of the modern and most accurate evidential methods of research, carving out its niche in various fields of medical science and practice. Therefore, our focus has been on laying the groundwork for its implementation in the process of conducting forensic medical examinations of gunshot injuries, which have garnered significant attention from all forensic physicians, particularly after unprovoked aggression from Russia and the onset of active hostilities in our country. The aim of the study was to improve the forensic medical diagnosis of projectile type in injuries from automatic firearm AKS-74U chambered in 5.45x39 mm caliber by utilizing spatial 3D modeling of specific elements within the wound channel. The entire series of experimental shots was conducted using an AKS-74U firearm, with a bullet caliber of 5.45x39 mm. As the research material, Roma Plastilina Number 1 ballistic clay, manufactured in the USA, was used for conducting standardized ballistic tests according to NIJ (National Institute of Justice) and HOSDB (Home Office Scientific Development Branch) standards. The series of experiments consisted of 15 gunshots; then the physical characteristics of the bullet, main morphological elements of the wound of skin and different portions of wound channel were investigated (195 measurements in general). The morphological features of individual elements within the wound channel were measured using conventional measurement tools, and also after their 3D modeling using graphic editors such as "Agisoft Photoscan" and "3ds max." Direct and strong correlations (ranging from 0.60 to 0.72) have been established between the initial velocity, kinetic energy, specific energy of bullet, and the diameter of the entry wound in 3D modeling, as well as the diameters of the wound channel in its central portion, measured both by conventional measuring tools and based on the results of their 3D modeling (р=0,02). Furthermore, inverse correlation relationships of moderate strength (ranging from -0.63 to -0.66) have been detected between the initial velocity, kinetic energy, specific energy, and the presence of abrasion collar around the entry wound (р=0,03). The created conditions allow to conduct the differentiation in diagnosing the type of projectile, the identification and study of new characteristics of key elements in firearm-related injuries, and improvement in measurement accuracy. They also enhance clarity and objectivity during the execution of forensic medical examinations in cases of combat-related firearm injuries.

DISCOVERY OF A NEW MORPHOLOGICAL FEATURE IN FORENSIC MEDICINE DURING THE STUDY OF GUNSHOT INJURY USING THREE-DIMENSIONAL MODELING OF THE WOUND CHANNEL

The use of spatial three-dimensional modeling of the main elements of a gunshot injury plays a significant part in the modern forensic medical examination. It allows not only to improve the visualization of such bodily injuries, to increase the objectivity and validity of expert conclusions, to accumulate an evidence basis for war crimes committed with the use of various types of firearms, but it also helps to discover new morphological features which couldn’t be detected when using traditional research methods. The work shows the process of detecting a new morphological feature during three-dimensional modeling of the wound channel caused by the IJ 70-01 pistol loaded with 9 mm cartridges.
 Aim of the work. Demonstration of new possibilities of three-dimensional spatial modeling in the process of the forensic investigation of a gunshot wound.
 Materials and methods. To achieve the aim of study, a series of experimental shots were fired from the IJ 70-01 automatic pistol loaded with 9 mm cartridges. To conduct bench ballistic tests according to the US standards – NIJ (National Institute of Justice), HOSDB (Home Office Scientific Development Branch) – standardized ballistic clay Roma Plastilina No.1 was used as the main material that absorbs the energy of the bullet and reproduces all the elements of wound ballistics. It was coated in pig skin with subcutaneous adipose tissue in order to recreate more true-to-life conditions of the gunshot injury. The generated wound channel was filled with Tropicalgin alginate impression material (Zhermack, Italy), which was mixed according to the manufacturer’s instructions; it has short setting time and reproduces the smallest details of the wound channel. Thereafter, the formed cast of the wound channel was subjected to a series of photographs at the appropriate angles and its 3D model was created with the help of the graphic design software “Agisoft PhotoScan” and “3ds max”.
 Results. The result of the conducted studies was obtaining a spatial three-dimensional model of the gunshot wound channel, which brings about new opportunities for its research. The implementation of three-dimensional modeling techniques made it possible to discover a new morphological feature – a helical torsion of the wound channel, the direction of which can indicate specific design features of the firearm used.
 Conclusions. The implementation of three-dimensional spatial modeling in the process of a gunshot trauma investigation sets conditions for increasing visibility and objectivity during conduction of such forensic medical examinations. At the same time, new opportunities are brought about for taking linear dimensions of the existing morphological features of the wound channel main elements with extended precision, the accumulation of demonstrative evidence basis in cases of such injuries, and the discovery of new morphological features for identification of the specific design features of the firearm used.

THE APPLICABLE VALUE OF 3D MODELING IN THE ASPECT OF FORENSIC MEDICAL DIFFERENTIAL DIAGNOSTICS OF THE TYPE OF A TRAUMATIC TOOL IN INJURIES FROM FIREARMS AND APPROXIMATE TO IT BY ITS CHARACTERISTICS

Implementation of up-to-date evidenced-based research methods is rather important in the process of conducting forensic expertise. One of them is 3D-modeling of body injuries of various genesis. The method has been widely applied into theory and practice of forensic medicine both by Ukrainian and foreign scientists. The article demonstrates new possibilities during making differential diagnostics of a traumatic tool type, which become informative due to the application of 3D modeling in the process of examination of injuries from firearms or other weapon approximate to it by its characteristics.
 Aim of the work. To improve the process of forensic differential diagnostics of the type of a traumatic tool by means of 3D-modelling of body injuries caused by small-caliber firearms or other weapon approximate to it by its characteristics, to create opportunities for the implementation of 3D-modelling techniques in the everyday practical work of forensic medical experts and forensic criminologists with the possibility of further adding the obtained results to the materials of criminal proceedings.
 Materials and methods. The material of the research was the results of experimental study when fired from small-caliber firearms and a gun for firing Flaubert cartridges. At the same time, measurements were made both by traditional measuring technique and in the process of 3D-modeling of the entrance gunshot wound on the skin of a pig and on the side of the subcutaneous fat tissue and the wound channel at its various intervals in ballistic plasticine Roma Plastilina №1, produced in the USA, used for ballistic tests according to NIJ, HOSDB standards. The results obtained were processed by means of the common methods of variation statistics applicable in medicine.
 Results. The study presents the major parameters and determines interdependence between the parameters when fired from a gun for firing Flaubert cartridges and small-caliber firearms, and morphological signs of gunshot injuries. Direct moderate and strong correlations are found between the initial speed, kinetic and specific energy of the bullet, and the length of the wound channel, diameter of the entrance wound, diameter of the wound channel in its middle portion and on exit measured by means of traditional measuring methods and those discovered in the process of their 3D-modeling (р≤0,05).
 Conclusions. The use of modern 3D-modeling techniques in the practice of forensic medical examination makes it possible to create 3D-models of both individual components of gunshot damage and the wound channel as a whole.
 At the same time, it becomes possible to study individual elements of gunshot damage and measure their sizes with significantly increased accuracy, store and re-analyze them if necessary.
 As a result, we get an improvement in the process of performing forensic medical examinations in cases of gunshot injuries with the possibility of conducting differential diagnosis of the type of traumatic projectile, studying new signs of gunshot injuries, increasing the visibility and objectivity of forensic medical conclusions during such examinations.

Hybrid numerical modeling of ballistic clay under low-speed impact using artificial neural network

Roma Plastilina No. 1 clay has been widely used as a conservative boundary condition in bulletproof vests, namely to play the role of a human body. Interestingly, the effect of this boundary condition on the ballistic performance of the vests is indiscernible. Moreover, back face deformation should be characterized by measuring the indentation in the deformed clay, which is important for determining the lethality of gunshots. Therefore, several studies have focused on modeling not only bulletproof vests but also the clay backing material. Despite various attempts to develop a suitable numerical model, determining the appropriate physical parameters that can capture the high-strain-rate behavior of clay is still challenging. In this study, we predicted indentation depth in clay using an artificial neural network (ANN) and determined the optimal material parameters required for a finite element method (FEM)-based model using an inverse tracking method. Our ANN-FEM hybrid model successfully optimized high-strain-rate material parameters without the need for any independent mechanical tests. The proposed novel model achieved a high prediction accuracy of over 98% referring impact cases.

Empirical and numerical study on Roma Plastilina #1 ballistic clay under various drop impact tests

The ballistic clay is used to assess protection performance of bulletproof vests. Applying a clay block behind targets conservatively provides similar behavior to the human body as a non-negligible boundary condition. Although understanding and interpreting RP deformation behavior is important, there is no distinctive model covering various impact conditions. We established a numerical model consolidated by a deep neural network which can determine physical input parameters and an empirical formula to understand RP behavior under various impact conditions referring to 59 cases, including our own experiments. The numerical model achieved high levels of accuracy of over 92.6% only when the diameter of the indenter was ø44.5 mm and ø63.5 mm. On the other hand, the empirical model achieved high levels of averaged accuracy of 87.4% for all the cases. The proposed empirical and numerical models can be utilized for assessing protection performance and interpreting impact event of bulletproof vests.

Results of experimental research of wound ballistics of separate types and calibers of modern bullets

There was made the analysis of wound ballistics of modern expansive bullets in comparison with shell bullets on 25 blocks of ballistic plasticine (ROMA PLASTILINA No. 1, Ballistic Testing Backing Material), made in the USA, in which one shot from an AKS-74 automatic firearm and carbine ZBROYAR Z-10 with an optical sight was fired. The bullet speed was the highest in 5.45x39 caliber cartridge with a V-max bullet. – 1185 m/s, low in the bullet caliber cartridge .308 Win with a bullet SP, – 664 m/s. The difference is significant at the level of significance α=0.05. In terms of the size of the entrance hole, the largest is from the bullet of cartridge .308 Win with a bullet SP – 10.0 cm, the smallest - from the bullet "PS" with a steel core 5.45x39 mm, cartridge sample of the year 1974 (7H6) – 1.2 cm. The difference is significant at the level of significance α=0.05. In the expansive bullet of type "V-Max" of shortgun cartridge of caliber 5.45x39 mm, the size of the entrance hole was 9.1 cm, with asterial shape having radial gaps and turned edges of ballistic plasticine on the outside. All cartridges with expansive bullets did not have an exit hole after the shot. The dimensions of the formed residual cavity were the largest after firing with .308 Win caliber cartridge with a bullet SP – 25.0x5.0 cm., the smallest – bullet of a military caliber cartridge of 5.45x39 mm (7H6) – 6.0x4.0 cm. The difference is significant at significance level α=0.05. The shape and character of the residual cavity in ballistic plasticine was significant for all expansive bullets, in contrast to the bullet of a military cartridge 5.45x39 mm (7H6), where no such changes are detected. The considerable signs of expansion properties and deformation of the bullet in the form of a "flower of death" were identified in the bullet of caliber cartridge .308 Win with a bullet SP, other bullets with expansive properties showed significant fragmentation, with the location of fragments both in the residual cavity and outside its borders at different distances. Expansive bullets differ significantly at the level of significance α=0.05. The low flight speed of bullets (m/s) of .308 Win caliber cartridges with bullets BTHP and SP is due to their structure, weight, and caliber. Bullet of type V-max with cartridge 5.45x39 mm has the highest speed – 1185 m/s, and due to its design has significant expansive properties. Common to expansive bullets is a entrance hole, the blind nature of the lesion with the presence of a large residual cavity, which is due to kinetic energy return 114.37 E, J/mm2 inside the object of lesion. Fragmentation of expansion bullets occurs inside an object with fragments located at different distances. A .308 Win caliber cartridge with SP bullet causes deformation of s bullet by the type of "death flower" causing significant damage.

Dynamic back face deformation measurement with a single optical fibre

A single optical fibre sensor is used to measure the dynamics of an impact. The method consists of sewing the optical fibre onto a woven Kevlar layer and placing it between the shoot pack and backing material. The measurement is accomplished by using the friction between the layer and the optical fibre to relate the optical fibre strain to impact deformation. Tests are done using a backing material of Roma Plastilina No.1 clay, and transparent ballistics gel with independent high-speed imaging. A final calculated BFD average error of 7.75% is presented as well as a timing error of 15.5% between the imaged dynamic BFD and the dynamic BFD determined by the FBG. This method is also tested at the U.S. Army Aberdeen Test Center in Maryland with a final calculated error of 7%.

Modeling of deformations of Roma Plastilina # 1 clay in column-drop tests by incorporating the coupled strain rate and temperature effects

Roma Plastilina (RP) # 1 clay has been used as a backing material in ballistic testing of body armor. Column-drop tests are conducted to assess the suitability of RP # 1 clay for ballistic tests. In the current study, deformations of RP # 1 clay induced by projectiles employed in column-drop tests are simulated using finite element models based on the Johnson-Cook (J-C) material model and a new constitutive model. Both the J-C and new models account for strain hardening, strain rate hardening and temperature softening effects exhibited by RP # 1 clay. However, the three effects are treated separately in the J-C model, while the coupling between the temperature and strain rate effects is considered in the new model, which contains seven material constants. The simulations are conducted using the explicit dynamic solver LS-DYNA, and a user-defined material module along with a computational algorithm is developed for the new model and implemented in LS-DYNA. The effect of the hydrostatic pressure is incorporated in the current simulations through using an equation of state (EOS) (with three different types), unlike in existing studies. The numerical results based on both the J-C and new constitutive models reveal that the hydrostatic pressure effect is insignificant for RP # 1 clay under the dynamic loading conditions in the column-drop tests. In addition, it is found that for RP # 1 clay tested at 37 °C the simulation results for the final penetration depth based on both the J-C and new models agree well with the experimental value. However, for RP # 1 clay tested at 23 °C (the room temperature), the permanent depth of penetration predicted using the J-C model differs significantly from what was measured experimentally, while that predicted by the new constitutive model is very close to the experimental value.

A new constitutive model for ballistic Roma Plastilina no. 1 clay

Roma Plastilina No. 1 (RP # 1) clay has been widely used as a backing material in ballistic tests of body armor. However, the constitutive behavior of RP # 1 clay is still not well characterized. In this article, a new constitutive model is proposed to describe the stress–strain relation of ballistic RP # 1 clay, which accounts for the coupled effects of strain hardening, strain-rate hardening, and temperature softening. The model is phenomenological and can be regarded as an extended Johnson–Cook model. The model contains nine parameters, all of which are calibrated using six true stress–true strain curves at two deformation temperatures and three strain rates obtained at the US Army Research Laboratory (ARL). The newly proposed constitutive model with the calibrated parameters is applied to predict six other true stress–true strain curves at another two temperatures, which are compared to the experimental curves that were also generated at the ARL. The non-uniqueness of the fitting parameter values is discussed, and an error analysis is conducted. The results of the error analysis show that the new constitutive model provides a fairly accurate prediction of the stress–strain behavior of ballistic RP # 1 clay.

Rheological Characterization of Next-Generation Ballistic Witness Materials for Body Armor Testing.

Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as “backface signature”). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure–property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.

Cure characteristics, mechanical properties and back face signature of ballistic rubber trauma pack

Curing characteristics, mechanical properties and back face signature (BFS) of natural rubber (NR) and chemically modified natural rubber (CNR) filled carbon black (CB) nanocomposites are reported. Five bullet shots for each samples at velocity of 367 ± 10 m s-1 and the indentation depths on oil based modelling clay backing known as Roma Plastilina No. 1 were measured. Results indicate that the minimum torque and maximum torque increase with increasing carbon black, whereas scorch time and cure time show decreasing trend. The value of tensile strength, elongation at break and modulus at 300% elongation (M300) improved with incorporation of 50 phr CB especially in the CNR filled composites. Further increment of CB reduces the enhancement of the mechanical properties. The CNR 50 recorded the lowest BFS of 4.55 mm indentation in depth. In conclusion, the CNR filled 50 phr carbon black is proven to be the most suitable for the trauma pack performance.

Two new penetration models for ballistic clay incorporating strain-hardening, strain-rate and temperature effects

Ballistic clay, such as Roma Plastilina No. 1 (RP # 1) clay, has been used as a standard backing material in back-face signature (BFS) tests of body armor. Hence, it is important to thoroughly understand penetration mechanics of ballistic clay. In the current paper, two analytical solutions for dynamic spherical cavity expansion in an infinite elastic-plastic solid are first derived by including the strain-hardening effect, strain-rate dependence and temperature influence. The elastic region in the solid is treated as either compressible or incompressible and described using Hooke's law, while the plastic region is regarded as incompressible and characterized using two different constitutive models, one of which is the well-known Johnson-Cook model and the other is a modified Johnson-Cook model simplified from a recently proposed model for ballistic clay. Based on these two dynamic spherical cavity expansion solutions, two models for penetration into a ballistic clay by a rigid projectile with a spherical or an ogival nose are then developed, which incorporate the coupled strain-hardening, strain-rate and temperature effects for the first time. The depth of penetration and impact time relations are obtained for non-penetration impacts, and the ballistic limit and residual velocity are determined for penetration impacts by each type of projectile. To quantitatively illustrate the two newly developed penetration models, they are directly applied to simulate drop tests and impact tests of RP # 1 clay. It is found that the predictions by the current new models agree fairly well with existing experimental data and simulation results.

Mechanical properties of silicone based composites as a temperature insensitive ballistic backing material for quantifying back face deformation

This paper describes a new witness material for quantifying the back face deformation (BFD) resulting from high rate impact of ballistic protective equipment. Accurate BFD quantification is critical for the assessment and certification of personal protective equipment, such as body armor and helmets, and ballistic evaluation. A common witness material is ballistic clay, specifically, Roma Plastilina No. 1 (RP1). RP1 must be heated to nearly 38°C to pass calibration, and used within a limited time frame to remain in calibration. RP1 also exhibits lot-to-lot variability and is sensitive to time, temperature, and handling procedures, which limits the BFD accuracy and reproducibility. A new silicone composite backing material (SCBM) was developed and tested side-by-side with heated RP1 using quasi-static indentation and compression, low velocity impact, spherical projectile penetration, and both soft and hard armor ballistic BFD measurements to compare their response over a broad range of strain rates and temperatures. The results demonstrate that SCBM mimics the heated RP1 response at room temperature and exhibits minimal temperature sensitivity. With additional optimization of the composition and processing, SCBM could be a drop-in replacement for RP1 that is used at room temperature during BFD quantification with minimal changes to the current RP1 handling protocols and infrastructure. It is anticipated that removing the heating requirement, and temperature-dependence, associated with RP1 will reduce test variability, simplify testing logistics, and enhance test range productivity.

Characterization of clay composite ballistic witness materials

Mechanical and thermal properties of Roma Plastilina Clay #1 (RP1) were studied through small-amplitude oscillatory shear (SAOS), large-amplitude oscillatory shear (LAOS), and differential scanning calorimetry (DSC), supplemented with thermogravimetric analysis, X-ray diffraction, and X-ray florescence. Rheological characterizations of RP1 through SAOS indicate that the clay composite softens as it is worked and slowly stiffens as it rests. Upon heating, the clay composite softens, prior work history is erased, and the composite undergoes a melting transition, although melted clay is significantly stiffer when returned to the usage temperature. Continuing mechanical characterizations into the LAOS or nonlinear region, RP1 transitions from a transient network to a viscous shear-thinning material as the temperature is increased. Using the MITlaos framework, RP1 exhibits intra-cycle strain stiffening and intra-cycle shear thinning at all temperatures.

Dynamic characterization of Roma Plastilina No. 1 from Drop Test and inverse analysis

Mechanical characterization of soft malleable materials represents a research challenge due to the impossibility to perform standard tests on this type of materials. Diverse characterization procedures are found in the literature for their characterization; however, little advances have been achieved at medium strain rates. This paper presents a characterization method for soft malleable materials to determine the material parameters associated with a given constitutive model. The characterization methodology posed as an inverse problem of Drop Test is formulated and solved as an optimization procedure. The input of the optimization procedure is the experimental measurement from the impact of a steel sphere, of specific diameter, freely released from a specific height on to the soft material. Specifically, the input data consist of the penetration history captured by high speed photography. The output of the procedure is the optimum set of material parameters determined by fitting a numerical simulation to the Drop Test experimental measurements. To evaluate and validate the performance of the proposed characterization method, experiments on Roma Plastilina No. 1 were conducted.

The effect of knife blade profile on penetration force in flesh simulants

A series of stab-penetration tests were carried out using model knife blades with different degrees of sharpness. Target blocks of flesh simulant were penetrated by the knife blades at constant low velocity and the penetration force was monitored. PSDB 10/93, a test protocol for stab-resistant body armour, recommends a modelling clay (Roma Plastilina) as a flesh simulant. From the stab-penetration tests it was found that Roma Plastilina has poor resemblance to flesh, and a simulant such as gelatine is more realistic. Bowie knife blades are specified in the test protocol while kitchen knives appear to be the most common in real incidents. More importantly, no required blade sharpness is specified in the test protocol, an aspect that could lead to inconsistencies in test results.