Wound ballistics of the pig mandibular angle: A preliminary finite element analysis and experimental study

Simulation and experimental studies of debris penetrating skull

Studying the critical kinetic energy (CKE) and critical specific kinetic energy (CSKE) of the debris penetrating the human skull is of great importance for the development of head protection devices. In general, obtaining human skull specimens and conducting direct penetration experiments is difficult. Finite element simulation, on the other hand, is an effective method for determining critical values. However, it is necessary to validate the modeling and simulation method before conducting simulations on the human skull. To validate the method, this study first established a finite element model of a pig skull and performed simulations of debris penetrating the skull. The modeling and simulation methods were verified by comparing the corresponding penetration experimental results on pig skulls with those of the simulations. As the modeling and simulation methods were indirectly validated, an anatomical human skull finite element model was developed to conduct simulations of spherical and cubic debris penetrating the skull to iteratively obtain the CKE and CSKE of the two pieces of debris. Finally, the influence of different attitudes of cubic debris on the penetration energy of the human skull was investigated.

Influence of impact velocity and impact attack angle of bullets on damage of human tissue surrogate -- ballistic gelatin

PURPOSE

Terminal performance of a bullet in human body is critical for the treatment of gunshot injury and optimization of bullet design. The effects of the impact velocity (v₀) and the impact attack angle (δ₀) of the bullet on its terminal performance was investigated, using a new evaluation method (called expansion method) based on the expansion of cracks and the permanent cavity wall in ballistic gelatin.

METHODS

Ballistic gelatin was used to simulate human body. The 7.62 mm × 39 mm rifle bullets with different v₀ (600-760 m/s) and δ₀ (0°-6°) were fired into the gelatin blocks. The gelatin block was cut into slices of about 20 mm thickness. The cracks and the permanent cavity on each slice were obtained manually. The damaged gelatin was determined using two methods: expanding the permanent cavity but ignoring the cracks, and expanding both the permanent cavity and the cracks. The relations between the damaged gelatin and v₀ and δ₀ were obtained using linear fitting method.

RESULTS

According to the distribution of the damaged gelatin along the penetration depth, the damaged gelatin block could be divided into two parts: the less damaged part and the severely damaged part. The length of the less damaged part depends mostly on δ₀; while the average damaged area of this part depends on both δ₀ as well as v₀. The cracks contributed significantly to the total volume of damaged gelatin, particularly when the expansion was larger than 1.9 mm. The total damaged gelatin increases with v₀, δ₀ and the expansion extent. The average length of equivalent cracks grew with v₀ and δ₀ when considering the cracks, and decreased with v₀ when ignoring the cracks.

CONCLUSION

The expansion method is suitable to investigate the influence of different factors of bullets on their terminal performance. The characteristics of the damaged gelatin have a linear relationship with the initial attack angle (δ₀) and the initial velocity (v₀) of the bullet.

The finite element method-based pattern recognition approach for the classification of patient-specific gunshot injury

Violence related injuries and deaths mostly caused by firearms are a major problem throughout the world. Understanding the factors that control the extent of hard-soft tissue wound patterns using computer imaging techniques, numerical methods, and machine learning algorithms may help physicians to diagnose and treat those injuries more properly. Here, we investigate the use of computational results coupled with the pattern recognition algorithms to develop an approach for forensic applications. Initially, computer tomography (CT) images of the patient whose leg was shot by a 9 × 19 parabellum bullet are used to construct the FE models of that patient’s femoral bone and the surrounding soft tissues. Then, Hounsfield units-based material properties are assigned to elements of the bone. To simulate the full range of loading conditions encountered in ballistic events, a constitutive model that captures the strain-rate dependent response is implemented. The entrance pathway vector of the bullet is directed in accordance with the patient’s wound and the simulations are deployed for the cases having various inlet velocities such as 150, 200, 250, 300, and 350 m/s. Once the FE results for each case are obtained, they are processed with supervised machine learning algorithms to classify the wound and inlet velocity correspondence. The results demonstrate that they can be diagnosed with a percent accuracy of 97.3, 97.5, and 98.3 for the decision tree (DT), k-nearest neighbors (kNN) and support vector machine (SVM) classifier, respectively. This approach may provide a useful framework in classifying the wound type, predicting the bullet impact velocity and its firing distance.

A scanning electron microscopy study of projectile entry fractures in cortical bone; genesis and microarchitectural features

The present paper presents a scanning electron microscope (SEM) analysis of the genesis and microarchitecture of experimentally induced cortical entry fractures in porcine scapulae impacted at velocities ranging from 54 to 897 m/s. SEM observation was conducted on polyurethane replicas cast from negative silicone moulds. Analysis of the sequence of fracture processes operative during projectile impact revealed the presence of ring cracks at the site of impact, confirming that penetration in sandwich bones is achieved by cone crack propagation. Despite impulsive loading, two forms of plastic deformation were identified in the cortical bone surrounding the entry fracture up to a maximum velocity of 871 m/s. Microscopic radial and concentric cracks were associated with projectile impact, and the role of pores and pits as stress concentrators was captured. Possible underlying mechanisms for the observed plastic deformation are described, and the diagnostic utility of SEM analysis is presented.

Numerical simulation and analysis of midfacial impacts and traumatic brain injuries

Backgrounds

The maxillofacial region is the exposed part of the human body and is susceptible to injury due to the limited protective equipment. Due to anatomic proximity of the maxillofacial skeleton and cranium, the force can be transmitted directly to the brain in case of maxillofacial impact, maxillofacial injuries are often accompanied with craniocerebral trauma. Therefore, it is necessary to study the biomechanical response mechanism of trauma to improve prevention of traumatic brain injury (TBI).

Methods

To investigate the biomechanical mechanism between the two injuries, a finite element (FE) head model including skull, midfacial bones and detailed anatomical intracranial features was successfully developed based on CT/MRI data. The model was validated by comparing it with one classical cadaver experiment. During the simulations, three different load forces were used to simulate common causes of injury seen in the clinic including boxing-type impact injury and car accident-type impact injury, and four locations on the model were considered as common injury sites in the midface.

Results

Twelve common impact scenarios were reproduced by FE simulation successfully. Simulations showed that there was a linear relationship between the severity of TBI and the collision energy. The location of TBI was directly related to the location of the impact site, and a lateral impact was more injurious to the brain than an anterior-posterior impact. The relative movement between the skull and brain could cause physical damage to the brain. The study indicated that the midfacial bones acted as a structure capable of absorbing energy and protecting the brain from impact.

Conclusions

This biomechanical information may assist surgeons better understand and diagnose brain injuries accompanied by midfacial fractures.

Helmet chinstrap protective role in maxillofacial blast injury

BACKGROUND

The protective role of helmet accessories in moderating stress load generated by explosion shock waves of explosive devices is usually neglected.

OBJECTIVE

In the presented study, the protective role of the helmet chinstrap against the impulse and overpressure experienced by the maxillofacial region were examined.

METHODS

The explosion shock wave and skull interaction were investigated under three different configurations: (1) unprotected skull, (2) skull with helmet (3) skull with helmet and chinstrap. For this purpose, a 3D finite element model (FEM) was constructed to mimic the investigated biomechanics module. Three working conditions were set according to different explosive charges and distances to represent different load conditions. Case 1: 500 mg explosive trinitrotoluene (TNT), 3 cm, case 2: 1000 mg TNT, 3 cm, and case 3: 1000 mg TNT and 6 cm distance to the studied object. The explosion effect was discussed by examining the shock wave stress flow pattern. Three points were selected on the skull and the stress curve of each point position were illustrated for each case study.

RESULTS

The results showed that the helmet chinstrap can reduce the explosive injuries and plays a protective role in the maxillofacial region, especially for the mandible.

Craniofacial injuries by firearms projectiles: An analysis of 868 deaths in the five regions of Brazil

Firearms injuries have a legal and medico-legal importance, and are especially lethal when they reach the craniofacial regions of the victim. The present study aims to identify the characteristics of craniofacial lesions resulting from firearm projectiles, to register the most affected craniofacial regions by this type of injury and to verify the demographic profile of the victims. A retrospective study was carried out on the autopsy records produced in the first semester of 2015, in five Institutes of Legal Medicine in Porto Velho, situated in the cities of João Pessoa, Vitória, Porto Alegre and Brasília. Data extracted included sex, skin color and age of the victim, craniofacial region reached, shooting distance, shape and size of the injuries and manner of death (homicide, suicide or accident). Based on the 868 reports analyzed, it was possible to observe 1700 entrance lesions of firearm projectiles in craniofacial regions. Among cases of known manner of death, homicides were the most frequent (97.0%). It was observed a higher frequency of male victims (93.3%), mixed race (62.0%), between the ages of 12 and 29 years (59.4%). In all cases considered as suicide or accident there was only one entrance wound, but in 82.8% of the homicides there were multiple gunshot wounds. The craniofacial most affected regions were temporal (25.2%) and occipital (19.8%). The most common sites of projectiles exit were the temporal (25.3%) and parietal (16.1%). All cases of suicide were related to contact shot (69.2%) or close-range shot (30.8%), and among the homicides the distant range shots were more frequent (54.0%). The shape of entrance wounds was mostly circular (56.8%) and oval (31.3%), and among the exit injuries, the lesions were irregular (43.3%) and starry (24.1%). The entrance wounds showed smaller sizes than the exit lesions (p < 0.0001). The data obtained are useful for guiding research that takes into account craniofacial trauma caused by firearm projectiles, makes it possible to compare this data with those of other countries and can base investigative conclusions based on the analyzes discussed in the present work.

Computational Approach to Identify Different Injuries by Firearms

Complications arise in the analysis of gunshot wounds to the maxillofacial region, when neither the projectile nor the gun is found at the crime scene. We simulated 5- and 15-cm firing distances at a human mandible to investigate the external morphology of entrance wounds based on fire range. The ammunition models, .40-caliber S&W, .380-caliber, and 9 × 19-mm Luger, were constructed with free-form NURBS surfaces. In a dynamic simulation, projectiles were fired against mandibular body 3D model at 5 and 15 cm. All entrance wounds presented oval aspect. Maximum diameter and von Mises stress values were 16.5 mm and 50.8 MPa, both for .40-caliber S&W fired at 5 cm. The maximum energy loss was 138.4 J for .40 S&W fired at 15 cm. In conclusion, the mandible was most affected by .40-caliber S&W and morphological differences were observable in holes caused by different incoming projectile calibers fired at different distances.

Dynamic finite element simulation of the gunshot injury to the human forehead protected by polyvinyl alcohol sponge

Although there are some traditional models of the gunshot wounds, there is still a need for more modeling analyses due to the difficulties related to the gunshot wounds to the forehead region of the human skull. In this study, the degree of damage as a consequence of penetrating head injuries due to gunshot wounds was determined using a preliminary finite element (FE) model of the human skull. In addition, the role of polyvinyl alcohol (PVA) sponge, which can be used as an alternative to reinforce the kinetic energy absorption capacity of bulletproof vest and helmet materials, to minimize the amount of skull injury due to penetrating processes was investigated through the FE model. Digital computed tomography along with magnetic resonance imaging data of the human head were employed to launch a three-dimensional (3D) FE model of the skull. Two geometrical shapes of projectiles (steel ball and bullet) were simulated for penetrating with an initial impact velocity of 734 m/s using nonlinear dynamic modeling code, namely LS-DYNA. The role of the damaged/distorted elements were removed during computation when the stress or strain reached their thresholds. The stress distributions in various parts of the forehead and sponge after injury were also computed. The results revealed the same amount of stress for both the steel ball and bullet after hitting the skull. The modeling results also indicated the time that steel ball takes to penetrate into the skull is lower than that of the bullet. In addition, more than 21% of the steel ball's kinetic energy was absorbed by the PVA sponge and, subsequently, injury sternness of the forehead was considerably minimized. The findings advise the application of the PVA sponge as a substitute strengthening material to be able to diminish the energy of impact as well as the load transmitted to the object.

Comparison of gunshot entrance morphologies caused by .40-caliber Smith & Wesson, .380-caliber, and 9-mm Luger bullets: a finite element analysis study

Firearms can cause fatal wounds, which can be identified by traces on or around the body. However, there are cases where neither the bullet nor gun is found at the crime scene. Ballistic research involving finite element models can reproduce computational biomechanical conditions, without compromising bioethics, as they involve no direct tests on animals or humans. This study aims to compare the morphologies of gunshot entrance holes caused by.40-caliber Smith & Wesson (S&W), .380-caliber, and 9×19-mm Luger bullets. A fully metal-jacketed.40 S&W projectile, a fully metal-jacketed.380 projectile, and a fully metal-jacketed 9×19-mm Luger projectile were computationally fired at the glabellar region of the finite element model from a distance of 10 cm, at perpendicular incidence. The results show different morphologies in the entrance holes produced by the three bullets, using the same skull at the same shot distance. The results and traits of the entrance holes are discussed. Finite element models allow feasible computational ballistic research, which may be useful to forensic experts when comparing and analyzing data related to gunshot wounds in the forehead.

NUMERICAL ANALYSIS OF A PROJECTILE PENETRATION INTO THE HUMAN HEAD VIA MESHLESS METHOD

In recent years, physicists, engineers and medical scientists have tried to demonstrate the biomechanics of gunshot wounds with numerical methods and experimental observations. Currently, the finite element method (FEM) is the most widely used numerical method among the studies related to ballistic wound injuries. However, when the FEM is used for the penetration analysis, the path of the projectile in the skull is subjected to extremely large deformations which will introduce errors due to distortion of elements. To overcome this error, the meshfree technique was established to simulate the gunshot wound as a preliminary study in which the skull was modeled by smoothed particle hydrodynamics (SPH) and the projectile was modeled by nondeformable rigid elements. In order to simulate a realistic penetration phenomenon, orthotropic material properties were defined for different regions (forehead, zygomatic and mandible) with material principal axis along the surface of the bones.

Human response to the ballistics impacts were determined in terms of force occurring along the pathway of the bullet in the skull, residual velocity of the projectile and penetration depth. The obtained results were compared with the data reported in literature. As a result, mechanical behavior of the head under ballistic impacts simulated by the SPH, compared well with the results determined by the data given in literature, which indicates the applicability of the SPH method as a powerful technique in simulating different gunshot wound mechanisms.

Finite element analysis of pedestrian lower limb fractures by direct force: the result of being run over or impact?

The elucidation and prediction of the biomechanics of lower limb fractures could serve as a useful tool in forensic practices. Finite element (FE) analysis could potentially help in the understanding of the fracture mechanisms of lower limb fractures frequently caused by car-pedestrian accidents. Our aim was (1) to develop and validate a FE model of the human lower limb, (2) to assess the biomechanics of specific injuries concerning run-over and impact loading conditions, and (3) to reconstruct one real car-pedestrian collision case using the model created in this study. We developed a novel lower limb FE model and simulated three different loading scenarios. The geometry of the model was reconstructed using Mimics 13.0 based on computed tomography (CT) scans from an actual traffic accident. The material properties were based upon a synthesis of data found in published literature. The FE model validation and injury reconstruction were conducted using the LS-DYNA code. The FE model was validated by a comparison of the simulation results of three-point bending, overall lateral impact tests and published postmortem human surrogate (PMHS) results. Simulated loading scenarios of running-over the thigh with a wheel, the impact on the upper leg, and impact on the lower thigh were conducted with velocities of 10 m/s, 20 m/s, and 40 m/s, respectively. We compared the injuries resulting from one actual case with the simulated results in order to explore the possible fracture bio-mechanism. The peak fracture forces, maximum bending moments, and energy lost ratio exhibited no significant differences between the FE simulations and the literature data. Under simulated run-over conditions, the segmental fracture pattern was formed and the femur fracture patterns and mechanisms were consistent with the actual injury features of the case. Our study demonstrated that this simulation method could potentially be effective in identifying forensic cases and exploring of the injury mechanisms of lower limb fractures encountered due to inflicted lesions. This model can also help to distinguish between possible and impossible scenarios.

Blast injuries to the human mandible: development of a finite element model and a preliminary finite element analysis

OBJECTIVE

In an attempt to explore new tools for constructing a model of blast injuries to the human mandible, a finite element method was used. This model allowed us to perform dynamic simulations and analyse the injury processes and severity of trauma to the human mandible from an explosion striking at the middle mandibular angle.

METHODS

A 3D finite element model of the human mandible was created using digitally visualised CT scanning data of the human mandible. It was used to dynamically simulate the complete injury process of a blast event to a human mandible (at the middle mandibular angle) under the injury conditions of a 600 mg TNT explosion. The model was also used to elucidate the subsequent mandibular damage and the dynamic distribution of several biomechanical indices (e.g., stress, and strain). The resulting data were subjected to a comparative analysis.

RESULTS

Simulation was successfully conducted for injury events in which 600 mg of TNT exploded at 3 cm, 5 cm and 10 cm from the middle mandibular angle of a human mandible; specifically, the simulation included the dynamic injury processes and the distribution of stress and strain in various parts of the damaged mandible. A comparison of the simulation data revealed that different blast distances resulted in considerable variation in the severity and biological indices of the mandibular injury.

CONCLUSION

The finite element model was able to dynamically simulate the blast-initiated trauma processes to a human mandible, which allowed for investigation of the severity of damage to the mandible under different injury conditions. This model and the simulation method are conducive for applications in basic studies and clinical investigations of blast-initiated injury mechanisms of bone tissues.

Dynamic simulation and preliminary finite element analysis of gunshot wounds to the human mandible

OBJECTIVE

Due to the complications arising from gunshot wounds to the maxillofacial region, traditional models of gunshot wounds cannot meet our research needs. In this study, we established a finite element model and conducted preliminary simulation and analysis to determine the injury mechanism and degree of damage for gunshot wounds to the human mandible.

METHODS

Based on a previously developed modelling method that used animal experiments and internal parameters, digital computed tomography data for the human mandible were used to establish a three-dimensional finite element model of the human mandible. The mechanism by which a gunshot injures the mandible was dynamically simulated under different shot conditions. First, the residual velocities of the shootings using different projectiles at varying entry angles and impact velocities were calculated. Second, the energy losses of the projectiles and the rates of energy loss after exiting the mandible were calculated. Finally, the data were compared and analysed.

RESULTS

The dynamic processes involved in gunshot wounds to the human mandible were successfully simulated using two projectiles, three impact velocities, and three entry angles. The stress distributions in different parts of mandible after injury were also simulated. Based on the computation and analysis of the modelling data, we found that the injury severity of the mandible and the injury efficiency of the projectiles differ under different injury conditions.

CONCLUSIONS

The finite element model has many advantages for the analysis of ballistic wounds, and is expected to become an improved model for studying maxillofacial gunshot wounds.