A comparison of gelatine surrogates for wound track assessment.

The use of ordnance gelatine has been widespread in the field of ballistics as a simulant for soft tissue when assessing ballistic threats. However, the traditional method of preparing ordnance gelatine is time-consuming and requires precision to ensure that the final mold meets the required specifications. Furthermore, temperature control is necessary post-production, and there are limitations on its usage duration. To address these issues, manufacturers have developed pre-mixed, gelatine-like products that are stable at room temperature and require less preparation time. Nonetheless, it is uncertain whether these new products can perform in the same manner as the gold standard of ordnance gelatine. This study used five types of blocks, including ordnance gelatine (10% and 20%), Clear Ballistics (10% and 20%) and Perma-Gel (10%) and subjected them to 9 mm, 0.380 Auto fired from a universal receiver and a 5.56 × 45 mm ammunition fired by a certified firearms instructor. Delta-V and total energy dissipation were measured after each test using data collected from ballistic chronographs placed in front of and behind each block. High-speed video was recorded, and a cut-down analysis conducted. The findings revealed variations in energy dissipation and fissure formation within the block, with greater energy based on fissure formation observed in the ordnance gelatine. Additionally, the high-speed video showed the occurrence of secondary combustions occurring in the premixed gelatines.

Review of non-penetrating ballistic testing techniques for protection assessment: From biological data to numerical and physical surrogates.

Human surrogates have long been employed to simulate human behaviour, beginning in the automotive industry and now widely used throughout the safety framework to estimate human injury during and after accidents and impacts. In the specific context of blunt ballistics, various methods have been developed to investigate wound injuries, including tissue simulants such as clays or gelatine ballistic, physical dummies and numerical models. However, all of these surrogate entities must be biofidelic, meaning they must accurately represent the biological properties of the human body. This paper provides an overview of physical and numerical surrogates developed specifically for blunt ballistic impacts, including their properties, use and applications. The focus is on their ability to accurately represent the human body in the context of blunt ballistic impact.

Thoughts and perspectives on biomechanical numerical models under impacts: Are women forgotten from research?

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the "sex specific properties/data" used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about "androcentrism," and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Experimental evaluation of earplug behavior in front of high-level impulse noise using laser Doppler vibrometer.

Hearing protection devices facing high-level impulse noises provide an attenuation, generally, between 20 and 40 dB. One reason for this limitation is the direct interactions between the protection device and the impulse waves. In the case of earplugs, direct transmissions through the earplug occur. These direct transmissions combine with the already well-studied indirect transmissions arising from wave propagation in the external ear's tissues (skin, cartilage, and bone). To evaluate the transmission induced directly by the earplug, an experimental protocol using a laser Doppler vibrometer was developed. Thus, the earplug's outer lateral face (OLF) displacements and acoustic pressure at the eardrum were measured simultaneously. Two earplugs (polyurethane foam and acrylonitrile butadiene styrene) inserted in an acoustic test fixture were stimulated with impulses ranging from 137 to 180 dB-peak. A slight earplug OLF movement in the ear canal varying from 1 µm to 0.1 mm could be observed, which is likely related to ear canal longitudinal compression. The earplug's OLF displacement and acoustic pressure variation at the eardrum strongly depended on the earplug type. These direct transmissions and underlying consequences considerably alter the protection efficiency.

A new biomechanical FE model for blunt thoracic impact.

In the field of biomechanics, numerical procedures can be used to understand complex phenomena that cannot be analyzed with experimental setups. The use of experimental data from human cadavers can present ethical issues that can be avoided by utilizing biofidelic models. Biofidelic models have been shown to have far-reaching benefits, particularly in evaluating the effectiveness of protective devices such as body armors. For instance, numerical twins coupled with a biomechanical model can be used to assess the efficacy of protective devices against intense external forces. Similarly, the use of human body surrogates in experimental studies has allowed for biomechanical studies, as demonstrated by the development of crash test dummies that are commonly used in automotive testing. This study proposes using numerical procedures and simplifying the structure of an existing biofidelic FE model of the human thorax as a preliminary step in building a physical surrogate. A reverse engineering method was used to ensure the use of manufacturable materials, which resulted in a FE model called SurHUByx FEM (Surrogate HUByx Finite Element Model, with HUByx being the original thorax FE model developed previously). This new simplified model was validated against existing experimental data on cadavers in the context of ballistic impact. SurHUByx FEM, with its new material properties of manufacturable materials, demonstrated consistent behavior with the corresponding biomechanical corridors derived from these experiments. The validation process of this new simplified FE model yielded satisfactory results and is the first step towards the development of its physical twin using manufacturable materials.

Validation of rib structural responses under dynamic loadings using different material properties: A finite element analysis.

In this paper, human rib finite element models were created and validated based on finite element simulations. Validation tests were conducted through replicating experimental configurations of ribs under dynamic anterior-posterior bending, and by comparing numerical rib structural responses and fracture locations against experimental data. Human rib cortical bone material properties from different loading modes (tension and compression), strain rates (0.5 strain/s and 0.005 strain/s) and ages as well as porcine rib material properties were applied. Comparison of rib structural responses with various material properties was investigated. Numerical force-displacement relationship, cortical strain, rotation and fracture location correspond well with published experimental data, which demonstrates the robustness of the finite element rib models. Numerical analysis reveals that numerical strain and rotation time histories with human rib cortical compressive material properties have a better correlation with experimental data compared to those with human rib cortical tensile material properties. Also, numerical rib structural responses were found to be sensitive to material properties from different loading modes, strain rates and ages. Therefore, it is necessary to consider the effect of material properties from different loading modes, strain rates and ages when establishing rib FE models. Meanwhile, it is also indicated that porcine rib material properties can obtain similar and reasonable results compared to human rib material properties. This was the first numerical study to apply human rib compressive material properties in investigating rib dynamic structural responses and compare the results with those from tensile material properties. The present study helps better understand human rib fractures in a high velocity impact (HVI) context in a numerical way.

Effect of blast loading on the risk of rib fractures: a preliminary 3D numerical investigation.

Blast is a complex phenomenon which needs to be understood, especially in a military framework, where this kind of loading can have severe consequences on the human body. Indeed, the literature lists a number of studies which try to investigate the dangerousness of such a phenomenon, both at experimental and numerical level, and the injuries that could occur when the fighters or police officers are stroke by blast wave. When focusing on primary blast effect, this paper analyses the effect of this loading on the occurrence of rib fracture, using previously developed injury risk curves.

From military to civil loadings: Preliminary numerical-based thorax injury criteria investigations.

Effects of the impact of a mechanical structure on the human body are of great interest in the understanding of body trauma. Experimental tests have led to first conclusions about the dangerousness of an impact observing impact forces or displacement time history with PMHS (Post Mortem human Subjects). They have allowed providing interesting data for the development and the validation of numerical biomechanical models. These models, widely used in the framework of automotive crashworthiness, have led to the development of numerical-based injury criteria and tolerance thresholds. The aim of this process is to improve the safety of mechanical structures in interaction with the body. In a military context, investigations both at experimental and numerical level are less successfully completed. For both military and civil frameworks, the literature list a number of numerical analysis trying to propose injury mechanisms, and tolerance thresholds based on biofidelic Finite Element (FE) models of different part of the human body. However the link between both frameworks is not obvious, since lots of parameters are different: great mass impacts at relatively low velocity for civil impacts (falls, automotive crashworthiness) and low mass at very high velocity for military loadings (ballistic, blast). In this study, different accident cases were investigated, and replicated with a previously developed and validated FE model of the human thorax named Hermaphrodite Universal Biomechanical YX model (HUBYX model). These previous validations included replications of standard experimental tests often used to validate models in the context of automotive industry, experimental ballistic tests in high speed dynamic impact and also numerical replication of blast loading test ensuring its biofidelity. In order to extend the use of this model in other frameworks, some real-world accidents were reconstructed, and consequences of these loadings on the FE model were explored. These various numerical replications of accident coming from different contexts raise the question about the ability of a FE model to correctly predict several kinds of trauma, from blast or ballistic impacts to falls, sports or automotive ones in a context of numerical injury mechanisms and tolerance limits investigations.

Biomechanical model of the thorax under blast loading: a three dimensional numerical study.

Injury mechanisms due to high speed dynamic loads, such as blasts, are not well understood. These research fields are widely investigated in the literature, both at the experimental and numerical levels, and try to answer questions about the safety and efficiency of protection devices or biomechanical traumas. At a numerical level, the development of powerful mathematical models tends to study tolerance limits and injury mechanisms in order to avoid experimental tests which cannot be easily conducted. In a military framework, developing a fighter/soldier numerical model can help to the understanding of many traumas which are specific to soldier injuries, like mines, ballistic impacts or blast traumas. The aim of this study is to investigate the consequences of violent loads in terms of human body response, submitting a developed and validated three-dimensional thorax finite element (FE) model to blast loadings. Specific formulations of FE methods are used to simulate this loading, and its consequence on the biomechanical model. Mechanical parameters such as pressure in the air field and also in internal organs are observed, and these values are compared to the experimental data in the literature. This study gives encouraging results and allows going further in soldier trauma investigations.

Anthropometric dependence of the response of a thorax FE model under high speed loading: validation and real world accident replication.

Finite element analysis is frequently used in several fields such as automotive simulations or biomechanics. It helps researchers and engineers to understand the mechanical behaviour of complex structures. The development of computer science brought the possibility to develop realistic computational models which can behave like physical ones, avoiding the difficulties and costs of experimental tests. In the framework of biomechanics, lots of FE models have been developed in the last few decades, enabling the investigation of the behaviour of the human body submitted to heavy damage such as in road traffic accidents or in ballistic impact. In both cases, the thorax/abdomen/pelvis system is frequently injured. The understanding of the behaviour of this complex system is of extreme importance. In order to explore the dynamic response of this system to impact loading, a finite element model of the human thorax/abdomen/pelvis system has, therefore, been developed including the main organs: heart, lungs, kidneys, liver, spleen, the skeleton (with vertebrae, intervertebral discs, ribs), stomach, intestines, muscles, and skin. The FE model is based on a 3D reconstruction, which has been made from medical records of anonymous patients, who have had medical scans with no relation to the present study. Several scans have been analyzed, and specific attention has been paid to the anthropometry of the reconstructed model, which can be considered as a 50th percentile male model. The biometric parameters and laws have been implemented in the dynamic FE code (Radioss, Altair Hyperworks 11©) used for dynamic simulations. Then the 50th percentile model was validated against experimental data available in the literature, in terms of deflection, force, whose curve must be in experimental corridors. However, for other anthropometries (small male or large male models) question about the validation and results of numerical accident replications can be raised.

Finite element modelling of paediatric head impact: global validation against experimental data.

Biomechanics of the human head has been widely studied for several decades. At a mechanical level, the use of engineering and finite element (FE) methods has allowed injury mechanisms to be investigated using biofidelic FE models. These models are generally validated using experimental data then used to simulate real-world head trauma in order to derive numerical tolerance limits, leading to efficient injury predicting tools. Due to ethical issues, experimental tests on the paediatric population remain prohibitive so direct validations of numerical models cannot be performed. However injury biomechanics on paediatric population is emerging with experimental tests on the paediatric cadavers or tests on biological tissue and the development of finite element models. The present paper proposes a new finite element model of a newborn head, simulating its main features, with material properties from the literature. Global validation of the model against experimental data in terms of skull deflection is performed and the model is used to simulate paediatric skull fracture coming from real-world head trauma.

Child head injury criteria investigation through numerical simulation of real world trauma.

Finite element modelling has been used for decades in the study of adult head injury biomechanics and determination of injury criteria. Interest is recently growing in investigation on pediatric head injury which requires elaboration of biofidelic models that take into account child's head particularities in terms of size, geometry, and mechanical properties. In this study, a finite element model of a 3-year-old child head is proposed. The model is reconstructed from real CT scan images and mechanical properties are extracted from available data in the literature. A large number of real accidents (25 falls) are reconstructed with proposed model using different brain constitutive relationships in order to investigate their influence on model response. Mechanical output parameters (HIC, pressure, shearing stress) are calculated from these simulations. Statistical analysis was performed in order to evaluate predictive capability of the parameters. Von Mises stress appears to be clearly the most predictive parameters, allowing clear distinction between injured and non-injured cases. To the authors' knowledge, this study proposes for the first time a statistically based neurological injury criterion for a pediatric population using finite element modelling.

Influence of the benign enlargement of the subarachnoid space on the bridging veins strain during a shaking event: a finite element study.

There is controversy regarding the influence of the benign enlargement of the subarachnoid space on intracranial injuries in the field of the shaken baby syndrome. In the literature, several terminologies exists to define this entity illustrating the lack of unicity on this theme, and often what is "benign" enlargement is mistaken with an old subdural bleeding or with abnormal enlargement due to brain pathology. This certainly led to mistaken conclusions. To investigate the influence of the benign enlargement of the subarachnoid space on child head injury and especially its influence on the bridging veins, we used a finite element model of a 6-month-old child head on which the size of the subarachnoid space was modified. Regarding the bridging veins strain, which is at the origin of the subdural bleeding when shaking an infant, our results show that the enlargement of the subarachnoid space has a damping effect which reduces the relative brain/skull displacement. Our numerical simulations suggest that the benign enlargement of the subarachnoid space may not be considered as a risk factor for subdural bleeding.

Biofidelic child head FE model to simulate real world trauma.

Biomechanics of human head has been widely studied since several decades. At a mechanical level, the use of engineering allowed investigating injury mechanisms developing numerical models of adult head. For children, the problem is more difficult and evaluating child injury mechanisms using data obtained from scaling adult injury criteria does not account for differences in morphology and structure between adults and children. During growth, child head undergoes different modifications in morphology and structure. The present paper compares the anthropometry and numerical simulations of a child head model based on medical CT scans to a child head model developed by scaling an adult head model using the method proposed by Mertz [H.J. Mertz, A procedure for normalizing impact response data, SAE paper 840884, 1984]. These analysis point out significant differences showing that scaling down an adult head to obtain a child head does not appear relevant. Biofidelic and specific child geometry is needed to investigate child injury mechanisms.

Finite element analysis of impact and shaking inflicted to a child.

This study compares a vigorous shaking and an inflicted impact, defined as the terminal portion of a vigorous shaking, using a finite element model of a 6-month-old child head. Whereas the calculated values in terms of shearing stress and brain pressure remain different and corroborate the previous studies based on angular and linear velocity and acceleration, the calculated relative brain and skull motions that can be considered at the origin of a subdural haematoma show similar results for the two simulated events. Finite element methods appear as an emerging tool in the study of the biomechanics of head injuries in children.